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

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Abstract
We present a catalog of 1147 candidate common proper motion binaries selected from the revised New Luyten Two-Tenths Catalog (NLTT). 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 pairs (801), halo subdwarf (116) pairs, or pairs containing at least one white dwarf (82). The disk and halo samples are complete to separations of Deltatheta = 500" and Deltatheta = 900", which correspond to similar to0.1 and similar to1 pc, respectively. At wide separations, both distributions are well described by single power laws dN/dDeltatheta proportional to (Deltatheta)(-alpha), with 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 similar to1 pc permits strong constraints on halo dark matter candidates. At somewhat closer separations (10"less than or similar toDeltathetaless than or similar to25"), 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.