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تسجيل مستخدم جديدThe combination of ground-based astrometric compilation catalogues with the HIPPARCOS Catalogue I. Single-star mode
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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 the combination of the basic FK5 with the HIPPARCOS Catalogue (i.e., in the FK6), the gain in accuracy is about a factor of two for the proper motions of single stars. The use of the GC still improves the accuracy of the proper motions by a factor of about 1.2. We derive and describe in detail how to combine a ground-based compilation catalogue with HIPPARCOS. Our analytic approach is helpful for understanding the principles of the combination method. In real applications we use a numerical approach which avoids some (minor) approximations made in the analytic approach. We give a numerical example of our combination method and present an overall error budget for the combination of the ground-based data for the basic FK5 stars and for the GC stars with the HIPPARCOS observations. In the present paper we describe the single-star mode of our combination method. This mode is appropriate for truly single stars or for stars which can be treated like single stars. The specific handling of binaries will be discussed in subsequent papers.
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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, 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 T_H ~ 1991.25, and a linear short-term prediction (STP mode) for epochs close to T_H. 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 catalog 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.
The combination of HIPPARCOS measurements with suitable ground-based astrometric data improves significantly the accuracy of the proper motions of bright stars. The comparison of both types of data allows us also to identify and to eliminate, at leas
t partially, cosmic errors in the quasi-instantaneously measured HIPPARCOS data which are caused by undetected astrometric binaries. We describe a simple averaging method for the combination of two independent compilation catalogues. The combination of the basic FK5 with HIPPARCOS leads to the Sixth Catalogue of Fundamental Stars (FK6). The accuracy of the FK6 proper motions is higher than that of HIPPARCOS by a factor of about 2 in the single-star mode, and by a factor of more than 4 in the long-term prediction mode which takes cosmic errors into account. We present also the error budget for a combination of the Boss General Catalogue (GC) with HIPPARCOS data. We point out problems with known binaries, and identify an ensemble of astrometrically excellent stars.
We present VIRAC version 1, a near-infrared proper motion and parallax catalogue of the VISTA VVV survey for 312,587,642 unique sources averaged across all overlapping pawprint and tile images covering 560 deg$^2$ of the bulge of the Milky Way and so
uthern disk. The catalogue includes 119 million high quality proper motion measurements, of which 47 million have statistical uncertainties below 1 mas yr$^{-1}$. In the 11$<K_s<$14 magnitude range the high quality motions have a median uncertainty of 0.67 mas yr$^{-1}$. The catalogue also includes 6,935 sources with quality-controlled 5 $sigma$ parallaxes with a median uncertainty of 1.1 mas. The parallaxes show reasonable agreement with the TYCHO-Gaia Astrometric Solution (TGAS), though caution is advised for data with modest significance. The SQL database housing the data is made available via the web. We give example applications for studies of Galactic structure, nearby objects (low mass stars and brown dwarfs, subdwarfs, white dwarfs) and kinematic distance measurements of YSOs. Nearby objects discovered include LTT 7251 B, an L7 benchmark companion to a G dwarf with over 20 published elemental abundances, a bright L sub-dwarf, VVV 1256-6202, with extremely blue colours and nine new members of the 25 pc sample. We also demonstrate why this catalogue remains useful in the era of Gaia. Futur
The statistical test described by Wielen et al.(1994) is used to derive new zero-points of ground-based Cepheid period-luminosity (PL) and period-luminosity-colour (PLC) relations. Eleven relations are compared with the Hipparcos data. Our results ar
gue for a typical increase of the adopted distance scale by about 8% +- 8%. Our zero-point for the PL relation of Caldwell & Laney (1991) is in agreement with that of Feast & Catchpole (1997).
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