标题： 冷气在热星团中：Westerlund 1中的红超巨星W26的风 显示英文标题

标题： Cold gas in hot star clusters: the wind from the red supergiant W26 in Westerlund 1

摘要： Westerlund 1星团中的大质量红超巨星（RSG）W26是越来越多被证明其风是从外部电离的一类RSG之一。这种密集风物质的命运对于大质量星团中第二代恒星形成模型来说非常重要。Mackey等人（2014）表明外部光致电离可以阻止RSG的风，并在密集静态壳中积累质量。我们使用外部光致电离风的1D辐射-流体力学模拟来预测来自具有和不具有密集壳的光致电离风产生的Halpha和[NII]发射。我们分析了W26周围环境中Halpha和[NII]发射的光谱，并将其与预测的合成发射进行比较。减速进入密集壳的慢速风的模拟显示出强烈的边缘增亮线发射，且线径向速度独立于风速。更快的风（>22公里/秒）不会形成密集壳，边缘增亮较少，线径向速度是风速的良好示踪剂。[NII]和Halpha线的亮度随距离W26的变化在仅考虑线通量时与观测结果相当吻合。然而，径向速度却不同：最亮的观测发射相对于恒星的径向速度蓝移约25公里/秒，而球对称风在零径向速度处有最亮的发射。我们的结果表明，包围W26的明亮星云必须是不对称的；我们建议它是由附近超级巨星W9的风的外部冲击压力限制的。我们在星云内的氮丰度下限为2.35倍太阳值。线比强烈支持光致电离而非冲击电离，因此即使观测到的星云是压力约束的，仍然应该在靠近恒星的地方存在一个电离前端和一个由光致电离约束的壳层。 显示英文摘要

摘要： The massive red supergiant (RSG) W26 in Westerlund 1 is one of a growing number of RSGs shown to have winds that are ionized from the outside in. The fate of this dense wind material is important for models of second generation star formation in massive star clusters. Mackey et al. (2014) showed that external photoionization can stall the wind of RSGs and accumulate mass in a dense static shell. We use 1D R-HD simulations of an externally photoionized wind to predict the Halpha and [NII] emission arising from photoionized winds both with and without a dense shell. We analyse spectra of the Halpha and [NII] emission in the environment around W26 and compare them with predicted synthetic emission. Simulations of slow winds that are decelerated into a dense shell show strongly limb-brightened line emission, with line radial velocities that are independent of the wind speed. Faster winds (>22 km/s) do not form a dense shell, have less limb-brightening, and the line radial velocity is a good tracer of the wind speed. The brightness of the [NII] and Halpha lines as a function of distance from W26 agrees reasonably well with observations when only the line flux is considered. The radial velocity disagrees, however: the brightest observed emission is blueshifted by ~25 km/s relative to the radial velocity of the star, whereas a spherically symmetric wind has the brightest emission at zero radial velocity. Our results show that the bright nebula surrounding W26 must be asymmetric; we suggest it is confined by external ram pressure from the wind of the nearby supergiant W9. We obtain a lower limit on the nitrogen abundance within the nebula of 2.35 times solar. The line ratio strongly favours photoionization over shock ionization, and so even if the observed nebula is pressure confined there should still be an ionization front and a photoionization-confined shell closer to the star.