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

Abstract

We report chemical abundances of 14 young α -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 α -rich stars to those of nearby bright red giants with a similar metallicity range (−0.7 < −0.2), we confirm their high α -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 α -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 α -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 α -rich stars.