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M. Sewilo (University of Wisconsin-Madison), E. Churchwell (University of Wisconsin - Madison), S. Kurtz (UNAM - Morelia), W.M. Goss (NRAO), P. Hofner (NRAO and New Mexico Tech)
An extensive study of hypercompact (HC) H II regions was initiated using the VLA to investigate the origin and nature of the broad (FWHM > 40 km s-1) lines detected toward 8 of them. HC H II regions are about ten times smaller and a hundred times denser than ultracompact (UC) H II regions. They show rising continuum spectral indices of \alpha ~ +1 (S\nu \propto \nu\alpha) from short cm to mm wavelengths, sizes \le 0.01 pc, electron densities \ge 105 cm-3, and emission measures \ge a few times 108 pc cm-6. HC H II regions may represent a new intermediate stage of early massive star evolution, the transition from the rapid accretion phase of massive star formation to the emergence of UC H II regions.
The nature of the line broadening in HC H II regions is uncertain. It may be produced by a combination of thermal, turbulent, electron impact broadening, and large scale motions (rotation, expansion, outflow, inflow, disk, etc.). We have obtained high spatial resolution observations of H92\alpha to H53\alpha recombination lines toward several HC H II regions to determine the main broadening contributions to the line profiles. Funding for this research was provided in part by NSF grant AST-0303689 (EBC), CONACyT grant E-36568 and DGAPA-UNAM grant IN118401 (SK), Research Corporation Grant CC4996 and NSF grant AST-0098524 (PH).
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.