2004ApJ...601..289C

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 Δθ=500'' and Δθ=900'', which correspond to ∼0.1 and ∼1 pc, respectively. At wide separations, both distributions are well described by single power laws dN/dΔθ∝(Δθ)^–α, with α=1.67±0.07 for the disk and α=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''≲Δθ≲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.