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Session 6 - Novae and Supernovae.
Display session, Monday, June 08
Atlas Ballroom,

[6.04] Hot Spiral Structure in the Accretion Disk of IP Pegasi Observed

E. Harlaftis (National Obs. of Athens, Greece), D. Steeghs (U. St. Andrews, UK)

We present observational evidence of spiral structure on the accretion disk of the dwarf nova IP Peg during outburst. Doppler tomograms of Balmer, ionized helium (HeII 4686A) and fluorescence emission lines show a two-arm spiral pattern on the disk image during early and maximum outburst. We show that its origin is related to the tidal interaction of the disk with the companion star. The structure is perpendicular to the binary axis with the spiral arm facing the gas stream being weaker. The arms span about 110 degrees each over the disk with velocities between 550 and 750 km/s. Such low velocities require a disk close or even larger than its tidal radius. Spiral waves have been found to be generated by the tides raised by the secondary star on the disk from computer simulations and may provide an efficient mechanism for transporting angular momentum out of the disk.

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Program listing for Monday