The Surprise Outburst of WZ Sge
Danny Steeghs (Southampton)
Host: Paul Groot

WZ Sge is the prototypical evolved cataclysmic variable harbouring an accreting white dwarf that has transformed its nearby companion star from a main sequence star into a low mass dwarf via gigayears of mass transfer. In July 2001, the system went into one of its rare outburst states around 10 years earlier than expected. I present some highlights from the multi-wavelength campaign covering the 2001 outburst event. The vast amount of data secured during this event provides an unprecedented coverage of a dwarf nova outburst. Complex line profile variability is present across all wavebands with remarkable similarity between optical, UV (Hubble Space Telescope) and X-ray (Chandra Telescope) line profiles. I will introduce the tomographic imaging techniques that are used to map the accretion flow in these systems and illustrate some recent applications such as the detection of the mass donor in Scorpius X-1. Optical spectroscopy of WZ Sge in the first few
days of the outburst revealed a hot accretion disc dominated by two spiral arms, resembling the discs of longer period dwarf novae in
outburst. Doppler tomography of the disc indicates a weakening of the spirals throughout the first weeks of the outburst while at the same time a bright spot signature is increasing in strength. The mass donor also revealed itself for the first time through narrow emission line components, directly constraining WZ Sge's system parameters.

This web site at the Italian Bellatrix Observatory has more information.