Physics
Scientific paper
Feb 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996prnc.rept.....d&link_type=abstract
Technical Report, Princeton Univ. NJ United States
Physics
Interstellar Matter, Interstellar Gas, H Ii Regions, Molecular Clouds, Polycyclic Aromatic Hydrocarbons, Photoelectric Emission, Star Clusters, Abundance, Fine Structure, Molecular Excitation
Scientific paper
Research was carried out in the following areas: (1) structure of molecular clouds: Bertoldi (in collaboration with C.F. McKee) investigated the structure of molecular clouds. Bertoldi & McKee (1992) conclude that many of the clumps in molecular clouds are actually pressure-confined. Only the more massive clumps are self-gravitating; the most massive of these are 'magnetically supercritical' (i.e., cannot be supported by magnetic pressure alone) and require generation of internal turbulence to support them. (2) Structure of HII regions: Bertoldi (in collaboration with E.B. Jenkins) investigated the implications of IMAPS ultraviolet observations of absorption toward pi-Sco by NII ions in the excited fine structure levels. The observed absorption indicates surprisingly high pressure in the region where the excited NII is located. Bertoldi and Jenkins (1992) concluded that this high-pressure 'clump' is probably a photoevaporating outflow from a protoplanetary disk around a low mass star. They argued that there are likely to be large numbers of such systems in the neighborhood of pi-Sco, presumably a gravitationally bound star cluster of which pi-Sco is the only bright member. (3) PAH molecules -- Charging and Photoelectric Heating: Bakes & Tielens (1994ab) studied the charging of PAH molecules by photoelectric emission and collisions with electrons, and evaluated the heating of the interstellar gas due to the photoelectric emission. They concluded that if PAH's are present in the ISM with the abundances required to explain the UIR emission bands, then the photoelectric heating by PAH's should be the dominant heating process in diffuse clouds and in photodissociation regions. The resulting rates of photoelectric heating by PAH's and small grains were used to study the thermal equilibrium of gas in photodissociation fronts illuminated by cool stars (Spaans et al. 1994), and the thermal equilibrium of interstellar gas (Wolfire et al. 1995). Publications supported by this grant are listed.
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