THE GALACTIC R CORONAE BOREALIS STARS: THE C{sub 2} SWAN BANDS, THE CARBON PROBLEM, AND THE {sup 12}C/{sup 13}C RATIO

Journal Article · Sat Mar 10 04:00:00 UTC 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/747/2/102· OSTI ID:22016255

Hema, B P; Pandey, Gajendra ^[1]

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1. Indian Institute of Astrophysics, Bangalore Karnataka 560034 (India)

Observed spectra of R Coronae Borealis (RCB) and hydrogen-deficient carbon (HdC) stars are analyzed by synthesizing the C{sub 2} Swan bands (1, 0), (0, 0), and (0, 1) using our detailed line list and the Uppsala model atmospheres. The (0, 1) and (0, 0) C{sub 2} bands are used to derive the {sup 12}C abundance, and the (1, 0) {sup 12}C{sup 13}C band to determine the {sup 12}C/{sup 13}C ratios. The carbon abundance derived from the C{sub 2} Swan bands is about the same for the adopted models constructed with different carbon abundances over the range 8.5 (C/He = 0.1%) to 10.5 (C/He = 10%). Carbon abundances derived from C I lines are about a factor of four lower than the carbon abundance of the adopted model atmosphere over the same C/He interval, as reported by Asplund et al., who dubbed the mismatch between adopted and derived C abundance as the 'carbon problem'. In principle, the carbon abundances obtained from C{sub 2} Swan bands and that assumed for the model atmosphere can be equated for a particular choice of C/He that varies from star to star. Then, the carbon problem for C{sub 2} bands is eliminated. However, such C/He ratios are in general less than those of the extreme helium stars, the seemingly natural relatives to the RCB and HdC stars. A more likely solution to the C{sub 2} carbon problem may lie in a modification of the model atmosphere's temperature structure. The derived carbon abundances and the {sup 12}C/{sup 13}C ratios are discussed in light of the double degenerate and the final flash scenarios.

• OSTI ID: 22016255
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 747; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
CARBON 12
CARBON 13
HELIUM
HYDROGEN
STAR EVOLUTION
STARS
STELLAR ATMOSPHERES