X-ray ionization and the Orion molecular cloud

Abstract

Recent observations of the Orion Nebula with the imaging proportional counter and the high resolution imager on the Einstein Observatory satellite have revealed that the presumably young stars in that region are strong X-ray emitters. The densest portion of the molecular cloud, which is also the portion with the greatest diversity of molecular species, is a few square arc minutes in size, while its conventional center (the KL Nebula) lies within an arc minute of the peak of the X-ray emission. The X-rays from the stars impinge on the neighboring molecular cloud's core with such intensity that they significantly affect its ionization equilibrium and chemistry. The present investigation has the objective to provide a quantitative account of these effects. Attention is given to simple estimates of the magnitude of X-ray ionization and its variation throughout the cloud, ionization and reaction rates, and a choice of models.