  From a detailed elemental abundance analysis of 102 F and G dwarf stars we
present abundance trends in the Galactic thin and thick disks for 14 elements
(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 (Bensby et al. 2003, 2004a). The 36 stars
that are new in this study extend and confirm our previous results and allow us
to draw further conclusions regarding abundance trends. The s-process elements
Y and Ba, and the r-element Eu have also been considered here for the whole
sample for the first time. With this new larger sample we now have the
following results: 1) Smooth and distinct trends that for the thin and thick
disks are clearly separated; 2) The alpha-element trends for the thick disk
show typical signatures from the enrichment of SNIa; 3) The thick disk stellar
sample is in the mean older than the thin disk stellar sample; 4) The thick
disk abundance trends are invariant with galactocentric radii (R_m); 5) The
thick disk abundance trends appear to be invariant with vertical distance
(Z_max) from the Galactic plane. Adding further evidence from the literaure we
argue that a merger/interacting scenario with 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 the most likely formation scenario for the
Galactic thick disk.
