SiO Towards Ultracompact H{\sc ii} Regions
Session 82 -- HII Regions
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

## [82.03] SiO Towards Ultracompact H{\sc ii} Regions

J.~M.~Acord,~Jr. (MPIfR), C.~M.~Walmsley (U.~Cologne), E.~B.~Churchwell (U.~Wisconsin-Madison)

Ultracompact (UC) H{\sc ii} regions are excellent tracers of recently formed O stars. In a number of cases there is evidence for molecular outflows originating close to the regions. Towards low mass star formation sites it is known that SiO is sometimes a better marker for molecular outflows than CO, especially in the highest velocity gas, possibly due to sputtering of dust grain mantles in shocks. We present the analysis of our observations of three rotational transitions in the ground vibrational state of silicon monoxide towards a sample of UC H{\sc ii} regions. The relative intensities of the $v=0$, $J=2\rightarrow1$, $3\rightarrow2$, and $5\rightarrow4$ lines are used to constrain the physical conditions in both the quiescent and shocked outflow gas.