Abstract. The combination of ground-based astrometric compilation catalogues, such as the FK5 or the GC, with the results of the ESA Astrometric Satellite HIPPARCOS produces for many thousands of stars proper motions which are significantly more accurate than the proper motions derived from the HIPPARCOS observations alone. In Paper I (Wielen, et al. 1999(Wielen, et al. , A&A, 347, 1046 we have presented a method of combination for single stars (SI mode). The present Paper II derives a combination method which is appropriate for an ensemble of "apparently single-stars" which contains undetected astrometric binaries. In this case the quasi-instantaneously measured HIPPARCOS proper motions and positions are affected by "cosmic errors", caused by the orbital motions of the photo-centers of the undetected binaries with respect to their center-of-mass. In contrast, the ground-based data are "mean values" obtained from a long period of observation. We derive a linear "long-term prediction" (LTP mode) for epochs far from the HIPPARCOS epoch TH ∼ 1991.25, and a linear "short-term prediction" (STP mode) for epochs close to TH. The most accurate prediction for a position at an arbitrary epoch is provided by a smooth, non-linear transition from the STP solution to the LTP solution. We present an example for the application of our method, and we discuss the error budget of our method for the FK6 (a combination of the FK5 with HIPPARCOS) and for the combination catalogue GC+HIP. For the basic fundamental stars, the accuracy of the FK6 proper motions in the LTP mode is better than that of the HIPPARCOS proper motions (taking here the cosmic errors into account) by a factor of more than 4.
This contribution gives some results on the kinematics and ages of stars near the Sun. These results are mainly based on the catalogue of nearby stars compiled by Gliese (1957, 1969 and minor recent modifications). Table I shows the number of objects under consideration. While the old catalogue (1957) contained only stars with distances r up to 20 pc, the new edition (1969) includes many stars with slightly larger distances. In Table I, a ‘system’ is either a single star or a binary or a multiple system. The number of systems with known space velocities nearer than 20 pc has increased by about 30% from 1957 to 1969. The first edition of Gliese’s catalogue (1957) has been analyzed in detail by Gliese (1956) and von Hoerner (1960).
Abstract.We present an analysis of the space motions of 742 subdwarf stars based on the sample of Carney et al. (1994, AJ, 107, 2240. Hipparcos parallaxes, TYC2+HIP proper motions and Tycho 2 proper motions were combined with radial velocities and metallicities from CLLA. The kinematical behavior is discussed in particular in relation to their metallicities. The majority of these sample stars have metal abundances of [Fe/H] > −1 and represent the thick disk population. The halo component, with [Fe/H] < −1.6, is characterized by a low mean rotation velocity and a radially elongated velocity ellipsoid. In the intermediate metallicity range (−1.6 ≤ [Fe/H] ≤ −1), we find a significant number of subdwarfs with disklike kinematics. We interpret this population of stars as a metal-weak thick disk (MWTD) population.
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