The first X-shooter observations of jets from young stars

Abstract

We present the first pilot study of jets from young stars conducted with X-shooter, on the ESO/Very Large Telescope. As it offers simultaneous, high-quality spectra in the range 300-2500nm, X-shooter is uniquely important for spectral diagnostics in jet studies. We chose to probe the accretion/ejection mechanisms at low stellar masses examining two targets with well-resolved continuous jets lying on the plane of the sky: ESO-HA 574 in ChameleonI and Par-Lup3-4 in Lupus III. The mass of the latter is close to the sub-stellar boundary (M* = 0.13 M·). A large number of emission lines probing regions of different excitation are identified, position-velocity diagrams are presented, and mass outflow/accretion rates are estimated. Comparison between the two objects is striking. ESO-HA 574 is a weakly accreting star for which we estimate a mass accretion rate of (in M ·yr-1), yet it drives a powerful jet with Ṁout∼ 1.5-2.7 × 10-9 M ·yr-1. These values can be reconciled with a magneto-centrifugal jet acceleration mechanism assuming that the presence of the edge-on disk severely depresses the luminosity of the accretion tracers. In comparison, Par-Lup3-4, with stronger mass accretion (logṀacc = ?9.1 ± 0.4 Ṁyr-1), drives a low-excitation jet with about M ∼ 3.2 × 10-10 M·yr-1 in both lobes. Despite the low stellar mass, Ṁout/ Ṁacc for Par-Lup3-4 is at the upper limit of the range usually measured for young objects, but still compatible with a steady magneto-centrifugal wind scenario if all uncertainties are considered. © 2011. The American Astronomical Society. All rights reserved.