Spectroscopic Follow-up of Young High-$\alpha$ Dwarf Star Candidates: Still Likely Genuinely Young

Abstract

The question of whether genuinely young high-$\alpha$ stars exist has been discussed for over a decade since their discovery from asteroseismology of giant stars as it is challenging to break the degeneracy between the binary interaction and the genuinely young scenarios. Young high-$\alpha$ stars are hard to explain with traditional chemical evolution model as the high-$\alpha$ disk is typically associated with the early epoch of star formation in the Milky Way. Combined with recent advances of gyrochronology, and that $^7$Li can serve as an unambiguous indicator for identifying merger products in dwarfs thanks to its low burning temperature, we identified young high-$\alpha$ dwarf candidate stars through their fast rotation in a previous study. In this paper, we performed high-resolution spectroscopic follow-up of these candidates using Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), and confirm 3 additional stars that are most likely genuinely young. Together with the star from the earlier paper, we find three out of four of them center around [Fe/H]=-0.5 dex, are ~5 Gyr old, and have a similar amount of elevated Li (~0.5 dex) and Al (~0.1 dex) compared to stars with matching $\log g$, $T_{\rm eff}$, Mg, and Fe within observational uncertainties, hinting at their common formation pathway.