Volume 542, June 2012
|Number of page(s)||11|
|Section||Stellar structure and evolution|
|Published online||07 June 2012|
Effects of thermohaline instability and rotation-induced mixing on the evolution of light elements in the Galaxy: D, 3He and 4He
1 Geneva Observatory, University of Geneva, Chemin des Maillettes 51, 1290 Versoix, Switzerland
2 INAF – Bologna Observatory, via Ranzani 1, 40127 Bologna, Italy
3 IRAP, CNRS UMR 5277, Université de Toulouse, 14, Av. E.Belin, 31400 Toulouse, France
4 Leibniz – Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
5 Physics Department, Trieste University, via Tiepolo 11, 34143 Trieste, Italy
6 INAF-Trieste Observatory, via Tiepolo 11, 34143 Trieste, Italy
Received: 28 February 2012
Accepted: 8 April 2012
Context. Recent studies of low- and intermediate-mass stars show that the evolution of the chemical elements in these stars is very different from that proposed by standard stellar models. Rotation-induced mixing modifies the internal chemical structure of main sequence stars, although its signatures are revealed only later in the evolution when the first dredge-up occurs. Thermohaline mixing is likely the dominating process that governs the photospheric composition of low-mass red giant branch stars and has been shown to drastically reduce the net 3He production in these stars. The predictions of these new stellar models need to be tested against galaxy evolution. In particular, the resulting evolution of the light elements D, 3He and 4He should be compared with their primordial values inferred from the Wilkinson Microwave Anisotropy Probe data and with the abundances derived from observations of different Galactic regions.
Aims. We study the effects of thermohaline mixing and rotation-induced mixing on the evolution of the light elements in the Milky Way.
Methods. We compute Galactic evolutionary models including new yields from stellar models computed with thermohaline instability and rotation-induced mixing. We discuss the effects of these important physical processes acting in stars on the evolution of the light elements D, 3He, and 4He in the Galaxy.
Results. Galactic chemical evolution models computed with stellar yields including thermohaline mixing and rotation fit better observations of 3He and 4He in the Galaxy than models computed with standard stellar yields.
Conclusions. The inclusion of thermohaline mixing in stellar models provides a solution to the long-standing “3He problem” on a Galactic scale. Stellar models including rotation-induced mixing and thermohaline instability reproduce also the observations of D and 4He.
Key words: Galaxy: evolution / galaxies: abundances / galaxies: formation
© ESO, 2012
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