next previous
Up: A proper motion study

1 Introduction

Globular clusters are important tracers of the chemical and dynamical evolution of the Milky Way. Since the orbits of globular clusters may have kept their characteristics from the early times of the formation of the Milky Way, we may extract from their kinematics some clues for the understanding of the origin of the Milky Way. However so far for only some 40 globular clusters absolute proper motions exist (Dinescu et al. 1999), which partly are of low quality (e.g. Dauphole et al. 1996). Nevertheless on the basis of a sample of 26 globular clusters Dauphole et al. (1996) found an indication of a metallicity gradient among the halo clusters and a mean rotation of about +40  km s-1  for the complete globular cluster sample. Additional data especial for southern clusters were determined by Dinescu et al. (1999 and references herein).

The results of the Hipparcos mission offer new possibilities for the determination of absolute proper motions of globular clusters and other objects of interest for galactic kinematics. Since previous studies have used mainly extragalactic objects as proper motion zero points, the use of Hipparcos reference stars offers a unique possibility for the determination of absolute proper motions at low galactic latitutes without suitable extragalactic background objects. Geffert et al. (1997) have determined absolute proper motions of 10 globular clusters with respect to Hipparcos. These were combined with data of 5 other clusters and the kinematics of this sample was studied by Brosche et al. (1997) and Odenkirchen et al. (1997). A complete discussion of these data together with additional proper motions was given recently in Dinescu et al. (1999). M 10 is a globular cluster located very near to the direction to the galactic center ( $l=15^\circ$, $b=23^\circ$), but at a distance of only 4.3 kpc from the Sun. Due to its metallicity of $[\mbox{Fe/H}] = -1.52\;$dex (Harris 1996) it belongs to the halo group of clusters according to Zinn's (1985) classification. The preliminary kinematical data of M 10 (Geffert et al. 1997) indicate a disk like motion, the most disk like motion found in the group of globular clusters, whose proper motions were determined using Hipparcos (Odenkirchen et al. 1997). However, this preliminary proper motion has the problem that only three to four Hipparcos stars could be used for the reduction of the plates. This made the previous solution very uncertain. Here we have included new photographic material (from Shanghai) and recent CCD observations to get a new determination of the absolute proper motion of M 10. Moreover, we use in addition to the Hipparcos catalogue the ACT catalogue (Urban et al. 1998). The ACT catalogue, due to its denser coverage of the sky, allows the use of more reference stars for the determination of the absolute proper motions.

Table 1: Photographic material used in this work

Plate No.
Epoch Emulsion Telescope

1902.6   DR HL
406 1905.6   R SH
262 1916.5   DR HL
309 1917.5   DR HL
312 1917.5   DR HL
314 1917.5   DR HL
CL57016 1957.5 103a-O R SH
CL57031 1957.6 103a-O R SH
CL57033 1957.6 103a-O R SH
1232 1976.6 IIa-O/BG 25 DR HL
1874 1994.5 IIa-O/BG 25 DR HL
1875 1994.5 IIa-O/BG 25 DR HL

DR HL = (D=0.3 m, f=5.1 m) double refractor of Bonn.
R SH = (D=0.4 m, f=7.0 m) refractor of Shanghai observatory.

next previous
Up: A proper motion study

Copyright The European Southern Observatory (ESO)