Sixteen overlooked open clusters in the fourth Galactic quadrant

Abstract

Aims. This paper has two main objectives: (1) To determine the intrinsic properties of sixteen faint and mostly unstudied open clusters in the poorly known sector of the Galaxy at 270 • − 300 • , to probe the Milky Way structure in future investigations. (2) To address previously reported systematics in Gaia DR2 parallaxes by comparing the cluster distances derived from photometry with those derived from parallaxes. Methods. Deep UBVI photometry of 16 open clusters was carried out. Observations were reduced and analyzed in an automatic way using the ASteCA package to get individual distances, reddening, masses, ages and metallicities. Photometric distances were compared to those obtained from a Bayesian analysis of Gaia DR2 parallaxes. Results. Ten out of the sixteen clusters are true or highly probable open clusters. Two of them are quite young and follow the trace of the Carina Arm and the already detected warp. The rest of the clusters are placed in the interarm zone between the Perseus and Carina Arms as expected for older objects. We found that the cluster van den Berg-Hagen 85 is 7.5 × 10 9 yrs old becoming then one of the oldest open cluster detected in our Galaxy so far. The relationship of these ten clusters with the Galaxy structure in the solar neighborhood is discussed. The comparison of distances from photometry and parallaxes data, in turn, reveals a variable level of disagreement. Conclusions. Various zero point corrections for Gaia DR2 parallax data recently reported were considered for a comparison between photometric and parallax based distances. The results tend to improve with some of these corrections. Photometric distance analysis suggest an average correction of ∼+0.026 mas (to be added to the parallaxes). The correction may have a more intricate distance dependency, but addressing that level of detail will require a larger cluster sample.

An investigation of open cluster Melotte 72 using Gaia DR2

“…ASteCA employs a Bayesian field star decontamination algorithm to compare the photometric, parallax, and proper motion distribution of the stars in the cluster region with a similar distribution in the surrounding field region (Perren et al 2015, 2020). We used the astrometric data of Gaia DR2 to obtain MP, see Figure 7.…”

“…In this paper, one of our main aims is to determine the mass function of Melotte 72 and re‐estimated its main astrophysical properties using the database of GAIA mission. We determined the membership probability (MP) of the cluster stars using the Automated Stellar Cluster Analysis (ASteCA) code (Perren et al 2015, 2020).…”

Open clusters with proper motions fully separatedfrom the field stars using Gaia DR2

“…Estimating distances to OCs as well as studying their distribution is needed to reconstruct the overall shape of the Galaxy. Perren et al (2020) use galactic open clusters as probes for the formation and evolution of the Milky Way disc.…”

Kalkayotl: A cluster distance inference code

“…In addition, the online resources 1 recommended by Luri et al (2018) provide detailed steps for the inference of cluster distance and size. Recently, Perren et al (2020) used the insight provided by these online resources to infer cluster distances based on a Gaussian prior. These authors marginalize the individual distances as well as the cluster intrinsic dispersion.…”

“…The previous studies can be classified into those that infer population parameters of either clusters and associations by marginalizing individual stellar distances (e.g., Wright & Mamajek 2018;Perren et al 2020, and the online resources mentioned above) and those that infer individual stellar distances but do not infer the population parameters (e.g., Bailer-Jones et al 2018;Anders et al 2019). To the best of our knowledge, the simultaneous inference of population parameters and individual distances has not been addressed in the literature.…”