Hunting for open clusters in Gaia EDR3: 664 new open clusters found with OCfinder

Abstract

Context. The improvements in the precision of the published data in Gaia EDR3 with respect to Gaia DR2, particularly for parallaxes and proper motions, offer the opportunity to increase the number of known open clusters in the Milky Way by detecting farther and fainter objects that have so far go unnoticed. Aims. Our aim is to keep completing the open cluster census in the Milky Way with the detection of new stellar groups in the Galactic disc. We use Gaia EDR3 up to magnitude G = 18 mag, increasing in one unit the magnitude limit and therefore the search volume explored in our previous studies. Methods. We use the OCfinder method to search for new open clusters in Gaia EDR3 using a Big Data environment. As a first step, OCfinder identifies stellar statistical overdensities in the five dimensional astrometric space (position, parallax and proper motions) using the DBSCAN clustering algorithm. Then, these overdensities are classified into random statistical overdensities or real physical open clusters using a deep artificial neural network trained on well-characterised G, GBP − GRP colour-magnitude diagrams. Results. We report the discovery of 664 new open clusters within the Galactic disc, most of them located beyond 1 kpc from the Sun. From the estimation of ages, distances and line-of-sight extinctions of these open clusters, we see that young clusters align following the Galactic spiral arms while older ones are dispersed in the Galactic disc. Furthermore, we find that most open clusters are located at low Galactic altitudes with the exception of a few groups older than 1 Gyr. Conclusions. We show the success of the OCfinder method leading to the discovery of a total of 1 310 open clusters (joining the discoveries here with the previous ones based on Gaia DR2), which represents almost 50% of the known population. Our ability to perform Big Data searches on a large volume of the Galactic disc, together with the higher precision in Gaia EDR3, enable us to keep completing the census with the discovery of new open clusters.