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Session 53 - Circumstellar Disks & Outflows Associated with YSOs.
Oral session, Tuesday, January 14
Piers 4/5,
Results are presented from J, H, and K-band long-slit spectrophotometry obtained towards HH7--11 and four of the H_2 emission-line fingers in the OMC--1 molecular outflow. The spectra contain multiple near-infrared H_2 emission lines that are diagnostic of temperatures, densities, and the UV radiation fields in these shocks. The excitation mechanisms responsible for the H_2 emission in these objects is determined based on H_2 line ratios. Collisions dominate the H_2 excitation in both objects. H_2 line ratios sensitive to density show that a range of density exists in the fingers of the OMC--1 outflow. Spectra of the OMC--1 outflow sample the H_2 excitation using various apertures located along the fingers. Changes are seen along the fingers in a direction outwards from the outflow source. Specifically, the line ratios change from values consistent with LTE predictions, requiring high densities, to values showing non-LTE effects, requiring lower densities. In HH7--11, the line ratios are similar for all of the spectra and show non-LTE effects. The H_2 line ratios sensitive to kinetic temperature show that in the OMC--1 outflow the temperatures increase outwards from the source along the fingers. In contrast, the same line ratios remain unchanged with position in HH7--11. In both objects there is evidence that for individual spectral apertures in the outflow there is a range of temperature in the H_2 emission-line regions as is expected for H_2 gas cooling behind shocks. The observations are compared with shock models in order to determine the type of shocks producing the H_2 emission. In HH7--11, the constancy of the H_2 line ratios provides evidence that the H_2 emission originates behind J-shocks. The observations of the OMC--1 outflow fingers support models in which the fingers are bow shocks formed as a stellar wind interacts with a clumpy molecular cloud environment.
