weighted spectral extraction of STIS with noise spectrum

Frank Valdes wrote on Apr 19, 1999

Q:  i have a 2D image of a completely reduced and wavelength calibrated  
STIS spectrum w/ 2 extensions. - ext1 is the data and ext2 is the noise
spectrum.  i would like to extract the unresolved spectrum from the ~10
pixel wide spectrum containing most of the signal, and i would like this
extraction to be weighted with the noise information i possess.  i read
your help file on apextract/apall, but the only weighting is by the
variance computed from gain and readnoise.  is there an iraf tast that
could handle my requirements?


A:  Unfortunately there is nothing specifically that will do what you want.
But is seems to me that you could accomplish this as follows.

1) Multiply the  data image with the noise image.
2) Extract this using no weighting; i.e. a simple sum across an aperture.
3) Use the same aperture definition to extract from the noise image.
4) Divide the extracted 1D spectrum*noise with the extracted 1D noise spectrum.

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Last post on Apr 19, 1999