Chemical enrichment and star formation in the Milky Way disk; II. Star formation history

Abstract

A chromospheric age distribution of 552 late-type dwarfs is transformed into a star formation history by the application of scale height corrections, stellar evolutionary corrections and volume corrections. We show that the disk of our Galaxy has experienced enhanced episodes of star formation at 0-1 Gyr, 2-5 Gyr and 7-9 Gyr ago, although the reality of the latter burst is still uncertain. The star sample birthsites are distributed over a very large range of distances because of orbital diffusion, and so give an estimate of the global star formation rate. These results are compared with the metal-enrichment rate, given by the age-metallicity relation, with the expected epochs of close encounters between our Galaxy and the Magellanic Clouds, and with previous determinations of the star formation history. Simulations are used to examine the age-dependent smearing of the star formation history due to age uncertainties, and the broadening of the recovered features, as well as to measure the probability level that the history derived to be produced by statistical fluctuations of a constant star formation history. We show with more than 98% level of confidence that the the star formation of our Galaxy was not constant.