First light with the Staranalyser

[sheeny]

Last night was first light with the Staranalyser.

It is easy enough to use in itself, but like all things new, there is a learning curve!;)

I captured 3 AVIs from Antares and 2 from Achernar with the TouCam, C8, K3ccdtools. I put in the f/6.3 reducer for the Achernar capture which helped to sharpen up the star image a bit.

I decided to use the ToUcam for 2 reasons:
The thread in the nose piece for the DMK was being cantankerous with the staranalyser (I have shortened the nose piece to use it with the PST)
The ToUcam gives a colour spectra which I thought might be easier to identify Fraunhofer lines on than a mono image...The spectra was wider than the ToUcam sensor so I had to capture across the diagonal. That's OK... can fix that later...

I stacked the avis in Registax, but found the rotate image option in Registax doesn't rotate the whole image inside a larger canvas, so the star image disappears:rolleyes:. This makes calibration difficult if you want to use the star image as one calibration point (which I do ATM as a newbie:P).

So I used PS CS3 to rotate the image and crop it. PS, however, doesn't save an image as a .PIC or .FITs file... so I saved it as a BMP, and loaded it back into Registax to save it as a FITS. I tried saving as a TIFF, but had no end of grief getting Registax to open it without errors...:shrug:. Registax always saves the FITS file as separate files for each channel, so it's necessary to convert the image to monochrome in PS before saving, so that any of the FITS files will have the full spectra.

Once I got the images in VSpec, identifying spectral features is the next challenge... There is a distinct absorption line/band in the IR part of the spectra. At first I thought it was Fraunhofer A, but the more I think about it I think it is the H20 absorption band at about 7250A. Anyway that's what I've assumed for the time being:lol::P.

Learning VSpec is going to be a challenge though, I feel...:whistle:

I've attached some images:

Antares spectrum image
Achernar spectrum image
Antares spectrum binned in PS
Antares spectrum binned and desaturated in PS
Antares spectrum produced from 1 (no binning in PS)
Antares spectrum produced from 4 (binned in PS)There is obviously a difference in the shape of the spectrum produced by binning in PS, so this is obviously an artifact and to be avoided (I was curious about that effect:P:)).

Al.

[Terry B]

Very interesting.
Where did you purchase the Staranalyser?

[sheeny]

http://www.patonhawksley.co.uk/staranalyser.html

Al.

[Starkler]

Very interesting. How do you calibrate the differing sensitivity of the cam vs wavelength of light?

[[1ponders]]

Wow, keep 'em coming Al. :thumbsup:

How did you get your focus Al? It seems the spectrum is a bit soft. :shrug: It would be interesting to try it with the mono cameras and colour filters as well (or without). You might find you get a sharper result. Top effort though!

[Terry B]

I would have thought that no filters makes more sense as you would get only part of the spectrum with each filter.
When I saw the colour image I wondered how it would work as different parts of the spectrum will be covered by each colour on the bayer array. I suppose as long as there is enough crossover and you are not trying to measure the absolute intensity at any particular frequency it will work with a colour sensor.

[[1ponders]]

I was thinking of the idea of no filter as well Terry, but I figured using an LRG combined tricolour imagine you could still get the desired result after combining the separate channels but the resolution should be better. It would be interesting to try. Of course the colour weight would have to be right.

[Merlin66]

Good start! Well done.
A couple of comments;
The overall shape of the spectra are influenced by the colour sensitivity and responce of the CCD. This can easily be corrected within VSpec ( there's a Tutorial on the subject)
Generally it not a good idea to manipulate the images to much incase the data gets corrupted. A stack, crop and into .pic or .fits format for VSpec is enough.
Keeping the spectral image parallel with the edge of the CCD ie run the specrum along a row of pixels will both improve the image and make analysis easier ie pixel count per dispersion.

If you are using a refractor, Focus for the spectra not the zero image. Due to the varying colour focus with lenses.
There's no benefit in using additional filters. Mono camera usually give abetter image ( you can always add false colour later, when you've worked out the wavelengths)
Vspec also has comparison spectra for all the star types, Antares is a M1.5 Ib and Achenar B3 V

Not sure I can analyse the images you've posted but if you email a copy I'll run it through for you.

[[1ponders]]

Thanks for the heads up info Ken, you've got my credit card finger itchin' :lol:

[sheeny]

Ah! Excellent question... That's somewhere in the learning curve ahead of me...;):P I have seen it mentioned in the tutorials, but as for details... I don't know yet.:whistle:


I focused with my prototype Bahtinov Mask. I doubt I could've got the focus much better actually... I think the softness is probably the seeing - it wasn't that flash and Antares was maybe only 20°-30° elevation at the time. I also stacked about the 30 best frames, but no sharpening, wavelets, etc. I'm not sure if that's the best way to go, or simply pick the best frame:shrug:. After a quick look on the Staranalyser forum, it seems others are stacking too, so I did that just cause I'm used to doing that on other photos:P.

The Achernar spectrum you may notice is very narrow in the red part of the spectrum and wide in the blue...:shrug:... I'm not sure why that is, but if I had to guess I'd say the focus was OK, but the blue light was being scattered more. I did put my f/6.3 FR in the train for that one though, so I might have to keep an eye on that... maybe that's the source of the blue spread?:shrug:


From the very little I have read, there is more to do in calibrating a colour image for the response of the camera than there is for a mono camera. Ultimately I plan to use the DMK, but for starters I'm playing with the ToUcam sinc eI figure the colour will help me to identify what I'm looking at in the spectra.:) When I find my legs I'll probably go mono just cause it'll simplify the process a bit.;)



Hmm. I don't know. You would have to have overlap between the filters, otherwise you'll miss sections of the spectra, but that you'll need to correct for the overlap... I suppose that's what you have to do with an RGB camera anyway...

I am fascinated by the length of the IR end of the spectrum... there's heaps there! It is no wonder a UV/IR filter has such a positive effect on images!

It's all baby steps at the moment:):thumbsup::P.

Al.

[sheeny]

I thought as much - good to have it confirmed!:thumbsup:

That makes sense too. I did wonder about that, but the VSpec tutorials suggested the diagonal and rotating afterwards, so it this stage while I'm learning it doesn't matter too much, but I'll keep it in mind as I get more serious.

Well, I'm using a C8, so at native FL there's only the corrector plate, but I'll probably use a FR to sharpen up the seeing... so I guess that's equivalent to a refractor:P.

Yeah, there's heaps in Vspec... and it all reads relatively easily in the tutorials, but, gee, I have some fun trying to get it to do what I want!:lol: It's just a matter of time and playing with it I suppose...


Thanks Ken! I'll send you a FITS file or 2. I appreciate your comments and help, Ken, as the resident spectroscopy guru on IIS!:thumbsup:

Al.

[Terry B]

When I started taking images through photometry filter this effect became very obvious. The attached files are frames of S Psc through B (blue) V (green) R (red) and I (IR) filters the exposure lengths are different for each filter but you get see how much of the light is in the IR for these big red , cool stars.

[sheeny]

Cool! More heat than light there!

Al.

[Merlin66]

S Pisc is a red variable , spectra M5-M7 so it has an excess of red, as you've found.
The Yahoo StarAnalyser group under Robin L. is a tremendous forum for this type of spectroscopy.
Try some bright white/ yellow stars for comparison ie Vega, Alpha Cen etc.
My Rainbow optics grating (200lpm) failed and I return it. Ended up with a Baader 207lpm grating. Positioned about 60mm infront of the CCD ( I use the Canon 350, MX7c and AtiK16ic) gives good images.
Much much easier to use than a Littrow; you don't have to worry about guiding on a slit!!!
The SA, Rainbow and Baader are limited by the seeing conditions and star image size. The smaller the image the better, so large apertures and low focal lengths are ideal.
Spend the time with VSpec it will reward you well.
For a quick solar spectrum use the reflection from a needle at 20 meters or so as a reflection slit.

[h0ughy]

fantastic Al - actual science !! impressive! ids that coming to IISAC? be good to have a look

[Merlin66]

I just had to mention, the images that TerryB has taken show the potential for amateur photometry with small apertures,
By using the standard photometric filters and exposures, as per TerryB, it is possible to get quite accurate stellar magnitudes (to within 0.01 mag) in the UBVIR ranges. These can be used to get a (B-V), (U-B) and (R-I) index for accurate spectral type analysis.

www.britastro.org/vss/ccd_photometry.htm (http://www.britastro.org/vss/ccd_photometry.htm)

This is a very well written introduction to photometry by Norman Walker.
Software like AstroArt 4, CCDSoft etc have photometric capablities.

[sheeny]

Yup! It's coming along...:D

Al.

[sheeny]

Hmmm... that sounds like an interesting experiment!:thumbsup: You's need a black background behind the needle wouldn't you to eliminate the background light?

Al.

[Merlin66]

Not really, the zero order may get a bit of background light but the spectrum is OK. A bit of dark/ black cloth ( Guns an' roses T shirt?) works well.

[Barrykgerdes]

If you want to experiment with star spectra there is an excellent program called spectra.exe, Google it. This program has the software to print a diffraction grate on clear film with a laser printer to place in front of your telescope while you take a shot of the star with your CCD. Read the manual that comes with it.

I found this program years ago (DOS era) but it is still available and runs at the command prompt or in a window. It is free!

Barry

[Heian]

Hi Al,
good to see another SA user on the IIS. :thumbsup: I'll second Ken's comments about the Yahoo group run by Robin L. Lot's of info and very helpful.
Robin sent me a number of emails about calibrating instrument response which I can pass if you want them, but they are also on the yahoo group site if you can track them down.
My comments on it's use are also:
1. use b+w as Vspec works better with them.
2. you can also place the SA in front of a std 135mm lens on a canon 350 and get workable spectra after 4 - 6 secs. The attachment below is one of them, working at approx 2.5Ang / px resolution. In this case I also used a 2x teleconverter. Taken from suburban Wollongong, so not too bad :)

cheers
Mark

[sheeny]

Thanks Barry. I tracked it down in google, but the page failed to load... I'll try again later.


Thanks Mark. I've had a quick browse of the archives now that I'm subscribed to the Staranalyser list. Looks good.

I intend to have a play with with my camera, though it isn't modded so the IR response will be poor.

I'm toying with the idea of getting a Meade f/3.3 focal reducer as well. Any reason this wouldn't be worthwhile with the Staranalyser?

Al.

[Barrykgerdes]

I just down loaded it successfully. I also printed out a diffraction grating on clear media. If I hold it up to the light I can see the 300 dpi grating. It printed OK on my HP 5P laser but nothing doing on my Magicolor

The program was originally written for a Meade Pictor 416 so it should be perfect for a Meade DSI. The sample spetra look quite good.

Barry

[Heian]

Al,
just my comment but spectra work with a SA is mainly done in the range of 3500 - 7000 Ang. To go outside that range would require a much more sophisticated spectroscope with a slit, higher resolution reflective grating and imaging selected areas of the spectra at a singe time.
The image below is of Fomalhaut taken with a DSI II mono and a ED80. The line at the tail of the spectra is atmospheric O2 + H2O. The hydrogen lines, H alpha, H beta and H gamma, are at the left hand side of the spectra and are of more interest.
A f/3.3 focal reducer would probably be overkill. A short f ratio will increase the "fishtail" effect of the wavelengths coming to different focus points, blurring the overall image. You can use it, but the total spectra would probably need multiple exposures as you focus on specific regions.
I experimented with the gear I had to see what effect / improvements I could get.
I'll be upgrading to a 120mm f/8.3 in the short term future.

cheers
Mark

[sheeny]

Thanks to Ken (merlin66) for doing some work on my spectra, I've been having a bit more of a play with Visual Spec... Still finding my way round and its all baby steps...:) Still heaps to learn, and I couldn't have gotten this far without Ken's help:thumbsup:... I'd still be trying to match up lines that just aren't meant to be:lol:.

The spectra are my raw capture for Antares (blue line), a reference spectrum from the library (Green line - M1III is about the closest I could find:shrug:), my first attempt at the reponse of my ToUcam (Orange line) and the corrected spectrum (brown line - actually its only corrected for the camera response not atmosphere as well:rolleyes:) ...but I'm getting there!:P:whistle: Some of it is a bit hit and miss, because the tutorials must be written for an earlier version of the program:shrug: because the menu options don't match:rolleyes:.

The second image are synthesized colour spectra produced from Visual Spec - not as captured. Cool feature that!:thumbsup::whistle:

Al.

[sheeny]

Thanks for the comments, Mark. I'll hold off on the f/3.3 reducer for the time being. BTW I made an adapter to fit the star analyser in from of my 300mm lens for the E-510, so I'll have a play with that as well.;)

Al.

[Merlin66]

Good to see you're getting some results!
I'm still a little surprised with the rapid drop off in camera responce in the UV... for some reason (??!) I though it was much better down there.
I need to go back and re-visit some calibration shots I took with the webcam and Canon350D. I did find significant differences with different lenses ie Canon Std lens v's Zuiko lens.
Plenty of bright stars in the southern Hemisphere and not to many guys with spectroscopes!! Oh, don't forget the red and variable stars... Eta Carinae must be getting ready to "blow" again.....let's catch it on the way up!!!

[sheeny]

I dunno either, Ken. I made an adapter to hold the Staranalyser in front of my 300mm lens on the E510, and when I had a quick play around with it the response in the blue end didn't seem much different to the ToUcam...:shrug: I had a play with the needle "slit" solar spectrum, but I came to the conclusion I was too close to the needle. I took the image maybe 2 metres from the needle, and in the viewfinder it looked OK, but in Visual Spec the lines really weren't distinct enough. I guess more distance will reduce the size of the "slit" so as long as my focus is good the resolution should be better.

Al.

[Merlin66]

Al,
The needle idea will work if you get the orientation and distance right.
An alternative I used is the Surpus Shed adjustable slit mounted ( wooden spacers/ gaffa tape) in the end of a length of PVC tube. I used a 50mm tube with a PVC 32-50mm reducer at the slit end, about 2 metre long.
This focussed with the Canon 350D standard lenses and the Baader grating.
Watch out for the rotation of the lens during focussing, I found the canon lens "rotated" while reaching automatic focus, and the grating had to be re-adjusted to align with the slit. To make it easier for me I wrapped a small elastic band around the thread of the grating to give me some rotation with resistance. (This set up can also be used with a flouro reference lamp for indoor trials)
I checked some of my Canon 350D calibration shots, and yes the responce drops dramatically below 380A ( makes observing the CaK lines difficult); I need to test and calibrate the ATiK16ic...... always something to do!!
Weather permitting I'll take some shots of Altair, Deneb and Vega over the next few nights for "practise" with the Baader mounted on the Genesis with various cameras......
My Littrow is temporarily out of commission while I re-set the neon calibration and add a back light to the slit.

[Heian]

Al,
when i was digging around learning about spectroscopy, I found this info on christian buil's website.

http://www.astrosurf.com/buil/baader/eval_us.htm
Basically it shows the std 350d uv/ir filter blocks out "almost everything" ! A modification using the baader filter will improve responses in the IR end, but the uv end still has the major drop off. Certainly taking out the filter altogether will greatly improve the overall response of the ccd chip.

It's an option I've looked at occasionally: modify a dslr or go for a true b+w ccd.
My initial decision is to go for a b+w ccd as the bayer matrix will also impact on the responsiveness / resolution of the system.
cheers
Mark

[Merlin66]

I agree 100%
The Canon is handy for Ohh Ahh shots, and I must say easy to use and set-up, but the spectral limitations with or without changing the filter in the blue-UV effectively make it unsuitable for these regions.
I've gone over to a ATiK16ic (mono) for this reason, downside is the small chip size and I now need multiple exposures along the spectrum.
Haven't tried it yet but the DSIproII (mono) may be an interesting alternative??
BTW it may be already figured out by some users, but the resolution of the Star Analyser/ Baader etc dramatically changes with the distance to the CCD. In an f10 cone, at 50mm distance the out of focus star image only covers 5 x 100 lines = 500line resolution, whereas when it's 100mm the resolution doubles to 1000lines at no extra cost!!

[Heian]

Ken / Al,
one of the things I've been working on is to increase the distance from SA to chip. The aim was to get a zero order image and then the spectra that covers the highest number of pixels, while still having both visible in the same image.
At least until I get a firm handle on doing a spectral resolution without the zero order being visible!
The DSI pro will get me to approx 14.8 ang/px. After some discussion with Robin Leadbetter that's good enough to contribute data to the ArasBeam database apparently, at least to do a low resolution "scan" of a number of stars on a regular basis..
Which is something that intrigues and interests me...
cheers
Mark

[sheeny]

Between my laptop dying :mad2: and the delivery and setup of my Skyshed POD :D I haven't been playing with the Staranalyser or Visual Spec.:sadeyes: Finally, I've got back to it...:)

Attached are some of last night's results for Betelgeuse:thumbsup:. I captured spectra for most of the bright stars in Orion last night, but the Betegeuse one has the most distinctive lines, and I knew I had a sample file that came with VSpec for it, so its the obvious one to start with;). I planned to swing over to Eta Car after Orion, but by that time it was clouded out (cloud started affecting my capture of Saiph).

Capture was with the C8, DMK, Staranalyser, IC Capture. I played around for a long while practicing focussing on the spectrum (rather than the star). I didn't refocus between captures, but when the lines in Betelgeuse jumped out, I figured focus wasn't a problem.:whistle:

I bought a new 1.25" nosepiece for the DMK and fitted a 7mm spacer ring as well to try to get the staranalyser further away from the camera. It would seem from this set of spectra on Betelgeuse I'm getting about 11.6 - 11.7 A / pixel.

Al.

[renormalised]

Nice results there, Al. I'm looking to grab a SA myself at some stage and start doing a bit more science. Will come in handy doing my course!!!.

[Terry B]

Very good.
With my set up using my ST9E the resolution is quite low at ~44A/pixel.
I could use my genesis CCD which has 9um pixels rather than 20um pixels and this will vastly improve the resolution but it means changing the camera on the scope (it's permanently there ) and this complicates my photometry data that I try to take each night.

[renormalised]

Here's a site some of you may not know, but it's a catalogue of spectra for stars of spectral classes O5 to M.... it's at Caltech...they're pretty old, but still useful....

An Atlas of Stellar Spectra (http://nedwww.ipac.caltech.edu/level5/ASS_Atlas/frames.html)

Should come in handy:)

[Merlin66]

Al,
Very interesting results!!
Looks like you're getting the hang of focussing and Vspec!!!
Your getting more practise than me at the moment.... been cloudy and raining since Xmas!
I set up a 50 micron artificial star (on the old Foucault tester) allows me to use the DuluxStar and Neon reference bulbs for "training"!!!!!

[sheeny]

Thanks for the link! I've bookmarked it.:thumbsup:



I got plenty of practice learning how to do that again, Ken! :lol: I might have fallen on my feet with Betelgeuse though. I had a go at the other Orion spectra today and of course they are all blue stars... I still seem to be suffering from a lack of blue response:shrug:. I'm using a different camera now (DMK rather than the ToUcam) and it persists... the library spectra don't seem anything like what I've captured...

I'm a bit doughy today after not much sleep so I'm letting it go till I'm thinking clearer.

Al.