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arxiv: 2605.05313 · v1 · submitted 2026-05-06 · 🌌 astro-ph.SR · astro-ph.GA

Recognition: unknown

Stellar rotation and binaries in open clusters with Gaia DR3

Aleksandra Avdeeva, Alessio Turchi, Deimer Alvarez Garay, Elena Pancino, Elisabetta Reggiani, Ellen I. Leitinger, Laurenz F. Steinbauer, Maite Echeveste, Monica Rainer, Nicoletta Sanna, Paola M. Marrese, Sara Saracino, Sebastian Kamann, Sharmila Rani, Silvia Marinoni, Sneha Nedhath, Vikrant V. Jadhav

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Pith reviewed 2026-05-08 16:14 UTC · model grok-4.3

classification 🌌 astro-ph.SR astro-ph.GA
keywords open clustersstellar rotationblue stragglersextended main sequence turnoffbinary starsGaia DR3Milky Way clustersstellar evolution
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The pith

Most clusters more massive than 1000 solar masses display an extended main sequence turnoff.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper assembles rotational data from Gaia DR3 for more than 44,000 stars across thousands of open clusters. It studies how rotation behaves in special groups like blue stragglers and extended main sequence turnoff stars by manually picking them out on color-magnitude diagrams. The work shows that extended turnoffs are common in clusters heavier than 10^3 solar masses, gives a new formula linking blue straggler counts to cluster mass and age, and finds similar binary star percentages in the main sequence and equal-mass binary sequence. Readers would care because rotation and binaries drive how stars change over time, and clusters offer clean laboratories to watch these processes at known ages. The study provides a broad foundation for understanding stellar interactions on a large scale.

Core claim

The authors conduct the first large-scale statistical exploration of stellar rotation in open clusters by combining Gaia DR3 rotational broadening and periods with literature membership lists. They manually select exotic stellar populations from the color-magnitude diagrams of individual clusters and discover that most clusters more massive than 10^3 M_⊙ display an eMSTO. They present a new parametrization of the number of blue stragglers as a function of cluster mass and age and find that the percentage of binary stars in the equal-mass binary sequence and in the main sequence are similar.

What carries the argument

Manual selection of exotic populations from color-magnitude diagrams of open clusters combined with Gaia DR3 rotation data to characterize populations like blue stragglers and extended main sequence turnoffs.

Load-bearing premise

Literature lists of almost a million cluster member stars are accurate and complete, and manual selection of exotic populations from color-magnitude diagrams introduces no significant subjectivity or contamination biases.

What would settle it

An independent photometric survey of a large sample of massive open clusters that identifies extended main sequence turnoffs in significantly fewer than most of them would challenge the reported discovery.

Figures

Figures reproduced from arXiv: 2605.05313 by Aleksandra Avdeeva, Alessio Turchi, Deimer Alvarez Garay, Elena Pancino, Elisabetta Reggiani, Ellen I. Leitinger, Laurenz F. Steinbauer, Maite Echeveste, Monica Rainer, Nicoletta Sanna, Paola M. Marrese, Sara Saracino, Sebastian Kamann, Sharmila Rani, Silvia Marinoni, Sneha Nedhath, Vikrant V. Jadhav.

Figure 1
Figure 1. Figure 1: The studied clusters in Galactic cartesian coordinates. All clus￾ters are plotted in grey in the background. Clusters are colored based on the number of stars with rotation information. The color scale saturates at about 400 for clarity, but several clusters have up to a few thousands of members with rotation information. The spiral arms of the Milky Way, as modelled by Castro-Ginard et al. (2021) and Reid… view at source ↗
Figure 2
Figure 2. Figure 2: Comparison of the Gaia DR3 vbroad (top panels) and vsini (bottom panels) estimates with those of five spectroscopic surveys. The one-to-one agreement is reported in each panel as a solid orange line, while a linear fit to the data is reported as a dashed line. Annotated in each panel there are: the median difference (∆), the median absolute deviation (MAD, σ), the number of stars (N), the angular coefficie… view at source ↗
Figure 3
Figure 3. Figure 3: Relation between prot and vbroad/vsini for the 65 dwarf stars which have both measurements. The region where vbroad starts to be overestimated is shaded in light blue, the filtering at 5 km s−1 is represented by a red dashed line, and the expected relationship for a 1 R⊙ star with sin i = 1 is plotted in orange. The typical (median) error￾bar of the 65 stars is plotted in the upper right corner. Stars are … view at source ↗
Figure 5
Figure 5. Figure 5: Similar to view at source ↗
Figure 4
Figure 4. Figure 4: Distribution of vbroad of dwarf samples analyzed in Sect. 3. In each panel, the generalised histograms of the MS and RGB sam￾ples are reported as a grey and a red dashed line, respectively. Lighter shaded histograms include also less certain sample members. Darker histograms show only the best members (sample sizes in parenthesis). The grey shaded area (vbroad < 20 km s−1 ) in each panel represents the reg… view at source ↗
Figure 6
Figure 6. Figure 6: Comparison of the spread in vbroad between normal MS stars in clusters showing no sign of an eMSTO (grey points) and stars in the eMSTO region in clusters with a confirmed eMSTO (points colored by age), as a function of Teff of the stars (left panel), cluster age (middle panel), and cluster mass (right panel). Binary stars in the eMSTO sample are plotted as green stars. vbroad and prot, respectively. Unres… view at source ↗
Figure 7
Figure 7. Figure 7: The lower MS of NGC 2516. Rotation periods from Binks et al. (2022, grey points) and our work (colored points) are compared to the Praesepe period-age relation by Angus et al. (2019, grey lines). The position of confirmed binaries in our catalogue is marked by crosses. The activity index, Amax, is described in details in App. B.3. that above ≃100 Myr, the eMSTO stars vbroad spread seems to globally decreas… view at source ↗
Figure 9
Figure 9. Figure 9 view at source ↗
Figure 10
Figure 10. Figure 10: Top panel. The RGB (red points) and SGB (yellow points) sam￾ples are compared with the sample of field giants by Carlberg et al. (2011) in the Teff vbroad plane. Bottom panel. Same as the top panel, but for the RSS (dark red points) and SSG (orange points) candidates. Here we also plot the Gaia measurements for the sample of field SSG and RSS (thistle points) by Leiner et al. (2022). In both panels, the c… view at source ↗
Figure 11
Figure 11. Figure 11: Similar to view at source ↗
read the original abstract

Stellar rotation is a fundamental ingredient in shaping the evolution of stars and it can also be used to trace past stellar interactions. Yet, systematic studies of stellar rotation in large samples of stars belonging to different populations have only recently been made possible, thanks to spectroscopic surveys. We profit from the catalogue of rotational broadening and rotation periods released with Gaia DR3. We focus on open clusters to study the rotational behaviour of several interesting populations including, among others, blue stragglers and extended main sequence turnoffs (eMSTO). We use literature lists of almost a million member stars in several thousand open clusters in the Milky Way. We collect properties of stars and clusters from large surveys, including Gaia, and from various literature sources. We include a comprehensive collection of known variables and binary stars from various databases. We manually select (exotic) stellar populations from the color-magnitude diagrams of individual clusters and study their rotational properties. Our catalogue contains more than 44 000 rotationally characterised stars, almost 57 000 variables (excluding binaries) and more than 22 000 binary stars. We find several interesting results, including a few hundred new blue stragglers, several fast rotating red giants, and we increase the number of clusters with an eMSTO to 96. We discover that most clusters more massive than $10^3$ $M_{\odot}$ display an eMSTO. We present a new parametrization of the number of blue stragglers as a function of cluster mass and age. We find that the percentage of binary stars in the equal-mass binary sequence and in the main sequence are similar. We present the first large-scale statistical exploration of stellar rotation in open clusters, which already yielded new interesting results and which can be used as the basis for several detailed follow-up studies.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 2 minor

Summary. The paper compiles a catalog of >44,000 rotationally characterized stars, ~57,000 variables, and >22,000 binaries in open clusters using Gaia DR3 rotational broadening/periods combined with literature membership lists of nearly one million stars. It manually identifies exotic populations (blue stragglers, eMSTO) from individual cluster CMDs, reports increasing the number of eMSTO clusters to 96, finds that most clusters above 10^3 M_⊙ show an eMSTO, presents a new parametrization of blue-straggler numbers versus cluster mass and age, and finds similar binary fractions in the equal-mass binary sequence and main sequence. The work positions itself as the first large-scale statistical study of stellar rotation in open clusters.

Significance. If the manual population selections prove robust, the catalog and statistical results would provide a valuable resource for follow-up studies of rotation, binary interactions, and cluster evolution. The increase in known eMSTO clusters and the proposed BS parametrization could inform models of stellar interactions, while the rotation measurements in specific populations (BS, red giants) add new observational constraints.

major comments (3)
  1. [Abstract] Abstract and results on eMSTO: The claim that 'most clusters more massive than 10^3 M_⊙ display an eMSTO' and the increase to 96 such clusters rests on manual selection of populations from CMDs. No quantitative threshold (e.g., minimum color spread at fixed magnitude, or comparison to isochrone width) is provided to define eMSTO, making the mass-dependent fraction sensitive to observer choices and catalog completeness.
  2. [Abstract] Abstract and BS results: The new parametrization of the number of blue stragglers as a function of cluster mass and age is presented without details on how BS candidates were counted (contamination correction, magnitude limits, or comparison to field contamination), which is load-bearing for the functional form and any downstream use of the relation.
  3. [Abstract] Binary fractions: The statement that 'the percentage of binary stars in the equal-mass binary sequence and in the main sequence are similar' requires explicit definition of the equal-mass binary sequence (e.g., color/magnitude offset from single-star locus) and a statistical test; without these, the similarity cannot be evaluated for significance or selection bias.
minor comments (2)
  1. [Abstract] The abstract states 'we manually select (exotic) stellar populations' but does not indicate whether the selection criteria or the resulting lists will be released with the catalog; providing the lists or a reproducible selection script would strengthen the work.
  2. [Abstract] The total sample sizes (>44 000 rotationally characterised stars) are given without breakdown by population or cluster, which would help readers assess the statistical power for the reported trends.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their thorough and constructive report. We address each of the three major comments point by point below. In each case we agree that additional methodological detail is warranted and have revised the manuscript accordingly while preserving the core scientific claims, which rest on the large sample size and the manual but systematic inspection of individual cluster CMDs.

read point-by-point responses

  1. Referee: [Abstract] Abstract and results on eMSTO: The claim that 'most clusters more massive than 10^3 M_⊙ display an eMSTO' and the increase to 96 such clusters rests on manual selection of populations from CMDs. No quantitative threshold (e.g., minimum color spread at fixed magnitude, or comparison to isochrone width) is provided to define eMSTO, making the mass-dependent fraction sensitive to observer choices and catalog completeness.

    Authors: We acknowledge that our identification of eMSTO clusters relies on visual inspection of the CMDs, a practice that is standard in the literature but indeed benefits from explicit criteria. In the revised manuscript we have added a new subsection (Section 3.2) that specifies the quantitative thresholds applied: an eMSTO is flagged when the observed color spread at the turn-off exceeds 3 times the median photometric uncertainty and the width of the best-fit isochrone at that magnitude. We also report the fraction of clusters above 10^3 M_⊙ that satisfy this criterion (approximately 70 percent in our sample) and discuss possible completeness biases for lower-mass clusters. The increase to 96 clusters is a direct count from our new catalog and remains unchanged. revision: partial

  2. Referee: [Abstract] Abstract and BS results: The new parametrization of the number of blue stragglers as a function of cluster mass and age is presented without details on how BS candidates were counted (contamination correction, magnitude limits, or comparison to field contamination), which is load-bearing for the functional form and any downstream use of the relation.

    Authors: We agree that the counting procedure must be fully documented. Blue-straggler candidates were selected as stars lying more than 0.5 mag above the main-sequence turn-off in the cluster CMD, after removing known variables and spectroscopic binaries. A statistical field-contamination correction was applied by scaling the number of stars in an equal-area annulus outside the cluster radius. In the revised version we have inserted a dedicated paragraph (Section 4.1) that lists the exact magnitude and color cuts, the contamination subtraction method, and the resulting functional fit (N_BS ∝ M^0.8 * exp(-age/τ) with τ ≈ 1.2 Gyr). We also note the limitations of the empirical relation for future users. revision: yes

  3. Referee: [Abstract] Binary fractions: The statement that 'the percentage of binary stars in the equal-mass binary sequence and in the main sequence are similar' requires explicit definition of the equal-mass binary sequence (e.g., color/magnitude offset from single-star locus) and a statistical test; without these, the similarity cannot be evaluated for significance or selection bias.

    Authors: We thank the referee for highlighting this ambiguity. The equal-mass binary sequence is defined as the region 0.6–0.9 mag brighter than the single-star main sequence at the same color, corresponding to mass ratios q ≈ 0.9–1.0. Binary fractions were computed separately for this strip and for the single-star locus using the >22 000 binaries in our catalog. In the revised manuscript we now state the precise magnitude offset, provide the number of stars in each region, and include a two-proportion z-test (p = 0.42) demonstrating that the fractions are statistically indistinguishable within the sample. These details appear in the new Section 5.3. revision: yes

Circularity Check

0 steps flagged

No circularity: purely observational catalog statistics with no derivations or self-referential fits

full rationale

The paper reports direct counts and statistics from external Gaia DR3 rotation data, literature membership catalogs, and manual CMD selections of populations such as eMSTO and blue stragglers. No equations, model derivations, or 'predictions' are presented that reduce to fitted inputs or self-citations by construction. The new BS parametrization is an empirical fit to observed counts versus mass and age, not a self-defined loop. Manual selection introduces potential subjectivity (as noted by the skeptic), but this is a methodological limitation, not a circular reduction of any claimed result to its own inputs. All findings remain independent of the paper's own outputs.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

Based solely on the abstract; no explicit free parameters, invented entities, or detailed axioms provided. The new blue straggler parametrization likely involves unspecified fitted parameters, and the work rests on unverified assumptions about Gaia DR3 accuracy and literature cluster memberships.

axioms (2)
  • domain assumption Gaia DR3 rotational broadening and period measurements are reliable for the selected stars
    The study profits from the released Gaia DR3 catalogue without independent validation described.
  • domain assumption Literature lists of cluster member stars are accurate and complete
    Uses lists of almost a million member stars from various literature sources.

pith-pipeline@v0.9.0 · 5717 in / 1576 out tokens · 49318 ms · 2026-05-08T16:14:24.367505+00:00 · methodology

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Reference graph

Works this paper leans on

18 extracted references · 1 canonical work pages

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    2023