QZ Serpentis: A Dwarf Nova with a 2 Hour Orbital Period and an Anomalously Hot, Bright Secondary Star*

摘要: We present spectroscopy and time-series photometry of the dwarf nova QZ Ser. The spectrum shows a rich absorption-line type K4 ± 2. K-type secondary stars are generally seen in novae with orbital periods Porb ~ 6 hr, but Ser absorption radial velocities show an obvious modulation [semiamplitude 207(5) km s-1] at = 119.752(2) minutes, much shorter than typical for such relatively warm prominent spectrum. Hα emission-line velocity is modulated same period roughly opposite phase. Time-series flickering superposed on two humps per orbit, consistent ellipsoidal variation secondary's light. second example short surprisingly secondary. Model calculations suggest that strongly enhanced helium had already undergone significant nuclear evolution when mass transfer began. Several sodium features unusually strong, which may indicate present-day surface was site CNO-cycle hydrogen burning past.