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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,
© 2003. The American Astronomical Soceity.