Accretion and outflow activity in proto-brown dwarfs

Abstract

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 [Fe II] and H2 lines associated with jet/outflow activity, and in the accretion diagnostics of Pa β and Br γ lines. The peak velocities of the [Fe II] lines (>100 km s−1) are higher than the H2 lines. The Class 0 proto-BDs show strong emission in the H2 lines but the [Fe II] lines are undetected, while the Class I objects show emission in both [Fe II] and H2 lines, suggesting an evolutionary trend in the jets from a molecular to an ionic composition. Extended emission with knots is seen in the [Fe II] and H2 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× 10−6 – 2× 10−8) M⊙ yr−1, while the mass loss rates are in the range of (4× 10−8 – 5× 10−9) M⊙ 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 Br 7-19 lines detected in the proto-BDs. The upper Brackett lines of Br 13–19 are only detected in the earlier stage systems. The ratios of the different Brackett lines with respect to the Brγ line intensity are consistent with the ratios expected from Case B recombination.