Optical High-resolution Spectroscopy of 14 Young α-rich Stars

We report chemical abundances of 14 young alpha-rich stars including neutron-capture elements based on high-quality optical spectra from HIRES/Keck. I and differential line-by-line analysis. From a comparison of the abundance patterns of young alpha-rich stars to those of nearby bright red giants with a similar metallicity range (-0.7 < [Fe/H] < -0.2), we confirm their high alpha-element abundances reported by previous studies based on near-infrared spectroscopy. We reveal for the first time low abundances of s-process elements and high abundances of r-process elements. All the abundances are consistent with those seen in the typical alpha-rich population of the Galactic disk, and no abundance anomalies are found except for Li-enhancement in one object previously reported and mild enhancement of Na in two stars. In particular, the lack of s-process enhancement excludes the hypothesis that mass transfer from asymptotic giant branch stars plays an important role in the formation of young alpha-rich stars. The high frequency of radial velocity variation (more than 50%) is also confirmed. We argue that mass transfer from low-mass red giants is the likely dominant formation mechanism for young alpha-rich stars.