Open AccessNear‐infrared echelle spectroscopy of Class I protostars: molecular hydrogen emission‐line (MHEL) regions revealed
Author(s) -
Davis Christopher J.,
Ray Thomas P.,
Desroches Louis,
Aspin Colin
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04560.x
Subject(s) - physics , astrophysics , outflow , emission spectrum , t tauri star , line (geometry) , protostar , infrared , spectral line , stars , forbidden mechanism , astronomy , star formation , geometry , mathematics , meteorology
Infrared echelle spectra are used to trace dynamic activity in the immediate vicinity of Class I outflow sources. The H 2 and Br γ observations presented here trace different components of these emission‐line regions; indeed, they are thought to trace the orthogonal processes of outflow and infall respectively. High‐velocity H 2 emission is detected in the extended lobes of nine outflows. In addition, complex H 2 line emission is observed within a few hundred au 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 blueshifted 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 case. The MHEL regions – which are in all cases preferentially blueshifted – are assumed to be associated with the base of each outflow. Br γ 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 peaks being blueshifted by ∼30 km s −1 . The profiles are typical of the permitted hydrogen line profiles observed in many T Tauri stars, and probably derive from magnetospheric accretion flows. We do not observe redshifted 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 models. No Br γ is detected in the extended flow lobes. Instead, the emission is confined to the source and is spatially unresolved along each flow axis.