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

Abstract 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 T eff range of 6200–6800 K with a depth of Δ A (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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> <mml:mo>&gt;</mml:mo> <mml:mn>25</mml:mn> </mml:math> km s −1 ) exhibit stronger lithium depletion than slow rotators ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mn>25</mml:mn> </mml:math> 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.