This animation (click on the picture in order to obtain a larger version!) shows phase resolved HST spectra (Burleigh and Jordan, A&A in prep.) of the magnetic white dwarf REJ 0317-853 ( Barstow, Jordan, O'Donoghue, Burleigh, Napiwotzki, Harrop-Allin et al., 1995)).

The observed spectra were binned into 12 phases (0-11) covering the total rotational period of 725 seconds (making REJ 0317-853 the fastest rotating known isolated white dwarf).

The model was calculated with the program for the radiative transport through the magnetized stellar atmosphere of a white dwarf written by Stefan Jordan.

The magnetic field geometry was chosen to match the observed spectra best. We assumed a configuration, in which the magnetic field was expanded into spherical harmonics up to l=2 (15 parameters). However, only the three latitude dependend parameters parametes for m=0 were significantly different from zero, so that the model shown here is almost cylindrically symmetric.

The animation shows the variation of the visible hemisphere relative to the observer from the earth showing different parts of the star at different times. The brighter the areas are, the larger the magnetic field is (the steps in greyscale correspond to steps of 100 MG).

The magnetic field of REJ 0317-853 is extremely nom-dipolar. A centered dipole varies by a factor of two between the poles and the equator, while the configuration shown here varies between 170 (the darkes grey) and 800 Megagauss (the bright spot).

The dipole field strength is 413 MG, but the contribution of the quadrupole and octupole relative to the dipole amounts 60% and 38%, respectively.

For more details see the paper ( by Burleigh, Jordan & Schweizer 1998).