IR diagnostics of embedded jets: velocity resolved observations of the HH34 and HH1 jets^*

¹ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone, Italy e-mail: garcia@mporzio.astro.it
² Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
³ Università degli Studi di Roma “Tor Vergata” – Dipartimento di Fisica, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy

Received: 9 November 2007
Accepted: 18 May 2008

Abstract

Context. We present VLT-ISAAC medium resolution spectroscopy of the HH34 and HH1 jets, driven by young Class 0/I sources.

Aims. Our aim is to derive the kinematics and the physical parameters associated with infrared jets, and to study how they vary with jet velocity.

Methods. We use several important diagnostic lines covered by our spectral range, such as , m and Hm, to probe both the atomic and the molecular jet components.

Results. In the inner jet region of HH34, we find that both the atomic and molecular gas present two components at high and low velocity (the so-called HVC and LVC), as reported by previous studies. The [] LVC in HH34 is detected up to large distances from the source (>1000 AU), at variance with TTauri jets where the LVC is usually confined within 200 AU from the star. In Hm, the LVC and HVC are spatially separated, with an abrupt transition from low- to high-velocity emission at ~. We moreover detect, for the first time, the fainter red-shifted counterpart down to the central source. This lobe shows several emission knots displaced symmetrically with respect to the corresponding blue-shifted gas. In HH1, we trace the jet down to ~ from the VLA1 driving source: the kinematics of this inner region is again characterised by the presence of two velocity components, one blue-shifted and one red-shifted with respect to the source LSR velocity. We interpret this double component as arising from the interaction of two different jets. We suggest that the red-shifted component could be part of the HH501 jet. Electron densities and mass fluxes have been measured separately for the different velocity components in the HH34 and HH1 jets. In the inner HH34 jet region, n_e increases with decreasing velocity, with an average value of ~1  10⁴ cm^-3 in the HVC and ~2.2  10⁴ cm^-3 in the LVC. Up to ~ from the driving source, and along the whole HH1 jet an opposite behaviour is observed instead, with n_e increasing with velocity. In both jets the mass flux is carried mainly by the high-velocity gas: lower limits on the mass flux of    yr^-1 have been found for HH34 and HH1, from the luminosity of the m line. A comparison between the position velocity diagrams and derived electron densities with models for magnetohydrodynamic (MHD) jet launching mechanisms has been performed for HH34. While the kinematical characteristics of the line emission at the jet base can be, at least qualitatively, reproduced by both X-winds and disc-wind models, none of these models can explain the extent of the LVC and the velocity dependence of electron density that we observe. It is possible that the LVC in HH34 represents gas not directly ejected in the jet but instead denser ambient gas entrained by the high-velocity collimated jet.