Near-infrared echelle spectroscopy of Class I protostars: molecular hydrogen emission-line (MHEL) regions revealed

Infrared echelle spectra are used to trace dynamic activity in the immediat e vicinity of Class I outflow sources. The H-2 and Br gamma observations pr esented here trace different components of these emission-line regions; ind eed, they are thought to trace the orthogonal processes of outflow and infa ll respectively. High-velocity H-2 emission is detected in the extended lobes of nine outflo ws. In addition, complex H-2 line emission is observed within a few hundred all of nine of the outflow sources. We refer to these H-2 emission regions as 'molecular hydrogen emission-line' regions, or MHELs, and compare their properties to those of forbidden emission-line regions (FELs) observed in classical T Tauri and some Herbig AeBe stars. Like the FELs, both low- and high-velocity components (LVCs and HVCs) are observed in H-2, with blueshif ted velocities of the order of 5-20 and 50-150 km s(-1) respectively. LVCs are more common than HVCs in MHEL regions, and like their FEL counterparts, the latter are spatially further offset from the exciting source in each c ase. The MHEL regions-which are in all cases preferentially blueshifted are assumed to be associated with the base of each outflow. Br gamma profiles are detected towards four of the Class I sources observed (SVS 13, IRAs 04239+2436, HH 34-IRS and GGD 27(1)) as well as towards the T Tauri star AS 353A. These lines are all broad and symmetric, the line pea ks being blueshifted by similar to 30 km s(-1). The profiles are typical of the permitted hydrogen line profiles observed in many T Tauri stars, and p robably derive from magnetospheric accretion flows. We do not observe redsh ifted absorption features (inverse P-Cygni profiles) in any of the sources, however. Nor do we detect a dependence on linewidth with inclination angle of the system to the line of sight, as is predicted by such accretion mode ls. No Br gamma is detected in the extended flow lobes. Instead, the emissi on is confined to the source and is spatially unresolved along each flow ax is.