SCYON Abstract

Received on December 29 2007

From Star Complexes To The Field: Open Cluster Families

AuthorsR. de la Fuente Marcos and C. de la Fuente Marcos
AffiliationSuffolk University Madrid Campus
To appear inApJ, 672, 342, 2008 January 1


The currently accepted paradigm for star formation assumes that field stars are born in clusters. These are not formed in isolation but in stellar complexes born out of giant molecular clouds. In the Galactic disk, molecular clouds have distinctive orbits, which, as they disappear after star formation is complete, may seed the Galactic disk with families of young clusters. These families gradually disperse to become individual clusters and, eventually, field populations.We investigate the existence of dynamical families of open clusters in the solar neighborhood using both age- and volume-limited samples from WEBDA in the framework of scan statistics. Our analysis indicates that a significant number of known young clusters organize in groups when age, spatial distribution, and kinematics are taken into account simultaneously. We find compelling statistical evidence for the presence of at least five dynamical families of young open clusters in the Milky Way disk associated to the underlying spiral structure. The young cluster population seems to be dominated by families of 10-20 objects; they are short-lived and the likely progenitors of classical moving groups, and stellar streams. Available observational data suggests that 50%-80% of newly formed open clusters dissolve within 20 Myr of formation to become field population. The overall age distribution of open clusters shows a steep decline, dN/dτ proportional to τβ, with β = -3.6±0.5 for clusters younger than 100 Myr, although it could be dependent on the local conditions as it ranges from β = -1.0±0.2 in the direction of Puppis to β = -2.8±0.5 in Norma. Due to the high rate of destruction among young clusters, any cluster-related coherent substructure must be younger than about 30 Myr unless it is the result of dynamically induced corotation resonances within the Galactic disk or minor mergers. The characteristic timescale for stars to become part of the field stellar populations is 10-20 Myr.