Photoelectric heating of interstellar gas.

Abstract

The emission of photoelectrons from interstellar dust grains is thought to be the dominant mechanism by which stellar radiant energy is transferred to interstellar gas. The purpose of this theoretical research is to refine previous models of photoelectric heating. The photoelectric emission rate is calculated for interstellar graphitic grains in a typical interstellar ultraviolet radiation field. The effect of the surface potential and photoelectron energy distribution is included. The free electron capture rate is calculated for several interstellar gas conditions as a function of temperature, electron density and grain charge. From the charge balance between photoemission and electron capture the grain charge distribution is obtained. The net heating rate is then calculated for appropriate grain sizes and a Mathis-Rurnpl-Nordsieck size distribution of grams.