Abstract
This paper investigates reliable memberships and fundamental astrophysical properties of the old (∼8 Gyr) open cluster NGC 6791 using the astrometric and photometric data of the Gaia data release 2 (\(\mathit{Gaia}\)-DR2). We identify 2536 likely cluster members (≥0.6) in a five-dimensional (5D) parameter space using a Gaussian mixture model (GMM) clustering method. Based on these reliable 5D cluster members, we determine the core and tidal radii of the cluster to be \(R_{c}=3.69^{\prime } \pm 0.23^{\prime }\) and \(R_{t}= 16.96^{\prime } \pm 2.29^{\prime }\), respectively. We find evidence for the presence of mass segregation in the cluster. Among the likely cluster members, we identify six blue subdwarfs, 43 blue stragglers, and 27 red clump giants. We find that 34 blue stragglers (∼79%) lie within the core radius (\({<}3.69^{\prime }\)) of the cluster, indicating that these stars may be formed by star collisions or by the evolution of primordial binaries within the dense core. The 27 red clump giants are used to accurately estimate the distance of the cluster. We determine a distance of 4118 ± 23 pc for the cluster using a Monte-Carlo simulation method. We confirm the presence of a significant zero-point offset (\({\sim}\, {-}0.055 \pm 0.004\) mas) in the \(\mathit{Gaia}\) parallaxes of the cluster members. Using the same simulation method, the mean proper motion and radial velocity of the cluster are found to be (\(\langle \mu _{\alpha }\cos \delta \rangle , \langle \mu _{\delta }\rangle )= (-0.434\pm 0.008,-2.266\pm 0.010)\) mas/yr and \(\langle V_{r} \rangle =-46.7\pm 0.6\) km/s, respectively.
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Acknowledgements
We are grateful to the anonymous referee for his/her detailed and very helpful comments that have helped improve this paper substantially. This research was supported by the National Natural Science Foundation of China (NSFC, Grant No. 11403004) and the Foundation of Changzhou University (Grant No. GJY18020008). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France.
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Gao, X. 5D memberships and fundamental properties of the old open cluster NGC 6791 based on \(\mathit{Gaia}\)-DR2. Astrophys Space Sci 365, 24 (2020). https://doi.org/10.1007/s10509-020-3738-2
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DOI: https://doi.org/10.1007/s10509-020-3738-2