spectro-aras.com

I have just been processing some Alpy spectra in version 6.1.1 and noticed that the instrument response (IR) I obtained using a MILES star was quite different from anything I used to have.
I tracked this down to the fact that the un-corrected spectrum has a much larger amplitude than before (direct compariosn with v5+ and v6+ variants of Isis).
There is a factor of around x5 in play...
I think this means the more subtle variations in IR are subsumed by an overall amplitude correction. The end result (IR corrected) is identical in both cases but:
(i) Can anyone confirm this behaviour?
(ii) Is there some 'switch' to go back to the old behaviour? (It would be nice to see IRs that look like their earlyioer version for comparison)

Cheers

Kevin

... Its actually not just a scaling, as the new (v6) spectra are still normalised in the desired range . So they now have a different shape being more 'peaked'..
??

Kevin

I understand from David Boyd that there was a change in policy over flats processing between the versions I am using that almost certainly accounts for the behaviour I am seeing.
Phew! (and thanks again David)

Yes after v5.9.3 the correction for the flat lamp spectrum using a nominal black body spectrum was removed. Unfortunately it is missing from the change log
http://www.astrosurf.com/buil/isis/new/release.html
personally I prefer to use v5.9.3 with the ALPY as the raw spectrum is less peaky which makes it easier to fit the response curve. You must not mix response curves between versions though

Cheers
Robin