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Description
Many of the open clusters listed in modern catalogues were first reported by visual astronomers as apparent over-densities of bright stars. As observational techniques and analysis methods improved, some of them have been shown to be chance alignments of stars and are not true clusters. Recent publications making use of Gaia DR2 data provided membership list for over a thousand clusters, but many nearby objects listed in the literature have so far evaded detection. We update the Gaia DR2 cluster census by performing membership determinations for known clusters that had been missed by previous studies, and for recently discovered clusters. We investigate a subset of non-detected clusters that according to their literature parameters should be easily visible in the Gaia . Confirming or disproving the existence of old, inner-disc, high-altitude clusters is especially important as their survival or disruption is linked to the dynamical processes that drive the evolution of the Milky Way. We employ the Gaia DR2 catalogue and a membership assignment procedure, as well as visual inspection of spatial, proper motion, and parallax distributions. We use membership lists provided by other authors when they are available. We derive membership lists for 150 objects, including 10 that were known prior to Gaia . We compile a final list of members for 1481 clusters. Among the objects that we are still unable to identify with Gaia data, we argue that many (mostly putative old, relatively nearby, high-altitude objects) are not true clusters. At present, the only confirmed cluster located further than 500pc away from the Galactic plane within the Solar circle is NGC 6791. It is likely that the objects discussed in this study only represent a fraction of the non-physical groupings erroneously listed in the catalogues as genuine open clusters, and that those lists need further cleaning.
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