2000ApJ...537..927T

The identification and study of the optical counterpart of the ROSAT-discovered AM Her system RX J2157.5+0855 is reported. We present high time-resolution spectrophotometric, spectropolarimetric, and multicolor CCD-photometric observations of this polar obtained when the system was actively accreting. The 3.375 hr orbital period of the system places it among a few long-period AM Her objects. The emission lines clearly reveal the presence of at least two different line components with different widths and radial velocity variations. The Balmer emission lines contain significant contribution from the X/UV-illuminated hemisphere of the secondary star. The Hα line is deblended into two components, which we identify with the secondary star and the accretion stream. The circular polarization unambiguously confirms the magnetic nature of this newly discovered cataclysmic variable with ~20 MG strength deduced by cyclotron emission modeling. Combining radial velocity and light curves with polarization variations provides additional information about the system geometry.