Lithium in Wide Binaries: Effective Temperature Governs Depletion while Rotation Plays a Minor Role

TL;DR

This study confirms that effective temperature primarily governs lithium depletion in main-sequence stars, with rotation playing a minor role, and identifies rare cases of lithium enrichment likely due to external or binary interactions.

Contribution

We demonstrate that effective temperature is the main factor in lithium depletion, and show that rotation is not an independent driver, while also identifying rare lithium enrichment cases.

Findings

Lithium abundance correlates strongly with effective temperature.

Rotation velocity is secondary and not an independent factor.

Rare lithium enrichment may result from planetesimal accretion or binary interactions.

Abstract

Using a sample of 116 wide binary systems as coeval and chemically homogeneous stellar pairs, we investigate the factors governing lithium depletion in main-sequence stars. We recover the well-established morphology of the lithium--effective temperature ($T_{\mathrm{eff}}$) relation, including the Li dip (6200--6600\,K), the Li plateau (6000--6200\,K), and a linear trend for cooler stars ($T_{\mathrm{eff}}$ $<$ 6000\,K), where lithium abundance increases by $\sim$0.15\,dex per 100\,K. We demonstrate that the apparent correlation between projected rotational velocity ($v\sin i$) and lithium abundance is secondary to the underlying $T_{\mathrm{eff}}$ dependence; $v\sin i$ is not an independent driver of lithium depletion in our sample. Notably, we identify an anomalous system within the Li dip where the primary star exhibits a $\sim$1.4\,dex lithium excess compared to its secondary companion at nearly identical $T_{\mathrm{eff}}$. We discuss two plausible origins for this anomaly: external enrichment via planetesimal accretion or planetary engulfment, and binary interactions with an unresolved tertiary companion. Our results confirm $T_{\mathrm{eff}}$ as the dominant parameter controlling lithium depletion, while highlighting that additional, non-standard processes can occasionally produce significant lithium enrichment.