Astrometric authentication of RX J2309.8+2135 as a nearby dwarf nova candidate

Abstract

RX J2309.8+2135 = 1RXS J230949.6+213523 is an X-ray source discovered through the ROSAT all-sky survey. The object was later identified with a star showing a spectrum resembling a cataclysmic variable (CV). Schwope et al. (2002, astro-ph/0210059) recently proposed the spectral type of M3, which would indicate a small distance. We have detected a large proper motion (~69 mas/yr) of this object. This detection authenticates RX J2309.8+2135 as a nearby dwarf nova candidate. Even at a reasonable distance of ~100 pc, which is inferred from the measured proper motion, the outburst maxima of RX J2309.8+2135 would reach V~9. RX J2309.8+2135 may belong to a hitherto unidentified class of long-period CVs with the lowest mass-transfer rates.