G0.481-0.037, an Isolated Compact H ii Region in Sgr B1

Abstract

We present a near-infrared spectrum of the isolated compact H ii region G0.481-0.037 taken with SpeX on the Infrared Telescope Facility. This spectrum shows strong lines of hydrogen Brγ, Brδ, Pα, and He i 2.059 μm. The radial velocity observed from the strongest line, Brγ, is V LSR = 77 ± 6 km s−1, significantly larger than the velocities of other ionized components of Sgr B1. We modeled the observed He i 2.059/Brγ ratio, 0.353 ± 0.075, with Cloudy C22.01 using model stellar atmospheres representing both dwarfs and giants. Our model ratios agree with the observed ratio for stellar effective temperatures of ∼34,500 K for dwarfs and ∼33,000 K for giants, from which we estimate late O spectral types for both luminosity classes. These values are consistent with the observed radio fluxes, given that the ionizing star of G0.481-0.037 is probably no longer embedded in its natal molecular cloud.