Lithium depletion boundary, stellar associations, and Gaia

TL;DR

This study revises lithium depletion boundary ages for stellar associations using Gaia data, providing more consistent and accurate age estimates, and highlights discrepancies among different methods and potential multiple populations in some groups.

Contribution

It offers a homogeneous re-evaluation of LDB ages for multiple stellar groups using Gaia parallaxes and multi-wavelength data, improving age accuracy and consistency.

Findings

LDB ages for 12 stellar associations were determined.

Discrepancies found between LDB ages and other methods.

Evidence suggests 32 Ori MG may contain multiple populations.

Abstract

Stellar ages are key to improving our understanding of different astrophysical phenomena. However, many techniques to estimate stellar ages are highly model-dependent. The lithium depletion boundary (LDB), based on the presence or absence of lithium in low-mass stars, can be used to derive ages in stellar associations of between 20 and 500~Ma. The purpose of this work is to revise former LDB ages in stellar associations in a consistent way, taking advantage of the homogeneous \textit{Gaia} parallaxes as well as bolometric luminosity estimations that do not rely on monochromatic bolometric corrections. We studied nine open clusters and three moving groups characterised by a previous determination of the LDB age. We gathered all the available information from our data and the literature: membership, distances, photometric data, reddening, metallicity, and surface gravity. We re-assigned membership and calculated bolometric luminosities and effective temperatures using distances derived from Gaia DR2 and multi-wavelength photometry for individual objects around the former LDB. We located the LDB using a homogeneous method for all the stellar associations. Finally, we estimated the age by comparing it with different evolutionary models. We located the LDB for the twelve stellar associations and derived their ages using several theoretical evolutionary models. We compared the LDB ages among them, along with data obtained with other techniques, such as isochrone fitting, ultimately finding some discrepancies among the various approaches. Finally, we remark that the 32 Ori MG is likely to be composed of at least two populations of different ages.