Abstract
Abstract The age–metallicity relation (AMR) is fundamental to study the formation and evolution of the disk. Observations have shown that this relation has a large scatter, which cannot be explained by observational errors only. That scatter is hence attributed to the effects of radial migration in which stars tracing different chemical evolution histories in the disk get mixed. However, the recent study of Nissen et al., using high-precision observational data of solar-type stars, found two relatively tight AMRs. One sequence of older and metal-richer stars probably traces the chemical enrichment history of the inner disk while the other sequence of younger and metal-poorer stars traces the chemical enrichment history of the outer disk. If uncertainties in age measurements increase, these sequences mix, explaining the scatter of the one relation observed in other studies. This work follows up on these results by analyzing an independent sample of red clump giants observed by APOGEE. Because ages for red giants are significantly more uncertain, the [C/N] ratios are considered as a proxy for age. This larger data set is used to investigate these relations at different Galactic radii, finding that these distinct sequences exist only in the solar neighborhood. The APOGEE data set is further used to explore different abundance and kinematical planes to shed light on the nature of these populations.
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