Left: ULTRACAM images (taken
every 2 seconds, but only one in every 5 shown) of the eclipsing
binary star NN Ser (centre) and a nearby field star (lower left)
obtained in May 2002 on the WHT. Right: The resulting light curve of
NN Ser, showing the deep eclipse when the white dwarf primary is
obscured by the red dwarf secondary star. These data will be used to
measure the white dwarf radius and the rate at which the orbital
period of the binary is decreasing. | |  |