Search for class II methanol masers at 23.1 GHz (original) (raw)

In the early days of methanol maser discoveries, the 9 2 -10 1 A + transition at 23.1 GHz was found to exhibit maser characteristics in the northern star-forming region W3(OH) and probable maser emission in two other sources. Attention subsequently turned to the 6.6-GHz 5 1 -6 0 A + methanol maser transition, which has proved a valuable tracer of early high-mass star formation. We have undertaken a new search for 23.1-GHz methanol masers in 50 southern star formation regions using the Parkes radio telescope. The target sources all exhibit class II methanol maser emission at 6.6 GHz, with 20 sources also displaying maser features in the 107.0-GHz 3 1 -4 0 A + methanol line. Strong emission at 23.1 GHz in NGC 6334F was confirmed, but no emission was detected in the remaining sources. Thus the 23.1-GHz methanol masers are rare.