Completeness of USNO-B for High Proper Motion Stars

I test the completeness of USNO-B detections of high proper motion (μ > 180 mas yr -1 ) stars and the accuracy of its measurements by comparing them to the revised New Luyten Two-Tenths catalog of Salim & Gould. For 14.5 < V < 18.5, only 6% of such stars are missing from USNO-B, while another 3% have large errors, mostly too large to be useful. Including both classes, incompleteness is 9%. These fractions rise toward both brighter and fainter magnitudes. Incompleteness rises with proper motion to ∼30% at μ = 1'' yr -1 . 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 9% 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 σ μ ∼ 4 mas yr -1 below which the reported errors should not be taken at face value. The small number of stars with relatively large reported errors (σ μ ≳ 20 mas yr -1 ) may actually have still larger errors than tabulated.