THE NEW LONG-PERIOD AM HERCULIS SYSTEM RX J0203.8+2959

We present the first detailed multi-wavelength study of the ROSAT-disc overed AM Herculis binary RX J0203.8+2959 comprising extended CCD and photoelectric photometry, phase-resolved spectroscopy with high and lo w spectral resolution and pointed ROSAT observations with the PSPC and the HRI. Between 1992 and 1997 the system displayed states of high an d low accretion with mean brightness levels of V = 15.5(m) and 18(m), respectively. A timing analysis revealed that the binary is rotating s ynchronously with a period of 4.6 hr and is thus one of the longest-pe riod polars known. The emission lines are structured showing narrow an d broad components. We could distinguish between line emission arising from the heated side of the secondary star and the accretion stream. Velocity information derived for a narrow emission line with suspected origin on the heated side of the companion star allowed us to constra in its orbital velocity and to phase its inferior conjunction. In addi tion the photospheric spectrum of the secondary star could be detected in the near-infrared. The strength of the TiO-bands was used to deter mine its spectral type as dM 2.5, which is consistent with a Roche lob e filling main sequence star, and to estimate the distance of the syst em to be similar to 600 pc. Definite confirmation of its magnetic natu re is given by the detection of cyclotron harmonics implying a field s trength of B = 38 +/- 2 MG. The accretion geometry could not be fixed unequivocally. The morphology of the optical light curves is suggestiv e of one active accretion region which undergoes no selfeclipse. A cor responding simple light curve pattern is not seen at X-ray wavelengths , it's time signature is dominated by instationary accretion of discre te blobs. We report on the occasional occurence of phase and colour-de pendent quasi-periodic oscillations at periods of similar to 7 and sim ilar to 14 min.