{"id":"decec248-97fa-48ed-a4ce-6670e4b1e065","arxiv_id":"2508.14161","paper_version":1,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Partially stripped stars can be more luminous than pure-helium stars of the same mass, with the maximum luminosity at an intermediate hydrogen profile slope, and new fitting relations are provided.","lead":"Stripped stars, such as Wolf-Rayet stars and helium stars, are usually modeled as either fully hydrogen-free or fully mixed. This paper shows that partially stripped stars, with a hydrogen envelope left behind, can be up to several times more luminous than their fully stripped counterparts of the same mass, and provides new mass-luminosity relations for them.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The one-parameter linear H-gradient family may not bracket real step-like profiles; if a step profile yields luminosity above the linear maximum, the claimed maximum MLR and mass inferences shift.","rationale":"The paper is a solid, well-executed numerical study, and the reader's ACCEPT with moderate confidence is reasonable. The most load-bearing concern is the one the reader already flagged: the synthetic grid's use of a single linear H-gradient parameterization to bracket all real partially stripped structures. The central result—that partially stripped configurations can be more luminous than pure-He stars—and the derived MLRs (especially the maximum and minimum curves) depend on this family adequately covering the luminosity range of real profiles. The authors' only treatment of non-linear (step-like) profiles is qualitative: they state in Sect. 2.4 that such features 'tend to reduce the luminosity' and fall between the min and max, but no quantitative test is presented. Because the H-shell luminosity is extremely sensitive to the shell's position and local gradient, and because the claimed maximum occurs at low s values that are only marginally represented in the evolution grid, the bracket property is not yet established. If it fails, the maximum MLR could be either an under- or over-estimate, directly affecting the inverse mass predictions that are a key deliverable of the paper. A concrete test—feeding actual evolutionary profiles into the structure solver, or constructing explicit step profiles—would settle this. Since the concern is specific and testable, and the paper's applicability hinges on it, I recommend a CONDITIONAL verdict: accept the paper contingent on this bracket verification. This is not a rejection; the underlying physics is plausible and the paper is otherwise careful, but the central claim deserves this additional check before the MLRs are used for quantitative mass/luminosity inference.","tokens_in":26196,"tokens_out":3586,"duration_ms":40581,"concrete_test":"Take the post-MS core-He-burning evolutionary models from Sect. 2.4 (which contain semiconvective step-like features) and, for a subset spanning Mtot, XH, Z, feed their actual composition profiles directly into the MESA structure solver using the same settings as Sect. 2.2 (dxdt_nuc_factor=0, mix_factor=0, relax_composition_filename, hydrostatic, thermal-balance threshold 0.1%). Compare the converged surface luminosity with the paper's predicted Lmin and Lmax at the same Mtot, XH, Z. If any evolutionary profile yields L > Lmax or L < Lmin by more than the typical fitting error (~0.02–0.03 dex), the linear-family bracket fails. As a second check, construct idealized step profiles (constant X= XH down to a shell mass m_shell, then a linear drop to X=0 over a small mass interval) and maximize luminosity over m_shell; if the maximum exceeds the linear-family Lmax, the central claim is quanti","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim—that for a given mass the maximum luminosity occurs at an intermediate H-profile slope and exceeds the pure-He value—rests on the synthetic grid of Sect. 2.2, in which every partially stripped structure is represented by a single linear H gradient s = dX/dQ. In Sect. 2.4 the authors acknowledge that their dedicated evolution grid develops 'small and large step-like features' in the H profile due to semiconvective and fully convective regions. They assert (Sect. 2.4) that the effect of such steps on the minimum and maximum MLRs is minimal because 'more H-rich material in the steps tends to reduce the luminosity,' so luminosities fall between the predicted minimum and maximum. However, this is a qualitative statement, not a quantitative test. The maximum luminosity in Fig. 5 occurs at s ≈ 1–3 for high XH, a regime populated in the evolution grid mainly during the MS and HG phase. If a step-like profile places the H-burning shell at a slightly different mass coordinate or with a different local gradient than any linear profile of the same Mtot, XH, and Z, the shell luminosity—which dominates the total budget (Fig. 3)—could in principle exceed the linear-family maximum. In that case the 'maximum' MLR of Eq. 2 would not be a true upper bound, and the inverse mass estimates (Sect. 3.4, Table 2) would be systematically too low. Conversely, if shallow, linear profiles of the kind producing L_max are not actually reachable by real stripping, the maximum curve would overestimate achievable luminosities. Either way, the bracket property that underpins the paper's applications is not verified. The reader's weakest_assumption identifies exactly this point, and it is the most load-bearing unverified input in the paper.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper revisits mass-luminosity relations (MLRs) for stripped stars by constructing a large grid of MESA synthetic structure models (5910 models) that represent partially stripped stars as a pure-He core plus an H-depleted envelope with a linear H/He gradient of slope s = dX/dQ. The grid varies total mass, surface H abundance XH, slope s, and metallicity (Z = 0.008 and 0.004), with explicit convergence to thermal and hydrostatic balance (0.1% luminosity mismatch). The central result is that, for fixed mass and XH, luminosity is non-monotonic in s: it rises from the chemically homogeneous limit (s = 0), reaches a maximum at intermediate s, and then declines to the pure-He limit (s = ∞). The maximum can exceed the pure-He luminosity by a factor of 2–4, because the H-burning shell contributes disproportionately to the total luminosity. The authors provide fit formulae for minimum, maximum, and pure-He luminosities and their inverses, and demonstrate the impact of the higher luminosities on winds with PoWRhd hydrodynamic atmosphere models. They apply the relations to four observed partially stripped stars and discuss implications for their evolutionary channels and masses.","tokens_in":26677,"tokens_out":3695,"duration_ms":47508,"significance":"If the central claim holds, the paper fills a genuine gap: existing MLRs cover either chemically homogeneous or fully stripped pure-He stars, neither of which captures the partially stripped configurations that binary evolution and recent observations indicate are common. The predicted over-luminosity of partially stripped stars directly affects inferred masses, Eddington parameters, wind mass loss, and supernova progenitor interpretations. The paper's strengths include the large and systematically constructed model grid, the explicit thermal-balance convergence criterion, the dedicated evolution grid used to motivate the slope range, quantitative CNO-abundance tests (≤0.02 dex), and the public Python script/online calculator for the MLR fits. The comparison with observed partially stripped stars is a useful sanity check, and the wind models illustrate a potentially drastic luminosity dependence of mass loss. The work is not circular: the luminosity behavior is a numerical output, and the fit coefficients are presented as fits to the grid.","major_comments":[{"comment":"The maximum MLR (Eq. 2) is the envelope over the one-parameter family of linear H gradients. The authors assert in Sect. 2.4 that step-like H profiles from semiconvective/convective regions have only minimal effect because 'more H-rich material in the steps tends to reduce the luminosity,' so real structures fall between the predicted minimum and maximum. This assertion is not tested quantitatively. Since the central claim — that the maximum luminosity for a given mass and XH is captured by the linear-family maximum — is load-bearing for the inverse mass estimates in Sect. 3.4 and Table 2, I ask for a direct test: take representative H profiles from the evolution grid (especially those with large step-like features), construct MESA structure models with those exact profiles using the same relax_composition approach, and compare the resulting luminosities with the Lmin/Lmax curves of Eq.","section":"Sect. 2.4 and Sect. 3.3"},{"comment":"For high XH, the luminosity maximum occurs at effective temperatures below 10 kK (dashed lines in Fig. 5), which is cooler than the observed partially stripped stars used for comparison in Sect. 5. The authors discuss this and choose to rely mainly on mass and luminosity, which is reasonable, but the practical utility of the maximum MLR for hot, partially stripped stars is then less direct than the abstract suggests. I would like the text to state more explicitly over which temperature range the maximum relation is intended to apply, and whether the cool maximum structures are expected to be realized in nature given the inflation uncertainties.","section":"Sect. 3.2 / Fig. 5"}],"minor_comments":[{"comment":"Minor typo: 'Mtot values ranges' should be 'Mtot values range'.","section":"Sect. 2.3"},{"comment":"F10 is fixed to 0.005 rather than fitted; this should be noted in the main text near Eq. (2), as it may otherwise be confused with a free coefficient.","section":"Sect. 3.3 / Table C.1"},{"comment":"The abscissa uses e^{-1/s} to map s = 0 to 1 and s = ∞ to 0. This is useful, but the dual axis labels (e^{-1/s} and s) could be clarified in the caption, since the non-expert reader may wonder about the mapping.","section":"Fig. 5 and Appendix B"},{"comment":"The PoWRhd wind models are only described by reference to Sabhahit et al. (2025); a sentence summarizing the inner boundary conditions or the mass-loss normalization would improve self-containedness.","section":"Sect. 4"},{"comment":"The statement that 'small and large step-like features can develop' would benefit from a figure or quantitative description of typical step amplitudes in the evolution grid, especially because the paper argues these steps do not affect the MLR extremes.","section":"Sect. 2.4"}],"recommendation":"major_revision","confidential_remarks":"The paper is well within the scope of A&A and the central result is interesting and likely correct. The main risk is the unaudited linear-profile assumption: the maximum MLR is an envelope over linear H gradients, and the authors' argument that real step-like profiles fall inside the band is only qualitative. A quantitative test using actual evolution-grid profiles would settle this and, if it passes, would make the paper fully convincing. I therefore recommend major revision rather than rejection: the requested test is well-defined and feasible within the manuscript's scope."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThis paper does what it says: it computes a large grid of MESA synthetic structures for stripped stars with a residual H envelope, maps the minimum and maximum luminosity as a function of mass and surface H, and provides fits plus an inversion. The new content is the partially stripped regime. Gräfener et al. had only the fully homogeneous and pure-He extremes; this shows the luminosity peaks at an intermediate H-profile slope and can beat the pure-He value by up to a factor of a few. I think that result is real. The grid is large (5910 models), the thermal-balance convergence criterion is explicit, CNO abundance effects are checked at the 0.02 dex level, and the fit errors are small. The observed Magellanic Cloud stars sit inside the predicted bracket. On the numerical side this is careful work.\n\nThe soft spot is exactly what the stress-test note says: the bracket property is only verified for a one-parameter family of linear H gradients. The evolution grid shows step-like profiles, and the paper dismisses their effect with a qualitative argument—more H-rich material in steps lowers luminosity. That may be right, but it is not a test. If a real step profile puts the H shell at a slightly different mass coordinate or with a different local gradient, the shell luminosity could in principle exceed the linear-family maximum. The 'maximum' relation would then not be a true upper bound, and the inverse mass estimates would shift. I do not think this sinks the paper. The qualitative claim that partial stripping can be more luminous than pure-He is robust, and the fitted relations are clearly presented as fits to the grid. But the max MLR should be advertised as 'maximum over our synthetic family' until step profiles are actually run, not as a universal upper limit.\n\nThe other caveat—cool effective temperatures at high XH for the maximum-luminosity models—is flagged by the authors and sensibly downplayed. They use luminosity and mass for the observational comparisons, which is the right choice given the larger temperature uncertainties.\n\nWho should read it: anyone modeling stripped-envelope SN progenitors, interpreting partially stripped stars in the Magellanic Clouds, or building wind models that need L/M inputs. It deserves a serious referee; the right ask in review is a quantitative step-profile test, not a rewrite. I would send it out, and I would cite it.","headline":"Worth taking seriously: the partially stripped MLRs fill a real gap and the non-monotonic luminosity behavior is credible, but the 'maximum' relation is only a maximum over a one-parameter linear-profile family, and the step-profile caveat is under-tested.","tokens_in":27146,"tokens_out":2692,"would_cite":true,"duration_ms":32026,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Partially stripped stars can outshine pure-helium stars of the same mass by up to a factor of several, because a thin hydrogen-burning shell — not the helium core — dominates the energy output; the paper turns this into new mass-luminosity","keywords":["stripped stars","mass-luminosity relation","partial stripping","helium stars","hydrogen shell burning","Eddington parameter","stellar winds","Wolf-Rayet stars"],"falsifier":"A partially or fully stripped star with a dynamically determined mass (from binary orbital motion) whose measured luminosity, for its measured surface hydrogen fraction, lies above the fitted maximum-luminosity curve by more than the ~0.03 dex fitting error — or below the minimum homogeneous curve — would refute the mass-luminosity relations. A softer check: measuring the wind of a star near the predicted maximum luminosity (e.g., a 10 solar-mass, XH = 0.1 object at log L/L_sun ≈ 5.48), where the models predict log Mdot ≈ -5.85 and v_inf ≈ 330 km/s; finding a fast (greater than 1000 km/s), wea","tokens_in":26153,"feed_emoji":"⭐","tokens_out":17302,"duration_ms":159013,"temperature":0.7,"pith_summary":"This paper asks how brightly a stripped star can shine for its mass after losing part or all of its hydrogen envelope, and answers with a result that reverses the usual expectation. Using synthetic stellar-structure models in which the leftover hydrogen is described by a single gradient slope, the authors find that luminosity rises with hydrogen content, peaks for a partially stripped configuration, and then falls toward the pure-helium value — so the most luminous configuration of a given mass is not the fully stripped one, but an intermediate one, brighter by a factor of two up to three or four. The cause is structural: the thin hydrogen-burning shell dominates the total luminosity budget even though the helium core holds most of the mass. The paper converts this into fitted minimum, maximum, and pure-helium mass-luminosity relations, and shows that the higher luminosities push these stars toward their Eddington limit, sharply raising predicted wind mass loss. That matters because partially stripped stars have recently been confirmed observationally, while the standard relations used to weigh them cover only the two extremes.","feed_headline":"Outshining helium: partly stripped stars shine 2–4 times brighter","feed_subtitle":"New fits replace the pure-helium brightness limit and predict winds up to ~30 times stronger","key_machinery":"The central object is the synthetic structure model: a MESA model built from a prescribed composition rather than evolved, with a pure-He core, an H-depleted envelope, and one H/He transition slope s = dX/dQ (Q a normalized mass coordinate; s = 0 fully homogeneous, s = ∞ pure He), relaxed to hydrostatic and thermal balance with burning and mixing switched off. These models expose the load-bearing mechanism: in a typical partially stripped star the H-burning shell contributes about three-quarters of the luminosity, the He core only about one-quarter. The practical machinery is fit relation Eq. (2) — the Gräfener et al. (2011) functional form plus an exponential XH term for the pure-He limit —","core_discovery":"For fixed total mass, stripped-star luminosity is non-monotonic in the hydrogen-profile slope s = dX/dQ: it rises steeply as a hydrogen-burning shell develops, peaks at an intermediate slope — the partially stripped configuration — then falls toward the pure-helium limit as opacity rises and mean molecular weight drops. The peak can exceed the pure-helium luminosity by a factor of roughly two, up to 3–4, overturning the homology intuition that the highest mean-molecular-weight configuration is the most luminous. The paper packages this into fit formulae for minimum, maximum, and pure-helium luminosities (and inverse masses), and shows with hydrodynamically consistent wind models that the Edd","pith_inferences":["If the central claim holds, the most over-luminous stripped stars should be found at surface hydrogen fractions around 0.1–0.3, the regime where the luminosity excess peaks; the current observed sample, with XH ≈ 0.3–0.7, sits on the descending branch, so targeted searches there would give the cleanest test.","Eclipsing-binary or asteroseismic masses for a handful of partially stripped stars could break the degeneracy between shallow-slope (early stripping) and steep-slope (late stripping) interpretations that the two-way relations currently leave open.","The same synthetic-slope construction could be extended to re-expanding post-He-burning structures with both He and H shells — explicitly outside this grid — which would probably push the minimum mass for a given luminosity even lower and affect the interpretation of objects like 2dFS 163.","If the stronger winds are real, the mass lost during the partially stripped phase should leave an abundance fingerprint (e.g., altered N/C and He/H) in subsequent Wolf-Rayet and stripped-envelope supernova progenitors, giving an independent check on the predicted 0.1–0.5 solar-mass envelope removal."],"forward_implications":["For a given luminosity and surface hydrogen fraction, a partially stripped star can be only about 60 percent as massive as a pure-helium star, so luminosity-based mass estimates for these objects need revision.","The maximum-luminosity curves bracket the measured masses and luminosities of the observed Magellanic Cloud stripped stars; the two lowest-mass objects are consistent with shallow slopes s ≈ 2–2.6, pointing to early core-He burning or Hertzsprung-gap binary stripping rather than wind stripping of an evolved supergiant.","At maximum luminosity, predicted mass-loss rates rise by about 1.5 dex and terminal velocities fall by about 1 dex relative to pure-He cases; over the few times 10^5 yr lifetime of the phase this can remove the entire residual envelope, turning a partially stripped star into a fully stripped one and potentially changing the supernova type (IIb vs. Ibc).","The wind models produce a double-horned He II 4686 Å emission profile in an otherwise cool spectrum, a signature that need not imply a disk or a black-hole companion.","For stars whose spectroscopically measured mass matches the pure-He value despite high surface hydrogen (2dFS 2553, Sk−71◦ 35), two different internal slopes are possible, so the relations define ranges of plausible internal structure rather than a unique answer."],"supporting_citations":[{"why":"Supplies the prior mass-luminosity fit relations for homogeneous and pure-He stars that this paper extends, and the functional form of the fit.","marker":"Gräfener et al. (2011)"},{"why":"Defines the H-profile slope s = dX/dQ and the technique of building synthetic structure models from prescribed composition profiles.","marker":"Schootemeijer & Langer (2018)"},{"why":"Provides the synthetic-structure-model approach and the opacity/mean-molecular-weight competition invoked to explain the luminosity downturn at low s.","marker":"Farrell et al. (2022)"},{"why":"Documents the MESA code in which all structure and evolution models are computed.","marker":"Paxton et al. (2011)"},{"why":"Supplies the diffusive semiconvection treatment used in the evolution grid that brackets the realistic slope range s ≈ 1–30.","marker":"Langer et al. (1983)"},{"why":"Supplies the four observed partially stripped Magellanic Cloud stars whose masses and luminosities bracket the MLR curves and whose internal slopes are inferred.","marker":"Ramachandran et al. (2023, 2024)"},{"why":"Supplies the additional observational stripped-star sample in the Magellanic Clouds used to test the relations.","marker":"Götberg et al. (2023)"},{"why":"Provides the few-times-10^5-yr lifetime of the partially stripped phase, used to estimate total envelope mass loss.","marker":"Dutta & Klencki (2024)"},{"why":"Documents the PoWRhd model inputs for the hydrodynamically consistent wind models.","marker":"Sabhahit et al. (2025)"}],"fun_headline_variants":["Partially stripped stars outshine pure-helium ones","Stripped-star brightness peaks at partial stripping","Partially stripped stars up to 4x brighter than pure He","New mass-luminosity fits for stripped stars","Maximum luminosity at partial stripping, not pure He"],"cache_read_input_tokens":2688,"weakest_assumption_plain":"The load-bearing premise is that one linear hydrogen gradient — the slope s = dX/dQ — captures the range of H/He profiles that real stripping leaves behind; if semiconvective steps make actual profiles deviate strongly from linear, the location and height of the luminosity maximum, and the fits built on it, could shift.","fun_headline_variants_meta":{"raw":{"variants":["Partially stripped stars outshine pure-helium ones","Stripped-star brightness peaks at partial stripping","Partially stripped stars up to 4x brighter than pure He","New mass-luminosity fits for stripped stars","Maximum luminosity at partial stripping, not pure He"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000229,"raw_usage":{"total_tokens":1370,"prompt_tokens":855,"completion_tokens":515,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":599,"completion_tokens_details":{"reasoning_tokens":439}},"tokens_in":599,"tokens_out":515,"duration_ms":5830,"temperature":1.0,"reasoning_tokens":439,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-05T18:44:32.340444+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A partially or fully stripped star with a dynamically determined mass (from binary orbital motion) whose measured luminosity, for its measured surface hydrogen fraction, lies above the fitted maximum-luminosity curve by more than the ~0.03 dex fitting error — or below the minimum homogeneous curve — would refute the mass-luminosity relations. A softer check: measuring the wind of a star near the predicted maximum luminosity (e.g., a 10 solar-mass, XH = 0.1 object at log L/L_sun ≈ 5.48), where the models predict log Mdot ≈ -5.85 and v_inf ≈ 330 km/s; finding a fast (greater than 1000 km/s), wea","supporting_citations":[{"cited_title":"& Langer, N","cited_arxiv_id":null,"evidence_quote":"Defines the H-profile slope s = dX/dQ and the technique of building synthetic structure models from prescribed composition profiles."},{"cited_title":"H., Meynet, G., & Eldridge, J","cited_arxiv_id":null,"evidence_quote":"Provides the synthetic-structure-model approach and the opacity/mean-molecular-weight competition invoked to explain the luminosity downturn at low s."},{"cited_title":"& Klencki, J","cited_arxiv_id":null,"evidence_quote":"Provides the few-times-10^5-yr lifetime of the partially stripped phase, used to estimate total envelope mass loss."}],"review_version":1}