From methanol masers to hot molecular cores

Abstract

We have found that methanol masers provide a signpost to the very earliest stages of the massive star formation process, before the onset of the UCHII region phase. They are invariably associated with embedded sources whose bolometric luminosities suggest they will soon become OB stars. Outflows frequently occur, and hot molecular cores are also associated with them. The absence of nearby UCHII regions implies that some cores must be internally heated. We also find cold sub-mm cores that do not have any other signposts of star formation. We suggest these may represent the earliest stages in the massive star formation process, soon after cloud collapse has begun.