Discovery of a Brown Dwarf with Quasi-spherical Mass Loss

Abstract

We report the serendipitous discovery of an elliptical shell of CO associated with the faint stellar object SSTc2d J163134.1-240060 as part of the “Ophiuchus Disk Survey Employing ALMA” (ODISEA), a project aiming to study the entire population of protoplanetary disks in the Ophiuchus Molecular Cloud from 230 GHz continuum emission and 12CO (J = 2–1), 13CO (J = 2–1) and C18CO (J = 2–1) lines readable in Band 6. Remarkably, we detect a bright 12CO elliptical shape emission of ∼3″ × 4″ toward SSTc2d J163134.1-240060 without a 230 GHz continuum detection. Based on the observed near-IR spectrum taken with the Very Large Telescope (KMOS), the brightness of the source, its three-dimensional motion, and Galactic dynamic arguments, we conclude that the source is not a giant star in the distant background (>5–10 kpc) and is most likely to be a young brown dwarf in the Ophiuchus cloud, at a distance of just ∼139 pc. This is the first report of quasi-spherical mass loss in a young brown dwarf. We suggest that the observed shell could be associated with a thermal pulse produced by the fusion of deuterium, which is not yet well understood, but for a substellar object is expected to occur during a short period of time at an age of a few Myr, in agreement with the ages of the objects in the region. Other more exotic scenarios, such as a merger with planetary companions, cannot be ruled out from the current observations.