IUE data reduction in IRAF

Petr Skoda wrote on May 26, 1998

Hello everybody,

I am trying to work with the IUE high dispersion data (MXHI) in IRAF
and have a lot of questions for IRAF gurus:

The data are in binary table, which is then translated by the iuetools
package into binary table FITS  with lambda expanded array then OIF
multispec format.  There are 60 orders of echelle data in it - each
order in separate line . The header contains the dispersion solution for
each order. Now problems:

As the data from neighbouring orders do overlap, there must be choosen
limits for each order and the order data  cut at these borders.  For
this I use the algorithms by Solano (1998)
which will take the one third of the overlaping region from order m and
the rest from m-1.
>From these data I want to have one large spectrum with concatenated
orders. This task doesn't solve the iuetools package.

I could find only task scopy for extracting cuted orders and scombine
for glueing together the orders. However there are problems :

Here is a part of code (with the evaluated value of variables for the
clarity)



scopy (input=swp47913.imh, output=sum47913, w1=1173.8600132649,
w2=1183.8862202, apertures=, beams=117, apmodulus=0, format=multispec,
renumber=no, offset=0, clobber=yes, merge=yes, rebin=no, verbose=yes)

and after one run of cycle

scopy (input=swp47913.imh, output=sum47913, w1= 1183.8862202,
w2=1194.08880079, apertures=, beams=116, apmodulus=0, format=multispec,
renumber=no, offset=0, clobber=yes, merge=yes, rebin=no, verbose=yes)

This doesn't work - there is a complain "Warning: Physical basis for
nonlinear dispersion functions don't match" and then  WFMSPEC: No
dispersion function;

I understand that the problem is in different dispersion relation, but I
can't switch rebin=yes, as this leads to the error segmentation
violation - recently announced bug.

I am afraid there is no solution for having the scombine produce the
multispec image with disjunctly cutted orders (and scombine them in the
image), so I switched format=onedspec
and then scombine each individual file with orders and  combine=average.

There is a another problem with the combining . When I cut the regions
as shown above
at the same value I have two data points in that particular wavelength -
when I sum them a peak is produced, when average and intermediate point
is there. I would like to have the cutted spectra realy disjunct (so
that even the combine=sum will not count two values) - so I need to fit
the edges  to     some    lambda_cut-dlambda, to avoid the last pixel in
data, but I do not know how to set the dlambda to represent only the
last pixel - value in data.
I can set some adhoc value, but if it is to large it could ignore more
pixels - and it will not probably be the same for all orders.

I suppose that such a problem of concatenting overlaping echelle oreders
must be tackled in IRAF , however I could not find anything in
description of echelle package nor in the echelle cookbook (reducing
echelle spectra with IRAF or so - I do not remember exactly).

Can you recommend me a solution ?

The last problem - the IUE data include the quality flags when the
unreliable value of flux is marked. I would like to produce from it a
kind of badpixel map, but I couldnt find how to apply it to scombine (in
imcombine I have the fix+,but I do not work with pixels but wavelengths
in scopy )

I also would like to know an alternative solution of working with the
original IUE FITS - there are binary tables (after conversion of
mxexpand routine ) with  columns  of wavelength values, flux, noise ,
quality flags etc.  Is it possible to catenate  the spectra at this
level  without rebining to wavelength, correctly mask out the bad pixels
according to quality flags and then  convert to one long OIF spectrum to
be able to use rv package for measuring radial velocity ?  Is there even
possible to measure RV and identify lines in STSDAS using the binary
tables directly ?

I am just getting acquitant with echelle data and IUE specifics and have
read a lot of  IRAF and STSDAS helps but the right solution still avoids
me ;-) .

I belive in a power of IRAF  to be able to handle all these problems  (
I might try to write some package code if you will show me the possible
way)

Regards  Petr Skoda

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Last post on May 26, 1998