Studies on the spectra of K-giants. III. Carbon, nitrogen and oxygen abundances.
Abstract
Carbon, nitrogen and oxygen abundances are derived for 23 bright K giants by means of a model atmosphere analysis of blends of the G and 4216 A bands and of literature data about the 6300 A of forbidden line of OI. The resulting abundances are accurate to + or - 0.1 dex and compare well with the published data, though the use of a lower gravity scale results in lower oxygen abundances. The results confirm the low value of the C/N ratio for Population I giants, this ratio being larger for low mass stars, in agreement with stellar evolution theory predictions. The sum of the carbon and nitrogen abundances is on the mean near the solar value and correlates well with the iron abundance, while the oxygen abundances are mildly dependent on the iron abundance. The carbon abundances exhibit a decline while nitrogen abundances increase with increasing luminosity. The C/N ratio anticorrelates with the C-12/C-13 ratio in evolved giants, indicating that non-standard processes must be included in the evolution of low mass stars.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 1985
- Bibcode:
- 1985A&A...148..105G
- Keywords:
-
- Giant Stars;
- K Stars;
- Stellar Atmospheres;
- Stellar Composition;
- Stellar Evolution;
- Stellar Spectra;
- Abundance;
- Carbon;
- Cn Emission;
- Late Stars;
- Nitrogen;
- Nuclear Fusion;
- Oxygen Spectra;
- Spectral Line Width;
- Stellar Luminosity;
- Astrophysics