A study of Be stars in clusters.
Abstract
Calibrated spectrograms at Ha of 566 stars in 29 young galactic clusters led to the detection of 41 Be stars in clusters. Using cluster membership, we have inferred ages and intrinsic B - V colors of Be stars for a discussion of their evolutionary states. Rotating stars can become Be stars in their early hydrogen burning evolution away from the main sequence. Both the fraction of stars showing hydrogen emission and the strength of emission appear to vary little during the first 80 percent of post-main-sequence evolution. However, at the onset of gravitational core contraction, both these features undergo a fourfold increase. Many stars in the core-contraction phase develop an intrinsic B - V excess of 0.15 mag, owing to the H - free-bound continuum radiation. Because of the great strength of Ha emission and the short time duration of the effect, the extreme Be stars would be excellent probes for studies of spiral structure and would also serve as probes for studies of ages and distances of extragalactic systems. Analysis of the corrected colors of the Be stars in clusters suggests that the Lucy and Solomon (1970) mechanism for reduction of effective surface gravity by ultraviolet resonance line scattering is probably important for the hotter Be stars. However, a discrepancy exists for the cooler stars between the predicted and observed colors. Subject headings: clusters: open - stars: Be - stars: evolution
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1976
- DOI:
- 10.1086/154194
- Bibcode:
- 1976ApJ...204..493S