Time-resolved infrared spectroscopy of WZ Sge during superoutburst: Evidence for spiral waves in the accretion disc

Time-resolved J and K band spectra were obtained for WZ Sge four days into its 2001 superoutburst. These data represent the first time-resolved IR spectra obtained of any dwarf nova during a superoutburst. The spectra show the usual broad emission lines due to H and He I plus strong He II (1.163 m), the latter line being essentially absent at minimum light. The J-band spectra contain complex line emission from C I, Fe I, Na I, and Ca I and show asymmetric H and He line emission from the accretion disc. The K-band continuum reveals an increasing slope to the red as seen during minimum light. Doppler maps produced from the IR spectra indicate the presence of asymmetric emission within the accretion flow, in agreement with the optical detection of prominent spiral arms present within the accretion disc.