The Circumstellar Disks of Brown Dwarfs

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

Authors:

Boucher et al

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 Gagn\'e 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 (M8γ), J12474428−3816464 (M9γ) and J02265658−5327032 (L0δ), and are candidate members of the TW Hya (∼10±3Myr), Columba (∼42+6−4Myr) and Tucana-Horologium (∼45±4Myr) associations, with masses of 120 and 13−18MJup. The M8−L0 objects in Columba and Tucana-Horologium are potentially among the first substellar disk systems aged ∼40Myr. Estimates of the new candidates' mean disk temperatures and fractional luminosities are in the ranges ∼135−520K and 0.021−0.15, respectively. New optical spectroscopy of J0501−4337 reveals strong Hα 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 β emission and shows signs of low surface gravity, consistent with accretion from a disk and a young age.