New 9.9-GHz methanol masers

The Australia Telescope Compact Array has been used to make the first extensive search for the class I methanol masers at 9.9 GHz. In total, 48 regions of high-mass star formation were observed. In addition to masers in W33-Met (G12.80-0.19) and G343.12-0.06 (IRAS 16547-4247) which have already been reported in the literature, two new 9.9-GHz masers have been found towards G331.13-0.24 and G19.61-0.23. We have determined absolute positions (accurate to roughly a second of arc) for all the detected masers and suggest that some class I masers may be associated with shocks driven into molecular clouds by expanding H ii regions. Our observations also imply that the evolutionary stage of a high-mass star-forming region when the class I masers are present can outlast the stage when the class II masers at 6.7-GHz are detectable, and overlaps significantly with the stage when OH masers are active.