On the nature of the strong cosmic H2O masers

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Abstract
It is shown that the minimum pump power necessary to explain the observed energy flux in a maser line is proportional to l−3, where l is the amplification length. The probable upper limits for l are estimated from the observed velocity gradients in several H2O clusters associated with the regions of star formation: they vary from ∼ 0.5 to ∼ 50 AU. Using the ‘equivalent pumping transition’ approximation, it is argued that with such small l all the previous models fail to explain the observed maser energy fluxes. It is shown that the degree of ionization in the H2O condensations could be much higher than commonly believed – up to ∼ 10−6–10−5, and that the electrons could be there appreciably (∼ 10 per cent) cooler than the H2 molecules. Two possible astrophysical models, based on the collision–collisional pump working in such a two-temperature gas, are proposed. The models develop the concept of the H2O masers as sites of interaction between the stellar wind of a young star and the gas condensations in its envelope, and they differ mainly by the mass of the star. It is suggested that the origin of the maser condensations can be related with the formation of giant protoplanets.

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