Lanthanum and Europium Abundances in a Large Sample of Galactic Disk Dwarf Stars

Astronomy and Astrophysics – Astronomy

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Scientific paper

Elemental abundance trends within the thin and thick disk stellar populations of the Milky Way argue for distinct large-scale evolution within those populations. Recent studies of the abundance trends of thin and thick disk stars have found that the run of [alpha/Fe] with [Fe/H] differs significantly, indicating unique star formation histories (Reddy et al. 2006, Brewer & Carney 2006, Bensby et al. 2003). The heavy element contributions are also different in the two populations, such that the r-process element [Eu/Fe] is higher at a given [Fe/H] in thick disk stars. In the thick disk, the s-process/r-process ratio may be lower overall (Mashonkina & Gehren 2001, Bensby et al. 2005). This evidence of the varying contributions of low and high mass stars is of particular interest in light of the possibility of chemical substructure in the Galactic disk. Based on high resolution (R 40,000) and high signal-to-noise (S/N 100) spectra of 600 nearby dwarf stars, we will present the s-/r-process ratio in the local disk population as traced by the abundace ratio La/Eu. Stellar parameters have been derived from photometry. The sample covers 800 K in effective temperature (5400 K < Teff < 6200 K) and 0.7 dex in metallicity (-0.5 dex < [Fe/H] < +0.2 dex). For such a large number of spectra we employ an abundance measurement technique based on minimizing the Chi-squared fit to synthetic template spectra. Stellar kinematics and population assignments have been calculated for the entire sample, which is composed primarily of thin disk stars.

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