Let Sleeping Stars Li: Mapping Turnoff Lithium, the Lithium Dip, & Testing Standard Model Predictions in GALAH DR4 Subgiants
Year: 2026
Type: preprint
Abstract: Lithium is an excellent tracer of stellar mixing. We reconstruct the end of the main sequence lithium depletion pattern using the GALAH DR4 3D-NLTE lithium dataset for 22,442 stars, complemented by masses and subgiant lithium dilution factors inferred from YREC stellar models. We recover the two canonical features seen in clusters: a cool plateau ($\mathrm{M_{[Fe/H]_{\odot}}} \sim 1.2 \mathrm{M_\odot}$) with a median $A(Li) = 2.42$, and a steep plunge into the lithium dip ($\mathrm{M_{[Fe/H]_{\odot}}} \sim 1.35 \mathrm{M_\odot}$) dominated by upper limits at $A(Li) < 1.5$. Above the dip, our data reveal a striking new pattern with a wide range of abundances. We argue this reflects severe rotationally induced mixing in most stars, with lithium preserved in a minority where gravitational settling suppresses mixing. Lithium depletion with intrinsic dispersion is universal across the sample. Predicted and observed dilution trends agree well below the dip. For higher-mass stars, dilution corrections agree with standard models, but our upper envelope lies below open cluster values. We attribute this to a shallower lithium preservation zone and further evidence for gravitational settling and radiative levitation. We detect lithium in $\approx25\%$ of dip stars, whereas clusters show none; neither blurring of a narrow mass feature nor binary contamination fully explains this. The cool plateau is 0.8 dex below the solar meteoritic value across a wide range of $[Fe/H]$. After accounting for pre-main sequence depletion, the plateau is elevated at $\geq [Fe/H]_{\odot}$, possibly evidence for lithium production.
Source: arXiv (Cornell University)
Institution: The Ohio State University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Award: G85054406
OpenAlex ID: W7222957565