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

We have carried out extensive observations of the bright eclipsing cat aclysmic variable RE 2107-05 using CCD and high-speed photoelectric ph otometry, low- and moderate-resolution phase-resolved optical spectros copy, broad-band linear and circular polarimetry, and optical spectrop olarimetry. We confirm that the system is a synchronized magnetic vari able of the AM Herculis type, with a spin/orbit period of 125.02 minut es. Both broad and narrow components are detected in the emission-line spectrum, with radial velocities phased appropriately for their origi n in the accretion stream and irradiated secondary star, respectively. In addition to the normal series of Balmer and helium lines, Fe II em ission from the funnel is conspicuous. Broad-band polarimetry records at least one linear polarization pulse per cycle and a strongly circul arly polarized bright phase persisting nearly 60% of the period. Fits of the polarization curves to models for radial accretion yield an orb ital inclination i = 80-degrees +/- 5-degrees and accretion spot colat itude delta = 40-degrees +/- 10-degrees. The spot leads the secondary in longitude by 23-degrees +/- 6-degrees. The optical spectrum commonl y displays cyclotron emission harmonics indicating a magnetic field st rength in the polar shock of 36 +/- 1 MG for an assumed shock temperat ure of 10 keV. This is to be compared with a mean surface value of app roximately 20 MG evident in Zeeman splitting of the photospheric Balme r lines during the faint orbital phase. Based on the M4V (+/-1) spectr al type evident at eclipse minimum, RE 2107-05 lies at a distance of 1 91(-115)+189 pc. There is no evidence for the white dwarf in the eclip se transitions, implying an absolute magnitude of M(V) > 12.0 and corr esponding temperature T(eff) < 13,000 K. For the corrected velocity am plitude of the secondary, K2 = 375 +/- 68 km s-1, the high-speed eclip se profiles provide rather crude estimates of the secondary radius and component masses. These are consistent with the secondary being an M4 V star, with M2 almost-equal-to 0.3 M., and a white dwarf mass of M1 a lmost-equal-to 0.90 M.. RE 2107-05 provides new insight into th flow o f accreting gas in an AM Her system. At certain phases, the broad comp onent of Halpha splinters into multiple components suggesting individu al coherent streamlines. Eclipse of the accretion funnel by the second ary star is evident in protracted ingress and egress components, displ aced approximately 15-degrees in longitude from the spot. These transi tions show remarkable differences in character from one eclipse to the next, signifying substantial changes in the magnetospheric interactio n on an orbital timescale.