{"id":"f63a7f80-cdf1-4a54-9de9-078df3dd7e61","arxiv_id":"2608.10737","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Multi-epoch spectro-polarimetry shows that Hα polarization varies strongly in most Herbig Ae/Be stars but remains nearly constant in classical Be stars over 28 months.","lead":"This paper tracks polarized light from 21 bright stars over 28 months, showing that hydrogen emission polarization changes strongly in young Herbig stars but stays steady in classical Be stars. It is among the few long-term spectro-polarimetric records and provides a reference sample for studying how gas disks around hot stars evolve.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Herbig/Be variability dichotomy rests on visual, error-free line-effect classifications; unquantified 1.2m/2.5m instrumental polarization for first-epoch Be data is an additional systematic.","rationale":"The reader's verdict is CONDITIONAL, and my concern is a refinement of their weakest assumption. The paper's value is the dataset, but the headline conclusion compares two small samples on the basis of visual classifications. The most dangerous failure mode is not fraud or modeling error; it is that a two-epoch, two-telescope, uncorrected-IP dataset cannot by itself establish a statistically significant class difference. I do not think the paper should be rejected; the observations are rare and the per-source discussion is careful. But the abstract's 'significant variability' needs to be backed by a number and a test. The proposed check is straightforward to do with existing data and would settle the concern. Therefore the reader's conditional accept remains the right verdict.","tokens_in":24610,"tokens_out":7576,"duration_ms":82688,"concrete_test":"Recompute the line-effect classifications quantitatively for every star and epoch: define A = p_line - p_cont (or the equivalent q,u excursion) with sigma_A propagated from per-bin sigma_P and continuum scatter; require A/sigma_A >= 3 in at least two adjacent bins for a detection; then count stars with a significant epoch-to-epoch change in A or morphology. Separately, obtain ProtoPol IP measurements on unpolarized standard stars on both the 1.2 m and 2.5 m telescopes (same epoch coverage as Table 2) and subtract them. If the Be 'constant' classification survives after correction and the Herbig variability count remains above, say, 7/11, the abstract's dichotomy is supported. If the quantitative reanalysis changes the 10/11 figure or the Be stability count, the claims must be softened.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The load-bearing step is the inference from two-epoch polarization profiles to an astrophysical Herbig/Be dichotomy. That step is not yet quantitative. Section 2 gives sigma_P for dynamically binned spectral elements, but Table 3 lists p_cont with no errors and classifies 'Line effect?' as a visual Yes/No; no threshold (e.g., Delta_p/sigma, number of contiguous bins) is stated. Some classifications are explicitly marginal: MWC 120 first epoch is called '2.5-3sigma above continuum' (Section 3.1), and AB Aur's second-epoch effect is 'sampled by a single resolution element.' Thus '10 of 11 Herbig stars showed detectable line effects' and 'significant variability for most' are partly selections from noisy, unresolved features. For the Be sample, the comparison is further compromised by the Table 2 note that first-epoch observations were made with ProtoPol on the 1.2 m telescope during commissioning while second-epoch data used the 2.5 m telescope, combined with the Section 2 statement that data are not corrected for instrumental polarization. An unknown 1.2 m IP offset or a 1.2 m/2.5 m IP difference could masquerade as stability or variability at the 0.1-0.3% level where Be line effects live. The central dichotomy therefore needs a propagated-error criterion and an IP bound before it can be called significant.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper presents multi-epoch H-alpha spectropolarimetry for 11 Herbig Ae/Be stars and 10 classical Be stars observed with the ProtoPol instrument on the PRL 1.2 m and 2.5 m telescopes over a 28-month baseline (December 2023 to March 2026). The central claims are that, across two epochs, the H-alpha line polarization remained relatively constant for the classical Be stars while the Herbig stars showed significant variability in amplitude and profile shape, and that this indicates evolving circumstellar scattering geometries on yearly timescales. The paper provides observation logs, line-effect classifications, continuum polarization values, and multi-epoch Stokes q-u diagrams, with individual source comments relating the new data to earlier literature.","tokens_in":24810,"tokens_out":2268,"duration_ms":24911,"significance":"If the dichotomy between variable Herbig line polarization and stable classical Be line polarization is robust, this would be a valuable contribution: multi-epoch spectropolarimetric datasets of this size and baseline are rare, and the stated result would support the picture that Herbig circumstellar geometries evolve on observable timescales while classical Be disks are more stable. The paper is also useful as a visibility study for small-aperture spectropolarimetry. However, the central claim currently rests on visual classifications and two-epoch comparisons without a published error budget on the continuum polarization values or a quantitative variability metric, so the significance of the dichotomy cannot yet be assessed from the manuscript alone.","major_comments":[{"comment":"Table 3 lists p_cont and theta_cont for each Herbig star without uncertainties, and the 'Line effect?' column is a binary visual classification with no stated detection threshold. The summary statement that 10 of 11 Herbig stars showed detectable line effects and that most showed significant variability depends on this classification. Several classifications are explicitly marginal: MWC 120's first-epoch effect is described as 2.5-3 sigma above continuum, and AB Aur's second-epoch effect is described as sampled by a single resolution element. Please provide propagated errors for p_cont and theta_cont, specify the detection threshold (e.g., minimum delta_p/sigma and number of contiguous bins), and re-derive the detection statistics with those criteria.","section":"Section 3, Table 3"},{"comment":"The paper states that the data have not been corrected for instrumental polarization, and Table 2 notes that most first-epoch Be observations were made with ProtoPol on the 1.2 m telescope during commissioning while second-epoch observations used the 2.5 m telescope. Because the Be line effects live at the 0.1-0.3% level, an uncorrected instrumental polarization offset that differs between the two telescopes or mounts could masquerade as stability or variability. The assertion that instrumental polarization is below 0.1% (based on prior papers) is not sufficient without a quantitative test that bounds the epoch-to-epoch instrumental difference, for example by observing an unpolarized standard star with both telescope configurations on overlapping nights.","section":"Section 2 and Table 2 note"},{"comment":"The central dichotomy -- 'significant variability for most Herbig stars' versus 'relatively constant' classical Be stars -- is presented qualitatively. No variability metric (e.g., delta_p / sigma_p between epochs, a chi-squared test of profile difference, or a comparison of line-effect significance distributions) is given. Because the two samples were observed under different instrumental configurations, the comparison needs a quantitative definition of variability applied uniformly, with errors propagated, before the astrophysical conclusion can be supported.","section":"Sections 3.2, 4.2, 5"}],"minor_comments":[{"comment":"There are several typographical errors, including 'Novemeber' in Figure 3 and Figure 8 and 'Decemeber' in Figure 6; these should be corrected before publication.","section":"Throughout"},{"comment":"The phrase 'the data have not been corrected for instrumental polarization, as it would only have a polarization bias effect on the data' is unclear; instrumental polarization is normally an additive contaminant in Stokes q and u, and the reason for not correcting it should be stated more precisely.","section":"Section 2"},{"comment":"The table would be easier to interpret if the continuum polarization values were given with uncertainties in the same table, and if the 'Line effect?' entries were accompanied by a short reference to the spectral bins or significance level used for the classification.","section":"Table 3"},{"comment":"Figures 1-3 and 4-6 use captions like 'Same as 1' and 'Same as 4'; the captions should be self-contained or explicitly identify the referenced figure number in each case.","section":"Figure captions"}],"recommendation":"major_revision","confidential_remarks":"The dataset is potentially valuable and the paper is clearly written, but the central variability dichotomy needs a quantitative error budget and an instrumental-polarization cross-check before it can be accepted. The lack of uncertainties in Table 3 and the visual-only line-effect classification are the main blockers; these are fixable within the manuscript's scope."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Worth a look for the dataset alone: 21 Herbig Ae/Be and classical Be stars observed in Hα spectropolarimetry at two epochs spanning 28 months. That is genuinely rare. The paper's per-source commentary is careful and properly set against Harrington & Kuhn (2009) and earlier work. It also does not hide its own limitations: Section 2 states the data are not corrected for instrumental polarization, and Table 2's note admits the first Be epoch came from ProtoPol on the 1.2m while the second used the 2.5m. Those admissions are to the authors' credit.\n\nThe soft spot is exactly where the stress-test puts it. The headline result—Herbigs variable, Be stars stable—rests on a visual Yes/No column in Table 3 with no detection threshold, no error bars on p_cont, and no propagation of the per-bin errors that Section 2 describes. Some classifications are explicitly marginal: MWC 120 is called '2.5-3σ above continuum' in one epoch, and AB Aur's second-epoch effect is a single resolution element. With those inputs, 'significant variability for most of the Herbig stars' is not yet a supported statement; it is a reasonable impression from the figures. The additional 1.2m/2.5m instrumental polarization worry is real because the Be constancy is the comparison baseline. An unknown IP offset at the 0.1-0.3% level could masquerade as stability or variability.\n\nThat said, the paper is not circular and does not over-fit. It is a campaign report, not a model-dependent analysis. The circularity burden is genuinely negligible. The central argument—that Herbig circumstellar scattering geometries evolve on yearly timescales while Be disks are more stable—is plausible and consistent with prior literature, but the quantitative support is thin.\n\nMy recommendation: send to peer review. A good referee can push for error bars on the continuum polarization, a stated detection criterion for line effects, and an instrumental polarization bound or null test across the two telescopes. If those come back clean, the dataset becomes a solid reference sample. Ideally the reduced data should be released. This is a fair conditional accept, not a desk rejection.","headline":"Valuable rare dataset; the Herbig/Be variability dichotomy needs quantitative error bars and an instrumental polarization bound before it can be taken as established.","tokens_in":25391,"tokens_out":2469,"would_cite":true,"duration_ms":24783,"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":"Over a 28-month campaign, Hα polarization changes shape in most Herbig Ae/Be stars while staying essentially constant in classical Be stars.","keywords":["spectro-polarimetry","Herbig Ae/Be stars","classical Be stars","Hα polarization","temporal variability","circumstellar scattering","depolarization effect","McLean effect"],"falsifier":"Interleaved polarimetric observations of an unpolarized standard star across the 28-month campaign on both telescopes; if the standard's measured polarization varies by more than the reported 0.1–0.3% error floor, the Herbig variability could be instrumental rather than astrophysical.","tokens_in":24361,"feed_emoji":"🔭","tokens_out":9035,"duration_ms":78936,"temperature":0.7,"pith_summary":"This paper reports a multi-epoch optical spectro-polarimetric campaign of 11 Herbig Ae/Be stars and 10 classical Be stars, observed with the ProtoPol instrument over 28 months. Its central finding is that the polarization across the Hα emission line remained largely constant in the classical Be stars but changed significantly in most of the Herbig stars, including changes in amplitude, position angle, and the emergence or disappearance of line effects. The result matters because polarization across emission lines traces the geometry of circumstellar scattering regions on scales far below direct imaging resolution; the observed temporal changes indicate that Herbig scattering geometries evolve on yearly timescales, while classical Be disks appear stable. The paper presents one of the few spectro-polarimetric datasets spanning more than two years for these object classes.","feed_headline":"Herbig stars' Hα polarization varies by year; Be disks steady","feed_subtitle":"Over 28 months, 10 of 11 Herbig Ae/Be stars varied in Hα polarization; classical Be stars barely moved.","key_machinery":"The central observable is the wavelength-resolved linear polarization across Hα, expressed as Stokes $q$ and $u$ and converted to degree $p$ and angle $\\theta$. The key mechanisms are Thomson scattering of continuum photons in an aspherical circumstellar disk or envelope, which produces continuum polarization; the depolarization effect, in which Hα photons emitted over an extended volume undergo fewer scatterings and show a polarization dip across the line; and the McLean effect, an enhanced polarization across a blue-shifted absorption trough. The paper relies on ProtoPol's dynamic binning to achieve a constant polarization error of roughly 0.1–0.3% per bin, and on the comparison of $p$ and $\\theta$ profiles from two epochs separated by 12–28 months to track changes in these scattering signatures.","core_discovery":"The paper claims that Herbig Ae/Be stars and classical Be stars differ dramatically in the long-term behavior of their Hα polarization. In the Herbig sample, 10 of 11 stars showed a detectable polarization line effect in at least one epoch, with sources such as MWC 120, MWC 480, MWC 758, HD 58647, and MWC 147 changing the amplitude, width, or morphology of their line effect between epochs separated by roughly a year. These changes include the appearance and disappearance of the McLean effect across blue-shifted absorption, the growth of depolarization signatures, and flipping of the polarization position angle. In contrast, the classical Be stars showed only stable depolarization signatures or non-detections, with the depolarization persisting over up to 27 months even when the Hα line profile itself changed. The paper interprets this contrast as evidence that the circumstellar scattering geometries of Herbig stars are dynamically evolving on observable timescales, whereas the scattering geometries of classical Be disks are relatively stable.","pith_inferences":["If the Herbig variability is real, yearly-cadence Hα spectropolarimetry with small-aperture telescopes could serve as a practical probe of episodic accretion or disk-wind reconfiguration in intermediate-mass pre-main-sequence stars, complementing interferometry and photometric monitoring.","The sample is biased toward bright stars known to show spectropolarimetric activity; the 10-of-11 variability fraction is likely an upper bound for the general Herbig population, and a volume-limited sample would be needed to convert this into a rate of morphological change.","A testable extension is to compare the epoch-to-epoch polarization changes with contemporaneous Hα equivalent-width or line-profile variability; if the polarization changes track changes in the emission-line strength, that would tie the geometry changes to the ionized-gas content rather than to viewing-angle shifts.","An independent same-telescope re-observation of the classical Be sample would rule out telescope-dependent instrumental polarization as the cause of the Herbig/Be contrast, since the Be first-epoch data were taken on a different telescope during commissioning."],"forward_implications":["A single-epoch spectropolarimetric observation is insufficient to classify a Herbig star's scattering geometry; the observed changes mean at least two epochs about a year apart are needed to detect whether the geometry is evolving.","The Herbig stars identified as variable—MWC 120, MWC 480, MWC 758, FS CMa, HD 58647, and MWC 147—become priority targets for higher-resolution or more frequent monitoring to link specific geometry changes to physical processes.","The stability of the classical Be depolarization signatures over about two years means Be disk scattering geometries can be treated as static on these timescales in modeling, even when line-profile changes are present.","Sources whose line effect appears or disappears between epochs demonstrate that the presence or absence of a polarization signature in a single epoch is not a reliable indicator of whether a scattering environment exists."],"supporting_citations":[{"why":"Defines the depolarization effect and establishes that roughly half of Herbig Be stars show Hα spectropolarimetric signatures, providing the interpretive baseline for the line effects this paper tracks.","marker":"(R. D. Oudmaijer & J. E. Drew 1999)"},{"why":"Extends the sample to Herbig Ae stars and disentangles viewing-angle effects from intrinsic geometry, establishing the interpretation of intrinsic versus depolarization signatures used here.","marker":"(J. S. Vink et al. 2002)"},{"why":"The previous rare multi-epoch spectropolarimetric study comparing HiViS with ESPaDOnS data, used as the reference for single-epoch literature values and the claim that multi-epoch variability has rarely been attempted.","marker":"(D. Harrington & J. R. Kuhn 2009)"},{"why":"Describes ProtoPol and its automated reduction pipeline; the first-epoch data for several sources were taken from this performance-verification paper.","marker":"(A. Maiti et al. 2026b)"},{"why":"Supplies the error propagation equations (σP, σθ) used to set SNR requirements and evaluate the significance of polarization measurements.","marker":"(F. Patat & M. Romaniello 2006)"},{"why":"Documents the McLean effect in Herbig Ae stars and scattering off rotating accretion discs, used to interpret polarization across blue-shifted absorption.","marker":"(J. S. Vink et al. 2005)"}],"fun_headline_variants":["Herbig Ae/Be stars vary in Hα polarization; Be disks steady","Multi-year survey: Herbig Hα polarization shifts, Be constant","Herbig stars' Hα polarization evolves; Be disks do not","28-month spectro-polarimetry: Herbigs vary, Be stars don't","Polarized light shows Herbig disks churning, Be disks stable"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the epoch-to-epoch differences in measured polarization are astrophysical rather than instrumental, even though the data were not corrected for instrumental polarization and the first epoch of the classical Be sample was taken with a different telescope during commissioning.","fun_headline_variants_meta":{"raw":{"variants":["Herbig Ae/Be stars vary in Hα polarization; Be disks steady","Multi-year survey: Herbig Hα polarization shifts, Be constant","Herbig stars' Hα polarization evolves; Be disks do not","28-month spectro-polarimetry: Herbigs vary, Be stars don't","Polarized light shows Herbig disks churning, Be disks stable"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000248,"raw_usage":{"total_tokens":1604,"prompt_tokens":1062,"completion_tokens":542,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":678,"completion_tokens_details":{"reasoning_tokens":445}},"tokens_in":678,"tokens_out":542,"duration_ms":5928,"temperature":1.0,"reasoning_tokens":445,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T18:18:53.441332+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Interleaved polarimetric observations of an unpolarized standard star across the 28-month campaign on both telescopes; if the standard's measured polarization varies by more than the reported 0.1–0.3% error floor, the Herbig variability could be instrumental rather than astrophysical.","supporting_citations":[],"review_version":1}