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I'm having two problems with scombine. The first is that none of the cosmic ray rejection algorithms work when I feed flux-calibrated spectra into scombine. Should they?Second, if I extinction calibrate my individual spectra, combine them in scombine, and then apply the flux calibration, I get a very different (and incorrect) result from when I extinction and flux-calibrate the individual spectra and then scombine them (aside from the cosmic ray issue). The main difference is that the former spectrum drops off rapidly in the blue, as if no extinction correction was applied. This problem is twice as bad if I scombine the spectra and then extinction and flux correct the scombined spectrum. I'm running IRAF on a mac and am using 10.4Any help would be greatly appreciated!

Scombine should reject cosmic rays on flux calibrated data. Of course the ccdclip method would require setting the noise mode parameters appropriately. But the more empirical mehtods (sigclip and avsigclip) should work. I would be glad to look at some data if you want.The concerns with combining, flux calibrating, and extinction correcting depend on how you do things. For one thing, the sensitivity function is derived from data in counts and with known exposure times. If you combine data then the sensitivity function may not be the correct one to use. I would need to understand, and possibly see, what a single uncalibrated spectrum and the combined uncalibrated spectrum are like. Again, if you provide data or graphs and/or header listings (since some operations depend on header keywords) I might be able to provide more explanation.Yours,
Frank Valdes