Emergence of a lithium dip in ~35 Myr "Snake" Open Clusters

TL;DR

This study discovers a lithium dip in the 35-million-year-old Snake cluster, earlier than previously known, and links faster stellar rotation to increased lithium depletion, challenging existing models of stellar evolution.

Contribution

It provides the first evidence of a lithium dip in a young cluster at 35 Myr and establishes a correlation between stellar rotation speed and lithium depletion.

Findings

Lithium dip appears at ~35 Myr, earlier than 150 Myr.

Fast rotators show stronger lithium depletion.

Lower temperature edge of lithium plateau reaches 5500 K.

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 $\Delta A(\mathrm{Li}) \approx 0.40$ 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.