Letter to the Editor

Clusters in the solar neighbourhood: how are they destroyed?

¹ Astronomical Institute, Utrecht University, Princetonplein 5, 3584CC Utrecht, The Netherlands e-mail: [lamers;gieles]@astro.uu.nl
² SRON Laboratory for Space Research, Sorbonnelaan 2, 3584CC, Utrecht, The Netherlands

Received: 8 May 2006
Accepted: 26 June 2006

Abstract

We predict the survival time of initially bound star clusters in the solar neighbourhood taking into account: (1) stellar evolution, (2) tidal stripping, (3) shocking by spiral arms and (4) encounters with giant molecular clouds. We find that the predicted dissolution time is M_i Gyr for clusters in the mass range of M_i. The resulting predicted shape of the logarithmic age distribution agrees very well with the empirical one, derived from a complete sample of clusters in the solar neighbourhood within 600 pc. The required scaling factor implies a star formation rate of 4  10²  Myr^-1  within 600 pc from the Sun or a surface formation rate of 3.5  10^-10  yr^-1 pc^-2 for stars in bound clusters with an initial mass in the range of 10² to 3  10⁴ .