We have derived the star formation history of the Milky Way disk over the last 2 Gyr with a time resolution of 0.05 Gyr from the age distribution diagram of a large sample of open clusters comprising more than 580 objects .
By interpreting the age distribution diagram using numerical results from an extensive library of N -body calculations carried out during the last ten years , we reconstruct the recent star formation history of the Milky Way disk .
Under the assumption that the disk has never been polluted by any extragalactic stellar populations , our analysis suggests that superimposed on a relatively small level of constant star formation activity mainly in small- N star clusters , the star formation rate has experienced at least 5 episodes of enhanced star formation lasting about 0.2 Gyr with production of larger clusters .
This cyclic behavior shows a period of 0.4 \pm 0.1 Gyr and could be the result of density waves and/or interactions with satellite galaxies .
On the other hand , the star formation rate history from a volume-limited sample of open clusters in the solar neighbourhood appears to be consistent with the overall star formation history obtained from the entire sample .
Pure continuous star formation both in the solar neighbourhood and the entire Galactic disk is strongly ruled out .
Our results also indicate that , in the Milky Way disk , about 90 % of open clusters are born with N \leq 150 and the slope in the power-law frequency distribution of their masses is about -2.7 when quiescent star formation takes place .
If the above results are re-interpreted taking into consideration accretion events onto the Milky Way , it is found that a fraction of the unusually high number of open clusters with ages older than 0.6 Gyr may have been formed in disrupted satellites .
Problems arising from the selection effects and the age errors in the open cluster sample used are discussed in detail .