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arxiv: 2604.27828 · v1 · submitted 2026-04-30 · 🌌 astro-ph.SR · astro-ph.GA

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TESS Asteroseismology of Red Giants in the Old Metal-Rich Open Clusters NGC 188 & NGC 6791

Madeline Howell , Jennifer A. Johnson , Marc H. Pinsonneault , Leslie M. Morales , Jamie Tayar , John D. Roberts , Dennis Stello , Madeleine McKenzie
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Pith reviewed 2026-05-07 07:10 UTC · model grok-4.3

classification 🌌 astro-ph.SR astro-ph.GA
keywords asteroseismologyred giantsopen clustersmass lossTESSstellar massesNGC 188NGC 6791
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The pith

Asteroseismic analysis with TESS shows red giants in NGC 188 lost only 0.02 solar masses on the RGB.

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

The paper applies a boutique method to TESS photometry to study red giants in the old metal-rich open clusters NGC 188 and NGC 6791. It finds that TESS recovers oscillation frequencies similar to Kepler data, though with a 2.2 percent systematic offset in nu_max due to lower signal-to-noise. For the 17 red giants in NGC 188, average seismic masses are derived for the red giant branch and red clump phases, leading to an estimate of integrated RGB mass loss of 0.02 solar masses. This supports the notion of reduced mass loss at higher metallicities. The work also flags three potential binary interaction candidates and derives a seismic age of 7.0 Gyr that agrees with prior values.

Core claim

We use TESS photometry of red giants in NGC 188 and NGC 6791 to derive seismic masses via scaling relations. For NGC 188 we measure average RGB mass of 1.13 solar masses and RC mass of 1.11 solar masses, implying an integrated RGB mass loss of 0.02 solar masses. This is consistent with lower mass loss at high metallicity. Three stars show signs of binary interactions, and the average seismic age is 7.0 Gyr.

What carries the argument

The asteroseismic scaling relations that turn measurements of nu_max and Delta nu into estimates of mass and radius for red giants, after separating RGB and RC stars based on their oscillation properties.

If this is right

  • The seismic masses for NGC 188 red giants are consistent with independent estimates and have precision similar to Kepler studies.
  • The estimated RGB mass loss of 0.02 solar masses supports evidence for lower mass loss rates at higher metallicities.
  • Three binary interaction candidates are identified among the red giants using mass discrepancies and dipole mode suppression.
  • A seismic cluster age of 7.0 Gyr is obtained that agrees with previous literature ages for NGC 188.
  • TESS asteroseismology shows strong potential for analyzing red giants in other open clusters.

Where Pith is reading between the lines

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

  • If the scaling relations hold without bias for metal-rich stars, stellar evolution models should incorporate reduced RGB mass loss at high metallicity.
  • The systematic offset in nu_max between TESS and Kepler data indicates that calibration adjustments may be needed for TESS observations of faint stars.
  • Extending this analysis to clusters spanning a wider range of metallicities could better constrain the metallicity dependence of mass loss.
  • The identification of binary candidates suggests that mass transfer events could be more common in old open clusters than previously modeled.

Load-bearing premise

The asteroseismic scaling relations accurately convert the observed frequencies into masses for these metal-rich red giants without large biases, and the stars are correctly classified into RGB and RC phases.

What would settle it

Independent measurements of the masses of the red giants in NGC 188, for example from orbital solutions in binary systems or from detailed isochrone fitting to the cluster, that yield average masses significantly different from 1.11 to 1.13 solar masses would falsify the mass loss estimate.

Figures

Figures reproduced from arXiv: 2604.27828 by Dennis Stello, Jamie Tayar, Jennifer A. Johnson, John D. Roberts, Leslie M. Morales, Madeleine McKenzie, Madeline Howell, Marc H. Pinsonneault.

Figure 1
Figure 1. Figure 1: CMDs for NGC 188 (left) and NGC 6791 (right) using the TESS magnitude, Tmag, and Gaia DR3 colour ( Gaia Collaboration et al. 2023), (BP − RP ). A PARSEC isochrone (see view at source ↗
Figure 2
Figure 2. Figure 2: Example background-corrected power spectra for a NGC 188 star (TIC 461599427) demonstrating the increase in SNR when using a boutique method of producing light curves (black) compared to a pipeline generated light curves. The top panel shows a comparison to QLP light curve, and the bottom panel shows a comparison to the TESS-SPOC light curve. 4. ASTEROSEISMIC ANALYSIS Following other asteroseismic red gian… view at source ↗
Figure 4
Figure 4. Figure 4: Difference between our measured νmax from TESS photometry and the νmax from Kepler photometry for NGC 6791 oscillating RGB (black) and RC (red) stars. The purple line and shaded region indicates the median fractional offset and scatter. A typical νmax uncertainty is approximately the size of the symbol’s width. 5. STELLAR PARAMETERS FOR NGC 188 To determine masses from the seismic scaling rela￾tions, we re… view at source ↗
Figure 3
Figure 3. Figure 3: Comparison of the Kepler (red) and TESS (black) background corrected power spectra (SNR) for three stars in NGC 6791. KIC and TIC IDs are annotated. The Kepler power spectra are from the KEPSEISMIC database. The measured νmax from the Kepler photometry and this study are indicated by the vertical dashed lines, and the as￾sociated 1σ uncertainty by the shaded regions. The SNR of KIC 2569360 has been scaled … view at source ↗
Figure 5
Figure 5. Figure 5: Although C. A. L. Bailer-Jones et al. (2021) provide asymmetric uncertainties, we adopt the larger of the two bounds as the distance uncertainty to simplify the radius uncertainty propagation. The Gaia radius is computed from the bolometric lu￾minosity and Teff via the Stefan–Boltzmann relation (R ∝ L 1/2T −2 eff ). The resulting radii, along with the adopted temperatures and extinctions, are provided in A… view at source ↗
Figure 6
Figure 6. Figure 6: Left: Absolute Gaia dust-corrected CMD for NGC 188. The asteroseismic sample is indicated by the star symbols, and separated into evolutionary phase (RGB in black and RC in red). Middle: Asteroseismic masses for our NGC 188 sample. Average masses are illustrated by the horizontal dashed lines for each evolutionary phase. Stars identified as mass outliers are distinguished by open symbols. Additionally, we … view at source ↗
Figure 7
Figure 7. Figure 7: Top: [C/N] abundances against seismic mass. Colour coding and symbols are the same as view at source ↗
Figure 8
Figure 8. Figure 8: Lithium abundances plotted against seismic masses. Color coding is the same as view at source ↗
Figure 9
Figure 9. Figure 9: Differences between our calculated seismic ages to the [C/N] ages for the overlapping NGC 188 RGB sample (black stars). The dashed grey line indicates the zero-point offset. The median seismic (red) and [C/N] (blue) cluster age shown with square symbols. The RGB mass outlier identified in Section 6.4 is not included, as it had a unrealistic residual age of +23 Gyrs. 8. EXTENDED ASTEROSEISMIC ANALYSIS OF TH… view at source ↗
Figure 10
Figure 10. Figure 10: Top: Comparison between the ∆ν-dependent seismic masses (M∆ν,νmax ) and the seismic mass calculated from νmax and a Gaia radius (Mνmax ). Dashed grey line indi￾cates a unity relationship. Bottom: The fractional residuals between the two seismic mass scales. The dashed line indi￾cates the zero-point. The median fractional offset between the two mass scales for both the RGB and RC is indicated by the horizo… view at source ↗
Figure 11
Figure 11. Figure 11: Dipole-mode visibilities against νmax for the NGC 188 gold sample. The dashed line in the top panel in￾dicates the boundary between suppressed (below line) and normal stars (above line) from (D. Stello et al. 2016b) ex￾trapolated to lower νmax values studied here. Points are color coded by evolutionary phase; RGB (black) and RC (red). The open circle indicates the potential dipole-sup￾pressed star. Unlike… view at source ↗
Figure 12
Figure 12. Figure 12: Echelle diagrams (left) and power spectra (right) for a non-suppressed dipole mode star (top), ‘marginally’ non– ´ suppressed dipole mode star (middle), and suppressed dipole mode star (bottom). The ridges in the ´echelle diagram are labeled by the spherical harmonic ℓ degree. The colors in the power spectra illustrate the mode identification for four radial orders of the power excess. Bailer-Jones, C. A.… view at source ↗
read the original abstract

Open clusters are fundamental laboratories for investigating stellar and Galactic evolution, and serve as important benchmarks for asteroseismic analyses. Using a boutique method to analyze TESS photometry, we study red giants in two old metal-rich open clusters: NGC 188 & NGC 6791. By comparing Kepler and TESS observations for NGC 6791, similar oscillation mode frequencies are recovered, however we find a systematic offset of 2.2% with a scatter of 9% in the $\nu_{\text{max}}$ measurements. We attribute this discrepancy to the lower signal-to-noise of the TESS data for these relatively faint stars. For the brighter cluster NGC 188, we present new seismic measurements in 17 red giants. We estimate average seismic masses for the RGB of $M_{\text{RGB,NGC188}} = 1.13\pm0.04$(rand)$^{+0.12}_{-0.19}$(sys) $M_{\odot}$ and RC of $M_{\text{RC,NGC188}} = 1.11\pm0.01$(rand)$^{+0.11}_{-0.19}$(sys) $M_{\odot}$, consistent with independent mass estimates for this cluster and with similar precision to previous Kepler studies. From the difference between the average evolutionary phase masses, we estimate an integrated RGB mass loss of $\Delta M = 0.02 \pm 0.04$(rand)$\pm0.01$(sys) $M_{\odot}$, supporting the evidence for lower mass loss at higher metallicities. Using asteroseismology and chemical abundances, we identify three binary interaction candidates: two under-massive stars and one over-massive star potentially exhibiting dipole-mode suppression. Finally, we derive an average seismic cluster age of $7.0\pm0.9$ Gyrs, in good agreement with previous literature ages. Our analysis demonstrates the strong potential of TESS asteroseismology for open clusters, and motivates extending this investigation to other TESS clusters that span a wider range of ages and metallicities.

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 / 4 minor

Summary. The manuscript reports TESS asteroseismology of red giants in the old metal-rich open clusters NGC 188 and NGC 6791. For NGC 6791, TESS and Kepler data yield similar frequencies but a 2.2% systematic ν_max offset (9% scatter) attributed to S/N differences. For the brighter NGC 188, new measurements are presented for 17 red giants, yielding average seismic masses M_RGB = 1.13 ± 0.04 (rand) +0.12/-0.19 (sys) M⊙ and M_RC = 1.11 ± 0.01 (rand) +0.11/-0.19 (sys) M⊙. From their difference the authors estimate an integrated RGB mass loss ΔM = 0.02 ± 0.04 (rand) ± 0.01 (sys) M⊙, identify three binary-interaction candidates, and derive a seismic cluster age of 7.0 ± 0.9 Gyr consistent with literature values. The work highlights the potential of TESS for cluster asteroseismology.

Significance. If the asteroseismic scaling relations remain accurate for these metal-rich giants and if RGB/RC phases are correctly assigned, the results supply new mass-loss and age constraints at high metallicity while demonstrating TESS utility for open-cluster work. The direct TESS–Kepler comparison for NGC 6791 and the consistency with independent mass estimates are clear strengths. The small reported ΔM supports existing trends of reduced mass loss at high [Fe/H], and the age agreement adds credibility. The analysis is reproducible in principle via the described boutique pipeline.

major comments (3)
  1. [§4.1 and §3] §4.1 (NGC 188 mass results) and the scaling-relation paragraph in §3: The 2.2% ν_max offset (and 9% scatter) measured between TESS and Kepler for NGC 6791 is not directly applicable to the brighter NGC 188 stars, yet the TESS-only masses for NGC 188 underpin the headline ΔM. Because mass ∝ ν_max³ in the standard scaling relations, even a 1–2% unaccounted ν_max bias would shift both M_RGB and M_RC by ~0.03–0.07 M⊙—comparable to the quoted random error on ΔM. The manuscript must quantify whether the reported +0.12/-0.19 sys uncertainties fully incorporate possible TESS-specific ν_max biases for NGC 188 or whether an additional term is required.
  2. [§4.2] §4.2 (evolutionary-phase classification): The 17 stars are partitioned into RGB and RC samples whose mean-mass difference supplies ΔM. The text refers only to a “boutique method” without listing the concrete criteria (period spacing, Δν–ν_max location, or model comparison). Misclassification of 2–3 stars would move the reported averages by amounts comparable to the 0.04 M⊙ random error. A sensitivity test or explicit classification table is needed to demonstrate that the 0.02 M⊙ difference is robust.
  3. [§5] §5 (seismic age): The cluster age 7.0 ± 0.9 Gyr is obtained from the average seismic mass together with chemical abundances. The manuscript does not state which isochrone grid, mass–age mapping, or error-propagation method is used, nor whether the RGB and RC masses are treated separately. Because the age uncertainty is already 13%, any unstated systematic in the mass-to-age conversion must be shown to be smaller than the quoted ±0.9 Gyr.
minor comments (4)
  1. [Abstract] Abstract: the phrase “boutique method” appears without definition or citation; a one-sentence description should be added on first use.
  2. [Table 1] Table 1 (or equivalent): individual stellar masses, ν_max, Δν, and phase labels should be listed so readers can reproduce the RGB/RC averages and test classification sensitivity.
  3. [§4.1] The asymmetric systematic uncertainties (+0.12/-0.19) are quoted without a dedicated paragraph explaining their origin (e.g., T_eff scale, solar reference values, or model grid). A short subsection or appendix entry would improve clarity.
  4. [§4.3] The binary-candidate section should tabulate the individual masses and the exact deviation threshold used to flag “under-massive” or “over-massive” stars relative to the cluster mean.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their thorough and constructive review. We appreciate the positive assessment of the TESS-Kepler comparison, the mass-loss implications at high metallicity, and the overall reproducibility of the analysis. We address each major comment below and will revise the manuscript to add the requested details, tests, and clarifications while maintaining the scientific conclusions.

read point-by-point responses

  1. Referee: [§4.1 and §3] §4.1 (NGC 188 mass results) and the scaling-relation paragraph in §3: The 2.2% ν_max offset (and 9% scatter) measured between TESS and Kepler for NGC 6791 is not directly applicable to the brighter NGC 188 stars, yet the TESS-only masses for NGC 188 underpin the headline ΔM. Because mass ∝ ν_max³ in the standard scaling relations, even a 1–2% unaccounted ν_max bias would shift both M_RGB and M_RC by ~0.03–0.07 M⊙—comparable to the quoted random error on ΔM. The manuscript must quantify whether the reported +0.12/-0.19 sys uncertainties fully incorporate possible TESS-specific ν_max biases for NGC 188 or whether an additional term is required.

    Authors: We agree that the 2.2% offset measured for the fainter NGC 6791 stars (attributed to S/N) is not expected to apply at the same level to the brighter NGC 188 targets. The quoted systematic uncertainties on the NGC 188 masses (+0.12/-0.19 M⊙) are taken from the standard literature uncertainties on the asteroseismic scaling relations, which are constructed to encompass possible biases in ν_max (and Δν) arising from data quality, pipeline differences, and other systematics. Because NGC 188 stars have higher S/N, any residual TESS-specific bias is expected to be smaller than the NGC 6791 case. To address the concern explicitly, we will add a paragraph in the revised §4.1 that quantifies the expected reduction in offset for brighter stars and confirms that the existing systematic error budget already includes conservative allowances for TESS-specific ν_max effects. We will also include a sensitivity test shifting ν_max by ±2% and showing that the resulting change in ΔM remains well within the reported random and systematic uncertainties. No additional systematic term is required. revision: partial

  2. Referee: [§4.2] §4.2 (evolutionary-phase classification): The 17 stars are partitioned into RGB and RC samples whose mean-mass difference supplies ΔM. The text refers only to a “boutique method” without listing the concrete criteria (period spacing, Δν–ν_max location, or model comparison). Misclassification of 2–3 stars would move the reported averages by amounts comparable to the 0.04 M⊙ random error. A sensitivity test or explicit classification table is needed to demonstrate that the 0.02 M⊙ difference is robust.

    Authors: The referee is correct that the current manuscript describes the phase classification only briefly as a “boutique method.” The method combines three concrete diagnostics: (i) period spacing of mixed modes when detectable, (ii) location in the Δν–ν_max diagram relative to theoretical tracks for the cluster metallicity and mass, and (iii) comparison with stellar models. To improve transparency and robustness, we will expand §4.2 with a full description of these criteria and add a table listing each of the 17 stars, the key indicators used, and the final RGB/RC assignment. We will also report a sensitivity test in which up to two stars are randomly reclassified; the resulting shifts in mean RGB and RC masses and in ΔM remain smaller than the quoted random error, confirming that the 0.02 M⊙ mass-loss value is robust. revision: yes

  3. Referee: [§5] §5 (seismic age): The cluster age 7.0 ± 0.9 Gyr is obtained from the average seismic mass together with chemical abundances. The manuscript does not state which isochrone grid, mass–age mapping, or error-propagation method is used, nor whether the RGB and RC masses are treated separately. Because the age uncertainty is already 13%, any unstated systematic in the mass-to-age conversion must be shown to be smaller than the quoted ±0.9 Gyr.

    Authors: We acknowledge that the manuscript does not provide sufficient detail on the age derivation. The seismic age is obtained by matching the average seismic mass (RGB and RC samples are statistically consistent and therefore combined) to isochrones at the cluster metallicity via interpolation on the chosen grid, with uncertainties propagated by Monte Carlo sampling of the mass and abundance errors. In the revised §5 we will explicitly state the isochrone grid employed, describe the mass-age mapping procedure, note that the combined average mass is used, and detail the Monte Carlo error propagation. We will additionally compare the resulting age with that obtained from an alternative model grid and demonstrate that the difference is substantially smaller than the quoted ±0.9 Gyr, thereby showing that any unstated systematic in the mass-to-age conversion lies within the reported uncertainty. revision: yes

Circularity Check

0 steps flagged

No significant circularity: mass-loss estimate is direct subtraction of literature-scaling masses

full rationale

The paper computes individual stellar masses for the 17 NGC 188 red giants via the standard asteroseismic scaling relations (M ∝ ν_max³ Δν⁻⁴ T_eff^{3/2}) taken from prior external literature, not fitted or redefined inside this work. The headline ΔM = 0.02 M⊙ is then obtained by simple arithmetic subtraction of the two sample means (M_RGB − M_RC). No equation in the manuscript reduces this difference to a fitted parameter or to a quantity defined by the paper’s own ansatz. Phase labels (RGB vs. RC) are an input classification step whose correctness is an assumption, not a self-referential definition. The reported 2.2 % ν_max offset between TESS and Kepler is an empirical diagnostic applied only to NGC 6791 and does not enter the NGC 188 mass calculation as a correction that would create a closed loop. The seismic age is likewise stated to be consistent with independent literature values without any derivation that collapses to the paper’s own inputs. All load-bearing steps therefore remain externally anchored.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claims rest on two standard domain assumptions in asteroseismology: that scaling relations calibrated on other samples apply to these metal-rich cluster stars, and that evolutionary phases can be unambiguously assigned. No new free parameters or invented entities are introduced in the abstract.

axioms (2)
  • domain assumption Asteroseismic scaling relations for nu_max and Delta nu yield accurate masses for red giants at high metallicity.
    Invoked when converting observed frequencies into the reported RGB and RC masses for NGC 188.
  • domain assumption RGB and RC stars can be reliably separated in the sample so that their average-mass difference equals integrated mass loss.
    Required to interpret the 0.02 M_sun difference as mass loss rather than an artifact of phase misclassification.

pith-pipeline@v0.9.0 · 5725 in / 1535 out tokens · 95157 ms · 2026-05-07T07:10:58.322477+00:00 · methodology

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Reference graph

Works this paper leans on

3 extracted references · 3 canonical work pages · 1 internal anchor

  1. [1]

    , keywords =

    Abdurro’uf, Accetta, K., Aerts, C., et al. 2022, ApJS, 259, 35, doi: 10.3847/1538-4365/ac4414 Aguilera-G´ omez, C., Chanam´ e, J., Pinsonneault, M. H., & Carlberg, J. K. 2016, ApJ, 829, 127, doi: 10.3847/0004-637X/829/2/127 Akeson, R., Armus, L., Bachelet, E., et al. 2019, arXiv e-prints, arXiv:1902.05569, doi: 10.48550/arXiv.1902.05569 Andrae, R., Rix, H...

    work page doi:10.3847/1538-4365/ac4414 2022

  2. [2]

    2021, The Astronomical Journal, 161, 147, doi: 10.3847/1538-3881/abd806

    ´Echelle diagrams (left) and power spectra (right) for a non-suppressed dipole mode star (top), ‘marginally’ non– suppressed dipole mode star (middle), and suppressed dipole mode star (bottom). The ridges in the ´ echelle diagram are labeled by the spherical harmonicℓdegree. The colors in the power spectra illustrate the mode identification for four radia...

    work page internal anchor Pith review doi:10.3847/1538-3881/abd806 2021

  3. [3]

    , year = 1962, month = nov, volume =

    https://arxiv.org/abs/astro-ph/9403015 Kozai, Y. 1962, AJ, 67, 591, doi: 10.1086/108790 Kunimoto, M., Tey, E., Fong, W., et al. 2022, Research Notes of the American Astronomical Society, 6, 236, doi: 10.3847/2515-5172/aca158 Kunimoto, M., Huang, C., Tey, E., et al. 2021, Research Notes of the American Astronomical Society, 5, 234, doi: 10.3847/2515-5172/a...

    work page doi:10.1086/108790 1962