XMM-Newton observations of the pre-polar HS0922+1333

Abstract

We report on XMM-Newton and accompanying phase-resolved optical observations of HS0922+1333, one out of nine pre-polars. It shows X-ray and UV variability correlated with the visibility of the main accretion spot. The spectral X-ray properties reveal a low temperature thermal plasma of ~1 keV with F_X more than one order of magnitude below the cyclotron flux. The UV data indicate a cool white dwarf with T_WD < 8000 K. We refine the ephemeris and determine a distance of 140 ± 50 pc. The derived location of the accretion spots yield a magnetic field axis laying nearly in the orbital plane. Optical spectroscopy uncovers a highly active secondary.