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Field Orientation Star Selection

• At least 2 Field Orientation Probes must be assigned in order to ``lock" the telescope onto the target field. We suggest, however, that 3 or more probes be assigned (1 near field center, two near the edges of the field) to provide redundancy and to serve as a check on astrometric ``goodness" and other possible fiber placement errors.
• Since assignment to a field orientation star can impact the assignment of fibers onto neighboring target objects, select several times more potential field orientation stars than are needed and let the assignment routine find the ones that have the smallest impact on neighboring fiber assignments.
• The stars selected for use by the Field Orientation Probes should fall in the magnitude range between m=10-15. (If there are clouds and/or the seeing is larger than 1 arc-second, stars fainter than 15th may not be visible with the FOPS TV camera.)
• If possible, keep the range in magnitude of your FOPS sample to 2 magnitudes or less so that the intensity of each star falls within the dynamic range of the FOPS TV camera.
• Make absolutely certain that the stars selected for use by the Field Orientation Probes have good astrometric solutions and were used (or measured) within the same solution as the target objects (ie. same zero point reference). Be careful of possible proper motion problems (ie. don't use old plates or catalogs). You must account for proper motion effects as our astrometry routines don't compensate for proper motion. Reject any stars with large uncertainties in their coordinates.

REMEMBER THAT THESE STARS ARE BEING USED TO LOCK AND GUIDE THE TELESCOPE ON YOUR TARGET FIELD!