Investigating 2M1155−79B: A Nearby, Young, Low-mass Star Actively Accreting from a Nearly Edge-on, Dusty Disk

Abstract

We investigate the nature of an unusually faint member of the ϵ Cha association ( D ∼ 100 pc, age ∼5 Myr), the nearest region of star formation of age <8 Myr. This object, 2MASS J11550336−7919147 (2M1155−79B), is a wide-separation (∼580 au), comoving companion to low-mass (M3) ϵ Cha association member 2MASS J11550485−7919108 (2M1155−79A). We present near-infrared (NIR) spectra of both components, along with analysis of photometry from Gaia Early Data Release 3, the Two Micron All Sky Survey, the Vista Hemisphere Survey, and the Wide-field Infrared Survey Explorer (WISE). The NIR spectrum of 2M1155−79B displays strong He i 1.083 emission, a sign of active accretion and/or accretion-driven winds from a circumstellar disk. Analysis of WISE archival data reveals that the mid-infrared excess previously associated with 2M1155−79A instead originates from the disk surrounding 2M1155−79B. Based on these results, as well as radiative transfer modeling of its optical/IR spectral energy distribution, we conclude that 2M1155−79B is most likely a young, late M star that is partially obscured by, and actively accreting from, a nearly edge-on circumstellar disk. This would place 2M1155−79B among the rare group of nearby ( D ≲ 100 pc), young (age <10 Myr) mid-M stars that are orbited by and accreting from highly inclined protoplanetary disks. Like these systems, the 2M1155−79B system is a particularly promising subject for studies of star and planet formation around low-mass stars.