NICMOS Observations of Shocked H_2 in Orion

摘要

HST NICMOS narrowband images of the shocked molecular hydrogen emission inOMC-1 are analyzed to reveal new information on the BN/KL outflow. Theoutstanding morphological feature of this region is the array of molecularhydrogen ``fingers'' emanating from the general vicinity of IRc2 and thepresence of several Herbig-Haro objects. The NICMOS images appear to resolveindividual shock fronts. This work is a more quantitative and detailed analysisof our data from a previous paper (Schultz etal. 1999). Line strengths for the H_2 1--0 S(4) plus 2--1 S(6) lines at 1.89 micron areestimated from measurements with the Paschen_alpha continuum filter F190N at1.90 micron, and continuum measurements at 1.66 and 2.15 micron. We compare theobserved H_2 line strengths and ratios of the 1.89 micron and 2.12 micron 1--0S(1) lines with models for molecular cloud shock waves. Most of the data cannotbe fit by J-shocks, but are well matched by C-shocks with shock velocities inthe range of 20--45 km/s and preshock densities of 10^{4} - 10^{6} cm^{-3},similiar to values obtained in larger beam studies which averaged over manyshocks. There is also some evidence that shocks with higher densities havelower velocities.