Observations made with the Extreme Ultraviolet Explorer (EUVE) of the two bright stars ϵ CMa (B2 II) and β CMa (Bl II-III) are discussed. The photospheres show excess EUV radiation. The wind of ϵ CMa exhibits the Bowen Fluorescence mechanism, along with high ionization stages that help explain the nature of the wind shocks. The pulsation and beat phenomena exhibited by the variable star β CMa suggest that deposition of residual pulsation energy might heat and modify the structure of the atmospheres of early-type stars near the β Cephei strip. The possibility that many other B stars show a large excess Lyman continuum radiation is considered as a possible source of the ionization of the warm ionized medium (WIM) in the galactic ISM.
Several years ago a three-parameter system of stellar classification has been proposed (1, 2), for the early-type stars (O-G): it was an improvement on the two-parameter system described by Barbier and Chalonge (3).
As part of a general investigation of interstellar clouds associated with southern HII regions we have begun a high-resolution study of the sodium D-line absorption in the directions of early-type stars that are likely to be associated with or located behind the clouds.
X-rays from early-type stars are emitted by the corona or the stellar wind. The materials in the surface layer of early-type stars are not contaminated by nuclear reactions in the stellar inside. Therefore, abundance study of the early-type stars provides us an information of the abundances of the original gas. However, the X-ray observations indicate low-metallicity, which is about 0.3 times of cosmic abundances. This fact raises the problem on the cosmic abundances.
EUV Radiation from B Stars: The Broad Implications for Stellar and Interstellar Astronomy