Effects of expanding compact H II regions upon molecular clouds - Molecular dissociation waves, shock waves, and carbon ionization

Abstract

view Abstract Citations (81) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effects of expanding compact H II regions upon molecular clouds: molecular dissociation waves, shock waves, and carbon ionization. Hill, J. K. ; Hollenbach, D. J. Abstract The effects of young expanding compact H II regions upon their molecular environments are studied, emphasizing the simultaneous evolution of the molecular hydrogen dissociation front and the shocked shell of gas surrounding the nebula. For H II regions powered by O5 stars embedded in molecular clouds of ambient density between 1000 and 10,000 per cu cm, the dissociation wave initially travels outward much more rapidly than the shock, but later decelerates and is swept up by the shock about 100,000 yr after the expansion begins. The 21-cm line of atomic hydrogen will be optically thick in both the preshock and postshock gas for most of this period. The most important coolant transitions are the forbidden O I line at 63 microns and, for times not less than about 100,000 yr, the rotational transitions of H2 and/or the rotational transitions of CO. The vibrational transitions of H2 are excited predominantly by ultraviolet pumping. The preshock and postshock carbon recombination-line emission measures are estimated. Publication: The Astrophysical Journal Pub Date: October 1978 DOI: 10.1086/156501 Bibcode: 1978ApJ...225..390H Keywords: Gas Dissociation; H Ii Regions; Interstellar Chemistry; Nebulae; Shock Wave Propagation; Stellar Evolution; Absorption Spectra; Carbon Monoxide; Emission Spectra; Gas Expansion; Hydrogen Ions; Infrared Spectra; Microwave Emission; Molecular Spectra; Stellar Models; Astrophysics; Expansion:H II Regions; H II Regions:Molecular Clouds; Molecular Clouds:Shock Waves full text sources ADS |