The blue straggler population of the open clusters Trumpler 5, Trumpler 20, and NGC 2477

Abstract

We present a study, based on Gaia DR2, of the population of blue straggler stars (BSS) in the open clusters Trumpler 5, Trumpler 20, and NGC 2477. All candidates were selected according to their position in the color-magnitude diagram, to their proper motion components, and to their parallax. We also looked for yellow stragglers, i.e., possible evolved blue stragglers. We found that Trumpler 5 hosts a large BSS population, which allowed us to analyze their radial distribution as a probe of the cluster's dynamical status. The BSS distribution was compared with that of red giant branch stars (RGB) to evaluate mass segregation. Our results indicate that blue straggler stars are not more centrally concentrated than RGB stars in any of the clusters. The radial distribution of BSS in Trumpler 5 is flat. Additionally, using a multi-epoch radial velocity survey conducted with the high-resolution spectrograph FLAMES/GIRAFFE at VLT, we measured the radial velocities of a sample of stragglers, for the sake of comparison with the mean radial velocity and the velocity dispersion of the clusters. Based on the radial velocity variations for different epochs, we roughly classified these stars as possible close-or long-period binaries.

20 pages, 5 figures, accepted for publication in AJ

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• Search for lithium-rich giants in 32 open clusters with high-resolution spectroscopy
• Determination of dynamical ages of open clusters through the A${}^{+}$ parameter -- I
• A photometric and astrometric study of the open clusters NGC 1664 and NGC 6939
• Asteroseismic age constraints on the open cluster NGC 2477 using oscillating stars identified with TESS FFI
• First direct detection of an RR Lyrae star conclusively associated with an intermediate-age cluster