Helium and Carbon Abundances in Late-B and Early-A Supergiants

Details Helium and Carbon Abundances in Late-B and Early-A Supergiants Helium and Carbon Abundances in Late-B and Early-A Supergiants

Feb 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000pasj...52..113t&link_type=abstract

Publications of the Astronomical Society of Japan, v.52, p.113.

Astronomy and Astrophysics

Astronomy

13

Stars: Abundances (He, C), Stars: Activity, Stars: Atmospheres, Stars: Evolution, Supergiants

Scientific paper

The abundances of carbon and helium were determined for representative late-B and early-A supergiants based on the C I lines (9078, 9089, 9095, 9112) in the near-IR, C II lines (4267, 6151), and the He I 6678 line, in an aim to investigate the nature of the envelope-mixing in these evolved stars based on the anomaly (if any) of these elements combined with that of N and O published before. It turned out that N tends to increase with a decrease in C, showing a tendency of conserving the sum of C+N nuclei, which suggests that the anomaly of C and N may be reasonably interpreted as being due to mixing of the CN-processed material. However, this increase/decrease in N/C, indicative of dredge-up of the H-burning product, is not accompanied by any He-enrichment. Even surprisingly, the observed tendency is just the opposite, i.e., [He/H] appears to decrease progressively in accordance with a lowering of [C/H]. Instead of regarding this apparent characteristics as being real, we tentatively speculate that some activity-related line-weakening mechanism (e.g., irradiance of X-rays) might act on the formation of He I lines, the extent of which is indirectly related to the efficiency of envelope mixing via stellar rotation.

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