Name/Affiliation: Basmah Riaz (Uni. of Hertfordshire, UK)
Proto-brown dwarfs identified with WISE and JCMT
We present an optical to sub-millimeter multi-wavelength study of two proto-brown dwarfs identified in a UKIDSS+WISE cross-correlated survey of the sigma Orionis cluster. We have looked into the various classification schemes, and both the observed properties and physical characteristics for the targets indicate a Class I classification. Both objects are detected at a >5-sigma level in the SCUBA-2 850um band, with the corresponding dust condensation masses of ~20-40 MJup. The spectra for both sources exhibit prominent emission in the accretion-associated Halpha and Ca II infrared triplet lines, and the forbidden emission lines of [OI], [SII], and [NII], indicating the presence of an outflow. The accretion and outflow rates determined from multiple line diagnostics are comparatively higher than Class II brown dwarfs, and the ratio of the outflow to accretion rate is more in line with Class I low-mass stars. Given the membership of these objects in a relatively evolved cluster of ~1-3 Myr of age, we consider an alternate formation mechanism for brown dwarfs, in the context of the ‘hybrid’ model of disk fragmentation, followed by ejection of a gaseous clump. The measured accretion rates can be explained either within the framework of episodic accretion or early formation phase of proto-brown dwarf disks. We also discuss the possibility of a prolonged Class I lifetime for substellar objects.