A Multiwavelength Study of AM Herculis during the 2002-2004 Low States

We present two epochs of low-state, near-IR spectroscopy of the polar prototype AM Her, along with K-band spectroscopy and JHK photometry. Combining our data with long-term (RoboScope) photometry of the system, we determine a new spectroscopic ephemeris for AM Her. According to the new ephemeris, the primary photometric minimum of the high-state light curve of the system is centered at phase zero. Our K-band spectrum, in which the Brγ and He I (2.06 μm) lines are essentially absent, confirms that during the low state, accretion was negligible. Ellipsoidal variations dominate the J-band light curve, whereas cyclotron harmonics are prominent in the H- and K-band light curves. Cyclotron emission during a time of negligible accretion has been observed in other low-M˙ polars. The Hα line is often triple peaked, and all three components follow the motion of the secondary star. The central peak likely originates from the irradiated inner hemisphere of the secondary. The blue/red satellite components reach velocities of ~300 km s^-1 with respect to the secondary and coincide in phase with flaring events recently discovered from a photometric campaign. We argue that the satellite behavior is consistent with motions in large loop coronal structures on the secondary star.