Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apj...230..485a&link_type=abstract
Astrophysical Journal, Part 1, vol. 230, June 1, 1979, p. 485-496.
Astronomy and Astrophysics
Astrophysics
146
A Stars, Open Clusters, Stellar Evolution, Stellar Spectra, Angular Velocity, B Stars, Chronology, Hydrogen, Orion Nebula, Stellar Rotation
Scientific paper
The age dependence of the frequencies of various types of abnormal stars in open clusters and associations is discussed. Spectra acquired at dispersions of 39 A/mm and 129 A/mm were used to determine the spectral types and luminosity classes of 661 stars in 14 open clusters and associations. The frequencies of Ap(Si), Ap(Hg,Mn) and Ap(Sr,Cr) stars are found to increase with age to a level about that of field stars, while the rotational velocities of Ap(Si) and Ap(Hg,Mn) stars decrease with time. Be stars in clusters exhibit a relatively constant frequency, roughly equal to that of Be field stars. The frequencies of stars with pronounced shell spectra are observed to remain constant with age, while stars with unusually broad hydrogen lines (Vb stars) occur only in the youngest clusters. The frequency of Am stars in clusters is not significantly different from that of field stars, and does not seem to depend on age, although rotational velocity is seen to decrease. It is concluded that Ap or Am stars develop from stars of various rotational speeds, with a subsequent decrease in rotational velocity.
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