Dust radiation fields and pumping of excited state OH masers in W3(OH) |
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Authors: | M D Gray |
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Institution: | Department of Physics, UMIST, PO Box 88, Manchester M60 1QD |
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Abstract: | I show that it is quite possible to obtain saturating amplification in the 13.44-GHz maser which is so far unique to W3(OH), using a combined radiative and collisional pumping scheme. The dominant radiative part of the pump involves far-infrared line overlap, and the far-infrared continuum is provided by dust, modelled as either a two-component mixture or composite grains. Transport of the far-infrared radiation is carried out via the accelerated lambda iteration method. The observational link between 13.44-GHz and 6035-MHz masers is reproduced by the model. Inadequate amplification in Sobolev models probably results from the optical depth limitations imposed by this approximation. I review the dust models used in far-infrared pumping models of OH masers, and conclude that the main consequence of moving from skewed blackbody functions to more sophisticated models is a selective pumping enhancement when ice mantles are included. |
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Keywords: | masers radiative transfer stars: formation dust extinction ISM: individual: W3(OH) |
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