Multi-Color Photometry of the 2001 Superoutburst of WZ sagittae

Abstract

We present the results of U-band and multi-color photometry during the 2001 superoutburst of WZ Sagittae. Our 10 nights of U-band photometry span the time interval from HJD 2452118 to 2452197 while our multi-color observations range from HJD 2452115 to 2452197. The U-band light curves are generally in agreement with other datasets obtained during the superoutburst showing highly modulated light early on, rebrightenings, and superhumps of similar shape and period (except during the rebrightening peak). One of our multi-color datasets fortuitously covers the first rebrightening and allows determination of the accretion disk color temperature before, during, and after the event. It is seen that the rebrightening is a change from a neutral disk (T~7000K) to an ionized disk (T$\sim$10000K) and back again. We develop a simple limit cycle model for this behavior which approximately predicts the semi-periodic timescale observed for the rebrightenings. We discuss our results in relation to accretion disk structure during superoutburst.