A shock model for infrared line emission from H2 molecules

Abstract

A shock model is considered for the H2 infrared line emission detected in the Orion Nebula by Gautier et al. (1976). The equations are solved which describe stationary gas flow and excitation of H2 in the radiative cooling region behind a shock. It is found that for the high densities needed to explain the observed line strengths, the populations of the vibration-rotation levels are nearly in LTE. By matching the calculated line strengths to the observations, it is found that the acceptable values of shock velocity and upstream molecular density must be between 8 and 21 km/s and between 100,000 and 1 million per cu cm, respectively.