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

¹ INAF-Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone, Italy e-mail: garcia@oa-roma.inaf.it
² Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
³ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁴ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland

Received: 16 September 2009
Accepted: 6 December 2009

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 (n_e) and mass ejection fluxes have been separately measured for the HVC and for the component at lower velocity (LVC) from the [Fe ii] lines. n_e 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 which is ~0.5-2 10^-7  yr^-1 and ~0.5-3.6 10^-8  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  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.