Abundances and evolutionary state of the early R stars
The results of the first spectoscopic study of a sample of early R stars are reported. From this data the abundances of C, N, O, Ti, Fe, /sup 12/C//sup 13/C and five elements formed by the s-process were derived. The direct measurement of the oxygen abundance is the first such determination for a warm carbon star. The abundance analyses were carried out with multi-layer, line blanketed model atmospheres and spectrum synthesis programs. Stellar parameters for comparison with the models (T/sub eff/, log g) were derived primarily from calibrated infrared photometry and an assumed stellar mass. With the exception of one star, HD 100764 which is 0.6 dex deficient, the iron-peak elements Ti and Fe have their solar values within the estimated errors (0.3 dex). Likewise, the s-process elements are solar. The /sup 12/C//sup 13/C ratios range from near 4 to 15. The oxygen abundance for the group is near solar. The total carbon abundance (/sup 12/C + /sup 13/C) is enhanced (by about 0.5 dex) relative to the sun and the nitrogen abundance is enhanced by a similar amount. These values contrast with the normal G-K giants which have carbon 0.3 dex deficient and nitrogen 0.3 dex enhanced. The oxygen isotopic ratios /sup 16/O//sup 17/O and /sup 18/O//sup 16/O do not have demonstrable enhancements relative to the solar system values of 2700 and 500 respectively. One star (HD 95404) was found not to be carbon rich (C/O is less than 1) and another star (HD 113801) has C/O near unity. The abundance pattern that emerges from this study is interpreted as the result of nuclear processing and mixing at the time of the helium core flash. It is suggested that the /sup 12/C produced during the flash is well processed to /sup 13/C and /sup 14/N by the capture of protons from the envelope.
- Research Organization:
- Texas Univ., Austin (USA)
- OSTI ID:
- 7132100
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
STARS
CHEMICAL COMPOSITION
CARBON
CARBON 12
CARBON 13
HELIUM BURNING
IRON
ISOTOPE RATIO
MASS
NITROGEN
OXYGEN
S PROCESS
SPECTROSCOPY
TITANIUM
CARBON ISOTOPES
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
ISOTOPES
LIGHT NUCLEI
METALS
NONMETALS
NUCLEI
STABLE ISOTOPES
STAR BURNING
STAR EVOLUTION
TRANSITION ELEMENTS
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
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