Disk and Halo Wide Binaries from the Revised Luyten Catalog: Probes of Star Formation and MACHO Dark Matter

Abstract

We present a catalog of 1147 candidate common proper motion binaries selected from the revised New Luyten Two-Tenths Catalog. Among these, we identify 999 genuine physical pairs using the measured proper-motion difference and the relative positions of each binary's components on a reduced proper-motion (RPM) diagram. The RPM positions also serve to classify them as either disk main-sequence (801), halo subdwarf (116), or pairs containing at least one white dwarf (82). The disk and halo samples are complete to separations of \theta=500" and \theta=900", which correspond to ~0.1 pc and ~1 pc, respectively. At wide separations, both distributions are well described by single power laws, dN/d\theta ~ \theta^{-\alpha}: \alpha=1.67+-0.07 for the disk and \alpha=1.55+-0.10 for the halo. The fact that these distributions have similar slopes (and similar normalizations as well) argues for similarity of the star-formation conditions of these two populations. The fact that the halo binaries obey a single power law out to ~1 pc permits strong constraints on halo dark-matter candidates. At somewhat closer separations (10"<\theta<25"), the disk distribution shows a pronounced flattening, which is detected at very high statistical significance and is not due to any obvious systematic effect. We also present a list of 11 previously unknown halo stars with parallaxes that are recognized here as companions of Hipparcos stars.