After taking some images an spectra of comet master, I tried to look at eta Carina. Did not land on it correctly, but saw that a few spectra seem wavy compared to most of the others. I circled them. Have not identified the star names as yet. Why are they wavy??
Both the stars are pulsating variables. The one at top-right is BO Car, an SRC-type variable and a red supergiant with a 0.8 magnitude amplitude and a period of about 131 days. The lower one is V515 Car, an SRB-type variable with the period irregular and undefined. The 'waviness' of both suggests that the spectra are simply reflecting the properties of these two stars, both being semi-regular pulsating variables, rather than being some particular issue with the photography! Beyond that.... I know nothing! Might be interesting to either chase up some spectra or spectral information on these stars, or attempt some better quality spectroscopy on them. Good work Al!
Both of those stars are have cool red type spectra. They look like K or M stars. The cooler stars have a sawtooth appearance due to TiO absorption bands. I have attached an example spectra. It is of T Aps which is a mira star with a M spectra.
After taking some images an spectra of comet master, I tried to look at eta Carina. Did not land on it correctly, but saw that a few spectra seem wavy compared to most of the others. I circled them. Have not identified the star names as yet. Why are they wavy??
regards, Alan
Hi Alan,
That's an interesting field. As well as the obvious emission lines in eta Car (so bright that they are also visible in the -1 order), did you spot the two Wolf Rayet Stars WR22 and WR24 showing an emission line in the red in your field ?
This Image is a single frame from this equipment, SA100, ISO800, 30sec, EON,80mm Orion ,Canon 450d unmod.
Quote:
Originally Posted by robin_astro
Hi Alan,
That's an interesting field. As well as the obvious emission lines in eta Car (so bright that they are also visible in the -1 order), did you spot the two Wolf Rayet Stars WR22 and WR24 showing an emission line in the red in your field ?
Robin
Are those the ones that seem to have a reverse spectra red on the left going to green , instead of blue going to red ? I can see two of those, one at upper centre left, and one lower centre below the wavy spectra.
Thanks all , for the info, more for me to learn...
The spectra running in the opposite direction are the -1 orders. The Star Analyser produces spectra either side of the star image (The zero order). The +1 order on the right of the star is by far the brightest and the one you want but there is also a faint "ghost" spectrum to the left of the star image. The Star Analyser instruction manual has more information on this. http://www.patonhawksley.co.uk/resources.html
You can see the zero order and +1, -1 spectra in Eta Car in your image, which I have marked (attached) I have also marked WR24 and WR22 and the red emission lines in them.
You will notice that the emission lines in the eta Car spectrum are out of focus (most obvious in the red) You can move the focusser in a bit to bring the spectrum into sharper focus. (The zero order star image will then be slightly out of focus but that does not matter as it is a sharp spectrum we are interested in.)
The pointer helps, trying to make reference chart for the next time.
Yes I see that the order is important, I was thinking how a star could have no blue section?
I used Sirius to focus my set up before going to the comet and Eta Carina. I'll chose a less bright one next time. I did concentrate on getting the spectra horizontal and as narrow a line. Perhaps a little less exposure will help with a few more frames to make a medium image. And then again, read the manual...8)
Do you guys know if something like the bottom section of this set up is available? I was thinking an lockable adjustable slip tube assembly could be used to allow for rotation and forward/back positioning, which might be part of my problem, of the SA100, for optimal focus.
Alan,
The 500mm fl you're using and the current spacing between the grating and the camera chip are giving good results.
The only issue I can see is the focus...
With practise this can be improved.
IMHO there's no need to spend $$$ on any special adaptors.
(Eta, as Robin said shows a spectrum in the -1 order, and I think if you look closely you'll even see a further -2 image !!)
I would take more spectral images to refine your focusing techniques and enjoy the ride!
When you want to start processing the image, I'd recommend trying BASS Project to prepare wavelength calibrated 1D profiles.
Well done!
I have a design for a three tube thing, that has rotation 90 deg and forward/Back 20-70 mm. T2 thread at the camera end. But will take me ages to make a prototype...8). Happy to share a rough sketch, for the mechs out there.
I have changed my tube arrangements, so I think focus will be better next time...
Why bother creating FITs Al? Unless you've done darks, flats, bias etc and have accurate calibration and a reference image for correction, you're not going to be submitting to a science archive! Just use BASS Project software which will graph pretty much any image file, including jpegs. You can work your way into the serious stuff later if you develop sufficient interest. The software is available in this group: https://uk.groups.yahoo.com/neo/groups/astrobodger/info
Attached are a few I graphed from your montage, calibration approximate based on the HB line in your EC spectrum. I feel your spectra are a bit overexposed or too much contrast or something in processing. And you should run the spectra to the right, not left. Keep it up!
+1 from me.
Rob's comments are on the mark.
BTW the "dip" in your spectra is caused by the Bayer matrix in the Canon cameras - I see exactly the same effect with both my modded 450D and a standard 1000D.
I thought I had my set up right, but last evening efforts where a bust.
The tube arrangement i have now allows me to rotate the SA independent of the camera, just need to get the forward back setting correct and adjustable. I am trying to set the SA100 at 60 mm from the camera sensor plane. With some 50 mm fwd/bck to see if any finer position is achievable.
I got the BASS software and am working on the processing steps.
Just use BASS Project software which will graph pretty much any image file, including jpegs. You can work your way into the serious stuff later if you develop sufficient interest. The software is available in this group:
And you should run the spectra to the right, not left. 
Keep it up! 
