Rapid Oscillations in Cataclysmic Variables. XV. HT Camelopardalis (=RX J0757.0+6306)

We present photometry and spectroscopy of HT Camelopardalis, a recently discovered X‐ray–bright cataclysmic variable. The spectrum shows bright lines of H, He i, and He ii, all moving with a period of 0.059712(1) days, which we interpret as the orbital period. The star’s brightness varies with a strict period of 515.0592(2) s and a mean full amplitude of 0.11 mag. These properties qualify it as a bona fide DQ Herculis star (intermediate polar), in which the magnetism of the rapidly rotating white dwarf channels accretion flow to the surface. Normally at V = 17.8, the star shows rare and very brief outbursts to V = 12–13. We observed one in 2001 December and found that the 515 s pulse amplitude had increased by a factor of ∼100 (in flux units). A transient orbital signal may have appeared as well.