STAR ANALYSER 100 USER MANUAL - Paton Hawksley Education
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1. This means that a much higher proportion of the light is directed into the spectrum compared with lower cost unblazed or holographic film gratings for example allowing far fainter objects to be recorded It is physically identical to a standard 1 1 4 inch filter This means it can be screwed onto a standard camera eyepiece nosepiece or included in a filter wheel The dispersion of the SA100 model has been matched to the small CCD chip sizes found in these cameras This means that when mounted on the camera nosepiece the complete spectrum and the zero order straight through image of the object can be imaged at the same time simplifying object identification and spectrum calibration The SA200 model has a higher dispersion and a low profile design which allows it to be mounted closer to the camera sensor for example in a filter wheel The delicate grating surface is protected by an antireflective coated glass cover This means that it can be cleaned if necessary 6 What kind of objects can I record The spectrum of any type of object can be recorded provided it is bright enough and appears approximately point like in the field of view This includes stars of course and planets provided a relatively short focal length telescope or camera lens is used Compact planetary nebulae also make interesting targets The STAR ANALYSER mounted in front of a wide angle camera lens can also record extended objects such as bright comets If you are2. discs The sealed unit is fixed in the cell in the correct alignment As with any optical device care should be taken to protect the optical surfaces It should be stored in its protective box when not in use After use any dew which may have condensed on the device should be allowed to evaporate before closing the box Avoid touching the glass Any dust should be removed with a blower brush or clean oil free canned air More stubborn marks and fingerprints can be removed with care using conventional lens cleaning techniques Lens cleaning fluids should be used very sparingly to avoid the risk of seepage of the fluid between the glass elements A quick look If you hold the Star Analyser up to you eye and view a compact source of white light through it you will see the light source flanked by a series of rainbow spectra stretching away in both directions One of the pair of spectra closest to the light source will look significantly brighter than the others This is the blazed first order spectrum and is the one we are aiming to image along with the straight through view of the light source the zero order If you look at the edge of the filter cell you will see a white line marking the direction of the blazed first order This The blazed first order spectrum will help identify the right spectrum and line it up in dominates the other orders in this the field of view of your camera view of a low energy light bulb First light V
3. in the desired orientation The ring is screwed into the internal thread of the camera nosepiece and the Star Analyser screwed in until it locks against it By adjusting how far the locking ring is screwed in the Star Analyser can be locked in the required orientation If desired the ring can be fixed in position with thread locking compound to ensure repeatability between observing sessions First check that the presence of locking ring does not affect the use of any other accessories you may want to screw into the nosepiece and be sure to use the removable type of locking compound in case you wish to remove the ring in the future Troubleshooting The spectrum seems very faint Are you sure you have found the right spectrum Move the telescope until the star image is on the right of the field You should just be able to see a faint spectrum running from right to left It should be much fainter than the spectrum on the other side of the star image If it is brighter rotate the Star Analyser through 180 degrees The spectrum is too long to fit across the field Take care not to confuse the infra red end of the wanted spectrum with the blue end of the next order spectrum which will be much fainter but will overlap This is because the dispersion The amount by which the light of given wavelength is deflected is too high The Star Analyser100 is designed to work with the majority of cameras and nosepieces You may however run into this pro
4. spectrum Note that this is not true for higher dispersion designs used in the same configuration and is a particular problem for prism based spectrometers All you have to do is measure the number of pixels from the centre of the star image to a feature of known wavelength in the image eg a Hydrogen Balmer line in a star such as Vega ora Telluric line due to the earth s atmosphere which can be seen in many spectra If you divide the wavelength by the number of pixels you have a calibration constant in angstroms per pixel or nm per pixel which can be used for all your measurements provided you do not change your setup 18 How can I convert my spectrum into a graph There are commercial and freeware programs which can take the image of a spectrum measure the pixel values along the line and convert them into a graph or a data file for use in a spreadsheet Some also have functions to aid calibration and analysis of your spectrum Examples of spectrum analysis software include RSpec http www rspec astro com Visual Spec http www astrosurf com vdesnoux ISIS http www astrosurf com buil isis isis_en htm 19 Can I use the STAR ANALYSER for visual observations Yes though the length of the spectrum will be rather short unless you can mount the STAR ANALYSER some distance before the eyepiece Note The SA200 will give a 2x longer spectrum compared with the SA100 This can be achieved for example by screwing it into the ingoing side of a di
5. the camera sensor the STAR ANALYSER is placed the more spread out the spectrum becomes If you mount it too close you will lose resolution Too far away and you will not be able to fit the whole spectrum in the camera frame You can work out the optimum distance for your camera using this on line calculator www patonhawksley co uk calculator Details of pixel size number of pixels and distance from the sensor to the nosepiece or mounting ring should be available from your camera manufacturer Typical distances for the SA100 are distances for the SA200 are approximately half these values 30 45mm for 1 4 size sensors 55mm running the spectrum diagonally 40 75mm for 1 3 size sensors 50 100mm for 1 2 size and larger sensors 14 What are the optional spacers for and will I need any See FAQ 13 for information on the recommended distance If you find that the distance for your setup is less than the minimum value we recommend purchasing sufficient spacers to bring the distance above the minimum Each spacer adds an adjustable 7 10mm If after consulting the on line calculator you are not sure if your particular setup requires spacers please e mail us with details of your camera and the sensor to nosepiece tip distance and we can advise you 15 How do I focus the spectrum image Just as in conventional astronomical imaging focusing can be tricky Focusing the zero order image of the star will get you somewhere near but you might find yo
6. N6ha 6 49 227328 78 16 52 19 41 51 16 WN7h 6 61 69402 133 20 05 57 35 47 18 WN5 6 7 172546 6 06 54 13 23 55 42 WN4 6 94 227390 79 16 54 19 41 49 12 WC7 6 95 49491 140 20 20 27 43 51 16 WC7pd 7 07 227822 90 17 19 29 45 38 24 WC7 7 45 69592 136 20 12 06 38 21 18 WN6 h 7 65 251264 40 11 06 17 65 30 35 WN8h 7 85 69755 138 20 17 00 37 25 24 WN5 8 1 69833 139 20 19 32 38 43 54 WN5 8 1 238408 25 10 44 10 59 43 11 WN6h 8 14 69677 137 20 14 32 36 39 40 WC7pd 8 15 186341 111 18 08 28 21 15 11 WC5 8 23 69541 134 20 10 14 36 10 35 WN6 8 23 251296 42 11 10 04 60 58 45 WC7 8 25 APPENDIX III TELLURIC LINES O2 Fraunhofer Band Wavelength A a 6276 6287 B 6867 6884 A 7594 7621 APPENDIX IV HYDROGEN BALMER LINES Alpha 6563 Beta 4861 Gamma 4340 Delta 4102 Epsilon 3970 Zeta 3889 Eta 3835
7. PATON HAWKSLEY EDUCATION LTD STAR ANALYSER 100 USER MANUAL v1 6 27th Jan 2014 CONTENTS INSTRUCTIONS Description Care and maintenance A quick look Using the locking ring First light Troubleshooting Processing Wavelength Calibration Displaying the results graphically Tips for recording spectra of faint objects Visual Use Further advice and information FREQUENTLY ASKED QUESTIONS APPENDIX I BRIGHT STAR SPECTRAL TYPES APPENDIX II TWENTY BRIGHTEST WOLF RAYET STARS APPENDIX III TELLURIC LINES 02 APPENDIX IV HYDROGEN BALMER LINES STAR ANALYSER 100 INSTRUCTIONS Description The Star Analyser 100 is a high efficiency 100 lines mm transmission diffraction grating blazed in the first order It is mounted in a standard 1 25 inch diameter threaded cell to be compatible with most telescopes and accessories It has been designed to make the production of low resolution spectrum images of a wide range of point like astronomical objects as easy as possible It complements a wide range of types of camera used in astro imaging It can however also be adapted for visual use A locking ring is also supplied to lock the grating in the desired orientation Care and maintenance The Star Analyser has been designed and built to give many years of trouble free service It cannot be dismantled by the user To protect the delicate diffraction grating surface it has been sealed between anti reflection coated glass cover
8. The most significant ones are The size of the star image which depends on the stability of the atmosphere and increases with the focal length of the telescope Distortion of the image due to chromatic coma which is independent of the grating or mounting distance but is worse for lower focal ratio telescopes Field curvature which changes the focus along the spectrum and is worse for higher dispersion gratings mounted close to the camera sensor The size of the camera pixels Because of these limitations the resolution of this type of spectrograph is restricted to typically 1 100 of the wavelength eg 5nm at 500nm independent of the diffraction grating design It does mean however that by choosing the grating design and mounting distance with care the whole spectrum and the undeflected star image can be fitted on the chip without losing any of the available resolution which makes the spectrograph more sensitive and easier to use The standard Star Analyser SA100 has a 100 lines mm grating with a 200 lines mm option SA200 for situations where the grating has to be mounted close to the camera sensor in a filter wheel for example Spectrographs used by professional astronomers achieve greater resolution by adding a slit and collimating optics but these are much more complex and cost many tens of times more 13 How far from the camera should the STAR ANALYSER be mounted See also What are the optional spacers for The further away from
9. agonal threaded for filters Note that achieving sufficient distance may be a problem with some telescopes particularly Newtonians where inward focus travel tends to be limited A cylindrical lens fixed over the eyepiece can be useful to spread the width of the spectrum and make the lines more visible Tapping the eyepiece with the finger sometimes produces a similar effect 20 Where can I share my results with other users or get advice You can get support by e mailing us or alternatively why not join the Yahoo group staranalyser where you can get support meet other users and share and discuss your results 21 Can I take spectra of stars without a telescope using a DSLR camera It is possible to take spectra of bright stars just by mounting the Star Analyser in front of a Digital SLR camera lens Best results are with the camera mounted on a tracking mount but spectra of the brightest stars can even be recorded using a camera on as fixed tripod See this link for more information on this technique http www threehillsobservatory co uk astro spectroscopy_11 htm APPENDIX I BRIGHT STAR SPECTRAL TYPES Star zeta Pup zeta Ori delta Ori delta Sco kappa Ori beta Cru epsilon Ori gamma Cas alpha Cru alpha Lup kappa Sco lambda Sco eta Cen beta Cen epsilon Cen alpha Vir beta CMa sigma Sgr epsilon CMa gamma Ori alpha Pav kappa Vel eta UMa alpha Eri eta CMa beta Tau alpha Gru alpha Leo beta Ori alpha And beta Per
10. avourite image processing package Note though that this should not be done if you plan to further analyse your spectra to make scientific measurements Further Vega spectrum broadened and processed to enhance the visibility of the lines analysis should always be done on the original unaltered spectrum Rotate the image so that the spectrum is horizontal with the star image on the left Produce a strip spectrum as follows Crop the image so it just shows the strip with the spectrum it will typically only be a few pixels high Resize the strip to the same width but only one pixel high then resize again to the same width but 30 pixels high Wavelength Calibration The distance along the spectrum can be calibrated in nm or angstroms per pixel 10 A nm so that the wavelengths of the features can be determined A rough calibration can be made using the following formula Dispersion A pixel 10000 pixel size um grating lines mm grating to CCD distance mm e g for the Star Analyser 100 at 60 mm distance from a camera with 6um pixels the dispersion would be 10000 6 100 60 10 A pixel For greater accuracy the wavelength of known lines identified in the spectrum can be used This need only be done Here the wavelength axis of the Vega spectrum has been Once for a given configuration calibrated using the atmospheric Oxygen line The provided the geometry remains Hydrogen Balmer lines were then iden
11. bjects which can be recorded Megapixel digital SLR cameras can also be used and the large sensor size means that the spectra of many stars in the field can be imaged simultaneously For precise scientific work a monochrome camera is easier to calibrate for intensity as there is no need to correct for the three colour filter responses Colour cameras however produce beautiful spectra displaying the actual colours of the spectral lines Note however that the infra red end of the spectrum will not be recorded if the infra red blocking filter present in most colour cameras is left in place 9 What type of telescope can I use See also How do I focus the spectrum Just about any telescope or even a camera lens can be used provided the object is bright enough and is reasonably stellar in appearance The simple arrangement of placing the grating in the converging beam of the telescope produces some aberrations The advantage of the low dispersion used in the STAR ANALYSER is that these are kept to a minimum There are some trade offs with focal length Less aberration is introduced by using long focal lengths but the resulting larger size of the stellar image will tend to limit the resolution In practise the STAR ANALYSER performs well with the typical focal lengths found in amateur telescopes though in poor seeing conditions or at focal lengths over 2m a focal reducer will generally improve the spectrum sharpness by reducing the size of the star image T
12. blem with cameras with smaller sensor chips and or longer than average nosepieces For example most Toucam owners may find it difficult to include the complete infra red end of the spectrum See the FAQ for more information on the optimum distance There are several solutions to this a Rotate the Star Analyser so the spectrum falls diagonally across the camera field This increases the available length by 2596 The spectrum image can easily be rotated back to horizontal with any image processing package Take care 1f making scientific measurements on rotated spectra though as the rotation can produce artifacts For scientifically accurate spectra the Star Analyser should be orientated so the spectrum is as horizontal as possible b Reduce the distance between the Star Analyser and the sensor by using a shorter nosepiece Some camera suppliers can supply shorter nosepieces which are designed primarily for use with focal reducers and where focus travel is limited The spectrum is rather short You can increase the length of the spectrum by increasing the grating to sensor distance See FAQ 13 amp 14 for more information If you do not have enough space to increase the distance to that recommended the Star Analyser 200 model which produces the same length of spectrum at half the distance may be more suitable for your application I cannot see any features in the spectrum Not all stars show clear features in their spectra Some features ca
13. da Vel beta UMi alpha Tau gamma Dra beta And alpha Sco beta Peg alpha Ori gamma Cru beta Gru gamma Vel Name Menkalinam Mizar Denebola Fomalhaut Ras Alhague Altair Alderamin Tureis Canopus Sargas Caph Marfak Procyon Polaris Al Wazor Sadr Rigil Kent Capella She Avior Pollux Deneb Kaitos Ankaa Dubhe Schedir Haratan Arcturus Wei Enif RasAlMuthallath Hamal Alamach Alphard Suhail Kochab Aldebaran Etamin Mirach Antares Scheat Betelgeuse Gacrux Al Dhanab Regor Mag Spect type 1 9 A2IV 2 27 A2VpSrsi 2 14 A3V 1 16 A3Va 2 08 ASIII 0 77 ATV 2 44 ATV 2 25 A8ib 0 72 FOI 1 87 F1II 2 25 F2ill 1 79 F5lb 0 38 FSIV 2 02 F7 lb llv 1 84 F8la 2 2 F8lb 0 01 G2V K1V 0 08 G8 1 86 KOII 1 14 Ko 2 04 KOIII 2 39 Ko 2 46 KOIII 1 79 KOllla 2 23 KOllla 2 06 KOIIIb 0 04 K1IIIbCN 1 2 29 K2 5111 2 39 K2Ib 1 92 Kall 2 K2IllabCa l 2 06 K3 IIb 1 98 K3III 2 21 KAIb II 2 08 KAIII 0 85 K5III 2 23 K5III 2 06 MOllla 0 96 M1 5I 242 M2 511 111 0 5 M2I 1 63 M3 5III 2 1 MBIII 1 78 WC8 07 5e APPENDIX II TWENTY BRIGHTEST WOLF RAYET STARS The Seventh Catalogue of Galactic Wolf Rayet Stars van der Hucht K A 2001 SAO WR R A Dec Type Mag V 219504 11 08 09 32 47 20 12 WC8 1 74 227425 7 16 54 59 41 09 03 WN9ha 5 29 252162 48 13 08 07 65 18 23 WC6 5 88 238353 22 10 41 18 59 40 37 WN7h 6 44 238394 24 10 43 52 60 07 04 W
14. ega type A Set your telescope and camera up on a bright star and centre it in the field Spectral type M stars are a good first target as they show nice broad spectrum lines which are easy to see Alternatively type A stars show narrow dark absorption lines due to Hydrogen You can see a list of the spectral types of all bright stars down to mag 2 5 in Appendix I Mount the Star Analyser in front of your camera orientating it so the direction indicated by the white mark is on the horizontal axis of the camera and to the right as you view from behind the camera You should still be able to see the image of the star but it will be somewhat fainter Adjust to bring the star back into focus Move the telescope slightly so that the star image is on the left edge of the frame You should then see the spectrum of the star spread out horizontally across the field with increasing wavelength blue to red running from left to right Note that because the light from the star is now spread out over many more pixels you may have to increase the exposure to see the spectrum clearly You should now be able to see some lines in the spectrum If not adjust the camera settings and focus slightly until you get the sharpest clearest spectrum Congratulations You have recorded your first spectrum with the Star Analyser Using the locking ring to fix the orientation of the spectrum A threaded locking ring is supplied which can be used to lock the Star Analyser
15. epsilon Sgr alpha Peg T CrB gamma Gem epsilon UMa alpha Lyr alpha CrB beta UMa gamma UMa gamma Cen delta Vel alpha CMa alpha Gem alpha Cyg beta Car Name Suhail Hadar Alnitak Mintaka Dschubba Saiph Mimosa Alnilam Cih Acrux Shaula Hadar Spica Murzim Nunki Adhara Bellatrix Joo Tseo Cih Benetnasch Archenar Aludra El Nath Al Na ir Regulus Rigel Alpheratz Algol Kaus Australis Markab Almisan Alioth Vega Alphecca Merak Phecda Koo Low Koo She Sirius Castor Deneb Miaplacidus Mag Spect type 2 25 Odlaf 2 05 O9 5lbe 2 23 BO 2 32 BO 3IV 2 06 BO 5lav 1 25 BO 5III 1 7 BOlae 2 47 BolVe 1 58 B1 2 3 B1 5111 2 41 B1 5111 1 63 B1 5IV 2 31 B1 5Vne 0 61 Billl 2 3 Billl 0 98 Billl B2V 1 98 B1II II 2 02 B2 5V 1 5 B2II 1 64 B2III 1 94 B2IV 2 5 B2IV 1 86 B3V 0 46 B3Vpe 2 45 B5la 1 65 B7III 1 74 B7IV 1 35 B7V 0 12 Bal 2 06 B8IVpMnHg 2 12 B8v 1 85 B9 5III 2 49 B9V 2 sdBe gM3 Q 1 93 AOIV 1 77 AOpCr 0 03 AOV 2 23 AOV 2 37 AOV 2 44 A0Ve 2 17 A1IV 1 96 A1V 1 46 A1V 1 58 A1V 1 25 A2lae 1 68 A2IV Star beta Aur zeta UMa beta Leo alpha PsA alpha Oph alpha Aql alpha Cep iota Car alpha Car theta Sco beta Cas alpha Per alpha CMi alpha UMi delta CMa gamma Cyg alpha Cen alpha Aur epsilon Car beta Gem beta Cet alpha Phe epsilon Cyg alpha UMa alpha Cas theta Cen alpha Boo epsilon Sco epsilon Peg alpha TrA alpha Ari gamma And alpha Hya lamb
16. he higher dispersion of the SA200 compared with the SA100 can be used to advantage with large aperture long focal length telescopes to increase the length of the spectrum without excessively increasing the distance from the sensor provided the camera sensor is large enough to fit the spectrum and star image in the same frame Some additional care is needed when focusing using an achromatic refractor as with these instruments not all colours particularly Violet and Infra red focus at the same point Particularly with a short focal length achromat you may find that not all the spectrum can be brought to focus at the same time and you may need to concentrate on one segment at a time The spectrum will appear fish tailed at the violet and or red ends Reflectors including Cassegrain designs do not show this effect Apochromats are affected less and if corrected for imaging including the Infra Red region may show no chromatic aberration Indeed the STAR ANALYSER is an interesting way of checking the chromatic correction of your telescope 10 How faint an object can I record Like normal astronomical imaging it depends on the size of telescope sensitivity of the camera you are using and your sky conditions but because the light from the object is spread out across the camera detector objects need to be perhaps 5 6 magnitudes brighter than for a normal image This is one of the reasons professional telescopes tend to be so huge In practise the s
17. jects Before imaging a faint object set up and focus on a bright A type star first The spectrum produced can also be used as a calibration check In crowded star fields unwanted star and spectrum images can interfere with the spectrum you want to record Rotate the camera so that the spectrum misses them If you have trouble with star trailing on long exposures orientate the grating so that the spectrum is at 90deg to the direction of drift This will prevent the drift blurring the spectrum Visual Use The Star Analyser can be fitted directly to the bottom of an eyepiece threaded for filters The length of spectrum can be increased by increasing the distance between the Star Analyser and the eyepiece This can be accomplished for example by attaching the Star Analyser to the incoming end of a star diagonal Note that these configurations require increased inward travel of the focuser which may not be available with some telescopes particularly Newtonians Further advice and information There is an on line community of Star Analyser users where you can get advice exchange ideas and share results at http groups yahoo com group staranalyser FREQUENTLY ASKED QUESTIONS FAQ 1 What is Spectroscopy It is the science of recording and analysing electromagnetic radiation eg light in terms of its wavelength colour 2 Why is Spectroscopy so important in Astronomy Astronomy is rather unusual among the sciences in that it is alm
18. lucky you might even catch a meteor spectrum using this technique 7 What can the spectrum tell me about an object The broad shape of the spectrum gives information about temperature For example the spectrum of cool Betelgeuse is quite different to that of hot Sirius Narrow absorption dark or emission bright lines tell us about the chemical elements that are present and how they are behaving For example the spectrum of Betelgeuse reveals the telltale signature of molecules in its atmosphere while stars like Vega show absorption lines due to hydrogen atoms Shifts from the expected wavelength of lines can give information about the way the object or different parts of it are moving The blue shift of hot gas rushing towards us after a supernova explosion and the redshift of a distant quasar due to the expansion of the universe are examples of the kind of processes which it is possible to record using the STAR ANALYSER 8 What type of camera can I use See also How faint an object can I record Because the spectrum image is so compact all the available spectrum information can contained within a length of just 500 pixels just about any electronic camera without a lens which can be fitted to a telescope in place of the eyepiece can be used For brighter targets webcams solar system imagers and video cameras are ideal for the beginner Long exposure CCD astro cameras can be used to record faint objects greatly increasing the range of o
19. n be quite subtle and only show up after further processing of the image Spectral types M and A probably show the most obvious lines See appendix I for a list of bright stars and their spectral types If you don t have any luck try a different star or try processing your spectrum image further as described in the Processing section The features are indistinct and smeared out This simple type of slitless spectrograph depends on the target being almost a point source If it is not for example if the seeing is bad or you are using a long focal length then sharp features in the spectrum can be smeared out and become indistinct Particularly if you are using a focal length of over 2m a focal reducer will often help to sharpen the spectrum features I cannot focus all positions along the spectrum at the same time There will be a slight shift in focus due to the increasing angle of the light beam from blue to red so you may find you have to compromise focus slightly at the far ends of the spectrum If you are using an achromatic refractor the focus errors will be larger due to chromatic aberration of the telescope Particularly with short focal length achromats you may find you can only focus part of the spectrum at a time See the FAQ for more information on focussing and other factors which affect resolution Processing The image of the spectrum can be enhanced to improve the visibility of the features in various ways using your f
20. ost entirely observational rather than experimental With the rare exception of a few meteorites and samples of moon rock just about everything we know about the universe and the objects in it comes from analysing the light and similar electromagnetic radiation such as radio and X rays coming from it Spectroscopy is a key tool in this process revealing the physical and chemical processes which drive the formation structure and evolution of the components of our universe 3 What is the STAR ANALYSER The STAR ANALYSER is a high efficiency blazed transmission diffraction grating designed to make recording spectra easy using a telescope and and webcam video camera DSLR CCD astro imager The device screws into the nosepiece of the imager like a standard 1 1 4 inch filter and allows the recording of the spectrum of any object that appears star like in the field of view 4 How does it work The STAR ANALYSER diffraction grating intercepts the light from the telescope and deflects disperses it into a line on the camera detector according to the colour or wavelength Longer redder wavelength light is diffracted more than shorter bluer wavelengths 5 What is special about the STAR ANALYSER The STAR ANALYSER has a number of design features which make it particularly effective and easy to use with popular low cost webcams video and astro imagers It contains a replica diffraction grating made from a high quality high efficiency blazed master
21. pectrum of the brighter planets and hundreds of stars down to mag 4 can be recorded using a modest 8 inch 200mm scope and a sensitive webcam or planetary imager Given good sky conditions and using the same aperture telescope with a sensitive monochrome CCD imager with long exposure capability recording the spectra of objects down to mag 13 is possible or even fainter if the camera is cooled allowing the measurement of quasar redshifts and the classification of bright supernovae to be performed Integrating video cameras long exposure colour imagers and DSLR will reach intermediate magnitudes to record bright comets or the fascinating supernova candidate Wolf Rayet stars for example 11 What wavelength range can I record The range depends on the response of the camera sensor and whether an infra red blocking filter is fitted An unfiltered CCD sensor will typically record from less than 400nm in the violet to beyond 800nm in the infra red Even colour sensors with any infra red filter removed will record into the near infra red as the colour filters built into the chip are transparent to infra red 12 What is the resolution of spectra produced by the STAR ANALYSER At first sight one might think that by using a grating with more closely spaced lines or mounting it further away one could increase the resolution as much as one liked In practise though there are several other factors which limit the resolution for this type of configuration
22. tified the same Appendices III and IV lists the wavelengths of the Hydrogen Balmer lines and lines from Oxygen molecules in the atmosphere which can often be identified in spectra and used for calibration The distance from the centre of the zero order star image to the identified line is measured in pixels and the result divided into the wavelength of the line to find the dispersion The distance along the spectrum can then be calibrated using the zero order star image as the origin Displaying the results graphically The image of the spectrum can be converted to graphical form using suitable software This technique is very effective for revealing faint features which might otherwise be missed in the image The software may also have tools to help with calibration and identification of features in the spectrum It is also possible to correct for variations in intensity of the spectrum with wavelength due to the response of the grating and camera sensor The spectrum of red giant delta Virginis converted to graphical form using Visual Spec software uncorrected for the spectral response of the spectrograph Examples of spectrum analysis software include RSpec WWW rspec astro com Visual Spec www astrosurf com vdesnoux ISIS www astrosurf com buil isis isis en htm The user is recommended to refer to the instructions supplied with their specific software for further information Tips for recording spectra of faint ob
23. u need to wind the focus in a touch more to achieve the best focus of the spectrum If any narrow absorption or emission lines can be seen these can be used to sharpen the focus If there are no obvious features then focusing to narrow the width of the line can get you nearer Once you have good focus it can be useful to note for future reference how much the focuser had to be moved compared with the zero order star image focus point Note that it may not be possible to obtain good focus at all wavelengths simultaneously when using an achromatic refractor due to the telescope design 16 How can I turn my narrow spectrum image into a wide strip Many image processing programs have all you need First rotate your spectrum image so it is horizontal and crop the image so it just shows the strip with the spectrum it will typically only be a few pixels high Resize the strip to the same width but only one pixel high then resize again to the same width but 30 pixels high and voila A professional looking strip spectrum which will make the spectral lines much easier to see 17 How can I calibrate my spectrum The STAR ANALYSER has been designed to make calibration as easy as possible With most configurations you will be able to capture the image of the star as well as the spectrum in the same frame The star image is your zero point Because the dispersion of the STAR ANALYSER is low the wavelength is essentially proportional to the distance along the
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