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Departmental Colloquium

Dynamic UC HII regions in Sgr B2: Flickering and Ionized Flows  
Guest Speaker
Chris DePree  
Guest Affiliation
Agnes Scott, Department of Physics and Astronomy  
Guest Affiliation Url  
Loris Magnani  
Thursday, February 7, 2013 4:00 pm - 5:00 pm  
Physics Auditorium (Rm 202)  

The Sgr B2 star forming region in our Galaxy contains a large sample of HII regions, and the diversity of morphologies and number of unusual broad line sources make it an ideal laboratory for testing theories of ultracompact (UC) HII region evolution. Recent high-resolution, radiation-hydrodynamic simulations show that the dense, rotating, accretion flows required to form massive stars quickly become gravitationally unstable. The resulting HII region flickers between hypercompact (HC) and UC sizes throughout the main accretion phase, rather than monotonically expanding. Imaged at 1.3 cm, the Sgr B2 region contains 49 regions, 25 of which are hypercompact (HC), with physical diameters < 5000 AU. We have re-observed this large sample of UC HII regions in the Sgr B2 region after 23 years in the three hybrid arrays in the 1.3 continuum and H66a and H68a lines with a resolution of 0.25². Preliminary results from these new 1.3 cm EVLA observations of Sgr B2 have revealed that 4 of the 49 sources have significant changes in flux density (>10 sigma).