Discovery of a Magnetic White Dwarf with Unusual Short-period Variability

Abstract

We report the discovery of a magnetic white dwarf which shows periodic variability with P = 110 min, colordependent amplitudes and a transient phase shift in the blue compared to the red lightcurve – a previously unknown type of variability for this type of object. We attribute the variations either to a close ultracool (thus far undetected) companion or, more likely, to magnetic spots with unusual temperature structure.