CCD ASTROMETRY OF ASTEROIDS IN THE EXTRAGALACTIC REFERENCE FRAME

This paper describes observations of asteroids made with the Flagstaff Astrometric Scanning Transit Telescope (FASTT), which is a 20 cm CCD transit telescope that can observe objects brighter than V similar to 17.5 mag directly in the extragalactic reference frame. This is accomp lished with differential reductions using ancillary FASTT observations of VI,BI radio reference objects [see Stone et al., AJ, 111, 1721 (19 96) for more details]. Positions determined with the FASTT are accurat e to +/-0.14 and +/-0.17 arcsec, respectively, in right ascension and declination for a single observation and are considerably more accurat e than most positions determined for asteroids. Currently, the FASTT i s observing asteroids for a number of projects that require very accur ate positions. Namely, the FASTT is supporting the NEAR spacecraft mis sion by determining positions for the targeted asteroids 253 Mathilde and 433 Eros, and previously, FASTT observations of the asteroids 951 Gaspra and 243 Ida were made in support of the Galileo project. When c ompared with accurate JPL ephemerides computed for these asteroids, di fferences between FASTT observed and JPL calculated positions were gen erally small (<0.08 arcsec), and the rms scatter comparing these resul ts was typically +/-0.18 arcsec in both coordinates. Moreover, the FAS TT is observing a number of asteroids that are gravitationally interac ting with other asteroids, and hopefully with enough observations, mas ses can be determined dynamically for some of them. There are only a f ew asteroids with accurate mass determinations. Approximately 1000 obs ervations of these asteroids have been taken with the FASTT with an ac curacy of similar to+/-0.16 arcsec in each coordinate. Finally, the FA STT is observing asteroids and stars that might be involved in occulta tion events. FASTT observations are being used to create accurate ephe merides for the asteroids involved as well as to determine very accura te positions for the background occultation stars. In particular, FAST T positional data were used in making the predictions for several rece nt successfully observed occultations (e.g., 654 Zelinda and 85 Io).