Photometric and polarimetric observations of the eclipsing polar SDSS J205017.84-053626.8

Abstract

Photometric and polarimetric observations of the eclipsing polar (AM Herculis system) Sloan Digital Sky Survey 2050-05 are reported, in which both sets of data are found to be modulated on a period of ∼94.2 min. This is the first detection of polarization in this system, unambiguously confirming its identification. Circular polarization variations are seen from ∼− 10 to +4 per cent, consistent with a ‘two-pole’ accretor. Both accreting poles are self-occulted by the white dwarf during parts of the orbit. The photopolarimetry from different epochs shows the system to be in different states. During the epochs showing a higher state the polarimetry suggests accretion occurs preferentially near the pole displaying positive circular polarization, and vice versa during the epoch showing a lower state. From the eclipses we estimate some of the system’s parameters.