A strong case for fast stellar rotation at very low metallicities

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Abstract
We investigate the effect of new stellar models, which take rotation into account, computed for a metallicity Z = 10^{-8} on the chemical evolution of the earliest phases of the Milky Way. These models are 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 interstellar medium nitrogen enrichment for log(O/H)+12 < 7 (or [Fe/H]< -3).We show that upon the inclusion of the 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}.

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