标题： H II区域中的自相似香槟流 显示英文标题

标题： Self-similar champagne flows in HII regions

摘要： （精简版）我们研究了最初自引力的、静态的、奇异的、等温的云核的膨胀情况。 对于 t > 0，气体被电离并加热到更高的均匀温度，这是由于中心形成了一颗发光但无质量的恒星所致。 假设中心恒星的质量和引力对后续 HII 区域运动的影响可以忽略不计，则该近似适用于距离大于约 100 天文单位的情况，并且适用于能够产生大质量恒星的云核。 如果初始电离和加热被近似为在 t = 0 时瞬间发生，那么由自我引力与热压失衡引起的随后流动（r >> 100 AU）将是自相似的。 由于密度剖面陡峭，压力梯度会产生一个冲击波前沿进入云层，加速气体至超音速，这被称为“香槟相”。 然后我们研究嵌入分子云中的 HII 区域膨胀的自相似解，这些分子云具有更普遍的幂律密度分布，指数 3/2 < n < 3。 在这种情况下，冲击波速度是指数 n 的递增函数，并且当 n 趋向于 3 时发散。 我们表明这是因为模型包括了一个原点，在该原点处驱动冲击波的压力发散，因为所包围的加热质量是无限的。 我们的结果表明，为了在显著的时间尺度上维持香槟流中观察到的发射度测量值，需要持续光蒸发附近中性气体的大规模储层（例如围绕电离源周围的盘状结构和/或小球状结构）。 显示英文摘要

摘要： (Abridged) We consider the expansion of an initially self-gravitating, static, singular, isothermal cloud core. For t>0, the gas is ionized and heated to a higher uniform temperature by the formation of a luminous, but massless, star in its center. The approximation that the mass and gravity of the central star is negligible for the subsequent motion of the HII region holds for distances much greater than about 100 AU and for the massive cloud cores that give rise to high-mass stars. If the initial ionization and heating is approximated to occur instantaneously at t=0, then the subsequent flow (for r >> 100 AU) caused by the resulting imbalance between self-gravity and thermal pressure is self-similar. Because of the steep density profile, pressure gradients produce a shock front that travels into the cloud, accelerating the gas to supersonic velocities in what has been called the ``champagne phase.'' We then study the self-similar solutions of the expansion of HII regions embedded in molecular clouds characterized by more general power-law density distributions with exponent 3/2 < n < 3. In these cases, the shock velocity is an increasing function of the exponent n, and diverges as n tends to 3. We show that this happens because the model includes an origin, where the pressure driving the shock diverges because the enclosed heated mass is infinite. Our results imply that the continued photoevaporation of massive reservoirs of neutral gas (e.g., surrounding disks and/or globules) nearby to the embedded ionizing source is required in order to maintain over a significant timescale the emission measure observed in champagne flows.