Information on resource 'ARIHIP astrometric catalogue'

The ARIHIP Catalogue is a suitable combination of the results of the HIPPARCOS astrometry satellite with ground-based data.

The ARIHIP contains 90842 stars in total. The best astrometric data for 90072 of these ARIHIP stars have been selected from the direct solutions given in the combination catalogues FK6(I), FK6(III), GC+HIP, and TYC2+HIP. Such direct solutions are appropriate for single stars or for objects which can be treated like single stars. For these 90072 stars with direct solutions, ground-based measurements have contributed to the astrometric data (mainly to the proper motions).

In addition the ARIHIP contains the original HIPPARCOS solutions for 770 stars which do not occur in one of these combination catalogues but are basically qualified for direct solutions.

Besides the astrometric data, the ARIHIP provides a variety of flags which inform about the known (or possible) binarity of each object. From the 90842 stars in the ARIHIP we have selected 73023 objects as "astrometrically excellent stars", since their instantaneous proper motions and mean (time-averaged) ones do not differ significantly. Hence most of the astrometrically excellent stars are well-behaving "single-star candidates" with good astrometric data. These stars are most suited for high-precision astrometry.

On the other hand, 2827 of the stars in the ARIHIP are Δμ binaries in the sense of Wielen et al. (1999). Many of them are newly discovered probable binaries with no other hitherto known indication of binarity. The ARIHIP gives, besides the classical "single-star mode" solutions (SI mode), other solutions which take into account the fact that hidden astrometric binaries among "apparently single-stars" introduce sizable "cosmic errors" into the quasi-instantaneously measured HIPPARCOS proper motions and positions.

The ARIHIP gives in addition to the SI mode the "long-term prediction (LTP) mode" and the "short-term prediction (STP) mode". These LTP and STP modes are on average the most precise solutions for apparently single stars, depending on the epoch difference with respect to the HIPPARCOS epoch of about 1991. The typical mean error of an ARIHIP proper motion in the single-star mode is 0.89 mas/year. This is about a factor of 1.3 better than the typical HIPPARCOS errors for these stars of 1.13 mas/year.

In the long-term prediction mode, in which cosmic errors are taken into account, the ARIHIP proper motions have a typical mean error of 1.15 mas/year, which is by a factor of more than 1.6 better than the corresponding error for the HIPPARCOS values of 1.89 mas/year (cosmic errors included).

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