Compulsory Deep Mixing of 3He and CNO Isotopes in the Envelopes of low-mass Red Giants

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Three-dimensional stellar modeling has enabled us to identify a deep-mixing mechanism that must operate in all low mass giants. This mixing process is not optional, and is driven by a molecular weight inversion created by the {sup 3}He({sup 3}He,2p){sup 4}He reaction. In this paper we characterize the behavior of this mixing, and study its impact on the envelope abundances. It not only eliminates the problem of {sup 3}He overproduction, reconciling stellar and big bang nucleosynthesis with observations, but solves the discrepancy between observed and calculated CNO isotope ratios in low mass giants, a problem of more than 3 decades standing. ... continued below

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Eggleton, P P; Dearborn, D P & Lattanzio, J C March 20, 2007.

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Three-dimensional stellar modeling has enabled us to identify a deep-mixing mechanism that must operate in all low mass giants. This mixing process is not optional, and is driven by a molecular weight inversion created by the {sup 3}He({sup 3}He,2p){sup 4}He reaction. In this paper we characterize the behavior of this mixing, and study its impact on the envelope abundances. It not only eliminates the problem of {sup 3}He overproduction, reconciling stellar and big bang nucleosynthesis with observations, but solves the discrepancy between observed and calculated CNO isotope ratios in low mass giants, a problem of more than 3 decades standing. This mixing mechanism operates rapidly once the hydrogen burning shell approaches the material homogenized by the surface convection zone. In agreement with observations, Pop I stars between 0.8 and 2.0 M{sub {circle_dot}} develop {sup 12}C/{sup 13}C ratios of 14.5 {+-} 1.5, while Pop II stars process the carbon to ratios of 4.0 {+-} 0.5. In stars less than 1.25 M{sub {circle_dot}}, this mechanism also destroys 90% to 95% of the {sup 3}He produced on the main sequence.

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PDF-file: 27 pages; size: 0.8 Mbytes

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  • Journal Name: Astrophysical Journal, vol. 677, N/A, February 29, 2008, pp. 581; Journal Volume: 677

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  • Report No.: UCRL-JRNL-229316
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 940503
  • Archival Resource Key: ark:/67531/metadc896590

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  • March 20, 2007

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  • Sept. 27, 2016, 1:39 a.m.

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  • Dec. 6, 2016, 7:54 p.m.

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Eggleton, P P; Dearborn, D P & Lattanzio, J C. Compulsory Deep Mixing of 3He and CNO Isotopes in the Envelopes of low-mass Red Giants, article, March 20, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc896590/: accessed September 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.