An analysis of the most distant cataloged open clusters

Abstract

Context. Several studies have been presented in the last few years applying some kind of automatic processing of data to estimate the fundamental parameters of open clusters. These parameters are then employed in larger scale analyses, for example the structure of the Galaxy’s spiral arms. The distance is one of the most straightforward parameters to estimate, yet enormous differences can still be found among published data. This is particularly true for open clusters located more than a few kiloparsecs away. Aims. We cross-matched several published catalogs and selected the 25 most distant open clusters (> 9000 pc). We then performed a detailed analysis of their fundamental parameters, with emphasis on their distances, to determine the agreement between the catalogs and our estimates. Methods. Photometric and astrometric data from the Gaia EDR3 survey was employed. The data were processed with our own membership analysis code, pyUPMASK, and our package for the automatic estimation of fundamental cluster parameters, ASteCA. Results. We find differences in the estimated distances of up to several kiloparsecs between our results and those cataloged, even for the catalogs that show the best matches with ASteCA values. Large differences are also found for the age estimates. As a by-product of the analysis we find that vd Bergh-Hagen 176 could be the open cluster with the largest heliocentric distance cataloged to date. Conclusions. Caution is thus strongly recommended when using cataloged parameters of open clusters to infer large-scale properties of the Galaxy, particularly for those located more than a few kiloparsecs away.