pith. sign in

arxiv: 2604.16803 · v1 · submitted 2026-04-18 · 🌌 astro-ph.SR · astro-ph.GA

W UMa-Type Contact Binaries in the Tidal Tails of Young Open Cluster COIN-Gaia 25 and Mamajek 4

Xiang Bin , Liu Liang , Zhu Liying , Shi Xiangdong , Liu Nianping This is my paper

Pith reviewed 2026-05-10 07:18 UTC · model grok-4.3

classification 🌌 astro-ph.SR astro-ph.GA
keywords contact binariesW UMa starstidal tailsyoung open clustersbinary formationorbital evolutionage constraints
0
0 comments X

The pith

A contact binary in a young cluster tidal tail must be younger than 371 million years, showing some such systems evolve on short timescales.

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

The paper identifies two W UMa-type contact binaries located within the tidal tails of young open clusters. Detailed modeling of their light curves classifies one as a deep, low-mass-ratio contact system whose position in the Mamajek 4 tail ties it to an age upper limit of 371 million years. This constraint leads the authors to argue that the total lifetime of certain contact binaries can be as brief as a few thermal timescales and that the system most likely formed through rapid orbital hardening in the gas-rich early phase of cluster evolution. A sympathetic reader would care because the result supplies a rare direct age bound on close binary formation and evolution inside dynamically active young stellar groups.

Core claim

The authors locate and confirm two contact binaries in the tidal tails of COIN-Gaia 25 and Mamajek 4. Photometric solutions show the Mamajek 4 system to be a deep contact binary with mass ratio near 0.13. Its membership in the tidal tail sets an age limit below 371 Myr, which the paper uses to conclude that some contact binaries reach advanced states and may dissolve within only a few thermal timescales, most plausibly after efficient orbital hardening mediated by gas dynamical friction during the cluster's gas-rich youth.

What carries the argument

Membership of the contact binary in the tidal tail of the young cluster Mamajek 4, which supplies a firm upper bound on the system's age and thereby on the duration of its contact phase.

If this is right

  • Some contact binaries can form, reach deep contact, and begin to dissolve within less than 371 million years.
  • Efficient orbital hardening, possibly driven by gas dynamical friction, operates in the gas-rich early stages of open-cluster evolution.
  • Tidal tails around young clusters provide clean laboratories for placing age limits on close binary systems.
  • The total lifetime of at least some W UMa-type binaries is limited to only a few thermal timescales.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Searches for contact binaries in additional young-cluster tails could yield more systems with tight age bounds and map how quickly the contact phase begins.
  • If the proposed gas-mediated hardening channel is common, population-synthesis models of field contact binaries would need to incorporate an early dense-environment channel.
  • The short lifetime implied here may help explain the observed scarcity of very young contact binaries outside clusters.

Load-bearing premise

The identified contact binaries are genuine members of the cluster tidal tails rather than unrelated field stars aligned by chance.

What would settle it

Kinematic or spectroscopic data showing the binary's motion or composition inconsistent with the Mamajek 4 tidal tail, or an independent age indicator placing the system older than 371 million years.

Figures

Figures reproduced from arXiv: 2604.16803 by Liu Liang, Liu Nianping, Shi Xiangdong, Xiang Bin, Zhu Liying.

Figure 1
Figure 1. Figure 1: The projections of the open clusters and their tidal t [PITH_FULL_IMAGE:figures/full_fig_p011_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Original and normalized average TESS data for ASASSN [PITH_FULL_IMAGE:figures/full_fig_p011_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Original and normalized average TESS data for ASASSN [PITH_FULL_IMAGE:figures/full_fig_p012_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: The normalized average TESS data and theoretical lig [PITH_FULL_IMAGE:figures/full_fig_p012_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: The MCMC corner plots for ASASSN-V J064923.44 [PITH_FULL_IMAGE:figures/full_fig_p013_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Geometrical structures for ASASSN-V J064923.44 [PITH_FULL_IMAGE:figures/full_fig_p013_6.png] view at source ↗
read the original abstract

Star clusters, as dynamically rich environments, are thought to be important sites for the formation of contact binaries. To investigate this, we conducted a systematic search for contact binaries within two young open clusters, COIN-Gaia 25 and Mamajek 4, and their associated tidal tails. From this search, we identified and confirmed two contact binary systems: ASASSN-V J064923.44+013758.4 in the tidal tail of COIN-Gaia 25, and ASASSN-V J173229.06-613712.5 in the tidal tail of Mamajek 4. Using TESS light curve data, we performed detailed modeling with a Markov Chain Monte Carlo (MCMC) method within the 2015 version of the Wilson-Devinney (W-D) code. The resulting photometric parameters are: q_ph = 0.316 (0.013), i= 76.9 (+1.3, -0.9) degrees, f=23.1 (+1.4, -1.9)% for ASASSN-V J064923.44+013758.4, and q_ph = 0.130 (0.004), i= 68.4 (+1.4, -1.3) degrees, f=66.3 (+5.0, -5.3)% for ASASSN-V J173229.06-613712.5. A cool-spot model located on the more massive component was successfully implemented for each system. The derived parameters classify ASASSN-V J173229.06-613712.5 as a deep, low-mass-ratio contact binary. Its location in the tidal tail of Mamajek 4 constrains its age to < 371 Myr, supporting the view that the total lifetime of some contact binaries may be as short as a few thermal timescales. After evaluating standard formation mechanisms, we propose that ASASSN-V J173229.06-613712.5 likely formed via efficient orbital hardening (potentially mediated by gas dynamical friction) during the early, gas-rich phase of its host cluster's evolution. This study demonstrates the value of young clusters and their tidal tails in providing robust age constraints to explore the formation and rapid evolution of contact binaries.

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

2 major / 3 minor

Summary. The manuscript reports the discovery of two W UMa-type contact binaries (ASASSN-V J064923.44+013758.4 and ASASSN-V J173229.06-613712.5) in the tidal tails of the young open clusters COIN-Gaia 25 and Mamajek 4. It presents MCMC-based Wilson-Devinney modeling of TESS light curves that yields photometric parameters (q_ph = 0.316, i = 76.9°, f = 23.1% for the first system; q_ph = 0.130, i = 68.4°, f = 66.3% for the second) together with cool-spot solutions on the more massive components. The paper uses the <371 Myr age of the Mamajek 4 tidal tail to constrain the lifetime of the second system and proposes formation via efficient orbital hardening mediated by gas dynamical friction in the early gas-rich phase of the cluster.

Significance. If the tidal-tail membership can be placed on a quantitative footing, the work supplies useful observational constraints on the formation timescales of contact binaries in young cluster environments and demonstrates the utility of tidal tails for age-dating. The MCMC light-curve analysis with reported uncertainties and successful spot modeling is a solid technical contribution.

major comments (2)
  1. [Abstract and §5] Abstract and §5 (Discussion/Conclusions): The headline claim that the total lifetime of some contact binaries may be as short as a few thermal timescales, together with the proposed formation channel via gas dynamical friction, rests entirely on the assertion that ASASSN-V J173229.06-613712.5 is a genuine member of the Mamajek 4 tidal tail. The manuscript states the systems were 'identified and confirmed' but supplies no membership probabilities, proper-motion or parallax offsets relative to the cluster mean, radial-velocity data, or field-contamination statistics. This assumption is load-bearing for the age upper limit and all subsequent interpretation.
  2. [§3] §3 (Light-curve analysis): The paper should report MCMC convergence diagnostics (e.g., Gelman-Rubin statistic, trace plots, or autocorrelation times) and the full posterior distributions for the free parameters (q_ph, i, f, spot parameters) so that the quoted uncertainties can be independently assessed.
minor comments (3)
  1. [Abstract] The abstract and introduction should briefly indicate the criteria used for 'confirmation' of membership even if the full analysis appears later.
  2. [Figures 2-3] Figure captions for the light-curve fits should explicitly state whether the plotted models include the cool-spot component and should show the residuals.
  3. [§3] Notation: clarify whether q_ph is strictly the photometric mass ratio from the Wilson-Devinney solution and whether any spectroscopic constraints were considered.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for their constructive and detailed review. The comments have helped us identify areas where the manuscript can be strengthened, particularly regarding membership justification and MCMC transparency. We respond to each major comment below and outline the planned revisions.

read point-by-point responses

  1. Referee: [Abstract and §5] The headline claim that the total lifetime of some contact binaries may be as short as a few thermal timescales, together with the proposed formation channel via gas dynamical friction, rests entirely on the assertion that ASASSN-V J173229.06-613712.5 is a genuine member of the Mamajek 4 tidal tail. The manuscript states the systems were 'identified and confirmed' but supplies no membership probabilities, proper-motion or parallax offsets relative to the cluster mean, radial-velocity data, or field-contamination statistics. This assumption is load-bearing for the age upper limit and all subsequent interpretation.

    Authors: We agree that the membership of ASASSN-V J173229.06-613712.5 is central to the age constraint and interpretations. The original identification relied on spatial coincidence with the published tidal tail of Mamajek 4 and consistency with Gaia DR3 proper motions and parallaxes. In revision, we will add a new subsection (in §2) with quantitative membership assessment: membership probabilities derived from a statistical model incorporating proper motion and parallax, explicit offsets relative to the cluster mean, and a field-contamination estimate using offset control fields. We will also explicitly note the absence of radial-velocity data. These additions will be referenced in the abstract and §5 to better support the <371 Myr age limit. revision: yes

  2. Referee: [§3] The paper should report MCMC convergence diagnostics (e.g., Gelman-Rubin statistic, trace plots, or autocorrelation times) and the full posterior distributions for the free parameters (q_ph, i, f, spot parameters) so that the quoted uncertainties can be independently assessed.

    Authors: We accept this recommendation. The revised manuscript will include MCMC convergence diagnostics in a new appendix: Gelman-Rubin statistics for all chains (targeting values <1.01), autocorrelation times, and summaries of the posterior distributions (medians with 16th/84th percentiles) for q_ph, i, f, and all spot parameters. Trace plots and corner plots will be provided in supplementary material or made available upon request. This will allow readers to independently evaluate the reliability of the reported uncertainties. revision: yes

standing simulated objections not resolved
  • Radial-velocity measurements for definitive membership confirmation are not available in existing data for these systems and cannot be added without new observations.

Circularity Check

0 steps flagged

No circularity: age bound and formation proposal rest on external cluster age plus standard modeling

full rationale

The paper reports photometric parameters from MCMC fitting of TESS light curves using the Wilson-Devinney code, then states that location in the Mamajek 4 tidal tail supplies an age upper limit of <371 Myr taken from the published cluster age. This step is a direct application of an external datum once membership is asserted; it does not reduce any fitted quantity to itself by construction, invoke a self-citation uniqueness theorem, or smuggle an ansatz. The subsequent formation proposal is presented as an interpretive evaluation after standard mechanisms are considered, without equations that loop back to the input data. The derivation chain is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

4 free parameters · 2 axioms · 0 invented entities

The central age and formation claims rest on cluster membership, standard assumptions of the Wilson-Devinney code, and the published age of Mamajek 4; no new entities are postulated.

free parameters (4)
  • mass ratio q_ph
    Fitted from light-curve modeling for each system (0.316 and 0.130).
  • inclination i
    Fitted photometric inclination for each binary.
  • fillout factor f
    Fitted contact degree for each system.
  • spot parameters
    Cool-spot temperature and location fitted on the primary component.
axioms (2)
  • domain assumption The binaries are physical members of the respective tidal tails and therefore share the cluster age.
    Invoked to convert spatial location into an age upper limit of <371 Myr.
  • standard math Wilson-Devinney assumptions hold: synchronous rotation, common envelope, and standard limb-darkening and gravity-darkening coefficients.
    Required for the 2015 W-D code to produce the reported q, i, and f values.

pith-pipeline@v0.9.0 · 5761 in / 1517 out tokens · 35208 ms · 2026-05-10T07:18:44.146083+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

4 extracted references · 4 canonical work pages

  1. [1]

    2020, ApJS, 249, 18 2 Cranmer, S

    Chen, X., Wang, S., Deng, L., et al. 2020, ApJS, 249, 18 2 Cranmer, S. R., & Winebarger, A. R. 2019, ARA&A, 57, 157 2 Eggen, O. J. 1967, MNRAS, 70, 111 3 Eggleton, P . P ., & Kiseleva-Eggleton, L. 2001, ApJ, 562, 1012 6 Fabrycky, D., & Tremaine, S. 2007, ApJ, 669, 1298 2 Faulkner, J. 1971, ApJ, 170, L99 2 Ferreira, T., Saito, R. K., Minniti, D., et al. 20...

    work page 2020

  2. [2]

    3 − 3 N walkers 50 N steps 1000-2000 Lucy, L. B. 1968a, ApJ, 153, 877 1 Lucy, L. B. 1968b, ApJ, 151, 1123 1 Lucy, L. B. 1976, ApJ, 205, 208 2, 6 Mateo, N. M., & Rucinski, S. M. 2017, AJ, 154, 125 3 Matt, S. P ., Brun, A. S., Baraffe, I., Bouvier, J., & Chabrier , G. 2015, ApJ, 799, L23 5 Mestel, L. 1968, MNRAS, 138, 359 2 O’Connell, D. J. K. 1951, Publica...

    work page 2000

  3. [3]

    0410 rms 0.0049711 0.010467 Gelman-Rubin statistic 1.202 1.090 Table 3: Absolute physical parameters estimated from the li ght curve solutions. Parameter ASASSN-V J064923.44 +013758.4 ASASSN-V J173229.06 − 613712.5 T1 (K) 5755 4596 T2 (K) 5695 4172 M1 (M⊙ ) 0.405 0.090 M2 (M⊙ ) 1.285 0.692 R1 (R⊙ ) 0.824 0.362 R2 (R⊙ ) 1.370 0.844 L1 (L⊙ ) 0.694 0.052 L2 ...

    work page 2024

  4. [4]

    The red square represents the contact binary candidate ZTF J 060411.97+215302.2, with a very high membership probability but excluded by the period-color re lationship

    The red circles represent the contact binaries of ASASSN-V J064923.44 +013758.4 and ASASSN-V J173229.06 − 613712.5, whose probability of being tidal tail members is h igher than 50 %. The red square represents the contact binary candidate ZTF J 060411.97+215302.2, with a very high membership probability but excluded by the period-color re lationship. Fig....

    work page 2088