Magnetic catalysmic variables: Development of models for X-ray emitting regions

• Applicant: Professor Dr. Klaus Werner
• Subject Area: Astrophysics and Astronomy
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 570900468

At present, the known population of cataclysmic variables has grown greatly, allowing detailed studies of the properties of this population of objects in the Milky Way to begin. This is due to the extensive survey works in both the X-ray (SRG/eROSITA) and optical (SDSS, 4MOST, LAMOST, ZTF) bands, accompanied by the work of the Gaia astrometric observatory. For a detailed comparison of the results of population synthesis with observations, among other things, it is necessary to know the masses of white dwarfs in these systems. Intermediate polars with observed hard X-ray emission are a subclass of cataclysmic variables for which fairly reliable determination of white dwarf masses is possible. The hardness of the X-ray spectrum in these objects depends mainly on the mass of the white dwarf, though the magnetospheric radii and the local accretion rates are also important. In total, the masses of about forty white dwarfs in intermediate polars have been determined from the shape of their hard X-ray spectra. Recently, however, there have been observational indications that the physics of accretion columns requires a more detailed consideration. In this project, we propose to develop new physical models of post-shock structures that will describe the X-ray spectra of intermediate polars with higher accuracy. This allows us to more accurately determine the masses of white dwarfs in these objects. In particular, we plan to take into account cyclotron cooling in tall low-luminosity accretion columns in a more correct way, and develop physically self-consistent models of Compton reflection from the white dwarf surface and the bottom of the accretion column. We also plan to consider the effect of relatively high plasma density on the thermal cooling rate of accretion columns and their emission spectra, since the currently used collisional approximation could be insufficient to describe the plasma of accretion columns.

• DFG Programme: Research Grants