NEW SPACE MOTION OF GALACTIC GLOBULAR-CLUSTER PALOMAR-5

A new space motion of the Galactic globular cluster Pal 5 has been obt ained on the basis of the proper motion determination from 11 Schmidt plates with a time baseline of 39 years. A field of 1 square degree wi th nearly 400 galaxies defining the absolute reference frame has been used in the differential astrometry from plate-to-plate solutions. Res idual systematic errors after the solutions with 2 x 6 plate constant polynomials have been investigated and removed. Typical proper motion errors of 2 to 3 mas/yr were obtained for individual stars with magnit udes 12 < B < 20. Although our result for the mean absolute proper mot ion of Pal 5 (mu(alpha)/l(delta)) = (-1.0 +/- 0.3, -2.7 +/- 0.4) mas/y r looks similar to the result of Schweitzer, Cudworth & Majewski (1993 ) based on different observations and reduction technique, the directi on of the space motion we derive is completely different from theirs. Although the position of Pal 5 is near the orbital plane suggested for the Sagittarius dwarf galaxy by Ibata et al. (1997), both proper moti on results suggest a total space velocity of Pal 5 significantly diffe rent from that to be expected from a tidally stripped fragment of the Sgr dwarf galaxy. In addition, our direction of motion of Pal 5 is alm ost in the opposite sense to that of the Sgr galaxy. Our Galactic orbi t determination of Pal 5 and the star counts on the deep Schmidt plate s indicate a smaller tidal radius of this globular cluster compared to previously published data of Webbink (1985) and Trager, King & Djorgo vski (1995).