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Our sample of cool dwarf stars from previous papers is extended in this studyincluding 15 moderately metal-deficient stars. The samples of halo and thickdisk stars have overlapping metallicities with [Fe/H] in the region from -0.9to -1.5, and we first compare chemical properties of these two kinematicallydifferent stellar populations independent on their metallicity. We presentbarium, europium and magnesium abundances for the new sample of stars. Theresults are based on NLTE line formation obtained in differential modelatmosphere analyses of high resolution spectra observed mainly using the UVESspectrogragh at the VLT of ESO. We confirm the overabundance of Eu relative toMg in the halo stars. Eight halo stars show the [Eu/Mg] ratios between 0.23 and0.41, whereas stars in the thick and thin disk display a solar Eu to Mg ratio.The [Eu/Ba] values found in the thick disk stars to lie between 0.35 and 0.57suggest that during the thick disk formation evolved low-mass stars started toenrich the interstellar gas by s-nuclei of Ba, and the s-process contributionto Ba varies from 30% to 50%. Based on these results, and using the chemicalevolution calculations by Travaglio et al. (1999), we estimate that the thickdisk stellar population formed on a timescale from 1.1 to 1.6 Gyr from thebeginning of the protogalactic collapse. In the halo stars the [Eu/Ba] ratiosare found mostly between 0.40 and 0.67, which suggests a duration of the haloformation of about 1.5 Gyr. For the whole sample of stars we present theeven-to-odd Ba isotope ratios as determined from hyperfine structure seen inthe Ba II resonance line lambda4554. Based on these data we deduce for thethick disk stars the ratio of the s/r-process contribution to barium as 30 : 70(+- 30%), in agreement with the results obtained from the [Eu/Ba] ratios.Comment: Accepted for A&A, 10 pages, 6 figure

Mg, Ba and Eu abundances in thick disk and halo stars