Two sequences in the age-metallicity relation as seen from [C/N]
  abundances in APOGEE
  The age-metallicity relation is fundamental to study the formation and
evolution of the disk. Observations have shown that this relation has a large
scatter which can not 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. 2020, using high precision observational data of
solar type stars, found two relatively tight age-metallicity relations. 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 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 analysing an independent sample of red clump giants observed
by APOGEE. Since ages for red giants are significantly more uncertain, the
[C/N] ratios are considered as a proxy for age. This larger dataset is used to
investigate these relations at different Galactic radii, finding that these
distinct sequences exist only in the solar neighbourhood. The APOGEE dataset is
further used to explore different abundance and kinematical planes to shed
light on the nature of these populations.
