1998A&A...333..531S

A new space motion of the Galactic globular cluster Pal 5 has been obtained 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 with nearly 400 galaxies defining the absolute reference frame has been used in the differential astrometry from plate-to-plate solutions. Residual systematic errors after the solutions with 2x6 plate constant polynomials have been investigated and removed. Typical proper motion errors of 2 to 3mas/yr were obtained for individual stars with magnitudes 12<B<20. Although our result for the mean absolute proper motion of Pal 5 (µ_α, µ_δ)=(-1.0±0.3, -2.7±0.4) mas/yr looks similar to the result of Schweitzer, Cudworth & Majewski (1993, ASP Conf. Ser., 48, 113) based on different observations and reduction technique, the direction 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. (1997AJ....113..634I), both proper motion results suggest a total space velocity of Pal 5 significantly different 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 almost in the opposite sense to that of the Sgr galaxy. Our Galactic orbit determination of Pal 5 and the star counts on the deep Schmidt plates indicate a smaller tidal radius of this globular cluster compared to previously published data of Webbink (1985IAUS..113..541W) and Trager, King & Djorgovski (1995AJ....109..218T).