Massive star formation of the sgr a east h_II regions near the Galactic center

A group of four compact H_II 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 ∼6 pc. We present a study of ionized gas based on the [Ne ii] (12.8 μm) line, as well as multi-frequency radio continuum, Hubble Space Telescope Paα, and Spitzer Infrared Array Camera observations of the most compact member of the H_II group, Sgr A East H_II 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_⊙ star with a luminosity of 8±3×10⁴ L_⊙. 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 3×10⁴ years giving a mass flux ∼3 ±10^-5 M_⊙ 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 H_II regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact H_II regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.