High Angular Resolution Imaging Spectroscopy of the Galactic Ultracompact H II Region K3-50A

Abstract

Gemini North adaptive optics (AO) imaging spectroscopy is presented for the Galactic ultracompact H II (UCH II) region K3 - 50A. Data were obtained in the K band using the Near-infrared Integral Field Spectrograph (NIFS) behind the facility AO module ALTAIR in natural guide star mode. The NIFS data cube reveals a complex spatial morphology across the 0.1 pc scale of the 3″ UCH II region. Comparison of the nebular emission to Cloudy ionization models shows that the central source must have an effective temperature between about 37,000K and 45,000K with preferred values near 40,000K. Evidence is presented for sharp density variations in the nebula which are interpreted as a clearing of material nearest the central source. High excitation lines of Fe III and Se IV show that the ionization of the nebula clearly changes with distance from the central source. A double lobed kinematic signature ( 25kms-1) is evident in the Brγ line map which may be related to the larger scale ionized flow detailed in earlier investigations. This signature and the large-scale flow are not co-aligned, but they may still be related. Though clearly resolved from the nebula, the central source itself remains buried, and the NIFS spectrum shows no evidence of photospheric lines.