Gopal C. Kilambi

Energy Distribution of Be Stars

Be stars are defined to be non-supergiant early-type stars of spectral type B showing at times Balmer emission lines in their spectra. These stars often develop strong stellar winds considered to be variable in nature (Slettebak 1988) and have high rotational velocities compared to normal stars of similar spectral types. They also tend to show an excess amount of energy in the near-and far-infrared region compared to normal stars which is presumed to be due the surrounding material around the central star. Thus, the observed energy is a combination of that due to the stellar source and the surrounding material. Various attempts have been made to disentangle the stellar energy component from that of the circumstellar component in order to understand the nature, size and temperature of the envelope. These include: a) Radius determination based on IR excess (Gehrz et al. 1974, Dachs and Hanuschik 1984; Waters et al. 1987) b) Radius estimates from polarization and spectrophotometric data (Jones 1979) c) Envelope dimensions derived from the width of shell absorption cores (Kogure 1969; Hirata and Kogure 1977) d) Dachs et al. (1992) attempted to understand the physical properties, flow patterns and density distribution of the gas by a comparison of synthetic emission line profiles and empirical profiles measured for real Be stars.

Mid-ultraviolet and optical photometry of helium stars

Mid-ultraviolet and optical photometric analysis of helium stars are presented. A linear relation exists between the effective temperature derived from model atmospheres and (1965-V)0 index. The effective temperatures derived from (1965-V)0 index are somewhat higher than that of MK spectral type estimates especially for late B-type helium objects.