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Paper: Metal Enrichment in the Earliest Phases of the Universe: The Very Metal-poor Halo Stars
Volume: 374, From Stars to Galaxies: Building the Pieces to Build Up the Universe
Page: 125
Authors: Chiappini, C.
Abstract: In this work we present chemical evolution models for the Milky Way at very low metallicities, and study the interstellar medium enrichment of the most abundant metals (CNO). In particular we show the impact in our results of the new stellar yields obtained from stellar models which take rotation into account.

We find that the new Z = 10−8 stellar yields computed for large rotational velocities 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 new stellar calculations in a chemical evolution model for the galactic halo with infall and outflow, both high N/O and C/O ratios are obtained in the very-metal poor metallicity range in agreement with observations. Moreover, our results offer a natural explanation for the large scatter observed in the N/O abundance ratio of normal metal-poor halo stars. Our findings give further support to the idea that stars at very low metallicities could have been fast rotators, achieving initial rotational velocities of the order of 600-800 kms−1. An important contribution to N from AGB stars is still needed in order to explain the observations at intermediate metallicities.

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