Dynamical Origin for the Collinder 132–Gulliver 21 Stream: A Mixture of Three Comoving Populations with an Age Difference of 250 Myr

Abstract

We use Gaia DR3 data to study the Collinder 132–Gulliver 21 region via the machine-learning algorithm StarGO and find eight subgroups of stars (ASCC 32, Collinder 132 gp 1–6, Gulliver 21) located in close proximity. Three comoving populations were identified among these eight subgroups: (i) a coeval 25 Myr old moving group (Collinder 132), (ii) an intermediate-age (50–100 Myr) group, and (iii) the 275 Myr old dissolving cluster Gulliver 21. These three populations form parallel diagonal stripe-shape overdensities in the U–V distribution, which differ from open clusters and stellar groups in the solar neighborhood. We name this kinematic structure the Collinder 132–Gulliver 21 stream, as it extends over 270 pc in the 3D space. The oldest population, Gulliver 21, is spatially surrounded by the Collinder 132 moving group and the intermediate-age group. Stars in the Collinder 132–Gulliver 21 stream have an age difference up to 250 Myr. Metallicity information shows a variation of 0.3 dex between the youngest and oldest populations. The formation of the Collinder 132–Gulliver 21 stream involves both star formation and dynamical heating. The youngest population (Collinder 132 moving group) with homogeneous metallicity is probably formed through filamentary star formation. The intermediate-age and oldest populations were then scattered by the Galactic bar or spiral structure resonance to intercept Collinder 132's orbit. Without mutual interaction between each population, the three populations are flying by each other currently and will become three distinct groups again in ∼50 Myr.

The Present-day Mass Function of Star Clusters in the Solar Neighborhood

“…We analyze the PDMF of 93 star clusters using Gaia DR 3 data. The stellar membership of 92 of the clusters is taken from previous studies (Pang et al 2021a(Pang et al , 2021b(Pang et al , 2022c(Pang et al , 2022aLi et al 2021). These studies determined stellar membership using the machine-learning algorithm StarGo.…”

“…In this study, we investigate a total of 93 star clusters. The identification of member stars of 92 of the target star clusters was carried out in Pang et al (2021aPang et al ( , 2021bPang et al ( , 2022cPang et al ( , 2022a and Li et al (2021). These studies established stringent criteria, requiring member stars to have parallax and photometric measurements with uncertainties within a 10% threshold.…”

“…To construct the PDMF of the target clusters, it is necessary to first compute the masses of individual member stars. Previous studies (Pang et al 2021a(Pang et al , 2021b(Pang et al , 2022c(Pang et al , 2022aLi et al 2021) have obtained the best-fitting isochrones for the 92 star clusters by assessing the locations of member stars in the color-magnitude diagram (CMD). The same procedure is carried out for NGC 6991 in this work (Figure A1 in the Appendix).…”

“…Note. The ages of the clusters are obtained from Pang et al (2021aPang et al ( , 2021bPang et al ( , 2022cPang et al ( , 2022a and are derived from PARSEC isochrone fitting. The age of NGC 6991 is obtained in this work (see Appendix).…”

“…The older and more enriched clusters potentially might not have originated in the solar neighborhood; rather, they might have migrated from the inner disk to their current local positions through radial migration processes (Minchev et al 2009). Recently, Pang et al (2022a) discovered the Collinder 132-Gulliver 21 Stream (270 pc long) in the solar neighborhood, with stellar populations showing an age difference of up to 250 Myr. The oldest generation in the stream is approximately 0.3 dex (based on Gaia DR3 data) more metal-rich than the youngest generation.…”