Li in Open Clusters: Cool Dwarfs in the Young, Subsolar Metallicity Cluster M35 (NGC 2168)

TL;DR

This study analyzes lithium abundances in G-K dwarfs of the young, subsolar metallicity cluster M35, revealing relationships between lithium depletion, rotation, and stellar evolution, and comparing these findings to other clusters like Pleiades.

Contribution

It provides new insights into lithium depletion patterns in M35, especially regarding the effects of rotation and metallicity, and compares these with other well-studied clusters.

Findings

Li abundance declines with decreasing T_eff from 3.15 to <=1.0.

High-Li, rapid rotators tend to be convective stars with higher rotation speeds.

M35's age is between that of M34 and Pleiades, with distinct Li and rotation distributions.

Abstract

Hydra spectra of 85 G-K dwarfs in the young cluster, M35, near the Li 6708 Angstrom line region are analyzed. From velocities and Gaia astrometry, 78 are likely single-star members which, combined with previous work, produces 108 members with T_eff ranging from 6150 to 4000 K as defined by multicolor, broad-band photometry, E(B-V ) = 0.20 and [Fe/H] = -0.15, though there are indications the metallicity may be closer to solar. A(Li) follows a well-delineated decline from 3.15 for the hottest stars to upper limits <= 1.0 among the coolest dwarfs. Contrary to earlier work, M35 includes single stars at systematically higher A(Li) than the mean cluster relation. This subset exhibits higher V_ROT than the more Li-depleted sample and, from photometric rotation periods, is dominated by stars classed as convective (C); all others are interface (I) stars. The cool, high-Li rapid rotators are consistent with models that consider simultaneously rapid rotation and radius inflation; rapid rotators hotter than the sun exhibit excess Li depletion, as predicted by the models. The A(Li) distribution with color and rotation period, when compared to the Hyades/Praesepe and the Pleiades, is consistent with gyrochronological analysis placing M35's age between the older M34 and younger Pleiades. However, the Pleiades display a more excessive range in A(Li) and rotation period than M35 on the low-Li, slow-rotation side of the distribution, with supposedly younger stars at a given T_eff in the Pleiades spinning slower, with A(Li) reduced by more than a factor of four compared to M35.