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

Using a sample of 116 wide binary systems as coeval and chemically homogeneous stellar pairs, we investigate the factors governing lithium (Li) depletion in main-sequence stars. We recover the well-established morphology of the Li–effective temperature ( T eff ) relation, including the Li dip (6200–6600 K), the Li plateau (6000–6200 K), and a linear trend for cooler stars ( T eff < 6000 K), where Li abundance increases by ∼0.15 dex per 100 K. We demonstrate that the apparent correlation between projected rotational velocity ( v sin i ) and Li abundance is secondary to the underlying T eff dependence; v sin i is not an independent driver of Li depletion in our sample. Notably, we identify an anomalous system within the Li dip where the primary star exhibits a ∼1.4 dex Li excess compared to its secondary companion at nearly identical T 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 eff as the dominant parameter controlling Li depletion, while highlighting that additional, nonstandard processes can occasionally produce significant Li enrichment.