Rotational period of WD 1953 - 011- A magnetic white dwarf with a star-spot

WD 1953-011 is an isolated, cool (7920 ⊥ 200 K) magnetic white dwarf (MWD) with a low average field strength (∼70 kG), and a higher than average mass (∼0.74 M⊙). Spectroscopic observations taken by Maxted et al. showed variations of equivalent width in the Balmer lines, unusual in a low-field white dwarf. Here we present V-band photometry of WD 1953-011 taken at seven epochs over a total of 22 months. All of the data sets show a sinusoidal variation of approximately 2 per cent peak-to-peak amplitude. We propose that these variations are due to a star-spot on the MWD, analogous to a sunspot, which is affecting the temperature at the surface, and therefore its photometric magnitude. The variations have a best-fitting period over the entire 22 months of 1.4418 d, which we interpret as the rotational period of the white dwarf.