Subaru IR echelle spectroscopy of Herbig-Haro driving sources. I. H₂ and [Fe II] emission

We present infrared echelle spectroscopy of three Herbig-Haro (HH) driving sources (SVS 13, B5-IRS 1, and HH 34 IRS) using Subaru IRCS. The large diameter of the telescope and wide spectral coverage of the spectrograph allowed us to detect several H₂ and [Fe II] lines in the H and K bands. These include H₂ lines arising from v = 1-3 and J = 1-11 , and [Fe II] lines with upper level energies of E/k = (1.1-2.7) × 10⁴ K. For all objects the outflow is found to have two velocity components: (1) a high-velocity (−70 to −130 km s⁻¹) component (HVC), seen in [Fe II] or H₂ emission and associated with a collimated jet; and (2) a low-velocity (−10 to −30 km s⁻¹) component (LVC), which is seen in H₂ emission only and is spatially more compact. Such a kinematic structure resembles optical forbidden emission line outflows associated with classical T Tauri stars, whereas the presence of H₂ emission reflects the low-excitation nature of the outflowing gas close to these protostars. The observed H₂ flux ratios indicate a temperature of (2-3) × 10³ K and a gas density of 10⁵ cm⁻³ or more, supporting shocks as the heating mechanism. B5-IRS 1 exhibits faint extended emission associated with the H₂-LVC, in which the radial velocity slowly increases with distance from the protostar (by ~20 km s⁻¹ at ~500 AU). This is explained as warm molecular gas entrained by an unseen wide-angled wind. The [Fe II] flux ratios indicate electron densities to be ~10⁴ cm⁻³ or greater, similar to forbidden-line outflows associated with classical T Tauri stars. Finally, the kinematic structure of the [Fe II] emission associated with the base of the B5-IRS 1 and HH 34 IRS outflows is shown to support disk-wind models.16 page(s