alpha-, r-, and s-process element trends in the Galactic thin and thick disks

Abstract:
From a detailed elemental abundance analysis of 102 F and G dwarf starswe present abundance trends in the Galactic thin and thick disks for 14elements (O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, Ba, and Eu).Stellar parameters and elemental abundances (except for Y, Ba and Eu)for 66 of the 102 stars were presented in our previous studies (Bensbyet al. 2003, 2004a). The 36 stars that are new in this study extend andconfirm our previous results and allow us to draw further conclusionsregarding abundance trends. The s-process elements Y and Ba, and ther-element Eu have also been considered here for the whole sample for thefirst time. With this new larger sample we now have the followingresults: 1) Smooth and distinct trends that for the thin and thick disksare clearly separated; 2) The alpha-element trends for the thick diskshow typical signatures from the enrichment of SNIa; 3) The thick diskstellar sample is in the mean older than the thin disk stellar sample;4) The thick disk abundance trends are invariant with galactocentricradii (R_m); 5) The thick disk abundance trends appear to be invariantwith vertical distance (Z_max) from the Galactic plane. Adding furtherevidence from the literaure we argue that a merger/interacting scenariowith a companion galaxy to produce a kinematical heating of the stars(that make up today's thick disk) in a pre-existing old thin disk is themost likely formation scenario for the Galactic thick disk.