Astrophysical Masers. V. Pump Mechanism for h, O Masers
1974; IOP Publishing; Volume: 191; Linguagem: Inglês
10.1086/152945
ISSN1538-4357
Autores Tópico(s)Astro and Planetary Science
Resumoview Abstract Citations (97) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Astrophysical Masers. V. Pump Mechanism for H2O Masers Goldreich, Peter ; Kwan, John Abstract The problem of determining the pump mechanism for strong H2O masers is considered. It is shown that for every class of pump models, very general constraints may be placed on the maser size and luminosity. A careful evaluation of these constraints indicates that collisional pumps and external radiative pumps are unlikely to account for the strong H2O masers associated with HII regions. It is proposed that these sources are powered by a hot-dust, cool-gas, internal radiative pump. Specifically, the pump mechanism involves the absorption by the H2O molecules of 6.3- photons which are emitted by the hot dust grains. These absorptions produce transitions from the rotational levels of the ground vibrational state to the rotational levels of the first-excited vibrational state. The pump action results because there are more absorptions per degenerate sublevel from the 523 level than from the 616 level. The heat sink in this pump model is provided by the cool H2 molecules which collisionally de-excite the H2O molecules from the first-excited vibrational state to the ground vibrational state. The hot-dust, cool-gas, pump model can operate only in the vicinity of a highly luminous, variable star. The variation in temperature of the dust grains which are heated by the radiation from the star is essential to prevent the dust and gas from coming into thermal equilibrium. One feature of this pump model is that at any point the dust temperature must vary from below to above the gas temperature. Thus, the strong intensity variations observed in H2O masers find a natural explanation in the model. Publication: The Astrophysical Journal Pub Date: July 1974 DOI: 10.1086/152945 Bibcode: 1974ApJ...191...93G full text sources ADS |
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