The Record Breaking Magnetic White Dwarf RE J0317-853

RE J0317-853 is a strongly magnetic white dwarf discovered as an EUV source by the ROSAT Wide Field Camera (WFC). The average optical and far-UV spectrum of this star could be matched by a dipole model, off-centred by 0.2 stellar radii in the direction of the southern magnetic pole, with a mean field strength of 340MG (Barstow, Jordan, Burleigh et al., 1995, MNRAS, 277, 971). Since RE J0317-853 has a cool DA white dwarf companion (LB 9802) just 16" away, we could use its atmospheric parameters (T=16,030+/-230K, log g=8.19+/-0.05) as an additional constraint on the parameters of RE J0317-853, assuming both stars lie at the same distance (highly likely). We found that RE J0317-853 is the hottest known magnetic white dwarf (T ~ 50,000K), and probably the most massive white dwarf ever discovered ( ~ 1.35M_sun). In addition, high speed photometry has shown that the optical brightness of RE J0317-853 varies almost sinusoidal with a period of 725 seconds. The only possible explanation is a change in surface brightness with rotation, and thus RE J0317-853 is spinning faster than any known isolated white dwarf. In order to analyse the magnetic field in detail, we have obtained time resolved far-UV spectra with HST/FOS, time resolved spectro-polarimetry with the Anglo-Australian Telescope (AAT), and additional data with the EUVE, Orfeus, and ROSAT satellites. We find that the magnetic field structure is actually extremely complex, and cannot in fact be described by the offset dipole model used previously to fit the mean spectrum. A preliminary analysis of the observations with new theoretical models shows that the data can be best represented by a magnetic field with two distinct field strengths, of ~200MG and ~500MG, on different hemispheres. We also identify one intriguing absorption feature at 1170{ Angstroms} as a dipole forbidden component of Lyman alpha (1sO-2sO), which is only possible due to the simultaneous presence of a magnetic and electric field.