出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We present the results of studies of a new class of 6.7GHz methanol maser sources with a ringlike emission structure discovered recently with the EVN. We have used the VLA to search for water masers at 22GHz and radio continuum at 8.4GHz towards a sample of high-mass star forming regions showing a ring-like distribution of methanol maser spots. Using the Gemini telescopes we found mid-infrared (MIR) counterparts of five methanol rings with a resolution of 0."15. The centres of methanol maser rings are located within, typically, only 0."2 of the MIR emission peak, implying their physical relation with a central star. These results strongly support a scenario wherein the ring-like structures appear at the very early stage of massive star formation before either water-maser outflows or HII regions are seen.
