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

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...

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Main Authors: Owusu, Evans (Author) , Ruiter, Ashley J (Author) , Kemp, Alex J (Author) , Buder, Sven (Author) , Seitenzahl, Ivo R (Author) , Rodriguez-Segovia, Nicolas (Author) , Pakmor, R (Author) , Cinquegrana, Giulia C (Author) , Storm, Nicholas (Author) , Eitner, Philipp (Author) , Bergemann, Maria (Author)
Format: Article (Journal)
Language:English
Published: January 2026
In: Monthly notices of the Royal Astronomical Society
Year: 2026, Volume: 545, Issue: 2, Pages: 1-13
ISSN:1365-2966
DOI:10.1093/mnras/staf2079
Online Access:Verlag, kostenfrei, Volltext: https://doi.org/10.1093/mnras/staf2079
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Author Notes:Evans K. Owusu, Ashley J. Ruiter, Alex J. Kemp, Sven Buder, Ivo R. Seitenzahl, Nicolas Rodriguez-Segovia, R. Pakmor, Giulia C. Cinquegrana, Nicholas Storm, Philipp Eitner and Maria Bergemann
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Summary: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.
Item Description:Veröffentlicht: 24. November 2025
Gesehen am 17.02.2026
Physical Description:Online Resource
ISSN:1365-2966
DOI:10.1093/mnras/staf2079

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