Intermediate-to-Low Mass Stars in Open Clusters and the Evolution of Li

TL;DR

This paper investigates lithium evolution in intermediate-to-low-mass stars within open clusters aged 1-3 Gyr, revealing patterns of Li variation linked to stellar evolution stages and providing insights into underlying processes affecting Li abundance.

Contribution

It presents new observational data on Li in stars across different evolutionary phases in open clusters, offering explanations for Li variation patterns related to the Lithium dip and stellar aging.

Findings

Li varies widely among stars on the hot side of the Lithium dip.

Li declines sharply in first-ascent giant stars with age.

Li patterns correlate with stellar mass, age, and evolutionary stage.

Abstract

Open clusters (OC) of 1-3 Gyr age contain intermediate-to-low-mass stars in evolutionary phases of multiple relevance to understanding Li evolution. Stars leaving the main sequence (MS) from the hot side of the Lithium dip (LD) at a fixed age can include a range of mass, varying degrees of core degeneracy, and helium ignition under quiescent or flash conditions. An ongoing survey of a significant sample of stars from the giant branch to below the LD in key open clusters has revealed patterns that supply critical clues to the underlying source of Li variation among stars of differing mass and age. While the LD is well established in OC of this age, stars on the hot side of the LD can exhibit Li ranging from the apparent primordial cluster value to upper limits similar to those found at the LD center, despite occupying the same region of the color-magnitude diagram (CMD). Stars on the first-ascent giant branch show a dramatic decline in measurable Li that correlates strongly with increasing age and reduced turnoff mass. We discuss how these trends can be explained in the context of the existence of the LD itself and the temporal evolution of individual stars.