  We study the possibility that the Milky Way's cool stellar disc includes
mergers with ancient stars. Galaxies are understood to form in a hierarchical
manner, where smaller (proto-)galaxies merge into larger ones. Stars in
galaxies, like the Milky Way, contain in their motions and elemental abundances
tracers of past events and can be used to disentangle merger remnants from
stars that formed in the main galaxy. The merger history of the Milky Way is
generally understood to be particularly easy to study in the stellar halo. The
advent of the ESA astrometric satellite Gaia has enabled the detection of
completely new structures in the halo such as the Gaia-Enceladus-Sausage.
However, simulations also show that mergers may be important for the build-up
of the cool stellar disks. Combining elemental abundances for 100 giant branch
stars from APOGEE DR17 and astrometric data from Gaia we use elemental
abundance ratios to find an hitherto unknown, old stellar component in the cool
stellar disk in the Milky Way. We further identify a small sample of RR Lyrae
variables with disk kinematics that also show the same chemical signature as
the accreted red giant stars in the disk. These stars allows us to date the
stars in the accreted component. We find that they are exclusively old.
