582 new open clusters in the Galactic disc of our Milky Way

Alfred Castro-Ginard et al. have found 582 new open clusters, using the data from the second release of the Gaia mission.

Open clusters are groups of gravitationally bound stars, that were formed in the same event – so they have the same chemical composition and age – and share a common position and proper motion. Those open clusters are fundamental objects in galaxies, and key for the understanding of the structure and evolution of the Milky Way. While young open clusters allow researchers to trace the star forming regions and to understand the star forming mechanisms, intermediate and old open clusters inform about the stellar processes and evolution of the Galactic disc.

The study and search for open clusters has been boosted by the second release of the Gaia mission data (DR2), which contained information about precise astrometric measurements of more than 1.3 billion stars. Since its publication, several studies have been finding new open clusters, but they were computationally limited to analyzing particular regions of the galactic disc,or dividing the search areas into smaller ones with a limited number of stars.

The ICCUB team, led by researcher Alfred Castro-Ginard, has been developing a new methodology, which has been published in two previous studies in 2018 and 2019. In 2018, they presented the method and applied it to a small data set. Later, they used it in a certain region of the galaxy, so they could test how the method worked with the Gaia data and in different parts of the galaxy. Castro-Ginard explains, “Before Gaia, we didn’t have a homogenous methodology to study and detect those objects, because we didn’t have such a big and precise data catalogue. That’s why we chose a machine-learning based method, which automatizes and allows the study of a big volume of data.”

They used the machine-learning based methodology to search for overdensities across the whole Galactic disc, using an unsupervised clustering algorithm -named DBSCAN – which pointed to several overdensities as plausible candidates for open clusters. Then, they confirmed those candidates as open clusters through a deep learning artificial neural network, which recognized isochrone patterns in the colour and magnitude.

“Before this methodology, they were around 1200 open clusters confirmed by Gaia”, says Castro-Ginard. ”Using Gaia’s data and our methodology, we have found more than 650 new clusters – 23 detected in 2018, 53 in 2019 and now, 528 more. This has improved and increased the catalogue, which now contains more than 2000 open clusters.”

You can read the whole article at Astronomy & Astrophysics 635, A45 (2020). https://arxiv.org/abs/2001.07122

See related articles:

Castro-Ginard et al., 2018. “A new method for unveiling open clusters in Gaia. New nearby open clusters confirmed by DR2”, Astronomy & Astrophysics, 618, id.A59. https://arxiv.org/abs/1805.03045

Castro-Ginard et al., 2019. “Hunting for open clusters in Gaia DR2: the Galactic anticentre”, Astronomy& Astrophysics, 627, id.A35. https://arxiv.org/abs/1905.06161