LONGSLIT: illumination correction

Frank Valdes wrote on Jun 26, 1998

Q:  At my last non-NOAO observing run, there were no sky flats taken from
which to make an illumination correction for longslit data. Do you
have any advice as to how I might cobble up some kind of correction
from dome flats themselves or object spectra?  There appears to be a
10% gradient from one end of the slit to the other (spatially) that
I'd dearly love to remove. Or is it hopeless?


A: The ILLUMINATION task in the long slit package can be used on your
object data to make an illumination correction.  In this task you mark
the regions of sky to exclude objects on the slit.  Clearly you would
want to use data with narrow profiles, that is stars and not some
extended source.  You could play various games to combine data but
probably one object observation should be enough to remove the gradient
you mention.  Once you get this correction you can just apply it to
your data or fold it in with the flat field.

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Last post on Jun 26, 1998