shelyak Alpy 600 User Manual Download

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DC0016B : feb.2014

Alpy 600

User Guide

Olivier Thizy

([email protected])

François Cochard

([email protected])

Summary of Contents for Alpy 600

Page 1: ...DC0016B feb 2014 Alpy 600 User Guide Olivier Thizy olivier thizy shelyak com François Cochard francois cochard shelyak com ...

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Page 3: ...Alpy 600 spectroscope User Guide Olivier Thizy olivier thizy shelyak com François Cochard francois cochard shelyak com February 2014 Ref DC0016 rev B ...

Page 4: ... Typical observation 21 2 5 Data reduction 21 2 5 1 Prepare master files 21 2 5 2 First pass raw profile 22 2 5 3 Second pass wavelength calibration 22 2 5 4 Third pass Response curve correction 24 3 Alpy 600 Stellar spectroscopy in slitless mode 26 3 1 Changing the slit position 26 3 2 Visual observation 26 3 3 Recording a star spectrum 27 3 3 1 Tuning the instrument 27 3 3 2 Stars observation 29...

Page 5: ...ion 37 5 2 5 One directory per observing session 37 5 2 6 Reduce your data quickly 37 5 3 Share your results 37 5 4 Get pro like quality spectra 37 6 Typical observing session 38 7 Appendix 39 7 1 Alpy Modules Accessories 39 7 1 1 Alpy Guiding module 39 7 1 2 Alpy Calibration module 39 7 1 3 DSLR camera barlow adapter 40 7 1 4 C mount camera adapter 41 7 1 5 Optical fiber adapter 41 7 2 Alpy 600 w...

Page 6: ...oscopy is a very large subject Some parts are very easy For instance looking visually at a spectrum during daylight or with a star requires no experience However if you want to take images or make scien tific measurements it is highly recommended to have some experience with your instrument telescope and camera In this document we assume that you re new to spectroscopy but that you re already fami...

Page 7: ...ons it is difficult to ensure that all the light from the object you re observing goes into the spectro scope This module will help you to observe con trol the spectroscope entrance The Calibration module For accurate results a spectrum must be properly calibrated in wave length and intensity The calibration module sim plifies this operation by providing both a calibra tion and white light It can ...

Page 8: ...gives the wavelength covered depending on the CCD length 1 3 Alpy 600 elements Remove the external body from the big ring CCD Sensor CCD length λ min λ max 4 mm 4560Å 6055 Å 5 mm 4293Å 6322 Å 1 2 6 4 mm 3920 Å 6695 Å KAF400 6 9 mm 3790 Å 6825 Å 9 mm 3650 Å 7380 Å 10 mm 3650 Å 7656 Å 11 mm 3650 Å 7923 Å 12 mm 3650 Å 8190 Å ICX694 12 5 mm 3650 Å 8319 Å 13 mm 3650 Å 8457 Å KAF1600 13 8 mm 3650 Å 8500...

Page 9: ...er only a partial spectrum is visible Optical dispersing element Grism grating prism Grating density 600 l mm Typical spectral dispersion 480 Å mm Input beam F ratio F 4 Telescope beam can be from F 4 to F 10 optimal luminosity performance is at F 5 Slit width standard 25 µm also included hole 3mm slit 300µm 100µm 50µm hole 25µm Slit length 3 mm except for hole 25µm Mechanical interface M42 x 0 75...

Page 10: ...rnal body is made with standard M42x0 75mm threads you can use a 2 eyepiece holder instead of the 1 25 one Several slits are available We ll see in the next chap ters how to change it and under which conditions to use each of them 1 4 Mechanical interfaces The Alpy 600 uses several standard threads for me chanical interfaces to adapt the instrument to your own setup The CCD camera interface is a s...

Page 11: ... at the sun it is far too bright Do not look directly at the Sun with or even without a telescope You ll see your first spectrum Look at different sources to see the different spectra types A tungsten lamp has a continuous spectrum A power saving lamp has several bright emission lines and some bands The Sun shows a continuous spectrum with a huge number of Fraunhofer absorption lines This shows th...

Page 12: ...them on the focal plane where we put the sensor To make the source point like we usually use a nar row slit only the light which goes through the slit is spread out The narrower the slit the higher resolu tion the spectrum is but the less light goes through there is a compromise to find for each case In Astronomy we re lucky stars themselve are point like So when looking at stars we can afford to ...

Page 13: ... spectrum is always at the same position in the image but it is more difficult to see visually To a certain extent this is a way to reproduce in the lab what will be seen with stars second line There is another useful case working in slitess mode This is applicable to stars which are point like The advantage is that you ll see a bigger star field and you ll be able to find easily the star you re l...

Page 14: ...Alpy 600 user guide Standard slit 25µm Hole 25µm Hole 3mm Wide slit 300µm Table 1 3 Alpy 600 slits 12 ...

Page 15: ... when changing its position and make sure that you can move it freely before turning it Cleaning the slit Over the time there can be some dust on the slit A dust particle in the slit is seen in the image as a dark line along the dispersion axis You can clean up the slit with a soft dry cloth or gently blow away loose particles 13 ...

Page 16: ...eed to add more optics behind the grating to create an image at the focal plane the CCD surface These optics are contained in the Alpy 600 body The body is threaded for tuning the distance be tween the optics and CCD when it is mounted in the CCD camera adapter The nominal distance is about 19 5mm A threaded ring is used to lock the body in the focused position Watch out that the optics do not tou...

Page 17: ...n If the source exceeds this level the camera considers it is like a maximum light and cannot see any details in it The Atik 314L camera has a dy namic range of 65535 ADU If a pixel in the image is above this value it means that image is saturated To solve this problem you must reduce the exposure time or reduce the source intensity if it is possible At the opposite end if the maximum level of the...

Page 18: ...will im mediately recognize the Sun spectrum Refer to this image to put it in the right position You ve completed the most complex part of spec troscopy with Alpy At this stage your camera is equiped with the spec troscope and any image you take will be a focused and horizontal spectrum of the light coming into the slit When The Alpy 600 is focused you can remove the core element and put it back q...

Page 19: ... calibration module Candle light Argon Neon Alpy calibration module Neon lamp Argon Habitat lamp White LED Power saving lamp Blue paper illuminated by a halogen lamp Red paper illuminated by a halogen lamp Table 2 1 Some examples of common light sources The color version of each spectrum is colorized by software 17 ...

Page 20: ...ool This docu ment isn t a tutorial of ISIS refer to the ISIS doc umentation 1 and specially the Alpy tutorial 2 but shows very quickly the basics for this first experience Here is how to proceed with your Sun spectrum Run ISIS ang go to the Settings tab Select ALPY 600 without calibration module in the spectrograph model and specify the working directory where you ve storedyour images FITS files ...

Page 21: ...s at least The 2D image has not been pre processed The spectrum is not calibrated in wavelength The profile is not corrected for the Instrumental Response In the next sections you ll learn how to proceed to make these corrections and calibrations 2 4 Reference images Digital imaging is affected by several instrumental effects such as offset thermal signal read out noise hot pixels and so on These ...

Page 22: ...l cells that are particularly sensitive to this thermal noise and tend to saturate quickly during long exposure These hot pixels have to be processed separately usually replaced by the average of the surrounding pixels An interesting prop erty of thermal noise is that it is linear with exposure time For example the thermal noise in a 2sec expo sure is twice the thermal noise in a 1 sec exposure Th...

Page 23: ...ade of neon argon and hy drogen which makes it very easy to calibrate in slit mode 2 4 5 Typical observation To get all the data you need for a high quality ob servation here is a suggested list of all the images that you should have before switching off the equip ment This is applicable for your Sun observation but is also valid for night observations 7 offset images or more 7 dark images or more...

Page 24: ...inly due to the flat field correction 2 5 3 Second pass wavelength calibration You now have to establish the calibration law the relationship between pixel position and wavelength to display the spectrum in wavelength units The more lines you have the more precise is the calibration The dispersion law is usually a 3rd order polynomial To reduce the Sun spectrum you will proceed in a special mode i...

Page 25: ...alculates the dispersion polyno mial law In the bottom area you have the RMS error re sulting from the calibration It should be around few Å here the error is of 3 7 Å Now re run the reduction process but selecting the Spectral calibration button in the 2 General tab You also have to select Predefined dispersion equa tion in the spectral calibration panel Display the spectrum you can see that it i...

Page 26: ...nce star to allow the correction of any instrumental effect ISIS includes a database of spectra recorded at dif ferent resolutions Here is how to get a G2V star ref erence spectrum In the 4 Profile tab click on the database button The database panel appears At the top left you can select an G2V star from the Pickles list This profile is different from yours This is due to the Instrumental Response...

Page 27: ...run the data reduction process three times the first time to get the raw profile the sec ond one to include the wavelength calibration and the last one to correct for the instrumental response curve This process needs to be done only once per ob serving session When you observe several objects in the same night you can reuse the calibration and the response curve to the first order you can conside...

Page 28: ...s also some drawbacks there is no way to use a calibration lamp which is an extended source and the position of the spectrum will move in the field depending on your telescope tracking In a few words using the Alpy 600 in slitless mode is the way to work when you have no guiding device but this is not the simplest way to get accurate mea surements The good news is that when you become familiar wit...

Page 29: ...ectrum is horizontal with blue on the left and red on the right You should see something like this You can now look at different stars and bright ob jects 3 3 Recording a star spectrum After observing visually you will certainly want to record images You ve learned how to proceed with spectrum acquisition and reduction you ve put the spectroscope on your telescope now it s time to do both together...

Page 30: ...f the telescope The external body includes a standard T mount thread M42x0 75mm If your telescope includes a 2 eyepiece holder you can remove the Alpy 600 eyepiece ring and replace it by a T mount to 2 adapter optional Plug in the cables power supply and USB and bal ance the instrument Do not forget to set your CCD temperature control We recommend setting up an empty direc tory on your PC to recor...

Page 31: ...of the spectrum there are clear absorption lines only for hot stars If your image is black it can be due to the im age visualization thresholds In AudeLA click on the auto button bottom left to adapt the thresholds to the image You can rotate the Alpy 600 in the eypiece holder the spectrum remains horizontal in the image This is nor mal the orientation of the spectrum only depends on spectroscope ...

Page 32: ...fore 5 flat field images or more take care of the right exposure time to get 80 of the maximum level 5 spectra of the reference star A or B type or more Point at several stars adapt the exposure time for each star and take 3 to 15 spectra of each of them 3 4 data reduction Create master files for offset dark flat fields and a cosmetic file from the master dark As you learnt in chapter 2 reduce you...

Page 33: ...rofile but now calibrated in Å see the scale in the bottom axis note that the spectrum has been cropped between 3650 and 7300 Å 3 4 3 Third pass The last operation is to establish the instrumental response curve In this document we used Regulus as reference star This is a B7V In the ISIS database Pickles there is no B7V but we can select a B8V the difference is not significant at our level Display...

Page 34: ... it must be shifted to match the new star position To do it you need to identify one line in the new spectrum and give its wavelength to ISIS For instance here is a spectrum of 38 Lyn another hot star In the 2D image you can easily identify the Balmer line at 4861 Å Measure its position and enter it in the ISIS field at the 3 Calibration tab Run the process and get the fully processed spec trum Co...

Page 35: ...s clearly a challenge but we did it ourseleves Observing with the wide slit The Alpy 600 includes several slits refer to section 1 7 One of them is the wide slit 300µm wide This is a trade off between the thin slit and the slitless mode Compared to slitless mode the size of the slit means that your spectrum is always at roughly the same po sition horizontally in the image and reduces the un certai...

Page 36: ...align your mount if you consider there is no such risk Pointing and tracking in wide slit mode with a flip mirror requires some experience but this is a real im provement compared to the slitless mode You will not be wasting your time if you do it Observing with the narrow 25µm slit This section is for people who like challenges It is possible to observe in full slit mode using the 25µm slit but i...

Page 37: ...portion of the light at the instrument The two main reasons for losing light at the spectro scope entrance are usually Telescope focusing If the focus is not optimal the object size will be bigger than the slit width and only some percentage of the object s light will enter in the instrument Position of the star in the slit When working in slit mode it is very easy to put the the star partly outsi...

Page 38: ...use the hot pixel map in the 2 General tab Simply enter the name of your map file in the field Cosmetic file and re run the data reduction ISIS will now include this hot pixel list in its calculation 5 1 6 Instrumental Response curve We have already described a simple way to get the Instrumental Response curve with ISIS In fact this is a tricky operation The response curve can evolve with some par...

Page 39: ...g you ll probably never reduce your data And having just raw data on your hard disk is the same as if you did nothing We strongly encourage you to reduce your data immediately after acquisition This way it is all fresh in your mind and there is much less risk of mistakes during the data reduction 5 3 Share your results Our experience shows that the best way to improve your data is to compare your ...

Page 40: ...calibration flat and check that all is Ok images correct file headers with proper data Prepare your target list Acquire dark and offset images and prepare mas ter images or copy from the master directory Get flat field images During observation For each target observation you will need to Locate the target start with a reference star Run the acquisition Get the calibration images Fill in the log f...

Page 41: ...you re using your Alpy 600 for astronomi cal observations the Alpy guding module is almost mandatory In the image below you can see the telescope field and the Alpy 600 slit During the night you can observe and control the star position vs the slit 7 1 2 Alpy Calibration module As described in this document getting high qual ity spectra requires reference images These images can be made manually b...

Page 42: ...However in some conditions a longer backfocus is required This is the case for DSLR camera usage A DSLR camera with a T mount adapter has a long backfocus 54 85mm compared to most CCD cameras 15 25mm range The Alpy DSLR camera barlow adapter extends the Alpy 600 backfocus to match that required by DSLR cameras Here the DSLR camera barlow adapter is mounted on the Alpy 600 Even though a CCD camera ...

Page 43: ... adapter of the Alpy 600 7 1 5 Optical fiber adapter Alpy 600 can be used with a fiber optics The opti cal fiber adapter has a Type FC connector 7 2 Alpy 600 with a DSLR camera Your Alpy 600 can be used with a DSLR camera A lot of people today have such a camera at home and it allows you to start in spectroscopy with a low investment Because of the long backfocus of DSLR cameras you must add the b...

Page 44: ... also use any lamp with emission lines such as Neon or Argon DSLR camera vs CCD camera You can use your Alpy 600 and DSLR camera with all Alpy modules and accessories guiding calibra tion fiber optics for lab activities as well as for As tronomy However keep in mind that a DSLR camera doesn t have the same performance as a CCD camera The main differences are Sensitivity A CCD camera is roughly ten...

Page 45: ...trictly limited to the vis ible domain Note that it is better to remove the IR cut filter from the DSLR camera to cover Hα this is a usual operation in astronomy The DSLR camera has a color sensor This makes raw images more complex to work with there is the Bayer matrix to manage Note that the over sampling in the DSLR camera configuration means that the Bayer matrix has no effect in practice on t...

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