High spectral and spatial resolution, mid-infrared fine-structure line observations toward two ultracompact H II (UC H II) regions (G29.96-0.02 and Mon R2) allow us to study the structure and kinematics of cometary UC H II regions. In our earlier study of Mon R2, we showed that highly organized mass motions accounted for most of the velocity structure in that UC H II region. In this work, we show that the kinematics in both Mon R2 and G29.96 are consistent with motion along an approximately paraboloidal shell. We model the velocity structure seen in our mapping data and test the stellar wind bow shock model for such paraboloidal-like flows. The observations and the simulation indicate that the ram pressures of the stellar wind and ambient interstellar medium cause the accumulated mass in the bow shock to flow along the surface of the shock. A relaxation code reproduces the mass flow's velocity structure as derived by the analytical solution. It further predicts that the pressure gradient along the flow can accelerate ionized gas to a speed higher than that of the moving star. In the original bow shock model, the star speed relative to the ambient medium was considered to be the exit speed of ionized gas in the shell.
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机译：对两个超紧凑H II（UC H II）区域（G29.96-0.02和Mon R2）的高光谱和空间分辨率，中红外精细结构线观察，使我们能够研究彗星UC H II区域的结构和运动学。在我们对Mon R2的早期研究中，我们表明，高度有组织的质量运动占了UC H II区域中大部分速度结构的原因。在这项工作中，我们表明Mon R2和G29.96中的运动学与沿着近似抛物面壳的运动一致。我们对在映射数据中看到的速度结构进行建模，并针对此类抛物面样流测试恒星风弓激波模型。观测和模拟表明，恒星风和周围星际介质的冲压压力导致弓形激波中的累积质量沿激波表面流动。松弛代码再现了由解析解导出的质量流的速度结构。它进一步预测，沿流的压力梯度可以使电离气体加速到比移动恒星更高的速度。在原始的弓形激波模型中，相对于环境介质的星速被认为是壳中电离气体的出口速度。
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