Atomic jets from class 0 sources detected by Spitzer: the case of   L1448-C
  We present Spitzer-IRS spectra obtained along the molecular jet from the Class 0 source L1448-C (or L1448-mm). Atomic lines from the fundamental transitions of [FeII], [SiII] and [SI] have been detected showing, for the first time, the presence of an embedded atomic jet at low excitation. Pure rotational H$_2$ lines are also detected, and a decrease of the atomic/molecular emission ratio is observed within 1 arcmin from the driving source. Additional ground based spectra (UKIRT/UIST) were obtained to further constrain the H$_2$ excitation along the jet axis and, combined with the 0--0 lines, have been compared with bow-shock models. From the different line ratios, we find that the atomic gas is characterized by an electron density n_e ~ 200-1000 cm^{-3}, a temperature T_e < 2500 K and an ionization fraction <~ 10^{-2}; the excitation conditions of the atomic jet are thus very different from those found in more evolved Class I and Class II jets. We also infer that only a fraction (0.05-0.2) of Fe and Si is in gaseous form, indicating that dust still plays a major role in the depletion of refractory elements. A comparison with the SiO abundance recently derived in the jet from an analysis of several SiO sub-mm transitions, shows that the Si/SiO abundance ratio is ~100, and thus that most of the silicon released from grains by sputtering and grain-grain collisions remains in atomic form. Finally, estimates of the atomic and molecular mass flux rates have been derived: values of the order of ~10$^{-6}$ and ~10$^{-7}$ M$_{\sun}$ yr$^{-1}$ are inferred from the [SI]25$\mu$m and H$_2$ line luminosities, respectively. A comparison with the momentum flux of the CO molecular outflow suggests that the detected atomic jet has the power to drive the large scale outflow. 
O. Dionatos, B. Nisini, R. Garcia Lopez, T. Giannini, C. J. Davis, M.   D. Smith, T. P. Ray, M. De Luca