Year: 2003
Type: article
Abstract: We have made imaging and spectroscopic observations of the ultracompact H II region K3-50A with a spatial resolution of 0 4 using a new mid-infrared instrument, the Cooled Mid-Infrared Camera and Spectrometer, on the 8.2 m Subaru Telescope. The spectra show thermal dust emission, 9.7 μm silicate absorption, and fine-structure line emissions of [Ne II] at 12.8 μm, [Ar III] at 8.99 μm, and [S IV] at 10.51 μm. From the maps of the continuum, line emissions, and/or derived dust parameters, we identify eight mid-infrared sources in K3-50A. Especially the central [Ne II] emission has been resolved into two peaks clearly. The ionization condition is investigated with the line flux ratios I ([Ar III])/ I ([Ne II]) and I ([S IV])/ I ([Ne II]). It is suggested that the spectral types of the ionizing stars in K3-50A correspond to B0-O8 V, which is much later than O5.5 V, the type estimated from radio continuum observations under a single-star assumption. The three line fluxes suggest a number of Ne + ions greater than what is ionized by a single star of any spectral type, but the numbers of Ar 2+ and S 3+ are similar to that formed by a single O8-O9 V star and that by a single O7-O9 V star, respectively. From these features as well as the dust temperature and the correspondence of each identified source with the near-infrared source, we propose that K3-50A is excited by at least two (possibly three) ionizing stars. This is the first convincing example that a massive stellar cluster is ionizing an ultracompact H II region.
Source: The Astrophysical Journal
DOI: 10.1086/345540
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W1978904596