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Sparse open clusters can be found at high galactic latitudes where looselypopulated clusters are more easily detected against the lower stellarbackground. Because most star formation takes place in the thin disk, theobserved population of clusters far from the Galactic plane is hard to explain.We combined spectral parameters from the GALAH survey with the Gaia DR2catalogue to study the dynamics and chemistry of five old sparse high-latitudeclusters in more detail. We find that four of them (NGC 1252, NGC 6994, NGC7772, NGC 7826) - originally classified in 1888 - are not clusters but areinstead chance projections on the sky. Member stars quoted in the literaturefor these four clusters are unrelated in our multi-dimensional physicalparameter space; the published cluster properties are therefore irrelevant. Weconfirm the existence of morphologically similar NGC 1901 for which we providea probabilistic membership analysis. An overdensity in three spatial dimensionsproves to be enough to reliably detect sparse clusters, but the whole6-dimensional space must be used to identify members with high confidence, asdemonstrated in the case of NGC 1901.

The GALAH Survey and Gaia DR2: (Non)existence of five sparse high-latitude open clusters