Multiwavelength Studies of Young OB Associations
We discuss how contemporary multiwavelength observations of young OB-dominated clusters address long-standing astrophysical questions: Do clusters form rapidly or slowly with an age spread? When do clusters expand and disperse to constitute the field star population? Do rich clusters form by amalgamation of smaller subclusters? What is the pattern and duration of cluster formation in massive star forming regions (MSFRs)? Past observational difficulties in obtaining good stellar censuses of MSFRs have been alleviated in recent studies that combine X-ray and infrared surveys to obtain rich, though still incomplete, censuses of young stars in MSFRs. We describe here one of these efforts, the MYStIX project, that produced a catalog of 31,784 probable members of 20 MSFRs. We find that age spread within clusters is real in the sense that the stars in the core formed after the cluster halo. This is consistent with some recent astrophysical models involving merging star-forming filaments. Cluster expansion is seen in the ensemble of (sub)clusters, and older dispersing populations are found across MSFRs. Long-lived, asynchronous star formation is pervasive across MSFRs.
This review rests on the labor and talents of the MYStIX team, particularly Patrick Broos, Konstantin Getman, Michael Kuhn, Tim Naylor, Matthew Povich, and Leisa Townsley. Many of the astrophysical results appear in the dissertation of Michael Kuhn and work led by Kostantin Getman; the author is especially grateful for their collaborative energy and thoughtful analysis. The MYStIX Project was principally supported at Penn State by NASA grant NNX09AC74G and AR7-18000X, NSF grant AST-0908038, and SAO/CXC grant AR7-18002X and ACIS Team contract SV-74018.
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