Relative astrometry with the Steward Observatory CCD/Transit Instrument

Abstract

The CCD/Transit Instrument can produce relative astrometry with 1-sigma errors of less than 40 mas for stars brighter than V = 17. This figure of merit is obtained from ten nights' data. This precision is obtained over a test region of 8 x 12 arcmin, using simple first-moment centering algorithms. Errors for stars with V from 17.0 to 18.8 range from 40 to 100 mas. Some 3-sigma proper motions are detected. The test field sample contains three stars with proper motions larger than 20 mas/year. Four of the five stars in the test region with colors indicating spectral type M2 or later have statistically significant proper motions.