BANYAN. VIII. New Low-Mass Stars and Brown Dwarfs with Candidate Circumstellar Disks

Abstract

We present the results of a search for new circumstellar disks around low-mass stars and brown dwarfs with spectral types >K5 that are confirmed or candidate members of nearby young moving groups. Our search input sample was drawn from the BANYAN surveys of Malo et al. and Gagné et al. Two-Micron All-Sky Survey and Wide-field Infrared Survey Explorer data were used to detect near- to mid-infrared excesses that would reveal the presence of circumstellar disks. A total of 13 targets with convincing excesses were identified: four are new and nine were already known in the literature. The new candidates are 2MASS J05010082$-$4337102 (M4.5), J08561384$-$1342242 (M8$\gamma$), J12474428$-$3816464 (M9$\gamma$) and J02265658$-$5327032 (L0$\delta$), and are candidate members of the TW Hya ($\sim 10\pm 3$Myr), Columba ($\sim 42_{-4}^{+6}$Myr) and Tucana-Horologium ($\sim 45\pm 4$Myr) associations, with masses of $120$ and $13-18M_{\mathrm{Jup}}$. The M8$-$L0 objects in Columba and Tucana-Horologium are potentially among the first substellar disk systems aged $\sim 40$Myr. Estimates of the new candidates' mean disk temperatures and fractional luminosities are in the ranges $\sim 135-520$K and $0.021-0.15$, respectively. New optical spectroscopy of J0501$-$4337 reveals strong H$\alpha$ emission, possibly indicating ongoing accretion, provides a detection of lithium absorption and a radial velocity measurement that is consistent with a membership to Columba. We also present a near-infrared spectrum of J0226$-$5327 that reveals Paschen $\beta$ emission and shows signs of low surface gravity, consistent with accretion from a disk and a young age.

11 pages, 4 figures, 3 tables, accepted for publication in ApJ

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