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

Abstract

Hydra spectra of 85 G–K dwarfs in the young cluster M35 near the Li 6708 Å line region are analyzed. From velocities and Gaia astrometry, 78 are likely single-star members that, combined with previous work, produce 108 members with T eff ranging from 6150 to 4000 K as defined by multicolor, broadband photometry, E ( B − V ) = 0.20, and [Fe/H] = −0.15, though there are indications the metallicity may be closer to solar. The Lithium abundance 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 (RRs) are consistent with models that simultaneously consider rapid rotation and radius inflation; RRs 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.