The age of the Galactic thin disk from Th/Eu nucleocosmochronology
III. Extended sample
Observatório Nacional/MCT, Rua General José Cristino 77, 20921-400 Rio de Janeiro, Brazil e-mail: [epeloso;licio]@on.br
2 Observatório do Valongo/UFRJ, Ladeira do Pedro Antônio 43, 20080-090 Rio de Janeiro, Brazil e-mail: [gustavo;lilia]@ov.ufrj.br
Accepted: 9 June 2005
The first determination of the age of the Galactic thin disk from Th/Eu nucleocosmochronology was accomplished by us in Papers I and II. The present work aimed at reducing the age uncertainty by expanding the stellar sample with the inclusion of seven new objects – an increase by 37%. A set of [Th/Eu] abundance ratios was determined from spectral synthesis and merged with the results from Paper I. Abundances for the new, extended sample were analyzed with the aid of a Galactic disk chemical evolution (GDCE) model developed by us is Paper II. The result was averaged with an estimate obtained in Paper II from a conjunction of literature data and our GDCE model, providing our final, adopted disk age with a reduction of 0.1 Gyr (6%) in the uncertainty. This value is compatible with the most up-to-date white dwarf age determinations (≲10 Gyr). Considering that the halo is currently presumed to be old, our result prompts groups developing Galactic formation models to include an hiatus of between the formation of halo and disk.
Key words: Galaxy: disk / Galaxy: evolution / stars: late-type / stars: fundamental parameters / stars: abundances
© ESO, 2005