OB associations are unbound groups of young stars made prominent by their bright OB members, and have long been thought to be the expanded remnants of dense star clusters. They have been important in astrophysics for over a century thanks to their luminous massive stars, though their low-mass members have not been well studied until the last couple of decades. This has changed thanks to data from X-ray observations, spectroscopic surveys and astrometry from Gaia that allows their full stellar content to be identified and their dynamics to be studied, which in turn is leading to changes in our understanding of these systems and their origins, with the old picture of Blaauw (1964) now being superseded. It is clear now that OB associations have considerably more substructure than once envisioned, both spatially, kinematically and temporally. These changes have implications for the star formation process, the formation and evolution of planetary systems, and the build-up of stellar populations across galaxies.

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OB 协会及其起源

OB 协会是由明亮的 OB 成员突出的未绑定的年轻恒星群，长期以来一直被认为是密集星团的扩展残余物。由于它们发光的大质量恒星，它们在天体物理学中的重要性已经超过一个世纪，尽管直到最近几十年才对它们的低质量成员进行了很好的研究。由于来自盖亚的 X 射线观测、光谱调查和天体测量的数据，可以识别它们的全部恒星成分并研究它们的动力学，这反过来又导致我们对这些系统及其起源的理解发生变化。 ，Blaauw (1964) 的旧照片现已被取代。现在很明显，OB 关联在空间、运动学和时间上都比以前设想的要多得多。