question about apsum, apall

Erika Ma. Benitez Lizaola wrote on Sep 09, 2003

Hi:

I'm currently reducing spectra with specred routines.
In the past I have had no problems with the programs
but now I do not understand why, after doing bias, flatfielding
and cosmicrays, I cannot extract the spectra, i.e. form 2 to
1 dimention.
The spectra were taken with a medium resolution spectrograph
and when I try to extract them with apsum or apall I got a graph
that clearly shows the spectra along the lines (which do not
corresponds to the dispertion axis).
I tried to change the dispaxis but I can't, also I've changed
the dispaxis from 2 to 1 in apex:


    (dispaxis = 1)              Dispersion axis (1=along lines, 2=along
columns)
    (database = "database")     Database
     (verbose = yes)            Verbose output?
     (logfile = "aplog")        Text log file
    (plotfile = "")             Plot file
     (version = "APEXTRACT V3.0: August 1990") 
        (mode = "ql")           
      ($nargs = 0)              


and the result is the same, a plot along the lines instead the
columns.


I will appreciate any help from you.

Sincerely,

Dr. E. Benitez.

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Simon O’Toole wrote on Sep 10, 2003

Hi,

> The spectra were taken with a medium resolution spectrograph
> and when I try to extract them with apsum or apall I got a graph
> that clearly shows the spectra along the lines (which do not
> corresponds to the dispertion axis).
> I tried to change the dispaxis but I can't, also I've changed
> the dispaxis from 2 to 1 in apex:

I have had this problem in the past as well. Have you tried using
hedit to put the dispaxis keyword into the FITS header? I think that
IRAF checks the FITS header first and uses what it finds there. If you
have tried this or it doesn't work when you do, another option might
be to use rotate in images.imgeom to rotate the dispersion axis. This
is not the ideal solution, but it should work.

Hope this helps.
Cheers,
Simon

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Frank Valdes wrote on Sep 10, 2003

Hi Erika,

There are two simple ways this confusing behavior could occur.  The first
is what Simon indicated.  If the header contains the keyword DISPAXIS then
this takes precedence over the parameter setting.  So changing the
parameter would have no effect on what you see when extracting.

The second is that since the tasks apall/apsum appear in several packages
you have to be sure to set the parameter in the package from which you
are running the task.  For instance if you load SPECRED and then edit
"dispaxis" in the APEXTRACT package parameters this won't change the
behavior of APALL in the SPECRED package.  If you do epar on APALL it will
show you the package; say specred.  Then do "epar specred".

Yours,
Frank Valdes

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Last post on Sep 10, 2003