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

Janez Kos, Gayandhi de Silva, Sven Buder, Joss Bland-Hawthorn, Sanjib Sharma, Martin Asplund, Valentina D'Orazi, Ly Duong, Ken Freeman, Geraint F. Lewis, Jane Lin, Karin Lind, Sarah L. Martell, Katharine J. Schlesinger, Jeffrey D. Simpson, Daniel B. Zucker, Tomaž Zwitter, Timothy R. Bedding, Klemen Čotar, Jonathan HornerThomas Nordlander, Denis Stello, Yuan Sen Ting, Gregor Traven

Research output: Contribution to journalArticlepeer-review


Sparse open clusters can be found at high galactic latitudes where loosely populated clusters are more easily detected against the lower stellar background. Because most star formation takes place in the thin disc, the observed population of clusters far from the Galactic plane is hard to explain. We combined spectral parameters from the GALAH survey with the Gaia DR2 catalogue to study the dynamics and chemistry of five old sparse high-latitude clusters in more detail. We find that four of them (NGC 1252, NGC 6994, NGC 7772, NGC 7826) - originally classified in 1888-are not clusters but are instead chance projections on the sky. Member stars quoted in the literature for these four clusters are unrelated in our multidimensional physical parameter space; the quoted cluster properties in the literature are therefore meaningless. We confirm the existence of visually similar NGC 1901 for which we provide a probabilistic membership analysis. An overdensity in three spatial dimensions proves to be enough to reliably detect sparse clusters, but the whole six-dimensional space must be used to identify members with high confidence, as demonstrated in the case of NGC 1901.

Original languageEnglish
Pages (from-to)5242-5259
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 2018 Jan 1
Externally publishedYes

Subject classification (UKÄ)

  • Astronomy, Astrophysics and Cosmology

Free keywords

  • Catalogues
  • Parallaxes
  • Proper motions
  • Surveys
  • Techniques: radial velocities


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