Proper-motion binaries in the Hipparcos Catalogue. Comparison with radial velocity data

TL;DR

This study identifies candidate binary star systems in the Hipparcos Catalogue by comparing proper motions with Tycho-2 data, evaluating detection efficiency using radial velocity data, and exploring the properties of various binary types.

Contribution

It introduces a method to detect proper-motion binaries using catalog comparisons and assesses its effectiveness with control data, including radial velocities and known binary samples.

Findings

Efficient detection of binaries with parallaxes >20 mas and periods 1000-30000 days.

Identification of 19 candidate triple systems.

Limited evidence for low-mass companions among barium stars.

Abstract

The comparison of the proper motions constructed from positions spanning a short (Hipparcos) or long time (Tycho-2) makes it possible to uncover binaries with periods of the order of or somewhat larger than the short time span, since the unrecognised orbital motion will then add to the proper motion. A list of candidate proper motion binaries is constructed from a chi^2 test evaluating the statistical significance of the difference between the Tycho-2 and Hipparcos proper motions for 103134 stars in common between the two catalogues (excluding components of visual systems). The paper focuses on the evaluation of the detection efficiency of proper-motion binaries, using different kinds of control data (mostly radial velocities). The detection rate for entries from the Ninth Catalogue of Spectroscopic Binary Orbits (SB9) is evaluated, as well as for stars like barium stars, which are known to be all binaries. Proper motion binaries are efficiently detected for systems with parallaxes in excess of ca. 20 mas, and periods in the range 1000 - 30000 d. The shortest periods in this range (1000 - 2000 d) may appear only as DMSA/G binaries (accelerated proper motion in the Hipparcos Double and Multiple System Annex). Proper motion binaries detected among SB9 systems having periods shorter than about 400 d hint at triple systems. A list of 19 candidate triple systems is provided. Binaries suspected of having low-mass (brown-dwarf-like) companions are listed as well. Among the 37 barium stars with parallaxes larger than 5 mas, only 7 exhibit no evidence for duplicity whatsoever (be it spectroscopic or astrometric). Finally, the fraction of proper-motion binaries shows no significant variation among the various (regular) spectral classes, when due account is taken for the detection biases.