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.
Highlights
Mass accretion and ejection are the fundamental processes during the early stages of star formation
While spatially extended optical jets and bipolar CO molecular outflows have been observed in numerous Class 0/I protostars (e.g., Reipurth & Bally 2001; Bally 2016; and references therein), near-infrared high-resolution spectroscopy and spectro-imaging observations in the past two decades have made it possible to study the kinematics of the outflowing gas and physical properties at the base of the jet within a few hundred au of the driving source in Class 0/I protostars (e.g., Davis et al 2001; 2003; 2011; Caratti o Garatti et al 2006; Antoniucci et al 2008; 2011; 2017; Garcia Lopez et al 2008; 2013; Takami et al 2006; Nisini et al 2005; 2016)
While multiple low and high velocity components are observed in both molecular hydrogen emission line (MHEL) and forbidden emission line (FEL), the higher velocity gas is slightly further offset from the driving source than the slower gas, and the kinematics of the H2 emission differs from [Fe II] emission, revealing complicated kinematic structures
Summary
Mass accretion and ejection are the fundamental processes during the early stages of star formation. While spatially extended optical jets and bipolar CO molecular outflows have been observed in numerous Class 0/I protostars (e.g., Reipurth & Bally 2001; Bally 2016; and references therein), near-infrared high-resolution spectroscopy and spectro-imaging observations in the past two decades have made it possible to study the kinematics of the outflowing gas and physical properties at the base of the jet within a few hundred au of the driving source in Class 0/I protostars (e.g., Davis et al 2001; 2003; 2011; Caratti o Garatti et al 2006; Antoniucci et al 2008; 2011; 2017; Garcia Lopez et al 2008; 2013; Takami et al 2006; Nisini et al 2005; 2016) These micro-jets are bright in [Fe II] forbidden and H2 ro-vibrational emission lines, showing the presence of forbidden emission line (FEL) regions and molecular hydrogen emission line (MHEL) regions in low-mass Class 0/I protostars.
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