The spatial distribution of the OH and H2O masers associated with W3/OH/, W49N, and W51

Abstract

Based on simultaneous dual-frequency VLBI observations from an almost E-W baseline of 228 km, relative positions are reported for: the H2O masers and the 1665 LCP, 1665 RCP, and 1667 RCP OH masers associated with W3(OH); the 1665 LCP, 1665 RCP, and 1667 LCP OH masers associated with W49 N; and the 1665 LCP OH masers associated with W51. Total power spectra and maps of the various masers are presented, and errors in the positions are evaluated. It is found that: (1) the H2O and 1665-MHz masing regions are well-separated and occupy two distinct regions of space in all three H II regions observed; (2) the 1667-MHz OH maser features in W49 N show a strong velocity gradient across the source, suggesting the presence of a rotating and collapsing or expanding cloud; and (3) the OH and H2O emissions in W49 N apparently arise from the same system, which is identified as a large cloud in which star formation is taking place. A lower limit of about 6000 solar masses is estimated for this cloud, indicating that W49 N may be a cluster of protostars.