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arxiv: 2606.17272 · v1 · pith:AGBWMEMZnew · submitted 2026-06-15 · 🌌 astro-ph.SR

Pre-nova Observations of T CrB: A view from the CHARA Array

Ryan Norris , Narsireddy Anugu , Thomas Gaudin , Magdalena Otulakowska-Hypka , Fabian Kaczmarek , Cameron Caruso , Cody Gustafson , Andrew Kotowski
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Rebecca Proni Nirupam Roy Fabien Baron Dipankar P.K Banerjee Dana K. Baylis-Aguirre Michelle J. Creech-Eakman Justin Linford Alexandre Gallenne Joanna Miko{\l}ajewska John D. Monnier Denis Mourard Ulisse Munari Nicolas Nardetto Rachael M. Roettenbacher Jennifer L Sokoloski Montana Williams C. E. Woodward Stefan Kraus Jean-Baptiste Le Bouquin Sorabh Chhabra Isabelle Codron Jacob Ennis Tyler Gardner Mayra Gutierrez Noura Ibrahim Cyprien Lanthermann Benjamin R. Setterholm Christopher D. Farrington Olli Majoinen Norm Vargas Douglas R. Gies Gail H. Schaefer Theo ten Brummelaar
This is my paper

Pith reviewed 2026-06-27 02:08 UTC · model grok-4.3

classification 🌌 astro-ph.SR
keywords T CrBrecurrent novaCHARA ArrayinterferometryRoche lobered giantsymbiotic starangular diameter
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The pith

CHARA Array observations measure the red giant in T CrB at 0.70 mas, matching its Roche lobe radius.

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

This paper presents interferometric observations of the red giant in the recurrent nova T CrB obtained with the CHARA Array before its next expected eruption. The team fits limb-darkened disk models to the visibility data from H-band and K-band observations to determine the star's angular diameter. The resulting physical radius at the literature distance is consistent with the Roche lobe volume radius from orbital solutions. This provides a pre-eruption measurement that supports the conclusion that the donor star fills its Roche lobe.

Core claim

The average limb darkened diameter of the star is 0.70±0.04 mas in H-band and 0.72±0.07 mas in K-band. Adopting a distance of 914 pc, the stellar radius is 69±5 R⊙ in H-band and 71±8 R⊙ in K-band. This is consistent with filling a Roche lobe volume radius of 71 R⊙ inferred from published orbital solutions.

What carries the argument

Limb darkened disk models fitted to squared visibilities from MIRC-X and MYSTIC on the CHARA Array.

If this is right

  • The red giant donor fills its Roche lobe.
  • A pre-eruption angular diameter baseline is now available for T CrB.
  • The radius is consistent between H and K bands.
  • The measurements support models of the symbiotic binary configuration.

Where Pith is reading between the lines

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

  • Future post-eruption observations could reveal if the radius changes.
  • This approach may be used on other recurrent novae to check donor filling factors.
  • Improved distance measurements would refine the radius comparison.

Load-bearing premise

The distance of 914 pc and limb-darkening coefficients from prior work apply to T CrB's red giant without change.

What would settle it

A significantly different parallax distance or interferometric diameter that makes the radius inconsistent with the Roche lobe radius would disprove the support for a filling donor.

Figures

Figures reproduced from arXiv: 2606.17272 by Alexandre Gallenne, Andrew Kotowski, Benjamin R. Setterholm, Cameron Caruso, C. E. Woodward, Christopher D. Farrington, Cody Gustafson, Cyprien Lanthermann, Dana K. Baylis-Aguirre, Denis Mourard, Dipankar P.K Banerjee, Douglas R. Gies, Fabian Kaczmarek, Fabien Baron, Gail H. Schaefer, Isabelle Codron, Jacob Ennis, Jean-Baptiste Le Bouquin, Jennifer L Sokoloski, Joanna Miko{\l}ajewska, John D. Monnier, Justin Linford, Magdalena Otulakowska-Hypka, Mayra Gutierrez, Michelle J. Creech-Eakman, Montana Williams, Narsireddy Anugu, Nicolas Nardetto, Nirupam Roy, Norm Vargas, Noura Ibrahim, Olli Majoinen, Rachael M. Roettenbacher, Rebecca Proni, Ryan Norris, Sorabh Chhabra, Stefan Kraus, Theo ten Brummelaar, Thomas Gaudin, Tyler Gardner, Ulisse Munari.

Figure 1
Figure 1. Figure 1: Variation in angular diameter with phase and date of the LDD angular diameters fit to the observations reported in this paper [PITH_FULL_IMAGE:figures/full_fig_p008_1.png] view at source ↗
read the original abstract

T CrB is a symbiotic recurrent nova consisting of a red giant and white dwarf with recent eruptions in 1866 and 1946 and an anticipated eruption in the mid 2020s. We report CHARA Array observations obtained with MIRC-X (H -band) and MYSTIC (K-band) in 2022-2025. We fit limb darkened disk models constrained with literature limb darkening coefficients to the squared visibilities as only the first visibility lobe is sampled. The average limb darkened diameter of the star across these epochs is $0.70\pm0.04$ mas in H-band and $0.72\pm0.07$ mas in K-band. Adopting a distance of $914^{+24}_{-22}$ pc, the stellar radius is $69\pm5~R_{\odot}$ in H-band and $71\pm8~R_{\odot}$ in K-band. This is consistent with filling a Roche lobe volume radius of $71~R_{\odot}$ inferred from published orbital solutions. These measurements provide a pre-eruption angular diameter and support a Roche lobe filling donor.

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 / 1 minor

Summary. The paper presents CHARA Array interferometric observations of the symbiotic recurrent nova T CrB in H and K bands from 2022-2025, fitting limb-darkened disk models constrained by literature limb-darkening coefficients to the squared visibilities (only the first lobe sampled). It reports average limb-darkened diameters of 0.70±0.04 mas (H-band) and 0.72±0.07 mas (K-band); adopting a distance of 914 pc yields stellar radii of 69±5 R⊙ and 71±8 R⊙, consistent with the 71 R⊙ Roche-lobe volume radius from orbital solutions, thereby providing a pre-eruption angular diameter and supporting a Roche-lobe filling donor.

Significance. If the external distance and limb-darkening coefficients prove appropriate, these are among the first direct interferometric angular-diameter measurements of a recurrent-nova donor star before eruption, supplying a concrete datum that can be compared against evolutionary models of mass transfer and eruption recurrence in symbiotic systems.

major comments (2)
  1. [Abstract] Abstract: the claim that the derived radii (69–71 R⊙) are 'consistent with' the Roche-lobe volume radius of 71 R⊙ is load-bearing for the central interpretation, yet rests on an adopted distance of 914 pc taken from prior literature; any systematic offset comparable to the quoted distance uncertainty (±22–24 pc) scales the physical radius by an amount comparable to the reported ±5–8 R⊙ uncertainties, removing the apparent agreement.
  2. [Abstract] Abstract: because only the first visibility lobe is sampled, the limb-darkened disk fits are constrained by literature limb-darkening coefficients; the manuscript supplies no quantitative fit diagnostics (reduced χ², residual plots, or tests of alternative LD laws) that would allow assessment of whether the model is adequate or whether the quoted diameter uncertainties fully capture possible systematic bias from the LD choice.
minor comments (1)
  1. [Abstract] The abstract should state whether the reported diameter uncertainties are purely statistical or already incorporate contributions from the fixed LD coefficients and distance.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful review and constructive comments on our manuscript. We address each major comment below and indicate where revisions will be made.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the claim that the derived radii (69–71 R⊙) are 'consistent with' the Roche-lobe volume radius of 71 R⊙ is load-bearing for the central interpretation, yet rests on an adopted distance of 914 pc taken from prior literature; any systematic offset comparable to the quoted distance uncertainty (±22–24 pc) scales the physical radius by an amount comparable to the reported ±5–8 R⊙ uncertainties, removing the apparent agreement.

    Authors: The stellar radius uncertainties (69±5 R⊙ and 71±8 R⊙) are derived after propagating the adopted distance uncertainty (914^{+24}_{-22} pc). The central values remain consistent with the Roche-lobe radius of 71 R⊙ within the reported 1σ errors. We will revise the abstract and add a clarifying sentence in the discussion to explicitly state that the consistency holds within the combined uncertainties on radius and distance. revision: partial

  2. Referee: [Abstract] Abstract: because only the first visibility lobe is sampled, the limb-darkened disk fits are constrained by literature limb-darkening coefficients; the manuscript supplies no quantitative fit diagnostics (reduced χ², residual plots, or tests of alternative LD laws) that would allow assessment of whether the model is adequate or whether the quoted diameter uncertainties fully capture possible systematic bias from the LD choice.

    Authors: We agree that quantitative fit diagnostics are needed to allow readers to evaluate model adequacy and possible systematic effects from the adopted limb-darkening coefficients. In the revised manuscript we will report the reduced χ² for each epoch, include a description of the visibility residuals, and add a brief discussion of the limb-darkening coefficients drawn from the literature together with any sensitivity tests performed. revision: yes

Circularity Check

0 steps flagged

No circularity: angular diameter obtained from direct visibility fit; radius uses external adopted distance and LD coefficients.

full rationale

The derivation chain consists of fitting limb-darkened disk models (constrained only by external literature LD coefficients) to the squared visibilities to obtain angular diameter, followed by multiplication by an adopted external distance (914 pc) to yield physical radius for comparison against an independent orbital Roche-lobe value. None of these steps reduces by the paper's own equations to a fitted parameter or self-citation chain; the angular diameter is a direct interferometric observable and the distance is explicitly external. This is a standard measurement-plus-adopted-constant workflow with no self-definitional or fitted-input-called-prediction structure.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central claim that the donor fills its Roche lobe rests on an adopted distance and literature limb-darkening coefficients; no new entities are postulated.

free parameters (1)
  • adopted distance = 914 pc
    Used to convert angular diameter to physical radius; taken from published orbital solutions rather than derived here.
axioms (2)
  • domain assumption Literature limb-darkening coefficients are applicable without adjustment to the red giant in T CrB
    Used to constrain the disk models fitted to the squared visibilities.
  • domain assumption The star can be adequately modeled as a limb-darkened disk when only the first visibility lobe is sampled
    Basis for the model fitting procedure described in the abstract.

pith-pipeline@v0.9.1-grok · 5932 in / 1462 out tokens · 65430 ms · 2026-06-27T02:08:21.760280+00:00 · methodology

discussion (0)

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