AAS 196th Meeting, June 2000
Session 13. EUVE
Oral, Monday, June 5, 2000, 10:00-11:30am, Highland B/J

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[13.06] EUVE TOO Helps Reveal Stages of Optical, X-ray, and EUV Emission Observed in SS Cygni Outburst

J. A. Mattei (American Assoc. of Variable Star Observers), C. W. Mauche (Lawrence Livermore National Lab.), P. J. Wheatley (U. of Leicester)

We present the best multi-wavelength coverage ever of a dwarf nova outburst obtained through the 1996 optical, EUVE, and RXTE observations. The recently compiled and analyzed data show the outburst of SS Cygni (the brightest dwarf nova) starts in the optical band and about a day later moves to the X-ray and EUV bands as the gas flow reaches the white dwarf. The dramatic switch at the start of the outburst from X-ray to EUV emission is the result of the boundary layer becoming optically thick as the mass transfer rate onto the white dwarf increases dramatically. The transition has not been observed before, and was only detected due to the rapid TOO response of EUVE and RXTE to the optical alert from the AAVSO observers. A detailed study of these data will reveal the nature of the gas flow through the disk, and help us understand why it is unstable.

An additional EUVE TOO for the dwarf nova OY Car was conducted in February of this year. We will discuss details of the selection of this target and the response of the amateur astronomers' community.

This work was partially funded through NASA/UCB Cooperative Agreement NCC5-138 and NAG5-7027.

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