Studies of the Peculiar a Stars. I. The Oxygen-Abundance Anomaly.
Abstract
Equivalent widths of the infrared oxygen blends XX 7772-7775 and X 8446 have been measured in 20 peculiar A stars and 3 A-type normal stars. The neighboring pair of Mg ii lines at X 7877 and X 7896 have also been measured. Both the 0 1 and Mg ii lines are quite insensitive to temperature and electron pressure and in normal stars behave almost identically in the range B8-F5. The oxygen lines are very much weaker in some peculiar stars than in the standard stars; this effect is strongly correlated with the B - V color. The Mg ii lines show no comparable trend. The results are interpreted as indicating abundance variations among the Ap stars Oxygen is deficient with respect to hydrogen by factors ranging from 8 to more than 100 in all Ap stars of the Si-Eu-Cr, Eu-Cr, Eu-Cr-Sr, and Sr classes, while in the Mn stars the oxygen abundance is normal. Assuming that they originated with a normal composition, the observed spectra of the oxygen-deficient Ap stars demand that, in general, 0 must have been transmuted into one or more of the elements H, He, C, N, Ne, and perhaps F. We discuss briefly some possible nuclear reactions (which must involve only H, He, and 016) that could be responsible for the inferred oxygen deficiency.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1962
- DOI:
- 10.1086/147393
- Bibcode:
- 1962ApJ...136..408S