Emergence of a Lithium Dip in ∼35 Myr “Snake” Open Clusters

We report the discovery of a lithium dip (Li dip) in the stellar “Snake” (age = 35 ± 5 Myr), challenging the classical view that Li dips emerge only at ages ≳150 Myr. Using high-resolution spectra from galah Data Release 4 (R ∼ 28,000) for 211 member stars, we identify a clear depletion feature in a Teff range of 6200–6800 K with a depth of ΔA(Li) ≈ 0.40 dex. Our analysis reveals two key advances: the Li dip appears ≳100 Myr earlier than the previous observations, and within the dip temperature range, a significant correlation is found between rotational velocity and lithium depletion. Specifically, fast rotators ( vsini>25 km s−1) exhibit stronger lithium depletion than slow rotators ( vsini<25 km s−1). This trend suggests that faster rotators develop stronger rotational shear at the convective-radiative boundary, which enhances turbulent mixing and accelerates lithium destruction. It is also found that the lower temperature edge of the lithium plateau can reach as low as 5500 K for the young open clusters.