1995A&A...293..764S

We report the discovery of two systems of cyclotron emisson lines in phase-resolved low-resolution spectra of the recently discovered AM Herculis binary RX J1938.6-4612. The fieldstrengths inferred are B₁≃47MG and B₂≃70-80MG, which might be indicative of a non-dipolar field structure. The latter value is the highest found so far for white dwarfs in cataclysmic variables. We present a spectroscopic ephemeris of sufficient accuracy to connect our optical and ROSAT All Sky Survey X-ray observations separated by a few years. Using this, the X-ray bright accretion spot which is visible for less than 40% of the binary cycle may be identified with the low-field accretion region. The high-field spot dominates the optical lightcurve. We find slight evidence for a quadratic term in the ephemeris, {dot}(P)=(-3.4±2.1)x10^–9. Low-state spectra reveal M-star features, Zeeman absorption troughs from the white dwarf and cyclotron emission lines originating in the high-field region. Photospheric Zeeman models using a slightly decentered dipole along the axis, z_off≃0.1R_wd, B_pole≃60MG, fit some absorption features in the blue spectral range and confirm the results of high-state cyclotron spectroscopy. The implied distance to RX J1938.6-4612 is ∼150-190pc.