Polar cataclysmic variables: what we know and what we don’t

Hauke Wörpel, Leibniz-Institut für Astrophysik Potsdam (AIP) - 24.10.16

Abstract:

Polars are strongly magnetised, synchronously rotating cataclysmic variables that accrete directly onto the magnetic poles of the white dwarf, rather than through an accretion disc. These objects are important laboratories for studying accretion in an environment of strong gravitational and magnetic fields. Polars are strong X-ray sources and contribute a significant portion of the Galactic X-ray emission.

I will review the current state of knowledge regarding polars and outline what is still unclear- particularly the soft excess, an overluminous blackbody-like component at low X-ray energies. This feature is common in polars discovered prior to 2000 but has gone missing in the XMM-Newton era. I will discuss my recent work studying XMM observations of a set of bright polars: tracking down the soft excess, new methods for precise eclipse timing, and prospects for future study.