Orbital periods of cataclysmic variables identified by the SDSS - V. VLT, NTT and Magellan observations of nine equatorial systems

Abstract

ABSTRACT We present Very Large Telescope (VLT) and Magellan spectroscopy and New Technology Telescope photometry of nine faint cataclysmic variables (CVs) which were spectroscopically identified by the Sloan Digital Sky Survey (SDSS). We measure orbital periods for five of these from the velocity variations of the cores and wings of their Hα emission lines. Four of the five have orbital periods shorter than the 2-3 h period gap observed in the known population of CVs. SDSS J004335.14-003729.8 has an orbital period of Porb = 82.325 ± 0.088 min; Doppler maps show emission from the accretion disc, bright spot and the irradiated inner face of the secondary star. In its light curve, we find a periodicity which may be attributable to pulsations of the white dwarf. SDSS J163722.21-001957.1 has Porb = 99.75 ± 0.86 min. By combining this new measurement with a published superhump period, we estimate a mass ratio of q ≈ 0.16 and infer the physical properties and orbital inclination of the system. For SDSS J164248.52+134751.4, we find Porb = 113.60 ± 1.5 min. The Doppler map of this CV shows an unusual brightness distribution in the accretion disc which would benefit from further observations. SDSS J165837.70+184727.4 had spectroscopic characteristics which were very different between the SDSS spectrum and our own VLT observations, despite only a small change in brightness. We measure P orb = 98.012 ± 0.065 min from its narrow Hα emission line. Finally, SDSS J223843.84+010820.7 has a comparatively longer period of Porb = 194.30 ± 0.16 min. It contains a magnetic white dwarf and, with g = 18.15, is brighter than the other objects studied here. These results continue the trend for the fainter CVs identified by the SDSS to be almost exclusively shorter period objects with low mass transfer rates. © 2008 RAS.