Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978a%26a....67..323e&link_type=abstract
Astronomy and Astrophysics, vol. 67, no. 3, July 1978, p. 323-332.
Astronomy and Astrophysics
Astrophysics
144
H Ii Regions, Hydroxyl Emission, Interstellar Masers, Water Masers, Abundance, Astronomical Models, Photochemical Reactions, Reaction Kinetics, Shock Fronts
Scientific paper
It is suggested that the OH maser spots associated with compact H II regions are located at the compressed shell between the shock and ionization fronts. Calculation of the abundances of various molecules yields sufficient OH densities spread over large enough distances to explain the observations. The chemistry behind the shock front is such that almost all the oxygen not tied in CO goes into H2O, which is then photodissociating to produce the OH. The masers are strongly saturated and pumped by collisions. As the H II region ages, its pressure and the shock velocity become smaller, the OH density (and presumably also the pump rate) decreases, and the maser turns off. The strong shock chemistry calculated also produces sufficient amounts of water to explain the low-velocity H2O masers. It is suggested that these masers are also located in the compressed shell of (still younger and smaller, hence unobserved) H II regions.
de Jong Teije
Elitzur Moshe
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