UBVRI-polarimetry of the AM Herculis star RX J0203.8+2959

¹ Tuorla Observatory, Väisäläntie 20, 21500 Piikkiö, Finland
² Osservatorio Astronomico di Torino, 10025 Pino Torinese, Italy
³ Department of Physics, 21400, Turku University, Finland

Corresponding author: S. Katajainen, sekataja@astro.utu.fi

Received: 15 December 1999
Accepted: 9 April 2001

Abstract

We present results of the first simultaneous UBVRI-photopolarimetric observations of the long period (4.6 hrs) AM Herculis system RX J0203.8+2959. The observed circular polarization shows both negative and positive polarization, from to in the B-band. A rise of the positive circular polarization is observed near the same orbital phase as a change in HR1 hardness ratio from soft to hard in the earlier ROSAT X-ray observations. The negative circular polarization is observed near orbital phases where a soft X-ray component was seen in ROSAT observations. Linear polarization pulses coincide with the sign reversal of the circular polarization, and coincide also with changes in the X-ray hardness ratio in earlier ROSAT data. The observed polarization variations favour two-pole accretion. Least square fits to the position angle curves during linear pulses suggest high orbital inclination, estimates from to = 73. The UBVRI-lightcurves show smooth variations with a broad maximum and minimum. RX J0203.8+2959 was in intermediate accretion state during observations in November 1998 (). The observed flux and circular polarization variations are reproduced by using constant temperature cyclotron emission models having two accretion regions and with parameters: , and colatitude for the negative pole, and , and for the main accreting positive pole, and assuming orbital inclination .