File:Wz-sge-disc-spirals.jpg

D. Steeghs and T. Marsh, Southampton University; E. Kuulkers, Space Research Organization Netherlands and Utrecht University; and W. Skidmore, University of St. Andrews, on behalf of a larger collaboration, report: "Strong spiral waves are present in the accretion disk of WZ Sge during the first week of its outburst (IAUC 7669, 7670). Phase-resolved spectroscopy, obtained between July 28.02 and 28.24 UT with the 2.5-m Isaac Newton Telescope (+ CCD spectrograph) at La Palma, yielded 2411 spectra (resolution 5700) covering four binary orbits that were used to construct Doppler tomograms showing the distribution of line emission in the binary frame. The He II (468.6 nm) and C III (464.7 nm) images reveal that the accretion-disk emission is dominated by two spiral arms. The H-beta and He I (492.1 nm) lines, on the other hand, are dominated by highly variable absorption cores. This was the first time that spiral arms have been observed in WZ Sge, making it also the first low-mass-ratio cataclysmic variable that displays spiral arms in its disk during outburst." (C) Copyright 2001 CBAT, (7675) Daniel W. E. Green. The original (larger) picture is on-line at http://www.astro.soton.ac.uk/~ds/wzsge_spirals.gif.