A catalog of new blue stragglers in open clusters with Gaia DR3

TL;DR

This study leverages Gaia DR3 to systematically identify blue straggler and related straggler stars in open clusters. By visually inspecting CMDs, refining memberships with pyUPMASK, and performing PARSEC-based isochrone fitting, it classifies 272 new stragglers (153 BSSs, 98 pBSSs, 21 YSSs) across 99 clusters, enhancing the known BSS census in the Milky Way by 11.2% and the cluster-coverage by 22.2%. The analysis reveals that older open clusters host more BSs, with BS frequency and density increasing with age, and shows a central concentration in radial distributions alongside a higher fraction of fast-rotating BSs in open clusters compared to globular clusters. These results imply multiple formation channels, with binary evolution playing a prominent role in open clusters and dynamical processes shaping distributions and rotation. The accompanying catalogs enable detailed future studies of BSS formation and cluster dynamical evolution in Gaia-era datasets.

Abstract

The high-precision {\it Gaia} data release 3 (DR3) enables the discovery of numerous open clusters in the Milky Way, providing an excellent opportunity to search for blue straggler stars in open clusters and investigate their formation and evolution in these environments. Using the member stars from literature open cluster catalogs, we visually inspected the color-magnitude diagram (CMD) of each cluster and selected cluster candidates that potentially host blue stragglers. We then reassessed cluster memberships using the {\tt pyUPMASK} algorithm with {\it Gaia} DR3 and performed isochrone fitting to derive physical parameters for each cluster, including age, distance modulus, mean reddening, and metallicity. Finally, we empirically identified straggler stars based on their positions relative to the best-fitting isochrone, zero-age main sequence (ZAMS), and equal-mass binary sequence on the CMD. In total, we identified 272 new straggler stars in 99 open clusters, comprising 153 blue stragglers, 98 probable blue stragglers, and 21 yellow stragglers. Compared to the reported blue straggler catalogs based on earlier {\it Gaia} data, our results increase the number of open clusters with stragglers in the Milky Way by 22.2\%, and the total number of blue stragglers by 11.2\%.

Figures (15)

• Figure 1: Position (a), proper motion (b), parallax distributions (c), and color-magnitude diagram (d) of one example cluster OC_0416. The point color represents the newly calculated membership probabilities of stars with a colorbar on the right. The subpanel inside the panel (d) is the histogram of membership probability for all stars, and the selected members in panel (d) have probabilities greater than 0.7.
• Figure 2: The color-magnitude diagrams of two example open clusters OC_0416 and FSR_1361. The color-coded symbols are the members with membership probabilities greater than 0.7. The solid and dashed black lines represent the best-fitting isochrone and zero age main sequence (ZAMS), and the grey dashed line refers to the equal-mass binary sequence. The best-fitting age parameters are shown in the panel. The triangles, squares, and pentagon are the blue straggler stars (BSSs), probable blue straggler stars (pBSSs), and yellow straggler star (YSS) identified in our work, respectively.
• Figure 3: Blue straggler number ($N_{\rm BS}$, BSS + pBSS), frequency ($N_{\rm BS} / N_{\rm TOMS}$), and density ($N_{\rm BS} / (\pi \cdot R_{\rm{Jac}}^{2})$) as a function of cluster algorithm age. The $N_{\rm TOMS}$ is the number of main sequence stars up to one magnitude below the turn-off point, and $R_{\rm{Jac}}$ is the Jacobi radius of each cluster from 2023AA...673A.114H. The grey dots (RJL) refer to the sample from 2021AA...650A..67R (BSS), 2021MNRAS.507.1699J (BSS + pBSS), and 2023AA...672A..81L (BSS + pBSS). The blue dots represent the BSS + pBSS sample in this work. The cluster members used for calculating the frequencies of the RJL sample (gray dots) are from 2023AA...673A.114H.
• Figure 4: The histograms of cluster distance (left panel), BS radial distance (middle panel), and normalized BS radial distance ($R_{\rm{BS}} / R_{\rm{Jac}}$, right panel) in OCs from 2021AA...650A..67R, 2021MNRAS.507.1699J, and 2023AA...672A..81L (RJL, grey solid line) and this work (blue dashed line). The cluster distances (Dist) of RJL sample and our sample are the 'dist50' from 2023AA...673A.114H and our Bayesian distances, respectively. The BS radial distance ($R_{\rm{BS}}$) is calculated with the formula of $R_{\rm{BS}} = \rm{Dist} \times \tan{(R_{\rm{deg}})}$, where $R_{\rm{deg}}$ is the angular size from the each BS to the cluster center. $R_{\rm{Jac}}$ is the cluster Jacobi radius from 2023AA...673A.114H.
• Figure 5: Left panel: projected rotational velocities for BSs as a function of absolute G magnitude. Right panel: histograms of projected rotational velocities for BSs. The grey points represent the BSs in OCs of 2021AA...650A..67R, 2021MNRAS.507.1699J, and 2023AA...672A..81L (RJL), blue points are the BSs in OCs for this work, and the blue histogram represents the samples of RJL and our work. The magenta points and histogram refer to the BSs in 8 GCs from 2023NatCo..14.2584F. The blue and magenta lines refer to their corresponding kernel density distributions. The $v\sin i$ for BSs in OCs are from Gaia DR3.