Accretion and outflow activity in proto-brown dwarfs

TL;DR

This study investigates accretion and outflow activities in proto-brown dwarfs using near-infrared spectroscopy, revealing evolutionary trends in jet composition and quantifying accretion and mass loss rates comparable to low-mass protostars.

Contribution

It provides the first detailed spectroscopic analysis of accretion and outflow processes in Class 0/I proto-brown dwarfs, highlighting evolutionary changes in jet composition and quantifying their accretion and mass loss rates.

Findings

Proto-BDs show evolutionary trend from molecular to ionic jets.

Accretion rates range from 2×10^{-6} to 2×10^{-8} Msun/yr.

Mass loss rates are between 4×10^{-8} and 5×10^{-9} Msun/yr.

Abstract

We present a near-infrared study of accretion and outflow activity in 6 Class 0/I proto-brown dwarfs (proto-BDs) using VLT/SINFONI spectroscopy and spectro-imaging observations. The spectra show emission in several [FeII] and H$_{2}$ lines associated with jet/outflow activity, and in the accretion diagnostics of Pa$\beta$ and Br$\gamma$ lines. The peak velocities of the [FeII] lines ($>$100 km s$^{-1}$) are higher than the H$_{2}$ lines. The Class 0 proto-BDs show strong emission in the H$_{2}$ lines but the [FeII] lines are undetected, while the Class I objects show emission in both [FeII] and H$_{2}$ lines, suggesting an evolutionary trend in the jets from a molecular to an ionic composition. Extended emission with knots is seen in the [FeII] and H$_{2}$ spectro-images for 3 proto-BDs, while the rest show compact morphologies with a peak on-source. The accretion rates for the proto-BDs span the range of (2$\times$10$^{-6}$ -- 2$\times$10$^{-8}$) Msun yr$^{-1}$, while the mass loss rates are in the range of (4$\times$10$^{-8}$ -- 5$\times$10$^{-9}$) Msun yr$^{-1}$. These rates are within the range measured for low-mass protostars and higher than Class II brown dwarfs. We find a similar range in the jet efficiency for proto-BDs as measured in protostars. We have performed a study of the Brackett decrement from the Br7-Br19 lines detected in the proto-BDs. The upper Brackett lines of Br13-Br19 are only detected in the earlier stage systems. The ratios of the different Brackett lines with respect to the Br$\gamma$ line intensity are consistent with the ratios expected from Case B recombination.