CH₃OH and H₂O maser associations at very high angular resolution

Abstract

6.7 and 12.2 GHz CH$_{3}$OH (methanol) and 22.2 GHz H$_{2}$O masers are believed to be good tracers of the earliest phases of high-mass star formation. Interferometric and VLBI (Very Long Baseline Interferometry) observations have shown that water masers are predominantly associated with the innermost portions of the jets/outflows emerging from (proto-)stellar objects. On the other hand, the astrophysical environment traced by the 6.7 GHz (and the associated 12.2 GHz) CH$_{3}$OH masers is still to be more precisely determined. So far, most high-resolution studies have focused either on CH$_{3}$OH or on H$_{2}$O masers and little is known on their connection, wehereas it would be important to study both types of maser emission in the same object. The goal of our long-term project is to perform interferometric and VLBI observations of H$_{2}$O and CH$_3$OH masers towards a selected sample of high-mass YSOs where both maser types have been detected. This work presents preliminary results obtained for a few objects of our sample, and discusses possible implications.