2010A&A...511A...5G

We present an analysis of the kinematics and physical properties of the Class I driven jet HH46-47 based on IR medium and low resolution spectroscopy obtained with ISAAC on VLT. Our aim is to study the gas physics as a function of the velocity and distance from the source and to compare the results with similar studies performed on other Class I and classical T Tauri jets as well as with existing models for the jet formation and excitation. The ratios and luminosities of several important diagnostic lines (e.g. [FeII]1.644, 1.600µm, [PII]1.189µm, and H₂ lines) have been used to derive physical parameters such as electron density, H₂ temperature, iron gas-phase abundance and mass flux. [FeII]1.644µm and H₂2.122µm position velocity diagrams (PVDs) have been additionally constructed to study the kinematics of both the atomic and molecular gas. Within 1000-2000AU from the source the atomic gas presents a wide range of radial velocities, from ~-230km/s to ∼100km/s. Only the gas component at the highest velocity (high velocity component, HVC) survives at large distances. The H₂ shows only a single velocity component at almost zero velocity close to the source while it reaches higer velocities (up to ∼95km/s) further downstream. Electron densities (n_e) and mass ejection fluxes ({dot}(M)_jet) have been separately measured for the HVC and for the component at lower velocity (LVC) from the [FeII] lines. n_e increases with decreasing velocities with an average value of ∼6000cm^–3 for the LVC and ∼4000cm^–3 for the HVC, while the opposite occurs for {dot}(M)_jet which is ∼0.5-2x10^–7M_☉/yr and ∼0.5-3.6x10^–8M_☉/yr for the HVC and LVC, respectively. The mass flux carried out by the molecular component, measured from the H₂ lines flux, is ∼4x10^–9M_☉/yr. We have estimated that the Fe gas phase abundance is significantly lower than the solar value, with ∼88% of iron still depleted onto dust grains in the internal jet region. This fraction decreases to ∼58%, in the external knots. Many of the derived properties of the HH46-47 jet are common to jets from young stellar objects (YSOs) in different evolutionary states. The derived densities and mass flux values are typical of Class I objects or very active T Tauri stars. However, the spatial extent of the LVC and the velocity dependence of the electron density have been so far observed only in another Class I jet, the HH34 jet, and are not explained by the current models of jet launching.