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 = $35\pm 5$ Myr), challenging the classical view that Li-dips emerge only at ages $\gtrsim 150$ Myr. Using high-resolution spectra from GALAH DR4 ($R\sim 28,000$) for 211 member stars, we identify a clear depletion feature in a $T_{\mathrm{eff}}$ range of 6200--6800 K with a depth of $\hat{I}”A(\mathrm{Li})\approx 0.40$ dex. Our analysis reveals two key advances: the Li-dip appears $\gtrsim 100$ 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 ($v\sin i>25$ km s${}^{-1}$) exhibit stronger lithium depletion than slow rotators ($v\sin i<25$ 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.

12 pages, 3 figures, 2 tables, accepted for publication in ApJL