An analysis of the most distant catalogued open clusters -- Re-assessing fundamental parameters with Gaia EDR3 and $\texttt{ASteCA}$

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 later on employed in larger scale analyses, for example the structure of the Galaxy's spiral arms. The distance is one of the more 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 kpc away. Aims. We cross-matched several published catalogues and selected the twenty-five 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 catalogues and our estimates. Methods. Photometric and astrometric data from the Gaia EDR3 survey was employed. The data was processed with our own membership analysis code (pyUPMASK), and our package for automatic fundamental cluster's parameters estimation (ASteCA). Results. We find differences in the estimated distances of up to several kpc between our results and those catalogued, even for the catalogues 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 catalogued to date. Conclusions. Caution is thus strongly recommended when using catalogued parameters of open clusters to infer large-scale properties of the Galaxy, particularly for those located more than a few kpc away.

Assessing the physical reality of Milky Way open cluster candidates

“…Thus, under the presence of 4 http://stev.oapd.inaf.it/cgi-bin/cmd relatively tight Main Sequences and small photometric errors, relatively large parameter uncertainties could suggest that different collections of isochrones are needed to map different parts of the observed Main Sequence. When dealing with true open clusters, typical intrinsic dispersions of fundamental parameters as estimated by ASteCA (Perren et al 2022, and references therein) are σlog(t /yr) ≈ 0.12, and σ[Fe/H] ≈ 0.21 dex. Table 2 shows that age uncertainties are notably large in most of the cases, suggesting that a range of ages represent the fitted Main Sequences.…”