Rotation period and magnetic field morphology of the white dwarf WD 0009+501

Abstract

We present new spectropolarimetric observations of the weak-field magnetic white dwarf WD 0009+501. From these data we estimate that the star's longitudinal magnetic field varies with the rotation phase from about -120 kG to about +50 kG, and that the surface magnetic field varies from about 150 kG to about 300 kG. Earlier estimates of the stellar rotation period are revised anew, and we find that the most probable period is about 8 h. We have attempted to recover the star's magnetic morphology by modelling the available magnetic observables, assuming that the field is described by the superposition of a dipole and a quadrupole. According to the best-fit model, the inclination of the rotation axis with respect to the line of sight is , and the angle between the rotation axis and the dipolar axis is . The dipole strength at the pole is about 340 kG, and the quadrupolar strength is about 300 kG.