Testing stellar yield prescriptions in omega+ : implications for rising sodium abundances in young thick disc stars

Le résumé fourni par la source

ABSTRACT We recently identified an upturn in [Na/Fe] for the population of solar-type stars in the Galactic young thick disc ($-0.3 < \mathrm{[Fe/H]} < +0.3$ dex) at supersolar metallicity in GALAH (GALactic Archaeology with HERMES) data. Here, we investigate the cause of this unexplained Na enrichment ($[{\rm Na/Fe}] \approx 0 \!-\!0.6$ dex) using the omega+ Galactic chemical evolution code. We investigate the increase of [Na/Fe] with four combinations of nucleosynthetic yields from the literature, with source contributions from core-collapse supernovae (CC SNe), asymptotic giant branch (AGB) stars, and Type Ia supernovae (SNe Ia). We focus on two possible causes for the Na enhancement: the ‘metallicity effect’ resulting from CC SNe at supersolar metallicity and the contribution of metal-rich AGB stars. We adopt two sets of SN Ia yields with one model assuming only Chandrasekhar-mass explosions, and another assuming only sub-Chandrasekhar-mass explosions. We find that the assumed SN Ia explosion has little effect on the [Na/Fe] Galactic chemical evolution modelling, and all Galactic chemical evolution models tested fail to reproduce the observed [Na/Fe] enrichment in the young thick disc population at supersolar metallicities. Our study indicates a possible ‘underpollution effect’ by SNe Ia, which are the dominant producers of iron, in the Galactic disc’s solar-type star population. These findings provide a step forward towards understanding the origin of the unexplained sodium enrichment at supersolar metallicities in the Galactic disc.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.