Vol 7, No 6

Generation of Interstellar Class II 72–81A+ and 72–81A- Methanol Masers

Han-Ping Liu, Jin Sun


Abstract New methanol maser lines at 72→63A−(86.6 GHz) and 72→63A+(86.9 GHz) together with two candidate methanol maser lines at 72→81A−(80.99 GHz) and 72→81A+(111.29 GHz) have been detected in W3(OH). We use a pumping mechanism, i.e., methanol masers without population inversion, to explain the formation of weak methanol masers of 72→81A+ and 72→81A−. We explain well why the line-shape of the transition 72→81A+ is not typical. A similar argument can be applied to the Λ-type level system 72A−, 63A− and 81A−, as well as to the 72→81A− 80.99 GHz masers.



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