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

Kos, Janez and de Silva, Gayandhi and Buder, Sven and Bland-Hawthorn, Joss and Sharma, Sanjib and Asplund, Martin and D'Orazi, Valentina and Duong, Ly and Freeman, Ken and Lewis, Geraint F. and Lin, Jane and Lind, Karin and Martell, Sarah L. and Schlesinger, Katharine J. and Simpson, Jeffrey D. and Zucker, Daniel B. and Zwitter, Tomaz and Bedding, Timothy R. and Cotar, Klemen and Horner, Jonathan and Nordlander, Thomas and Stello, Denis and Ting, Yuan-Sen and Traven, Gregor (2018) The GALAH survey and Gaia DR2: (non-)existence of five sparse high-latitude open clusters. Monthly Notices of the Royal Astronomical Society, 480 (4). pp. 5242-5259. ISSN 0035-8711

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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.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Published version deposited in accordance with the copyright policy of the publisher.
Faculty/School / Institute/Centre: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 15 Feb 2019 01:19
Last Modified: 17 Feb 2019 23:13
Uncontrolled Keywords: radial velocities; catalogues; surveys; parallaxes; proper motions; astrophysics; astrophysics of galaxies; solar and stellar astrophysics
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Identification Number or DOI: 10.1093/mnras/sty2171

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