CNO ABUNDANCES OF HYDROGEN-DEFICIENT CARBON AND R CORONAE BOREALIS STARS: A VIEW OF THE NUCLEOSYNTHESIS IN A WHITE DWARF MERGER
- Instituto de Astrofisica de Canarias, C/ Via Lactea s/n, 38200 La Laguna (Spain)
- National Optical Astronomy Observatory (NOAO), Tucson, AZ 85726 (United States)
- W. J. McDonald Observatory, University of Texas at Austin, 1 University Station, C1400. Austin, TX 78712-0259 (United States)
We present high-resolution (R {approx} 50, 000) observations of near-IR transitions of CO and CN of the five known hydrogen-deficient carbon (HdC) stars and four R Coronae Borealis (RCB) stars. We perform an abundance analysis of these stars by using spectrum synthesis and state-of-the-art MARCS model atmospheres for cool hydrogen-deficient stars. Our analysis confirms reports by Clayton and colleagues that those HdC stars exhibiting CO lines in their spectrum and the cool RCB star S Aps are strongly enriched in {sup 18}O (with {sup 16}O/{sup 18}O ratios ranging from 0.3 to 16). Nitrogen and carbon are in the form of {sup 14}N and {sup 12}C, respectively. Elemental abundances for CNO are obtained from C I, C{sub 2}, CN, and CO lines. Difficulties in deriving the carbon abundance are discussed. Abundances of Na from Na I lines and S from S I lines are obtained. Elemental and isotopic CNO abundances suggest that HdC and RCB stars may be related objects, and that they probably formed from a merger of an He white dwarf with a C-O white dwarf.
- OSTI ID:
- 21300655
- Journal Information:
- Astrophysical Journal, Vol. 696, Issue 2; Other Information: DOI: 10.1088/0004-637X/696/2/1733; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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