Elemental abundance survey of the Galactic thick disc

Abstract

We have performed an abundance analysis for F- and G- dwarfs of the Galactic thick-disc component. A sample of 176 nearby (d ≤ 150pc) thick-disc candidate stars was chosen from the Hipparcos catalogue and subjected to a high-resolution spectroscopic analysis. Using accurate radial velocities combined with the Hipparcos astrometry, kinematics (U, V and W) and Galactic orbital parameters were computed. We estimate the probability for a star to belong to the thin disc, the thick disc or the halo. With a probability P ≥ 70 per cent taken as certain membership, we assigned 95 stars to the thick disc, 13 to the thin disc, and 20 to the halo. The remaining 48 stars in the sample cannot be assigned with reasonable certainty to one of the three components. Abundances of C, O, Na, Mg, Al, Si, Ca, Se, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Ba, Ce, Nd and Eu have been obtained. The abundances for the thick-disc stars are compared with those for the thin-disc members from Reddy et al. The ratios of α-elements (O, Mg, Si, Ca and Ti) to iron for thick-disc stars show a clear enhancement compared to thin-disc members in the range -0.3 -0.3. The observed compositions of the thin and thick discs seem to be consistent with the models of galaxy formation by hierarchical clustering in a Lambda cold dark matter (ACDM) universe. © 2006 RAS.