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Thank you for your help.
I haven't got much further but with Rob's advice I managed to crop fits files in AIP4WIN. I managed to straighten this one with less moves in Iris (I used geometry, rotate as before - perhaps there is a better method), and I changed it to grey scale in Iris, and saved as a pic file. I also felt I had more control of the thresholds levels, though still not quite sure what is best to aim for. Knowing that little peak was H alpha meant I could calibrate it for wavelength, though the numbers have rather swamped the tiny spectrum. Is there any way to control this? I think Altair was higher in the sky than gamma Cas, and obviously a different direction so probably not ideal, but the best I've got. I will check out Christian Buil's page on atmospheric extinction, thanks.
I couldn't get into the files to save the latest profile so I didn't know what else to do other than attaching it.
Cheers,
Jan
To: staranalyser@yahoogroups.com
From: robin@...
Date: Wed, 8 Jul 2009 10:48:12 +0100
Subject: Re: [staranalyser] gamma Cas spectra
>Is it better to continue with stacked raw images for the calibration, and to use images taken the same night? Any tips are welcome.
For highest accuracy it is best to take a calibration star on the same night and approximately the same elevation as the target, particularly if the target is low in the sky. This helps to make the atmospheric extinction similar. In practise though you should get a reasonable result using instrument response calibrations from other runs. As a variable star observer you might be interested in the effects of extinction on spectra. Christian buil has recently added a page on the ARAS website on how to correct low resolution spectra for extinction here. (It is not for the beginner though!)
http://www.astrosur
Note that if you have used the "spectra" "correct tilt of a 2D spectra" function of IRIS to level the spectrum, this changes the X scale so the wavelength calibration of calibration star and target will only be comparable if they were both changed by the same angle. The "geometry" "rotate" function does not change the scale but can give more pronounced wave artifacts in the spectrum.
Best Regards,
Robin
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