Massive Star Formation Of The Sgr A East H II Regions Near The Galactic Center

A group of four compact HII regions associated with the well-known 50 km s(-1) molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of similar to 6 pc. We present a study of ionized gas based on the [Ne II] (12.8 mu m) line, as well as multi-frequency radio continuum, Hubble Space Telescope Pa alpha, and Spitzer Infrared Array Camera observations of the most compact member of the HII group, Sgr A East HII D. The radio continuum image at 6 cm shows that this source breaks up into two equally bright ionized features, D1 and D2. The spectral energy distribution of the D source is consistent with it being due to a 25 +/- 3M(circle dot) star with a luminosity of 8 +/- 3x10(4) L-circle dot. The inferred mass, effective temperature of the UV source, and the ionization rate are compatible with a young O9-B0 star. The ionized features D1 and D2 are considered to be ionized by UV radiation collimated by an accretion disk. We consider that the central massive star photoevaporates its circumstellar disk on a timescale of 3x10(4) years giving a mass flux similar to 3 x 10(-5) M-circle dot yr(-1) and producing the ionized material in D1 and D2 expanding in an inhomogeneous medium. The ionized gas kinematics, as traced by the [Ne II] emission, is difficult to interpret, but it could be explained by the interaction of a bipolar jet with surrounding gas along with what appears to be a conical wall of lower velocity gas. The other HII regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact HII regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.National Science Foundation AST-0807400, AST-0607312National Aeronautics and Space AdministrationAstronom