IR diagnostics of embedded jets: Kinematics and physical characteristics of the HH46-47 jet *

Abstract

Context. 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. Aims. 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. Methods. The ratios and luminosities of several important diagnostic lines (e.g. [Fe ii] 1.644, 1.600 μm, [P ii] 1.189 μm, and H2 lines) have been used to derive physical parameters such as electron density, H2 temperature, iron gas-phase abundance and mass flux. [Fe ii] 1.644 μm and H2 2.122 μm position velocity diagrams (PVDs) have been additionally constructed to study the kinematics of both the atomic and molecular gas. Results. Within 1000-2000 AU from the source the atomic gas presents a wide range of radial velocities, from ̃-230 km s-1 to ̃100 km s-1. 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 ̃95 km s -1) further downstream. Electron densities (ne) and mass ejection fluxes (Mjet) have been separately measured for the HVC and for the component at lower velocity (LVC) from the [Fe ii] lines. ne increases with decreasing velocities with an average value of ̃6000 cm -3 for the LVC and ̃4000 cm-3 for the HVC, while the opposite occurs for Mjet which is ̃0.5-2 × 10-7 M⊙; yr-1 and ̃0.5-3.6 × 10-8 M⊙ yr-1 for the HVC and LVC, respectively. The mass flux carried out by the molecular component, measured from the H2 lines flux, is ̃4 × 10-9 M⊙ yr-1. 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. Conclusions. 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. © ESO, 2010.