iraf.net

Hello Anupama,Thank you for including the data. I do not believe there were any
significant changes between the two versions of IRAF for the aperture
extraction. Unless you used exactly the same aperture definitions,
that is the database/ap* files, there could be other things going
on. There are also parameters which are not recorded in the headers
which might differ.Since the sky is such a strong contaminant I might suggest that you
extract both an object and a sky aperture. In other words, don't use
the sky subtraction features in APEXTRACT but instead extract a
spectrum centered on the object and one that is offset to sky. Then
use the SKYTWEAK or TELLURIC tasks. These are designed to
empirically adjust to give the best removal including any dispersion
axis shifts and intensity variations with position.I hope this helps. Without having the exact set of parameters and
aperture definitions I can't comment further on the difference
between the two versions.Please convey my regards to Sunetra Giridhar.Yours,
Frank ValdesOn Oct 25, 2005, at 1:17 AM, G.C.Anupama wrote:>
> I am facing problem with the background sky subtraction while
> extracting
> spectra using apall.
>
> I find that the night sky emission lines are not well subtracted. I am
> currently using V2.12.2. However, I did not face any such problem
> when I
> was using V2.11.
>
> I have attached with this mail samples of spectra extracted using
> V2.12.2
> (mcneil_new.fits) and V2.11 (mcneil_old.fits). The improper
> subtraction of
> the OH night sky emission lines is very evident in the first half
> of the
> spectrum, which corresponds to wavelength regions beyond 7600 A.
>
> I request your help/suggestion in this matter.
>
> Regards,
>
> G.C. Anupama
>
> **********************************************************************
> *********
> Dr. G. C. Anupama
> Indian Institute of Astrophysics Ph: +91-80-5530672 Ext 344
> Koramangala, Bangalore 560 034 Fax: +91-80-5534043
> India e-mail: gca@iiap.res.in
> gca@iiap.ernet.in
>
> http://www.iiap.res.in/personnel/gca/gca.html
> **********************************************************************
> *********
>
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> <mcneil_old.fits>
> <mcneil_new.fits>