摘要：Context.The low-mass members of OB associations, expected to be a major component of their total population, are in most cases poorly studied because of the difficulty of selecting these faint stars in crowded sky regions. Our knowledge of many OB associations relies on only a relatively small number of massive members.Aims.We study here the Sco OB1 association, with the aim of a better characterization of its properties, such as global size and shape, member clusters and their morphology, age and formation history, and total mass.Methods.We use deep optical and near-infrared (NIR) photometry from the VPHAS+ and VVV surveys, over a wide area (2.6° × 2.6°), complemented bySpitzerinfrared (IR) data, andChandraand XMM-Newton X-ray data. A new technique is developed to find clusters of pre-main sequence M-type stars using suitable color-color diagrams, complementing existing selection techniques using narrow-band Hαphotometry or NIR and ultraviolet (UV) excesses, and X-ray data.Results.We find a large population of approximately 4000 candidate low-mass Sco OB1 members whose spatial properties correlate well with those of Hα-emission, NIR-excess, UV-excess, and X-ray detected members, and unresolved X-ray emission. The low-mass population is spread among several interconnected subgroups: they coincide with the HIIregions G345.45+1.50 and IC4628, and the rich clusters NGC 6231 and Trumpler 24, with an additional subcluster intermediate between these two. The total mass of Sco OB1 is estimated to be ~ 8500M⊙. Indication of a sequence of star-formation events is found, from South (NGC 6231) to North (G345.45+1.50). We suggest that the diluted appearance of Trumpler 24 indicates that the cluster is now dissolving into the field, and that tidal stripping by NGC 6231 nearby contributes to the process.
关键词：Key wordsenopen clusters and associations: individual: Sco OB1open clusters and associations: individual: NGC6231open clusters and associations: individual: Trumpler 24stars: pre-main sequenceX-rays: stars
