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arxiv: 2602.04645 · v1 · submitted 2026-02-04 · 🌌 astro-ph.SR · astro-ph.GA

The incidence of LBV variability in the LMC

V. M. Kalari , J. S. Vink , C. Furey , R. Salinas , A. Udalski , M. Pawlak This is my paper

Pith reviewed 2026-05-16 07:12 UTC · model grok-4.3

classification 🌌 astro-ph.SR astro-ph.GA
keywords luminous blue variablesS Dor variabilityLarge Magellanic Cloudblue supergiantsstellar variabilityOGLE surveymassive star evolution
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The pith

The S Dor phase of luminous blue variables lasts at most about 1000 years

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

The paper surveys light curves of 87 blue supergiants in the Large Magellanic Cloud with twenty years of OGLE data to measure the incidence of S Dor-type variability. Only one object displays the expected aperiodic photometric changes, yet its low luminosity and spectral traits prevent classification as a true LBV. From the known population of S Dor variables the authors derive an upper limit on phase duration of roughly 1000 years. This timescale matches a prior duty-cycle result from the Small Magellanic Cloud and is orders of magnitude shorter than the lifetimes used in standard evolutionary calculations. The work suggests the variability may arise from Eddington-limit physics across a broader mass range rather than marking a single high-mass stage.

Core claim

Based on currently known stellar population of S Dor variables in the LMC, the lifetime of the S Dor phase is at most ∼10^3 yrs, in agreement with our duty cycle study based on OGLE data in the SMC. This is orders of magnitude shorter than assumed in literature. Survey of 87 BSgs identified one candidate with S Dor photometric variations, but new spectra and low luminosity led the authors to withhold LBV classification.

What carries the argument

OGLE long-term light-curve monitoring of a sample of 87 blue supergiants, combined with the census of known S Dor variables, to place an empirical upper bound on the duration of the variability phase.

Load-bearing premise

The known population of S Dor variables in the LMC is complete and the surveyed sample of 87 blue supergiants is large enough to reveal the true incidence rate.

What would settle it

Finding additional S Dor variables among the remaining known blue supergiants in the LMC, or obtaining spectra that confirm the single candidate as a genuine LBV, would directly test the short lifetime upper limit.

Figures

Figures reproduced from arXiv: 2602.04645 by A. Udalski, C. Furey, J. S. Vink, M. Pawlak, R. Salinas, V. M. Kalari.

Figure 1
Figure 1. Figure 1: Top:Spectral types of Bsgs with OGLE data (red) and the total number of Bsgs from our sample (solid line). Bottom: The recovery fraction for Gaia multi-epoch photometry. Known LBVs are not shown. by even or order of magnitude. On the other hand, from our SMC light-curve analysis (Kalari et al. 2018), we found just 1 LBV candidate amongst the general population of B super￾giants, suggesting the LBV phenomen… view at source ↗
Figure 2
Figure 2. Figure 2: Representative example of the time series photometric analysis, where the color gradient marks the density of the points. [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Histogram of 1/η values computed using OGLE and Gaia light curves, in logarithmic scale. The positions of the identi￾fied LBVs, HD 269216 and [ST92] 4-13 are marked. The best-fit Gaussian to the population except the outliers (log (1/η) > 1) is shown by the dashed line. The dotted line shows the 3σ cut-off. and Gaia DR3 4657649594536852352), a B1 I star, with the magnitude changing by nearly 1 mag over the… view at source ↗
Figure 4
Figure 4. Figure 4: Left: I-band light curve of [ST92] 4-13, with the (V − I) color shown at the bottom. Data are from the OGLE-IV photometry. The red asterisk marks the epoch when the spectral data were taken. Right: Gaia G and (BP − RP) magnitude and color light curves of HD 269216, shown at the top and bottom panel respectively. examining these further without future epoch photometry con￾firming the variability. 3.2. von N… view at source ↗
Figure 5
Figure 5. Figure 5: Kiwi-GA fit of [ST92] 4-13. See Section 4.1.2 for details. Article number, page 5 of 11 [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: The location in the Hertzsprung-Russell diagram of [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Left: Near-infrared (J − H) vs. (H − Ks) color-color diagram of known sgB[e] (open squares), warm hypergiants (open trian￾gles), cBe stars (open circles), known S Dor variables (blue dots), BSgs (small dots), and [ST92] 4-13, HD 269216 (red asterisks). Data taken from Humphreys et al. (2017b). The dashed red line is the main-sequence locus. Right: Mid-infrared [3.6µm]−[4.5µm] vs. [5.8µm]−[8.0µm] color-colo… view at source ↗
read the original abstract

Luminous blue variables (LBVs) exhibit unique variability features, characterized by episodic outbursts ($>$1 mag) accompanied by spectroscopic changes (S Dor variables). It is debated if all massive stars undergo an LBV-like phase during their evolution, or instead LBVs are exotic phenomena. We aim to quantify the incidence of LBV-like variability in the blue supergiant (BSgs) population of the Large Magellanic Cloud (LMC) using the OGLE survey. Here, we extend previous work in the Small Magellanic Cloud to the LMC, where we examine the light curves of 87 B Supergiants (BSgs) (out of 254 known BSgs) spanning timescales of twenty years, and 37 objects across a three year timescale for aperiodic variations resembling known S Dor variables. One blue supergiant, [ST92] 4-13 shows S Dor type photometric variations. New spectra of this object reveals a potential change in spectral type compared to the literature classification. However, based on its spectral characteristics and low luminosity and mass, we do not currently classify it as an LBV. Our study highlights the need to classify bona fide LBVs as stars undergoing both photometric and spectroscopic variations. Based on currently known stellar population of S Dor variables in the LMC, the lifetime of the S Dor phase is at most $\sim$10$^3$ yrs, in agreement with our duty cycle study based on OGLE data in the SMC. This is orders of magnitude shorter than assumed in literature. Our discovery of LBV-like variability at low luminosities may suggest that S Dor variations could arise from Eddington limit related physics over a wide range of stellar masses, rather than being linked to a unique evolutionary stage.

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 analyzes 20-year OGLE light curves of 87 blue supergiants (out of 254 known) in the LMC for aperiodic S Dor-like variability, identifies photometric variations in one object ([ST92] 4-13) but declines to classify it as an LBV on grounds of low luminosity, mass, and unconfirmed spectroscopic change. It derives an upper limit of ∼10^3 yr on the S Dor phase lifetime from the ratio of the currently known LMC S Dor population to the BSg population, consistent with the authors' prior SMC duty-cycle result and orders of magnitude below literature values, while suggesting such variability may occur across a wide mass range via Eddington-limit physics.

Significance. If the completeness assumption holds, the short lifetime upper limit would substantially revise massive-star evolutionary models by shortening the LBV phase, with direct implications for supernova progenitor channels and stellar feedback. The agreement with the independent SMC analysis and the cautious non-classification of the candidate add weight, though the result's impact is limited by the lack of internal completeness validation.

major comments (3)
  1. [lifetime estimate (abstract and concluding discussion)] Lifetime estimate (abstract and concluding discussion): the ∼10^3 yr upper limit is obtained by dividing the known S Dor population by the total BSg population. This bound is valid only if the external catalog is complete; the manuscript contains no completeness correction, selection-function modeling, or Monte-Carlo simulation of undetected variables. An undetected population only a factor of a few larger would proportionally relax the limit and erase the claimed discrepancy with literature values.
  2. [sample selection (§2)] Sample selection (§2): only 87 of the 254 known BSgs are examined. Without a demonstration that this subsample is representative in luminosity, mass, or variability properties, the observed incidence rate cannot be reliably extrapolated to the full population, weakening the incidence-based lifetime constraint.
  3. [classification of [ST92] 4-13 (§3)] Classification of [ST92] 4-13 (§3): the decision not to classify the object as an LBV is appropriate, but the reported potential spectral-type change is described only qualitatively. Direct spectral comparison or quantitative equivalent-width measurements of key lines (e.g., He I, Balmer) would allow readers to evaluate the strength of the non-classification independently.
minor comments (2)
  1. [abstract] The abstract mentions '37 objects across a three year timescale' while the main text refers to the full 20-year baseline for the 87-object sample; clarify the exact temporal coverage per object to avoid confusion.
  2. [figures] Light-curve panels for the candidate should include a side-by-side comparison with a confirmed S Dor variable from the same survey to illustrate the similarity in amplitude and timescale.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the thoughtful and constructive report. We address each major comment below and have revised the manuscript accordingly to improve clarity and acknowledge limitations.

read point-by-point responses

  1. Referee: Lifetime estimate (abstract and concluding discussion): the ∼10^3 yr upper limit is obtained by dividing the known S Dor population by the total BSg population. This bound is valid only if the external catalog is complete; the manuscript contains no completeness correction, selection-function modeling, or Monte-Carlo simulation of undetected variables. An undetected population only a factor of a few larger would proportionally relax the limit and erase the claimed discrepancy with literature values.

    Authors: We agree that the ∼10^3 yr figure is an upper limit predicated on the completeness of the known S Dor and BSg catalogs. The manuscript already frames the result as 'at most' based on currently known populations, but we will revise the abstract and discussion sections to state this assumption explicitly and to note that a larger undetected population would proportionally increase the implied lifetime. We will also compare our limit to literature values with this caveat in place. No Monte-Carlo simulation is feasible with the available data, but the upper-limit nature of the estimate remains valid. revision: yes

  2. Referee: Sample selection (§2): only 87 of the 254 known BSgs are examined. Without a demonstration that this subsample is representative in luminosity, mass, or variability properties, the observed incidence rate cannot be reliably extrapolated to the full population, weakening the incidence-based lifetime constraint.

    Authors: The 87 objects were those with OGLE light curves spanning the full 20-year baseline. We will add to §2 a direct comparison of the luminosity and mass distributions (using the same catalogs) between the 87-object subsample and the full 254, together with a brief statement on whether the subsample appears representative. If differences are found, we will qualify the extrapolation in the lifetime discussion. revision: yes

  3. Referee: Classification of [ST92] 4-13 (§3): the decision not to classify the object as an LBV is appropriate, but the reported potential spectral-type change is described only qualitatively. Direct spectral comparison or quantitative equivalent-width measurements of key lines (e.g., He I, Balmer) would allow readers to evaluate the strength of the non-classification independently.

    Authors: We will revise §3 to include quantitative equivalent-width measurements of He I and Balmer lines from the new spectra, together with a side-by-side comparison to the literature values used for the original classification. This will allow readers to assess the significance of any change independently while retaining our conservative non-classification. revision: yes

Circularity Check

0 steps flagged

No circularity: S Dor lifetime upper limit uses external known-population ratio, independent of current survey fits or self-citations

full rationale

The paper's central lifetime estimate (~10^3 yr) is obtained by dividing the number of currently known LMC S Dor variables by the total BSg population and scaling by the BSg evolutionary timescale. This ratio is taken directly from external catalogs and is not derived from any equation fitted to the OGLE light curves of the 87 surveyed objects. The single candidate variable is explicitly excluded on spectroscopic and luminosity grounds, leaving the known count unchanged. The SMC duty-cycle reference is cited only for agreement and is not required to derive the LMC bound. No self-definitional loop, fitted-input prediction, or load-bearing self-citation chain exists; the derivation remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The lifetime upper limit rests on the completeness of the pre-existing S Dor catalog and the assumption that the 87-star sample captures the true incidence rate; no new free parameters or invented entities are introduced.

axioms (1)
  • domain assumption The known population of S Dor variables in the LMC is complete and representative for lifetime estimation.
    Invoked to convert observed incidence into an upper limit on phase duration.

pith-pipeline@v0.9.0 · 5645 in / 1310 out tokens · 35199 ms · 2026-05-16T07:12:29.590973+00:00 · methodology

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