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

TL;DR

This study analyzes blue straggler stars in three open clusters using Gaia DR2 data, revealing their distribution and binary status to understand cluster dynamics and stellar evolution.

Contribution

First comprehensive Gaia DR2-based analysis of blue straggler populations in multiple open clusters, including their spatial distribution and binary characteristics.

Findings

Blue stragglers are not more centrally concentrated than red giants.

The radial distribution of BSS in Trumpler 5 is flat.

Some BSS are identified as potential binary systems.

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.