The age of the Galactic thin disk from Th/Eu nucleocosmochronology

II. Chronological analysis

¹ Observatório Nacional/MCT, Rua General José Cristino 77, 20921-400 Rio de Janeiro, Brazil e-mail: epeloso@on.br, licio@on.br
² Observatório do Valongo/UFRJ, Ladeira do Pedro Antônio 43, 20080-090 Rio de Janeiro, Brazil e-mail: lilia@ov.ufrj.br

Received: 26 November 2004
Accepted: 15 December 2004

Abstract

The purpose of this work is to resume investigation of Galactic thin disk dating using nucleocosmochronology with Th/Eu stellar abundance ratios, a theme absent from the literature since 1990. [Th/Eu] abundance ratios for a sample of 20 disk dwarfs/subgiants of F5 to G8 spectral type with , determined in the first paper of this series, were adopted for this analysis. We developed a Galactic chemical evolution model that includes the effect of refuse, which are composed of stellar remnants (white dwarfs, neutron stars and black holes) and low-mass stellar formation residues (terrestrial planets, comets, etc.), contributing to a better fit to observational constraints. Two Galactic disk ages were estimated, by comparing literature data on Th/Eu production and solar abundance ratios to the model (), and by comparing [Th/Eu] vs. [Fe/H] curves from the model to our stellar abundance ratio data ((), yielding the final, average value . This is the first Galactic disk age determined via Th/Eu nucleocosmochronology, and corroborates the most recent white dwarf ages determined via cooling sequence calculations, which indicate a low age (≲) for the disk.