Spatially resolved H_2 emission from a very low-mass star

Abstract

Molecular outflows from very low-mass stars (VLMSs) and brown dwarfs have been studied very little. So far, only a few CO outflows have been observed, allowing us to map the immediate circumstellar environment. We present the first spatially resolved H2 emission around IRS54 (YLW52), a ~0.1-0.2 Msun Class I source. By means of VLT SINFONI K-band observations, we probed the H2 emission down to the first ~50 AU from the source. The molecular emission shows a complex structure delineating a large outflow cavity and an asymmetric molecular jet. Thanks to the detection of several H2 transitions, we are able to estimate average values along the jet-like structure (from source position to knot D) of Av~28 mag, T~2000-3000 K, and H2 column density N(H2)~1.7x10^17 cm^-2. This allows us to estimate a mass loss rate of ~2x10^-10 Msun/yr for the warm H2 component . In addition, from the total flux of the Br Gamma line, we infer an accretion luminosity and mass accretion rate of 0.64 Lsun and ~3x10^-7 Msun/yr, respectively. The outflow structure is similar to those found in low-mass Class I and CTTS. However, the Lacc/Lbol ratio is very high (~80%), and the mass accretion rate is about one order of magnitude higher when compared to objects of roughly the same mass, pointing to the young nature of the investigated source.