AN X-RAY SELECTED WHITE-DWARF PLUS M-DWARF BINARY - RX-J0458.9-6628

A new close binary containing a DA white dwarf and a dwarf M star has been identified from its X-ray emission. The spectra of both stars are seen with about equal flux at similar to 4600 Angstrom. H and Ca II e mission, associated with the M star, is also present, Limited photomet ry does not show any variability, but radial-velocity changes indicate the binary period lies in the range from similar to 0.7 to a few days . The small observed velocity range and lack of pronounced emission-li ne changes suggest a low-inclination system. The DA velocities are poo rly determined but suggest the unlikely conclusion that it may be the less massive star in the binary.