EDP Sciences
Free access
Volume 372, Number 3, June IV 2001
Page(s) 945 - 951
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20010549

A&A 372, 945-951 (2001)
DOI: 10.1051/0004-6361:20010549

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

S. Katajainen1, F. Scaltriti2, V. Piirola1, H. J. Lehto1, 3 and E. Anderlucci2

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

(Received 15 December 1999 / Accepted 9 April 2001)

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 $+7\%$ to $-5\%$ 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 $i = 67^{\circ+21}_{-24}$ to $\it i$ = 73 $^{\circ+13}_{-15}$. 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 ( V= 15.7 - 16.7). The observed flux and circular polarization variations are reproduced by using constant temperature cyclotron emission models having two accretion regions and with parameters: $kT = 10 \rm keV$, ${\Lambda} = 10^{5}$ and colatitude $\beta= 120^{\circ}{-}140^{\circ}$ for the negative pole, and $kT = 20 \rm keV$, ${\Lambda} = 10^{4}$ and $\beta= 20^{\circ}{-}30^{\circ}$ for the main accreting positive pole, and assuming orbital inclination $i\sim70^{\circ}$.

Key words: stars: magnetic fields -- novae, cataclysmic variables -- stars: individual: RX J0203.8+2959 -- accretion, accretion disks -- polarization

Offprint request: S. Katajainen, sekataja@astro.utu.fi

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