Detection of lithium in nearby young late-M dwarfs

TL;DR

This study identifies lithium in nearby late-M dwarfs to determine their youth and mass, discovering new young brown dwarfs and candidates, and setting limits on debris disks around these objects.

Contribution

First detection of lithium in several late-M dwarfs, confirming their young brown dwarf status and providing new benchmarks for studying substellar objects.

Findings

Detected lithium absorption in four targets

Identified two young brown dwarfs and two candidates

No debris disks detected around the three observed targets

Abstract

Late M-type dwarfs in the solar neighborhood include a mixture of very low-mass stars and brown dwarfs which is difficult to disentangle due to the lack of constraints on their age such as trigonometric parallax, lithium detection and space velocity. We search for young brown dwarf candidates among a sample of 28 nearby late-M dwarfs with spectral types between M5.0 and M9.0, and we also search for debris disks around three of them. Based on theoretical models, we used the color $I-J$, the $J$-band absolute magnitude and the detection of the Li I 6708 $\AA$ doublet line as a strong constraint to estimate masses and ages of our targets. For the search of debris disks, we observed three targets at submillimeter wavelength of 850 $\mu$m. We report here the first clear detections of lithium absorption in four targets and a marginal detection in one target. Our mass estimates indicate that two of them are young brown dwarfs, two are young brown dwarf candidates and one is a young very low-mass star. The closest young field brown dwarf in our sample at only $\sim$15 pc is an excellent benchmark for further studying physical properties of brown dwarfs in the range 100$-$150 Myr. We did not detect any debris disks around three late-M dwarfs, and we estimated upper limits to the dust mass of debris disks around them.