Open Clusters In The Milky Way And Their Revealed Evolution Of The Spiral Arm Structure

Based on the high-precision astrometric and photometric data from the Gaia satellite,we conducted systematic and innovative studies on open clusters(OCs)in the Milky Way,including the detection of OCs,the formation of OCs,the rotation of the nearby OCs,and the evolution of the Galactic spiral arm structure revealed by OCs.The unprecedented Gaia data sets offer an excellent opportunity to hunt for more OCs in the Milky Way.Based on previous studies,we developed a sample-based cluster search method with high spatial resolution.In addition to re-detecting more than 2000 known OCs or OC candidates,we identified 758 new OC candidates,whose detailed astrometric parameters,ages,and radial velocities have been determined.The newly discovered OC candidates significantly expand the catalog of Galactic OCs and open new horizons for relevant astrophysical studies.Young OCs containing classical Cepheids can help to optimize the zero point of the period-luminosity relation of Cepheids,and thereby to constrain the cosmic distance scale.However,the number of these objects found in the Milky Way is only 33,which is still quite small.Our comprehensive analysis using Gaia data has identified a total of 45 OCs housing 50 classical Cepheids,making it the largest sample of OCs harboring classical Cepheids.This catalog can help to establish the cosmic distance scale and serve as essential indicators to empower firmer constraints on Hubble’s law in cosmology.OCs are rare survivors of embedded clusters that gestate in molecular clouds,and the initial conditions for their formation are still poorly understood.Using the data from the Gaia satellite,we developed a dynamical approach to estimate the mass of the progenitor clumps that gave birth to OCs,and found their statistical characteristics are almost consistent with those observed in the Milky Way.Furthermore,observations indicate that the young OCs contain many massive O-type stars,as expected from the estimated progenitor clumps.We proposed that the destructive stellar feedback from O-type stars may lead to the disintegration of numerous or most embedded clusters,while only those with sufficient density can survive as OCs.Unveiling the nature of the rotation of OCs is crucial to comprehending their formation,evolution and eventual dissipation.However,our knowledge of their internal kinematics characteristics,such as rotation,is still quite limited.We have developed an original set of methods to study this puzzle.Using the high-precision data provided by Gaia,for the first time,we analyzed the three-dimensional rotation of the OCs near the Sun,including the Praesepe,Pleiades,Hyades,and a Persei cluster.The rotations of the Praesepe,Pleiades,and Hyades cluster were successfully detected,and a weaker rotation signal was detected in the a Persei cluster.Additionally,we analyzed the kinematics of the member stars in the Praesepe and Pleiades cluster,and found that the rotation of member stars within the tidal radius of clusters probably follows Newton’s classical theorems.The structure and evolution of the spiral arms of our Milky Way have been basic yet long-standing questions in astronomy.In particular,the lifetime of spiral arms remians a puzzle and has not been well constrained from observations.For the first time,we studied the evolution of the spiral arms of the Galaxy using a large catalogue of OCs based on the Gaia data.We analyzed the distribution,kinematics,evolution of the scale height,and regression characteristics of OCs,and found an evidence that the nearby spiral arms are compatible with a long-lived spiral pattern that may have remained stable for the past 80 million years.The evolutionary characteristics of the nearby spiral arms suggest that the dynamic spiral mechanism might not be prevalent for our Galaxy.Instead,the density wave theory is more consistent with the observational properties of OCs.