Cosmic Origins Spectrograph Instrument Handbook for Cycle 17

7.8 Acquisition Techniques for Crowded Regions

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Acquiring targets that lie in crowded regions can be difficult. During its early use we will test the ability of COS to work in this situation. For the present it is necessary to first acquire a nearby point source that is isolated enough to not cause problems (at least 5 arscec from another UV source), and to then use POSTARG to offset to the desired object. This method would also work for acquiring objects that are not quite point sources themselves.

When doing this, you should refine the centering of the initial target before offsetting. Also be aware of potential bright object concerns that will now apply over a broader region.