A BROAD OBSERVATIONAL STUDY OF THE ECLIPSING MAGNETIC CATACLYSMIC VARIABLE RE-2107-05

We have carried out extensive observations of the bright eclipsing cataclysmic variable RE 2107-05 using CCD and high-speed photoelectric photometry, low- and moderate-resolution phase-resolved optical spectroscopy, broad-band linear and circular polarimetry, and optical spectropolarimetry. We confirm that the system is a synchronized magnetic variable of the AM Herculis type, with a spin/orbit period of 125.02 minutes. Both broad and narrow components are detected in the emission-line spectrum, with radial velocities phased appropriately for their origin in the accretion stream and irradiated secondary star, respectively. In addition to the normal series of Balmer and helium lines, Fe II emission from the funnel is conspicuous. Broad-band polarimetry records at least one linear polarization pulse per cycle and a strongly circularly polarized bright phase persisting nearly 60% of the period. Fits of the polarization curves to models for radial accretion yield an orbital inclination i = 80-degrees +/- 5-degrees and accretion spot colatitude delta = 40-degrees +/- 10-degrees. The spot leads the secondary in longitude by 23-degrees +/- 6-degrees. The optical spectrum commonly displays cyclotron emission harmonics indicating a magnetic field strength in the polar shock of 36 +/- 1 MG for an assumed shock temperature of 10 keV. This is to be compared with a mean surface value of approximately 20 MG evident in Zeeman splitting of the photospheric Balmer lines during the faint orbital phase. Based on the M4V (+/-1) spectral type evident at eclipse minimum, RE 2107-05 lies at a distance of 191(-115)+189 pc. There is no evidence for the white dwarf in the eclipse transitions, implying an absolute magnitude of M(V) > 12.0 and corresponding temperature T(eff) < 13,000 K. For the corrected velocity amplitude of the secondary, K2 = 375 +/- 68 km s-1, the high-speed eclipse profiles provide rather crude estimates of the secondary radius and component masses. These are consistent with the secondary being an M4V star, with M2 almost-equal-to 0.3 M., and a white dwarf mass of M1 almost-equal-to 0.90 M.. RE 2107-05 provides new insight into th flow of accreting gas in an AM Her system. At certain phases, the broad component of Halpha splinters into multiple components suggesting individual coherent streamlines. Eclipse of the accretion funnel by the secondary star is evident in protracted ingress and egress components, displaced approximately 15-degrees in longitude from the spot. These transitions show remarkable differences in character from one eclipse to the next, signifying substantial changes in the magnetospheric interaction on an orbital timescale.