Most “Young” α-rich Stars Have High Masses but are Actually Old

Recent observations have revealed a population of $\alpha$-element abundances enhanced giant stars with unexpected high masses ($\gtrsim$1 $M_\odot$) from asteroseismic analysis and spectroscopy. Assuming single-star evolution, their imply young ages ($\tau<6$Gyr) incompatible the canonical Galactic chemical evolution scenario. Here we study chemistry kinematics large sample such $\alpha$-rich, high-mass red branch (RGB) drawn LAMOST spectroscopic surveys. Using Gaia, found these share same as high-$\alpha$ old stellar in thick disk. The show that massive $\alpha$- iron-peak element similar to those disk stars. However, portion them exhibit higher [(N+C)/Fe] [Ba/Fe] ratios, which implies they gained C- Ba-rich materials extra sources, presumably asymptotic (AGB) companions. results support previous suggestion RGB are products binary evolution. Their thus mimic "young" single stars, yet fact belong an intrinsic population. To fully explain abundance patterns our variety channels, as, main-sequence (MS) + RGB, MS AGB, required, pointing diverse formation mechanisms seemly rejuvenated cannibals. With this larger sample, confirm earlier findings most, if not all, $\alpha$-rich seem be old.