High - resolution imaging of ultracompact H II regions

We present the results of an extensive imaging campaign on the ultracompact Hii region G5.89-0.39 at nearand mid-infrared wavelengths. High-resolution data were taken in the H , K ′, and L bands using ESO’s adaptive optics system ADONIS. They are complemented by conventional narrowband images in Brγ and H2(1−0)S1 as well as by mid-infrared broadand narrow-band images. We also mapped the 1.3 mm continuum emission from the source using the SEST. We use our data to consistently explain the morphological appearance of G5.89-0.39 at all observed wavelengths as well as its spectral energy distribution. The complete model of the source consists of a spherical shell of dust with an inner, dustfree cavity of 7.6×1016 cm radius surrounding a star of spectral type O6 ZAMS. Two outflows escape this shell in opposite directions. Half of the whole configuration is evidently obscured by a very massive cloud of cold dust. Comparisons with earlier models and other ultracompact Hii regions are drawn to put G5.89-0.39 in the context of massive star formation.