The CNO Abundances of the CH Stars in Omega Centauri
Open Access
- 1 January 1974
- journal article
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 166 (1) , 89-99
- https://doi.org/10.1093/mnras/166.1.89
Abstract
The Swan bands in the spectra of the ω Cen CH stars RGO 55 and RGO 70 have been analysed, using synthetic spectra calculations, and yield C 12 /C 13 ∼ 10 and [C/H] ∼ −0.8, the latter abundance being obtained under the assumption that [O/H] = –1.3. The nitrogen abundance, [N/H], obtained from bands of the blue and red CN systems, is approximately solar for both of the stars. The UBV colours of the CH star models show ultra-violet excesses of ∼0.3 mag when compared with normal giant models, in agreement with photometry of the cluster stars. The models also show that the fact that the CH stars are grouped with the red variables in the cluster c–m diagram is caused by the reddening effects of the carbon features on B–V . The weak appearance of the Ca I 4226 line in CH star spectra is shown to be caused to a large extent by the great strength of the CH and CN features.Keywords
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