Absolute Proper Motions to B ～22.5. IV. Faint, Low-Velocity White Dwarfs and the White Dwarf Population Density Law

摘要

The reduced proper-motion diagram (RPMD) for a complete sample of 819 faint (B≤ 22.5) stars with high-accuracy proper motions σμ～1 mas yr~-1) in an area of 0.3 deg~2 in the north Galactic pole field SA 57 is investigated. Eight stars with very large reduced proper motions are identified as faint white dwarf candi- dates. On the basis of larger than 6 σeasured proper motions and the lack of photometric variability over a 20 yr baseline, we discriminate these white dwarf candidates from the several times more numerous quasi- stellar objects (QSOs), which can potentially occupy a similar location in the RPMD.