1995A&A...300..283I

The exciting discovery of strong gamma ray emission in the 3-7MeV range from the Orion molecular cloud complex by the COMPTEL experiment on GRO is indicative of enhanced abundance of low-energy C and O nuclei in these star-forming regions. A model of in-situ acceleration by the termination shocks of young stellar objects with strong winds is examined. It is found that if the magnetic field strength in the molecular cloud is below 1mG and/or the total thermal pressure in the ambient environment is less than 4x10^–8dynes cm²/s, the termination shock of a protostar with a mass loss rate of M{dot}∼10^–8M_☉/yr would have a radius "Great Attractor" 100AU. Under this condition, the oxygen ions from ionization of neutral gas could be accelerated to an energy "Great Attractor" 10-20MeV/nucleon as inferred by the COMPTEL observations. To explain the enrichment in the heavy nuclei, sputtering of the condensed matter of icy composition is invoked. An important consequence of this scenario is that the dust grains and icy planetesimals serving as building blocks of cometary nuclei could have been thoroughly irradiated in this episode of heavy cosmic ray bombardment. Isotopic analysis of samples collected at the nucleus surface or comas of comets might provide the linkage between the gamma ray emission from Orion and the early history of our solar system.