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Дата изменения: Fri Jan 25 15:33:06 2002
Дата индексирования: Tue Oct 2 09:46:44 2012
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Extreme helium stars and hot RCB stars

As well as RCB stars with F- and G-type spectra, the `extreme helium stars' (EHes) are low-gravity A- and B-type stars with weak or no Balmer lines, strong neutral helium and ionized carbon lines ([Jeffery 2000]). Two of these, MVSgr and DYCen, are thought to show RCB-like activity, although they are not very active. The surface carbon abundance of DYCen is $\sim1\%$ by number, the remainder being predominantly helium ([Jeffery & Heber 1993]. MVSgr, on the other hand, appears to be quite carbon-poor in comparison with most EHes ([Jeffery et al. 1988]). A more active B-type helium star, V348Sgr shows strong emission lines at all times, and has a surface carbon abundance of $\sim10\%$ by numbers ([Jeffery 1995]).