The spectral classification of the beta Cephei stars and their location in the theoretical Hertzsprung-Russell diagram.
Summary. Spectral types on the MK system are presented for 17 bright p Cephei variables, 7 bright suspected variables and 23 fainter suspected variables. Classification of the fainter stars is based on new plates obtained at the Haute-Provence Observatory The bright variables are located in the observational HR diagram by means of the photometric parameters Q and p, and their position relative to normal B stars is discussed. A transformation to the (log Teff, Mbol) plane enables us to compare the positions of both normal stars and p Cephei variables with evolutionary tracks. We find that the variables occupy a very restricted region in the observational HR diagram, but that this region is also populated by many normal B stars. In the theoretical HR diagram, this "instability strip" is shown to coincide with the region traversed three times by a star in the course of its post-main- sequence evolution: once in the core hydrogen-burning phase, once in the secondary contraction phase, and once in the shell hydrogen-burning phase. A natural hypothesis is that the normal B stars in this region are in the core hydrogen-burning phase, while the p Cephei variables are in one of the two later stages of evolution. Key words: p Cephei stars - variable stars - spectral classification - HR diagram - stellar evolution
Astronomy and Astrophysics
- Pub Date:
- January 1973