IR photometry and polarimetry of 2A0311−227

Abstract

The X-ray source 2A0311 − 227 has recently been identified with a star whose spectrum and polarization properties show it to be an AM Herculis type binary. These binaries are thought to consist of a synchronously rotating magnetic white dwarf, with a surface field of 108G, accreting matter from a cooler companion star. The highly circularly polarized radiation emitted by these systems is thought to be due to cyclotron radiation originating in an accretion column at one or both poles of the white dwarf. We describe here IR light curves of 2A0311 − 227 at 1.25 and 2.2µm, together with circular polarimetry at 1.25µm. The light curves show a deep narrow minimum which does not have an optical counterpart, and the 1.25µm polarimetry shows circular polarization which is much lower than that in the optical.