EDP Sciences
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Volume 434, Number 1, April IV 2005
Page(s) 301 - 308
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20042438

A&A 434, 301-308 (2005)
DOI: 10.1051/0004-6361:20042438

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

II. Chronological analysis
E. F. del Peloso1, L. da Silva1 and L. I. Arany-Prado2

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 )

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 $-0.8\le{\rm [Fe/H]}\le+0.3$, 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 ( $8.7^{+5.8}_{-4.1}~{\rm Gyr}$), and by comparing [Th/Eu] vs. [Fe/H] curves from the model to our stellar abundance ratio data (( $8.2\pm1.9)~{\rm Gyr}$), yielding the final, average value $(8.3\pm1.8)~{\rm Gyr}$. 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 ($\lesssim$ $10~{\rm Gyr}$) for the disk.

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

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© ESO 2005