Our results demonstrate the importance of the new astrometric catalogues (Hipparcos, ACT) for the determination of absolute proper motions of objects located in the galactic plane. For these objects no extragalactic link of the proper motion system is available due to the absence of suitable objects. We show that the differences between the solutions based on the ACT catalogue and the corresponding one based on the Hipparcos catalogue are small. Although this result has to be checked using data of other fields, it would offer a range of applications for the ACT catalogue because of its larger number of stars. Moreover, even reaching only moderate accuracy on the wide field CCD frames with respect to small field CCD observations, our results indicate that these observations may supersede the photographic plates in near future.
The new data of M 10 show an eccentricity of the orbit of 0.41, which would place the cluster now in the range of eccentricities from 0.4 to 0.8 found for the majority of the globular clusters (Odenkirchen et al. 1997). The rotational velocity changed to km s-1 with respect to the km s-1 found in Odenkirchen et al. (1997). According to its moderate eccentricity and rotational velocity, M 10 belongs rather to the halo class of objects. This is in line with its metallicity. However, the z-distance from the galactic plane does not exceed 3 kpc, which would be more characteristic for a thick disk object.
As noted already in Dinescu et al. (1999) recent age determinations (Hurley et al. 1989; Richer et al. 1996; Chaboyer et al. 1996; Buonano et al. 1998) agree that M 10 is an old halo cluster. Together with NGC 6626, NGC 6752 (Dinescu et al. 1999) and M 71, which has according to Geffert & Maintz (2000) a much higher age, M 10 establishes a group of high age globular clusters with orbits of a disk or thick disk character. This result would imply that at the time when the oldest globular clusters were born, the Milky Way had already a gas distribution with a disk component, where the gas enabled the formation of clusters. On the other hand the recent age determination by Rosenberg et al. (1999) places M 10 in the middle of the age distribution of globular clusters.
Piotto & Zoccali (1999) have found an unusual steep luminosity function of M 10 in comparison with other clusters. Our data indicate that this luminosity function was generated more likely by internal dynamics of the cluster than by the motion in the Galaxy. If the luminosity function would be affected by the crossing of the cluster through the galactic plane, one would rather expect a more flat luminosity function for M 10 due to the evaporation of faint stars as it was found recently for the globular cluster NGC 6712 (De Marchi et al. 1999).
We are indebted to H.-J. Tucholke (Bonn) for measuring some of the refractor plates. It is a pleasure to thank K.S. de Boer (Bonn) for helpful discussions. This research has made use of the Simbad database (see Wenger et al. 2000), operated at CDS, Strasbourg, France.
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