2004ApJ...602..948L

Following an outburst in 2001 July, the UV flux of WZ Sge has declined slowly toward preoutburst levels. Here we describe new 1150-1710 Å Hubble Space Telescope STIS spectra of WZ Sge obtained between 2002 April and 2003 March to follow the decline. A combined analysis of these and spectra obtained in the fall of 2001 show that if logg=8.5, then the white dwarf temperature decreased from 23,400 K in 2001 October, shortly after the steady decline of the system began, to 15,900 K 17 months later. The UV flux in 2003 March was still 2.4 times higher than that measured prior to the outburst, so the system was still recovering from the outburst. During this period, the shape of the spectrum and the flux from the system are consistent with a logg=8.5 and 0.9 M_☉white dwarf at the astrometrically determined distance to WZ Sge. Although the spectrum from 2001 September resembles that of a white dwarf at a temperature of 28,200 K, the implied radius is smaller than in the remainder of the observations. If the entire white dwarf was visible in 2001 September, then either a second component, such as the disk emission, was distorting the spectrum or, more likely, the temperature of the white dwarf photosphere was not uniform then. The metal lines in the spectra of WZ Sge have weakened with time. Model fits that allow for material along the line of sight to the white dwarf photosphere are substantial improvements over models that assume all the lines arise from the photosphere. This obviates the need to explain very unusual abundance ratios in the photosphere and complicates the determination of the rotation rate of the white dwarf.