Spatially resolved H₂ emission from a very low-mass star^{⋆,⋆⋆,⋆⋆⋆}

¹ Max – Planck – Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: rgarcia@mpifr-bonn.mpg.de
² INAF – Osservatorio Astronomico di Roma via Frascati 33, 00040 Monteporzio Catone, Italy

Received: 15 January 2013
Accepted: 23 February 2013

Abstract

Context. 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.

Aims. We present the first spatially resolved H₂ emission around IRS54 (YLW 52), a ~0.1–0.2 M_⊙ Class I source.

Methods. By means of VLT SINFONI K-band observations, we probed the H₂ emission down to the first ~50 AU from the source.

Results. 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 A_V ~ 28 mag, T ~ 2000−3000 K, and H₂ column density N(H₂) ~ 1.7 × 10¹⁷ cm^-2. This allows us to estimate a mass loss rate of ~2 × 10^-10 M_⊙ yr^-1 for the warm H₂ component. In addition, from the total flux of the Br γ line, we infer an accretion luminosity and mass accretion rate of 0.64 L_⊙ and ~3 × 10^-7M_⊙ yr^-1, respectively. The outflow structure is similar to those found in low-mass Class I and CTTS. However, the L_acc/L_bol 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.