The small-scale HH34 IRS jet as seen by X-shooter

Context. Atomic jets are a common phenomenon among young stars, being intimately related to disk accretion. Most studies have been performed on jets from pre-main sequence stars. However, to date very little detailed information has been gathered on jets from young embedded low mass sources (the so-called class I stars), especially in the inner jet region. Aims. We exploit a diagnostic analysis based on multiwave spectroscopic observations to infer kinematics and physical conditions of the inner region of the prototypical class I jet from HH34 IRS. Methods. We use a deep X-shooter spectrum covering the wavelength range 350 2300 nm at resolution between similar to 8000 and similar to 18 000 (i.e., Delta V similar to 17 - 27 km s(-1)), which allows us to detect lines in a wide range of excitation conditions (from E-up similar to 8000 to similar to 31 000 cm(-1)) and to study their kinematics. Statistical equilibrium and ionization models are adopted to derive the jet main physical parameters. Results. We separately derive the physical conditions for the extended high velocity jet (HVC, V-r similar to -100 km s(-1)) and for the low velocity and compact gas (LVC, V-r similar to 20 - 50 km s(-1)) located on-source. Close to the jet base (< 200 AU from source) the HVC gas is mostly neutral (x(e) < 0.1) and very dense (n(H) > 5 x 10(5) cm(-3)). The LVC gas has the same density and AV as the HVC, but it is at least a factor of two colder. Iron abundance in the HVC is consistent with the solar value, while it is a factor of 3 subsolar in the LVC, suggesting an origin of the LVC gas from a dusty disk. From the derived total density we infer that the jet mass flux rate is > 5 x 10(-7) M-circle dot yr(-1). We find that the relationships between accretion luminosity and permitted line luminosity derived for T Tauri stars cannot be directly extended to class I sources embedded in reflection nebulae since the permitted lines are seen through scattered light. An accretion rate of similar to 7 x 10(-6) M-circle dot yr(-1) is instead derived from an empirical relationship connecting. M acc with L([O I])(HVC). Conclusions. The class I HH34 IRS jet at small scale shares many kinematical and physical properties with the jets from the most active classical T Tauri (CTT) stars. However, the HH34 IRS jet is denser as a consequence of the larger mass ejection rate with respect to typical values in CTTs jets. These findings suggests that the acceleration and excitation mechanisms in collimated jets are not influenced by evolution and are similar in CTTs and in still embedded sources with high accretion rates.