An improved catalog of halo wide binary candidates

TL;DR

This paper presents an improved catalog of halo wide binary candidates, analyzing their properties, membership, and orbital characteristics to better understand the halo population and its dynamics.

Contribution

The paper compiles and verifies a comprehensive catalog of halo wide binaries, including new membership assessments and orbital calculations, enhancing previous datasets.

Findings

Distribution of binary separations follows a power law up to certain limits.

Halo-like binaries have larger maximum separations than disk-like binaries.

The catalog is used to constrain the masses of halo MACHOs in a companion study.

Abstract

We present an improved catalog of halo wide binaries, compiled from an extensive literature search. Most of our binaries stem from the common proper motion binary catalogs by Allen et al. (2004), and Chanam\'e \& Gould. (2004) but we have also included binaries from the lists of Ryan (1992) and Zapatero-Osorio \& Martin (2004). All binaries were carefully checked and their distances and systemic radial velocities are included, when available. Probable membership to the halo population was tested by means of reduced proper motion diagrams for 251 candidate halo binaries. After eliminating obvious disk binaries we ended up with 211 probable halo binaries, for 150 of which radial velocities are available. We compute galactic orbits for these 150 binaries and calculate the time they spend within the galactic disk. Considering the full sample of 251 candidate halo binaries as well as several subsamples, we find that the distribution of angular separations (or expected major semiaxes) follows a power law $f(a) \sim a^{-1}$ (Oepik's relation) up to different limits. For the 50 most disk-like binaries, those that spend their entire lives within $z = \pm 500$~pc, this limit is found to be 19,000 AU (0.09 pc), while for the 50 most halo-like binaries, those that spend on average only 18\% of their lives within $z = \pm 500$~pc, the limit is 63,000 AU (0.31 pc). In a companion paper we employ this catalog to establish limits on the masses of the halo massive perturbers (MACHOs).