The star formation rate in the Milky Way: Results from stars and planetary nebulae

Abstract

The star formation rate (SFR) is still a poorly known characteristic of the Milky Way, especially concerning the possibility of an irregular SFR, compared to a constant rate. Some recent results based on the distribution of dwarf stars with chromospheric ages suggest at least two major bursts in the past 10 Gyr, while other investigations are consistent with an approximately constant SFR. The SFR also shows important spatial variations, particularly concerning the radial variations along the galactic disc. In this work, we investigate two different problems relative to the galactic SFR: (i) We estimate the star formation rate in the galactic disc based on the age distribution of the planetary nebula central stars (CSPN), and compare these results with previous investigations based on dwarf stars. The CSPN ages were derived on the basis of five different methods, involving the observed nebular metallicities and kinematical properties; (ii) We derive radial abundance gradients from several elements in planetary nebulae, and compare these results with recent determinations based on younger objects, such as HII regions and cepheid variables. Since the gradients are linked to the formation process of the galactic disc, we can estimate the spatial variation of the SFR. Preliminary results indicate that at least one major star formation burst is obtained, as well as a relatively smooth variation of the SFR along the galactocentric radius.