Orbital periods of cataclysmic variables identified by the SDSS. II. Measurements for six objects, including two eclipsing systems

摘要

Continuing our work from Paper I (Southworth et al., 2006) we presentmedium-resolution spectroscopy and broad-band photometry of seven cataclysmicvariables (CVs) discovered by the SDSS. For six of these objects we deriveaccurate orbital periods, all which are measured for the first time. For SDSSJ013132.39+090122.2, which contains a non-radially pulsating white dwarf, wefind an orbital period of 81.54 +/- 0.13 min and a low radial velocityvariation amplitude indicative of an extreme mass ratio. For SDSSJ205914.87+061220.4, we find a period of 107.52 +/- 0.14 min. This object is adwarf nova and was fading from its first recorded outburst throughout ourobservations. INT photometry of SDSS J155531.99-001055.0 shows that this systemundergoes total eclipses which are 1.5 mag deep and occur on a period of 113.54+/- 0.03 min. A NOT light curve of SDSS J075443.01+500729.2 shows that thissystem is also eclipsing, on a period of 205.965 +/- 0.014 min, but here theeclipses are V-shaped and only 0.5 mag deep. Its low emission-line strengths,orbital period and V-shaped eclipse unambiguously mark it as a novalike object.WHT photometry of SDSS J005050.88+000912.6 and SDSS J210449.94+010545.8 yieldsperiods of 80.3 +/- 2.2 and 103.62 +/- 0.12 min, respectively. Photometry ofthe seventh and final system, SDSS J165658.12+212139.3, shows only flickering.Our results strengthen the conclusion that the faint magnitude limit of theSDSS spectroscopic database implies that the sample of CVs contained in it hasquite different characteristics to previously studied samples of these objects.Five of the six orbital periods measured here are shorter than the observed 2-3hr CV period gap. Two systems have periods very close to the minimum orbitalperiod for hydrogen-rich CVs.