Eclipse mapping of starspots on XY UMa in 1992 and 1995

Abstract

We present and analyse V-band light curves of the detached eclipsing binary system XY UMa, obtained in 1992 October, 1995 March and November, and 1996 February. The light-curve morphology of this system is known to vary on time-scales of a few days. We have used eclipse mapping techniques to search for evidence that cool starspots are the agents responsible for the variability of the light curve. We derive a new set of geometric system parameters, which we find to be very similar to those derived by Hilditch & Bell. The image derived from the 1992 light curve shows an amorphous band of unresolved spots with a low filling factor, extending over much of the inward-facing hemisphere of the primary. This result is consistent with the extent of the dark-zone model proposed by Hilditch & Bell in their earlier analysis of this same light curve. Irregularities in the primary eclipse profile observed in 1995 and early 1996 are consistent with the eclipse of a dark spot or spots on the inner face of the primary. The major spot in this region appears to be resolved on our 9° surface grid, indicating that the spot consists of an unbroken umbral region some 15° in radius.