MLS110213:022733+130617: a new eclipsing polar above the period gap

Polars are magnetic cataclysmic variables: shortperiod binaries in which a low-mass main-sequence star transfers matter to a magnetic white dwarf via an accretion column (Cropper 1990). A stand-off shock is formed near the white-dwarf surface, followed by a hot post-shock region that cools down by cyclotron radiation mainly in optical and infrared wavelenghs and free-free emission in X-rays. Cyclotron process produces high polarizarion degrees. Over 135 polars and polar candidates were identified so far: 26 percent of them have periods over the period gap ( P > 3h) and only 6 of these systems are eclipsing (Ritter & Kolb 2011). We have obtained photometry and polarimetry at Observatorio do Pico dos Dias (OPD) and spectroscopy at SOAR telescope of MLS110213:022733+130617: a polar candidate identified and monitored by the Catalina Sky Survey (CSS, Drake et al. 2009). Phase-folded photometry and circular polarization are presented in Figure 1. From the time of the mid-eclipse observed in the light curves of the OPD photometric data we estimated an orbital period of 3.787 hours. This period is above the period gap and only three other eclipsing systems show longer periods. CSS long term observations show the system in two distinct brightness states, 1.5 mag apart. This kind of variation in polars is explained as variations in the mass rate accretion. Our polarimetric data were obtained in the high state of brightness (HS). The circular polarization varied in the range 3 to 15% in the R-band, which confirms that this component is mainly due to cyclotron emission from the accretion column. The polarization does not have a standstill at zero, and there are phases when the signal changes, indicating a region always visible, but observed from the backside in some phases, or two accretion regions. A spectrum in the energy range 4500-7000 A was obtained convering the phase interval 0.7-0.88. The spectrum shows a flat continuum and no con-