Two micron narrowband imaging of the Sagittarius D H II region

We present 2 mu m narrowband images of the core H II region in the Galactic star-forming region Sagittarius D. The emission-line images are centered o n 2.17 mu m (Br gamma) and 2.06 mu m (He I). The H II region appears at the edge of a well-defined dark cloud, and the morphology suggests a blister g eometry as pointed out in earlier radio continuum work. There is a deficit of stars in general in front of the associated dark cloud indicating the H II region is located in between the Galactic center and the Sun. The lesser spatial extent of the He I line emission relative to Br gamma places the e ffective temperature of the ionizing radiation field below 40,000 K. The He 12.06 mu m to Br gamma ratio and Br gamma/far-infrared dust emission put T -eff at about 36,500-40,000 K as derived from ionization models.