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(SPIRE) Handbook - Herschel

1. Note this table is available in the SPIRE calibration context spire_cal_12_2 under Phot ColorCorrApertureList 94 CHAPTER 5 SPIRE FLUX CALIBRATION l l qe ot 1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 Relative Spectral Response 0 1 0 0 0 1 CI I I I LL I L pL 1 L l I I I I I I L I I I 100 200 300 400 500 600 700 800 Wavelength micron HFI 857 SPIRE PMW Extended HFI 545 SPIRE PLW Extended SPIRE PSW Extended Figure 5 16 Relative Spectral Response Functions R v for the five wavebands Planck HFI 545 and HFI 857 Herschel SPIRE PLW SPIRE PMW and SPIRE PSW 5 3 Absolute flux offset estimation of SPIRE maps via cross calibration with Planck HFI Herschel SPIRE detectors are only sensitive to relative variations as a consequence the maps are constructed such that their median level is approximately zero hence the absolute bright ness of the observed region is unknown Planck HFI detectors are similar to the SPIRE ones however its observing strategy allows it to almost observe a sky s great circle every minute having a 1 rpm spinning rate By comparing the sky brightness as measured by COBE FIRAS at the galactic poles where the dust emission is lower HFI is capable of setting an absolute offset to its maps Planck Collaboration VIII 2013 Planck maps are in units of MJy sr and in order to recalibrate the SPIRE maps to the ab
2. euijedig pyepuels 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 85 It is important to note that since the SPIRE photometer flux calibration is performed on the timeline data the beam areas equivalent to the beams of the timeline data must be used when calibrating extended emission in terms of surface brightness Jy pixel or sr This means that the beam areas corresponding to the 1 pixel scale in Table 5 3 should be used when converting from Jy beam to Jy pixel For the purposes of point source extraction beam fitting etc where the absolute scale of the beam model is unimportant the appropriate FWHM for a map with a given pixel scale should be used 5 2 13 Photometer calibration accuracy SPIRE photometer observations are subject to several kinds of uncertainty Absolute calibration uncertainty This component is associated with our knowledge of the brightness of the primary calibrator Neptune and is estimated at 4 R Moreno private communication It is correlated across the three bands i e flux densities in the three bands will move up or down in a linearly correlated manner in the event of this calibration being revised Relative calibration uncertainty This uncertainty arises from the ability of the instru ment to reproduce a measurement of the same flux at the same time This is a random contribution and has been estimated by careful analysis of repeated measurements of a bright source actually Neptune itself
3. 00 jm B 1 5 Relative Beam Sold Angle Relative Beam Solid Angle 0 90 250um 350um 500m oes as 10 15 20 25 a EN E siis diu Ee 2 Temperature K 1 Spectral index a Figure 5 10 The variation of effective beam area relative to the beam area used in the pipeline Qpip 1 The areas are plotted agains source spectral index left and against grey body temperature for two values of the grey body index 8 See Table 5 4 and 5 5 correction and the beam solid angle must be used Raw empirical data This product is the raw data set from which the empirical beam maps were derived It has been made available so that users who wish to apply a custom data processing steps can also apply this processing to the beam model data thereby obtaining a model representative of the beam within their reduced maps Optical model of photometer beams The theoretical model of the beams is based on an optical model of the telescope and the in strument which has been shown by analysis of in flight data to provide a highly representative characterisation of the low level structure in the beams The model is based on computations of the response function of the end to end optical train of the Herschel observatory and SPIRE photometer at individual in band wavelengths then summing the monochromatic response with specific weights The model contains the reconstructed wave front error distribution of the telescope taken
4. 2 6 107 2410 2210 e 9 2 0 107 1 8 10 1 6 107 1410 1210 5g in 1 hour W m 1 0 107 8 010 TT TTT TTTTTTT TTT TTTTTTT TTT TTTTTTT TTT TTT d LL Lil L1 JI I Li Jititit Lil LILILLILI Lil LII 6 0 1075 Gu a LLL LB LL LLL B LLL B B LLL Lr lrrrirtrry 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 Frequency GHz Figure 4 3 FTS point source line flux sensitivity vs frequency across the FTS bands The current sensitivity black line is estimated from repeated observations of dark sky and cal ibration objects in comparison to the previous values dashed grey line estimated at the start of the mission to a conservatism factor that was applied to the modelled sensitivities to account for various uncertainties in the sensitivity model A number of important points concerning the FTS sensitivity should be noted 1 For the standard recommended smoothing of FTS spectra via apodization the extended Norton Beer function 1 5 Naylor amp Tahic 2007 the amplitude of the secondary maxima and minima of the Sinc function can be reduced at the expense of broadening of the spectral resolution element and hence the instrumental line shapes by a factor of 1 5 Apodization is not recommended for spectra with many lines or lines with very low signal to noise 2 The integrated line flux sensitivity for an unres
5. can be S for the spectral cube from the short wavelength array 197 313 um or L for the long wavelength array cube 303 671 jum 6 4 User reprocessing and further data analysis of SPIRE data User reprocessing scripts are available in HIPE these are explained in greater detail in the SPIRE Data Reduction Guide with particular emphasis on when it is desirable to reprocess the observation In addition to the reprocessing user pipelines there are a number of utility scripts in HIPE which are useful for a number of further data analysis steps like astrometry correction for the timeline data and the subsequent map making removal of background from spectra correction of the spectra for semi extended sources etc Please consult the SPIRE Data Reduction Guide for details 108 CHAPTER 6 SPIRE OBSERVATIONS IN THE HERSCHEL SCIENCE ARCHIVE 6 5 Access to calibration files Each SPIRE observation context downloaded from the HSA contains also the calibration tree as shown in Figure 6 3 The calibration tree in an observation context only contains calibration files that are relevant for the particular sub instrument i e for a Spectrometer observation only the calibration files with relevance for the Spectrometer pipeline or data analysis are available A standalone calibration tree can also be downloaded from the Herschel Science Centre however the structure of the standalone calibration tree is different and there are two ver
6. extdPxW Level 2 products only in HIPE v10 and above To convert the point source pipeline output to extended source calibration the flux densities should be multiplied by Kptoz 91 289 51 799 24 039 for 250 350 500 wm The maps are then in units of surface brightness specifically MJy sr The standard extended source pipeline products have this factor applied along with relative gains of individual bolometers and a zero point calibration based on Planck HFI data The point source flux densities can be colour corrected to a spectrum different from vS const by applying the point source colour correction parameter Kop Likewise the extended source surface brightness maps can be colour corrected using the extended source colour correction parameter Kcor For the same measured signal the extended source calibration is typically 196 lower than the point source calibration The conversion between flux density and surface brightness can be achieved by multiplying or dividing by the effective beam solid angle which also varies with the assumed source spectrum Current flux calibration accuracy is estimated at 5 596 dominated by the 4 absolute uncertainty in the Neptune model and largely correlated across the bands Extended sources have an additional 496 uncertainty due to uncertainty in the measured beam area For highest accuracy in the extraction of point source flux density from a map careful atten tion must b
7. Aperture photometry of point sources starting from point source maps 1 Use the Level 2 map products which give flux densities in Jy beam for point sources with a v S const spectrum NB To increase the accuracy the observations should be reprocessed with relative gains applied between Level 1 timeline fluxes and Level 2 map fluxes Convert the map to surface brightness using the pipeline beam solid angle Qpip as given in Table 5 2 Note that most HIPE aperture phometry tasks require a maps in units of Jy pixel Perform the aperture photometry Apply the beam correction factor as given in Table 5 4 or Table 5 5 for a greybody Colour correct for the true source spectrum using the point source colour correction parameters cap in Table 5 6 or Table 5 7 for a grey body If the recommended apertures are used then the aperture corrections listed in Table 5 8 should be applied If a different aperture and or background annulus is used then in the SPIRE Calibration Tree the table Phot RadialCorrBeam provides the normalised beam area also known as the Encircled Energy Fraction for the full range of apertures from 0 to 700 Note that this normalised beam area is for a source with apip 1 For any other non standard apertures the aperture corrections could be computed from the beam maps available on the SPIRE Public wiki 5http herschel esac esa int twiki bin view Public SpirePhotometerB
8. SPIRE Flux Calibration The information in this chapter is based on Griffin et al 2013 Bendo et al 2013 Swinyard et al 2014 5 1 Calibration sources and models SPIRE flux calibration is based on Neptune for the photometer and on Herschel telescope and Uranus for the spectrometer The SPIRE calibration programme also includes observations of Mars asteroids and stars to enable a consistent and reliable flux calibration and cross calibration with PACS and HIFI and with other facilities The currently assumed asteroid and stellar models are briefly described below for information 5 1 1 Neptune and Uranus angular sizes and solid angles The adopted equatorial radii 1 bar level req and eccentricities e for Uranus and Neptune are summarised in Table 5 1 and are based on the analysis of Voyager data by Lindal et al 1987 and Lindal 1992 These are similar to the values used in the ground based observations by Griffin amp Orton 1993 Hildebrand et al 1985 and Orton et al 1986 Table 5 1 Adopted planetary radii and eccentricity values Planet Equatorial radius Polar radius Eccentricity Reference Teg km ry km Eq 5 2 Uranus 25 559 4 24 973 20 0 2129 Lindal et al 1987 Neptune 24 766 15 24 342 30 0 1842 Lindal 1992 Uranus 25 563 24 949 0 024 Griffin amp Orton 1993 Neptune 24 760 24 240 0 021 Hildebrand et al 1985 Orton et al 1986 57 58 CHAPTER 5 SPIRE FLUX CAL
9. is provided in the Herschel Science Centre web portal http herschel esac esa int 1 2 Purpose and Structure of Document The purpose of this handbook is to provide relevant information about the SPIRE instrument in order to help astronomers understand and use the scientific observations performed with it The structure of the document is as follows first we describe the SPIRE instrument Chap ter 2 followed by the description of the observing modes Chapter 3 The in flight per formance of SPIRE is presented in Chapter 4 The flux calibration schemes for both the 7 8 CHAPTER 1 INTRODUCTION Photometer and the Spectrometer are explained in Chapter 5 The high level SPIRE data products available from the Herschel Science Archive are introduced in Chapter 6 The list of references is given in the last chapter 1 3 Acknowledgements This handbook is provided by the Herschel Science Centre based on inputs by the SPIRE Consortium and by the SPIRE instrument team 1 4 Changes to Document 1 4 1 Changes in version 2 5 post operations There were numerous small changes and corrections to the text The major ones are given below e The name of the document was changed from SPIRE Observers Manual to SPIRE Handbook keeping the version numbering with the previous document i e the first version of the Handbook is 2 5 e The Spectrometer units were changed everywhere from wavenumbers in cm to fre quency in GHz
10. 5 2 9 Photometer beam maps and areas 000 00 ee eae 71 5 2 10 Computed conversion factors for SPIRE 77 5 2 11 Non standard processing 222222 79 5 2 12 Application of colour correction parameters 80 5 2 13 Photometer calibration accuracy llle 85 5 2 14 A note on point source extraction from SPIRE Level 2 maps 86 oO URE e Lol ou ecce ew ee ke ER ee ee RYE gee 88 5 3 SPIRE maps calibrated with Planck 0 000000 eee 94 5 4 SPIRE Spectrometer Flux Calibration eee 97 5 4 1 Spectrometer beam properties oea ea a 000 98 5 4 2 Extended sources and spectral mapping ln 99 5 4 3 Bright source mode 2222222 100 5 4 4 Spectrometer calibration accuracy llle 100 6 SPIRE observations in the Herschel Science Archive 103 6 1 SPIRE processing levels and structure of the observational context 103 6 2 HSA archive file for SPIRE observations 22 000 106 6 3 Which products should I use for data analysis lll 107 6 4 User reprocessing and further data analysis of SPIRE data 107 6 5 Access to calibration files lt lt s se s smoar add a eee ee eee 108 Bibliography 111 CONTENTS Chapter 1 Introduction 1 1 The Observatory The Herschel Space Observatory Pilbratt et al 2010 is the fourth cornerstone mission in ESA s science programme Herschel was successfully launched on 14
11. 7 5 4 15 arcmin Approximate HIFI position Approximate PACS position Figure 2 2 SPIRE location on sky with respect to the other two instruments sharing the Herschel focal plane The centre of the SPIRE photometer is offset by 11 from the centre of the highly curved focal surface of the Herschel telescope shown by the large shaded circle 2 2 4 Photometer calibration source PCAL PCAL is a thermal source used to provide a repeatable signal for the bolometers Pisano et al 2005 It operates as an inverse bolometer applied electrical power heats up an emitting element to a temperature of around 80 K causing it to emit FIR radiation which is seen by the detectors It is not designed to provide an absolute calibration of the system this will be done by observations of standard astronomical sources The PCAL radiates through a 2 8 mm hole in the centre of the BSM occupying an area contained within the region of the pupil obscured by the hole in the primary Although optimised for the photometer detectors it can also be viewed by the FTS arrays PCAL is operated at regular intervals in flight in order to check the health and the responsivity of the arrays 2 2 5 Photometer detector arrays The three arrays contain 139 250 wm 88 350 jum and 43 500 um detectors each with its own individual feedhorn The feedhorn array layouts are shown schematically in Figure 2 4 The design features of the detectors and feedhorn
12. TUranus C point where MuUranus is the Uranus model described in Section 5 1 2 and in Swinyard et al 2014 and Iuranus is the observed Uranus spectrum in units of W m Hz sr This conversion Cpoint v can be accessed from the SPIRE Calibration Tree within HIPE 5 4 1 Spectrometer beam properties The FTS beam profile has been measured directly as a function of frequency by mapping a point like source Neptune at medium spectral resolution Makiwa et al 2013 The beam profile shows a complex dependence on frequency due to the SPIRE FTS optics and the multi moded nature of the feedhorn coupled detectors The feedhorns consist of conical concentrators in front of a circular section waveguide and the diameter of the waveguide determines the cut on frequencies of the electromagnetic modes that are propagated Chat topadhaya et al 2003 Murphy amp Padman 1991 Makiwa et al 2013 fitted the measured Neptune data using a superposition of Hermite Gaussian functions They found that within the uncertainties of the measurement only the zeroth order function i e a pure Gaussian was required for the SSW band However the SLW band required the first three basis functions These fitted functions are a convenient mathematical description of the beam rather than directly representing the electromagnetic modes propagating through the waveguides The beam is well fitted by radially symmetric functions The resulting FWHM of the f
13. Tests of how the measured flux density of point sources in map data have been performed using standard large and small scan map observations of Neptune for 500 um only and y Dra for all three bands to test the pixelisation corrections given by Equation 5 44 Maps from these data were generated at various pixel scales the data were fitted with Gaussian functions and then the resulting median flux densities in the case of the y Dra data or median measured model flux density ratios in the case of Neptune were examined to understand how the measured flux densities vary as a function of pixel size For 250 um data these tests demonstrated that Eq 5 44 provides an accurate correction for point source flux densities measured by PSF fitting in maps in all situations For 350 um data these tests demonstrated that Eq 5 44 provides an accurate correction for point source flux densities measured by PSF fitting in maps for only sources at the centres of small 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 87 scan maps The results from the 350 um large scan map data indicate that the measured flux densities may be lower by a few percent than what is implied by Eq 5 44 if the source is not centered within scan legs although the exact decrease in flux density depends on the location of the source relative to the scan legs For 500 jum we found that Eq 5 44 did not provide an accurate correction Instead the following empirical equation should be
14. The bolometers are coupled to the tele Feedhorn array 300 mK stage scope beam by conical feedhorns located directly in front of the detectors on the 3He stage Short waveguide sections at the feedhorn exit apertures lead into the detector cavities The feedhorn entrance aperture diameter is set at 2A where is the design wavelength and F is the fi nal optics focal ratio This provides the maximum aperture efficiency and thus the best possible point source sensitiv ity Griffin et al 2002 The feedhorns are hexagonally close packed as shown in the photograph in Figure 2 10 and schematically in Figure 2 4 and Figure Kevlar 2 7 in order to achieve the highest pack suspension ing density possible A centre centre dis tance of 2FA in the focal plane corre sponds to a beam separation on the sky Figure 2 10 Photograph of a SPIRE detector array of 2 D where D is the telescope di module 1 7 K stage and interface to 1 7 K box ameter This is approximately twice the beam FWHM so that the array does not produce an instantaneously fully sampled image A suitable scanning or multiple pointing jiggling scheme is therefore needed for imaging observations 2 4 2 He cooler and thermal strap system The same He cooler design Duband et al 1998 shown in Figure 2 11 is used for both SPIRE and PACS instruments This type of refrigerator consists of a sorption pump and an 22 CHAPTER 2 THE SPIRE INSTRUMENT evapor
15. Zero Path Difference 10 CHAPTER 1 INTRODUCTION Chapter 2 The SPIRE Instrument 2 1 Instrument Overview SPIRE consists of a three band imaging photometer and an imaging Fourier Transform Spec trometer FTS The photometer carries out broad band photometry A AA z 3 in three spectral bands centred on approximately 250 350 and 500 um and the FTS uses two over lapping bands to cover 194 671 jum 447 1550 GHz Figure 2 1 shows a block diagram of the instrument The SPIRE focal plane unit FPU is approximately 700 x 400 x 400 mm in size and is supported from the 10 K Herschel optical bench by thermally insulating mounts It contains the optics detector arrays three for the photometer and two for the spectrometer an internal He cooler to provide the required detector operating temperature of 0 3 K filters mechanisms internal calibrators and housekeeping thermometers It has three temperature stages the Herschelcryostat provides temperatures of 4 5 K and 1 7 K via high thermal conductance straps to the instrument and the He cooler serves all five detector arrays Both the photometer and the FTS have cold pupil stops conjugate with the Herschel sec ondary mirror which is the telescope system pupil defining a 3 29 m diameter used portion of the primary Conical feedhorns Chattopadhaya et al 2003 provide a roughly Gaussian illumination of the pupil with an edge taper of around 8 dB in the case of the photometer The
16. et al 2010 In orbit performance of the Herschel SPIRE imaging Fourier trans form spectrometer SPIE 7731 29 BIBLIOGRAPHY 113 Nguyen H et al 2010 A amp A 518 L5 Oliver S et al 2012 The Herschel Multi tiered Extragalactic Survey HerMES MNRAS 424 1614 Orton G S et al 1986 Submillimeter and Millimeter Observations of Uranus and Neptune Icarus 67 289 Orton G S et al 2014 submitted to Icarus Pilbratt G et al 2010 Herschel Space Observatory An ESA facility for far infrared and submillimeter astronomy A amp A 518 L1 Pisano G et al 2005 Applied Optics IP 44 3208 Planck Collaboration VIII 2013 A amp A submitted arXiv 1303 5069 Poglitch A et al 2010 The Photodetector Array Camera and Spectrometer PACS on the Herschel Space Observatory A amp A 518 L2 Rownd B et al 2003 Design and performance of feedhorn coupled arrays coupled to submil limeter bolometers for the SPIRE instrument aboard the Herschel Space Observatory Proc SPIE 4855 510 Sandell G Jessop N and Jenness 2001 T SCUBA Map Reduction Cookbook http www starlink rl ac uk star docs sci1 htx scii1 html Sudiwala R V Griffin M J and Woodcraft A L 2002 Thermal modelling and characteri sation of semiconductor bolometers Int Journal of Infrared and mm Waves 23 545 Swinyard B et al 2003 Proc SPIE 4850 698 Swinyard B M et al 2010 In flight calibration of the Herschel S
17. giving an optical path rate of 2 mm s due to the factor of four folding in the optics Radiation frequencies of interest are encoded as detector output electrical frequencies in the range 3 10 Hz For an FTS the resolution element in wavenumbers is given by Ao 1 2 x OPDmax where OPDmaz is the maximum optical path difference of the scan mirror In frequency the resolution element is A f cAo where c is the speed of light The maximum mechanical scan length is 3 5 cm equivalent to an OPDmax of 14 cm hence the highest resolution available is Ao 0 04 cm or A f 1 2 GHz in frequency space The frequency sampling of the final spectrum can be made arbitrarily small by zero padding the interferogram before the Fourier transformation but the number of independent points in the spectrum are separated in frequency space by A f and this is constant throughout the wavelength range from 194 to 671 um covered by the FTS 2 3 SPECTROMETER DESIGN 17 2 3 2 Spectrometer optics and layout The FTS Swinyard et al 2003 Dohlen et al 2000 uses two broadband intensity beam splitters in a Mach Zehnder configuration which has spatially separated input and output ports This configuration leads to a potential increase in efficiency from 50 to 100 in comparison with a Michelson interferometer One input port views the 2 6 diameter field of view on the sky and the other an on board reference source SCAL Two bolometer arrays at the output ports
18. giving the in beam flux density The conversion to surface brightness was then achieved by dividing by the beam area The inaccuracy of this method is twofold As shown in greater detail in Griffin et al 2013 firstly the beam solid angle does not scale with A but as A due to the finite size of the Herschel optics Secondly because differently extended sources illuminate 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 67 the aperture in a different way and the collecting aperture varies along the filter band with frequency there is not a single value for the beam area that is appropriate for all source types See Section 5 2 12 for an indication of the effect of these changes In the following we will concentrate on the two extreme cases point source and infinitely extended source A fully extended source is characterised by its surface brightness Is vo at frequency vo usually measured in MJy sr and its spectral index ag for Is v Is vo v vo It is assumed to uniformly fill the entire beam which has an effective area Q v which varies with frequency This variation is discussed in Section 5 2 9 Under these assumptions the measured RSRF weighted flux density is thus Qao JPassvanad Is v R v v v dv _ Is vo Pestana v s R v n v 8 v dv Ss J Passtand R v n v dv 7 v9 ene R v n v dv 5 18 The source surface brightness at frequency vo is therefore given by E 4 R v n v dv E Is vo Ss E assbana KMmong s
19. high level Level 2 Level 2 5 and Level3 Data Products Quality Control is carried out by the Herschel Science Centre and quality summary is included in the observation only if there are some concerns regarding the science grade of the final products 6 1 SPIRE PROCESSING LEVELS AND STRUCTURE OF THE OBSERVATIONAL CONTEXT105 SPIRE Pipeline Delivered to Users Raw Data Products l Level 0 5 Raw ADU counts converted to meaningful units Calibrated Timelines Image and Spectral maps Merged Parallel Maps Mosaiced maps Quality Control Figure 6 2 The processing levels of the SPIRE pipeline and user deliverables Level2 5 and Level3 are only available for the Photometer and for subsets of observations 106 CHAPTER 6 SPIRE OBSERVATIONS IN THE HERSCHEL SCIENCE ARCHIVE Level 2 5 and Level3 products are only available for the SPIRE photometer starting from HIPE v11 and later Level 2 5 is for the combined maps from Parallel mode observations done in both nominal and orthogonal scan directions While Level3 maps are the merged maps over a contiguous area of the same observing programme e g the combined map of the deep and wide maps over the same area as in some of the fields of the HerMES GT see Oliver et al 2012 Note that the Level 2 5 and Level3 maps are made using the timelines at Level 1 i e the final maps are not a mosaic of the already available Level 2 maps 6 2 HSA archive file for SPIRE obs
20. solid lines n v dashed lines 5 2 2 Calibration flux densities When observing a calibration source the property that is directly proportional to the in band power is f Se v R v dv e Passband SCalib KBeam T R v Jg 5 6 Passband where Sc is the calibrator flux density at the telescope aperture and KBeam is a correction factor for partial resolution of the calibrator by the telescope beam For a Gaussian beam profile coupling to a uniformly bright disk planet or asteroid the beam correction factor is given by e g Ulich amp Haas 1976 Kalma to VL UR G 5 7 x Beam where 6 is the angular radius of the disk and Beam is the beam FWHM The corresponding 250 350 500 wm beam correction factors are small 0 995 0 997 0 999 for Neptune Scalp for Neptune has been used in the derivation of the flux density conversion module parameters that are applied in the pipeline and which are in turn used to derive the RSRF weighted source flux density Ss 64 CHAPTER 5 SPIRE FLUX CALIBRATION 5 2 3 Response of a SPIRE bolometer to incident power The output signal voltage of a SPIRE bolometer depends on the absorbed signal power which is in turn a function of the source power collected by the telescope For NTD bolometers with a given applied bias voltage the small signal responsivity varies with the voltage across the bolometer with an approximately linear relationship over a wide range of background load
21. 0 0 60 0 85 0 95 0 5244 0 7756 0 8710 4 0 0 82 0 97 1 03 0 7441 0 9177 0 9903 5 0 0 94 1 02 1 04 0 8704 0 9808 1 0339 6 0 0 99 1 03 1 03 0 9414 1 0084 1 0479 7 0 1 02 1 03 1 02 0 9811 1 0196 1 0501 8 0 1 03 1 02 1 00 1 0031 1 0230 1 0475 9 0 1 03 1 01 0 99 1 0150 1 0226 1 0433 10 0 1 03 1 00 0 98 1 0208 1 0204 1 0385 15 0 1 00 0 97 0 94 1 0182 1 0049 1 0188 20 0 0 97 0 95 0 93 1 0064 0 9933 1 0070 25 0 0 96 0 94 0 91 0 9966 0 9856 0 9997 30 0 0 94 0 93 0 91 0 9894 0 9803 0 9948 35 0 0 94 0 93 0 90 0 9840 0 9766 0 9913 40 0 0 93 0 92 0 90 0 9800 0 9738 0 9887 B 20 3 0 0 63 0 88 0 98 0 5487 0 7998 0 9031 4 0 0 85 0 99 1 04 0 7688 0 9370 1 0122 5 0 0 96 1 02 1 04 0 8922 0 9944 1 0469 6 0 1 01 1 03 1 03 0 9591 1 0172 1 0543 7 0 1 03 1 02 1 01 0 9948 1 0246 1 0517 8 0 1 03 1 01 0 99 1 0132 1 0251 1 0456 9 0 1 03 1 00 0 98 1 0220 1 0224 1 0387 10 0 1 02 0 99 0 96 1 0253 1 0184 1 0320 15 0 0 99 0 96 0 92 1 0149 0 9977 1 0068 20 0 0 96 0 94 0 90 0 9993 0 9837 0 9926 25 0 0 94 0 92 0 89 0 9875 0 9748 0 9840 30 0 0 93 0 91 0 88 0 9790 0 9687 0 9783 35 0 0 92 0 91 0 88 0 9728 0 9645 0 9743 40 0 0 91 0 90 0 87 0 9681 0 9613 0 9714 Note this table is available in the SPIRE calibration context spire_cal_12_2 under Phot ColorCorrk for a larger range of 6 from 0 to 3 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 93 Table 5 8 Aperture corrections as a function of assumed s
22. 0 9817 0 9786 0 9785 0 9471 2 0 1 0016 1 0011 0 9913 0 9877 0 9876 0 9678 1 5 1 0019 1 0016 0 9974 0 9948 0 9948 0 9855 1 0 1 0000 1 0000 1 0000 1 0000 1 0000 1 0000 0 5 0 9960 0 9963 0 9990 1 0031 1 0032 1 0111 0 0 0 9899 0 9906 0 9945 1 0041 1 0044 1 0187 0 5 0 9818 0 9829 0 9864 1 0031 1 0035 1 0226 1 0 0 9716 0 9732 0 9751 0 9999 1 0006 1 0229 1 5 0 9594 0 9615 0 9606 0 9945 0 9955 1 0195 2 0 0 9454 0 9481 0 9432 0 9871 0 9885 1 0126 2 5 0 9296 0 93829 0 9230 0 9776 0 9794 1 0022 3 0 0 9121 0 9161 0 9005 0 9661 0 9684 0 9885 3 5 0 8930 0 8978 0 8757 0 9527 0 9555 0 9717 4 0 0 8725 0 8780 0 8492 0 9375 0 9409 0 9521 4 5 0 8507 0 8571 0 8210 0 9206 0 9245 0 9298 5 0 0 8278 0 8350 0 7916 0 9020 0 9067 0 9053 Note this table Phot ColorCorrk is available in the SPIRE calibration context spire cal 12 2 under 92 CHAPTER 5 SPIRE FLUX CALIBRATION Table 5 7 Colour correction factors Kcop and Kcoig as a function of the modified blackbody temperature T in Kelvins for a source with emissivity indices 6 1 5 and 6 2 0 Columns 2 3 4 give the values for 250 350 500 um for a point source flux density columns 5 6 7 give the values for 250 350 500 um for an extended source surface brightness The extended source colour corrections include the variation of beam area Point source Kcorp Extended source Koo T PSW PMW PLW PSW PMW PLW B 15 3
23. 0 9933 1 0187 1 0664 10 0 464 36 802 49 1647 55 1 0022 1 0250 1 0735 15 0 451 96 788 28 1617 33 1 0297 1 0435 1 0936 20 0 446 08 781 82 1604 10 1 0433 1 0521 1 1026 25 0 442 79 778 24 1596 83 1 0510 1 0570 1 1076 30 0 440 71 775 99 1592 27 1 0560 1 0600 1 1108 35 0 439 31 774 47 1589 17 1 0594 1 0621 1 1130 40 0 438 30 773 37 1586 92 1 0618 1 0636 1 1145 Note KBeam is available in the SPIRE calibration context spire cal 12 2 in a table called Phot ColorCorrBeam and for a larger range of possible 6 form 0 to 3 To recover Qeg one can multiply KBeam by pip that is provided in the metadata of the table 5 2 PHOTOMETER FLUX CALIBRATION SCHEME Table 5 6 Colour correction factors Kcop and Kco with apip assumed source spectral index Columns 2 3 4 give the values for 250 350 500 um for a point source flux density columns 5 6 7 give the values for 250 350 500 um for 91 1 as a function of an extended source surface brightness The extended source colour corrections include the variation of beam area The colour correction factors for a Black Body in the Rayleigh Jeans regime i e S v are shown in boldface Point Source Kcoip Extended source Kcoig ag PSW PMW PLW PSW PMW PLW 4 0 0 9800 0 9791 0 9333 0 9406 0 9409 0 8696 3 5 0 9884 0 9875 0 9525 0 9550 0 9551 0 8977 3 0 0 9948 0 9940 0 9687 0 9677 0 9676 0 9236 2 5 10 9992 0 9986
24. 10 pixels 500 um 14 pixels Figure 5 8 Log scale images for the empirical SPIRE beam model at 250 350 and 500 um from left to right respectively The top row uses a 1 pixel scale for all maps and the bottom row uses the nominal SPIRE map pixel scales of 6 10 and 14 from left to right respectively reconstruction becomes less reliable at low resolution particularly with respect to the Airy ring pattern at higher radii from the source peak The values of the beam FWHM and solid angle given in Table 5 3 are correct for a source with the same spectral index as Neptune See Table 5 4 for the effective beam area at a range of source spectral indices Although the diffuse and point source backgrounds have been removed from the beam maps there is a 4 uncertainty on the measured and effective beam solid angles This will likely be reduced further following the on going analysis of observations conducted in late 2012 Frequency dependent beam profiles and beam areas The beam areas given in Table 5 3 are correct when observing a source with the same spectral index as Neptune For all other sources the beam profile and area must be colour corrected This requires having a frquency dependent model of the beam The beam maps in Figure 5 8 can be used to produce azimuthally averaged radial beam profiles as plotted in Figure 5 9 Each radial profile is split into two sections a inner core section which is assumed to
25. CRE HERSCHEL eroe THE SPECTRAL AND PHOTOMETRIC MAGING RECEIVER SPIRE HANDBOOK HERSCHEL DOC 0798 version 2 5 March 17 2014 SPIRE Handbook Version 2 5 March 17 2014 This document is based on inputs from the SPIRE Consortium and the SPIRE Instrument Control Centre The name of this document during the active observing phase of Herschel was SPIRE Observers Manual The versioning is continued with the new name Document editor and custodian Ivan Valtchanov Herschel Science Centre European Space Astronomy Centre European Space Agency Contents 1 Introduction 1 1 1 2 1 3 1 4 1 5 2 The Pol 2 2 2 3 2 4 The Observatory Le bo ee Shek BE A ee EO a C dis Purpose and Structure of Document o 25 6684 RESTE Acknowledgements 2 22 less Changes to Document llle 1 4 1 Changes in version 2 5 post operations List of AOPOBVBASO 24 434 24 4 909 kd 33 EER Fed e ORY ed yov A esed ag SPIRE Instrument Instrument Overview 2224s Photome ter desig 2 4 uos be Raa 6 8o Aor Ro ox em koe Vos Rom ow Rs 2 2 1 Optics and yout 2122 eco dew 99 ey Ae Y o3 Rex Y xs 22 2 Beans steering mirror BSM o os ci ee ox COS oy 42 2 9 Fikes and passbands ie 6 sagopa nie Gee mom RR Y x 2 2 4 Photometer calibration source PCAL 2 2 5 Photometer detector arrays ooo ea a eee ee eee Spectrometer design saoao e 2 3 1 Fourier Tran
26. E 0 10 0 05 0 00 lU 1 20 2 30 35 4 45 5 55 60 Wavenumber cm SSW SLW Figure 2 6 SPIRE Spectrometer filter transmissions for the central detectors Sudiwala et al 2002 and details of the SPIRE bolometers are given in Turner et al 2001 Rownd et al 2003 and Chattopadhaya et al 2003 Radiation Thermal conductance Bias current Thermometer Figure 2 8 Basic principles of bolometer operation The basic features of a bolometer and the principles of bolometer operation are outlined here and are illustrated in Fig ure 2 8 The radiant power to be de tected is incident on an absorber of heat capacity C Heat is allowed to flow from the absorber to a heat sink at a fixed temperature To by a thermal con ductance G the higher G the more rapidly the heat leaks away A ther mometer is attached to the absorber to sense its temperature A bias current I is passed throughout the thermome ter and the corresponding voltage V is measured The bias current dissipates electrical power which heats the bolometer to a temperature T slightly higher than T With a certain level of absorbed radiant power Q the absorber will be at some temperature T dictated by the sum of the radiant and electrical power dissipation If Q changes the ab sorber temperature will change accordingly leading to a corresponding change in resistance 20 CHAPTER 2 THE SPIRE INSTRUMENT Figure 2 7 A schematic vie
27. May 2009 from Kourou French Guiana and performed science and engineering observations until 29 Apr 2013 when the liquid Helium coolant boiled off Herschel was in an extended orbit around the second Lagrangian point L2 of the system Sun Earth After the end of operations with the last command sent on 17 June 2013 the satellite was put into a safe disposal orbit around the Sun Herschel telescope s passively cooled 3 5 m diameter primary mirror is currently the largest one ever flown in space The three on board instruments the Heterodyne Instrument for Far Infrared HIFI De Graauw et al 2010 the Photodetector Array Camera and Spectrometer PACS Poglitch et al 2010 and the Spectral and Photometric Imaging Receiver SPIRE Griffin et al 2010 performed photometry and spectroscopy observations in the infrared and the far infrared domains from 60 um to 672 um This spectral domain covers the cold and the dusty universe from dust enshrouded galaxies at cosmological distances down to scales of stellar formation planetary system bodies and our own solar system objects A high level description of the Herschel Space Observatory is given in Pilbratt et al 2010 more details are given in the Herschel Observers Manual The first scientific results are presented in the special volume 518 of Astronomy amp Astrophysics journal Information with latest news documentation data processing and access to the Herschel Science Archive HSA
28. Mode Single Pointing or Raster selection See Section 3 3 2 for details Note that if Raster is selected then size of the map Length and Height must be given Image Sampling Sparse Intermediate or Full See Section 3 3 3 for details Spectral Resolution High Medium Low or High and Low See Section 3 3 1 for details Repetition factor The number of spectral scan pairs to be made at each position Note that if High and Low resolution is selected you can independently control the number of pairs for each resolution Length In arcmin The length of the raster map along the rows Height In arcmin The height of the raster map 44 CHAPTER 3 OBSERVING WITH SPIRE 16 spacing Intermediate 1 beam spacing 2 FOV from HSpot Spacecraft Z direction orcsec 35 beam 14 spacing Full 5 beam spacing 1234 a KAJ Spacecraft Z direction arcsec 16 15 14 13 E bot 35 beam 100 Figure 3 17 The FTS mapping pattern with intermediate image sampling for SSW and SLW 4 point jiggle top and full sampling 16 point jiggle bottom The red circle shows the 2 unvignetted field of view of the FTS The spacing of the beams is indicated for each of the detector arrays and the two image sampling modes The red dots show the central detector of each array at the 4 jiggle positions top and the 16 jiggle positions bottom Map centre offset Y Z In arcmin The offset of the r
29. SCAL SED SLW SMEC SNR S N SPG SPIRE SSW ZPD Astronomical Observation Request Astronomical Observation Template Beam Steering Mirror Detector Control Unit Data Processing Digital Processing Unit European Space Agency FPU Control Unit Far Infrared Radiation Field of View Focal Plane Unit Fourier Transform Spectrometer Herschel Common Software System Heterodyne Instrument for the Far Infrared Herschel Interactive Processing Environment The Herschel Science Archive The Herschel Science Centre based in ESAC ESA Spain Herschel Observation Planning Tool Interactive Analysis Instrument Level Test i e ground tests of the instrument without the spacecraft Inter Stellar Medium Junction Field Effect Transistor Local Standard of Rest Noise Equivalent Power Optical Path Difference Photodetector Array Camera and Spectrometer Photometer Calibration Source Proto Flight Model of the instrument SPIRE Photometer Long 500 um Wavelength Array SPIRE Photometer Medium 350 wm Wavelength Array SPIRE Photometer Short 250 wm Wavelength Array Photometer Thermal Control Unit Root Mean Square Relative Spectral Response Function Spectrometer Calibration Source Spectral Energy Distribution SPIRE Long 316 672 um Wavelength Spectrometer Array Spectrometer Mechanism Signal to Noise Ratio Standard Product Generation Spectral and Photometric Imaging REceiver SPIRE Short 194 324 um Wavelength Spectrometer Array
30. Temperature K Figure 5 14 Colour correction parameters for point sources cap left and extended sources cag right vs assumed modified blackbody source temperature The colour correction factors are plotted for two values of emissivity index 6 1 5 and f 2 e The extended colour corrections Kcooiz should only be applied to maps which are in surface brightness units e g MJy sr or Jy pix These standard colour corrections are recommended to observers and assume either a point like source or an infinitely extended source 5 2 11 Non standard processing It is not feasible to describe all possible procedures in this document The colour corrections and beam areas given in this document assume the following source properties e A power law or modified blackbody spectral energy distribution e Either a point like or completely uniform i e infinitely extended spatial variation 80 CHAPTER 5 SPIRE FLUX CALIBRATION A more general calibration procedure is required when either or both of these two assumptions does not apply Firstly the source spectral energy distribution can be more generally defined as f v vo usually given relative to a fiducial frequency vo such that f vo 1 Secondly a more general spatial variation of the source can be considered though we restrict ourselves here to circularly symmetric cases expressed relative to a scale width 69 as g 0 0o We also assume that the spectral and spatial variati
31. beam correction factor as given in Table 5 4 or Table 5 5 for a greybody 5 Colour correct for the true source spectrum using the point source colour correction parameters Kcop in Table 5 6 or Table 5 7 for a grey body 6 If the recommended apertures are used then the aperture corrections listed in Table 5 8 should be applied If a different aperture and or background annulus is used then in the SPIRE Calibration Tree the table Phot RadialCorrBeam provides the normalised beam area also known as the Encircled Energy Fraction for the full range of apertures from 0 to 700 Note that this normalised beam area is for a source with apip 1 For any other non standard apertures the aperture corrections could be computed from the beam maps available on the SPIRE Public wiki 7 The source flux density is then given in the units specified by the aperture photometry routine usually Jy or mJy Extended source photometry starting from point source maps 1 Use Level 2 point source map products called psrcPxW which give flux densities in Jy beam for point sources with a vS const spectrum 8http herschel esac esa int twiki bin view Public SpirePhotometerBeamProfileAnalysis 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 83 Multiply by the Kpi g conversion parameter to convert maps to surface brightness in MJy sr for an infinitely extended source with a vS const spectrum as given in Table 5 2
32. bright fully extended object observed in the central detectors is in theory 1 with the following contributions e The systematic uncertainty in telescope model of 0 06 e The statistical repeatability estimated at 1 e An additive continuum offset of SLW 3 4 x 107 29 W m Hz sr SSW 1 1 x 10719 W m Hz sr In practice truly extended sources tend to be faint and the uncertainty is therefore dominated by the additive offsets When the source extent is larger than the beam size but not fully extended or if there is structure inside the beam then the uncertainties are dominated by the source beam coupling see Wu et al 2013 and significantly greater than 1 In the mapping mode the variations between detectors become important and the overall repeatability has been measured to be 7 see Benielli et al 2013 for a full discussion of mapping mode observations The off axis detectors are less well calibrated especially outside the unvignetted part of the field The level of absolute flux accuracy and repeatability obtained with the SPIRE FTS compares favourably with the SPIRE photometer figures of 1 5 repeatability and 4 absolute Bendo et al 2013 and is rather better than quoted for either of the other two spectrometers on Herschel PACS and HIFI which both quote flux uncertainties in the 10 15 range The level of calibration accuracy achieved is due to the spectrometric nature of an FTS whe
33. co aligned detector are tabulated in Table 3 2 and the HSpot screenshot is shown in Figure 3 10 The instrumental noise decreases as the reciprocal of the square root of the number of ABBA repetitions however note that the instrumental noise for a single repetition of this mode is expected to equal the extragalactic confusion noise for sources fainter than 1 Jy Table 3 2 Point source mode sensitivities Source flux range 1 c instrumental noise level 250 um 350 um 500 um 0 2 1 Jy 7 mJy 7 mJy 7 mJy lt 4 Jy S N 200 gt 4 Jy S N 100 When to use this mode The SPIRE Point Source mode is recommended for bright isolated sources in the range 0 2 4 Jy where the astrometry is accurately known and accurate flux measurement is required For sources fainter than 200mJy where the background produces a significant contribution or at fluxes higher than 4 Jy where pointing jitter can introduce large errors the Small Map mode is preferable For Point Source mode the effective sky confusion level is increased due to chopping and nodding by a factor of approximately 22 for the case of extragalactic confusion noise and should be added in quadrature to the quoted instrumental noise levels The result of the measurement is therefore affected by the specific characteristics of the sky background in the vicinity of the source and will depend on the chop nod position angle in the event of 3 3 SPIRE SPECTROMETER AOT 37 an asymmetric
34. e g Bendo et al 2013 It should be noted that the flux of Neptune actually varies due to its well known distance from the observatory With more systematic effects potentially contributing this is a more realistic estimate of random uncer tainty than repeated observations of a bright source at constant flux The results show that this component is of the order of 1 5 Bendo et al 2013 At present we recommend that the overall calibration uncertainty for the SPIRE photometer taking these two contributions into account should be taken conservatively as 5 5 the direct rather than quadrature sum of the absolute and relative calibration uncertainties It should be noted that this is dominated by the absolute component and is thus largely correlated across the three bands Photometric uncertainty This component is due to the source measurement errors The photometer pipeline produces timelines representing the the in beam flux density and some random detector noise will be present in the timelines Any astrometric errors will also introduce additional noise when timelines are combined in mapmaking In addition in order to derive estimates of for example the flux density of a point or compact source users will need to employ some suitable fitting or aperture photometry technique and additional uncertainties can be introduced due to confusion or source crowding In addition slight differences in the choice of pipeline parameters e g
35. for the deglitching and baseline subtraction modules may produce slightly different results at the level of a few percent It is important to note that these photometric uncertainties will be significant or dominant except for sources which stand out very clearly above any confusion noise or local sky back ground fluctuations in which case the calibration uncertainties described above will become significant or dominant Assessment of the photometric uncertainties will depend on the par ticular sky brightness distribution and on the source extraction or background subtraction methods and is is therefore something to be done carefully by the user 86 CHAPTER 5 SPIRE FLUX CALIBRATION See Section 5 2 14 for some additional considerations relating to the process of point source extraction Extended source calibration uncertainty In addition to the components described above the calibration accuracy of extended sources is limited by the uncertainty on the SPIRE beam solid angle Griffin et al 2013 This is based on measurements of Neptune with a diffuse and point source backgrounds removed from the resulting maps This background removal leaves an uncertainty of 4 on the resulting beam solid angles though this may be improved upon at a later date through the analysis of shadow observations of the same region of sky 5 2 14 A note on point source extraction from SPIRE Level 2 maps The SPIRE flux calibration is time line based Jy bea
36. offsets different for each bolometer that must be removed before map making to derive the flux density from the sky Values of K K and K3 have been derived from calibration observations Bendo et al 2013 and are used in the pipeline flux conversion module together with the standard colour correction parameter KmMonp see the next subsection to produce the SPIRE flux density timelines 5 2 4 Conversion of RSRF weighted flux density to monochromatic flux density for point sources Definition of a monochromatic flux density requires the adoption of a standard frequency for the band and some assumption about the shape of the source spectrum The approach adopted for SPIRE and PACS is to assume that the spectrum is a power law across the band defined by the flux density at a standard frequency vo and a spectral index ag 1 corresponding to vS being flat across the band Ss v Ss vo z 5 13 For the standard SPIRE pipeline we choose values of vo to correspond to wavelengths of 250 350 and 500 um for the three bands and monochromatic flux densities at those frequencies 66 CHAPTER 5 SPIRE FLUX CALIBRATION are generated by the pipeline Under this assumption the measured RSRF weighted flux density the in band power weighted by the source spectrum and the RSRF to which the bolometer output voltage due to the source is proportional in the linear regime is thus J Ss v RG n v dv S f vesR v n v dv Ss
37. rates etc are only set once at the beginning of the Herschel operational day when the particular instrument is in use There are however detector set tings that are set up at the beginning of each observation like the bolometer A C offsets It is not possible to change the settings dynamically throughout an observation and this may have implications mainly signal clipping or signal saturation for observations of very bright sources with strong surface brightness gradients 23 24 CHAPTER 3 OBSERVING WITH SPIRE PCAL During SPIRE observations the photometer calibration source PCAL is operated at intervals to track any responsivity drifts Originally it was planned to use PCAL every 45 minutes but in flight conditions have shown excellent stability and following performance verification phase a new scheme has been adopted where PCAL is only used once at the end of an observation This adds approximately 20 seconds to each photometer observation For the spectrometer this can take a few seconds longer as the SMEC must be reset to its home position 3 2 SPIRE Photometer AOT This SPIRE observing template uses the SPIRE photometer Section 2 2 to make simulta neous photometric observations in the three photometer bands 250 350 and 500 wm It can be used with three different observing modes e Large areas maps This mode is for covering large areas of sky or extended sources larger than 5 arcmin diameter The map is made by scanning th
38. scale with frequency and an outer constant section which does not scale The monochromatic beam profile at some effective frequency veg is taken to be the same as the RSRF weighted beam profile as measured on Neptune The core section of the beam 74 CHAPTER 5 SPIRE FLUX CALIBRATION Table 5 3 Basic 2 D Gaussian parameters for beams based on measurements of Neptune using maps with a 1 pixel size Uncertainties in the beam FWHM values and areas are estimated at lt 1 and uncertainties in the beam solid angles at 4 Band PSW PMW PLW ONep 1 29 1 42 147 MajorxMinor FWHM arcsec 18 3x17 0 24 7x23 2 37 0x33 4 Geometric mean FWHM 6nep arcsec 17 6 23 9 35 2 Ellipticity 8 1 6 6 10 9 Measured beam solid angle QNep arcsec 450 795 1665 Isophotal frequency veg GHz 1215 14 865 43 610 18 The isophotal frequency is the frequency at which the solid angle of the monochromatic beam is equal to the solid angle of the beam as measured on Neptune using the model discussed in the text is then scaled with frequency as a power law with an index y 0 85 4 This power law is conventionally referred to as scaling with wavelength hence the negative index used here The monochromatic beam profile at a given frequency is then given by Dconst ant 0 B 0 v max f Bose 8 v v 7 5 32 The modelled RSRF weighted beam profile when observing a source with spectral index og is thus R v v s
39. scan length of the map in arcmin It corresponds to the length in the first scan direction Height This is the size of the map in arcmin in the other dimension The maximum allowed Length and Height for cross linked large maps Scan Angles A and B are 226 arcmin for both directions For scans in either Scan Angle A or Scan Angle B the maximum Length is 1186 arcmin and the maximum Height is 240 arcmin Scan speed This can be set as Nominal 30 s the default value or Fast 60 s Scan direction The choices are Scan Angles A and B the default option giving a cross linked map Scan Angle A or Scan Angle B 28 CHAPTER 3 OBSERVING WITH SPIRE Map centre offset Y Z This is the offset in arcmin of the map centre from the input target coordinates along the Y or Z axes of the arrays The minimum offset is 0 1 and the maximum allowed is 300 Map Orientation mm n This can be set at either Array or Array with Sky Unique AOR Label SPhoto 0000 A Constraint The latter option can be entered by se aoee None Specified lecting a range of map orientation angles for the ob NewrTargets Ernie rares servation to take place The orientation angle is mea sured from the equatorial coordinate system North to the direction of the middle scan leg direction positive Number of visible stars for the target None Specified Instrument Settings East of North following the Position Angle conven Source typ
40. ssew dv Spip o Koop A Spev Spip Vo Passband 5 24 Putting apip 1 gives R v n v v dv ag 1 Passband K new x 5 25 ColP A Spew Vo f R v n v v new dv Passband Similarly for a fully extended source the source surface brightness can be derived from the extended pipeline output which is provided in units of MJy sr as follows Is vo Kote Siew pip vo 5 26 Putting Qpip 1 into 5 19 and 5 21 gives as 1 JPassband R v n v v dv Koo os vg 7 A i JPassvband pP nen R v n v v dv 5 27 Note that in the calculation of Kmong and Kcow the monochromatic beam solid angle 0 v is required which is well described by a power frequency law with index 1 7 see Section 5 2 9 Eq 5 36 70 CHAPTER 5 SPIRE FLUX CALIBRATION As well as taking into account the variation of the RSRF and aperture efficiency with fre quency these colour correction parameters for extended sources also take into account the variation of the effective beam solid angle with frequency It is important to note that these extended source colour corrections should only be applied to a map which is in surface brightness units and which assumes ag 1 If the map in question is in flux density units i e Jy beam then it should be converted to surface brightness first using the conversion Kptop in Eq 5 22 Also note that this conversion parameter applies only to maps with the standard colour of o
41. the maps due to dead bolometers change from observation to observation when Low resolution is selected only continuum information can be entered and returned plus the unapodised resolving power When High and Low resolution is selected data are returned for the two different resolutions the low resolution sensitivity does not take into account the possibility to get the low resolution part from the high resolution spectrum Bright source mode Optional when the source is expected to be very bright see Section 5 4 3 for more details then this option provides a way to switch the detectors to bright mode settings thus avoiding signal clipping Using this mode leads to 25 s increase in the overhead time because the detector A C offsets are set at the start of the observation at each jiggle position 3 3 5 Spectrometer dark sky observations Dark sky observation is performed during every Herschel operational day when the SPIRE FTS is being used The observation is in sparse spatial sampling and high resolution mode with a number of repetitions equal or higher than the largest number of high resolution repetitions in any planned observation for the day The location of the dark sky was carefully chosen to be always visible with no bright sources and with very low galactic foreground emission The actual position of the dark sky is RA 265 05 deg Dec 65 0 deg J2000 0 close to the North Ecliptic Pole A snapshot of the FTS footprint on the ph
42. used P 1 0 0018 p 0 00037 62 5 45 where pix is the pixel size in arcsec Performing the pixelisation correction introduces an additional uncertainty which is best to determine empirically At this time this has only been characterized for 500 wm maps The fractional uncertainty due to the pixelisation correction is given by Up 0 0023 0 00113 Op ix 5 46 The default HIPE pixel sizes for 250 350 500 um are Opi 6 10 14 arcsec The corresponding pixel size correction factors given by Eqs 5 44 and 5 45 are P 0 951 0 931 0 902 From Eq 5 46 the corresponding percentage uncertainties introduced into the point source flux density estimation at 500 um is 1 5 This uncertainty should be added in quadrature to the other statistical uncertainties of the measurement Note that similar uncertainties may be appropriate to apply to 250 and 350 um data but have not yet been derived The pixelisation corrections presented here have been derived for and tested on images created by the naive mapmaker incorporated within HIPE which uses a nearest neighbour mapping algorithm Other mapping techniques may not necessarily recreate beams with the same shape and so it may not be appropriate to apply the same pixelisation corrections The following approach will yield the correct flux density of an isolated point source in an otherwise blank map 1 Associate each map pixel flux density value with the central
43. with v S flat across the band ag apip 1 will not be the case for most observations For instance at SPIRE wavelengths planets and other solar system objects will typically have a spectral index of 2 corresponding to black body emission in the Rayleigh Jeans region Dust sources will typically have a steeper spectrum with ag 3 4 Only for very cold dust or strongly red shifted sources will a power law begin to fail being a good approximation For the highest calibration accuracy a colour correction can be applied by the astronomer based on other information for instance measurements in other SPIRE or PACS bands and or data from other telescopes Depending on the nature and temperature of the source the true spectral index could be different for the three SPIRE bands as illustrated in Figure 5 7 which could apply in the case of a cold dust source Given the width of the SPIRE bands and the nature of the observed source SEDs in most cases it will be appropriate to assume that the source spectrum follows a power law across the band but with a different spectral index os Let SG vo be the point source flux density new 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 69 Log S Log vy Figure 5 7 Illustration of the possibility of different source spectral indices for the three SPIRE bands at vo for that spectral shape We then have from Eq 5 15 RW n vv dv 1 2 QSnew pip Passband Ss vo ug f R v n v v
44. 0 60 CHAPTER 5 SPIRE FLUX CALIBRATION 02 July 2009 for which Ceres thermal spectrum was derived using the STM This initial calibration has now been superseded by the Neptune based calibration The changes to the flux calibration scale are quite small but the uncertainties are now much improved Asteroid spectra for selected date Flux Density Jy Yoo 200 300 400 500 600 700 Wavelength um Figure 5 2 Standard Thermal Model spectra of 1 Ceres 2 Pallas 3 Juno and 4 Vesta for Dec 9 2009 5 1 5 Stellar calibrators At present the PACS photometer calibration is based on a set of standard stars identified by the Herschel Calibration Steering group HCalSG These stars are also being observed by SPIRE as part of the SPIRE PACS cross calibration programme which will include detailed comparison of the stellar based and Neptune based calibrations The eight stars are a Boo a Tau y And 8 Peg y Dra Sirius and a Cet Model spectra for these stars have been generated by Leen Decin based on the MARCS stellar atmosphere code of Decin amp Eriksson 2007 covering 2 200 um The quoted estimated uncertainty is 196 for that wavelength range Figure 5 3 shows the model FIR SEDs for the eight stellar calibrators with extrapolations to the SPIRE photometer bands based on the spectral index a in the 150 200 wm range The latter is fairly uniform varying between 1 99 and 2 034 for the eight sources Computations covering wav
45. 168 or OD 168 it had flux densities of 9300 5000 2500 Jy at 250 350 500 wm The nominal Herschel telescope background is equivalent to approximately 230 250 270 Jy so that Mars is equivalent to 40 20 10 time the nominal telescope brightness 5 1 4 Asteroid models The larger asteroids can also be used as FIR submillimetre calibration sources and were particularly important in the early part of the mission when Uranus and Neptune were not visible The most accurate asteroid models are the thermophysical models of M ller amp Lager ros 2002 which have been tabulated by M ller 2009 and must be computed in detail for a given observation date and time there can be significant variations in brightness associated with the asteroid rotation period For planning and estimation purposes the asteroid Stan dard Thermal Model STM Lebofsky et al 1986 can be used to estimate the expected flux densities As an illustration STM spectra for 9 Dec 2009 are shown in Figure 5 2 for the four largest asteroids 1 Ceres 2 Pallas 3 Juno and 4 Vesta Note that STM asteroid spectra are all of approximately the same shape close to that of a Rayleigh Jeans black body the monochro matic flux density ratios are typically 1 98 for S359 S500 and 3 7 3 8 for S259 S500 where S250 9359 and S599 are the flux densities in the three SPIRE Photometer bands The initial SPIRE photometer flux calibration was based on observations of 1 Ceres on OD 5
46. 5 15 outlines the basic steps that should be followed using the standard pipeline products The steps are presented in greater detail in the SPIRE Data Reduction Guide The four main procedures are Point source fitting from timelines 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 81 Use Level 1 timeline products which give flux densities in Jy beam of for point sources with a vS const spectrum Use timeline source fitting algorithms and obtain the source flux density Colour correct the flux density for the true source spectrum using the point source colour correction parameters in Table 5 6 or Table 5 7 for a grey body The source flux density is then provided in the units specified in the source fitting routine usually Jy or mJy Point source photometry from maps 1 Use Level2 point source map products called psrcPxW in HIPE v10 and above which give flux densities in Jy beam for point sources with a vS const spectrum Use your chosen map based source extraction fitting procedure The beam FWHM should be Nep as given in Table 5 3 The beam solid angle if required should be the pipeline beam solid angle Qpip as given in Table 5 2 Colour correct for the true source spectrum using the point source colour correction parameters in Table 5 6 or Table 5 7 for a grey body The source flux density is then provided in the units specified in the source fitting routine usually Jy or mJy
47. 5 19 1 v R v n v Q v dv Passband and so the conversion parameter Kyfonk is given by 4 R v n v dv Kmong a Passband 5 20 1 v R v n v Q v dv Passband From HIPE v10 and above an additional set of maps are provided in units of MJy sr As with the point source pipeline these products assume a source with ag 1 and are given by lpip vo Kmone as 1 Ss 5 21 The additional steps included in the processing for these products beyond the standard pipeline processing are 1 Relative gain factors are applied to the signal of each bolometer taking into account small differences in the ratio between peak and integral between individual bolometers Therefore the sensitivities of the individual bolometers to an extended source improve the consistency of photometric gains of bolometers reducing residual striping in maps with predominantly extended sources 2 The maps are produced assuming a fully extended source with a spectral index of ag 1 3 The maps are converted from flux density units Jy beam to surface brightness units MJy sr taking into account the variation of the beam with frequency see Sec tion 5 2 9 4 The maps are zero point corrected based on the Planck HFI maps see Section 5 3 This is a linear offset applied to the entire map 68 CHAPTER 5 SPIRE FLUX CALIBRATION The conversion from the extended source calibrated pipeline output Jpip to the source surface brightness Js vo of
48. 5 and 8 2 see Hildebrand 1983 for the observed ranges of 8 in astronomical sources are given for a range of temperatures in Table 5 7 and Figure 5 14 Both sets of colour corrections assume the input maps are for source spectral indices of Qpip 1 and maintain the units of the map either flux density of surface brightness The extended source colour corrections include the variation in beam solid angle so KBeam need not be applied separately e The point source colour corrections Kop should only be applied to maps which are in flux density units e g Jy beam 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 79 I zi 2 S oo 2 o a o b 2 bo 1 Conversion factor Keoiz Colour Correction factor Kcoip i oO S 2 0 1 2 3 4 5 Hi S32 1 0 1 2 3 4 5 ES Spectral index a Spectral index a Figure 5 13 Colour correction parameters for point sources cap left and extended sources cag right vs assumed source spectral index b 250um B 20 250um B 1 5 350um f 2 0 9 350um L5 500um B 2 0 o 500um 1 5 250 um B 2 0 350 um B 2 0 500 um B 2 0 250 um B 1 5 350 um B 1 5 500 um B 1 5 B Iz a 2 S aL TT PEEP ire o a ry ee 800cnone Colour Correction factor Kcoip T B Colour Correction factor Kcoir T B 0 855 i 5 10 15 20 25 30 35 40 0 E 5 10 15 20 25 30 35 40 Temperature K
49. 880 08 0 9642 0 9667 0 9407 3 0 479 05 845 32 1857 69 0 9715 0 9731 0 9521 2 5 475 56 839 69 1835 29 0 9786 0 9796 0 9637 2 0 472 15 834 02 1812 94 0 9857 0 9863 0 9756 1 5 468 76 828 31 1790 71 0 9928 0 9931 0 9877 1 0 465 39 822 58 1768 66 1 0000 1 0000 1 0000 0 5 462 01 816 85 1746 88 1 0073 1 0070 1 0125 0 0 458 65 811 12 1725 43 1 00147 1 0141 1 0251 0 5 455 29 805 40 1704 38 1 0222 1 0213 1 0377 1 0 451 94 799 71 1683 80 1 0298 1 0286 1 0504 1 5 448 61 794 06 1663 76 1 0374 1 0359 1 0631 2 0 445 81 788 47 1644 30 1 0451 1 0433 1 0756 2 5 442 04 782 93 1625 47 1 0528 1 0507 1 0881 3 0 438 80 777 47 1607 32 1 0606 1 0580 1 1004 3 5 435 62 772 09 1589 86 1 0683 1 0654 1 1125 4 0 432 47 766 80 1573 13 1 0761 1 0728 1 1243 4 5 429 39 761 60 1557 12 1 0838 1 0801 1 1359 5 0 426 36 756 52 1541 85 1 0915 1 0873 1 1471 Note KBeam is available in the SPIRE calibration context spire cal 12 2 in a table called Phot ColorCorrBeam To recover Qeg one can multiply KBeam by Qpip which is provided in the metadata of the table Download the script from here ftp ftp sciops esa int pub hsc calibration SPIRE PHOT SpireHandbook_section52 py 90 CHAPTER 5 SPIRE FLUX CALIBRATION Table 5 5 Effective beam solid angle Qeg and beam correction factor KBeam for a source with grey body spectrum for emissivity indices 6 1 5 and 6 2 0 These values should be used t
50. B 0 v dv Bno Passband a 0 as w 5 33 Passband and the effective beam area Qef by Og ag Boo 270 d 5 34 0 The frequency dependence of the beam FWHM and solid angle as measured at a specific frequency can then be approximated by power laws 6 v ONep E 5 35 Veff yx OQ v Qnep 5 36 Veff where Veg is the isophotal frequency These functions will be useful if converting to a source spectrum not defined by either a power law or a grey body as the colour corrections will have to be calculated as described for the chosen spectrum see Section 5 2 6 The value of y is calculated from simulations of the SPIRE optics and takes into account the change in diffraction from the focal plane array and the edge taper at the edge of the primary mirror 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 75 250um High freq edge 350um Band centre 500um 3 2 2 2 247 Low freq edge Normalised response 1074 6 0 100 200 300 400 500 600 700 1075 100 200 300 400 500 600 700 Angle arcsec Angle arcsec Figure 5 9 Left Normalised radial beam profiles of the three SPIRE bands as measured on Neptune Right The PSW beam profile at the band centre solid line and the high frequency dashed line and low frequency dotted line band limits The separation between the Core and Constant sections of the beam profile are clearly seen The value of veg the i
51. IBRATION In calculating the planetary angular sizes and solid angles a correction is applied for the inclination of the planet s axis at the time of observation and the apparent polar radius is given by Marth 1897 1 2 Tp a Teq 1 cos 5 1 where is the latitude of the sub Herschel point and e is the planet s eccentricity 1 2 T e 5 2 P The observed planetary disc is taken to have a geometric mean radius rgm given by Tgm rag rp 4 E 5 3 For a Herschel planet distance of Dy the observed angular radius 0 and solid angle Q are thus 0 2 and Q 62 5 4 p Dy p Typical angular radii for Uranus and Neptune are 1 7 and 1 1 respectively 5 1 2 Neptune and Uranus models Models of Uranus and Neptune have been agreed by the Herschel Calibration Steering Group HCalSG as the current standards for Herschel and are available on the HSC calibration ftp sitet The models currently used for SPIRE are the ESA 4 tabulations for both Uranus based on Orton et al 1986 2014 and for Neptune based on the updated model of Moreno 1998 2010 The absolute systematic flux uncertainty for Neptune is estimated to 4 R Moreno private communication while comparing Uranus and Neptune the absolute uncer tainties are of the order of 396 Swinyard et al 2014 The Uranus and Neptune disk averaged brightness temperature spectra are plotted in Fig ure 5 1 In the Hersc
52. LW right taken from a real observaiton The white circle is with 5 diameter The pixel size is 6 10 14 for PSW PMW PLW and the colour code represents the number of bolometer hits in each sky pixel When to use this mode This mode has the same sensitivity as the Large Map mode but for small areas it uses less time 3 2 SPIRE PHOTOMETER AOT 33 W 10 ue geo 4 B s LA y arcsec Figure 3 9 Left the 7 point hexagonal jiggle pattern Note that the central point is revisited at the end The seven points are used to fit the 2 D beam as shown in the drawing Right the image shows the central co aligned pixels as they appear on the sky The circles numbered 1 and 2 show the detectors on which a point source is viewed via the chopping and nodding which is described in detail in the text The angular positions of detectors are also shown 3 2 3 Point Source Note that this mode was never used for science observations However for completeness we provide the details similarly to the previous two photometry modes Description A mini map is made around the nominal position to make sure that the source signal and position can be estimated This mini map is made by moving the BSM around to make the map as shown in Figure 3 9 for one detector The 7 point map is made by observing the central position and then moving the BSM to observe six symmetrically arranged positions jiggle offset from the central position by
53. Lebofsky L A et al 1986 A Refined Standard Thermal Model for Asteroids Based on Ob servations of 1 Ceres and 2 Pallas Icarus 68 239 Lindal G F et al 1987 The Atmosphere of Uranus Results of Radio Occultation Measure ments with Voyager 2 J Geophys Res 92 14987 Lindal G 1992 The Atmosphere of Neptune an Analysis of Radio Occultation Data Ac quired with Voyager 2 Astron J 103 967 Mandel L amp Wolf E 1995 Optical coherence and quantum optics CUP Mather J C 1982 Bolometer noise nonequilibrium theory Applied Optics 21 1125 Makiwa G et al 2013 Beam profile for the HerschelSPIRE Fourier transform spectrometer Applied Optics 52 3864 Marth A 1897 On the Apparent Disc and on the Shadow of an Ellipsoid MNRAS 57 442 Moreno R 1998 PhD Thesis Universit Paris VI Moreno R Neptune and Uranus planetary brightness temperature tabulation available from ESA Herschel Science Centre ftp ftp sciops esa int pub hsc calibration 2010 M ller Th amp Lagerros J S V 2002 Asteroids as Calibration Standards in the Thermal Infrared for Space Observatories A amp A 381 324 Murphy J A amp Padman R 1991 INfrared Physics 31 291 M ller Th 2009 Asteroid Calibration Quality Information for COP and Early PV 8 May 2009 Asteroid quality TM 08052009 pdf available from ESA Herschel Science Centre Naylor D amp Tahic K 2007 J Opt Soc Am A 24 3644 Naylor D
54. PIRE instrument A amp A 518 L4 Swinyard B M et al 2014 Calibration of the Herschel SPIRE Fourier Transform Spec trometer accepted in MNRAS arXiv 1403 1107 Teanby N A amp Irwin P G J 2013 An External Origin for Carbon Monoxide on Uranus from Herschel SPIRE ApJ 175 49 Turner A D et al 2001 Si3N4 micromesh bolometer array for sub millimeter astrophysics Applied Optics 40 4921 Ulich B L amp Haas R W 1976 Absolute Calibration of Millimeter Wavelength Spectral Lines ApJS 30 247 Wu R et al 2013 Observing extended sources with the Herschel SPIRE Fourier Transform Spectrometer A amp A 556 116
55. Passband sw Passband 5 14 Rv oS Ry Passband Passband The monochromatic source flux density at frequency vo which is produced by the pipeline is therefore given by UD f R n v dv e Passband Ss vo Sg pos R v n v dv Passband Kyonp Ss 5 15 The measured RSRF weighted flux density is thus multiplied by KMonp to derive the monochromatic flux density at the standard wavelength to be quoted to the user The standard SPIRE pipeline assumes ag 1 to generate the conversion parameter K4p as J RY nv dv n 1 Passband Kap Kmonp as 1 wp Reg 5 16 Passband and therefore a pipeline output of Spip KapSs 5 17 The peak value of a calibrated SPIRE Level 1 timeline reflects the flux density of a point source with rS const spectrum at the reference wavelength of the filter when the associated bolometer is moved centrally across that source To derive the flux density for an extended source the appropriate extended source corrections must be applied for which the procedure is given in Sections 5 2 5 5 2 6 and 5 2 12 5 2 5 Conversion of RSRF weighted flux density to monochromatic surface brightness for fully extended sources Previous versions of this document up to and including v2 4 advised a different method of extended source calibration than what is recommended here They advised using a conversion parameter with weighted RSRF to approximate the variation across the band
56. Perform the required photometry If the recommended apertures are used then the aperture corrections listed in Table 5 8 should be applied If a different aperture and or background annulus is used then in the SPIRE Calibration Tree the table Phot RadialCorrBeam provides the normalised beam area also known as the Encircled Energy Fraction for the full range of apertures from 0 to 700 Note that this normalised beam area is for a source with apip 1 For any other non standard apertures the aperture corrections could be computed from the beam maps available on the SPIRE Public wiki Colour correct for the true source spectrum using the extended source colour correction parameter cog in Table 5 6 or Table 5 7 for a grey body The source surface brightness is then given the units specified in the photmetry routine usually MJy sr Extended source photometry starting from extended source maps 1 Use Level2 extended source map products called extdPxW which give surface brightnesses in MJy sr for infinitely extended sources with a vS const spectrum Perform the required photometry If the recommended apertures are used then the aperture corrections listed in Table 5 8 should be applied If a different aperture and or background annulus is used then in the SPIRE Calibration Tree the table Phot RadialCorrBeam provides the normalised beam area also known as the Encircled Energy Fraction
57. The 4 5 K optics are mounted on the SPIRE internal optical bench 2 2 PHOTOMETER DESIGN 13 Table 2 1 SPIRE overall characteristics Sub instrument Photometer Spectrometer Array PSW PMW PLW SSW SLW Band jum 250 350 500 194 313 303 671 Resolution A AA 3 3 3 4 2 5 40 1000 at 250 um variable Unvignetted field of view 4 x 8 2 0 diameter Beam FWHM size arcsec 17 6 23 9 35 2 17 21 29 42 a the spectral resolution can be low LR A f 25 GHz medium MR A f 7 2 GHz or high HR A f 1 2 GHz Only HR and LR were used in science observations See Section 4 2 1 for details b The photometer beam FWHM were measured using fine scan observations of Neptune on beam maps with 1 pixels see Section 5 2 9 The FTS beam size depends on wavelength see Section 5 4 1 for more details Mirrors M7 M8 and a subsequent mirror inside the 1 7 K box form a one to one optical relay to bring the M6 focal plane to the detectors The 1 7 K enclosure also contains the three detector arrays and two dichroic beam splitters to direct the same field of view onto the arrays so that it can be observed simultaneously in the three bands The images in each band are diffraction limited over the 4 x8 field of view 2 2 20 Beam steering mirror BSM The BSM MA in Figure 2 3 is located in the optical path before any subdivision of the incident radiation into photometer and spectrometer o
58. Two scan pairs are deemed essential 3 3 SPIRE SPECTROMETER AOT 39 for redundancy in the data The desired integration time is set by increasing the number of scan pairs performed corresponding to the number of repetitions entered in HSpot gt Zero Optical Path Difference Path Difference Figure 3 13 Diagram to show how the SMEC moves in terms of optical path difference during one repetition for High Medium and Low spectral resolution The low resolution SMEC scan range is always covered during High or Medium resolution observations Low Resolution Usage and Description To make continuum measurements at the resolution of A f 25 GHz A AA 48 at A 250m The SMEC is scanned symmetrically about ZPD over a short distance It takes 6 4 seconds to perform one scan in one direction at low resolution This mode is intended to survey sources without spectral lines or very faint sources where only an SED is required Medium Resolution Usage and Description blueThe medium resolution of A f 7 2 GHz A AA 160 at A 250 jum was never used for science observations High Resolution Usage and Description The high resolution mode gives spectra at the highest resolution available with the SPIRE spectrometer A f 1 2 GHz this corresponds to A AA 1000 at 250 um High resolution scans are made by scanning the SMEC to the maximum possible distance from ZPD It takes 66 6 s to perform one scan in one direction at high r
59. a context for a high level Quality Control The entire SPIRE Observational Context is shown in Figure 103 104 CHAPTER 6 SPIRE OBSERVATIONS IN THE HERSCHEL SCIENCE ARCHIVE 6 1 for all products from the raw building block data to the final high level processed end products from the pipeline Level 0 5 Processed 1 Final Level 2 3 amp QC Figure 6 1 The complete Observation Context of a SPIRE observation Each SPIRE observation in the HSA has already been processed through the standard pipelines to several levels this processing is known as Systematic Product Generation SPG All observations are regularly reprocessed in bulk whenever there is a new release of the Herschel Common Software System HCSS The SPG version present in the metadata of any Observational Context reflects the HCSS version of the reprocessing The different processing levels of the SPIRE pipeline and user deliverables are outlined in Figure 6 2 In general LevelO data corresponds to the raw data formatted from the raw telemetry by an external pre processing stage These Level0 Data Products are then passed through a processing stage referred to as the Engineering Conversion that creates the Level 0 5 Data Products in a meaningful and manageable form The SPIRE AOT specific pipelines then process these Level0 5 Data Products to produce the science usable calibrated Level 1 Data Products Further advanced processing to create products such as maps produce the
60. a fixed angle nominally 6 and then returning to the central point once more note that the 7 in 7 point refers to the number of different positions At each of these positions chopping is performed between sets of co aligned detectors Figure 3 9 right to provide spatial modulation and coverage in all three wavelength bands The chop direction is fixed along the long axis of the array Y and the chop throw is 126 The nominal chop frequency is 1 Hz Sixteen chop cycles are performed at each jiggle position Nodding once every 64 seconds is performed along the Y axis to remove differences in the background seen by the two detectors Figure 3 9 right shows the central row of co aligned pixels At the first nod position nod A at 0 0 the source is repositioned with the BSM on detector 1 and the chopping is performed between 1 and 2 Then the telescope nods at 126 as shown in the figure this is nod B and 34 CHAPTER 3 OBSERVING WITH SPIRE the target is repositioned with the BSM on detector 2 The chopping is between 2 and 3 Note that in this scheme detector 4 is not used This is one AB cycle The standard Point source photometry observation uses ABBA cycle i e we repeat in reverse the same scheme To acquire further integration time the ABBA nod pattern is repeated an appropriate number of times ABBA ABBA etc The chop and nod axis is the same and is parallel to the long axis of the array to allow switching between co a
61. a source with a particular colour is achieved through applying the colour correction discussed in Sections 5 2 6 and 5 2 10 There are some cases in which users may wish to convert from point source flux densities to extended source surface brightnesses as part of their own data reduction The first of the steps above is achieved by applying the relative gains in the pipeline and cannot be replicated by a simply multiplicative factor or offset The second and third steps above can be achieved by multiplying the point source pipeline map by Kptop KwonE o 1 Kap Kpton 5 22 The value of this parameter is given in Table 5 2 Note that this parameter converts to the calibration for extended source and also changes the units from flux density Jy beam to surface brightness MJy sr In practice the pipeline uses a parameter K4g which is defined as Kap KMonE 1 Qeg a 1 5 23 where Qe a 1 is the effective beam solid angle for a source with spectral index a 1 see Section 5 2 9 These values are also given in Table 5 2 Since the extended source maps are in units of surface brightness they depend on the effective beam solid angle The colour correction for such a map must therefore take into account the variation in the beam solid angle and so is different from that for a point source see Section 5 2 6 5 2 6 Colour correction for power law spectra The assumption that the source has a spectrum
62. a with different spectral resolutions e High resolution HR 38 CHAPTER 3 OBSERVING WITH SPIRE e Medium resolution MR e Low resolution LR e High and Low resolutions H LR Spectra can be measured in a single pointing using a set of detectors to sample the field of view of the instrument or in larger spectral maps which are made by moving the telescope in araster For either of these it is possible to choose sparse intermediate or full Nyquist spatial sampling In summary to define an observation one needs to select a spectral resolution high medium low high and low an image sampling sparse intermediate full and a pointing mode single or raster These options are described in more detail in the next sections The HSpot input parameters for all SPIRE Spectrometer observing modes are shown in Figure 3 12 In the following sections we describe each one of the options 80 9 SPIRE Spectrometer Unique AOR Label SSpec 0000 copy Target 3c279 Type Fixed Single Position 12h56m11 17s 5d47m21 5s New Target Modify Target Target List OO SPIRE Spectrometer j Number of visible stars for the target None Specified Unique AOR Label SSpec 0000 Instrument Settings Target 3c279 Type Fixed Single Spectral Resolution Position 12h56m11 17s 5d47m21 5s Image Sampling E Pointing Mode e O HighH 2 Sparse x NewTarget Modify Target Target List O Sing
63. ance lt c lt eo cra nania r db aba igrana 49 ALi BONSI eue Ge Ante eRe e Xy d h a AEE ad s 49 42 Spectrometer ae sots end eie Pe A ak we he aT ee oen d YU 51 4 2 1 Spectral range line shape and spectral resolution 51 4 2 2 Wavelength scale accuracy 2 222 53 B28 cll cT 53 5 SPIRE Flux Calibration 57 5 1 Calibration sources and models 000 ee eee ee eee 57 5 1 1 Neptune and Uranus angular sizes and solid angles 57 5 1 2 Neptune and Uranus models 0 000 eee eee 58 5 1 3 Marsmodels 4 2 2 2 o RR doen BR E E XR ROUES 58 D l Asteroid modele 4 654 2644 44 gend ede Ra E RA A Sx DES 59 5 15 Stelar calibrated esos sog o oe ox omm ee E Rmo Row ed ae 60 5 2 Photometer flux calibration scheme 00000 eee eee 61 5 2 1 Photometer Relative Spectral Response Function 62 5 2 2 Calibration flux densities 200000022000 63 5 2 8 Response of a SPIRE bolometer to incident power 64 5 2 4 Conversion of RSRF weighted flux density to monochromatic flux den sity for point sources sosoo 65 CONTENTS 5 5 2 5 Conversion of RSRF weighted flux density to monochromatic surface brightness for fully extended sources 000000 eee 66 5 2 6 Colour correction for power law spectra c n 68 5 2 7 Colour correction for modified black body spectra 70 5 2 8 Conversion of in beam flux density to surface brightness 71
64. area of just under 4 degrees square whereas single direction scans can be up to nearly 20 degrees in the scan direction and just under 4 degrees in the other direction Hence with a single scan direction it is possible to make very long rectangular maps Note that cross scan observations for highly rectangular areas are less efficient as many shorter scans are needed in one of the directions The dimensions of the area to be covered are used to automatically set the length and the number of the scan legs The scan length is set such that the area requested has good coverage throughout the map and that the whole array passes over all of the requested area with the correct speed The number of scan legs is calculated to ensure that the total area requested by the user is observed without edge effects a slightly larger area will be covered due to the discrete nature of the scans Hence the actual area observed will always be bigger than what was requested The area is by default centred on the target coordinates however this can be modified using map centre offsets given in array coordinates This can be useful when one wants to do 26 CHAPTER 3 OBSERVING WITH SPIRE Uniform scan speed distance Scan leg Map area covered to uniform sensitivity user required area SPIRE 250 um array size Figure 3 2 Large Map coverage showing the scan direction with respect to the SPIRE arrays the scan leg separation step and the unif
65. aster map centre from the input target coordinates along the Y or Z axes of the arrays Minimum is 0 1 maximum 300 Map Orientation Either Array or Array with Sky Constraint If Array with Sky Constraint is selected then range of the map orientation is constrained This is a scheduling constraint and should therefore only be used if necessary Angle from to In degrees East of North In the case that Array with Sky Constraint is selected the angles between which the raster rows can be constrained to are entered here Source Flux Estimates Optional if the estimated line flux in 107 W m and or the estimated continuum se lectable units either Jy or 107 W m um is entered along with a wavelength then the expected SNR for that line or continuum will be reported back in the Time Estimation as well as the original values entered The time estimator always returns l o flux sensitivity l o continuum sensitivity and unapodised resolving power for 8 standard wavelengths Note 3 3 SPIRE SPECTROMETER AOT 45 Figure 3 18 Intermediate top and Full bottom spatial sampling coverage maps for SLW left and SSW right from a real SPIRE FTS mapping observation The sky spectral pixel spaxel sizes are 35 top left 17 5 bottom left 19 top right 9 5 bottom right The number of bolometer hits in each sky pixel are encoded with colour The coverage maps depend on the observational day and hence the holes in
66. ator and uses porous material which absorbs or releases gas depending on its temper ature The refrigerator contains 6 litres of liquid He At the beginning of the cold phase all of this is contained in liquid form in the evaporator The pump is cooled to 2 K and cryo pumps the He gas lowering its vapour pressure and so reducing the liquid temperature The slow evaporation of the He provides a very stable thermal environment at 300 mK for around 48 hours under constant heat load in normal observing and operational circumstances Once most of the helium is evaporated and contained in the pump then the refrigerator must be recycled This is carried out by heating of the sorption pump to 40 K in order to expel the absorbed gas The gas re condenses as liquid at 2 K in the evaporator Once all of the He has been recondensed the pump is cooled down again and starts to cryo pump the liquid bring ing the temperature down to 0 3 K once again This recycling takes about 2 5 hours and is usually performed during the daily telecommunications period DTCP Gas gap heat switches con trol the cooler and there are no moving parts The confinement of the He in the evaporator at zero g is achieved by a porous material that holds the liquid by capillary attraction A Kevlar wire suspension supports the cooler during launch whilst min imising the parasitic heat load Copper straps connect the cooler Figure 2 11 SPIRE cooler 0 3 K stage to the five det
67. background Note that although it is possible to set a chop avoidance angle within HSpot this will constrain the possible dates for the observation Figure 3 11 Example of possible chop area on a realistic background The example in Figure 3 11 shows a scan map observation of a 220 mJy source The circle drawn around the source corresponds to the chop and or nod throw used in the Point Source mode Moving around the circumference of the circle it is found the background can vary between 30mJy depending on the chop nod position angle used for the observation Therefore due to the problems of confusion noise and the dependence of the result on the position angle of the observation the point source AOT is not recommended for sources fainter than 200 mJy for which a small scan map will produce a better measurement including an accurate characterisation of the background For Point Source mode observations of bright sources gt 4 Jy the uncertainties are dominated by pointing jitter and nod position differences resulting in a S N of the order of 100 at most the uncertainties in the data will also be limited by the accuracy of the flux calibration which will be at least 5 Users should be aware of these effects and take them into consideration 3 3 SPIRE Spectrometer AOT This observing mode is used to make spectroscopic observations with the SPIRE Fourier Transform Spectrometer Section 2 3 The Spectrometer can be used to take spectr
68. can be used for background removal please consult the SPIRE Data Reduction Guide We strongly encourage the observers to contact the FTS User Support Group via the Herschel helpdesk whenever they have questions or need assistance regarding the use the FTS 48 CHAPTER 3 OBSERVING WITH SPIRE Chapter 4 SPIRE in flight performance In this section we summarise the achieved in flight performance The pre flight performance of SPIRE was estimated using a detailed model of the instrument and the telescope and the results of instrument level and Herschel system level tests Some details of the model as sumptions and adopted parameters are given in e g Griffin 2008 The optimal parameters for each observing mode i e the AOTs used in HSpot were based on the optimisation and evaluation of the instrument performance during Commissioning and Performance Verifica tion phases These were further checked and updated using Science Demonstration phase observations as well as Routine phase calibration and science observations 4 1 Photometer performance 4 1 1 Sensitivity The photometer sensitivity in scan map mode has been estimated from repeated scan maps of dark regions of extragalactic sky A single map repeat is constituted by two nearly orthog onal scans as implemented in the SPIRE only Large Map AOT Multiple repeats produce a map dominated by the fixed pattern sky confusion noise with the instrument noise having integrated down to a n
69. cover overlapping bands of 194 313 um SSW and 303 671 um SLW As with any FTS each scan of the moving mirror produces an interferogram in which the spectrum of the entire band is encoded with the spectral resolution corresponding to the maximum mirror travel The FTS focal plane layout is shown in Figure 2 5 A single back to back scanning roof top mirror serves both interferometer arms It has a frictionless mechanism using double parallelogram linkage and flex pivots and a Moir fringe sensing system A filtering scheme similar to the one used in the photometer restricts the passbands of the detector arrays at the two ports defining the two overlapping FTS bands Mirror mechanism Detector array Beam modules divider 2nd port calibrator Figure 2 5 SPIRE FPU spectrometer side layout 2 3 3 Spectrometer calibration source SCAL A thermal source the Spectrometer Calibrator SCAL Hargrave et al 2006 is available as an input to the second FTS port to allow the background power from the telescope to be nulled thus reducing the dynamic range because the central maximum of the interferogram is proportional to the difference of the power from the two input ports SCAL is located at 18 CHAPTER 2 THE SPIRE INSTRUMENT the pupil image at the second input port to the FTS and has two sources which can be used to simulate different possible emissivities of the telescope 2 and 4 The in flight FTS calibration measureme
70. ctral range over which FTS data is currently be calibrated Note that the final spectra may extend beyond these limits because of the correction for the telescope velocity i e the final spectra are provided in the local standard of rest LSR reference frame Band Spectral Range SSW 958 GHz 313 um to 1546 GHz 194 jum SLW 447 GHz 671 um to 990 303 jum 0 8 F 0 6 E a 02L Normalized line flux Normalized line flux L o N A E pe be eee pg Pe el EE ee E E 5 0 S 10 15 15 10 zo 0 5 10 15 Frequency GHz Frequency GHz 1 c 4 un u us oL Figure 4 2 The FTS instrumental line shape the Sinc function The average line shape in black for the two central detectors from unresolved CO lines in the HR spectrum of NGC 7027 SSWD4 left and SLWC3 right The grey curves show the line shapes for all 30 observations of NGC 7027 are of the order of 1 60 of the resolution element The error on the integrated line flux is estimated at less than 1 For the sinc function the spectral resolution in the natural units of wavenumbers Aoc is the distance from the peak to the first zero crossing i e Ao 1 22 max where Lmax is the maximum optical path difference created by the scan mirror travel The wavenumbers are converted to frequencies using Af GHz 1077 c Ao cm 1 where c is the speed of light There were three observing modes with three differe
71. d demodulates and digitises the detector signals the FPU Control Unit FCU controls the cooler and the mechanisms and reads out all the FPU thermometers and the Digital Processing Unit DPU runs the on board software and interfaces with the spacecraft for commanding and telemetry A summary of the most important instrument characteristics is shown in Table 2 1 and the operational parts of SPIRE are presented in the subsequent sections A more detailed description of SPIRE can be found in Griffin et al 2010 SPIRE shares the Herschel focal plane with HIFI and PACS and it relative position with respect to the other two instruments is shown in Figure 2 2 2 2 Photometer design 2 2 1 Optics and layout The photometer opto mechanical layout is shown in Figure 2 3 It is an all reflective design Dohlen et al 2000 except for the dichroics used to direct the three bands onto the bolometer arrays and the filters used to define the passbands Ade et al 2006 The input mirror M3 lying below the telescope focus receives the f 8 7 telescope beam and forms an image of the secondary at the flat beam steering mirror BSM M4 Mirror M5 converts the focal ratio to f 5 and provides an intermediate focus at M6 which re images the M4 pupil to a cold stop The input optics are common to the photometer and spectrometer and the separate spectrometer field of view is directed to the other side of the optical bench panel by a pick off mirror close to M6
72. derations to be taken into account when preparing FTS ob servations These are based on our current knowledge of the FTS performance Most of them are described in details in this chapter as well as in Chapters 4 and Section 5 4 SED like mode The use of low or medium spectral resolution to get the overall spectral energy distribution is not recommended without SPIRE photometry observation the 3 3 SPIRE SPECTROMETER AOT 47 removal of the telescope and instrument background may lead to significant offsets in the absolute continuum level Long observations The rms noise in HR observations with 100 repetitions 4 hours beats down following the time law Longer observations are better to be split into AORs with no more than 100 120 repetitions as there is no guarantee that instrument stability issues will not have considerable impact on the observation Mapping For fully sampled maps spatial pixels in the spectral cube can be co added resized to enhance sensitivity Calibration errors or other imperfections however may lead to worse signal to noise than achievable in theory Background Dark sky observation is always performed during F TS observing days this is part of the SPIRE instrument calibration time If a local background foreground needs to be separated from the source then it is up to the observer to define the location and the depth of this observation It will be part of the proposal In some cases the FTS off axis detectors
73. detector angular offset products ElecCross Spectrometer Electrical Crosstalk table InstRsrfList Set of spectrometer instrument RSRF products LpfPar Spectrometer Low Pass Filter Parameters NonLinCorrList Set of spectrometer non linearity correction products OpdLimits Spectrometer OPD Limits table OptCross Spectrometer Optical Crosstalk table PcalModel Spectrometer PCAL Response Model table SmecStepFactor Spectrometer Step Factor table TeleModel Spectrometer OD dependent Telescope Model Correction TeleRsrfList Set of spectrometer telescope RSRF products TempDriftCorrList Set of temperature drift correction products Bibliography Ade P et al 2006 Proc SPIE 6275 62750U Audley D et al 2007 in Proc Exploring the Cosmic Frontier Astrophysical Instruments for the 21 Century Springer Verlag p 45 Bendo G et al 2013 MNRAS 433 3062 Benielli D et al 2013 Experimental Astronomy submitted Cantalupo C M Borrill J D Jaffe A H Kisner T S Stompor R 2010 ApJS 187 212 Chattopadhaya G et al 2003 IEEE Trans Microwave Theory and Techniques 51 2139 Decin L amp Eriksson K 2007 Theoretical Model Atmosphere Spectra Used for the Calibration of Infrared Instruments A amp A 472 1041 2007 De Graauw Th et al 2010 The Herschel Heterodyne Instrument for the Far Infrared HIFI A amp A 518 L6 Dohlen K et al 2000 Proc SPIE 4013 119 Dowell D et al 2003 Proc SPIE 4855 73 D
74. e En tion The orientation constraint means a scheduling O Small Maj Muse constraint and should therefore be used only if neces Repetition factor Source Flux Estimates and Bright Source Setting Sary Repetition 1 Source Flux Estimates Large Map Parameters Angle from to Length arcmin 4 0 Height arcmin 00 In the case when Array with Sky Constraint is se Select the speed Nominal EZ x RU DUE TES lected the pair of angles in degrees between which Map centre offset Y arcmin 0 000 the middle scan leg can lie along Map centre offset Z arcmin 0 000 Orientation mpa en Source Flux Estimates optional Angle from degrees An estimated source flux density in mJy and or ngle to degrees a an estimated extended source surface brightness Observation Est Add Comments CAOR Visibility MJy sr may be entered for any of the three pho Cu e tometer bands in which case the expected S N for that band will be reported back in the Time Esti mation The sensitivity results assume that a point source has zero background and that an extended source is not associated with any point sources T he point source flux density and the extended source sur face brightness are treated independently by the sen sitivity calculations If no value is given for a band the corresponding S N is not reported back The time estimation will return the corresponding S N as well as the o
75. e Major revisions in the Flux Calibration chapter 5 The Photometer section 5 2 is based on the published papers by Griffin et al 2013 Bendo et al 2013 The Photometer section includes a number of guidelines on how to perform aper ture photometry and the applicable corrections colour corrections and conversions of the pipeline flux densities of S v sources to sources with different spectral shapes The conversion parameters are tabulated for the most frequent cases of spectral shapes of astronomical sources power law or modified blackbody The Spectrometer section 5 4 is based on Swinyard et al 2014 Fulton et al 2013 Hopwood et al 2013 Changes in Section 5 2 9 and 5 4 1 providing the final best knowledge beam mea surements for the photometer and the spectrometer respectively e A number of sub sections that were useful for preparing observations were removed from this version as not relevant anymore If they are needed from historical reasons or otherwise they are still available in the previous version of this document The previous versions of this document are available at the Herschel Science Centre http herschel esac esa int Docs SPIRE pdf spire om v24 pdf 1 5 LIST OF ACRONYMS 9 1 5 List of Acronyms AOR AOT BSM DCU DP DPU ESA FCU FIR FOV FPU FTS HCSS HIFI HIPE HSA HSC HSpot IA ILT ISM JFET LSR NEP OPD PACS PCAL PFM PLW PMW PSW PTC RMS rms RSRF
76. e is needed The photon noise level arising from unavoidable statistical fluctuations in the amount 2 4 COMMON INSTRUMENT PARTS 21 of background radiation incident on the detector dictates the required sensitivity In the case of SPIRE this radiation is due to thermal emission from the telescope and results in a photon noise limited NEP on the order of a few x10 7 W Hz 2 The bolometers are de signed to have an overall NEP dominated by this contribution To achieve this the operating temperature for the SPIRE arrays must be of the order of 300 mK The operating resistance of the SPIRE bolometers is typically a few MQ The outputs are fed to JFETs located as close as possible to the detectors in order to convert the high impedance signals to a much lower impedance output capable of being connected to the next stage of amplification by a long cryoharness The thermometers are biased by an AC current at a frequency in the 100 Hz region This allows the signals to be read out at this frequency which is higher than the 1 f knee frequency of the JFETs so that the 1 f noise performance of the system is limited by the detectors themselves and corresponds to a knee frequency of around 100 mHz The detailed design of the bolometer arrays must be tailored to the background power that they will experience in flight and to the required speed of response The individual SPIRE photometer and spectrometer arrays have been optimised accordingly
77. e of several degrees at the nominal scan speed As with most observing systems high SNR predictions should not be taken as quantitatively correct This is because small errors such as pointing jitter other minor fluctuations in the system or relative calibration errors will then become significant That is why a SNR of 200 is taken as the maximum achievable for any observation and HSpot will never return a value of SNR greater than 200 4 2 Spectrometer 4 2 1 Spectral range line shape and spectral resolution The FTS spectral range given in Table 4 2 represents the region over which the FTS sensitivity estimates and calibration are reliable The instrumental line shape of all FTS instruments is a sinc function due to the truncation of the interferogram by the limited travel of the moving mirror the SMEC The observed line shapes for the two central detectors derived from observations of isolated and unresolved lines are shown in Figure 4 2 The actual line shape deviates slightly from an ideal sinc function with a noticeable asymmetry in the first sinc minimum towards higher frequencies i e at positive frequencies in Fig 4 2 this effect is more pronounced for the SSWD4 detector The reason for this asymmetry is still under investigation however this effect does not affect significantly the line centroids as well as the integrated line fluxes the measured line offsets 52 CHAPTER 4 SPIRE IN FLIGHT PERFORMANCE Table 4 2 Spe
78. e paid to the effect of finite map pixel size on peak flux density and a pixelisation correction uncertainty that is introduced into the flux density estimate Users are recom mended to use timeline based source fitting methods for photometry of point sources For extended sources the frequency dependent beam must be taken into account which poses specific challenges for semi extended sources 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 89 Appendix tables for various conversions A script for the Herschel Interactive Processing Environment HIPE is available and can be used to calculate the conversion parameters shown in the following tables The script uses the framework presented in this subsection and allows calculation of correction parameters for power low indices ag or modified blackbody parameters 8 T that are not shown in the tables For any problems in using the script in HIPE please contact the Herschel Science Centre helpdesk Table 5 4 Effective beam solid angle Qeg and beam correction factor Kpeam for a source with spectral index ag The values used in the pipeline for ag apip 1 are shown in bold These values should be used to convert between flux density and surface brightness using the same spectral index as for the colour correction Effective beam solid angle Beam correction factor Qer arcsec KBeam as PSW PMW PLW PSW PMW PLW 4 0 486 64 856 40 1902 40 0 9563 0 9605 0 9297 3 5 482 68 850 89 1
79. e possible to perform the ob servation during certain time periods Fewer days will be available to make that observation than the number of days that the target is visible target visibility does not take into account the constraint as it is a constraint on the observation not the target itself In setting a constraint the observer will need to check that not all observing dates have been blocked and that it is still possible to schedule the observation Note also that as explained earlier parts of the sky do not change their orientation with respect to the array and therefore it is not possible to set the orientation of the map in certain directions the ecliptic as the array is only orientated in one way on the sky These constraints on when the observation can be performed make scheduling and the use of Herschel less efficient hence the observer will be charged extra overheads to compensate Alternatively raster observations can be split into several concatenated AORs to allow some tailoring of the coverage to match the source shape but note that every concatenated AOR will be charged the 180 second slew tax User Input The map parameters are similar to those for the Photometer Large Map The Spectrometer parameters are listed in Section 3 3 4 42 CHAPTER 3 OBSERVING WITH SPIRE Spocecraft Z direction arcsec Spacecraft Z direction arcsec 200 100 0 100 200 RARO eic we ann Spocecroft Y direction arcsec Spacecraft Y di
80. e sparse mode extended sources observed in the sparse mode and extended sources observed in mapping mode The calibration described in this paper has been implemented in the pipeline corresponding to HIPE version 11 To summarise for point sources observed on the centre detectors SSWD4 and SLWC3 the measured repeatability is 6 with the following contributions e Absolute systematic uncertainty in the models from comparison of Uranus and Neptune models determined to be 3 e The statistical repeatability determined from observations of Uranus and Neptune with pointing corrected estimated at 1 5 4 SPIRE SPECTROMETER FLUX CALIBRATION 101 e The uncertainties in the instrument and telescope model which lead to an additive continuum offset error of 0 4 Jy for SLW and 0 3 Jy for SSW e The effect of the Herschel pointing APE Note that the pointing uncertainty results only in a reduction in flux and is therefore not a true statistical uncertainty on the recovered flux level A large pointing offset also results in a significant distortion of the SSW spectrum of a point source and a mismatch between the SLW and SSW spectra Providing one is convinced that the source in question has no spatial extension the SLW portion of the calibrated spectrum can be used to correct any apparent gain difference between the SLW and SSW spectra For sparse observations of truly extended sources the absolute uncertainty in flux for a reasonably
81. e telescope e Small area maps This is for sources or areas with diameters smaller than 5 arcmin The map is made by two short cross scans with the telescope e Point source photometry This mode is for photometric observations of isolated point sources It uses chopping jiggling and nodding observing the source at all times This mode was never used for science observations 3 2 1 Large Map Description The build up of a map is achieved by scanning the telescope at a given scan speed Nominal at 30 s or Fast at 60 s along lines This is shown in Figure 3 1 As the SPIRE arrays are not fully filled the telescope scans are carried out at an angle of 42 4 deg with respect to the Z axis of the arrays and the scan lines are separated by 348 to provide overlap and good coverage for fully sampled maps in the three bands This is shown schematically in Figure 3 1 One scan line corresponds to one building block Cross linked scanning or cross scanning is achieved by scanning at 42 4 deg Scan A angle and then at 42 4 deg Scan B angle see Figure 3 3 The cross scan at Scan A and B is the default Large Map scan angle option in HSpot This ensures improved coverage of the mapped region Although the 1 f knee for SPIRE is below 0 1 Hz Griffin et al 2010 the cross scanning also helps to reduce the effect of the 1 f noise when making maps with maximum likelihood map makers like MADMAP Cantalupo et al 2010 Note that the 1 f
82. eamProfileAnalysis 82 CHAPTER 5 SPIRE FLUX CALIBRATION 7 The source flux density is then given in the units specified by the aperture photometry routine usually Jy or mJy Aperture photometry of point sources starting from extended maps This method uses the extended source maps available for products processed with HIPE v10 and above These have the relative gains applied which improve the reliability of the mea surements and so do not require reprocessing but are calibrated for an infinitely extended source Relative to the point source calibration the extended one produces slightly lower fluxes by 0 5 1 see K4g K4 in Table 5 2 though this is well within the errors resulting from the uncertainties on the beam solid angle 4 1 Use the Level 2 extended source map products called extdPxW which give surface brightness in MJy sr for infinitely extended sources with a vS const spectrum 2 If desired recalibrate the map for a point source in units of flux density recommended a Convert back to point source calibration by dividing by the Kpiog parameter given in Table 5 2 This produces maps in Jy beam Ensure that the units of the map are set accordingly b Divide the maps by the pipeline beam solid angle Qpip given in Table 5 2 to convert the map units to surface brightness Note that most aperture photometry tasks require a map in units of Jy pixel 3 Perform the aperture photometry 4 Apply the
83. ecifically in Table 5 4 and 5 5 and Figure 5 10 5 2 9 Photometer beam maps and areas Updated analysis of the SPIRE photometer beam data and resulting beam parameters are available on the SPIRE Public wiki and comprise the following e new empirical beam maps based on fine scan map measurements of Neptune e the raw data used for the above e a theoretical model including coverage of the sidelobes and low level structure due to the secondary mirror supports unchanged from the previous issue e an updated analysis of the diffuse and point source backgrounds http herschel esac esa int twiki bin view Public SpirePhotometerBeamProfileAnalysis 72 CHAPTER 5 SPIRE FLUX CALIBRATION Empirical beam maps The empirical beam products consist of two sets of three beam maps one for each photometer band The product is derived from scan map data of Neptune performed using a custom fine scan observing mode with the nominal source brightness setting where the detector array and its surroundings were scanned at a distance of only 2 3 between scan legs In these fine scan observations each bolometer is scanned over Neptune in four different directions The data were reduced using the standard HIPE scan map pipeline the median baseline subtractor with a circular exclusion zone of 8 diameter and the naive map maker Each map constitutes an averaging in the map over all of the individual bolometers crossing the source and represent
84. ector arrays and are held rigidly at various points by Kevlar support modules The supports at the entries to the spectrometer and photometer 1 7 K boxes are also designed to be light tight 2 4 3 Warm electronics There are three SPIRE warm electronics units The Detector Control Unit DCU provides the bias and signal conditioning for the arrays and cold electronics and demodulates and digitises the detector signals The FPU Control Unit FCU controls the He cooler the Beam Steering Mechanism and the FTS scan mirror and also reads out all the FPU thermometers The Digital Processing Unit DPU runs the on board software interfaces with the spacecraft for commanding and telemetry The 130 kbs available data rate allows all photometer or spectrometer detectors to be sampled and the data transmitted to the ground with no on board processing Chapter 3 Observing with SPIRE 3 1 Introduction Any observation with SPIRE or any of the Herschel instruments was performed following an Astronomical Observation Request AOR made by the observer The AOR is constructed by the observer by filling in an Astronomical Observation Template AOT in the Herschel Observation Planning Tool HSpot Each template contains options to be selected and pa rameters to be filled in such as target name and coordinates observing mode etc How to do this is explained in details in the HSpot user s manual while in the relevant sections in this chapter we exp
85. ectrometer bolometers receive radiation from the combination of the astronomical source the telescope and the instrument itself It is therefore necessary to subtract the excess emission to recover the source spectrum This is done using the following model Vobs Fisource Source Ha Mre Rinst Minst 5 50 where Vops is the measurement Rgource Rte and Rist are the RSRFs applicable to the source telescope and instrument contributions and Igource Mre and Minst are the corre sponding intensities In the case of the instrument Myst is due to the thermal emission from within the 5 K FPU enclosure The model of the emission from the telescope is determined using the emissivity of the primary and secondary mirrors measured before the launch by Fischer et al 2004 c 9 5 c l lt 0 0336 0 273 5 51 V V where v is the frequency in kHz During the mission the emissivity of the primary mirror was found to change with time and so is corrected by a time dependent factor Eeorr Hopwood et al 2013 The final emission from the telescope assuming that there is no stray light and taking account of emission from both the primary M1 and secondary M2 mirrors and reflection from the secondary is taken to be Mra 1 m2 Ecors Mi B Ti v m28 Tma v 5 52 where B T v is the Planck function as given in Eq 5 28 expressed in terms of frequency so that the final units can be easily converted to J
86. ed S N for each resolution If the number of repetitions for the high and low resolution parts are nH and nL respectively then the achieved low resolution continuum sensitivity will correspond to nH nL repetitions because low resolution data can also be extracted from every high resolution scan 3 3 2 Pointing Modes A pointing mode and an image sampling are combined to produce the required sky coverage Here the pointing modes are described Single Pointing Mode Usage and Description This is used to take spectra of a region covered by the instrument field of view 2 diameter circle unvignetted With one pointing of the telescope only the field of view of the arrays on the sky is observed Raster Pointing Mode Usage and Description This is used to take spectra of a region larger than the field of view of the instrument 2 diameter circle The telescope is pointed to various positions making a hexagonally packed map see example in Figure 3 14 At each position spectra are taken at one or more BSM positions depending on the image sampling chosen see Section 3 3 3 The HSpot input parameters are shown in Figure 3 12 right Details The area to be covered determines the number of pointings in the map The distances between individual pointings are 116 along the rows and 110 between the rows as shown in Figure 3 14 The number of pointings needed to cover the map is rounded up to ensure that the whole of the requested area
87. edure as for a power law spectrum and derive the colour correction parameters f v R v n v dv B ap Passband K T _ pip B T 5 29 Cap T B v B T vo x f VP B T v R v n v dv eee Passband 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 71 for a point source and f v R v n v Qe v dv B api Passband K T 8 PP B T x 5 30 cote T B Yo T vo f v8B T v ROJN Qea v dv pad Passband for an extended source Note that api 1 by convention 5 2 8 Conversion of in beam flux density to surface brightness The in beam astronomical flux density at a given frequency v is defined as S v B04 v I 0 dQ 5 31 AT where 0 0 7 is a radial angular offset from the beam centre 0 27 is an azimuthal angular offset B 0 v is the normalised frequency dependent beam distribution T 0 is the sky intensity surface brightness distribution and dQ is a solid angle element in the direction defined by 0 9 The point source pipeline produces flux densities in terms of Jy beam The surface brightness Jy arcsec or Jy sr can be obtained from the flux density by dividing it by the effective beam area Likewise the extended pipeline produces surface brightnesses in terms of MJy sr which can be converted to a flux density by multiplying by the effective beam area The effective beam areas as a function of frequency and of source spectral index are given in Section 5 2 9 and sp
88. egligible value This sky map can then be subtracted from individual repeats to estimate the instrument noise The extragalactic confusion noise levels for SPIRE defined as the standard deviation of the flux density in the map in the limit of zero instrument noise are provided in detail in Nguyen et al 2010 The measured extragalactic confusion and instrument noise levels are given in Table 4 1 for the nominal scan speed 30 s Instrument noise integrates down in proportion to the square root of the number of repetitions and for the fast scan speed 60 s the instrument noise is V2 higher as expected from the factor of 2 reduction in integration time per repeat The achieved instrument noise levels are comparable to the pre launch estimates which were 9 6 13 2 11 2 mJy in beam at 250 350 500 um very similar for the 250 and 500 wm bands and somewhat better for the 350um band In SPIRE PACS Parallel mode the achieved SPIRE instrument noise level per repeat is different to that for a single repeat in SPIRE only mode due to the different effective integration time per beam see the SPIRE PACS Parallel Mode Observers Manual 49 50 CHAPTER 4 SPIRE IN FLIGHT PERFORMANCE Sigma mJy beam 40 60 ntegration Time s Figure 4 1 Pixel noise vs integration time for all pixels in deep SPIRE photometer fields The derived instrument noise is shown in red the confusion floor is show in blue and the total no
89. egrating the above expression between some fixed bolometer voltage Vo and Vm Vm Vin B vw f K i Dx dV 5 11 Vo Vo SO e Vm K3 K Vm Koln 5 12 8 Ki Vm Vo Kaln e 5 12 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 65 3x10 eee Bolometer model Fitted f V 2 25 10 1 5x104 RV Oyi V 75x10 1 14 18 22 26 3 Operating point voltage V mV Figure 5 6 Typical plot of f V vs V for a nominal 350 wm bolometer The blue points correspond to the bolometer model and the red line is the fitted function using Eq 5 10 Ideally Vo would be the bolometer voltage in the absence of any astronomical signal i e what would be measured when observing blank sky in otherwise identical conditions The resulting flux density would correspond to that from the sky calibrated with respect to the blank sky level Vo is therefore derived from standard calibration observations of a dark area of sky in scan map mode under the nominal conditions bias voltage and frequency bolometer and instrument FPU Level 1 temperature and telescope temperature Ideally the conditions would be the same for the calibration and science observations but small differences are inevitable in practice Vo thus differs from the ideal value by an amount much larger than most astronomical signals This means that the raw flux density values produced by the pipeline have additive
90. elengths up to 700 um are awaited In the meantime the available SEDs can be extrapolated with reasonable accuracy to SPIRE wavelengths assuming no excess emission due to a chromospheric component or to a cold dust component around the star The presence of any such excess would lead to a higher flux density so the extrapolated figures can be taken as lower limits 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 61 be aaa Se ee cers ee et ae a Se Alpha Boo Alpha Tau Beta Peg I Beta And I Alpha Cet Gamma Dra 100 SNC AN Sinus Beta Umi Alpha Boo extrapolation Alpha Tau extrapolation E Beta Peg extrapolation J Beta And extrapolation e Alpha Cet extrapolation 10 ewe Gamma Dra extrapolatioy c Sirius extrapolation x a Umi extrapolation Flux Density Jy Wavelength microns Figure 5 3 FIR SEDs model for the eight stellar calibrators with extrapolations to the SPIRE photometer bands using Decin amp Eriksson 2007 5 2 Photometer flux calibration scheme The photometer pipeline produces monochromatic in beam flux densities Jy beam at stan dard frequencies corresponding to 250 350 and 500 um and calculated under the assumptions of i a point source observation and ii a flat vS spectrum i e vS const The cali bration is carried out at the level of the detector timelines Level 1 data pr
91. erature drift correction using thermometers located on each of the arrays which are not sensitive to the sky signal but track the thermal drifts This correction works well and has 4 2 SPECTROMETER 51 Table 4 1 Estimated SPIRE Photometer sensitivities For the Parallel mode sensitivities please consult the The SPIRE PACS Parallel Mode Observers Manual Band 250 350 500 1 o extragalactic confusion noise mJy in beam 5 8 6 3 6 8 SPIRE only scan map 30 s scan rate 1 c instrument noise for one repeat i e two cross linked scans A B 9 0 7 5 10 8 mJy in beam 1 o instrument noise for one repeat i e one scan A or B mJy beam 12 8 10 6 15 3 SPIRE PACS Parallel Mode 20 s slow scan rate 1 o instrument noise for one repeat i e one scan A nominal mJy in 7 3 6 0 8 7 beam 1 o instrument noise for one repeat i e one scan B orthogonal mJy 7 0 5 8 8 3 in beam SPIRE PACS Parallel Mode 60 s fast scan rate 1 o instrument noise for one repeat i e one scan A nominal mJy in 12 6 10 5 15 0 beam 1 o instrument noise for one repeat i e one scan B orthogonal mJy 12 1 10 0 14 4 in beam been further improved with the recent update of the flux calibration parameters Detector timelines to de correlate thermal drifts over a complete observation can produce a 1 f knee of as low as a 1 3 mHz This corresponds to a spatial scal
92. ervations When a SPIRE observation is downloaded from the Herschel Science Archive it will be packed in a special tar file with a structure and content as shown in Figure 6 3 Note that the rel evant fits file names are not human readable but the names of the higher level folders should match the corresponding context For example the Photometer maps calibrated for extended emission see Section 5 2 5 are under level2 extdPxW and the point source cali brated ones see Section 5 2 4 under level2 psrcPxW where x is S M L for 250 350 500 um correspondingly Name v 3 1342201265 B 1342201265 herschel ia obs ObservationContext 431394 jpg gt L3 browselmageProduct gt L3 browseProduct hspire13422012650bs 1390915684105 fits gz E levelo c level 5 E levell 3 level2 gt E extdPLW gt LJ extdPLWdiag gt LU extdPMW Name gt i extdPMWdiag v 3 1342268302 gt Lu extdPSW L 1342268302 herschel ia obs ObservationContext 474801 jpg gt L3 extdPSWdiag E browselmageProduct hspire1342201265 20level2context 1390915682583 fits gz browseProduct 4 vvv vv Cal psrcPLW P hspire13422683020bs 1392990915643 fits gz gt LU psrcPLWdiag tet s gt E psremw gt G3 level gt L3 psrcPMWdiag v L3 level2 v L3 psrcPSw gt 3j HR apodized spectrum P hspirepsw1342201265 20pmp 1390915681827 fits gz v 3 HR unapodized spectrum gt L3 psrcPSWdiag hspireunapod 1342268302 HR 20spss 13929908716109 fits gz gt L3 logOb
93. ervers Manual parts of the sky do not change their orientation with respect to the array and therefore it is not possible to set the orientation of the map in certain directions the ecliptic as the array has always the same orienatation The constraints on when the observation can be performed make scheduling and the use of Herschel less efficient hence the observer will be charged 10 minutes observatory overheads instead of 3 minutes to compensate see the Herschel Observers Manual Warning Setting a Map Orientation constraint means that your observation can only be performed during certain periods and the number of days that your observation can be scheduled will be reduced from the number of days that the target is actually visible because 3 2 SPIRE PHOTOMETER AOT 27 250 um array Figure 3 3 Large Map scan angles it is a constraint on the observation not the target itself In setting a constraint you will need to check that it is still possible to make your observation User inputs The user inputs in HSpot are shown Figure 3 4 and summarised below Repetition factor The number of times the full map area is repeated to achieve the required sensitivity For cross linked maps Scan Angles A and B there are two coverages per repetition one in each direction For single scan direction observations Scan Angle A or Scan Angle B one coverage is performed per repetition Length This is the
94. esolution This mode is best for discovery spectral surveys where the whole range from 194 to 671 um can be surveyed for new lines It is also useful for simultaneously observing sequences of spectral lines across the band e g the CO rotational ladder In this way a relatively wide spectral range can be covered in a short amount of time compared to using HIFI although with much lower spectral resolution than achieved by HIFI see the HIFI Observers Manual Low resolution spectra can also extracted by the pipeline from high resolution observations Consequently the equivalent low resolution continuum rms noise for the number of scan 40 CHAPTER 3 OBSERVING WITH SPIRE repetitions chosen can also be recovered from a high resolution observation i e improving the sensitivity to the continuum For cases where the signal to noise ratio SNR for this extracted low resolution spectrum is not sufficient for the scientific case the following High and Low resolution mode is available High and Low Resolution Usage and Description This mode allows to observe a high resolution spectrum as well as using additional integration time to increase the SNR of the low resolution continuum to a higher value than would be available from using a high resolution observation on its own This mode saves overhead time over doing two separate observations The number of high resolution and low resolution scans can differ and will depend on the requir
95. for the full range of apertures from 0 to 700 Note that this normalised beam area is for a source with api 1 For any other non standard apertures the aperture corrections could be computed from the beam maps available on the SPIRE Public wiki Colour correct for the true source spectrum using the extended source colour correction parameter cg in Table 5 6 or Table 5 7 for a grey body The source surface brightness is then given the units specified in the photmetry routine usually MJy sr http herschel esac esa int twiki bin view Public SpirePhotometerBeamProfileAnalysis 8http herschel esac esa int twiki bin view Public SpirePhotometerBeamProfileAnalysis CHAPTER 5 SPIRE FLUX CALIBRATION 84 pol ur UMOYS ore uLioj1od ppnous osn oy sdo3g uoeIs ur ore sjonpoud JosN oY on q ur ore syonpoid ourpodtid oy Aors UT UMOYS ore sour odid prepueys ou syonpoid ourpodid 193ouro30ud prepueys oy SUISN UT poA oAur sdo3s oY SULMOYS 31eqoMO T GTG IMIA sn nuue punoJSxoeq pur ainjiode 10 ypes prepuejs osn Kxounougg 3a4nj1od y aep nuuy gc QEL E S AQLL Ady osn WHM sn as Bq 110jaanj1ad yop youdOVa aN 1109a 1nj 1ad yop Joudova 8 S AWL E S AL Myon X wWHAWosn 10 9B 1 xassng Suny 324nog eugoun BBS uoIsIoAUOD SME PANET xn Aui el pSpUS XH ysuoo ga AUOC XN UOT291107 jurod odoz qsuoo ga Auo Xn d
96. from ground measurements taking into account the dominant impact of the flight environmental conditions gravity release cryo vacuum operation as well as the detailed pupil obscuration from the full observatory geometry The full SPIRE instrument optical model including the entire photometer train up to focal plane is also implemented see Figure 5 11 The simulated source is a coherent point source with continuum Rayleigh Jeans RJ spectrum representative of most bright point sources with brightness temperature The effect of the detector feedhorn is taken into account by including further pupil apodisation with a spectrally varying edge taper and associated spectral shift of the diffraction focus within each band which has been characterised during SPIRE ground calibration The full band response is obtained by spectral weighting of the set of individual responses The weights are obtained by product of the Rayleigh Jeans source spectrum with the instrument RSRF in each band the spectral in band throughput AQ and finally the spectral in band coupling all derived from flight model instrument level ground calibration 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 77 Figure 5 11 View of the model geometry left and reconstructed telescope pupil optical path difference map from environmental ground measurements by Herschel Observatory industrial contractors right The derived beam models can be considered as static noise free point so
97. g 1 and so any colour correction that has been applied should be reversed Table 5 2 Values of Kap KwouE o 1 Kpton Qpip and Kap for the three SPIRE bands K4p is the pipeline point source flux conversion parameter KMmong a 1 is the conversion to monochromatic surface brightness for an extended source with o 1 for Kptog is the conversion from point source flux density to extended source surface brightness for a source spectrum a 1 Qpip is the beam solid angle for a source with ag 1 ie QOeg 1 Kap is the flux conversion parameter used in the pipeline defined as Kwosg o 1 Qpip whcih converts to the flux density of an extended source while K4g K4p is the ratio of the two pipeline conversion parameters PSW PMW PLW Kap 1 0102 1 0095 1 0056 KwonE MJy sr per Jy beam 92 216 52 290 24 173 Kptoz MJy sr per Jy beam 91 289 51 799 24 039 Qpip arcsec 465 39 822 58 1768 66 Kap 1 0087 1 0110 1 0049 Kap Kap 0 9986 1 0015 0 9993 5 2 7 Colour correction for modified black body spectra For some sources the approximation to a power law spectrum is not accurate This is par ticularly true of sources with low blackbody temperatures Assuming a modified blackbody also known as a greybody with a spectrum Ig v B T v where is the dust emissivity index and B T v is the Planck blackbody function 2hy 1 B T v Qo gwT 5 28 we can follow the same proc
98. hat the user rotates the beam map so that it matches the position angle of the user s data The position angle of HIPE maps can be found in the primary FITS header and is specified by the POSANGLE keyword Table 5 3 summarises the basic beam parameters for data binned into 1 map pixels The FWHM values are determined by fitting an asymmetric 2 D Gaussian to the beam maps and the beam areas are computed by integrating explicitly under the measured beam profiles It is recommended to use the as measured beam area in 1 maps in the flux density to surface brightness conversion The main beams are approximated by Gaussian profiles with the nominal FWHM values of 18 1 24 9 36 4 measured on maps with 6 10 14 pixels The explicit integration un der the measured beams in standard maps with 6 10 14 pixels produces beam areas of 533 936 1808 arcsec which are larger by factors of approximately 1 18 1 17 1 08 at 250 350 500 um than those derived from higher resolution beam scans maps with 1 pixel These are derived by rebinning the updated background removed beam maps to the stan dard SPIRE skybin sizes The basic beam parameters vary as a function of pixel scale with the FWHM values and beam areas increasing with pixel size This is expected since the fidelity of the surface brightness 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 73 250 pm 1 pixels 350 um 1 pixels 500 um 1 pixels 250 um 6 pixels 350 um
99. hel range the disk averaged brightness temperatures increase with wavelength as deeper layers in the atmosphere are probed The planets have similar tempera tures despite Neptune s greater distance from the Sun because Neptune has an internal heat source This also leads to a more dynamic neptunian atmosphere resulting in some prominent spectral features whereas the Uranian spectrum is largely featureless see e g Teanby amp Irwin 2013 Typical photometer 250 350 500 um calibration flux densities see Section 5 2 for precise definition are 160 100 60 Jy for Neptune and 370 250 150 Jy for Uranus 5 1 3 Mars models Web based models of the martian continuum by Emmanuel Lellouch and Bryan Butler are available at http www lesia obspm fr perso emmanuel lellouch mars and http www aoc nrao edu bbutler work mars model1 lftp ftp sciops esa int pub hsc calibration PlanetaryModels 5 1 CALIBRATION SOURCES AND MODELS 59 Moreno Model Uranus and Neptune Brightness Temperature Spectra 80 a AT NNUS d 10 Jy ait f ji B aa ULEUEE 50 50 100 150 200 250 300 350 400 450 500 550 600 650 700 Brightness Temperature K Wavelength microns Figure 5 1 Currently adopted models Moreno 2010 Orton et al 2014 of the brightness temperature spectra of Uranus and Neptune Mars is a very bright source for SPIRE For example at the time of its observation by SPIRE on 29 Oct 2009 Herschel operational day
100. ing and bath temperature conditions This translates to a corresponding relationship for the differential sensitivity of the system to the RSRF weighted flux density S dV dV mo 5 8 qg V gt ag KV 5 8 To allow for the fact that the responsivity operating point voltage relationship will not be exactly linear we let FV 5 9 Note that 1 f V is specific to a particular bolometer and bias setting 2 f V is negative since absorbed power causes a decrease in bolometer voltage however in the rest of this document we take it to be positive for convenience assuming that a correction factor of 1 is applied In order to obtain S we need to integrate f V Various fitting functions for f V have been investigated and it is found that the most suitable function is of the form Ko V K3 where K1 K and K3 are constants K has units of Jy V K has units of Jy and K3 has units of V f V Ki c 5 10 An example plot of f V vs V is shown Figure 5 6 and corresponds to a typical SPIRE 350 um bolometer The nominal operating point blank sky in this case would be close to 3 mV and the range covered by the plot covers a sky brightness range up to more than 10 times the telescope brightness The blue points are derived from a bolometer model and the red line corresponds to the best fit K parameters using Eq 5 10 A flux density corresponding to a measured RMS bolometer voltage Vm can be derived by int
101. ion 5 4 SPIRE SPECTROMETER FLUX CALIBRATION 97 5 4 SPIRE Spectrometer Flux Calibration The information in this Section is based on Swinyard et al 2014 The calibration of the spectrometer follows a different method to that adopted for the pho tometer The FTS detector output is not a direct measurement of the flux density integrated over the passband as in the photometer but depends on the Fourier components of the spec tral content Therefore Equation 5 12 is not directly applicable but an analogous equation can be used to correct for any non linearity between absorbed power and bolometer voltage before transforming into the frequency domain The parameters in this scheme are derived from a thermal model of the bolometer response to absorbed power Once a linearised voltage timeline has been obtained the signal versus optical path difference is calculated using the spectrometer mechanism position and corrections for phase error in forward and backward scans due to the time response of the bolometers and electrical filters are made see Fulton et al 2008 At this stage the timeline is referred to as an interferogram linearised voltage vs optical path difference The next step is to subtract the baseline of the interferogram and apply further phase cor rection An apodization function smoothing function in Fourier space can be applied if desired The final interferogram is then Fourier transformed into the spectral domain The sp
102. ion angle does not fall between the derived angles can be identified As the chopping is on the Y axis then the pair of chop avoidance angles A1 A2 corresponds to two pairs of Herschel focal plane position angles PA1 PA2 A1 A2 90 deg which have to be avoided Warning The constraints on when the observation can be performed make scheduling and the use of Herschel less efficient The observer will be charged extra 10 minutes in overheads rather than the usual 3 to compensate Table 3 1 The basic parameters for the Point Source mode Parameter Value Chop Throw 126 63 Chopping frequency 1Hz Jiggle position separation 6 Nod Throw 126 63 Central co aligned detector PSW E6 PMW D8 PLW C4 Off source co aligned detectors PSW E2 E10 PMW D5 D11 PLW C2 C6 Number of ABBA repeats 1 Integration time 256 s Instrument observing overheads 124 s Observatory overheads 180 s Total Observation Time 560 s User Inputs The user input in HSpot are shown in Figure 3 10 and explained below Repetition factor The number of times the nod cycle ABBA is repeated to achieve the required sensitivity Number of chop avoidances An integer between 0 and 3 Chopping Avoidance Angles From To To be used when number of chop avoidances is greater than zero A From To pair defines a range of angles to be avoided Note that also the range 180 degrees is also avoided The interval is defined in equatorial coordinate
103. is the RSRF S v R v v Figure 5 4 RSRF weighted flux density defined as the integral of the source spectrum weighted by the instrument RSRF The three photometer RSRFs are shown in Figure 5 5 The solid lines correspond to the overall filter transmission functions and give the RSRFs R v for the case of a point source The dashed lines give the aperture efficiency r v again for a point source Note that the absolute vertical scale in Figure 5 5 is irrelevant to the computations here as all relevant parameters involve ratios of RSRF integrals The RSRF curves and aperture efficiencies can be accessed from the SPIRE Calibration Tree in the Herschel Interactive Processing Environment HIPE The calibration of extended sources is achieved by applying the corrections for extended sources detailed in 5 2 5 An extended source is defined here as a source that fills the entire beam solid angle with a uniform surface brightness The accurate calibration of a source which is semi extended with respect to the beam depends on the exact details of the surface brightness distribution and is beyond the scope of this document 5 2 PHOTOMETER FLUX CALIBRATION SCHEME 63 Spectral Response Aperture Efficiency 0 8 500 um 350um 0 6 0 4 0 2 e o Spectral Response and Aperture Efficiency arb units 0 4 0 6 0 8 1 0 1 2 1 4 1 6 Frequency THz Figure 5 5 Photometer RSRFs and aperture efficiencies R v
104. is mapped The area is by default centred on the target coordinates however this can be modified by map centre offsets given in array coordinates Note that for raster maps the target centre does not necessarily correspond to the centre of the detector array see Figure 3 14 As the map is not circular and because the orientation of the array on the sky changes as Herschel moves in its orbit the actual coverage of the map 3 3 SPIRE SPECTROMETER AOT Al 1 4 row separation T T T e 400r Coverage QD H endsat 4 di l centreof c L even rows Oo 2 Q O 4 L 4 Q L Coverage J oO begins at ui centre of 18 O odd rows ne L 1 N L L kj oO 200r Q L e Map centre 4 e L height 4 Q N 400r 13 m L 4 n 1 n L i L 400 200 O 200 400 Spacecraft Y direction arcsec Figure 3 14 Ratser map with the SPIRE FTS will rotate about the requested centre of the map usually the target coordinates unless an offset is used except for sources near the ecliptic see the Herschel Observers Manual To force the actual area to be observed to be fixed or to vary less the Map Orientation settings of Array with Sky Constraint can be used to enter a pair of angles which should be given in degrees East of North to restrict the orientation of the rows of the map to be within the angles given Setting a Map Orientation constraint means that it will not b
105. ise is in green Taken from Nguyen et al 2010 Figure 4 1 shows the manner in which the overall noise integrates down as a function of repeats for cross linked maps with the nominal 30 s scan rate The overall noise is within a factor of 2 of the 250 350 500 um confusion levels for 3 2 2 repeats Notes 1 All sensitivity values correspond to nominal source strength settings For bright source settings recommended for sources brighter than 200 Jy in any band the achieved sensitivities are degraded with respect to nominal setting by factors of 3 8 3 2 2 6 for 250 350 500 um It should be noted however that in practice S N values gt 200 should not be regarded as reliable in any case 2 All scan map sensitivity values are for nominal scan speed of 30 s Figures for 60 s scale as V2 An important aspect of the photometer noise performance is the knee frequency that char acterises the 1 f noise of the detector channels Pre launch a requirement of 100 mHz with a goal of 30 mHz had been specified In flight the major contributor to low frequency noise is temperature drift of the He cooler Active control of this temperature available via a heater thermometer PID control system has not been implemented in standard AOT opera tion as trials have shown that a better solution in terms of overall noise performance is to apply a temperature drift correction in the data processing The scan map pipeline includes a temp
106. its the sensitivity see Herschel Confusion Noise Estimator for more details It is important to keep in mind that the galactic confusion noise can vary considerably over the sky When to use this mode Large map mode is used to cover large fields larger than 5 diameter in the three SPIRE photometer bands Note that the mode can still be used even for input height and width OO SPIRE Time Estimation Summary je SPIRE Time Estimation Summary Band Point Source Point source 1 c Extended S Extended S Extended S Band Point Source Point source 1 c Extended S Extended S Extended S um Flux S N instrument Surface S N l o um Flux S N instrument Surface S N l o Density mJy in beam Brightness instrument Density mJy in beam Brightness instrument mJy MJy sr MJy sr mJy MJy sr MJy sr 250 9 0 0 8 250 12 8 1 1 350 7 5 0 3 350 10 6 0 5 500 10 8 0 2 500 15 3 0 3 On source integration time per map repetition s 3051 Number of map repetitions 1 Total on source integration time s 3051 1 3051 Instrument and observation overheads s 951 Observatory overhead s 180 Total time s 4182 3051 951 180 Note to change the observation time change the repetition factor on the AOR main screen It multiplies the on source integration time per map repetition to give the total on source time Confusion noise estimation summary Band Est 1 0 Est 1 0 Est l o um Confusion Noise Confusi
107. itted profile note that this is not Gaussian in shape for SLW and the equivalent solid angles are shown in Figure 5 18 together with the expectation for basic diffraction calculated as the FWHM of an Airy pattern with effective mirror diameter 5 4 SPIRE SPECTROMETER FLUX CALIBRATION 99 of 3 287 m The beam size matches the diffraction limit only at the low frequency end of each band where the waveguide is single moded As further modes propagate their superposition leads to rather larger beam sizes than expected from diffraction theory The beam profile shapes are included in the SPIRE FTS calibration tree and can be used to correct for the frequency dependent source beam coupling if a good model of the source spatial distribution is available Wu et al 2013 gt 35 Beam FWH sE F SLW SSW 4 4r 4 oF L J L 4 3c J e I r H H 4 lt E J g lt H J dL J o EL J mir m 4 E J 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 Frequency GHz Figure 5 18 The FWHM top and area bottom of the SPIRE FTS beam profile as fitted by Makiwa et al 2013 The grey dashed line in the top plot shows the expected FWHM from diffraction theory 5 4 2 Extended sources and spectral mapping Spectral mapping observations are performed using all of the detectors in the spectrometer arrays In the case of fully sampled Nyquist sampled or intermediate sampled twice Nyquist spacing maps the
108. k are provided with links Product Description ApertureEfficiency SPIRE Aperture efficiency Section 5 2 1 and Figure 5 5 BeamProfList SPIRE beam maps with 6 10 14 pixels Section 5 2 9 and Fig ure 5 8 BolPar Photometer Bolometer Parameter Table BsmOpsList Set of BSM Ops products BsmPos Photometer BSM Position Table ChanGain Photometer Channel Gain Table ChanMaskList Set of channel mask products ChanNoiseList Set of channel noise products ChanNum Photometer Channel Number Mapping Table ChanRelGain Photometer Channel Relative Gain Table ChanTimeConst Photometer Channel Time Constant Table ChanTimeOff Photometer Channel Time Offset Table ColorCorrApertureList ColorCorrBeam ColorCorrHfi ColorCorrK List DetAngOffList ElecCross FluxConvList InstModeMaskList LpfPar Opt Cross PcalModel RadialCorrBeam Rsrf TempDriftCorrList Set of Aperture correction products for standard apertures of 22 30 42 Table 5 8 SPIRE beam corrections Kpeam with spectral index and temper ature product Eq 5 39 and Tables 5 4 and 5 5 Spire HFI Cross calibration color correction product Section 5 3 Eqs 5 49 and 5 49 Set of source type colour correction products Section 5 2 and Ta bles 5 6 and 5 7 Set of detector angular offset products Photometer Electrical Crosstalk Table Set of photometer flux conversion products Set of instrument mode mask products Photometer Low Pass Filter Parameters Photometer Optical Cros
109. l paths before recombining By changing the Optical Path Difference OPD of the two beams with a moving mirror an interferogram of signal versus OPD is created This interferogram is the Fourier transform of the incident radiation which includes the combined contribution from the telescope the instrument and the source spectrum The signal that is registered by the Spectrometer detectors is not a measurement of the integrated flux density within the passband like in the case of the Photometer but rather the Fourier component of the full spectral content Performing the inverse Fourier transform thus produces a spectrum as a function of the frequency 16 CHAPTER 2 THE SPIRE INSTRUMENT Figure 2 4 A schematic view of the photometer bolometer arrays the bolometer names are also shown Each circle represents a detector feedhorn Those detectors centred on same sky positions are shaded in blue the dead bolometers are shaded in grey The 4 x 8 unvignetted field of view of each array is delineated by a red dashed rectangle The three arrays overlap on the sky as shown in the rightmost figure where the PLW 500 wm PMW 350 jum and PSW 250 um are depicted by red green and blue circles respectively The circle sizes in the rightmost figure correspond to the FWHM of the beam The spacecraft coordinate system Y Z is also shown The nominal mode of operation of the FTS involves moving the scan mirror continuously nominally at 0 5 mm s
110. lain the AOT user inputs Once the astronomer has made the selections and filled in the parameters on the template the template becomes a request for a particular observation i e an AOR If the observation request is accepted via the normal proposal evaluation time allocation process then the AOR content is subsequently translated into instrument and telescope spacecraft commands which are up linked to the observatory for the observation to be executed There are three Astronomical Observation Templates available for SPIRE one for doing pho tometry just using the SPIRE Photometer one to do photometry in parallel with PACS see The Parallel Mode Observers Manual for details on observing with this mode and one using the Spectrometer to do imaging spectroscopy at different spatial and spectral resolutions Building Blocks Observations are made up of logical operations such as configuring the instrument initialisation and science data taking operations These logical operations are referred to as building blocks The latter operations are usually repeated several times in order to achieve a particular signal to noise ratio SNR and or to map a given sky area Pipeline data reduction modules work on building blocks see Chapter 6 Configuring and initialising the instrument It is important to note that the config uration of the instrument i e the bolometer parameters like setting the bias the science data and housekeeping data
111. le Pointing O lctermediate O Medium M Raster E bowl O Fu O High and Low H L Number of visible stars for the target None Specified Repetition factor Source Flux Estimates and Bright Source Setting Repetition 40 Source Flux Estimates Instrument Settings Raster Map Parameters is Spectral Resolution Length arcmin 0 0 ut Image Sampling Pointing Mode e 5 e High H Height arcmin 0 0 fee parse Single Pointing i Medium M T zx Intermediate z Map centre offset Y arcmin 0 0 Raster LowL OQ Full E EA Map centre offset Z arcmin 0 0 7 High and Low H Orientation Repetition factor Source Flux Estimates and Bright Source Setting Map Orientation Caray 1 EM Repetition 2 Source Flux Estimates Source Flux Estimates Angle from degrees 0 Angle to degrees f Observation Est Add Comments AOR Visibility Observation Est C Add Comments C AOR Visibility z D GD Figure 3 12 The HSpot initial screen for the SPIRE Spectrometer AOTs point source mode left and raster right 3 3 1 Spectral Resolution The Spectrometer Mirror Mechanism SMEC is scanned continuously at constant speed over different distances to give different spectral resolutions see Section 2 3 For every repetition two scans of the SMEC are done one in the forward direction and one in the backward direction making one scan pair as shown in Figure 3 13
112. ligned pixels As Herschel moves in its orbit the orientation of the array on the sky changes To avoid chopping nearby bright sources onto the arrays see e g Figure 3 11 pairs of angles can be defined up to three pairs are allowed which will prevent the observation being made when the long axis of the arrays lies between the specified angles Note that both the specified angle range and its equivalent on the other side of the map 180 degrees are avoided Setting a chop avoidance criterion means that an observation will not be possible during certain periods and the number of days on which the observation can be made will be reduced from the number of days that the target is actually visible visibility in HSpot does not take into account the constraint In setting a constraint you will therefore need to check that it is still possible to make your observation and that you have not blocked out all dates Note also that as explained in the Herschel Observers Manual parts of the sky near the ecliptic plane do not change their orientation with respect to the array and therefore it is not possible to avoid chopping in certain directions Bao SPIRE Time Estimation Summary Band Flux S N l o um density noise mJy my 250 7 0 350 7 0 500 7 0 Banon SPIRE Photometer Unique AOR Label SPhoto 0000 On source time per repetition s 256 Target None Specified Number of repetitions 1 New Target _ et at Total on source integ
113. m As a result the signal level in a map pixel depends on how the square map pixel size compares to the size of the beam Only in the limit of infinitely small map pixels would a pixel co aligned with a point source register the true source flux density It is important to note that no pixel size correction factors are incorporated in the SPIRE Level 2 map making For a given map pixel the flux density value represents the average in beam flux density measured by the detectors while pointed within that area Taking the pixel value for the flux density of an isolated co aligned point source in an otherwise blank map would thus yield an underestimate of the true flux density The necessary correction factor is a function of the map pixel size and the beam size and is a simple multiplicative factor For a symmetrical Gaussian beam of FWHM pea a square pixel of side pix and a co aligned source the correction factor is P Tae fm erf gt may 5 44 where erf is the error function erf x 2 tee dt However in the general case the source will be randomly aligned with respect to the map pixel resulting in a slightly different correction and a small random uncertainty corresponding to the actual offset of the source with respect to the pixel centre for a particular observation Moreover the source is not completely covered on infinitesimal scales the beams are only sampled along the locations where the detectors crossed over the beam
114. may change in future versions of HIPE Table 6 1 The high level folders in the Herschel Science Archive file Each of the folders should contains one multi extension compressed FITS file For the photometer the structure is also applicable for Level 2 5 and Level3 when available For the Spectrometer only the high resolution HR case is shown replace HR with LR for observations performed in low resolution There will be both the HR and the LR variants for the observations with the H LR mode Similarly only an unapodized example is given if the smoothed apodized spectra are needed then use apodized instead Photometer Level2 psrcPxW Point source calibrated maps in units of Jy beam extdPxW Extended source calibrated maps with Planck zero level offset in units of MJy sr Spectrometer sparse mode Levell Point 0 Jiggle 0 HR Extended source calibrated spectra per FTS detector unapodized spectrum in units of W m Hz a7 Level2 HR_unapodized_spectrum Point source calibrated spectra per detector in units of Jy Spectrometer mapping mode Levell Point 0 Jiggle x HR Extended source calibrated spectra per F T S detector unapodized spectrum per jiggle position x in units of W m Hz sr t x can be from 0 to 3 for intermediate sampling maps and from 0 to 15 for fully sampled maps Level2 HR_SxW_unapodized_spectrum SxW spectral cubes in units of W m Hz srt
115. n Figure 3 16 For a point source this requires accurate pointing and reliable knowledge of the source position to be sure to have the source well centred in the central detector beam Intermediate Image Sampling Usage and Description This is to produce imaging spectroscopy with intermediate spatial sampling 1 beam spacing This gives intermediate spatial sampling without taking as long as a fully Nyquist sampled map This is achieved by moving the BSM in a 4 point low frequency jiggle giving a beam spacing of 16 3 25 3 in the final map as shown in Figure 3 16 and Figure 3 17 T he input number of repetitions is performed at each of the 4 positions to produce the spectra The coverage maps for the SSW and SLW in this mode are shown in Figure 3 18 left column Full Image Sampling Usage and Description This allows fully Nyquist sampled imaging spectroscopy of a region of the sky or an extended source This is achieved by moving the BSM in a 16 point jiggle to provide complete Nyquist sampling 1 2 beam spacing of the required area The beam spacing in the final map is 8 1 12 7 as shown in Figure 3 16 and in Figure 3 17 The input number of repetitions is performed at each one of the 16 positions to produce the spectra The coverage maps for the SSW and SLW in this mode are shown in Figure 3 18 right column 3 3 4 User input parameters for all Spectrometer AOTs The user inputs shown in Figure 3 12 are given below Pointing
116. nally packed detectors each with its own individual feedhorn see Figure 2 7 The array modules are similar to those used for the photometer with an identical interface to the 1 7 K enclosure The feedhorn and detector cavity designs are optimised to provide good sensitivity across the whole wavelength range of the FTS The SSW feedhorns are sized to give 2FA pixels at 225 wm and the SLW horns are 2A at 389 um This arrangement has the advantage that there are many co aligned pixels in the combined field of view The SSW beams on the sky are 33 arcsec apart and the SLW beams are separated by 51 arcsec Figure 2 7 shows also the overlap of the two arrays on the sky with circles representing the FWHM of the response of each pixel The unvignetted footprint on the arrays diameter 2 contains 7 pixels for SLW and 19 pixels for SSW outside this circle the data is not well calibrated The design features of the detectors and feedhorns are described in more detail in Section 2 4 1 2 4 Common Instrument Parts 2 4 1 Basic bolometer operations The SPIRE detectors for both the photometer and the spectrometer are semiconductor bolometers The general theory of bolometer operation is described in Mather 1982 and 1The peak emission of a blackbody of 5 K using Wien s displacement law is at 580 um 2 4 COMMON INSTRUMENT PARTS 19 Wavelength xm 700 600 500 400 300 200 0 35 TTT TTT Tt T 0 30 0 25 g BS 2 020 E Nn amp 0 15 e H
117. noise will be less significant at the faster scan speed Real coverage maps for the cross scanning and single direction scanning for the different SPIRE bands can be found in Section 3 2 1 When 1 f noise is not a concern the observer can choose either one of the two possible scan angles A or B The two are equivalent in terms of observation time estimation overheads 3 2 SPIRE PHOTOMETER AOT 25 Y Axis Scanning angle between Z axis and scan direction Scan direction f Scan leg separation Scan legs are slightly longer than the user requested length to rotation of scan ensure the user pattern dependent on requested area is date properly covered R A requested map area Figure 3 1 Large Map build up with telescope scanning showing the scan angle the scan legs and the guaranteed map area sensitivities but one may be favourable especially when the orientation of the arrays of the sky does not vary much due to either being near the ecliptic plane or to having a constrained observation see below To build up integration time the map is repeated an appropriate number of times For a single scan angle the area is covered only once For cross linked scanning one repetition covers the area twice once in each direction Hence cross linked scanning takes about twice as long and gives better sensitivity and more homogeneous coverage see Figure 3 6 Cross linked scanning is limited to an
118. nt Lmax although only two were used for science observations HR with Af 1 2 GHz and LR with Af 25 GHz The FWHM in km s of an unresolved line for the HR mode is FWHM kms 7 1 20671 Af 1 4472 gt 4 1 um Hence the line FWHM for the SSW is between 280 450 km s and between 440 970 kms for the SLW The resolving power A AA f Af ranges from 370 to 1288 at the two extremes of the FTS bands The spectral range and spectral resolution for the central detectors SSWD4 and SLWC3 see Figure 2 7 also applies to the other detectors across the spectrometer arrays used for spectral 4 2 SPECTROMETER 53 mapping 4 2 2 Wavelength scale accuracy The FTS wavelength scale accuracy has been verified using line fits to the CO lines in five Galactic sources with the theoretical instrumental line shape sinc profile The line centroid can be determined to within a small fraction of the spectral resolution element 1 20 if the signal to noise is high There is a very good agreement between the different sources and across both FTS bands see Swinyard et al 2014 for more details 4 2 3 Sensitivity The currently up to date FTS sensitivity for a point source observation is summarised in Table 4 3 The integrated line flux sensitivity estimated from in flight data is plotted as a function of wavelength in Figure 4 3 and compared to the previous estimate taken at the start of the mission Table 4 3 FTS point source sen
119. nts of Vesta Neptune and Uranus with SCAL turned off showed that the signal at the peak of the interferogram is not saturated or at most only a few samples are saturated which means that SCAL is not required to reduce the dynamic range This is a consequence of the lower emissivity of the telescope and the low straylight in comparison with the models available during the design of the FTS On the other hand using the SCAL adds photon noise to the measurements and it was decided that it will not be used during routine science observations An additional benefit from having the SCAL off is that it and the rest of the instrument are at a temperature between 4 5 5 K and the thermal emission from these components is limited to the low frequencies only detectable in the SLW bandt 2 3 4 Filters and passbands The spectral passbands are defined by a sequence of metal mesh filters at various locations and by the waveguide cut offs and provide two overlapping bands of 194 313 wm SSW and 303 671 um SLW The spectrometer filters transmissions are shown in Figure 2 6 Note that the filter transmissions are only provided here for information they are not actually used in the spectrometer processing or calibration More useful information provide relative spectral response curves RSRF presented in greater details in Fulton et al 2013 an in Section 5 4 2 3 5 Spectrometer detector arrays The two spectrometer arrays contain 19 SLW and 37 SSW hexago
120. o convert between flux density and surface brightness using the same temperature and emissivity as for the colour correction The effective beam solid angles and beam correction factors are integrated over the RSRF and source spectrum following Eq 5 34 and Eq 5 39 Effective beam solid angle Beam correction factor Qen T 8 arcsec KBgeam T 8 Temp K PSW PMW PLW PSW PMW PLW B 1 5 3 0 552 21 904 96 1934 27 0 8428 0 9090 0 9144 4 0 517 05 874 11 1838 10 0 9001 0 9411 0 9622 5 0 502 31 853 11 1778 56 0 9265 0 9642 0 9944 6 0 491 54 838 31 1739 43 0 9468 0 9812 1 0168 7 0 483 31 827 51 1712 33 0 9629 0 9940 1 0329 8 0 476 88 819 37 1692 75 0 9759 1 0039 1 0448 9 0 471 76 813 08 1678 08 0 9865 1 0117 1 0540 10 0 467 62 808 10 1666 78 0 9952 1 0179 1 0611 15 0 455 25 793 82 1635 68 1 0223 1 0362 1 0813 20 0 449 35 787 30 1622 00 1 0357 1 0448 1 0904 25 0 446 03 783 68 1614 47 1 0434 1 0496 1 0955 30 0 443 95 781 41 1609 75 1 0483 1 0527 1 0987 35 0 442 53 779 87 1606 53 1 0517 1 0548 1 1009 40 0 441 51 778 75 1604 20 1 0541 1 0563 1 1025 B 2 0 3 0 542 63 900 70 1914 12 0 8576 0 9133 0 9240 4 0 514 36 869 10 1816 96 0 9048 0 9465 0 9734 5 0 499 53 847 75 1757 52 0 9316 0 9703 1 0063 6 0 488 57 832 79 1718 78 0 9526 0 9877 1 0290 7 0 480 20 821 92 1692 11 0 9692 1 0008 1 0452 8 0 473 69 813 76 1672 91 0 9825 1 0108 1 0572 9 0 468 52 807 46 1658 58
121. oducts The SPIRE Level 2 photometer products maps are also calibrated in terms of in beam flux den sity Jy beam though starting with HIPE v10 additional surface brightness products are available These are calibrated in units of MJy sr assuming an infinitely extended source with vS const The primary calibration standard for the photometer is Neptune It has a well understood submilimmetre spectrum it is point like in the SPIRE beams and it is bright enough to provide high SNR and not so bright as to introduce non linear response from the detectors We adopt the disk averaged brightness temperature spectrum of Neptune based on the ESA 4 version Moreno 1998 which has an estimated absolute uncertainty of 4 The detailed computations and the appropriate corrections for an extended source or to convert to a different assumed source spectrum are described in this section and with more details in 62 CHAPTER 5 SPIRE FLUX CALIBRATION Griffin et al 2013 5 2 1 Photometer Relative Spectral Response Function In a SPIRE photometer observation the property of the source that is directly proportional to source power absorbed by the bolometer is the integral over the passband of the flux density weighted by the instrument Relative Spectral Response Function RSRF as indicated in Figure 5 4 f Ss v R v dv 5 Passband 5 5 Passband where Ss v represents the in beam source flux density at the telescope aperture and R v
122. offset in arcmin of the map centre from the input target coordinates along the Y or Z axis of the arrays The minimum offset is 0 1 and the maximum allowed is 4 Source Flux Estimates optional E300 An estimated source flux density in mJy may be entered for a band in which case the expected S N for that band will be reported back in the Time Estimation The sensitivity results assume that a point source has zero background If no value is given for a band the corresponding S N is not reported back 32 CHAPTER 3 OBSERVING WITH SPIRE Bright Source Setting optional this mode has to be selected if the expected flux of the source is above 200 Jy see Section 4 1 1 Time estimation and sensitivity The time estimation and sensitivities are shown in Figure 3 7 right The sensitivity estimates and the caveats are the same as the Large Map mode Coverage maps The coverage maps at 250 350 and 500 um from a real observation are shown in Figure 3 8 For a given observation the area covered by both scan legs defines a central square of side 5 although the length of the two orthogonal scan paths are somewhat longer than this In practice due to the position of the arrays on the sky at the time of a given observation the guaranteed area for scientific use is a circle of diameter 5 140 Figure 3 8 Example coverage maps for Small Map mode for the three photometer arrays PSW left PMW centre and P
123. olved line is in principle independent of the resolution for an FTS 3 For point source observations a sparse map covering the full FTS field of view is also generated The full field of view is 2 6 diameter but the outer ring of detectors is partially vignetted The unvignetted field of view is specified as 2 diameter Data from the full field of view are available 4 For very bright sources a bright source mode is available T he sensitivity for this mode is reduced compared to the nominal mode by a factors of approximately 2 for the SLW array and 4 for the SSW array Guidance on the use of the bright source mode is provided in Section 5 4 3 4 2 SPECTROMETER 95 5 As for the photometer the maximum achievable SNR should be taken as 200 6 For spectral mapping a Integrated line flux sensitivity is essentially the same as for point source for a given map point in terms of W m in beam b For a fully sampled map spatial pixels in the spectral cube can be co added resized to enhance sensitivity as in the photometer but it is best to assume no enhance ment in sensitivity as calibration errors or other imperfections may counteract the gain that is available in principle Continuum calibration should be cross checked by including a map with the photometer in the programme this will generally occupy only a small fraction of the time for the FTS observations 56 CHAPTER 4 SPIRE IN FLIGHT PERFORMANCE Chapter 5
124. on Noise Confusion Noise Level for Level for Level per Pixel Point Sources Extended Sources my mJy M y sr 250 350 500 Update Confusion Noise Estimation Confusion Noise Estimator Messages Details or On source integration time per map repetition s 1526 Number of map repetitions 1 Total on source integration time s 1526 1 1526 Instrument and observation overheads s 474 Observatory overhead s 180 Total time s 2180 1526 474 180 Note to change the observation time change the repetition factor on the AOR main screen It multiplies the on source integration time per map repetition to give the total on source time Confusion noise estimation summary Band Est l o Est 1 0 Est l o um Confusion Noise Confusion Noise Confusion Noise Level for Level for Level per Pixel Point Sources Extended Sources mJy mJy MJy sr 250 350 500 Confusion Noise Estimator Messages Details GoD Update Confusion Noise Estimation Figure 3 6 Large Map time estimation and sensitivity for a filed of 60 x 60 and one repetition for a cross linked scan A and B left and single scan direction right of 5 however the efficiency is low and the map size will be much larger than the requested 5 x 5 field The coverage map for a single scan observation is inhomogeneous due to missing or noisy bolometers see Figure 3 5 Even though the 1 f noise is not a big effect e
125. ons are independent In general the in band power is calculated as follows f fos uis RO nb av Passband f R v n v dv Passband where Is vo is the monochromatic peak surface brightness of the source and the parameter y v is given by Ss Is vo 5 40 y v 09 fso 0 g 0 00 20 d 5 41 where B v 0 is the monochromatic beam profile at frequency v The conversion from the in band power to the monochromatic peak surface brightness is therefore given by a general form of KMong given by f R v n v dv Passband 5 42 fv vo y v 00 R v n v dv KmMmonE f g vo NN Note that for a infinitely extended source where g 0 09 1 the y v 09 parameter in Eq 5 41 is simply the integral over the beam profile and so is given by the monochromatic beam area v Combining Eqs 5 42 and 5 20 we see that for a general source characterised by spectral variation f v vo and spatial variation g 0 00 the colour correction required to convert from the extended pipeline maps to the true peak surface brightness is fia Q v R v n v dv Koag f g vo ET 5 43 f v vo y v 80 R v v dv Passband where y v 09 is as given in Eq 5 41 A straightforward application of this procedure for a Gaussian source distribution g 0 09 for a range of 0o is given in Griffin et al 2013 5 2 12 Application of colour correction parameters The flowchart in Figure
126. orm sensitivity coverage region The darker the shading the deeper the coverage dithering or to observe the core of an object plus part of its surroundings but does not mind in which direction from the core the surrounding area is observed The scans are carried out at a specific angle to the arrays and the orientation of the arrays on the sky changes as Herschel moves in its orbit The actual coverage of the map will rotate about the target coordinates depending on the exact epoch at which the data are taken except for sources near the ecliptic plane where the orientation of the array on the sky is fixed see the Herschel Observers Manual This is shown in Figure 3 1 To guarantee that the piece of sky you want to observe is included in the map you can oversize the area to ensure that the area of interest is included no matter what the date of observation This works well for square like fields but for highly elongated fields the oversizing factor would be large To reduce the amount of oversizing needed for the map you can use the Map Orientation Array with Sky Constraint setting to enter a pair of angles A1 and A2 which should be given in degrees East of North The orientation of the map on the sky with respect to the middle scan leg will be restricted within the angles given This reduces the oversizing but the number of days on which the observation can be scheduled is also reduced Note also that as explained in Herschel Obs
127. otometer map of the dark sky region is shown in Figure 3 19 46 CHAPTER 3 OBSERVING WITH SPIRE Figure 3 19 SPIRE FTS footprint at the location of the standard dark sky centre RA 265 05 deg Dec 69 deg J2000 0 The background image is the SPIRE photometer map at 250 um The brightest source visible in this snapshot just outside the unvignetted region 1 South of the centre has flux density of 50 mJy The dark sky observation is used to improve upon the FTS pipeline processing as it represents the telescope and instrument response to a dark sky signal see Section 5 4 for more details This may improve significantly the quality of the spectra especially for faint targets because the telescope and instrument thermal conditions during the dark sky observation will be very close to those during the actual science observation It is important to note that this standard dark sky measurement is using SPIRE calibration time and thus it is not charged to the observers All FTS dark sky observations are publicly available through the Herschel Science Archive HSA However if the observer wishes to separate different foreground background components then he she should plan a dedicated FTS observation close to the location of the target at the relevant off position This time will be part of his observation and will be charged to his science programme 3 3 6 Considerations when preparing FTS observations There are some important consi
128. ource spectral index assuming apertures of 22 30 40 radius at 250 350 500 um The left three columns assume that the background is removed based on the emission in an annulus within 60 90 while the right three columns assume that no background removal is done as part of the aperture photometry If different radii for the aperture or annulus are used then the aperture corrections will need to be recalculated from the beam profile Background included No Background a PSW PMW PLW PSW PMW PLW 4 0 1 2729 1 2305 1 2231 1 2704 1 2230 1 1959 3 5 1 2708 1 2302 1 2208 1 2683 1 2226 1 1949 3 0 1 2694 1 2298 1 2187 1 2669 1 2222 1 1940 2 5 1 2683 1 2294 1 2163 1 2659 1 2217 1 1930 2 0 1 2674 1 2290 1 2150 1 2650 1 2213 1 1920 1 5 1 2665 1 2286 1 2136 1 2642 1 2209 1 1910 1 0 1 2659 1 2282 1 2119 1 2634 1 2205 1 1900 0 5 1 2651 1 2278 1 2107 1 2627 1 2200 1 1891 0 0 1 2643 1 2274 1 2091 1 2620 1 2196 1 1881 0 5 1 2637 1 2271 1 2075 1 2612 1 2191 1 1872 1 0 1 2629 1 2266 1 2052 1 2605 1 2187 1 1862 1 5 1 2622 1 2262 1 2046 1 2598 1 2183 1 1853 2 0 1 2614 1 2258 1 2015 1 2591 1 2178 1 1844 2 5 1 2607 1 2254 1 2013 1 2584 1 2174 1 1835 3 0 1 2599 1 2251 1 1979 1 2576 1 2169 1 1826 3 5 1 2592 1 2247 1 1972 1 2569 1 2165 1 1817 4 0 1 2585 1 2242 1 1960 1 2562 1 2161 1 1809 4 5 1 2578 1 2238 1 1949 1 2555 1 2156 1 1801 5 0 1 2571 1 2234 1 1940 1 2548 1 2152 1 1793
129. position of the pixel 2 Derive the map pixel flux density that would have been recorded had the source been co aligned with a pixel centre This can be done by fitting the appropriate function to these data points and deriving the peak value This function to be fitted is the beam profile convolved with the map pixel size If the true beam profile were a 2 D Gaussian the constrained parameters of this function would be major axis minor axis position angle and the free parameters would be peak value position of peak value 3 Divide the resulting peak value by the pixelisation correction factor P This method may not be feasible or appropriate in all cases due to various effects such as limited S N sky background confusion noise astrometric errors non Gaussianity of the beam shape etc Any adopted method must take into account the definition of map pixel flux density given in boldface text above More detailed guidelines on performing SPIRE photometry are provided in the SPIRE Data Reduction Guide chapter 5 88 CHAPTER 5 SPIRE FLUX CALIBRATION 5 2 15 Summary The photometer pipeline produces monochromatic in beam flux densities at 250 350 and 500 um calculated under the assumptions a flat v S spectrum and e a point source observation PxW products where x S M L for 250 350 500 um respectively in HIPE v9 and previous and psrcPxW products in HIPE v10 onwards e an observation of an infinitely extended source
130. ptical chains and is used both for photometer and F TS observations For photometric observations the BSM is moved on a pattern around the nominal position of the source For the FTS the BSM is moved on a specific pattern to create intermediate or fully sampled spectral maps It can chop up to 2 along the long axis of the Photometer s 4 x 8 field of view and simultaneously chop in the orthogonal direction by up to 30 This two axis motion allows jiggling of the pointing to create fully sampled image of the sky T he nominal BSM chop frequency for the photometer is 1 Hz however this chop and jiggle mode was never used for science observations For scanning observations the BSM is kept at its home position 2 2 3 Filters and passbands The photometric passbands are defined by quasi optical edge filters Ade et al 2006 located at the instrument input at the 1 7 K cold stop and directly in front of the detector arrays the reflection transmission edges of the dichroics and the cut off wavelengths of the feedhorn output waveguides The filters also serve to minimise the thermal loads on the 1 7 K and 0 3 K stages The three bands are centred at approximately 250 350 and 500 um and their relative spectral response curves RSRF are given in much more detail in Section 5 2 1 see Figure 5 5 14 CHAPTER 2 THE SPIRE INSTRUMENT SPIRE Photometer position 1 Z always towards the Sun SPIRE Spectrometer m FOV radius position i
131. ration time s 256 1 256 Number of visible stars for the target None Specified Instrument and observation overheads s 124 Observatory overhead s 180 Instrument Settings Total time s 560 256 124 180 Source type Point Source Note to change the observation time change the repetition factor on the AOR main screen Small Map It multiplies the on source integration time per repetition to give the total on source time O Large Map Confusion noise estimation summary Repetition factor Source Flux Estimates and Bright Source Setting Source Flux Estimates Repetitian 1 Source x Estimates Band Est 1 0 Est 1 0 Est 1 0 Ch um Confusion Noise Confusion Noise Confusion Noise oppin xd Level for Level for Level per Pixel Number chop avoidances 0 Point Sources Extended Sources mJy Avoidance Avoidance Avoidance mJy MJy sr From 0 From 0 From 0 250 350 To 0 To 0 To 0 500 Observation Est Add Comments AOR Visibility ME z Update Confusion Noise Estimation Confusion Noise Estimator Messages a Figure 3 10 HSpot user inputs for Point Source mode left and the HSpot time estimation for Point Source mode right 3 2 SPIRE PHOTOMETER AOT 35 A practical tip is to transform the pair of chop avoidance angles A1 A2 to pairs of position angles of the Herschel focal plane Then with the help of the HSpot target visibility tool the days when the focal plane posit
132. re both the continuum and narrow spectral features are observed in the same measure ment Thus spectral features with a wide frequency structure are observed together and can be analysed and corrected for simultaneously This is not possible with monochromating devices where essentially only a single frequency structure is observed leading to possibly unknown spectral features causing calibration uncertainties for instance standing waves or broad spectral features in the instrument response function The penalty in instantaneous sensitivity due to the increased photon noise in an FTS is therefore compensated to some extent by the much higher level of calibration fidelity achieved 10See the observers manuals available at the Herschel Science Centre 102 CHAPTER 5 SPIRE FLUX CALIBRATION Chapter 6 SPIRE observations in the Herschel Science Archive In this chapter we briefly describe the data products and the data structure coming from SPIRE observations A comprehensive explanation and practical guidelines for accessing the data running the pipeline and doing quick interactive analysis can be found in the SPIRE Data Reduction Guide which can be accessed also from the help documentation inside the Herschel Interactive Processing Environment HIPE The data structure for the Herschel mission is unusual for astronomers as it is object oriented the underlying pipeline processing and the database that hold all the data are based on Ja
133. re the index 7 is for the particular Planck HFI band with vo 545 GHz or vo 857 GHz and R v is the corresponding HFI filter RSRF Having K for HFI and Kcoig for SPIRE then we can derive the overall conversion factors from HFI to SPIRE assuming a modified blackbody source spectrum Ig v B T v Kes7Is vgs7 Kawr Visi B T vg57 K57 pmw T B KO Is vpmw JEN BW B T VPMW K T B KsisIs vsas Kas vias B T vsus 5 48 545 PLWV4 KPUW T v PLW 8 ColE 8 Y PLW KoE Vppw B T VPLW Kss7 Is vss7 Kasr ves B T vasz PSW Koop Is vpsw KE Ubaw B T vpsw Kg57psw T 6 with vs45 545 GHz and vas 857 GHz for the HFI and vpyw 865 55 GHz vppw 599 58 GHz and vpsw 1199 17 GHz for the three SPIRE bands Note that the conversion Ks57 psw is only given for completeness as the PSW band only marginally overlaps with the HFI 857 GHz band It is evident that the colour correction and consequently the cross calibration depends on the assumed greybody spectrum The colour correction factors computed with a fixed 8 1 8 and different temperatures are shown in the upper panel of Figure 5 17 Using the two Planck HFI maps at 545 and 857 GHz we can derive the ratio Eygpi T 8 of the HFI intensities for a range of temperatures to eliminate this dependence from the colour correction factors is V545 B vsas T B 1 8 Rum T x 5 49 e V857 B vg57 T B 1 8 ve Fig
134. rection arcsec Figure 3 15 Spectrometer raster example to show spacing of the individual pointings for the long wavelength array SLW left and the short wavelength array SSW right for interme diate image sampling 3 3 3 Image Sampling The pointing and an image sampling mode are combined to produce the required sky coverage Here the image sampling options are described and figures are given to show the sampling Note that the figures show only the unvignetted detectors Figure 3 16 SPIRE Spectrometer spatial sampling sparse left intermediate centre and full right The small green and magenta circles indicate the regions where spectra will be observed for different spatial samplings The green circles show SSW and the magenta show SLW the large red circle of 2 diameter is to guide the eye for the unvignetted field of view Sparse Image Sampling Usage and Description In conjunction with a single pointing to measure the spectrum of a point or compact source well centred on the central detectors of the Spectrometer To provide sparse maps either for a single pointing or a raster grid of pointings The BSM is not moved during the observation producing a single array footprint on the sky The result is an observation of the selected source position plus a hexagonal pattern sparse map of 3 3 SPIRE SPECTROMETER AOT 43 the surrounding region with beam centre spacing of 32 5 50 5 in the SSW SLW bands as shown i
135. resulting data are regridded into a regular spectral cube by the pipeline The flux density calibration of individual detectors is carried out using the telescope as the standard calibrator Flat fielding across detectors is taken into account by deriving a separate RSRF for each bolometer It should be noted that the RSRF derived from the telescope emission is valid for a uniformly extended source that completely fills the detector field of view The treatment for semi 100 CHAPTER 5 SPIRE FLUX CALIBRATION extended sources i e those that are not fully extended or point like is described in greater detail in Wu et al 2013 and it is implemented as an interactive task in HIPE 5 4 3 Bright source mode In the measured interferogram the total power received is reflected in the amplitude of the modulation at zero path difference ZPD This means that once a certain source strength is reached the amplitude of modulation may exceed the dynamic range and the interferogram can be clipped Signal clipping can occur either at the maximum or the minimum of the interferogram it can be corrected if there are only a small number of consecutive clipped samples but for very bright sources the clipping can be more severe In cases where it is impossible to correct for clipped interferograms close to ZPD the continuum shape and level will be affected across the spectrum The bright source mode addresses this problem by using a different bias amplit
136. riginal values entered if applicable Bright Source Setting optional this mode has to be selected if the expected flux of the source is above 200 Jy see Section 4 1 1 Figure 3 4 Large Map parameters in HSpot Coverage Maps Coverage maps for cross scanning and for single direction scanning for each of the three bands are shown in Figure 3 5 These were taken from standard pipeline processing of real observations with SPIRE Note that the coverage maps are given as number of bolometer hits per sky pixel The standard sky pixels for the SPIRE Photometer maps are 6 10 14 see Section 5 2 9 3 2 SPIRE PHOTOMETER AOT 29 Figure 3 5 Example coverage maps for Large Map mode for the three photometer arrays PSW left PMW centre and PLW right The top row is for a single scan A observation The bottom row is for a cross linked scan of 30 x 30 field the white square is the user requested area The pixel size is 6 10 14 for PSW PMW PLW and the colour code represents the number of bolometer hits in each sky pixel Time estimation and sensitivity The estimated time to perform a single scan and cross linked scans for one square degree field 60 x 60 and one repetitions are given in the HSpot screenshots in Figure 3 6 The sensitivity estimates are subject to caveats concerning the flux density calibration see Section 5 2 The reported 1 o noise level does not include the confusion noise which ulti mately lim
137. s from the celestial north to the Y spacecraft axis long axis of the bolometer positive East of North following the Position Angle convention This effectively defines an avoidance angle for the satellite orientation and hence it is a scheduling constraint Source Flux Estimates optional An estimated source flux density in mJy may be entered for a band in which case the expected S N for that band will be reported back in the Time Estimation The sensitivity results assume that a point source has zero background If no value is given for a band the corresponding S N is not reported back 36 CHAPTER 3 OBSERVING WITH SPIRE Bright Source Setting optional this mode has to be selected if the expected flux of the source is above 200 Jy see Section 4 1 1 Time estimation and sensitivity The SPIRE Point Source mode is optimised for observations of relatively bright isolated point sources In this respect the accuracy of the measured flux is more relevant than the absolute sensitivity of the mode The noise will be a function of three contributions For a single ABBA repetition e The instrumental noise will be a constant value e There will be some underlying confusion noise which will vary from field to field e There will be a flux dependent uncertainty introduced by pointing jitter that will be some fraction of the total flux The current 1 o instrumental noise uncertainties for a single ABBA repetition using the central
138. s are described in more detail in Section 2 4 1 The relative merits of feedhorn coupled detectors as used by SPIRE and filled array de tectors which are used by PACS and some ground based instruments such as SCUBA 2 Audley et al 2007 and SHARC II Dowell et al 2003 are discussed in detail in Griffin 2 3 SPECTROMETER DESIGN 15 Beam Beam SPIRE optical steering bench 4 5 K 3He mirror cooler Detector 1 7 K box array modules Figure 2 3 SPIRE FPU photometer side layout et al 2002 In the case of SPIRE the feedhorn coupled architecture was chosen as the best option given the achievable sensitivity the requirements for the largest possible field of view and high stray light rejection and limitations on the number of detectors imposed by space craft resource budgets The detector feedhorns are designed for maximum aperture efficiency requiring an entrance aperture close to 2FA where A is the wavelength and F is the final optics focal ratio This corresponds to a beam spacing on the sky of 24 D where D is the telescope diameter The array layouts are shown schematically in Figure 2 4 a photograph of an array module is show in Figure 2 10 2 3 Spectrometer design 2 3 1 Fourier Transform Spectrometer Concept and Mode of Operation The SPIRE Fourier Transform Spectrometer FTS uses the principle of interferometry the incident radiation is separated by a beam splitter into two beams that travel different optica
139. s the realistic point source response function of the system including all scanning artefacts It is worth noting that in a normal SPIRE scan map any individual source in the map will be covered by only a subset of bolometers leading to low level beam profile variations from position to position in the map about the average profile presented here These beam products also represent the measurement of a source with a particular spectral shape v i e different from the standard v reference spectrum assumed by the pipeline products A source with a different spectral shape will produce slightly different beam parameters The beam maps for all three bands are displayed in log scaling in Figure 5 8 Four individual maps one from each of the four observations from which the final beam products are derived are also available should the user want to investigate the beam stability The beam product maps are 10 x 30 in scale and include the same extensions and header information as the nominal maps output from HIPE There are two versions of each map one high resolution with a 1 pixel scale and another with the nominal SPIRE output map pixel scale of 6 10 14 per pixel for 250 350 500 um The data have also been normalised to give a peak flux of unity in all three bands Note that the ellipticity seen in the maps is not a function of scanning direction but is constant with position angle When using these beam models it is advised t
140. sContext V hspire1342268302 20level2context 1392990914077 fits gz gt 3 quality gt LU logObsContext 1342201265 herschel ia obs ObservationContext 431394 xml aaa eee inate povero herschel ia obs ObservationContext xm gt gt L3 auxiliary calibration v L3 calibration gt 3 Phot gt 3j Phot gt Gi Reset gt 3 Reset H SCalContext_1390915605484 fits gz H SCalContext_1392990877728 fits gz gt Spec gt Gi Spec gt 3 TelemMaskList gt 3 TelemMaskList Figure 6 3 The content and the folder structure of a Herschel Science Archive tar file for SPIRE Photometer left and the Spectrometer sparse mode right Note this structure is applicable for observations processed with HIPE v11 The final FITS file with the point source calibrated map at 250 um is indicated with an arrow on the left panel Similarly the final FITS table with the point source calibrated unapodized spectra is shown on the right 6 3 WHICH PRODUCTS SHOULD I USE FOR DATA ANALYSIS 107 6 3 Which products should I use for data analysis In most cases the Level 1 and Level2 SPIRE data in the HSA are of a sufficient scientific quality to be used as a starting point for any further data analysis e g photometry line flux measurements etc In Table 6 1 we summarise where these final products can be found in the HSA tar file Note that this information is applicable to contexts produced with the systematic processing with HIPE v11 the structure
141. same He cooler design Duband et al 1998 is used in SPIRE and in the PACS instru ment Poglitch et al 2010 It has two heater controlled gas gap heat switches thus one of its main features is the absence of any moving parts Liquid confinement in zero g is achieved by a porous material that holds the liquid by capillary attraction A Kevlar wire suspension system supports the cooler during launch whilst minimising the parasitic heat load The cooler contains 6 STP litres of He fits in a 200 x 100 x 100 mm envelope and has a mass of 1 7 kg Copper straps connect the 0 3 K stage to the five detector arrays and are held rigidly at various points by Kevlar support modules Hargrave et al 2006 The supports at the entries to the 1 7 K boxes are also light tight All five detector arrays use hexagonally close packed feedhorn coupled spider web Neutron Transmutation Doped NTD bolometers Turner et al 2001 The bolometers are AC biased with frequency adjustable between 50 and 200 Hz avoiding 1 f noise from the cold JFET readouts There are three SPIRE warm electronics units the Detector Control Unit DCU 11 12 CHAPTER 2 THE SPIRE INSTRUMENT FPU Cooler Mechanisms Calibrators Thermometers Detector Arrays Cryostat Wall SPIRE Warm Electronics Spacecraft Commanding Electronics and Telemetry Figure 2 1 SPIRE instrument architecture provides the bias and signal conditioning for the arrays and cold electronics an
142. sform Spectrometer Concept and Mode of Operation 2 3 2 Spectrometer optics and layout 2l 2 8 8 Spectrometer calibration source SCAL 2 8 4 Filters and passbands 2 ccr 2 3 5 Spectrometer detector arrays 2l llle Common Instrument Parts 222524 YR eX Pom Rx 2 4 1 Basic bolometer operations llle 2 4 2 He cooler and thermal strap system 2 ln 2 4 8 Warm electronics 2 om oom RR Rom ee a c oo oo N N N 11 11 12 12 13 13 14 14 15 15 17 17 18 18 18 18 21 22 4 CONTENTS 3 Observing with SPIRE 23 Dl AMPOCMCHOM 2 G4 2 oases ghee Rakes de Roxc do A Re Ye eee a 23 Dee SPIRE Photometer AUT so sapete 44 Pw bow IR RU S de 24 dA Lange Map uo n eoea sem RR x x Rok ance See we X XI atc 24 2 2 2 Sm l Map 45 ooo ego prae Rok RR OE puo bo E ROS D Wo ura 30 0 2 9 Pont GOUTE 0393s cse komo k Yo de Seu uev x e AR aou ORE UE Ry e 33 3 8 SPIRE Spectrometer AOT no saung a s ra rl t nh 37 3 3 1 Spectral Resolution s soe sa wa Xe oe eee I ee x 38 2 9 2 Pomtine Modes 245 04 245 2 cee eee RM bee RUE OA Y YR XR 40 4 9 Image BamplBE os uw eoo a m Rye o ROM deck v ee e Rn 42 3 3 4 User input parameters for all Spectrometer AOTs 43 3 3 5 Spectrometer dark sky observations cl 45 3 3 6 Considerations when preparing FTS observations 46 4 SPIRE in flight performance 49 4 1 Photometer perform
143. sions a java archive file with extension jar that is useful for HIPE and a zip file with the standalone calibration files all in one folder herschel spire ia cal data SCal Some calibration files are useful for data analysis outside the Herschel Interactive Processing Environment In Table 6 2 and 6 3 we all products in the calibration tree This is applicable for SPIRE_CAL_12_2 or later The products are FITS files tables or images that are available in the calibration context in the tar file from the HSA which in general can be opened with any FITS viewer topcat fv ds9 Aladin etc The FITS files have all the relevant metadata keywords with descriptions and the table columns have the correct units so these should be straightforward to use Most of the calibration files are only useful for the low level pipeline processing see e g the SPIRE Data Reduction Guide but there are some that are needed for further data analysis The latest standalone SPIRE calibration tree is available at ftp ftp sciops esa int pub hsc calibration latest_cal_tree 6 5 ACCESS TO CALIBRATION FILES 109 Table 6 2 The content of the SPIRE Photometer calibration tree SPIRE CAL 12 2 Each product name corresponds to a context in the calibration tree in HIPE These products are also available in the HSA tar file under a folder with a name or part of the name matching the first column Products with relevance to particular sections in this Handboo
144. sitivity for high resolution HR and low resolution LR observations Line flux Continuum HR HR LR Band AF 5g 1hr AS 50 1hr um Wm x10 y SSW 194 2 15 1 79 0 083 SSW 214 1 56 1 30 0 063 SSW 282 1 56 1 30 0 063 SLW 313 2 04 1 70 0 082 SLW 392 0 94 0 77 0 037 SLW 671 2 94 2 20 0 106 In principle the integrated line flux sensitivity is independent of the spectral resolution In practice only high resolution mode should be adopted for line observations For an FTS the limiting sensitivity for the continuum scales as the reciprocal of the spectral resolution and the LR sensitivities in Table 4 3 are thus scaled by factors of 21 25 1 2 with respect to the HR The 5 c 1 hr limiting integrated line flux is typically 1 5 x 10717 W m for both SSW and SLW bands With currently available data processing the noise level continues to integrate down as expected for at least 100 repeats i e 100 forward and 100 reverse scans total on source integration time 4 hours Note that this is a considerable improvement with respect to the quoted performance in v2 1 of this document and in Griffin et al 2010 The achieved F TS sensitivity is better than pre launch predictions by a factor of 1 5 2 This is attributable to the low telescope background the fact that the SCAL source is not used and 54 CHAPTER 4 SPIRE IN FLIGHT PERFORMANCE 3 0 10 peo 2 8 107
145. solute calibration coming from Planck the first step needed is to take the extended source calibrated maps from SPIRE These are available as level 2 products extdPxW maps and are produced as explained in detail in Section 5 2 5 in particular taking into account the frequency dependence of the beam solid angle Q v SPIRE and HFI share two channels with overlapping wavebands as shown in Figure 5 16 SPIRE PMW and HFI 857 have a similar filter profile while SPIRE PLW and HFI 545 are visibly offset The filter profiles are not identical thus a colour correction from HFI to SPIRE waveband is needed In addition both SPIRE and the HFI maps assume a fully extended 5 3 SPIRE MAPS CALIBRATED WITH PLANCK 95 source with intensity Ig v v but the actual spectrum of the sky is closer to that of a greybody with a particular dust emissivity index f ie Is v v B T v with the Planck blackbody function B T v given in Eq 5 28 Hence the proper colour correction calculation should incorporate the more realistic source spectrum as well as the differences in the RSRFs The SPIRE colour correction Kcgg in the case of a greybody with different T and 6 are explained in Section 5 2 7 and tabulated in Table 5 7 For the HFI we can follow Eq 5 30 and derive the factor K to convert from the HFI pipeline spectrum to a greybody taking O pip f wtR v dv K B 1g T Passband 4 i oR f v B T v Riv dv Ce Passband whe
146. sophotal frequency is fitted for each band such that the modelled beam solid angle for a source with Neptune s spectral index aNep is equal to the measured solid angle QNep The values for all these parameters in the three SPIRE bands are given in Table 5 3 It is these values of monochromatic beam solid angle Eq 5 36 that are required when calculating the values of KMong and Kcow Note that the monochromatic beam FWHM and solid angle are defined as a power law relative to the isophotal frequency reg and use that fact that Q veg QNep and similarly for the FWHM If they are scaled with v vo then the nomalisation factors must also be changed to 0 vo and vo such that jo 0 7 5 37 8 9 0 Z 5 38 where the values of Q vo are 465 819 1730 arcsec for Ag c vo 250 350 500 um ie equivalent to Qeg as 1 The effective beam solid angles for sources with a range of spectral or grey body indices using Eq 5 32 5 34 are given in Table 5 4 and 5 5 respectively and plotted in Figure 5 10 Since much of the pipeline analysis is performed assuming a source with ag 1 a beam correction parameter Kpeam og is also provided such that Qela Dei B 5 39 If used in conjunction with colour correction the same spectral index for both the colour 76 CHAPTER 5 SPIRE FLUX CALIBRATION 250m f 2 0 350um B 2 0 500 um f 2 0 250 41m B 1 5 o 350um f 1 5
147. stalk Table Photometer PCAL Response Model Table SPIRE radial beam profile and normalized beam areas i e the EEF Section 5 2 9 and Figure 5 9 Photometer Relative Spectral Response Function Section 5 2 1 and Figure 5 5 Set of temperature drift correction products 110 CHAPTER 6 SPIRE OBSERVATIONS IN THE HERSCHEL SCIENCE ARCHIVE Table 6 3 The content of the SPIRE Spectrometer calibration tree SPIRE_CAL_12_2 Each product name corresponds to a context in the calibration tree in HIPE These products are also available in the HSA tar file under a folder with a name or part of the name matching the first column Products with relevance to particular sections in this Handbook are provided with links Product Description BandEdge Spectrometer Band Edges BeamParamList Set of Spectrometer beam parameters and point source conver sions Section 5 4 1 Figure 5 18 and Eq 5 55 BeamProfList Set of Spectrometer 3 D beam maps i e as spectral cubes BolPar Spectrometer bolometer parameter table BolPhaseList Set of bolometer phase products Bright GainList Set of bolometer bright mode products BsmOpsList Set of BSM Ops products BsmPos Spectrometer BSM Position table ChanGain Spectrometer Channel Gain table ChanMaskList Set of channel mask products ChanNum Photometer Channel Number Mapping table ChanTimeConstList Set of channel time constant products Chan TimeOff Spectrometer Channel Time Offset table DetAngOffList Set of
148. tion 12h56m11 17s 5d47m21 5s e mle Madnyrrargene Tere Total on source integration time s 37 1 37 Instrument and observation overheads s 132 Number of visible stars for the target 9 Star tracker target Ra 14 047 degrees Dec 5 789 degrees Observatory overhead s 180 Total time s Instrument Settings Source type O Point Source 349 23741324180 Note to change the observation time change the repetition factor on the AOR main screen It multiplies the on source integration time per repetition to give the total on source time Small Map Confusi f 5 O Large Map onfusion noise estimation summary Repetition factor Source Flux Estimates and Bright Source Setting Band Est 1 0 Est 1 0 Est 1 0 c um Confusion Noise Confusion Noise Confusion Noise Repetition 1 Source Flux Estimates Level for Level for Level per Pixel Sul Map Parameters Point Sources Extended Sources mJy mJy MJy sr Map centre offset Y arcmin 0 000 250 Map centre offset Z arcmin 0 000 350 500 Observation Est Add Comments AOR Visibility d Update Confusion Noise Estimation Confusion Noise Estimator Messages Cre _ Details E Figure 3 7 User inputs in HSpot for Small Map AOT left and Small Map mode time estimation sensitivity estimate for one repetition of the map Repetition factor The number of repeats of the 1x1 scan pattern Map Centre Offset Y and Z This is the
149. uband L et al 1998 Cryogenics 48 95 Fischer J et al 2004 Cryogenic far infrared laser absorptivity measurements of the Herschel Space Observatory telescope mirror coatings Applied Optics 43 3765 Fulton T et al 2008 Proc SPIE Vol 7010 70102T Fulton T et al 2013 Experimental Astronomy submitted Griffin M J 2008 The SPIRE Analogue Signal Chain and Photometer Detector Data Pro cessing Pipeline SPIRE UCF DOC 002890 Issue 6 November 2008 Griffin M J amp Orton G S 1993 The Near Millimeter Brightness Temperature Spectra of Uranus and Neptune Icarus 105 537 Griffin M J et al 2002 Applied Optics 31 6543 Griffin M J et al 2006 Herschel SPIRE Design Performance and Scientific Capabilities Proc of SPIE 6265 7 111 112 BIBLIOGRAPHY Griffin M J et al 2010 The Herschel SPIRE Instrument and its in flight performance A amp A 518 L3 Griffin M J et al 2013 MNRAS 434 992 Hargrave P et al 2006 Proc SPIE 6275 627513 Hartman R C et al 1996 Simultaneous Multiwavelength Spectrum and Variability of 3C 279 from 10 to 1074 Hz ApJ 461 698 Hildebrand R 1983 The Determination of Cloud Masses and Dust Characteristics from Submillimetre Thermal Emission QJRAS 24 267 Hildebrand R et al 1985 Far infrared and Submillimeter Brightness Temperatures of the Giant Planets Icarus 64 64 Hopwood R et al 2013 Experimental Astronomy submitted
150. ucts called extdPxW are converted to surface bright ness by dividing by the effective beam solid angle for a vS const source The values of 78 CHAPTER 5 SPIRE FLUX CALIBRATION PSW broadband lin scale PSW broadband lin scale PSW broadband linscale 1 864002 1 86002 Z arcsec FLUX 2 aresec FLUX 1 8e 002 005 1 8e 002 4 62 006 462 006 V 8e 002 1 amp e 002 Y arcsec Y farcsed Y arcsec PMW broadband log scale PSW broadband log scale PLW broadband log scale 1 8e 002 Ziarcsed u Z arcsec Jog FLUX Z areseed logFLUX 1 8e4002 Y acseo Y arcsec Y arcsec Figure 5 12 Theoretical photometer beams for 250 350 and 500 um left centre and right respectively with linear scaling top row and logarithmic scaling bottom row these conversion parameters in units of MJy sr per Jy beam are given in Table 5 2 These are applied in the standard extended source pipeline products called extdPxW in HIPE v10 and after Note that the extended source maps products also have relative gains applied to the individual detector timelines and are zero point corrected from Planck maps Factors Kcop and Kg for colour correction The colour correction parameters Kcoip and KQcog have been computed for various values of ag and the results following Eq 5 25 and 5 27 are shown in Figure 5 13 and Table 5 6 The colour correction parameters Kc op and Kcow for greybodies with 8 1
151. ude and phase for the bolometers to lower their responsivity and so reduce the maximum modulation in the interferogram For mapping observations in bright mode the dynamic range of the detectors is set at every jiggle position to maximize the number of interferograms within the dynamic range for nominal mode this is only done once at the beginning of the observation The advantage in using bright mode is that clipping is significantly reduced and in most cases should be eliminated for the central detector pair for sources up to the strength of Mars 15 000 Jy This means that the absolute level and shape of the spectrum can be well calibrated However as noted in Section 4 2 3 due to the reduction in responsivity needed for bright mode the sensitivity is reduced compared to nominal mode by a factors of approximately 2 for the SLW array and 4 for the SSW array As clipping occurs only around the peak modulation in the interferogram spectral lines are relatively unaffected the information about spectral lines is spread through the interferogram up to large optical path differences Very bright targets e g Orion Sgr B2 Mars were observed with the FTS using a bright source mode otherwise these sources would have saturated the detectors 5 4 4 Spectrometer calibration accuracy The overall absolute calibration uncertainty is summarised in this section We break the uncertainties into three categories point sources observed in th
152. urce reference maps complementary to the empirical maps which being flight measured and pipeline generated include the additional effects among others of electronics detection scanning processing and map reconstruction and general additional background noise from sky and observatory Figure 5 12 shows the theoretical beam models all given at a 0 6 sampling over a 6 x 6 angular extent and in the spacecraft coordinate system Y Z rotation via the user s defined position angle will transfer into the relevant sky coordinate systems The model beam product provides significantly higher detail at greater radius but presently is released only at 6 x 6 scale Larger scale beam models e g up to 1 deg scale at lower sampling e g standard 6 10 14 have been generated in order to provide better estimates on integrated beam extent effective surface area and may be released later 5 2 10 Computed conversion factors for SPIRE Factor Kmonp to convert RSRF weighted flux density to monochromatic flux den sity For the standard spectral index of ai 1 adopted for Herschel the values of Kmonp for the three SPIRE bands are given in Table 5 2 These are applied in the standard point source pipeline products called PxW in HIPE v9 and before psrcPxW in HIPE v10 and after Factor Kpiog to convert point source monochromatic flux density to monochro matic extended source surface brightness The extended pipeline Level 2 prod
153. ure 5 17 bottom panel shows the same colour correction factors as function of the ratio Hgpi From the ratio of the two HFI maps converted using Eq 5 47 we can obtain the average Ry and then the KyFy 5sprre factors 96 CHAPTER 5 SPIRE FLUX CALIBRATION w in N w in o N o HTATTTTTTATTTTTTTTTTTTZITTTTTTTTTTTTTT K Factor CT K Factor o in e o 10 100 T K k857toPMW e io 0 8 10 1 2 14 1 6 1 8 20 ratio 545 857 k857toPMW k545toPLW ratio545over85 k857toPSW K545toPLW k857toPSW Figure 5 17 Left the three colour correction factors Kufi spire and the ratio Ry as a function of dust temperature assuming a fixed dust emissivity index 6 1 8 Right the three colour correction factor KyHFfI spre as a function of the ratio Rypy for 8 1 8 The SPIRE calibration context SPIRE_CAL_12 or above contains the precomputed Rypr and Kyri spire for a range of temperatures T from 5 K to 300 K for 6 1 8 These are available in a table called Phot ColorCorrHfi How to calibrate in practice the SPIRE maps so that they have the absolute offset from Planck is explained in detail in the SPIRE Data Reduction Guide section 4 1 The final Level2 SPIRE maps extdPxW in units of MJy sr in the Herschel Science Archive are already recalibrated to the Planck absolute offset following the assumptions described in this sect
154. va No other ground based or space observing facility provides similar access to the collected data up to now In some situation the data access and the data structure may seem confusing In such cases please do not hesitate to contact the helpdesk of the Herschel Science Centre 6 1 SPIRE processing levels and structure of the observational context All standard Herschel SPIRE observations are now publicly available in the Herschel Science Archive HSA Getting observations from the HSA is explained in greater detain in Section 1 4 of the HIPE Data Analysis Guide In order for the user to know where to look for the products of interest maps spectra spectral maps one has to be a familiar with the data structure of the archive file downloaded from the HSA All SPIRE data products are grouped into contexts A context is a special kind of product linking other products in a coherent description and can be thought of as an inventory or catalogue of products The SPIRE processed observation consists of many such contexts enclosed within one observation context Each processing level in the SPIRE pipeline has a context and the entire observation has a context Thus a complete observation may be thought of as a big SPIRE onion as depicted in Figure 6 1 Moreover contexts are not just for higher processed data products but there are contexts for Calibration Products contexts for Auxiliary Products e g telescope pointing mirror temperatures etc and
155. ven for single scan maps our advice is to use cross linked maps when a better flux reconstruction is needed i e deep fields faint targets etc 3 2 2 Small Map Description The SPIRE Small Map mode is designed for observers who want a fully sampled map for a small 5 dimeter area of sky The original SPIRE Small Map mode was initially a 64 point Jiggle Map However after analysis and investigation this has been replaced by a 1 x 1 small scan map using nearly orthogonal at 84 8 deg scan paths The Small Scan Map mode is defined as follows e 1x1 nearly orthogonal scan paths e Scan Angles are fixed at 42 4 degrees with respect to the Spacecraft Z axis e Fixed scan path with guaranteed coverage of 5 diameter circle 3 2 SPIRE PHOTOMETER AOT Fixed scan speed 30 s Map offsets available User inputs Calibration PCAL flash made only at end of Observation Otherwise identical to the SPIRE Large Scan Map mode The user inputs in HSpot are shown in Figure 3 7 left and described below 31 16 0 6 SPIRE Time Estimation Summary Band Point Source Point Source 1 c Extended Extended Extended um Flux S N instrument Surface S N l o Density mJy in be Brightness instrument mJy Mjy sr M y sr 250 9 0 0 77 350 25 0 34 leon 7 500 10 8 0 24 Unique AOR Label SPhoto 0000 On source time per repetition s 37 Target 3c279 Type Fixed Single Number of repetitions 1 Posi
156. w of the FTS bolometer arrays the bolometer names are also shown Each circle represents a detector feedhorn Those detectors centred on same sky positions are shaded in blue the dead bolometers are shaded in grey The 2 6 unvignetted field of view of each array is delineated by a red dashed circle The two arrays overlap on the sky as shown in the rightmost figure where the SLW and SSW are depicted by red and blue circles respectively The bold red circle delineates the 2 unvignetted field of view for FTS observations The circle sizes in the rightmost figure correspond to the FWHM of the beam The spacecraft coordinate system Y Z is also shown and hence in output voltage In the case of the SPIRE detectors the ab sorber is a spider web mesh composed of sil icon nitride with a thin resistive metal coat ing to absorb and thermalise the incident ra diation The thermometers are crystals of a Neutron Transmutation Doped NTD germa nium which has very high temperature coef ficient of resistance A magnified view of an actual SPIRE bolometer is shown in Figure 2 9 Spider web mesh Figure 2 9 Magnified view of a SPIRE bolometer the thermometer size is The main performance parameters for bolo 10x100x300 um metric detectors are the responsivity dV dQ the noise equivalent power NEP and the time constant r C G In order to achieve high sensitivity low NEP and good speed of response operation at low temperatur
157. y The temperatures of the telescope primary and secondary mirrors 7j and Two are measured by thermistors on the spacecraft and are available as auxiliary products in the observation context 98 CHAPTER 5 SPIRE FLUX CALIBRATION The emission due to the internal temperature of the instrument is calculated using FPU thermistors which measure the instrument baseplate temperature Tinst Minst B Tinst v 5 53 The final source spectrum is obtained from Igource Vobs R nst Minst nd Rre Mqa Rsource 5 54 where Voy is the observed spectrum in units of V GHz The telescope and instrument RSRFs are derived from observations of a dark region of the sky made throughout the mission and stored as calibration files Fulton et al 2013 The RSRF applicable to the source is derived from the telescope RSRF for uniformly extended emission with units of V GHz W m Hz s The final source spectrum has units of W m Hz er which can be converted to MJy sr by multiplying by 107 A point source conversion factor related to the spectrometer beam shape see next section is required to convert from the extended calibration to a point source calibration It should also be noted that channel fringes and spectral features in the passband of the instrument will change as a function of source extent The point source conversion factor is determined from observations and a model of Uranus and defined as Mitranus 5 55

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