DETAILED ANALYSIS OF NEARBY BULGELIKE DWARF STARS. Ⅲ. α-ELEMENT AND HEAVY-ELEMENT ABUNDANCES

摘要

The present sample of nearby bulgelike dwarf stars has kinematics and metallicities characteristic of a probable inner disk or bulge origin. Ages derived by using isochrones give 10-11 Gyr for these stars, and metallicities are in the range -0.80 ≤ [Fe/H] ≤ +0.40. We calculate stellar parameters from spectroscopic data, and chemical abundances of Mg, Si, Ca, Ti, La, Ba, Y, Zr, and Eu are derived by using spectrum synthesis. We found that [++-elements/Fe] show different patterns, depending on the element. Si/Fe, Ca/Fe, and Ti/Fe ratios decline smoothly for increasing metallicities and essentially follow the disk pattern. O and Mg, products of massive supernovae, and also the r-process element Eu are overabundant relative to disk stars, showing a steeper decline for metallicities [Fe/H] > -0.3 dex, and [s-elements/Fe] roughly track the solar values, with no apparent trend with metallicity for [Fe/H] < 0, showing subsolar values for the metal rich stars. Both kinematical and chemical properties of the bulgelike stars indicate a distinct identity of this population when compared with disk stars.