Triangulum-Andromeda overdensity: a region with a complex stellar
  population
  The Triangulum--Andromeda (TriAnd) overdensity is a distant structure of the
Milky Way located in the second Galactic quadrant well below the Galactic
plane. Since its discovery, its nature has been under discussion, whether it
could be old perturbations of the Galactic disk or the remains of a disrupted
former dwarf galaxy. In this study, we investigate the kinematics and chemical
composition in 13 stars selected as TriAnd candidates from 2MASS photometry.
The sample was observed using the GRACES high-resolution spectrograph attached
to the Gemini North telescope. Based on radial velocities obtained from the
spectra and the astrometric data from GAIA, three different kinematic criteria
were used to classify our sample stars as belonging to the TriAnd overdensity.
The TriAnd confirmed members in our sample span a range in metallicities,
including two metal-poor stars ([Fe/H] $\sim$ -1.3 dex). We show that the
adopted kinematical classification also chemically segregates TriAnd and
non-TriAnd members of our sample, indicating a unique chemical pattern of the
TriAnd stars. Our results indicate different chemical patterns for the [Na/Fe],
[Al/Fe], [Ba/Fe], and [Eu/Fe] ratios in the TriAnd stars when compared to the
chemical pattern of the local disk; the paucity of studies chemically
characterizing the outer disk population of the Milky Way is the main obstacle
in establishing that the TriAnd population is chemically similar to field stars
in the outer disk. But TriAnd chemical pattern is reminiscent of that found in
outer disk open clusters, although the latter are significantly more metal-rich
than TriAnd.
