Spectra-L200 - JTW Astronomy
Contents
1. Boar 124 I 318 P 200 Inm When finished click Apply amp OK The title and sub title will now show on the chart You can right click on the chart and select Show notes here to reposition the notes as required Determining Resolution and R value I like to show the dispersion 0 537 A pixel in the notes Also the calculated resolution R value Unhide the reference lamp image strip and select it as the active strip yellow border The neon lines now show on the graph Select the Measurement and Element lines icon Under the Measurement options tab select FWHM Select a suitable line on the reference profile the range selected 667 4838 to 668 1553 will come up and the selected line turns red Tick the Show results when run and click run In the new screen you ll see the calculated FWHM of the selected line 0 22nm and the R value 3003 Fie Chart Selection maga Lakra Operation Took Hale els a L E Pede re Ve Ayia EO Furn nas SI IR FATA Fami apticra Viney Fase 7 Saabin Dan UT EET ih E BB EES pe V1389 Ce Eg Width 469 Cen 7 PuHM aser edt EO Ha Ramon MAiA inen zu T hen nin Run Delmi a mpo onthe char dc beka a mga arrea Dus N File Chart Selection Image Calibration Operation Tools Help Image Strip View IF 2 0 wh 7 Kazi hd Image ks ar FESSES reall ou LE ciam IER ae pr Measureme2. Spectra L200 Users Manual for the Spectra L200 JTW Astronomy Revised June 2014 Welcome to the world of Spectroscopy The Spectra L200 Littrow slit spectroscope has been designed as a robust scientific instrument and provides the amateur the ability to collect spectra at low or high resolution easy to install on your telescope and use The Littrow Spectroscope The design of the Littrow spectroscope as applied in the Spectra L200 uses a fixed but selectable entrance slit gap through which the light from the target object 1s focused normally from your telescope The expanding light beam is then reflected from a small precision front surface mirror to a collimating lens This lens then transmits a parallel light bundle to the reflective diffraction grating The grating generates a series of spectra The precision grating used in the Spectra L200 has a blazed profile to maximise the light dispersed into the resulting spectrum To record different target wavelengths within the spectrum the grating can be rotated using a precision micrometer The grating holder is set at a slight angle to the optical axis to reflect the spectrum back to the collimator The spectrum is then re focused by the collimating lens to the imaging camera at the focal plane E Lol i Entrance slit Grating Collimating lans y c e Fi Focal plane pt a X s eg 6 M mme
3. lamp module This should be rated for 1A E Fig 12 2 nosepiece fitted Fig 13 Borg camera focuser fitted To ensure that you obtain the best results and resolution from your Spectra L200 there are few key steps which should be followed a Setup the imaging camera on the Spectra L200 to achieve good alignment and focus b Set up the guider to give good focus on the reflective slit plate c Setthe entrance slit gap to suit your target and seeing conditions Setting up the imaging camera The object is to position the camera CCD securely at the best focus position and have the target spectrum lying exactly along the horizontal axis of the camera If the camera 1s not set at the correct angle the spectral image will appear tilted across the field of view setting the camera focus This 1s initially best done on the bench You need to illuminate the entrance slit with a suitable light source A piece of greaseproof paper tracing paper over the inlet port gives a good diffuse light As you ll probably be moving on to calibrating the grating rotation use an energy saving fluoro lamp Position the lamp a metre or so from the inlet port such that it fully illuminates the slit The entrance slit gap should be set reasonable narrow around 29 micron The adaptors necessary to set the camera CCD at or close to the design back focal position should already be in place Provision for camera rotation to reduce tilt should
4. Fig 1 Typical Littrow optical layout Overview of the Spectra L200 wn E LN a P Fig 2 Spectra L200 General View Starting at the front we have the inlet port This has a female T thread connection and your telescope nosepiece adaptor should be fitted here When you look inside you see the reflective guide slit arrangement Fig 3 Inlet port showing slit plate reference mirror retracted The slit gap visible as a thin black line in the mirror surface and the selection number should be seen in the middle The front protective plate provides a clear guide aperture of 7mm x 20mm There are 12 slit pinhole options available selected by turning the external thumbwheel The index detent maintains the slit gap on the optical axis SSF ED gt 43m DoZ Znum z aT Spm Doc EMGLumm Fig 4 T humbwheel indexing for slit gap EX The guide system comprises of the reflective slit plate a small front surface mirror and a doublet lens which projects the image of the slit and hence the target field of view to your guide eyepiece or guide camera located in the external holder Two thumbscrews are provided to lock the guide eyepiece camera after focusing 14 Fig 5 Guide amera tube At the side of the slit block there s a flip mirror arrangement The actuating knob on the side allows this mirror to be retracted held in place with a small magnetic catch this 1s its normal position when acq
5. The On Off switch powers the lamp To obtain a reference spectrum the flip mirror should be swung down this then allows the lamp to illuminate the slit plate 1n line with the optical axis An exposure around 2 6sec should be enough to record a good spectrum Check that the lines are not overexposed Switch off the lamp and return the flip mirror to the stop position to record your target spectrum As an alternative an argon neon lamp can be supplied This provides reference lines into the blue region of the visual spectrum Summary The success of your spectroscopic results will depend very much on the stability of the telescope mount spectroscope combination This means in real terms that the spectroscope should be fitted and aligned and well supported and not moved on and off the telescope unnecessarily Many amateurs dedicate a telescope to their spectroscope work Likewise moving the imaging camera on and off the spectroscope means checking and re checking focus and alignment every time it s much easier in the longer term to have a dedicated camera for the spectroscope Getting precise focus of the target star on the entrance slit and the spectrum or at least the region of interest in the imaging camera is a critical step in achieving maximum resolution and repeatability of results Spend the time get it right Slit spectroscopy isn t easy The challenges can be daunting at times When it all comes together the
6. is a locking screw for the front of the grating holder and usually needs no adjustment The larger white Nylon thumbscrew applies a small amount of pre load onto the precision bearing within the holder this minimises any unwanted movement in the bearing At the rear of the plate towards the micrometer position there are three screws a central M4 socket head and two M3 socket head screws These act against each other in a push pull arrangement to apply a tilt to the grating housing Adjusting the grating tilt 1 Select a pinhole slit say 96micron size 2 Set up the imaging camera or eyepiece Illuminate the inlet port with a lamp or use the bright daytime sky to produce a spectral image in the CCD field of view 3 Rotate the camera to remove any visible tilt the spectrum should sit horizontally across the field Adjusting the grating tilt will cause the spectral image to move up down in the field of view The object is to bring it close to the centre height of the chip 5 Loosen the Nylon pre load thumbscrew by a couple of turns do NOT remove it completely Using the Allen keys NOTE tightening the central M4 screw will RAISE the spectrum in the field of view 6 Slowly and gently tighten the M4 adjusting screw at the same time as releasing the two M3 socket head screws until the spectrum is sitting across the middle of the FOV loosen the M4 adjusting screw at the same time as tightening the two M3 sock
7. openphdguiding org With the Spectra L200 the highly reflective glass chromed slit plate provides the guide image Using the telescope focuser the target star and the surrounding field is brought to a focus on the slit plate this is the image seen in the guide camera Using the telescope controls the target star should be positioned exactly on the slit gap Close to the middle of the slit length The target star or a suitable field star close by can then be used for the guiding routine Fig 20 Guider view of slit plate Usually the slit length is orientated to sit either along the RA or Dec axis To minimise unnecessary direction reversal corrections the Dec alignment is preferred Setting the guide camera entrance slit focus Prior to using the guide system it s necessary to mount the guide camera and adjust the focus and orientation of the camera field of view This can be done on the bench with subdued lighting illuminating the entrance slit plate The Spectra L200 guide port is designed for a guide camera fitted with a 1 25 standard nosepiece You can use any suitable camera for guiding but the SX Lodestar camera is a proven performer and recommended With the reference flip mirror retracted the reflective open area around the entrance slit gap 1s visible to the guide camera The transfer optics are designed to give visibility to the maximum possible field of view Set up your guide camera and image acquisition soft
8. satisfaction of seeing your results makes up for all the effort Typical data observing run In Appendix C we attach a BASS Project tutorial which covers the basics of recording your first spectrum and how to conduct the basic processing to obtain a 1D calibrated profile Recommended Reading Astronomical Spectroscopy for Amateurs K M Harrison Springer 2010 Practical Amateur Spectroscopy S F Tonkin Springer 2002 Stars and their Spectra J B Kaler CUP 2011 Spectroscopy The Key to the Stars Keith Robinson Springer 2007 Optical Astronomical Spectroscopy C R Kitchin Taylor amp Francis 1995 Introduction to Astronomical Spectroscopy I Appenzeller CUP 2013 Handbook of CCD Astronomy S B Howell CUP 2010 Webpages Forum Groups of Interest http www astronomicalspectroscopy com index html https groups yahoo com neo groups astronomical_spectroscopy info http www astrosurf com aras http www ursusmajor ch astrospektroskopie richard walkers page http spektroskopieforum vdsastro de Appendix A Technical Specifications Model Spectra L200 Weight 1315 gms Inlet port female T thread 42mm x 0 75 pitch Housing laser cut 1 5mm aluminium anodised Components CNC precision machined aluminium anodised Internal surfaces Black flocked to reduce IR reflections Back focus distance inlet port to entrance slit 55mm Back focus distance imaging port to CCD 60mm D
9. strip and select profile properties The tab Display allows you to select your colour of choice Save the project Copying the final annotated Chart You can save a copy of the profile chart as a png jpeg or bmp by right clicking on the chart and saving with your selected name saving profile as a 1D fits file The profile can be saved as a fits file by clicking the 1D icon and saving The fits profile will now also be displayed on the graph ses gs S JE dh we 1 Ne pommes ES P D E PISO lt V13898 Cen Ha Regan 02314 I har Henn zr ELTE NI anes Speck ALDI K 31541 Ereg Tox 120 see Cipanon USN Apel Re 30073 E ea Bm BBC ES Yeavetangtt nmi I SSS Normalising the profile Normalising works best for me on a 1D profile You don t have to get involved in any rescaling of the Y axis Close the reference and original spectrum profiles right click on the image strip and select remove image just leaving the 1D profile on the chart Click Image normalise flux scale and enter the wavelength interval you want to use Any reasonable flat section of the continuum can be used Click Apply then Close Seietan Sane FS amem In eng mnga wii bee ed io Loir ol of N Continuum Ha a inm Ft me ll es Cabin Opernten image Normaleed Flux be k Tacie Seka am IE ERES Tah Arme 1369 Cen Ha Ragion Gao 14 aT TA
10. zii a Fey Kes v1368 Cen Ha Region east V sneatarxtfi rim You can save this profile chart with Name and Notes by saving the project with a new name or save just the normalised profile as a 1D fits illo REGI quM e n pa aS O Fan Hasan Sheen Hiber w Dara rude red ie M BL 3161 uses 5537 Apol Re ARI Fer Hanas Sele Marlene DHS Sari YEZ Lb 2141 Esprit TO x TED R i Diagana D EX7 Spinal Fi Sy
11. CT i or cR m m om enc on d uw nl du Wb a ada a uas a m dull n a 4549 w s w ug 35a a mui m w 1 mcmom d w u u m la am w un l d mliulnu Ma m zu dr m u u li in m uu ww m mor n mcm wb o3 wa mw x x 7 T ao a E H 3a de Fig 27 Typical high resolution solar spectrum The above section shows the solar lines between 5800 5900 Na doublet Even greater detail 1s given on the solar spectrum obtained on the BASS2000 website http bass2000 obspm fr solar_spect php step 1 Suggested entrance slit gap settings The thumbwheel is used to index the entrance slit plate exposing different slit gaps You can select widths from 19 micron through to 96 micron The choice of slit gap width will be dictated by the seeing conditions the effective focal length EFL of the telescope and the required resolution of the spectrum to be recorded The normal slit gap selected would be just smaller than the anticipated FWHM Full width half maximum size of the target star The excess starlight at the sides of the slit gap 1s used for guiding Fig 28 Details of slit gap pinhole v s FWHM image CAOS Shown above is a diagram of the typical star image 1a a narrow slit gap superimposed 1b and a pinhole superimposed 1c The residual halo is the light available for guiding The resulting light entering the spectroscope 1s shown in 1d and le For typical seeing conditions of 3 arc sec the following table gives some guide
12. also be available I also strongly recommend that you orientate the spectrum central to your CCD frame and horizontal across the larger axis This reduces the tilt angle and possible loss of resolution The absorption emission lines within the spectrum height will probably end up showing a slant where the absorption emission lines look slanted relative to the spectrum This is normal It can easily be corrected in your normal processing Do NOT be tempted to align the absorption emission line vertically get the spectrum horizontal across the CCD chip Fig 14 Spectral image showing tilt across the CCD Fig 15 Spectrum corrected for tilt showing the slant of the lines within the spectrum Set up the camera to give a 0 5 sec exposure this will vary camera to camera and we ll reset the exposure again later You can access the slit zero order image by rotating the grating to a position where it acts as a front surface mirror approx 1450 on the micrometer then use this setting for the initial focusing Otherwise adjust the grating rotation until you get an image of the slit on the CCD Adjust the grating position to bring the image close to the middle of the frame This may require fine adjustment of your grating tilt angle See Appendix B Now vary the exposure to get a well exposed image of the slit zero order or a tight clean emission line Overexposing the image will swamp the detail ENED oe m 3 ee
13. and keep the results with the instrument When you actually use the spectroscope at night on the telescope it will come in very very handy e ele e rl H 3 cpe 222 222222 222222 Birr Mies temm TI zm KT SS a os L200 Spectrograph with 15040 Hmm Frank Johns 5u4 2012 Eds SUS ZZ bo II d M x AT dL a i L Caste al Majer d haar tram Fastere RL 120 rede L 1950 7600 i 1440 T53 1450 TAES EN 1460 7341 n 1470 7550 tz 1450 Teel 13 1440 DLE d 1500 Th 15 1540 ZI LN isz adz EA 1530 EET Me 1540 L i a 1550 Ke T 1560 554 21 1570 d H Alpha Eg 1550 Ede m zx 1550 6345 zd 1600 Za L ES 1610 e174 4 E 1620 ATL z IE 1620 edd a 25 1640 Rat Y P za 1650 Bebe Ha a 50 1660 5774 i 3M 1e70 STi 32 1650 Berd JEJ 1640 5545 59 1700 5440 25 Trio 5347 ik 17z0 z TN 1730 5213 1740 5115 Ha A 1750 IE T en as TTT EN 1770 diti HE eka va sre AUT TTT 1720 deed z TE 1800 a574 m PEPESE PPP PA TE PP uo 45 1810 4452 dE 1520 ddzz Hicram s t r 47 1830 di55 Hamma 4i 1540 dd ES 1450 did H Delka 106 Rp ien d 5k td 51 1870 440 b E 1880 sah 7h 5i 1240 3437 3 Fig 25 Excel spreadsheet prepared for micrometer head calibration Frank Johns These settings can be used to prepare a calibration graph and can be used to position the centre wavelength on a target spectrum Using an annotated solar spectrum we can do the same calibration in more detail by recording the obvious Fraunhofer absor
14. ced condition and be able to be guided to lock on to the target star for at least 10 20 mins The telescope must be well collimated and the focuser robust enough to hold the weight of the spectroscope and camera s with NO sag or movement With the spectroscope rigidly attached and the target star image in or very close to the slit gap adjust the focus to give the tightest star image you can get If your guide software has the capability of measuring the star size FWHM make use of it to find the best focus Use ONLY the focuser on the telescope Don t touch the imaging camera Bring the target star image into the middle of the slit gap height The closer the image is to the center of the slit height the closer it 1s to the optical axis and the centre of the CCD chip Take an exposure of the spectrum to confirm the star 1s actually there Move the star image from one side of the slit using the fine controls on your mount to the other to ensure you are actually seeing the central core and not just one of the edges Take exposures after every adjustment The height of the spectrum recorded will depend on the seeing conditions this size should be similar to the optimum entrance slit gap used Using the Reference Lamp The Spectra L200 is fitted with a low voltage power source to drive a reference lamp used for calibration of your spectrum Reference lamps provide a useful source of fixed markers and by comparing the k
15. ciently accurate to get the necessary readings Set up the spectroscope on the bench with a piece of white paper tracing paper over the inlet port Point the inlet port towards the Fluoro lamp Wind the micrometer slowly inwards to locate the bright zero order image of the slit This should be found at a micrometer reading of approx 1450 Position the image close to the centre of the CCD field of view and note the actual reading Continue slowly winding the micrometer until you pick up the bright emission line in the blue centre the image and record the reading Repeat this for the line in the green the double yellow line and the broader red line Example For a 600 mm grating Zero Order 0000A 1445 Fluoro Blue 4358A 1255 Flouro Green 5461A 1210 Fluoro Yellow 5779A 1195 Fluoro Red 6113A 1182 Fa KH die ma Clas Carawcc Cor Taceo Pas redee Hmm SS Vie tm IES I BHT STEL ITE BT e 0 89 SHS He He Ha Hr Ea A eee owe Ga deh ie Kea a HS Dr H H 7 0 Rab H id R br Len 98H an LL K dl beg hnm Cet Pecos STG lsezn LE FI Fig 24 Yellow flouro doublet 600 mm grating These readings will form the basis of our instrument calibration curve We will need to generate a new calibration curve when we change gratings or micrometer The following illustration shows a typical micrometer calibration curve based on a solar spectrum Thanks to Frank J It is important to do this calibration
16. d the central Y value The image is then cropped about 80 pixel high i e Y1 540 Y2 460 based on a centre of 500 The file can be saved as novaCen1264 d c fit The suffix d for dark corrected and c for cropped Using exactly the same crop settings open the reference lamp images and apply Save as Neon1264 c fit This ensures that the centre of the reference lamp image is exactly the same as the spectrum Important when applying slant smile corrections These images are then opened in BASS Project for calibration and processing Summary At the end of the observing session you should have A cropped dark corrected stacked exposure of your target spectrum Atleast one cropped reference lamp spectrum BASS Project Open BASS and select the reference lamp image FIRST This ensures that the calibration of the subsequent spectra are linked to the reference spectrum S Es EE spectrum Fi Char Searicn konse Cibin Operation Tosh Hak zx fu H n T Il P d K Sire Vie n i z E S HAASE E nx iz Ern 21 IEEE aL pe REC p inu i Li yn ll U aw za e i l ge ei I acc a E b eee M Den Ji be e Pints i luncaliorated i BASS presents the imported images as a series of Image Strips at the top of the window It automatically then produces a profile based on the full height of each image strip You can see the reference lamp peaks superimposed on the raw target profile The spectrum of th
17. e Argon lamp Set the target star image onto the centre of the slit height and position it into onto the slit gap confirm guiding is OK Take a 10sec 30 sec trial exposure to confirm the spectral image is horizontal and close to the centre height of the CCD chip You may need to take a longer exposure if you need to accurately determine confirm the central wavelength Commence the sequence of exposures Take an exposure of the reference lamp Example Based on the recent Nova Cen results Over the period various gratings 300 1200 600 mm were used The equipment used was a Genesis 4 f5 with the Spectra L200 mounted on a NEQ6pro mount The mount is controlled through Carte du Ceil CdC and EQmod Lodestar guide camera and ATik 314L for imaging PHD V2 2 or AA5 for guiding and AstroArtV5 for acquisition Depending on the data requirements you want to record use the micrometer head to pre set the central wavelength to the required target wavelength 1 e Ha Cee ae T aa 55958 retre Pao ipa Sate img i ES tere man F odes alate s pra ensis iere LER U ae ss COP R EIS weg 4 Eae m Eregi cemut l ZE 8 mania 1 9 Snag ET l L JE T Eur BT 8 M eh o T Tas Feu Tac a LLL LI amp Mete iius EEGuco4sc ee Emir IES Mame KB raw jmwqomzeun This shows a typical run set up the guide image 1s at the left hand side with the target star locked in the guide
18. e Ld tah amp d didi eire ee rmi ee PERDE MESI ar TURIS d Kr DET EET zl amp J m rr m LDILJ LR al Kez See Gi faet eee De T KEK la rari come 7 Pan Hn aeia B Teir H2 Ha reget fu F ig 16 Zero order slit Image The image should show a bright vertical band probably slightly out of focus The next job is to make adjustments of the camera spacers focuser to bring this image to best focus Trial and error If you use T thread adaptors you can rotate them to see the impact don t worry too much about the tilt angle this can be corrected at the end By the time you finish the slit gap zero order should appear as a clean crisp tight bright line in the centre of the CCD chip If you re using a bright emission line then again this should appear regular and the edges of the slit gap clean in sharp focus For normal CCD cameras the Borg Hutech helical focuser 7315 and a suitable T thread adaptor available from JTW Astronomy is highly recommended Note that the sweet spot i e a field of view within the depth of focus limit is around 10mm diameter For a DSLR the frame width 1s 22mm At the extreme edges of the image the spectrum will be well out of focus This will severely impact on the clarity and resolution of the spectrum recorded You need to take this into account when determining your best focus for your CCD Focus on your region of interest and acc
19. e nova shows clearly the Ha emission Tilt Corrections It s much better to correct any tilt of the spectrum across the CCD by adjustment of the imaging camera This is the recommended method Any residual tilt can be corrected using the Image tilt drop down menu Tick the box to apply the corrections to all image strips Slant corrections You can correct for the inevitable slant found in Littrow spectroscopes using the Image slant drop down menu Tick the box to apply the corrections to all image strips Save both images this time indicating the correct that has been applied neonl264 c tilt fit as neon1264 c tilt smile fit novacen1264 d c s tilt fit as novacenl264 d c s tilt smile fit Fin Chad Seactn image Cabra Operate Teak Hele one yen aed ew es cs SAP elie Lae Hb onde Sat Nana Soy Dm 8 ran E Gn ha mage Clang E verbo line o bs gira hiend d hA rasili medier Lies Tuta Erap T Pma amaga a Teyr piy Lora D DE dae D Ut E Fa 754 hieni 372 1283 Feds St ERI He Tid Selecting the binning region and sky removal To extract the optimum data from your spectrum the vertical binning zone should be selected to encompass the full height of the spectrum without including excessive sky background Make sure the target spectrum image strip is selected it will display a yellow border Increasing the brightness this doesn t change the underlying image helps to determine where t
20. ept that extreme edge of your frame may record at a lesser resolution F ig 17 Borg Hutech 7315 helical focuser and T thread adaptor If the camera has been rotated to achieve focus e g when rotating T thread spacers it needs to be reset back to the horizontal without changing the focus 18 TST2We adaptor front view Fig 19 TST2We adaptor rear view When using the T thread configuration the addition of a TS rotary adaptor TST2We above works very well and only takes up 5 5mm of back focus http www teleskop express de shop index php manufacturers_1d 39 this can be combined with a TS EOSs zero length T2 adaptor to save space when a DSLR is used The inner section of the standard T2 camera adapter on the front of the DSLR body can be rotated by slightly loosening the three small grub screws remember to retighten them when you re finished Once we have achieved this good focus it will be fixed for that camera The only change will occur when we compensate for chromatic variations Preparing the guide camera Introduction Guiding the telescope to maintain the image of the target star exactly on the entrance slit gap for maximum efficiency is normally achieved by using a suitable guide camera and guiding software which then communicates any corrections to the telescope mount Your image acquisition software e g AstroArtV5 MaximDL etc may include a guiding option PHD2 3 1s also recommended http
21. equent processing the blue region must be at the left hand side The image if necessary can be flipped horizontally before opening in BASS Project Take some time to remove any tilt subsequent processing is MUCH easier when the spectrum sits exactly across the horizontal axis of the CCD chip The choice of slit gap width will be dictated by your telescope focal length seeing conditions and resolution required Having a calibration curve of the grating rotation wavelength using the micrometer settings makes things much easier A good calibration can be easily done using a bright sky solar spectrum and the prominent Balmer Mg Na telluric lines To achieve best SNR the guiding software should be capable of holding the target star on the slit gap for the duration of the exposure sequence The optimum exposure of the subs will be determined by your target brightness telescope aperture camera QE and guiding accuracy Sequence Darks based on the target camera temperature 1 e 10deg and the optimum sub exposure in this case 120sec A set of ten darks were stored in the folder You may need to take a series minimum 9 exposures to suit your set up Bias and flats for this introductory tutorial these will be ignored Set up a storage folder by date object Take an exposure of the reference lamp before and after the target star Usually needs an 8sec exposure with the Neon and a 20 sec exposure for th
22. esign focal ratio f7 and above f10 for 1800 I mm grating Entrance Slit Plate reflective chrome plated glass 1 5mm thick Reflective guide aperture 7mm x 20mm Slit gap height 6mm Available slit gaps 19 24 29 34 39 43 48 72 96 micron Available pinholes 19 48 96 micron Guide optics enhanced coated front surface mirror achromat doublet lens Reduction ratio x0 625 Pick off mirror enhanced coated front surface mirror Collimating lens 40mm 36mm clear aperture 200mm focal length achromat doublet Gratings 150 300 600 1200 1800 I m 30mm x 30mm Optometric blazed 550nm reflection gratings Reference lamp Neon bulb standard 12V DC centre positive 2 1 5 5mm plug 1A max Standard resolution 600 l mm grating R 3000 9 micron pixel Website http www jtwastronomy com products spectroscopymain html Appendix B Adjusting the grating holder The Spectra L200 is supplied with reflective gratings pre assembled and mounted on a quick change access plate The Littrow design used in the Spectra L200 requires that the axis of the grating be tilted slightly relative to the optical axis The gratings are adjusted and aligned prior to shipping but provision is made to re set the grating alignment via adjusting screws Fig 34 Grating access cover showing the grating tilt adjust screws Looking at the top of the access plate you will see a series of screws The small dome head screw towards the collimator position
23. et head screws to DROP the spectrum When you are satisfied with the alignment ensure the M3 screws are tight 7 Finger tighten the nylon tensioning screw this just needs to be firm DO NOT over tighten This will bring the alignment of the grating to the optical axis Zero Order Grating position The micrometer setting of approx 1450 should set the grating square to the optical axis This means the grating acts like a mirror and any light through the slit will be reflected directly back to the collimator lens and then focused to the camera eyepiece This provides a Zero Order image for adjustment or calibration Appendix C Processing spectral images in BASS Project This brief tutorial describes how to process spectral images from a slit spectroscope to obtain a fully calibrated normalised profile Preamble AstroArtV5 was used for image acquisition and basic pre processing If you use a different software it will have similar capabilities you need to check the manual The usual focusing of the imaging camera to the reference lamp to give minimum FWHM and the target star focused on the slit gap to give minimum spectral height apply If the length of the slit is orientated either along the RA or Dec Dec axis prefered it gives the potential of better guiding PHD and AAS can guide at sub pixel levels so the target star should stay well on the slit gap Understand and note the orientation of the spectrum image For subs
24. he top and bottom edges lie Click Selection Set active binning region Click and pan across the spectrum to select the region When set you ll see the green strips top and bottom Once the binning zone is finalised select an area above Set subtraction region1 then below this zone Set subtraction region2 to extract the sky background and any light pollution from the spectrum You ll see these areas bounded by the pink lines Click the Refresh icon to apply the zones Tacs Helo Waa 900 Were 1 Est Far rage Calibration It s easier to start with a print out of the lamp spectra to give a wide overview of the spectrum Knowing the central wavelength setting and looking at the features in your target spectrum Ha telluric etc will give some guidance Obviously the number of available lines will vary with the grating dispersion The Neon annotated graph from Christian Buil s excellent website will help you get started 6143 06 6402 25 035 16 6334 6074 34 6217 28 T 6304 79 7032 44 6163 59 5831 88 k 266 49 6020 00 7245 17 5928 47 T173 94 Make sure the 1 image strip the reference lamp is selected Click the calibration icon The line selection box has the standard lines for both Neon and Argon lamps Starting from the left click and drag the mouse over the emission peaks to select the peak and enter the selected wavelength File Chet Select
25. ing the use of the reference lamp and acquiring reference spectra The use of the SimSpecV4 spreadsheet 1s strongly recommended This 1s available for download from the JTW website or the Y Group astronomical spectroscopy The spreadsheet allows you to enter the parameters of your telescope and camera etc and will assist in determining the optimum entrance slit gap show the wavelength coverage and resolution for the selected grating Grating selection The grating is the heart of the spectroscope and the selection of the grating used will have a significant impact on the brightness and resolution of the spectrum obtained Coarse gratings 150 lmm and 300 I mm provide ideal low resolution approx 5 5A with the 300 I mm spectra on faint objects or projects which require extended spectral coverage As we increase the number of lines on the grating 600 lmm or 1200 l mm the resolution increases at the cost of reduced spectral coverage and when we use the high resolution grating 1800 I mm the resolution will be better than 0 8A but with a much reduced coverage only 210A SNR Signal to noise ratio The quality of the spectrum produced is also measured in terms of the SNR This 1s directly related to the efficiency of your camera the magnitude of the target and obviously the total exposure time used A minimum target SNR 20 should be your goal SNR 50 is a good result and SNR gt 200 is ProAm standard The use of the SimSpecV4 spread
26. ion image Calitwhon Openten Joos Hip Vygeuu arp Ere EX E43 Lern T Uc12254 766271354 PE iinan SETA DSTI Vum MER m j rit dL EX HE 19 LAR Do this for as many lines as required the more the better You can select a non linear quadratic solution if you have enough lines Using non linear solutions will give a more accurate result and are the recommended method If the wavelengths selected don t match the reference the dotted calibration indicators will be seen off set to the actual emission lines Check your selection and correct the entries as needed Hn mmu zo m IEEE mr e a r m v vn D t e ie ame a A s Am cap d i 18 rel bm SE H ark ris E H dE H Id N e opm ESTE ume 1333 Can Ha Reger HOTA ET ka z aa a wE ERE I ai bs 5 li Mua pi a E X i m mit B EE DE b E oux NE LE K E When calibration is complete press finish and the pixel scale on the main window will now show the wavelengths in nm and the dispersion in nm pixel Sabo duat fs Ham chy bx HT E E 1 zi Bm mi s RR Lre Pes Wesmengh Exe p IN v2 KRE nmm D lz ma ign SDT REIT r mm nz aired tessa ij a Sere EX ES SUIS LETT lunes a m cai EFT ENT L ERO bes EET Eds HE01 19151551 th lar aie fb oi xS 0553513219 12558 TELE The default BASS setting is a Linear calibration You can see based on
27. lines Slit gap micron EFL mm 19 1500 24 1700 29 2000 34 2500 39 2750 43 3000 48 3600 Fig 29 Sample guider images showing target star being positioned close to slit gap The SimSpecV4 spreadsheet can be used to generate results based on your actual telescope and seeing conditions The width of the entrance slit also defines the quality of the spectrum produced The spectral image is made up of strips the width of which related to the slit gap usually defines the wavelength resolution To maximise the resolution and clarity of the spectrum the imaging camera must have a pixel size less than 50 the slit gap For very faint stars a large slit gap 748 micron will maximise the light throughput but the resolution will be limited by the size of the seeing disk This is called slitless spectroscopy Focus the target star onto the entrance slit The guide camera must be focused on the slit gap before we start See previous section The backfocus distance from the nosepiece adaptor to the entrance slit is 55mm you can first focus at this distance using an eyepiece on a suitable extension adaptor Start by using a bright star they are easier to find and give a bright zero order spectral image NOTE You will not succeed in focusing your target star on a narrow 19 micron or so slit gap if your telescope and mount are not capable The mount must be able to hold all the equipment in a good balan
28. nown reference wavelengths to a target spectrum taken with the same grating setting can allow you to accurately determine a wavelength calibration of your spectrum It is usual to take one reference spectrum before and after a target spectrum By comparing the two you can compensate for any mechanical distortions Fig 30 Typical Neon forest emission lines in the red region 5852 49 n3 ng D 6143 06 5402 25 ds 5382 98 6296 16 B334 4 os E 607434 6217 28 T 8304 75 dd NUM 6747 04 703241 T 6030 00 TT 6506 i 03 6673 23 6588 85 7245 17 D2 8329 47 T Wt i 717394 7438 90 T l LL ame n am a ULLA ni IU J cod 5300 Boa S na EDO a ESC bod G00 ro rida rato 7300 T40 T5D Fig 31 Annotated Neon spectrum C Buil The standard lamp uses a neon bulb This provides a good series of defined reference emission lines in the red region of the spectrum around Ha i i DA 1 l kerene a Tu I E rog Erie Ns klar simi ui n REM JB n o ivy r a G ERE ee eee Fig 32 Neon reference lamp is around 6200A 600 mm grating E heii E EE IDEE s a L3 Venga eame carior 4L Lbh T iei Sel T Xt E F Fog Fab Fig 33 Neon spectrum around Ha region 600 l mm grating Operation of the Reference lamp The reference lamp 1s powered by a 240V circuit fed from a 12V DC source
29. nt sand Ele ments i L JL LLLA s o s AAT S ILE Element Lines Measurement Options Measurement Options s Measurement Results Profile neonlze4 c fit Selected Starr amp 807 48nm 308 08 pa E Selected End gt amp e amp B8 16nmm 318 55 pa Selected Width 0 67nm 12 437 pax Max Flux 2078 53 at 6507 83nm 912 43 pa Min Flux 293 53 at 5867 49nm 306 08 px Flux Hange 2365 0 Rverage Flux 1024 05 BMS 1345 77 Std Deviation B73 17 SHR EZET Continuum Slope 10 01 ADU nm 0 54 ADU nx E FWHM 0 22 nm Rh 3003 48 ceo7 53nmi r m V1369 Cen Ha Region 020314 4 Select a region on the chart to take a measurement OT neoni254 c t 2 navacen1254 J lt n 3000 29500 2000 I 1500 1000 500 La mire m Rr darem 25 g HEISE Xn Fis Char Scion knage Cabe eee Tesh Helo a Ieas Aes il V1388 Cen Ha Aegon Gataia ELI iin i iil r f Ran Herron T l Sale i Esos w merwtit pet ps LRS Sg 3148 x f Expose Ix Tz20 38 XXE E eem AL Dap ase 2537 verd A Sy ZU l L GT mpl i 1 SS pun Fi 7 Ere EM EID M EE EJE HE Ear Wavelength inm Note the legend 01 neon 02 nova etc are applied by BASS These can also be relocated in a similar fashion as the notes To change the colour of the profile right click on the image
30. on the reference image strip and select hide This just leaves the calibrated target profile on the screen Fila Chet Sekebon image Cahhnrabcon Opemtion Teds Hep SIS e Logs uel T s Re A eS Pr 5642 eevee H reg 272 E48 Prod ATi 21351 Hell Daam 2 05273 rre Click the Chart Edit Project Chart Settings On the first screen type in the Title and Sub title as U R BASS Project nai File Chart Selection Image Calibration Operation Tools Help 5 a cola lid T fae m UT Chart Colours K Axis Y Axis Advanced Ranges Notes 1369 Cen Title Sub title Ha Region 020314 Chart width 1000 V1369 Cen Ha Region 020314 Chart height 400 Image strip zx height m Background chart image 02 novacenl 264 d c fit 4500 4000 S000 1500 L i Click the Notes tab and type in any notes you d like to record on the chart R essa Emir Tr Hnr c T Fie Char acion EM Caliban pab Tech Haig EATE A ee Al lor Re E Chat Lobum Xm T brag Advanced Ranges iore v1369 Cen Ha Regon 02097 khan hara SE nr Mayiburniong Carum paca LONE E EZE Asi 3104 Expemse y 127 eee Dipran 557 fel H Ker Hare i i Tana Harit PET M Figh ereas cici Hw chari da dlv or fada rein Garani E paci Gha Auk 314 1 aie 10s 12X D pp n 1 r Dipy CEN A T As beta OE a m z U
31. ption lines in the solar spectrum Using the solar spectrum for micrometer calibration No telescope required Point the inlet port towards a bright daylight sky Wind the micrometer to view the various absorption lines The prominent lines seen are the Fraunhofer lines Line Wavelength Source K 3933 Ca II H 3968 Ca II h 4102 H delta g 4227 Ca I G 4308 Ca Fe G Band f 4340 H gamma e 4383 Fe d 4668 F 4861 H beta C 4958 FeI b2 5173 Mg I bl 5184 Mg I E 5269 Fe D2 5890 Na I D1 5896 Na I a band 6276 6287 C 6563 H alpha B band 6867 6884 Atmospheric O2 A band 7594 762 Atmospheric O2 These are shown on the Liege solar spectral atlas http fermi jhuapl edu liege s00 0000 html Liege Solar Spectral Atlas 3601 0 9300 0 Angstrom units 4000 euo guga FORO BU UU euo Wavelength fang stram units ita from Photometric Atlas of the Solar Spectrum fram 3000 to 10 000 A by L Delbouille L Neven and Roland stitut d Astrophysique de Universite de Liege Observatoire Royal de Belgique Liege Balgique 1973 wage copyright 2O02 by Roy sterner Johns Hopkins University Applied Physics Laboratory At level 0 Click on spectrum to zoom in Fig 26 Liege solar spectrum The highly detailed solar spectrum by Lunette Jean R sch also highly recommended http ljr bagn obs mip fr observing spectrum y mE 1 1 1 1 t lm t toos nl d I lian nan 88 dep qo oder pra vp h MET eo ioo nepos ores ce M
32. r touched with the fingers Any finger prints marks etc are impossible to remove and can seriously affect the performance of the grating DON T TOUCH ee T Meus ST Fig 10 Grating assembly The grating adjustment micrometer head is located on the end of the housing behind the grating assembly This is used to rotate the grating in its holder to bring the required target wavelength into the imaging camera field of view Fig 11 Grating adjustment micrometer head Preparing the Spectra L200 To use the Spectra L200 on your telescope you need to 1 Adda telescope adaptor to the inlet port This can be a 1 25 or 2 recommended to T thread nosepiece or an SCT to T thread adaptor if using a Meade or Celestron SCT 2 Use T thread adaptors to fit your imaging camera to the housing The nominal backspace 1s 60mm which allows the fitment of a standard T2 DSLR adaptor or various T thread spacers when using a CCD camera The achromatic collimator used in the Spectra L200 will give slightly different focus positions for blue UV red and green regions of the spectrum For best resolution this needs to be accommodated For normal CCD cameras the Borg Hutech helical focuser 7315 and a suitable T thread adaptor available from JTW Astronomy is highly recommended The horizontal axis of the camera should lie parallel to the base of the housing See later 3 Asuitable 2 1 5 5mm 12VDC centre positive power cable for the reference
33. s are then removed from the housing and the access cover complete with grating can then be removed for safe storage Mounting a new grating is the reverse of the above Again the micrometer head should be withdrawn to a reading around 2000 the access cover positioned on the housing and the three thumbscrews hand tightened Calibrating the Micrometer Head The precision 0 to 25mm micrometer head fitted to the Spectra L200 controls the rotation of the grating holder It can rotate the grating through approximately 45 degrees which is sufficient to ensure full spectral coverage from Zero Image to 7500A with all gratings The easiest way to calibrate the micrometer head 1s either by using a fluoro energy saving lamp or imaging the solar spectrum no telescope required Fluoro lamp micrometer calibration All fluoro lamps show a series of bright line emissions The wavelengths of these lines are well established and can therefore be used to prepare a calibration curve for your Spectra L200 OSRAM Dulux Mobil fluo lamp 2 883 A pixel 5460 74 Hg 5874 4358 33 5789 66 Hg 4500 5000 5500 6000 6500 7000 Fig 23 Fluoro energy saving lamp spectrum C Buil Set the slit gap to say 39 micron not critical The imaging camera should be fitted and focused on the Spectra L200 See Setting the camera focus above Alternatively a 15mm eyepiece can be used in the imaging port if you have the necessary adaptors This is suffi
34. sheet 1s strongly recommended to obtain a first estimate of exposure times and probable SNR outcomes It s recommended that you start out with a medium resolution grating The 600 I mm grating 1s included as standard with the Spectra L200 With an ATik 314L camera and a ten minute exposure you will record ninth magnitude star spectra with a good SNR Signal to noise ratio of around 50 The wavelength coverage of the chip 1s approx 720A and the resolution better than 2 7A The final spectrum will show sufficient detail for many projects Removing and replacing the gratings The gratings supplied with the Spectra L200 allow a wide range of low to high resolutions and give differing wavelength coverage The selection of the grating used depends on the needs of the spectrum required See above NOTE Reflection gratings are very delicate and can easily be damaged They should never be handled at any time and should be stored in dust tight containers when not in use The gratings come pre assembled in a rotating housing which is mounted on an access plate There are fine adjustment screws provided to ensure the tilt of the grating holder matches the optical axis of the instrument Appendix B gives further detail on these adjustments should they be necessary Changing over the grating 1s a simple and quick process The micrometer head should be adjusted to a reading of around 2000 to release it from grating contact The three large Thumbscrew
35. software The image of the spectrum being recorded is in the AAS screen A sequence has been set to give 10 x 120 sec exposures nnns lt Mies ih Bum Hec fee E H WP Frim Documents libra TET z Destap fortuna Mw vs paetos a Deswri cute Hen Dry rra xcd ami j Tups an v cnl DB ngn L Xi Fri SMT L25 abt STT Fie Las KE Bi omami A0 Fr INAH 12 9 dl FIT Fin 24727 5B 2 Linna E apam 384309 25117001 LI48 al ET Fite Paz eB S ncm M novel 40 At AMF LIA Ahi FIT Fits 247 Kb Music Bi nten al BET fit N0IUH ELJ4L A FTT Fig raz KB isi Pictures z B oven AX Fr 2 337 2004 bash AM FT Fite 2377 KB Bl vides E ntre MANI fd S917301 234 AM HT Fie 7427 KB E nog HH Fri iuda L1 kd FIT Fin 231 KE E Hera arap E orim M fit 3UNTIA D aM FT ERS zAT KB 4 Sue Harrison SUEHOME E nmg M2 Fri SAI LiOH ARA FIT Fin a7 ali E nre enl MAIL P Mii 133 4M T File LAIN KDE 3 dH ponp The reference lamp and target images are stored here The micro settings were used to distinguish different regions when doing multiple exposures 1 e 1264 for Ha 1360 for Na 1390 for Hb etc AstroartV5 in the Processing tab allows all the darks and lights to be selected and stacked I prefer to stack the darks as Median stacking and the target as Average Dark here opes moon T Fria for ogee T Erde ee Plur Ake 2 om e e C If hot pixels are evident apply a hot pixel filter to suppress them The stacked spectral image is inspected to fin
36. the selected lines this gives a RMS error of 0 013nm 0 13A Selecting a Quadratic calibration for this example gives an RMS of only 0 0019nm 0 019A almost an x10 improvement het Seno imaje lt Calieion Openton Tools Hip 561 eai Fe Hem B SPOT ar hial 671 FH hod Another Prini frir Lre Pnp Wpengh Er p LL Li aru pui ari r E e nius eeu TOT z 531410 ntm IA PO ZA Lite Gu 2T eu TANTRA Caste hR J PALS aer 0351518514583 844 17 e O Ei E 7991919 0DETMEHE TERRAE 1 3 D 1 i H a a Once calibration is complete the X scale changes from pixel to wavelength nm and the dispersion 1s displayed Save the project by clicking the save icon Give it a name and reference which will make sense to you later You ll probably find an reminder screen message It will ask you to save the changed image strips caused by the application of the tilt slant correction Right click on each image strip and select save If you want to retain the original image recommended give the corrected a new name add s to the end Slant corrected You can also remove the calibration lines Un click Calibration show calibration points and right click on the reference image strip and select hide This just leaves the calibrated target profile on the screen Now save the project Adding Title and Notes If you haven t done it already right click
37. uiring target spectra The mirror can be flipped down onto the stop to allow the reference lamp to illuminate the slit when taking a reference spectrum for wavelength calibrations x B4 f 1 T i j v K pn a loas 2 a O Mounted on the outside surface of the housing is the reference lamp assembly This holds the power electronics for the reference lamp interchangeable which is mounted at the top The lamp illuminates a small aperture which 1s then via the flip mirror projected to the slit gap This module needs a 12V power supply This should be a 2 1 5 5mm centre positive 12VDC supply Supplied by user Fig 6 Inlet port showing reference mirror in position DEI E m dumm fes MP RP Calibration Driver B Fig 7 Reference lamp and driver At the bottom of the housing there s the imaging port This again has a female T thread Your imaging camera should be mounted to this port The back focus distance is 60mm the distance from the housing to the CCD F ig 8 Imaging camera port The grating assembly which has various screws for adjustment is held in place on the housing by three large thumbscrews Removing these thumbscrews allows the grating to be removed replaced S Fig 9 Grating access cover and thumbscrews CAUTION The reflective gratings used in the Spectra L200 are very precise delicate optics The front surface of the grating must be protected at all times and neve
38. ware adjust the exposure to give a clear image of the slit area g iplis E LE sa MARE m a RR k e i Fig 21 Slit gap from QHY5L II guide camera Slide the guide camera nosepiece in out of the guide tube until you can see an image of the entrance slit This will appear as a very fine dark line against a brighter background Carefully adjust the position of the camera to bring the line into clear and tight focus Lock the guide camera in position using the thumbscrews Adding a par focal ring to the nosepiece can be useful if the guide camera is being removed replaced B 4 Fig 22Guide camera and parfocal ring To assist in positioning the target star on the slit gap it is recommended that the guide camera body be orientated to show the slit length sitting exactly horizontal or vertical in the field of view The guide camera 1s now fixed and should not be moved These preliminary adjustments have been done in the comfort of your home We need now to consider the final steps needed to make the Spectra L200 easy to use in the real life situation on a telescope in the dark Preparing for spectral acquisition The Spectra L200 has to be configured to suit the project program being considered This entails 1 Selection of the best grating SNR 2 Calibration of the micrometer head into wavelength settings 3 Selecting the optimum entrance slit gap for the telescope seeing conditions 4 Understand
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