THE FIRST X-SHOOTER OBSERVATIONS OF JETS FROM YOUNG STARS

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 300–2500 nm, 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 Chameleon I 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  ∼ 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 ( M☉ yr−1), drives a low-excitation jet with about  ∼ 3.2 × 10−10 M☉ yr−1 in both lobes. Despite the low stellar mass, / 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.