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[18.07] Chandra HETG Observations of SS Cyg and U Gem in Quiescence and Outburst

C. W. Mauche, D. A. Liedahl (LLNL), K. S. Long (STScI), J. C. Raymond (CfA), P. Szkody (Univ. of Washington), P. J. Wheatley (Univ. of Leicester), J. A. Mattei (AAVSO)

We targeted SS Cyg and U Gem in quiescence and outburst with the Chandra HETG to study the response of the boundary layer of nonmagnetic cataclysmic variables to changes in the mass-accretion rate. In all cases the hard X-ray spectra are adequately described by multi-temperature thermal plasmas, but when SS Cyg goes into outburst it becomes dimmer in hard X-rays and displays a dramatic shift in its relative line strengths (from predominately H- to predominately He-like lines), whereas when U Gem goes into outburst it becomes brighter in hard X-rays and displays only a minor shift in its relative line strengths. In both cases, the emission lines becomes significantly broader in outburst, signaling the presence of a broad range of either Kepler or expansion velocities.

Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.