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Deep Circulation in Red Giant Stars: A Solution to the Carbon and Oxygen Isotope Puzzles?

Wasserburg, G. J. and Boothroyd, Arnold I. and Sackmann, I.-Juliana (1995) Deep Circulation in Red Giant Stars: A Solution to the Carbon and Oxygen Isotope Puzzles? Astrophysical Journal Letters, 447 (1). L37-L40. ISSN 2041-8205. doi:10.1086/309555.

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The long-standing puzzle of low ^(12)C/^(13)C in low-mass red giant branch (RGB) stars, and the more recent puzzle of low ^(18)O/^(16)O ratios in asymptotic giant branch (AGB) stars and in circumstellar Al_2O_3 grains preserved in meteorites, can be resolved by deep circulation currents below the bottom of the standard convective envelope. These currents transport matter from the nonburning bottom of the convective envelope down to regions where some CNO processing can take place ("cool bottom processing"). Modeling circulation with separate downward and upward streams, we found that, to resolve both discrepancies, the base of the extra mixing had to reach a temperature TP close to that of the H-burning shell, namely, Δ log T ≈ 0.17 from the base of the H-shell for both RGB and AGB stars. While the envelope composition depends sensitively on TP, it is insensitive to the speed or geometry of mixing. This indicates that our stream circulation model is generic, so that more sophisticated mixing models with the same TP would yield similar results. On the AGB, our models predict that stars with low ^(18)O/^(16)O can be either S or C stars but must have low ^(12)C/^(13)C (~4) and elevated ^(14)N. Cool bottom processing also destroys ^3He, so that galactic (D + ^3He) decreases with time; this removes the strongest lower limit on the baryon density Ω_b from big bang nucleosynthesis models.

Item Type:Article
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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1995 American Astronomical Society. Received 1995 March 6; accepted 1995 April 25. This paper was much improved by penetrating comments and creative suggestions by M. Busso and critical reading and comments by G. Huss, G. Bazan, C. A. Barnes, R. F. Christy, and R. Gallino. A. I. B. wishes to thank S. D. Tremaine and P. G. Martin for the support provided by the Canadian Institute for Theoretical Astrophysics. This work was supported in part by a grant from the Natural Sciences and Engineering Research Council of Canada, NASA grants NAGW-3040, NAGW-3337, NAGW-3297, and NSF grant PHY 94-20470. Contribution No. 5498(892), Division of Geological and Planetary Sciences of Caltech.
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Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
NSFPHY 94-20470
Subject Keywords: early universe; nuclear reactions, nucleosynthesis, abundances; stars: abundances; stars: late-type
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Caltech Division of Geological and Planetary Sciences5498
Lunatic Asylum Lab892
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Record Number:CaltechAUTHORS:20131211-143437708
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Official Citation: Deep Circulation in Red Giant Stars: A Solution to the Carbon and Oxygen Isotope Puzzles? G. J. Wasserburg et al. 1995 ApJ 447 L37
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42964
Deposited By: Ruth Sustaita
Deposited On:12 Dec 2013 15:48
Last Modified:10 Nov 2021 16:31

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