From: Andrew Fruchter (fruchter@stsci.edu)
Date: Wed Apr 07 2004 - 11:26:59 PDT
Hi Searchers,
I have just approved visits F0-F5 for observation. However, you should
know that you are using a very non-standard approach to grism
observations. You are not taking a direct image in each visit (indeed
the standard mode takes one associated with each dither position).
This opens you up to the possibility of sub-pixel shifts between the
direct image and the grism spectra.
In principle one generally should not need a direct image. One should
be able to use the zeroth order image (and this could be a more
accurate way to align spectra in many cases). However, the calibration
work necessary for this approach to be used has not been done, as far
as I know.
Cheers,
Andy
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