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J. P. Cassinelli (University of Wisconsin)
One of the most exciting results from the EUVE satellite was the discovery that two of the brightest EUV sources are hot stars, epsilon CMa (B2 II) and beta CMa (B1 II - III). The EUV photospheric fluxes (504 - 730 Å) from each of the stars was found to exceed the predictions of model atmospheres by an order of magnitude. The wind of epsilon CMa showed clear evidence for the operation of the Bowen fluorescence machanism in the strong Lyman alpha line of He II (304 Å) and the resonance line of OIII (374 Å). Also seen were numerous emission lines of ions from Fe IX to Fe XVI. More recent Chandra observations of hot stars have shown the benefits of very high spectral resolution of wind broadened emission line profiles. The expected benefits from future high resolution EUV observations are described. The possiblity that the upper atmospheres of hot stars are affected by mechanical or magnetic heating is described in terms of the observations of the pulsations of the star beta CMa, for which the EUV amplitudes are very large, and ground based magnetic observations of beta Cep, which has a recently measured magnetic field of 360 Gauss. The information from EUV spectra of hot stars is shown to be qualitatively different from that obtainable at other wavelengths. This work is supported by NASA grant NAG5-9226.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.