Radio continuum emission at OH and H2O maser sites

A search for centimeter radio continuum emission associated with OH and H2O masers has been made toward 26 fields containing 45 separate maser sites u sing the Australia Telescope Compact Array (ATCA) at 8.2 and 9.2 GHz. The s ensitivity achieved for fields not limited by dynamic range is similar to 0 .15 mJy rms. This is the deepest radio search for embedded stellar sources at sites containing OH and H2O masers made to date. Only 17 compact continu um sources were detected within 2 " of the 45 maser sites searched. The abs ence of 3 cm continuum emission at the mJy level in 62% of the maser sites shows that most OH/H2O maser sites do not contain well-developed ultracompa ct H II regions (UCHIIs). The implications of this result on the nature of the source pumping the maser emission are discussed. While other possibilit ies cannot be ruled out, we argue that many maser sites without detected UC HIIs are most likely massive stars still in the pre-main-sequence contracti on stage.