New space motion of the Galactic globular cluster Palomar 5


Ralf-Dieter Scholz, Potsdam, Mike Irwin, Cambridge/UK, Michael Odenkirchen, Bordeaux, Helmut Meusinger, Tautenburg


Complete text (abstract only):

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 (Scholz et al. 1998). 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 2 × 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 magnitudes 12 < B < 20 . Although our result for the mean absolute proper motion of Pal 5 (µRA, µDec) = (-1.0 ± 0.3, -2.7 ± 0.4) mas/yr looks similar to the result of Schweitzer, Cudworth & Majewski (1993) 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. (1997), 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 as suggested by Lin (1996). 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 (1985) and Trager, King & Djorgovski (1995).



Ibata R.A., Wyse R.F.G., Gilmore G., Irwin M.J., Suntzeff N.B., 1997, AJ 113, 634

Lin D.N.C., 1996, The mass of the Galactic halo, Magellanic stream, Galactic satellites, and the warp of the Galactic disk. In: O. Lahav, E. Terlevich, R.J. Terlevich (eds.), Gravitational dynamics, Cambridge University Press, Cambridge, p. 15

Scholz R.-D., Irwin M., Odenkirchen M., Meusinger H., 1998, A&A 333, 531

Schweitzer A.E., Cudworth K., Majewski S., 1993, ASP Conf. Ser. 48, 113

Trager S.C., King I.R., Djorgovski S., 1995, AJ 109, 218

Webbink R.F., 1985, Structure parameters of Galactic globular clusters, In: Goodman J., Hut P. (eds.), Dynamics of Star Clusters, Proc. IAU Symp. 113, Kluwer Acad. Publ., Dordrecht, p. 541

Bibliographical details:

Ralf-Dieter Scholz, Mike Irwin, Michael Odenkirchen, Helmut Meusinger: New space motion of the Galactic globular cluster Palomar 5. In: Peter Brosche, Wolfgang R. Dick, Oliver Schwarz, Roland Wielen (Eds.): The Message of the Angles - Astrometry from 1798 to 1998. Proceedings of the International Spring Meeting of the Astronomische Gesellschaft, Gotha, May 11-15, 1998. (Acta Historica Astronomiae; 3). Thun ; Frankfurt am Main : Deutsch, 1998, p. .