The Distribution of Open Clusters in the Galaxy

Hektor Monteiro,Douglas A Barros,Wilton S Dias,Jacques R D Lépine

doi:10.3389/fspas.2021.656474

Hektor Monteiro, Douglas A Barros + Show 2 more

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https://doi.org/10.3389/fspas.2021.656474

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Abstract

In this work we explore the new catalog of galactic open clusters that became available recently, containing 1,750 clusters that have been re-analyzed using the Gaia DR2 catalog to determine the stellar memberships. We used the young open clusters as tracers of spiral arms and determined the spiral pattern rotation speed of the Galaxy and the corotation radius, the strongest Galactic resonance. The sample of open clusters used here is increased by dozens of objects with respect to our previous works. In addition, the distances and ages values are better determined, using improvements to isochrone fitting and including an updated extinction polynomial for the Gaia DR2 photometric band-passes, and the Galactic abundance gradient as a prior for metallicity. In addition to the better age determinations, the catalog contains better positions in the Galactic plane and better proper motions. This allow us to discuss not only the present space distribution of the clusters, but also the space distribution of the clusters's birthplaces, obtained by integration of the orbits for a time equal to their age. The value of the rotation velocity of the arms (28.5 ± 1.0 km s−1 kpc−1) implies that the corotation radius (Rc) is close to the solar Galactic orbit (Rc/R0 = 1.01±0.08), which is supported by other observational evidence discussed in this text. A simulation is presented, illustrating the motion of the clusters in the reference frame of corotation. We also present general statistics of the catalog of clusters, like spatial distribution, distribution relative to height from the Galactic plane, and distribution of ages and metallicity. An important feature of the space distribution, the corotation gap in the gas distribution and its consequences for the young clusters, is discussed.

Highlights

The open clusters are known to constitute one of the best classes of objects to investigate the Galactic structure and Stellar Dynamics, since they have relatively precise ages estimated from isochrone fits
The data obtained on velocities, distances and ages allow us to present the analyses of the distribution of the open clusters in the solar neighborhood, The Distribution of Open Clusters exploring the birthplaces and actual positions on the Galactic plane
The knowledge of the present day positions and the birthplaces of the open clusters, from the Galactic orbits integrated backward in time, allow us to revisit the value of spiral pattern rotation speed of the Galaxy ( p) and the Galactic corotation radius (Rc)

Summary

Introduction

The open clusters are known to constitute one of the best classes of objects to investigate the Galactic structure and Stellar Dynamics, since they have relatively precise ages estimated from isochrone fits. The data obtained on velocities, distances and ages allow us to present the analyses of the distribution of the open clusters in the solar neighborhood, The Distribution of Open Clusters exploring the birthplaces and actual positions on the Galactic plane. The present day position of the young open clusters shown in Figure 1 reveals the spiral structure of our Galaxy in the extended solar neighborhood. The knowledge of the present day positions and the birthplaces of the open clusters, from the Galactic orbits integrated backward in time, allow us to revisit the value of spiral pattern rotation speed of the Galaxy ( p) and the Galactic corotation radius (Rc). The star density is explained by the stellar orbits that are not perfectly circular, and come close to each other in some regions of the Galactic disk. The mathematical description of the grooves and of the orbits can be found in Junqueira et al (2013)

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