The age of the Galactic thin disk from Th/Eu nucleocosmochronology
III. Extended sample
1
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
Received:
25
April
2005
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