Abstract
We constructed an improved catalog of halo wide binaries, compiled from an extensive literature search. Probable membership to the halo population was checked by means of reduced proper motion diagrams for 252 candidate halo binaries. After eliminating disk stars we end up with 212 probable halo binaries, for 150 of which galactic orbits could be computed, and the time they spend within the galactic disk calculated. Taking the full sample of 252 candidate halo binaries as well as several subsamples, we find that the distribution of angular separations (or expected major semiaxes) follows a power law with an exponent -1 (Oepik's relation) up to different limits. For the 50 most disk-like binaries, those that spend their lives entirely within z = ±500 pc, this limit is found to be 19000 au, while for the 50 most halo-like binaries, those that spend on average only 0.18 of their lives within z = ±500 pc, the limit is 63000 au. We employ this catalog to establish limits on the masses of the halo massive perturbers (MACHOs). We find that different subsamples of binaries give different upper limits for that MACHO mass. Taking into account the dynamical effects of the disk on the passing binaries, as well as the non-uniform density of the halo, we obtain 13 M_⊙ as an upper limit for the mass of the MACHOs. This limit, together with lower limits on their mass from other studies, practically excludes their existence in the galactic halo.
