Completeness of USNO-B for High Proper-Motion Stars

I test the completeness of USNO-B detections of high proper-motion (μ > 180mas yr) stars and the accuracy of its measurements by comparing them to the revised NLTT (rNLTT) catalog of Salim & Gould. For 14.5 < V < 18.5, only 6% of such stars are missing from USNO-B while another 4% have large errors, mostly too large to be useful. Including both classes, incompleteness is 10%. These fractions rise toward both brighter and fainter magnitudes. Incompleteness rises with proper motion to ∼ 30% at μ = 1 yr. It also rises to ∼ 35% at the Galactic plane, although this is only determined for relatively bright stars V . 14. For binaries, incompleteness rises from 10% at separations of 30 to 47% at 10. The proper-motion errors reported internally by USNO-B are generally correct. However, there is floor of σμ ∼ 4mas yr −1 below which the reported errors should not be taken at face value. The small number of stars with relatively large reported errors (σμ & 20mas yr ) may actually have still larger errors than tabulated. Subject headings: astrometry – methods: statistical