A Sample of Cataclysmic Variables from the 400d X-Ray Survey

We present a sample of eight cataclysmic variables (CVs) identified among the X-ray sources of the 400 square degree (400d) X-ray ROSAT/PSPC survey. Based on this sample, we have obtained preliminary constraints on the X-ray luminosity function of CVs in the solar neighbourhood in the range of low luminosities, L_X∼10²⁹-10³⁰ erg s^-1 (0.5-2 keV). We show that the logarithmic slope of the CV luminosity function in this luminosity range is less steep than that at L_X >10³¹ erg s^-1. Our results show that of order of thousand CVs will be detected in the SRG/eROSITA all-sky survey at high Galactic latitudes, which will allow to obtain much more accurate measurements of their X-ray luminosity function.