2022ApJ...933..151Z

We investigated the observational properties of Triangulum-Andromeda (TriAnd), Monoceros Ring (MRi), and Anti-Center Stream (ACS) in the anticenter region using K giants, M giants, and RGB stars from LAMOST and SDSS survey. The Friends of Friends algorithm was applied to select member stars of these structures. We found a new spur of TriAnd at l ∼ 133° based on member stars selected in this work and compiled from the literature. The distributions of radial velocity and proper motion of its member stars indicate that TriAnd is gradually moving away from the Sun. The comparisons of [Fe/H] and [α/Fe] between TriAnd and thick-disk/halo stars reveal that TriAnd is likely to originate from the thick disk. MRi and ACS are adjacent in space with a boundary around latitude 30°, and there is no significant difference between the two structures in velocity, proper motions, and orbits. We suggested that MRi and ACS probably have a common origin. We made projections of the four structures in three-dimensional space for the exploration of the movements between the Sagittarius (Sgr) stellar stream and MRi, and found that a new spur was formed by the Sgr stream members in the velocity distribution as it passed through the MRi region.