| Abstract: | All interstellar methanol maser sources can be divided into two classes. Their spectra are distinctive. In particular, the
prominent Class II maser transitions, 6.7GHz and 12.2GHz lines show enhanced absorption toward Class I sources. We notice
that the 6.7 and 12.2GHz methanol masers toward Class II sources are associated with each other and coexist toward ultracompact
HII regions. Therefore we suggest a new pumping mechanism – methanol masers without population inversion. It can be used to
explain the formation of 6.7GHz methanol masers while the 12.2GHz methanol masers are regarded as driving coherent microwave
field. In this paper, we demonstrate that the new mechanism is associated with astronomical conditions and does not contradict
with other mechanisms.
This revised version was published online in July 2006 with corrections to the Cover Date. |
