Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994ap%26ss.221..277c&link_type=abstract
Astrophysics and Space Science (ISSN 0004-640X), vol. 221, no. 1-2, p. 277-285
Astronomy and Astrophysics
Astronomy
5
B Stars, Giant Stars, Main Sequence Stars, Stellar Atmospheres, Stellar Physics, Stellar Winds, X Ray Astronomy, Brightness, Density Distribution, Extreme Ultraviolet Radiation, Rosat Mission, Stellar Luminosity, Stellar Models, X Ray Spectra
Scientific paper
Recent observations of the X-ray and EUV emission of non-supergiant B stars are summarized. As compared with O stars, the X-rays of most of the near-main-sequence B stars are soft, and the stars show a departure from the Lx = 1007Lbol relation. Using line driven wind models to provide an estimate of the density distribution, it is concluded that a major fraction of the wind emission measure is hot, whereas in shocked wind theory less than 10 percent of the wind emission measure should be hot. The X-ray observations suggest that all of the B stars are X-ray emitters with a basal X-ray luminosity of about 10-8.5Lbol. For the Be stars, the X-ray emission is that which is expected from a normal B-star wind coming from the poles, as in the Wind Compressed Disk (WCD) model of Be-stars. None of the stars, including the beta Cep stars, show noticeable variability in their X-rays. Extreme Ultraviolet Explorer (EUVE) observations of epsilon CMa B2 II, find it to be the brightest object in the EUV sky at 500 to 700 A. It shows a Lyman continuum flux that is a factor of 30 higher than line blanketed model atmospheres. The EUVE spectra show emission lines both from high stages of ionization ( Fe IX to Fe XVI) and from low stages ( HeII and O III). The He II Lyman alpha results from recombination follwing X-ray photoionization in the wind, and the O III resonance line is found to be present because of the Bowen fluorescence mechanism. Thus, there is and intersting coupling between the wind production by the EUV photospheric emission, the production of X-ray and line EUV emission by winds, and the production of fluorescence by recombination in the wind; all of these processes are now observable in B stars.
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