For my Chrissy present I "arranged" that my wife gave me a star analyser as a present.
It is not the easiest thing to master but I'm giving it a go. I have taken spectra of various stars and tried to calibrate them using my ST9E.
The programme recommended id Visual Spec and it is far from user friendly and a bit prone to crashing.
anyway here is my first reasonably successful attempt.
The star is V385 Car. This is a may 7.7 WR star with strong emission lines.
The exposure is only 15 secs.
I'm pleased that I have been able to calibrate the image reasonably well compared with a spectrum I downloaded from CDS.
Now to try to identify other things.
Terry, if you want to learn more about spectra and how to analyse them, I can give you an exercise I used as part of my course, dealing with spectra and how to interpret them. It's quite interesting to do the exercise
However I can tell you that the broad peak you've got near the beginning is most likely a NII/III line, down around the 450nm (4350-4550A) area. If you look at the CDS graph, you'll see the peak right at the beginning, that would be your HeI or even II peak. The Ha line would be emission from hydrogen present on or near the star. WR stars are typically hydrogen poor in their spectra (usually none) and where a strong Ha line appears, it's most likely from one of the least evolved of the type, a WNL (late type). The strong NII/III (ionised Nitrogen) peak indicates it's a WNL star and probably a WN7-8 by the strength of the peak. The strong CIII peak is unusual in that nitrogen normally predominates over carbon in these types, however there is some carbon present in their spectra.
All in all, that's a nice spectrum you took there and a fine job taking it
Last edited by renormalised; 18-01-2009 at 08:07 PM.
Hi Terry,
Here's a link to quite a good book on the subject. http://freebookspot.org/TopTen.aspx?Category_ID=96
Just scroll down and you'll find.....
"Spectroscopy: The Key to the Stars: Reading the Lines in Stellar Spectra"
You can download the book as a .pdf, and if you like it go buy the hardcopy.
Hope you find it useful.
Thanks for the info. Thanks for the link to the book. I've downloaded it and will read it later. I do have some astrophysics texts from my masters and will have to read them again also.
The star is WR40 and it is a WN8 star according to the catalogue.
I attached a pic with the wavelengths on it and I'm sure you are correct with the id of the lines. I just didn't bother labelling anymore
The Star Analyser is a 100line/mm transmission grating, similar to Rainbow Optics one from the US. Baader had a 201lpm version, but not sure it's still available.
Paton-Hawksley also sell an "educational" range of gratings, 100/200/300 lpm at very reasonable prices. Great way to start spectroscopy.
VSpec and IRIS are very good freeware programs to capture and analyse spectra.
Hi Terry,
Here's a link to quite a good book on the subject. http://freebookspot.org/TopTen.aspx?Category_ID=96
Just scroll down and you'll find.....
"Spectroscopy: The Key to the Stars: Reading the Lines in Stellar Spectra"
You can download the book as a .pdf, and if you like it go buy the hardcopy.
Hope you find it useful.
Thanks very much for the link. There is a lot of material available with this resource other than spectroscopy - some of which is very useful for many registered IISers users.
For me, I've just downloaded the brilliant "Encyclopaedia of astronomy and astrophysics" in three parts, which to read (and carry) for me had to be done at the local library. 'nough reading for months!
Again this basically highlights a small discussion area for Books and Literature, as indirectly discussed in another thread.
Good stuff!
I've had another go at this using my genesis CCD rather than the ST9.
The difference is that the ST9 calibrates to ~44 A/pixel and the Genesis/Audine (with 9um pixels) gives me 13.5 A/pixel. This gives better resolution.
The attached file is a graph of Beta Car processed with Vspec.
It is calibrated for instrument response but not for absolute flux.
The spectrum is synthesized from the the spectral data as my original was taken with a mono camera.. The H lines are clearly visible even into the deep purple end.
The absorption from atmospheric O2 and H2O are also clearly visible.
Looking good!!
I'd be interested in your set up.
Which telescope?
What distance between the SA and the CCD chip?
You seem to be able to get down below 400nm which is very good.
I'm just struggling a bit so far down in the UV. My "trials" with a 80mm cemented doublet definately showed you didn't need a UV-IR filter! The lens does it for you! I made the mistake of trying to use the Canon ( convenience!) and wondered what was going wrong.
The Canon is no good, drops to about 10%, the MX7c & DSI II are just below 40-50% efficient, the QHY5 drops to 30%, the webcam's are below 20% and the best so far are the Atik16ic at around 60% and the DMK21 at 50%
Keep it up; you're getting some good results!!!
Looking good!!
I'd be interested in your set up.
Which telescope?
What distance between the SA and the CCD chip?
You seem to be able to get down below 400nm which is very good.
I'm just struggling a bit so far down in the UV. My "trials" with a 80mm cemented doublet definately showed you didn't need a UV-IR filter! The lens does it for you! I made the mistake of trying to use the Canon ( convenience!) and wondered what was going wrong.
The Canon is no good, drops to about 10%, the MX7c & DSI II are just below 40-50% efficient, the QHY5 drops to 30%, the webcam's are below 20% and the best so far are the Atik16ic at around 60% and the DMK21 at 50%
Keep it up; you're getting some good results!!!
Thanks
I haven't measured the distance from the SA to the CCD- not that easy to do. The SA is in a filter wheel and the CCD cameras don't have the position of the CCD on the outside.
The scope is a VC200L. This has no corrector plate but does have a correcting lens in the draw tube.
My Genesis/Audine camera does have a very old UV filter as it's front glass but it obviously doesn't block the deep violet very well.
The kodak chips in my 2 cameras are both "E" chips that are suppose to have an improved blue response but they are still much more responsive in the red. I have found doing photometry with a blue filter that I need about 2x the exposure in blue for a similar flux compared to a V filter. The red needs 2/3 the exposure of the V and IR is about the same as the V filter.
I haven't tried a colour camera yet but might give it a go with my 40D.
I had a dabble with the star analyser a while ago. I still have it and your work has me thinking about doing some more.
I too used the grid in my filter-wheel, difficult to align the lines with the camera (ST-7).
Great work, look forward to seeing more.
Now off to check out the book site.
You don't need to align the lines with the ST7 (although this does make it easier)
You just open the image in Iris, select a region of the spectrum and issue the command "L_ori"
It then tells you the angle that the image needs to be rotated. You then use the "ROT" command with this angle in it and the spectrum is nicely horizontal.
The distance from the grating to the CCD, when its used in a converging beam affects the resolution. The further from the chip the better the resolution.
If you can, you should align the spectra to be parallel to the CCD pixels. This significantly reduces the amount of artifacts which can be produced during processing. IRIS does a good job, but initial alignment is even better!!
Would be interested to see the results from various camera's. Betelgeuse with its broad bands makes a good object.
Next thing you'll be looking at fitting a slit to observe nebulae!!
that my wife gave me a star analyser as a present. 
