Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978a%26a....66..395g&link_type=abstract
Astronomy and Astrophysics, vol. 66, no. 3, June 1978, p. 395-405. Research supported by the Max-Planck-Gesellschaft zur Foerde
Astronomy and Astrophysics
Astrophysics
52
Astronomical Models, Hydroxyl Emission, Interstellar Radiation, Line Spectra, Cosmic Dust, Electron Transitions, Infrared Spectra, Interstellar Gas, Interstellar Masers, Molecular Interactions, Particle Collisions, Radiative Transfer
Scientific paper
A model that can explain observations of OH lines in a variety of interstellar clouds is developed which takes into account both collisional excitation of OH by neutral and charged particles and also radiative excitation by far-IR emission from interstellar grains. Calculations are performed which show that: (1) inversion of the 1720-MHz line is due to collisional excitation by neutral particles, at least for dust temperatures below 40 K; (2) higher dust temperatures can invert either the 1720- or the 1612-MHz line; (3) inversion of the 1612-MHz line is favored in clouds with a sufficiently high OH column density; (4) main-line inversion can be obtained for grain temperatures exceeding 100 K; (5) inversion of the 1612-MHz and main lines is sensitive to the shape of the IR spectrum radiated by the grains; and (6) OH excitation is sensitive to collisions with charged particles. The results are applied to the interstellar cloud in front of 3C 123, the dust cloud 4C (part of the Rho Oph complex), and the cloud in front of G 326.7+0.6. An upper limit of the order of 0.00001 is placed on the fractional ionization for the cloud in front of 3C 123, and a value as high as 0.0001 is suggested for 4C.
Elitzur Moshe
Guibert Jean
Quang Rieu Nguyen
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