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Preparing Your Object List for the Multislit Program

The available field-of-view for COSMIC multi-slits is ~13' x 8'. It is suggested that the width of the multi-slit pattern be less than 4 arc-min, preferably even less than this, to ensure that the spectra have approximately the same central wavelength (and hence spectral coverage) and to avoid problems with spatial distortion. Since the multi-slit masks are made by a photographic reproduction process, the width of each slit can be set by the user.

A FORTRAN program exists for converting an object list into a 4 times enlargement negative version of the slitmask. It is called cosmicslitmask.f and can be found at The COSMIC slitmask assignment program takes a list of offsets (arc-sec East and arc-sec North, where East and North are positive) of objects from the center of a field. It is a simple program, assuming a constant plate scale (11.9''/mm) for the prime focus, and ignoring the complications of spatial distortion, gnomic projections, etc.

The output of this program consists of a text file and a plot file. You should create two separate plot files--one which includes the object number above each slit, the other with only the slits and the identification label. The latter plot is the one that needs to go to the photographic lab for reduction.

Note the field identification label on the upper left corner of the plot. The position angle for the mask in terms of the COSMIC ``base position angle'' is given in this label. The limits on rotation for the COSMIC base position angle is 70 to 300 degrees.

Make sure to take to the mountain printed copies of all 3 of these files (one text and two plots) for each mask you design. You should also have a good image of the field with all of the objects identified.

Roy Gal