Carbon and eruptive stars : surface enrichment of lithium, carbon, nitrogen, and C13 by deep mixing.

Abstract

view Abstract Citations (163) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Carbon and eruptive stars: surface enrichment of lithium, carbon, nitrogen, and 13C by deep mixing. Sackmann, I. -J. ; Smith, R. L. ; Despain, K. H. Abstract It appears possible to form carbon stars from stars of both low ( 1 M0) and intermediate (5 M0) masses and from both population types. A single helium shell flash followed by deep mixing suffices for the former case, but on the order of 100 such flashes are required for the latter. No more than the order of 100 flashes are possible for the former and 1000 for the latter. The Cameron-Fowler mechanism for the production of high lithium abundances in late-type stars is shown to work satisfactorily, producing 7Li/H up to about 10- in a single flash. This value is nearly independent of mass and population type. Eruptive stars may result when the deep convective envelopes reach into helium-burning iayers. Large amounts of energy can be liberated in a very short time; e.g., the binding energy of the envelope, 1048 ergs, can be exceeded in 106 sec. Many of the gross features of the R Coronae Borealis stars can be understood by erupting carbon star models. For example, observed surface abundances of H, He, 7Li, 12C/16O, 14N/12C, and 12C/13C can be accounted for. For an unrepeated deep mixing, an upper limit can be placed on the mass of a carbon star, namely, 2 M0.. For short-duration mixing, 7Li/H reaches its peak value (7Li/H 12C/16O > 1 or <1, depending on the mass, 10- < 14N/12C < 1, and S < 12C/13C < 100; for intermediate-duration mixing, 7Li/H < 10-8, 12C/16O < 1, 1 < 14N/12C < 40, and 2.4 < 12C/13C < 5; for long-duration mixing, 7Li/H = 0, 12C/16O > 1, 14N/12C = 40, and 12C/13C = 3.2. These abundance ratios agree quite well with the observations in the oxygen and carbon stars, S, Ba ii, C, and CH, ordering these spectral types in a sequence determined by the duration of deep mixing. Repeated deep mixing can explain the observations known for S, Ba II, and C stars when they are considered to be intermediate-mass objects. S stars would be interpreted as those with few flashes, Ba ii stars as those with an intermediate number of flashes, and C stars super-rich in 7Li as those with a very large number of flashes. Subject headings: Ba ii stars - carbon stars - interiors, stellar - nuclear reactions - R Coronae Borealis stars Publication: The Astrophysical Journal Pub Date: February 1974 DOI: 10.1086/152666 Bibcode: 1974ApJ...187..555S full text sources ADS | data products SIMBAD (9)