2008AJ....135..618C

The metallicities and abundance ratios, [X/Fe], of 12 elements – C, Na, Mg, Si, S, Ca, Ti, Cr, Ni, Y, Zr, and Ce – are determined for 14 old and 24 young metal-rich stars based on high resolution, high S/N spectra obtained with the HIDES spectrograph attached to the 1.88 m telescope of Okayama Astrophysical Observatory (Okayama, Japan). The results show that there is no any significant difference in the [X/Fe] versus [Fe/H] trend for these elements between the two groups of stars. This is consistent with the kinematics of the two groups of stars being similar to that of the thin disk. In connection with the abundance analysis, we found that iron abundances from Fe II lines are generally higher than those from Fe I lines for cool metal-rich stars. In particular, the [S/Fe] ratio strongly depends on stellar temperature. In view of this, the chemical evolution of the element sulfur can only be traced by selecting solar-type stars within a critically narrow temperature range. Inspecting a large sample of metal-rich stars, we found that young metal-rich stars generally have kinematics similar to that of the local thin disk, while old metal-rich stars show two different kinematic distributions, one with V_LSR~-10km.s^–1 and the other with V_LSR∼ -50km.s^–1. Abundances of this new population of old metal-rich stars with a slight lag in the Galactic rotation have already been investigated by the present authors. We compared the abundance patterns for the three groups of metal-rich stars, and did not find any significant difference in abundance ratios for the elements investigated. These results indicate an inhomogeneous metallicity enhancement but similar nucleosynthesis history for the Galactic evolution of the thin disk from the beginning to the present.