Photometric Variability and Rotation in Magnetic White Dwarfs

We present a search for long term (months - years) photometric variability in a sample of ten isolated magnetic white dwarfs using observations taken with the Liverpool Robotic Telescope between March 2005 and January 2007. These stars had previously been found to be photometrically stable on short (hours - one week) timescales [1]. We construct differential light curves for each target and then use CLEAN and Lomb-Scargle periodograms to determine any periodicity that may be present. Photometric variability is detected in two of the targets during the observed timescale - G240-72 and G227-28. We find no variability in the remaining eight targets above the 1% level. Finally, we search for any correlations between the spin periods and intrinsic physical properties of magnetic white dwarfs, such as the magnetic field strength, temperature, mass and age.