Optical polarization and X-ray data on the AM HER star RE J1844-74

We report optical and X-ray observations of the AM Her system RE J1844-74 using the Anglo-Australian Telescope (AAT) and ROSAT. From previously published data and these new data we derive a new accurate ephemeris for the spin period of the white dwarf. We find we cannot simultaneously fit the green and red polarization data. However, we can fit them separately using different values of the plasma parameter, Lambda. We investigate the possible reasons for this result. Furthermore, we find that the polarization data require long narrow accretion arcs. This in contrast to results on eclipsing AM Her systems which tend to favour accretion regions that are relatively small. We briefly explore the possible effects that may influence the determination of the size of the accretion region from these different methods. We find evidence that the main accretion region of RE J1844-74 has a magnetic field strength ~10 MG less than its secondary pole, and that the system inclination is moderately high. Our X-ray data are out of phase with the optical data, consistent with our current view of the accretion flow in AM Her systems.