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

Free access article

Issue		A&A Volume 440, Number 3, September IV 2005


Page(s)		1153 - 1159
Section		Stellar atmospheres
DOI		http://dx.doi.org/10.1051/0004-6361:20053307

A&A 440, 1153-1159 (2005)
DOI: 10.1051/0004-6361:20053307

III. Extended sample

E. F. del Peloso^{1, 2}, L. da Silva¹, G. F. Porto de Mello² and L. I. Arany-Prado²

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)

Abstract
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 $T_{\mathrm{G}}=(8.8\pm1.7)~\mbox{Gyr}$ 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 ( $\lesssim$ 10 Gyr). Considering that the halo is currently presumed to be $(13.5\pm0.7)~\mathrm{Gyr}$ old, our result prompts groups developing Galactic formation models to include an hiatus of $(4.7\pm1.8)~\mathrm{Gyr}$ between the formation of halo and disk.

Key words: Galaxy: disk -- Galaxy: evolution -- stars: late-type -- stars: fundamental parameters -- stars: abundances

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