EUVE Observations of SS Cygni

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Session 45 -- CVs/Symbiotic Stars
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[45.04] EUVE Observations of SS Cygni

C.W.Mauche (LEA/LLNL), J.C.Raymond (CfA), J.A.Mattei (AAVSO)

Target-of-opportunity observations of the dwarf nova SS~Cyg were made by the Extreme Ultraviolet Explorer (EUVE) satellite on 1993 August 17--23. The observations cover the rise and plateau phases of a rare symmetric outburst which began on August $\sim 15.5$ and which reached maximum at $V\sim 8.3$ on August $\sim 20$. During the observations, the EUV brightness of the source as measured by the EUVE Deep Survey instrument (40--190~\AA ) rose from $\sim 0.02$ counts~{\rm s}$^{-1}$ to $\sim 5$ counts~{\rm s}$^{-1}$. The EUV light curve rose more steeply than the optical light curve, manifesting a delay of $\sim 1$ day on August 17, but only $\sim 0.5$ day on August 19. The EUV spectrum recorded during this interval extends from the short-wavelength cutoff of the EUVE spectrometer at $\sim 70$~\AA \ down to $\sim 130$ \AA . The spectrum is extremely rich in emission and absorption features due to high-ionization species of Ne, Mg, Si, S, and Fe superposed on a weak `blue' continuum.

We present the optical and EUV light curves and short-wavelength EUV spectrum of this outburst of SS~Cyg. Simple models are used to constrain the physical conditions of the EUV-radiating plasma as well as the column density of neutral material to the source due to the ISM and possibly the wind of this dwarf nova.

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