Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young (several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known O stars. Follow-up spectroscopy of three other bow shock-producing stars showed that they are O-type stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular shells typical of luminous blue variable and late WN-type Wolf-Rayet stars.
The O star hinterland of the Galactic starburst, NGC 3603
非常明亮和紧凑的大质量年轻星团NGC 3603被引用为银河系中星暴的一个例子，并与大麦云中的R136/30剑鱼座区域进行了大量研究。在这里，我们建立在Mohr-Smith等人（2017）发现的大量红O星的基础上。我们构建了一个包含288颗具有自行的候选O星的列表，位于以NGC 3603为中心的1.5x1.5平方度的天空区域中，通过将Mohr-Smith et al.（2017）目录与Gaia DR 2（Gaia Collaboration et al. 2018）进行交叉匹配。这为第一次全面检查NGC 3603晕中这些大质量恒星的自行提供了基础，相对于研究得更好的中心区域。我们确定了多达11个可能的O型星喷射-其中8个将在0.60和0.95百万年前被喷射（支持c.1百万年的年龄已被归因于明亮的星团中心）。七个候选的抛射体被安排在星团核心以南的部分环中，半径为9-18弧分（如果星团距离7千秒差距，则为18-36秒差距）。我们还表明，该星团有一个光环的进一步100 O星延伸到半径至少为5弧分，增加了图片的NGC 3603作为一个缩小版本的R136/30 Dor地区。
