A Gaia View on the Star Formation in the Monoceros OB1 and R1 Associations

Abstract

Stellar kinematics provides the key to understanding the star formation process. In this respect, we present a kinematic study of the Monoceros OB1 (Mon OB1) and R1 (Mon R1) associations using the recent Gaia data and radial velocities of stars derived from high-resolution spectroscopy and the literature. A total of 728 members are selected using the criteria based on the intrinsic properties of young stars, parallaxes, and proper motions. The spatial distribution and kinematic properties of members show that these associations have distinct substructures. In Mon OB1, we find one northern group and two southern groups. Mon R1 is composed of three small stellar groups that are spatially and kinematically distinct. Some stars are found in a halo around these two associations. We detect patterns of expansion for most stellar groups in the associations. In addition, two stellar groups in Mon OB1 show the signature of rotation, which provides an important constraint on cluster formation. The star formation history of Mon OB1 is slightly revised. Star formation first occurred in the southern region and subsequently in the northern region. Recent star-forming events ignited deeper into the southern region, while some stars are escaping from Mon OB1, forming a halo. Mon R1 might have formed at the same epoch as the formation of the northern group in Mon OB1. Given that star formation is taking place on different scales along a large arc-like structure, Mon OB1 and Mon R1 may be the results of hierarchical star formation.

The cosmic DANCe of Perseus

“…the core and halo of Gorgophone), which has also been observed in other star-forming regions (e.g. Kuhn et al 2022;Lim et al 2022) and is predicted by the hierarchical star formation scenario (Ward & Kruijssen 2018).…”

The Kinematics of the Young Stellar Population in the W5 Region of the Cassiopeia OB6 Association: Implication for the Formation Process of Stellar Associations

“…Our previous studies have shown that stellar groups constituting the substructure in associations are spatially and kinematically distinct (Lim et al 2019(Lim et al , 2020(Lim et al , 2021(Lim et al , 2022. This means that they are individually different physical systems.…”

“…Most OB associations are distributed along the Galactic plane (Wright 2020), and therefore a large number of field interlopers are observed together in the same field of view. The selection of members is a procedure of crucial importance to obtain reliable results as emphasized by our previous observational studies (e.g., Lim et al 2020Lim et al , 2021Lim et al , 2022. We selected members through two steps.…”

“…However, cluster expansion alone cannot explain the origin of substructures commonly found in stellar associations. Such substructures are composed of stellar groups (or subclusters; Kuhn et al 2014) that are kinematically distinct (Lim et al 2019(Lim et al , 2021(Lim et al , 2022. The formation of substructures can naturally be explained by star formation along filaments in almost all turbulent clouds (André 2015).…”

The Molecular Clouds in a Section of the Third Galactic Quadrant: Cloud Catalog

“…We searched for the 12 CO signal within [−200, 200] km s −1 and found it only in the range of [−20, 70] km s −1 . The data covered a total area of 250 deg 2 , which contains some interesting and well-known MCs, star clusters, and nebulae, such as Mon OB1 (Lim et al 2022), NGC 2264 (Herbig 1954), the Rosette Nebula (Schneider et al 1998;Di Francesco et al 2010), Maddalena (Maddalena & Thaddeus 1985), and Sh 2-287 (Sharpless 1959). Li et al (2018) found evidence for a cloud−cloud collision in the Rosette Molecular Cloud, and the abundance ratios of 13 CO to C 18 O in the cloud have a mean value of 13.7, which is 2.5 times larger than the solar system value (Wilson & Matteucci 1992).…”