The Oph-Sco-Lup-Cen-Cru-Mus-Cha Star-formation Region

The origin of the extended group of OB associations and molecular clouds situated between about galactic longitudes 360° to 290°, from Ophiuchus to Chamaeleon, is discussed. We consider that a satisfactory model must be able to explain the main properties of these associations, like the spatial distribution of the stars, the geometry of the interstellar clouds, the space velocities and age distribution of the premain sequence (PMS) and OB stars. A brief review is presented of some of the conflicting models that have been proposed in the literature, like the Gould Belt model and sequential star formation. We argue that the presence of a spiral arm can explain most of the observations of that super-association.