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Title: Chemical composition and evolutionary state of the early R stars

Abstract

A sample of 11 stars classified R0-R5 has been analyzed to determine (i) iron-peak metal abundances, (ii) abundances of elements produced by the s-process, (iii) the light element abundances (C,N, and O), and (iv)= the carbon isotopic ratio /sup 12/C//sup 13/C. Abundances are reported relative to the Sun. With the expection of HD 100764, which has an iron abundance 0.6 dex lower than the Sun's, the iron abundance of 10 stars is near solar. The s-process elements have no demonstrable enhancement in the sample, unlike the Ba II stars of the same temperature and the cooler carbon stars. The enhancement of carbon relative to the G-K giants found in the analysis of eight stars is 0.7 dex, with one star having Croughly-equal O (HD 113801), while another star (HD 95405) is probably not a carbon star (C/O = 0.87). Relative to the ordinary G-K giants, nitrogen is enhanced by a small amount (0.2 dex). In contrast, oxygen has nearly the value found in the Sun and in normal giants, except in the case of HD 100764 where O is probably as underabundant as Fe. The /sup 12/C//sup 13/C ratio ranges for near 4 to 14 for nine stars, indicating anmore » enrichment of /sup 13/C with respect to the majority of faint giants. For HD 156074 the oxygen isotopic ratios /sup 16/O//sup 17/O and /sup 16/O//sup 18/O do not have detectable departures from the solar system values. The lack of oxygen depletion indicates that the CNO cycle operating near equilibrium is not responsible for the fact that C/O>1 in these stars. Based on the early R stars' position in the H-R diagram, their space number densities, and their enhanced carbon abundances, it is here suggested that they result from mixing at the time of, or closely following, the helium core flash.« less

Authors:
Publication Date:
Research Org.:
Department of Astronomy, University of Texas at Austin
OSTI Identifier:
6654507
Resource Type:
Journal Article
Journal Name:
Astrophys. J., Suppl. Ser.; (United States)
Additional Journal Information:
Journal Volume: 55:1
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CARBON STARS; CHEMICAL COMPOSITION; NUCLEOSYNTHESIS; STAR EVOLUTION; ABUNDANCE; BARIUM IONS; CARBON; CARBON 13; CARBON 14; CARBON BURNING; CNO CYCLE; NEUTRONS; NITROGEN; NITROGEN 13; NITROGEN 14; OXYGEN; OXYGEN 16; OXYGEN 17; OXYGEN 18; R PROCESS; S PROCESS; BARYONS; BETA DECAY RADIOISOTOPES; BETA-MINUS DECAY RADIOISOTOPES; BETA-PLUS DECAY RADIOISOTOPES; CARBON ISOTOPES; CHARGED PARTICLES; ELECTRON CAPTURE RADIOISOTOPES; ELEMENTARY PARTICLES; ELEMENTS; EVEN-EVEN NUCLEI; EVEN-ODD NUCLEI; FERMIONS; HADRONS; IONS; ISOTOPES; LIGHT NUCLEI; MAIN SEQUENCE STARS; MINUTES LIVING RADIOISOTOPES; NITROGEN ISOTOPES; NONMETALS; NUCLEI; NUCLEONS; ODD-EVEN NUCLEI; ODD-ODD NUCLEI; OXYGEN ISOTOPES; RADIOISOTOPES; STABLE ISOTOPES; STAR BURNING; STARS; SYNTHESIS; YEARS LIVING RADIOISOTOPES; 640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar, Radio & X-Ray Sources

Citation Formats

Dominy, J F. Chemical composition and evolutionary state of the early R stars. United States: N. p., 1984. Web. doi:10.1086/190946.
Dominy, J F. Chemical composition and evolutionary state of the early R stars. United States. https://doi.org/10.1086/190946
Dominy, J F. 1984. "Chemical composition and evolutionary state of the early R stars". United States. https://doi.org/10.1086/190946.
@article{osti_6654507,
title = {Chemical composition and evolutionary state of the early R stars},
author = {Dominy, J F},
abstractNote = {A sample of 11 stars classified R0-R5 has been analyzed to determine (i) iron-peak metal abundances, (ii) abundances of elements produced by the s-process, (iii) the light element abundances (C,N, and O), and (iv)= the carbon isotopic ratio /sup 12/C//sup 13/C. Abundances are reported relative to the Sun. With the expection of HD 100764, which has an iron abundance 0.6 dex lower than the Sun's, the iron abundance of 10 stars is near solar. The s-process elements have no demonstrable enhancement in the sample, unlike the Ba II stars of the same temperature and the cooler carbon stars. The enhancement of carbon relative to the G-K giants found in the analysis of eight stars is 0.7 dex, with one star having Croughly-equal O (HD 113801), while another star (HD 95405) is probably not a carbon star (C/O = 0.87). Relative to the ordinary G-K giants, nitrogen is enhanced by a small amount (0.2 dex). In contrast, oxygen has nearly the value found in the Sun and in normal giants, except in the case of HD 100764 where O is probably as underabundant as Fe. The /sup 12/C//sup 13/C ratio ranges for near 4 to 14 for nine stars, indicating an enrichment of /sup 13/C with respect to the majority of faint giants. For HD 156074 the oxygen isotopic ratios /sup 16/O//sup 17/O and /sup 16/O//sup 18/O do not have detectable departures from the solar system values. The lack of oxygen depletion indicates that the CNO cycle operating near equilibrium is not responsible for the fact that C/O>1 in these stars. Based on the early R stars' position in the H-R diagram, their space number densities, and their enhanced carbon abundances, it is here suggested that they result from mixing at the time of, or closely following, the helium core flash.},
doi = {10.1086/190946},
url = {https://www.osti.gov/biblio/6654507}, journal = {Astrophys. J., Suppl. Ser.; (United States)},
number = ,
volume = 55:1,
place = {United States},
year = {Tue May 01 00:00:00 EDT 1984},
month = {Tue May 01 00:00:00 EDT 1984}
}