Evidence of enhanced formation episodes in the Galactic open cluster system

Aims. The exciting debate about the existence of signs of enhanced formation of Galactic open clusters (OCs) is revisited here on the basis of a revised age distribution. Methods. The data were taken from the recently updated 2009 version of the Dias et al.'s 1787 OC catalogue. Results. We found that the present OC's age distribution presents two primary excesses at t similar to 10-15 Myr and 1.5 Gyr, which are signs of enhanced formation episodes similar to those that occurred in other galaxies (e.g., M51, NGC 1705). When restricting the OC sample to those located in the solar neighbourhood, with the aim of avoiding incompleteness effects, we also find that these clusters are engraved with clear signs of enhanced formation at both ages.