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REVIEW 3 major objections 5 minor 11 references

Thirty-Three New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble

T0 review · 3 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash

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Pith's one-line read NPOI measures 33 stars, 21 with 2% diameter precision

desk verdict Useful new NPOI diameter catalog, but the printed limb-darkening visibility equation is mis-normalized and must be fixed before the central results are reliable. read the letter →

arxiv 2505.23514 v1 pith:IHFIUGAM submitted 2025-05-29 astro-ph.SR

Ellyn K. Baines , James H. Clark III , Henrique R. Schmitt , Jordan M. Stone , Kaspar von Braun This is my paper
classification astro-ph.SR
keywords stellarangulardiametersopticalinterferometryNPOIlimbdarkeningeffectivetemperatureradiisurfacebrightnessrelationsGaiaparallaxes
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper claims that 33 new limb-darkened angular diameters measured with the Navy Precision Optical Interferometer are reliable: 21 of them reach 2% or better precision, and six more reach 5%. From each diameter the authors derive physical radius, bolometric flux, luminosity, and effective temperature, using Gaia or Hipparcos parallaxes and spectral energy distribution fits. Combined with 145 stars from four earlier NPOI papers, the resulting 178-star sample matches the (V-K) color-diameter relation to about 1%, the JMMC catalog with a slope of 0.969, and Gaia-based diameter estimates with a slope of 0.996. The central point is that a homogeneous interferometric sample can validate and calibrate the indirect methods that supply most stellar diameters. A fair reader should take the claim as: NPOI angular diameters are accurate at the few-percent level, and the ensemble is a useful cross-check for stellar models and for surveys such as Gaia.

What carries the argument

The argument rests on the limb-darkened disk visibility model: calibrated visibility squared is fit using the Hanbury Brown et al. expression with a linear limb-darkening coefficient, and the coefficient is taken from Claret and Bloemen (2011) ATLAS models in the R band, iterated against the derived effective temperature. Uncertainties come from the Tycner et al. bootstrap, which resamples entire scans rather than individual points. Bolometric flux and extinction are obtained from fitting Pickles spectral templates to published photometry, and effective temperature follows from the van Belle et al. relation between bolometric flux, limb-darkened diameter, and the Stefan-Boltzmann constant.

What would settle it

Observe the six stars measured near or below the formal resolution limit (for example, sigma Boo at 0.714 +/- 0.205 mas) with a longer-baseline optical interferometer; if the independently measured limb-darkened diameters disagree with the NPOI values by more than the quoted uncertainties, the claim that these sub-resolution diameters are reliable, or the bootstrap error estimates, fails.

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Extended reading notes

Core claim

The paper's central claim is that the 33 newly presented limb-darkened angular diameters, and the radii, bolometric fluxes, luminosities, and effective temperatures derived from them, are accurate and astrophysically useful. The claim is supported by internal agreement: for stars with previous interferometric measurements, the NPOI values generally overlap, and the 178-star ensemble follows the (V-K) surface-brightness relation with a fitted line of f(x) = 1.001x + 0.068, within about 1%. The JMMC catalog comparison gives f(x) = 0.969x + 0.088, and the Gaia-based comparison gives f(x) = 0.996x + 0.246, with the larger offset showing that Gaia diameters are useful for ensembles but not for individual stars. The paper explicitly treats every target as effectively single and slowly rotating, and flags that known binaries or rapid rotators (such as beta Cyg A, alpha Cep, eta Cep, and sigma Gem) have diameters that should be read as single-star values.

Load-bearing premise

Every target is treated as a single, slowly rotating star with a symmetric disk; for stars with unresolved companions or rapid rotation, such as beta Cyg A and alpha Cep, this can bias the quoted angular diameter.

Editorial extensions

If this is right

  • The 33 new diameters, combined with earlier NPOI samples, produce a 178-star ensemble that traces the (V-K)-based surface-brightness relation with a fitted slope of 1.001 and agreement within about 1%.
  • Twenty-one stars now have limb-darkened diameters at or below 2% uncertainty, the threshold generally considered astrophysically useful, making them benchmark values for stellar evolution models and exoplanet host characterization.
  • The ensemble comparison to JMMC catalog diameters (slope 0.969) and Gaia-based estimates (slope 0.996 with a 0.246 mas offset) shows that the NPOI sample can serve as a cross-calibration anchor for indirect diameter estimators.
  • The six targets measured near or below the NPOI's formal resolution limit show the largest fractional uncertainties, demonstrating where the instrument's diameter measurements degrade.
  • For stars with known companions or rapid rotation, the single-star diameters presented here should be used with caution because the model cannot account for asymmetry or binarity.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • Editorial inference: The near-1% agreement with the (V-K) surface-brightness relation suggests the NPOI ensemble could be used to re-derive color-based diameter calibrations with direct interferometric anchors, reducing the systematic floor of dwarf-star temperature scales.
  • Editorial inference: The alpha Cep diameter of 1.674 mas likely reflects the equatorial rather than the polar size; a gravity-darkened model fitted to the same visibilities would test this, and if confirmed, similar single-diameter treatments of other rapid rotators would need a rotation-dependent correction.
  • Editorial inference: The 0.246 mas offset in the Gaia-diameter comparison implies that a statistical correction calibrated on this NPOI ensemble could be applied to Gaia-based radii in large surveys, though the scatter would remain too large for individual stars.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 5 minor

Summary. The paper reports new limb-darkened angular diameter measurements for 33 stars observed with the Navy Precision Optical Interferometer (NPOI), with formal uncertainties at or below 2% for 21 targets. For each program star the authors also derive physical radius, bolometric flux, extinction, effective temperature, and luminosity using Gaia/Hipparcos parallaxes and SED fits. The new measurements are combined with previous NPOI diameters to assemble a catalog of 178 entries, which is compared with diameters predicted from (V-K) color relations, the JMMC Stellar Diameters Catalog, and Gaia-based estimates. The analysis follows standard interferometric practice: calibrated visibilities, uniform-disk and limb-darkened model fitting, a modified bootstrap estimator for uncertainties, and an iterative loop between the limb-darkening coefficient and the derived effective temperature.

Significance. If the quoted diameters and uncertainties are accurate, the paper provides a valuable set of interferometric angular diameters, including several stars that have not been measured before at high angular resolution, and a useful ensemble for testing surface-brightness and color-based diameter estimation. The authors are transparent about known companions, outliers, and the limitations of the single-star assumption. The machine-checkable parts are the visibility fits and bootstrap uncertainties; the central diameter claims are supported by the data and standard methods. However, the incorrect normalization in Eq. (1) and the duplicate, mutually inconsistent entries in the ensemble table undermine the reproducibility and the quantitative claims until they are fixed.

major comments (3)
  1. [Section 3, Eq. (1)] The limb-darkened visibility formula as printed is not correctly normalized. The denominator should be ((1-μλ)/2 + μλ/3), not (1 - μλ/2 + μλ/3). With the printed normalization the model does not equal V²=1 at zero baseline and would bias all fitted θLD values in a u-dependent way if the fitting code implements it literally. Please correct Eq. (1) and state explicitly which normalization was used by the fitting code. If the code uses the correct form, the equation is a misprint that must be fixed to make the analysis reproducible; if it uses the printed form, the entire Table 5 is suspect.
  2. [Section 6 / Table 9] The ensemble table contains duplicate entries for HD 161797 and HD 187929, listed as separate rows from different NPOI papers. For HD 161797 the two NPOI values are 1.880±0.008 mas and 1.957±0.012 mas, which disagree by about 5σ in the measured diameters; for HD 187929 the two values agree. Including both entries as independent points in the ensemble fits weights HD 161797 twice and hides a real reproducibility issue. The authors should either select one measurement per star or explicitly justify retaining both entries and discuss the discrepancy.
  3. [Section 5 / Table 5] The single-star, non-rotating assumption is violated for several of the targets claimed to have 2% or better precision. In particular, HD 203280 (α Cep) is a known rapid rotator with published polar and equatorial diameters of 1.355±0.009 and 1.625±0.050 mas; the quoted 0.4% uncertainty on the 1.677 mas diameter is much smaller than the known oblateness-induced ambiguity. Similarly, HD 183912 (β Cyg A) is a multiple system and HD 173764 (β Sct) is a spectroscopic binary with a detected secondary at the NPOI sensitivity limit. The abstract's claim that 21 targets reach 2% or better should be qualified by excluding or separately flagging stars for which the single-star model is known to be inadequate, or by providing a quantitative systematic-error estimate for those targets.
minor comments (5)
  1. [Section 6 text and Table 9 note] The text states the combined sample contains 178 stars, but Table 9 lists two stars twice, so the count appears to be 178 entries rather than 178 unique stars; please clarify the wording and adjust the title or text accordingly if needed.
  2. [Section 6 and Figure 5 footnote] The fit without HD 42995 is given as f(x)=1.001x+0.068 in the figure caption but as f(x)=1.006±0.012 + 0.069±0.050 in the footnote; these numbers should be reconciled.
  3. [Section 6, Gaia comparison] The text attributes the Gaia-based angular diameters to Cruzalèbes et al. (2013), but Table 9 notes they are from Gaia Collaboration et al. (2018) and Table 8 cites Cruzalèbes et al. (2019); please correct the reference assignment.
  4. [Abstract and Section 5, HD 224014] The paper notes for ρ Cas that the diameter fit 'may not be of significant value without knowledge of the pulsation phase', yet this star is counted among the 21 targets with 2% or better uncertainty; the abstract and conclusion should mention this caveat explicitly.
  5. [Throughout] There is a typo in the abstract ('mid-A to to mid-K'), and the phrase 'we deal almost entirely with measurements before the first minimum' could be clarified by noting the maximum spatial frequency for each target in Table 5.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: NPOI angular diameters are direct visibility fits, and the Teff/limb-darkening feedback loop plus external ensemble comparisons do not reduce to the inputs.

full rationale

The central results, the limb-darkened angular diameters, are obtained by least-squares fitting of uniform-disk and limb-darkened visibility models to calibrated NPOI visibilities. They are not defined in terms of the derived stellar parameters. The limb-darkening coefficient is taken from external Claret & Bloemen (2011) tables, and although Teff feeds back into μλ, the paper explicitly documents a convergent iterative loop: μλ changed by an average of 0.01 and θLD by an average of 0.4% after the first pass. That is a small self-consistent correction, not a fitted input renamed as a prediction. Calibrator diameters are estimated from SED fits to published photometry and model atmospheres, independently of the science targets, so the calibrated visibility scale is not manufactured from the claimed output. The derived radii and effective temperatures use the measured θLD with Gaia/Hipparcos parallaxes and SED bolometric fluxes; these are standard, externally grounded calibration relations rather than circular reductions. The ensemble comparisons in Section 6 use the Mozurkewich et al. (2003) and Adams et al. (2018) color–surface-brightness relations, the JMMC catalog, and Gaia predictions; the paper does not state that these were calibrated on the same NPOI measurements, so any overlap cannot be asserted as a circular step under the evidence rule. Self-citations to Baines et al. (2014, 2018, 2021, 2023) serve to identify archival data and describe methodology, not to supply a load-bearing uniqueness theorem. The paper's own caveats about pulsation phase, rapid rotation, and possible companions are acknowledged modeling limitations and fall under correctness risk, not circularity. The externally noted possible normalization issue in Eq. (1) is a reproducibility/correctness concern; it does not make the derivation equivalent to its inputs. No circular step can be exhibited from the text.

Assumptions & free parameters 1 free parameters · 5 assumptions · 0 invented entities

The measured diameters are direct observables, so the ledger is small. The main fitted quantity is extinction A_V of each star; the main assumptions are the single/non-rotating star model and the adopted limb-darkening and atmosphere grids.

free parameters (1)
  • Extinction A_V (per star) = 0.00 to 1.11 mag (Table 7)
    Fitted to each star's photometry as part of the SED fit using Pickles (1998) templates and the Cardelli et al. (1989) reddening law. A_V directly affects the bolometric flux and hence effective temperature and luminosity.
assumptions (5)
  • domain assumption Each target is effectively single and not a rapid rotator, so a single symmetric disk model is sufficient.
    Stated in Section 2. Violated by known cases such as alpha Cep (oblate rapid rotator) and beta Cyg A (companion), potentially biasing diameters.
  • domain assumption Linear limb-darkening coefficients from Claret & Bloemen (2011) in the R band with a microturbulent velocity of 2 km/s are adequate.
    Section 3. The authors note a more refined wavelength-dependent treatment is possible; they observe mostly before the first visibility minimum.
  • domain assumption Model atmospheres (Castelli & Kurucz 2003) and template spectra (Pickles 1998) accurately represent the target and calibrator SEDs.
    Sections 3 and 4. Calibrator diameters and target bolometric fluxes depend on these models.
  • standard math The bootstrap resampling method of Tycner et al. (2010) provides a valid estimate of statistical diameter uncertainty.
    Section 3. The method resamples whole scans; it does not capture systematic model errors.
  • domain assumption Published parallaxes are accurate, with the exception that the authors reject the Gaia DR3 negative parallax for HD 224014.
    Section 4 and 5. Radii depend on parallax; for HD 224014 the DR3 value is discarded as unphysical.

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Cite this review

Pith. "Pith review of Thirty-Three New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble." pith.science (2026). https://pith.science/paper/IHFIUGAM

@misc{pith2026250523514,
  author       = {Pith},
  title        = {Pith review of: Thirty-Three New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/IHFIUGAM}},
  note         = {Machine review of arXiv:2505.23514}
}
read the original abstract

We present new angular diameter measurements for 33 stars from the Navy Precision Optical Interferometer, reaching uncertainties on the limb-darkened diameter of 2% or less for 21 targets. We also determined the physical radius, bolometric flux, luminosity, and effective temperature for each star. Our sample is a mix of giant, subgiant, and dwarf stars, and span spectral classes from mid-A to to mid-K. We combined these 33 stars with samples from previous publications to analyze how the NPOI diameters compare to those obtained using other means, namely (V-K) color, the JMMC Stellar Diameters Catalog, and Gaia predictions.

Figures

Figures reproduced from arXiv: 2505.23514 by the authors.

Figure 1
Figure 1. An example probability density solution for the diameter fit to HD 3712/α Cas visibilities as described in Section 3 [PITH_FULL_IMAGE:figures/full_fig_p030_1.png] view at source ↗
Figure 2
Figure 2. Top panel: The θLD fit for HD 3712/α Cas. The solid red line represents the visibility curve for the best fit θLD, the points are the calibrated visibilities, and the vertical lines are the measurement uncertainties. Bottom panel: The residuals (O-C) of the diameter fit to the visibilities. The plots for the remaining stars are available on the electronic version of the Astronomical Journal [PITH_FULL_IMAGE:figures… view at source ↗
Figure 3
Figure 3. Top panel: Comparison of the angular diameters measured here versus previously measured interferometric diameters from the literature. The error bars are included but are often smaller than the open circle indicating the measurement. The dotted line is the 1:1 ratio. When more than one measurement was available in the literature, we used the most recent measurement (see [PITH_FULL_IMAGE:figures/full_fig_p032_3.png] view at source ↗
Figures from the paper (4 more)
Figure 4
Figure 4. Figure 4: A color-magnitude diagram of our new stars (red squares), past NPOI targets (large black circles), and targets from JMMC (Bourg´es et al. 2014, small black points) that fall within the limits of the NPOI observable range of declination higher than -10 deg and brighter …
Figure 5
Figure 5. Figure 5: Top panel: Comparison of the angular diameters measured here versus diameters predicted using the relations from the Mozurkewich et al. (2003) paper (Eq. 3 and 4 in Section 6). Note that the NPOI errors are often smaller than the open circle indicating the data point, …
Figure 6
Figure 6. Figure 6: Top panel: Comparison of the angular diameters measured here versus diameters predicted using the relations from the Adams et al. (2018) paper. As in [PITH_FULL_IMAGE:figures/full_fig_p035_6.png]
Figure 7
Figure 7. Figure 7: Top panel: Comparison of the limb-darkened angular diameters measured here versus diameters from JMMC (Bourg´es et al. 2014). The linear fit is f(x) = 0.969x+0.088. Bottom panel: The same, but from Gaia (Gaia Collaboration et al. 2018; Cruzal`ebes et al. 2019), with a …

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Works this paper leans on

11 extracted references · 2 canonical work pages

  1. [3]

    Star in range?

    Allende Prieto & Lambert (1999); 4. Huang et al. (2010); 5. Gebran et al. (2016); 6. Soubiran et al. (2016); 7. Le Borgne et al. (2003); 8. S´ anchez-Bl´ azquez et al.(2006); 9. Zorec et al. (2009); 10. Clem et al. (2004); 11. Friedemann (1992); 12. Neckel et al. (1980); 13. Hunter et al. (2006); 14. Jenkins (2009); 15. Gontcharov & Mosenkov (2018); 16. v...

    work page 1999

  2. [13]

    doi:10.1016/0083-6656(72)90023-2 Gontcharov, G. A. & Mosenkov, A. V. 2018, VizieR Online Data Catalog, II/354 Griffin, R. F. 2008, The Observatory, 128, 21 Griffin, R. F. 2009, The Observatory, 129, 198 H¨ aggkvist, L. & Oja, T. 1970, A&AS, 1, 199 Hanbury Brown, R., Davis, J., & Allen, L. R. 1974b, MNRAS, 167, 121. doi:10.1093/mnras/167.1.121 Hanbury Brown, R...

    doi:10.1016/0083-6656(72)90023-2 2018

  3. [28]

    & Vazdekis, A

    doi:10.3847/1538-4357/ac91c4 Koleva, M. & Vazdekis, A. 2012, A&A, 538, A143. doi:10.1051/0004-6361/201118065 Kornilov, V. G., Volkov, I. M., Zakharov, A. I., Kozyreva, L. N., Kornilova, L. N., & et al. 1991, Trudy Gosudarstvennogo Astronomicheskogo Instituta, 63, 4 Le Borgne, J.-F., Bruzual, G., Pell´ o, R., et al. 2003, A&A, 402, 433. doi:10.1051/0004-63...

    doi:10.3847/1538-4357/ac91c4 2012

  4. [120]

    2020, A&A, 640, A2

    doi:10.3847/1538-4357/aa8ef7 Salsi, A., Nardetto, N., Mourard, D., et al. 2020, A&A, 640, A2. doi:10.1051/0004-6361/202038012 969 x + 0.088 S´ anchez-Bl´ azquez, P., Peletier, R. F., Jim´ enez-Vicente, J., et al. 2006, MNRAS, 371, 703. doi:10.1111/j.1365-2966.2006.10699.x Schaefer, G. H., Brummelaar, T. T., Gies, D. R., et al. 2014, Nature, 515, 234. doi:...

    arXiv 2020

  5. [212]

    R., & McSwain, M

    doi:10.3847/1538-3881/aa6749 Huang, W., Gies, D. R., & McSwain, M. V. 2010, ApJ, 722, 605. doi:10.1088/0004-637X/722/1/605 Hummel, C. A., Benson, J. A., Hutter, D. J., et al. 2003, AJ, 125, 2630. doi:10.1086/374572 Hummel, C. A., Mozurkewich, D., Armstrong, J. T., et al. 1998, AJ, 116,

    doi:10.3847/1538-3881/aa6749 2010

  6. [251]

    T., Ciardi, D

    doi:10.1086/386343 van Belle, G. T., Ciardi, D. R., ten Brummelaar, T., et al. 2006, ApJ, 637,

    doi:10.1086/386343 2006

  7. [494]

    T., Creech-Eakman, M

    doi:10.1086/498334 15 van Belle, G. T., Creech-Eakman, M. J., & Hart, A. 2009, MNRAS, 394, 1925. doi:10.1111/j.1365-2966.2008.14146.x van Belle, G. T., Lane, B. F., Thompson, R. R., et al. 1999, AJ, 117, 521 van Belle, G. T., van Belle, G., Creech-Eakman, M. J., et al. 2008, ApJS, 176, 276-292. doi:10.1086/526548 van Belle, G. T. & von Braun, K. 2009, ApJ...

    arXiv 2009

  8. [550]

    K., Armstrong, J

    doi:10.1086/305365 Baines, E. K., Armstrong, J. T., Clark, J. H., et al. 2021, AJ, 162, 198. doi:10.3847/1538-3881/ac2431 Baines, E. K., Armstrong, J. T., Schmitt, H. R., et al. 2014, ApJ, 781, 90. doi:10.1088/0004-637X/781/2/90 Baines, E. K., Armstrong, J. T., Schmitt, H. R., et al. 2018, AJ, 155, 30. doi:10.3847/1538-3881/aa9d8b Baines, E. K., Blomquist...

    arXiv doi:10.48550/arxiv.astro-ph/0405087 2021

Show all 11 references
  1. [981]

    2016, A&A, 587, A12

    doi:10.1051/0004-6361:20011124 Wittkowski, M., Chiavassa, A., Freytag, B., et al. 2016, A&A, 587, A12. doi:10.1051/0004-6361/201527614 Zhao, M., Monnier, J. D., Pedretti, E., et al. 2009, ApJ, 701, 209. doi:10.1088/0004-637X/701/1/209 Zorec, J., Cidale, L., Arias, M. L., et al...

    1991 doi

  2. [1227]

    A., & Megeath, S

    doi:10.1086/381295 Cohen, M., Wheaton, W. A., & Megeath, S. T. 2003, AJ, 126, 1090. doi:10.1086/376474 Colina, L., Bohlin, R. C., & Castelli, F. 1996, AJ, 112, 307. doi:10.1086/118016 Cruzal` ebes, P., Jorissen, A., Rabbia, Y., et al. 2013, MNRAS, 434, 437. doi:10.1093/mnras/s...

    2003 doi

  3. [2502]

    J., Simon, R

    doi:10.1086/378596 Mozurkewich, D., Johnston, K. J., Simon, R. S., et al. 1991, AJ, 101, 2207. doi:10.1086/115843 Neckel, T., Klare, G., & Sarcander, M. 1980, Bulletin d’Information du Centre de Donnees Stellaires, 19, 61 Nordgren, T. E., Germain, M. E., Benson, J. A., et al. ...

    1991 arXiv

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