The Galactic kinematics of cataclysmic variables

Abstract

Kinematical properties of CVs were investigated according to population types and orbital periods, using the space velocities computed from recently updated systemic velocities, proper motions and parallaxes. Reliability of collected space velocity data was refined by removing 34 systems with largest space velocity errors. The 216 CVs in the refined sample were shown to have a dispersion of 53.70 +/- 7.41 kms(-1) corresponding to a mean kinematical age of 5.29 +/- 1.35 Gyr. Population types of CVs were identified using their Galactic orbital parameters. According to the population analysis, seven old thin disc, nine thick disc and one halo CV were found in the sample, indicating that 94 % of CVs in the Solar Neighbourhood belong to the thin-disc component of the Galaxy. Mean kinematical ages 3.40 +/- 1.03 and 3.90 +/- 1.28 Gyr are for the nonmagnetic thin-disc CVs below and above the period gap, respectively. There is not a meaningful difference between the velocity dispersions below and above the gap. Velocity dispersions of the non-magnetic thin-disc systems below and above the gap are 24.95 +/- 3.46 and 26.60 +/- 4.18 kms(-1), respectively. This result is not in agreement with the standard formation and evolution theory of CVs. The mean kinematical ages of the CV groups in various orbital period intervals increase towards shorter orbital periods. This is in agreement with the standard theory for the evolution of CVs. Rate of orbital period change was found to be dP/dt =-1.62(+/- 0.15) x10(-5) sec yr(-1).