2024ApJ...960...52B

We explore the kinematic and chemical properties of the Monoceros stellar overdensity by combining data from the Two Micron All Sky Survey, Wide-field Infrared Survey Explorer, APOGEE, and Gaia. Monoceros is a structure located toward the Galactic anticenter and close to the disk. We have identified that its stars have azimuthal velocity in the range of 200 < v_ϕ (km s^–1) < 250. Combining their kinematics and spatial distribution, we designed a new method to select stars from this overdensity. This method allows us to easily identify the structure in both hemispheres and estimate their distances. Our analysis was supported by comparison with simulated data from the entire sky generated by the Galaxia code. Furthermore, we characterized, for the first time, the Monoceros overdensity in several chemical abundance spaces. Our results confirm its similarity to stars found in the thin disk of the Galaxy and suggest an in situ formation. Furthermore, we demonstrate that the southern and northern regions of Monoceros exhibit indistinguishable chemical compositions.