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AMBER User Manual

1. 2y PP ciz k Viz cos k dij k Viz sin i k 1 The quantities c k and d k are called the carrying waves and are displayed on Fig 5 These waves are in quadrature so that each pixel is sensitive to a complex number Therefore we can write the photometry subtracted interferogram icorr k as icorr k 2 moll 2 M k xC 3 where C is a vector of the values Rij corresponding respectively to the real and imaginary part of the correlated flux 2 P P V for all baselines and M k is a matrix with the values of the carrying wavesc k and d k The matrix M k is the so called pixel to visibilities matrix P2VM During calibration one can measure the P2VM and then inverse it so that for each pixel we get the visibility 4 4 Instrument performances The user should read the AMBER webpages http www eso org instruments amber inst for the latest information on the AMBER performance 4 5 Instrumental contrast The inherent instrumental contrast of AMBER is measured during the P2VM calibration procedure that occurs every time that we change the spectral set up of the instrument after the fibers The P2VM observation is automatically included in the standard templates and thus requires no input or configuration by the observer Please read section 4 3 for an extensive explanation of the use of the P2VM during data reduction 5 Instrument features and problems to be aware of The AMBER instrument is
2. External fringe tracking with FINITO This is available only on the ATs and allows AMBER to reach longer DITs as FINITO is freezing the fringes on the detector The advantage is twofold first in MR and HR modes it is always possible to read out the full spectral range on the detector secondly the longer DITs allows going much fainter than with the short DITs used without fringe tracking 3 2 Other VLT instruments AMBER yields information at scales between A B and A D A single mode instrument like AMBER has therefore no direct access to structures larger then A D Like for radio interfer ometer one might need in certain cases information at small spatial frequencies in order to inject it with the data collected with AMBER The best suited instrument that can give access to this data is the NAOS CONICA and SINFONI instruments which measures diffraction limited images in the the same wavelength domain as AMBER With NAOS CONICA it is possible to do both imaging and spectrography and SINFONI is unique in that it does full field spectrography in a 3 by 3 field Further information on these instruments can be found at http www eso org instruments naco and http www eso org instruments sinfoni The MIDI instrument is similar to AMBER but operates with two telescopes in the N band AMBER and MIDI instruments use the same interferometric infrastructure and many aspects regarding observing preparation and scheduling are very similar
3. http www eso org observing etc Since we had problems in service mode in the past with over resolved targets which appeared resolved in imaging mode at the acquisition or for which no fringes were found we encourage the user to collect as much information on their target as possible before submitting an AMBER proposal AMBER User Manual VLT MAN ESO 15830 3522 14 7 1 6 Guaranteed time observation objects It is important to check any scientific target against the list of guaranteed time observation GTO objects This guaranteed time period covers the full P80 To make sure that a target has not been reserved already the list of GTO objects can be downloaded from http www eso org observing proposals gto amber index html 7 1 7 Calibrator Stars High quality measurements require that the observer minimises and calibrates the instrumental losses of visibility To get a correct calibration the user should use appropriate calibrator stars in terms of target proximity calibrator magnitude and apparent diameter In the case of AMBER the calibrator is observed after the science target using the same templates For each science target a calibrator star must be provided by the user with the submission of the Phase2 material To help the user to select a calibrator a tool called CalVin is provided by ESO CalVin can be used from any web browser Like VisCalc CalVin can be used on the web from http www eso org observing etc
4. DDH o o 00 00 N N So mee kel AMBER User Manual VLT MAN ESO 15830 3522 7 1 4 Coud guiding with the ATs TLO Geometry oses eee ed ee EDR 7 1 6 Guaranteed time observation objects 7 1 7 Calibrator Stars 7 1 8 Field of View 7 1 9 Complex fields 7 1 10 Bright objeets 7 2 Choice of AMBER configuration 7 2 1 Instrument set up 7 2 2 Observing modes 7 2 3 Calibration cycle 2 6 066 s 25 7 2 4 Calibrating the background emission 7 2 5 Standard calibration the instrumental visibility Std 8 Introducing Observation Blocks OBs 8 1 Standard observation OBS Std 8 1 1 Observing cycle 8 2 Computing time overheads for added bands 9 Bibliography 10 Glossary 11 Acronyms and Abbreviations vi 13 13 14 14 14 14 14 15 15 15 16 16 16 16 16 16 17 17 18 19 AMBER User Manual VLT MAN ESO 15830 3522 1 1 INTRODUCTION AMBER the near infrared red focal instrument of the VLTI operates in the bands J H and K ie 1 0 to 2 4 um The instrument has been designed to be used with two or three beams thus enabling also the use of closure phase techniques The magnitude limits of AMBER are K 7 with Low Resolution LR HK on UTs and K 5 on the ATs K 4 with Medium Resolution K band MR K on the UTs and K 1 6 on the ATs and K 1 5 with High Resolution K band HR
5. OBs are put into a queue schedule in OT which later send OBs to the instrument Template A template is a sequence of operations to be executed by the instrument The observation software of an instrument dispatches commands written in templates not only to instrument modules that control its motors and the detector but also to the telescopes and VLTI sub systems Template signature file TSF File which contains template input parameters Visitor Mode VM The classic observation mode The user is on site to supervise his her program execution AMBER User Manual VLT MAN ESO 15830 3522 19 11 Acronyms and Abbreviations AD Applicable document AMBER Astronomical Multi BEam Recombiner AO Adaptive optics AT Auxiliary telescope 1 8m CfP Call for proposals CS Constrain set DI Differential Interferometry DIT Detector Integration Time DDL Differential Delay line DL Delay line DRS Data Reduction Software ESO European Southern Observatory ETC Exposure Time Calculator FINITO VLTI fringe tracker FT Fringe tracker IRIS InfraRed Image Stabiliser LR Low Resolution MACAO Multiple Application Curvature Adaptive Optics MR Medium Resolution MIDI MID infrared Interferometric instrument MIR Mid InfraRed 5 20 microns NDIT Number of individual Detector Integration NIR Near InfraRed 1 5 microns OD Observation Description OB Observation Block OT Observation Toolkit OPC Observation P
6. 3522 16 7 2 3 Calibration cycle 7 2 4 Calibrating the background emission It is necessary to measure the sky and the instrumental emission in order to subtract this background to the science images The procedure consists in observing a source free region This observation is performed with the same set up as the science observation and close in time about 5 minutes and is included in the estimated time for the science observation 7 2 5 Standard calibration the instrumental visibility Std It is necessary to determine the instrumental complex visibility that affects multiplicatively the measured visibility The procedure consists in observing a point like source or a target which intrinsic visibility is known the reference object has to be close to the science object This observation has to be performed with the same set up as the science observation and close in time 8 Introducing Observation Blocks OBs For general VLT instruments an Observation Block OB is a logical unit specifying the telescope instrument and detector parameters and actions needed to obtain a single observation It is the smallest schedulable entity which means that the execution of an OB is normally not interrupted as soon as the target has been acquired An OB is executed only once when identical observation sequences are required e g repeated observations using the same instrument setting but different targets a series of OBs must be constructed
7. An OB can contain only one target but can contain several telescope offsets to measure the sky for example In the case of interferometry instruments the situation is a little bit different since we need calibrator stars to assess the atmosphere instrument system visibility cf sec 7 2 3 Thus each science object OB should be accompanied by a calibrator OB These OBs should be identical in instrument setup having only different target coordinates Moreover with single telescope instruments any OB can be performed during the night In the case of interferometric instrument the instant of observation define the location of the observation in the u v plan 8 1 Standard observation 0BS Std The same exposure cycle can be used for two or three telescopes If only two telescopes are available 2 UTs the third pupil is closed up in the spectrograph cold pupil plane in order to reduce the background The correction of instrumental biases is based on the use of a reference star and the sequence of operations is as presented in Fig 6 8 1 1 Observing cycle A standard observation with AMBER in P80 can be split in the several sub tasks 1 Configuration Setup of the desired spectral resolution wavelength range and DIT AMBER User Manual VLT MAN ESO 15830 3522 17 8 2 Internal calibration of the chosen instrument configuration P2VM see sec 4 2 4 Acquisition Slew telescopes to target position on sky and slew the delay
8. M8 deformable mirror of the UT The M8 is mounted on a tip tilt correction stage In this case the telescope is tracking in field stabilisation mode In this mode the Nasmyth guide probe camera tracks on a selected guide star observable within the 30 arcmin Nasmyth FOV which is centred on the science target by tip tilting the M2 When at limit the M2 is offloaded to the alt az axes of the telescope The tip tilt mount of the M8 is offloaded by offsetting the Nasmyth guide probe position and therefore by offsetting the M2 or the alt az axes The sensitivity of MACAO is V 16 for a 20 Strehl at 2 2um compared to the 50 strehl at V lt 12 at which the AMBER limiting magnitudes were estimated In practice with AMBER MACAO can be used with V 17 with the limitations that reduced Strehl will yield Note There is also the additional constraint that the object should be fainter than V 1 for MACAO to work properly The user should also be aware that Coud guiding is not guaranteed to work for objects with 15 lt V lt 17 and the user should preferably select another guide star If the target to observed is fainter than V 17 it is possible to perform off target Coud guiding provided a suitable guide star exists This guide star must be brighter than V 17 and closer than 57 5 arcsec to the target to be observed with AMBER It should be clear that the fainter the Coud guide star the less optimal correction on the science object ie object
9. The matrix calibration system OPM MCS is set of plane parallel plates which can be introduced in the beam sent by the OPM CAU in order to introduce the 4 delays in one beam necessary to calibrate the matrix of the pixel to visibility linear relation Several components of the AMBER instrument such as the dichroics the fibers the filters the beam splitter the cryostat window are optimised for only one polarisation Then the other polarisation will provide only a small gain in flux but can produce a substantial loss in contrast To avoid this one polarisation is eliminated by polarisation filters OPM POL located on the AMBER table before the dichroics 4 3 From images to visibilities The raw data produced by AMBER are images of the overlap of the 3 beams dispersed by a prism LR or grisms MR and HR Because of the beam splitter one get in addition 3 AMBER User Manual VLT MAN ESO 15830 3522 9 Figure 3 Photography of AMBER at Paranal AMBER User Manual VLT MAN ESO 15830 3522 10 photometric outputs corresponding to each beam An image of the detector image is displayed on Fig 4 The fringes are processed for each wavelength individually In fact 3 fringe system are present in the interferometric output and the first action consists in separating them apart Dur ing the calibration the carrying wave corresponding to each baseline are recorded and the interference term of the base ij is for the pixel k mig k
10. guide star exists This guide star must be brighter than Vmag 13 and closer than 57 5 arcsec to the target to be observed with AMBER If Vmag is fainter than 12 there is a risk that Coud guiding cannot be performed depending on the off axis distance and on the sky conditions seeing To It should also be noted that the expected correction with STRAP drops with distance between the science target and the Coud guide star Having a Coud off axis guide star at the formal maximum off axis distance will not allow AMBER to reach the specified limiting magnitudes Thus it is strongly recommended that the Coud guide star is brighter than Vmag 12 and as close to the science target as possible Note that unlike the UTs the ATs have no possibility of guiding if they cannot guide with the Coud Therefore it is mandatory to use a suitable Coud guide star either the target itself or an off axis guide star 7 1 5 Geometry Important parameters of the instrument to be taken into account for the preparation of the observing schedule are the VLTI geometry during observation u v coverage The selection of the baseline requires the knowledge of both the geometry of the VLTI and of that of the target To assess observability of a target with VLTI it is suggested to use the VisCalc soft ware as this is the only ESO supported software The front end of VisCalc is a comprehensive web based interface VisCalc can be used from any browser from the URL
11. lines to the expected zero OPD position and bring the DLs in tracking state pre defined sidereal trajectory a As stated in Secs 7 1 3 and 7 1 4 the user has the possibility to use a guide star for the Coude systems different from the target He she will have to indicate the coordinates of this star which for the UTs should be brighter than V 17 and fainter than V 1 and within a l arcmin radius from the science target On the ATs the limits are stricter where the object has to be brighter than V 13 Injection Adjustment Adjust telescope positions so the beams from the target will centre on the injection fibers in AMBER Fringe Search Search the optical path length OPL offset of the tracking delay lines yielding fringes on AMBER actual zero OPD by OPD scans at different offsets When fringes are found the atmospheric piston is calculated and the OPL offsets corresponding to zero OPD are applied If FINITO is used the above step is performed by FINITO and not by AMBER Observations Start to record data of interest with suitable DIT In P80 it is foreseen to only use DITs of 25ms or 50 ms for standard absolute phase observations and DITs of 100 ms for differential phase observations The longer DIT allows a larger wavelength range in MR K or HR K observations If FINITO is used longer DITs are available Computing time overheads for added bands The user should assume that 90 minutes are required for
12. one calibrated visibility point ie a measurement of the science object and a measurement of an interferometric calibrator star This applies to LR HK and to Medium Resolution Observations MR or High Resolution Modes HR for one spectral setting Users interested in obtaining visibility measurements at several spectral positions inside the K band should add 30 minutes for each additional spectral band Similarly if the user is interested to repeat the same spectral band to obtain more frames with sufficient SNR then the user should add 30 minutes for each repeated spectral band A maximum of 3 bands per observation is allowed 9 Bibliography e Observing with the VLT Interferometer Les Houches Eurowinter School Feb 3 8 2002 Editors Guy Perrin and Fabien Malbet EAS publication Series vol 6 2003 EDP Sciences Paris e The Very Large Telescope Interferometer Challenges for the Future Astrophysics and Space Science vol 286 editors Paulo J V Garcia Andreas Glindemann Thomas Hen ning Fabien Malbet November 2003 ISBN 1 4020 1518 6 AMBER User Manual VLT MAN ESO 15830 3522 18 e Observing with the VLT Interferometer Wittkowski et al March 2005 The Messenger 10 119 p14 17 reference documents templates calibration plan maintenance manual science technical operation plan Glossary Constraint Set CS List of requirements for the conditions of the observation that is given inside an OB OBs are onl
13. phase reconstruction If fringes are present at all three baselines and the fringes for all baselines are analysed si multaneously then we obtain a relation called closure phase The closure phase relations are independent from any antenna based atmospheric or instrumental phase offsets affecting the beams before arriving to the telescopes If all spatial frequencies have their phases in partially redundant closure phase relations an iterative algorithm allows to compute all phases step by step Then it is therefore possible to reconstruct the image if the u v plane is well filled or to constrain the models if only some closure phases are available 2 3 AMBER characteristics The main capabilities of AMBER are summarised in Table 1 It should be noted that the Instrument Visibility Accuracy in the table only reflects the current status of the instrument and is expected to improve in the coming periods AMBER User Manual VLT MAN ESO 15830 3522 Table 1 AMBER characteristics and observing capabilities Description Specification Number of beams Two or Three Spectral coverage JHK 1 2 5 um Spectral resolution in K R 35 R 1500 R 12000 Spectral resolution in J amp H same as in K Instrument contrast 0 8 Visibility accuracy 9 30 Optical throughput 2 in K 1 in J and H Detector size Detector read out noise Detector quantum efficiency 1024 x 1024 detector array 11 377
14. wavelength This is the case when observing a structure which is present in a spectral line whereas the continuum corresponds to an unresolved structure One can then calibrate the measurement in the line by those in the continuum and the knowledge of the absolute visibility is not required just the ratio between the visibility at a given wavelength and a reference channel 2 2 3 Relative phase variation with wavelength If the instrument is operated simultaneously at different wavelengths then one can measure the variation of the phase with the wavelength The principle is exactly the same as in astrometry except that the reference is the source itself at a given wavelength The most remarkable aspect of this phase variation is that it yields angular information on objects which can be much smaller than the interferometer resolution limit This features comes from the possibility to measure accurately phase variations much smaller than 27 When the object is non resolved the phase variation f A f Ao yields the variation with wavelength of the object photocenter A et An This photocenter variation is a powerful tool to constrain the morphology and the kinematics of objects where spectral features result from large scale relatively to the scale of the source spatial features Note that if this is attempted over large wavelength ranges the atmospheric effects has to be corrected in the data reduction 2 2 4 Closure phase and
15. 0 8 Observables V F A VUE A V F Ao F A F ro D123 A AMBER User Manual VLT MAN ESO 15830 3522 6 3 AMBER within the VLT interferometer 3 1 VLTI infrastructure AMBER is the final stage of an overall infrastructure It is part of a VLTI well defined plan The general concept of the VLTI is to provide an interferometric focus to the instruments like modern telescopes provide almost diffraction limited beams to their instruments Therefore the VLTI infrastructure works like a general facility which supplies the following functions Sampling of the u v plane with 4 fixed Unit Telescopes UTs and 3 movable Auxiliary Telescopes ATs with baselines ranging from 8m to 200m Collection of light with four 8m Unit Telescopes UTs and three 1 8m Auxiliary Tele scopes ATs Wavefront correction at the telescopes in the first phase adaptive optics for the UTs MACAO and tip tilt correction for the ATs STRAP Transportation of the primary and secondary beams from the telescopes to the focal lab Compensation by the delay lines DLs of the optical path difference due to the sidereal motion Correction of the slow lt 1 Hz tip tilt motion of the beams caused by tunnelling seeing effects by means of a fast detector sensing the beam motions and sending corrections to the X Y table so that the beams are kept centred on the optical axis IRIS IRIS uses 25 of the K band for the guiding
16. 15830 3522 22 Cki2 amp dk42 Ge N Choa amp dk23 OD gt 0 2 10 20 30 40 C3 ba 0 2 L ei 0 0 4 o lt 0 2 10 20 30 40 Pixels Figure 5 Example of carrying wave c k solid green line and d k dashed red line AMBER User Manual VLT MAN ESO 15830 3522 Figure 6 Standard observation mode Std OBS Std 23
17. 7 1 8 Field of View AMBER is a single mode instrument and therefore the field of view FoV is limited to the Airy disk of each individual aperture i e 250 mas for the ATs in K and 60mas for the UTs in K For most observations this will not come into effect but can be limiting to observations of objects that consists of several components f ex binaries stars with disk and or winds etc The observer should be aware that if the components are separated by more than the FoV only one of the components will be seen by AMBER 7 1 9 Complex fields For normal observations of single objects there are no special constraints on the seeing it is suf ficient that MACAO or STRAP are working within the normal constraints see Sections 7 1 3 and 7 1 4 When observing complex fields with several objects within a few arcseconds the situation is more complex For fields with several objects within 1 to 3 arcseconds it is not guaranteed that MACAO will perform properly It is therefore recommended to use a guide star in this situation For fields with objects with separations less than an arcsecond MACAO will resolve the ob jects down to 0 1 0 15 arcsec Due to the way that light is injected into AMBER injection procedure only maximises the flux injected into the fiber it cannot be guaranteed in the case of separations smaller than 0 2 0 3 arcsec that the proper target has been injected into the fiber These kind of observations will have to follow a non sta
18. E 2 2 Science accessible with the different observables e AC Absolute visibility VU Fa lt eee bodes ee eda we bee ee 2 2 2 Relative visibility V f A V f AQ e de 5 EELER ew Ee e 2 2 3 Relative phase variation with wavelength 2 2 4 Closure phase and phase reconstruction 2 3 AMBER characteristics s su 4 424 84 Ge wa Oe dea De ee eae 3 AMBER within the VLT interferometer 3A VOT inirasteueture 6 se he ee k bee BS ewe eR ee ee Be Eo 3 2 Other VET iistraments ss roes d se ea ee ee mee be wee be en ea AMBER overview aA AMBER Pe s 3 ce eo hw er n we n ORS ee RA RTR R k 4 2 AMBER layout 4 2 1 4 2 2 4 2 3 4 2 4 Wert Opies e 2id 42 4840 e 84688 Bee hE SOed 6 OSH EES Seere 64 64 bw 6 saca wae eR Ew AES OES we EE HE Calibration Umit e aen E bec owe ee ee ee ee eens Hoo From images to vVISiDItUGS e ccs gre be pie Se eee eS ee Se eG oo aA menene ENEE cv dg ee whe EP BOER DASHES ARERR ES AS Instrumental contrast s e sea 4 05s boie eee eR ee eS 5 Instrument features and problems to be aware of AMBER in P80 6 1 Service and Visitor Modes 2 tbe tedre ae Epea au 7 Preparing the observations TI Cheice ot the VLTI configuration 2 4 seden ebb eee dae Ee EES Tele AO ooi et eee ee bee ee be ees Oe ES Pe oe eds 7 1 2 Baselines TLS Coud guidine with the UTS s eed ae bed ewe RE ae ee Ed wR oF FP Fe eS Sr A A A Ga Ga k Wd
19. ER Instrument webpage http www eso org instruments amber index html Any change of the spectral configuration requires an internal calibration i e spectral calibra tion and P2VM calibration This is automatically taken care of by the internal calibration plan and no action or setups are needed from the user Note that only one spectral configuration is allowed in one OB Any change of the neutral densities the polarises the ADC the position of the fiber heads i e all elements located before the spatial filters does not require internal calibrations They can be used or not depending on the source characteristics 7 2 2 Observing modes The situation is now more complex as FINITO the external fringe tracker is now available on the ATs Without FINITO either on the UTs or on the ATs the observing mode is characterised by the detector integration time DIT Currently only fixed DITs of 25 50 or 100ms ATs only are offered using the UTs and ATs With FINITO on the ATs longer DITs are available allowing in all spectral modes to read out the full spectral range The user should consult with the AMBER Instrumentation webpages for further information on the available integration times It should be noted that the choice of DIT without FINITO affects the width of the central band in MR K and HR K observations The user should check the AMBER Template Manual and the AMBER webpages for further information AMBER User Manual VLT MAN ESO 15830
20. EUROPEAN SOUTHERN OBSERVATORY Organisation Europ ene pour des Recherches Astronomiques dans l H misph re Austral Europ ische Organisation ftir astronomische Forschung in der s dlichen Hemisphare ESO European Southern Observatory Karl Schwarzschild Str 2 D 85748 Garching bei Miinchen O Very Large Telescope Paranal Science Operations AMBER User Manual Doc No VLT MAN ESO 15830 3522 Issue 80 Date 18 02 2007 F Rantakyro 18 02 2007 Prepared EENHEETEN Date Signature A Kaufer Approved a trace k th dE aes Date Signature 0 Hainaut Released 2 0 ok oe os oes be dinier ne 54848 VERSE se Date Signature AMBER User Manual VLT MAN ESO 15830 3522 This page was intentionally left blank AMBER User Manual VLT MAN ESO 15830 3522 Change Record Issue Rev Date Section Parag affected Remarks 80 2007 02 18 FINITO FINITO AMBER Information Spectral Modes HR K for ATs ill AMBER User Manual VLT MAN ESO 15830 3522 This page was intentionally left blank AMBER User Manual VLT MAN ESO 15830 3522 Contents 1 INTRODUCTION Li Sope or tie manual s e ous ds eG ee eRe ee ER 1 2 What s new in this issue of the AMBER User Manual 1 3 Acknowledgments A reunat BOHR SD EE A E A E E SE Ho 1 4 On the contents of the AMBER User Manual 1 5 Contact Information 2 Capabilities of the instrument 21 What measures AMBER 2 422 586 2654 6S oe eR Ree ER
21. K on UTs Using AMBER with an external fringe tracker FINITO now available in P80 on the ATs it is possible to reach K 3 in all modes ie for LR KH MR K and HR K 1 1 Scope of this manual This document summarises the features and possibilities of the Astronomical Multi BEam combineR AMBER of the VLT as it will be offered to astronomers for the six month ESO observation period number 80 P80 running from October 1st 2007 to March 31st 2008 Only the features that are supported by ESO for P80 are given in this document The bold font is used in the paragraphs of this document to put emphasis on the important facts regarding AMBER in P80 and should be considered by the reader 1 2 What s new in this issue of the AMBER User Manual The external fringe tracker FINITO is now available on the ATs allowing K 3 in all spectral modes LR KH MR K and HR K FINITO is either taking 100 of the H band flux or 75 if the user is interested in the H band in LR KH AMBER is now always using IRIS for guiding and IRIS is taking 25 of the K band flux The user should give the H and K band magnitudes of the target with an estimation of the expected visibility in both K and H bands 1 3 Acknowledgments The editor thanks Fabien Malbet LAOG Grenoble who delivered the document which formed the first first version of this manual in February 2005 The editor also thanks Markus Wittkowski at ESO Garching for his comments and Stephane Brillant and Stan Stef
22. More information on MIDI can be found at the following web address http www eso org instruments midi AMBER User Manual VLT MAN ESO 15830 3522 7 Figure 1 Basic concept of AMBER 1 multi axial beam combiner 2 cylindrical optics 3 anamorphosed focal image with fringes 4 long slit spectrograph 5 dispersed fringes on 2D detector 6 spatial filter with single mode optical fibers 7 photometric beams 4 AMBER overview 4 1 AMBER principle Figure 1 summarises the key elements of the AMBER concept AMBER has a multi axial beam combiner A set of collimated and parallel beams are focused by a common optical element in a common Airy pattern which contains the fringes 1 in Fig 1 The output baselines are in a non redundant set up i e the spacing between the beams is selected for the Fourier transform of the fringe pattern to show separated fringe peaks at all wavelengths The Airy disk needs to be sampled by many pixels in the baseline direction an average of 4 pixels in the narrowest fringe i e at least 12 pixels in the baseline direction while in the other direction only one pixel is sufficient To minimise detector noise each spectral channel is concentrated in a single column of pixels 3 in Fig 1 by cylindrical optics 2 in Fig 1 The fringes are dispersed by a standard long slit spectrograph 4 in Fig 1 on a two dimensional detector 5 in Fig 1 For work in the K band with resolutions up
23. d because of the limited wavelength range over which a fiber can remain single mode The three spatial filters inputs are separated by dichroic plates For example the K band spatial filter OPM SFK is fed by dichroic which reflect wavelengths higher than 2 um and transmit the H and J bands After the fiber outputs a symmetric cascade of dichroics combines the different bands again but the output pupil in each band has a shape proportional to the central wavelength of the band Therefore the Airy disk and the fringes have the same size for all central wavelength This allows to use the same spectrograph achromatic optics for all bands and to have the same sampling of all the central wavelengths Then the beams enter the cylindrical optics anamorphoser OPM ANS before entering the spectrograph SPG through a periscope used to align the beam produced by the warm optics and the spectrograph 4 2 2 Spectrograph The spectrograph has an image plane cold stop a wheel with cold pupil masks for 2 or 3 telescopes The separation between the interferometric and photometric beams is performed in a pupil plane inside the spectrograph after the image plane cold stop 4 2 3 Detector After dispersion the spectrograph chamber sends the dispersed image on the detector chip DET 4 2 4 Calibration unit The Calibration and Alignment Unit OPM CAU contains all calibration lamps and can emulate the VLTI in the integration test and calibration phases
24. e of baselines closure phase capability and the photon collecting power of the VLTI a wide range of astronomical sources can be targeted What follows is a brief presentation of the major objectives which are in no way a full listing of all scientific possibilities of the instrument Most of these objectives need the PRIMA astrometry fringe stabiliser and dual feed facility or FINITO fringe tracker to realise the objectives to their full extent but even without these AMBER will be able to make great advances in several areas including the following areas e Hot extrasolar planets Determination of planetary mass orbital parameters and the spectra of the planet and the star e Active Galactic Nuclei Spatially resolve the Broad Line Region and to constrain its ge ometry and kinematics The ionised disks around the putative Massive Black Hole can be studied to constrain its morphology size and velocity and density field Measuring the wavelength dependence of the central point source the shape and size of circum nuclear dust structures as well as additional structures e g the inner region of jets circumnuclear starburst regions or bars in order to test AGN models e Circumstellar material in hot cold and young old stars Constraints on the size and morphology of the disk including velocity and density fields Similarly jets and bipolar outflows can be studied obtaining sizes morphology and velocity and density fields e B
25. inaries Direct measurement of actual orbital motions and the masses of the stars e Stellar structure Measurements of the radius ellipticity surface activity and limb darkening effects 2 2 1 Absolute visibility V f A If the source is bright or if a bright reference star is close enough it is possible to obtain an un biased estimate of the source visibility amplitude from the fringe contrast A visibility measure for a single baseline can constrain the equivalent size of the source for an assumed morphology Visibility measures for several spatial frequencies obtained through Earth rotation different wavelength different baseline constrain severely the models However the interpretation of the results remains always model dependent Different images can lead to similar visibilities and discriminating between models usually requires measures with high accuracy AMBER User Manual VLT MAN ESO 15830 3522 4 In general the phase of the fringes cannot be related to the phase of the source Fourier transform because of the atmospheric phase jitter Only relative phase measurements are possible for sufficiently close spectral bands This can be extended to spectral bands further away using a correct model of the atmospheric effects but this is out of the scope of the standard data reduction 2 2 2 Relative visibility V f V f Ao In some cases one is interested in the variation of the target spatial intensity distribution with the
26. l in Paranal for their comments 1 4 On the contents of the AMBER User Manual Section 2 of this manual is aimed at users who are not familiar with the AMBER instrument and who are interested in an overview of its capabilities Section 3 describes the AMBER instrument within the VLTI framework and section 4 provides the description of the instrument the instrument layout sec 4 2 the expected performances sec 4 4 and a reference to instrument features to be kept in mind while planning the observations or reducing the data sec 5 It can be consulted by users who want to prepare an Observing Proposal Phase I but should definitively be read by those who have been granted observing time and have to prepare their observations Phase II In Section 6 I present some added information pertinent to observing with AMBER in P80 Section 7 provides the basic information needed AMBER User Manual VLT MAN ESO 15830 3522 2 to prepare a program the configuration of the VLTI sec 7 1 the identification of the observing modes and of the standard settings sec 7 2 1 5 Contact Information The aim of this manual is to make the users get acquainted with the AMBER instrument before writing proposals In particular sections3 1 2 4 and 4 3 are aimed at astronomers not used to interferometric observations This document is evolving continually and needs to be updated and improved according to needs of the astronomers All questions and suggesti
27. ndard extensive procedure to perform the injection adjustment and will require the presence of the PI Visitor Mode 7 1 10 Bright objects In Low Resolution observations LR of very bright objects Kmag lt 0 the detector can saturate even with using Neutral density filters during excellent weather conditions The user should consult the webpages for the latest information on the magnitude limits If possible AMBER User Manual VLT MAN ESO 15830 3522 15 the user should try to use the MR spectral configuration if the scientific goals still can be achieved in this mode 7 2 Choice of AMBER configuration 7 2 1 Instrument set up The instrument set up is defined by the spectral configuration of the instrument and the 3T configuration In each 3T configuration the spectral configuration can be R 35 75 K band and 100 H band with IRIS guiding Low HK R 1500 K in medium resolution Medium K 12 1 and Medium K 12 3 R 12000 High resolution K band observations On the ATs with FINITO the following modes are available R 35 75 K band and 25 H band with IRIS guiding and FINITO fringe tracking Low_HK R 1500 K in medium resolution with FINITO fringe tracking Medium K_1_2 1 and Medium K 1 2 3 R 12000 High resolution K band observations with FINITO as an external fringe tracker The details on the exact wavelength ranges DITs and central wavelengths available can be found on the AMB
28. ng proposals AMBER User Manual VLT MAN ESO 15830 3522 12 Considering a target which has a scientific interest and for which AMBER could reveal inter esting features the first thing to do is to determine whether this target can be observed with AMBER or not At this point AMBER is offered with conservative performance estimates The details of the current magnitude limits can be found at the AMBER instrument webpage http www eso org instruments amber inst 7 1 Choice of the VLTI configuration 7 1 1 Telescopes The available telescopes for AMBER are the 8m Unit Telescopes UTs and the 1 8m Aux iliary Telescopes ATs For detailed information on the UTs ATs and their active optics subsystems please see Sections 7 1 3 and 7 1 4 What is important in the choice of telescopes is the needed light collecting area and the baseline between the telescopes and not the maximal baseline across the mirror 7 1 2 Baselines For a list of the offered telescope configurations please refer to the to the VLTI baseline page at http www eso org paranal insnews vlti This page contains detailed information about the baseline lengths angles and available telescope triplets using the UTs or the ATs 7 1 3 Coud guiding with the UTs Each UT is equipped with an adaptive optics system called MACAO It consists of a Roddier wavefront curvature analyser using an array of 60 avalanche photodiodes This analyser applies a shape correction on the
29. not yet fully commissioned The following caveats should be taken into consideration e Vibrations have been found in the VLTI arm which have been partially fixed Residual vibrations may still exist e OPD model may not be completely optimised and time can be lost to find fringes in particular in the LR mode AMBER User Manual VLT MAN ESO 15830 3522 11 e Due the the absence of a fringe tracking system FINITO the spectral coverage can be severely limited to a dozen of pixels on the UTs On the ATs FINITO is available and thus in all modes the full spectral range can be read out on the detector e Differential visibilities and phases see sections 2 1 and 2 2 3 can be used e AMBER is a single mode instrument and therefore the field of view is limited to the Airy disk of each individual aperture i e 250 mas for the ATs in K and 60 mas for the UTs in K 6 AMBER in P80 AMBER combines most of the aspects that usually exist independently in several astronomical instruments It involves visibility measurements interferometry spectral dispersion spec troscopy and background level corrections Hence AMBER in its final configuration will feature a large number of modes selectable by the user However most of the modes are still under development In P80 the only modes offered will be the High Resolution K band HR K Medium Resolution K band MR K and the low resolution K band LR HK with a spectral resolution A AA of appro
30. of astrophysical information can be extracted from any individual AMBER measurement for a given baseline configuration 2 1 What measures AMBER AMBER is a beam combiner for up to three beams feeding a spectrograph and a camera working in the near infrared from 1 to 2 5 microns It is a single mode instrument which means that each baseline give access to only one point in the frequency space per spectral channel For this baseline the instrument is designed to measure the absolute visibility in each spectral channel the relative visibility i e the ratio between the visibility in each spectral channel and the visibility in a reference spectral channel average of several other channels for example AMBER User Manual VLT MAN ESO 15830 3522 3 the phase difference i e the difference between the phase in each spectral channel and the phase in a reference channel This is the main purpose of Differential Phase observations the closure phase when used with three beams for the following spectral resolutions 35 1500 and 12000 and a spectral coverage containing the K H and J bands The scope of this manual is limited to the measure and calibration of single or triplets u v points and do not address the use these measurements to constrain astrophysical models or the image reconstruction process 2 2 Science accessible with the different observables Thanks to the combination of instrument performance choic
31. ons should be channelled through the ESO User Support Department email usd help eso org and homepage http www eso org org dmd usg The AMBER Home Page web page is found at the following URL http www eso org instruments amber Any user of the instrument should visit the web page on a regular basis to be kept informed about the current instrument status and developments 2 Capabilities of the instrument What follows is not intended to be perfectly accurate from a mathematical point of view but to remind what is accessible in practice In principle the contrast and phase of the fringes observed on a source with given baseline B and wavelength yield the amplitude and phase of the Fourier transform of the source brightness distribution at the spatial frequencies f B A If this Fourier function is sufficiently sampled in the Fourier plane then an inverse Fourier transform yields a model independent reconstruction of the image of the object at the wavelength with an angular resolution A Bmax Besides the sensitivity limits two classes of problems make this imaging process quite difficult First calibrating the measurements i e deducing the object visibility and phase from the fringes contrast and position Second making measurements at a sufficiently sampled Fourier plane can be time consuming This is why although making images will actually be the goal of AMBER on the VLTI in some cases it is worth examining what kind
32. rogram Committee OPD Optical path difference OPL Optical path length Phase I Proposal Preparation and Submission POPE Phase II Proposal Preparation QC Quality Control REF Reference documents SM Service Mode SNR Signal to noise ratio STRAP System for Tip tilt Removal with Avalanche Photo diodes TBC To be confirmed TBD To be defined TSF Template Signature File UT Unit telescope 8m VIMA VLTI Main Array array of 4 UTs VINCI VLT INterferometric Commissioning Instrument VISA VLTI Sub Array array of ATs VLT Very Large Telescope VLTI Very Large Telescope Interferometer VM Visitor mode AMBER User Manual VLT MAN ESO 15830 3522 00o0 20 AMBER User Manual VLT MAN ESO 15830 3522 21 tudun RealTime Display 1 0 03 01 11 i il Ur Jus SMULE Ur Mee Es og imaga Mint ramara IANGS_RT M nae x ZR vjs Wolne liraz TEE mips EH falu Syk Oul Levak j Au lu auade cubs Sud z n Becke rv ESS BR im jatten Hc poticrn Deng Fi Fea pat Frama Lula Int E me H ware Bo selec au WW za wre NM esse ZO Corio see zu Figure 4 Image of the fringes recorded by AMBER in medium resolution around 2 1 microns using an artificial light source The wide stripes are the photometric spectrum of the 3 beams and the band with narrow stripes is the interferometric channel with the fringes AMBER User Manual VLT MAN ESO
33. s close the limiting magnitudes of AMBER should use bright Vmagi13 AMBER User Manual VLT MAN ESO 15830 3522 13 guide stars and not request seeing worse than 0 8 A detailed description of the MACAO performance vs Coud guide star magnitude can be found at URL http www eso org instruments sinfoni inst aosystem html There are also a few weather condition constraints for proper MACAO performance e Seeing lt 1 5 arcsec e 7 gt 1 5 ms e Airmass lt 2 These constraints do not affect Service observations as OBs are only classified as A or B if MACAO has been performing within the tolerances The constraints are given here for Visitor mode observations to give the user the conditions under which MACAO will perform as expected Thus during non ideal weather conditions outside the MACAO performance ranges the user could ameliorate the effects to some degree by only using brights guide stars and only observe at high elevation 7 1 4 Coud guiding with the ATs Each AT is equipped with the tip tilt corrector called STRAP It consists of a avalanche photodiode quadrant which measures the tip tilt of the incoming wavefront The measured tip tilt is compensated by acting on the M6 mobile mirror When at the limit M6 is offloaded to the alt az axes of the telescope The sensitivity of STRAP on the ATs is Vmag 13 If the target to observed is fainter than Vmag 13 it is possible to perform off target Coud guiding provided a suitable
34. to 12 000 the spectrograph must be cooled down to about 60 C with a cold slit in the image plane and a cold pupil stop In practice we found it simpler to cool it down to liquid nitrogen temperature To produce high accuracy measurements it is necessary to spatially filter the incoming beams to force each one of them to contain only a single coherent mode To be efficient the spatial filter must transmit at least 10 more light in the guided mode than in all the secondary modes For the kind of imperfect AO correction Strehl ratios often lt 50 available for the VLTI the single way to achieve such high filtering quality with decent light transmission is to use single mode optical fibers 6 in Fig 1 The flux transmitted by each filter must be monitored in real time in each spectral channel This explains why a fraction of each beam is extracted before the beam combiner and sent directly to the detector through a dispersive element 7 in Fig 1 The instrument must also perform some beam cleaning before entering the spatial filter such as correcting for the differential atmospheric refraction in the H and J bands or in some cases eliminating one polarisation AMBER User Manual VLT MAN ESO 15830 3522 8 4 2 AMBER layout Figure 2 shows the global implementation of AMBER with the additional features needed by the actual operation of the instrument 4 2 1 Warm optics There are three spatial filters one for each spectral ban
35. ximately 12000 1500 and 35 respectively In LR HK mode the K band will be acquired simultaneously with the H band IRIS which is always used is taking 25 of the K band flux and H band is sent undiminished to AMBER Note that if FINITO is used on the ATs then FINITO will use either 75 or 100 of the H band flux On the ATs the external fringe tracker FINITO is now available See the AMBER instrument webpage http www eso org instruments amber inst for the most recent information on the exact wavelength ranges and section 7 2 1 for the configuration options for the spectrograph 6 1 Service and Visitor Modes For P80 AMBER is offered in service mode and in visitor mode see Sect 10 During all the period the unique contact point at ESO for the user will be the User Support De partment email usd helpG eso org and homepage http www eso org org dmd usg The visitor mode is more likely to be offered for proposals requiring non standard observation procedures The OPC will decide whether a proposal should be observed in SM or VM As for any other instrument ESO reserves the right to transfer visitor programs to service and vice versa 7 Preparing the observations Submission of proposals for AMBER should be done through the ESOFORM It is important to carefully read the following information before submitting a proposal as well as the ESO FORM user manual The ESOFORM package can be downloaded from http www eso org observi
36. y executed under this set of minimum conditions Observation Block OB An Observation Block is the smallest schedulable entity for the VLT It consists of a sequence of Templates Usually one Observation Block include one target acquisition and one or several templates for exposures Observation Description OD A sequence of templates used to specify the observ ing sequences within one or more OBs Proposal Preparation and Submission Phase I The Phase I begins right after the Call for Proposal CfP and ends at the deadline for CfP During this period the potential users are invited to prepare and submit scientific proposals For more infor mation http www eso org observing proposals index html Phase II Proposal Preparation P2PP Once proposals have been approved by the ESO Observation Program Committee OPC users are notified and the Phase II begins In this phase users are requested to prepare their accepted proposals in the form of OBs and to submit them by Internet in case of Service mode The software tool used to build OBs is called the P2PP tool It is distributed by ESO and can be installed on the personal computer of the user See http www eso org observing p2pp Service Mode SM In Service Mode opposite of the Visitor Mode the observations are carried out by the ESO Paranal Science Operation staff PSO alone Observations can be done at any time during the period depending on the CS given by the user

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