The discovery of near-infrared polarized cyclotron emission in the intermediate polar BG Canis Minoris

BG CMi is the only intermediate polar known to be magnetic. New observations reported here reveal that its wavelength dependence of circular polarization increases rapidly into the infrared, from VI= -0.25%±0.06% in the optical red to VJ= -1.74%±0.26% (1.25 μm). This dramatic rise, which may even continue to a level of -4% at H (1.5 μm), is the first conclusive identification of cyclotron emission in an intermediate polar, and confirms that the long-held basic model of a magnetic accreting white dwarf is correct. The field in the cyclotron emission region of BG CMi is likely in the range ≡5 - 10 MG.