Abundance Ratios in GALAH DR2 and Their Implications for Nucleosynthesis

Using a sample of 70,924 stars from the second data release of the GALAH optical spectroscopic survey, we construct median sequences of [X/Mg] versus [Mg/H] for 21 elements, separating the high- /"low-Ia" and low- /"high-Ia" stellar populations through cuts in [Mg/Fe]. Previous w...

Full description

Saved in:
Bibliographic Details
Published in:The Astrophysical journal 2019-12, Vol.886 (2), p.84
Main Authors: Griffith, Emily, Johnson, Jennifer A., Weinberg, David H.
Format: Article
Language:English
Subjects:
Astrophysics
Chemical evolution
Collapse
Copper
Dependence
Enrichment
Galactic disk
Galaxy abundances
Iron
Metallicity
Nuclear capture
Nuclear fusion
Nucleosynthesis
Organic chemistry
Polls & surveys
Separation
Star & galaxy formation
Star formation
Stellar abundances
Stellar evolution
Stellar nucleosynthesis
Stellar populations
Supernova
Supernovae
Titanium
Yield
Yttrium
Zinc
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Using a sample of 70,924 stars from the second data release of the GALAH optical spectroscopic survey, we construct median sequences of [X/Mg] versus [Mg/H] for 21 elements, separating the high- /"low-Ia" and low- /"high-Ia" stellar populations through cuts in [Mg/Fe]. Previous work with the near-IR APOGEE survey has shown that such sequences are nearly independent of location in the Galactic disk, implying that they are determined by stellar nucleosynthesis yields with little sensitivity to other chemical evolution aspects. The separation between the two [X/Mg] sequences indicates the relative importance of prompt and delayed enrichment mechanisms, while the sequences' slopes indicate metallicity dependence of the yields. GALAH and APOGEE measurements agree for some of their common elements, but differ in sequence separation or metallicity trends for others. GALAH offers access to nine new elements. We infer that about 75% of solar C comes from core-collapse supernovae and 25% from delayed mechanisms. We find core-collapse fractions of 60%-80% for the Fe-peak elements Sc, Ti, Cu, and Zn, with strong metallicity dependence of the core-collapse Cu yield. For the neutron capture elements Y, Ba, and La, we infer large delayed contributions with non-monotonic metallicity dependence. The separation of the [Eu/Mg] sequences implies that at least ∼30% of Eu enrichment is delayed with respect to star formation. We compare our results to predictions of several supernova and asymptotic giant branch yield models; C, Na, K, Mn, and Ca all show discrepancies with models that could make them useful diagnostics of nucleosynthesis physics.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ab4b5d