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Issue A&A
Volume 449, Number 2, April II 2006
Page(s) L27 - L30
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20064866

A&A 449, L27-L30 (2006)
DOI: 10.1051/0004-6361:20064866

Letter

A strong case for fast stellar rotation at very low metallicities

C. Chiappini1, 2, R. Hirschi3, G. Meynet2, S. Ekström2, A. Maeder2 and F. Matteucci4

1  Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italia
    e-mail: Christina.Chiappini@obs.unige.ch
2  Observatoire Astronomique de l'Université de Genève, 1290 Sauverny, Switzerland
3  Dept. of Physics and Astronomy, University of Basel, 4056 Basel, Switzerland
4  Dipartimento di Astronomia, Universitá degli Studi di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italia

(Received 16 January 2006 / Accepted 20 February 2006)

Abstract
We investigate the effect of new stellar models taking rotation into account and computing for a metallicity Z = 10-8 on the chemical evolution of the earliest phases of the Milky Way. These models were computed under the assumption that the ratio of the initial rotation velocity to the critical velocity of stars is roughly constant with metallicity. This naturally leads to faster rotation at lower metallicity, as metal-poor stars are more compact than metal-rich ones. We find that the new Z = 10-8 stellar yields have a tremendous impact on the nitrogen enrichment of the interstellar medium for log(O/H) + 12 < 7 (or $\rm [Fe/H]< -3$). We show that including Z = 10-8 stellar yields in chemical evolution models, both high N/O and C/O ratios are obtained in the very-metal poor metallicity range, in agreement with observations. Our results give further support to the idea that stars at very low metallicities could have rotational velocities of the order of 600-800 km s-1.


Key words: stars: rotation -- Galaxy: evolution





© ESO 2006


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