{"id":"257f9a2b-f535-45f1-be58-1d5d97000e5f","arxiv_id":"2507.01746","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"Six years of SPIRou data on AU Mic refine the star's evolving magnetic field, revise the masses of planets b and c, and keep candidate planet e alive at about 21 Earth masses.","lead":"Using six years of infrared spectra from the SPIRou instrument, astronomers mapped the changing magnetic field of the young star AU Mic and sharpened the masses of its two transiting planets. The results give one of the best looks yet at how a very young star and its close-in planets co-evolve, including a likely third planet whose signature persists as more data arrive.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 33.11 d period of candidate e is only 2.8 d from the 1-yr alias at 30.3 d, yet the MCMC uses a Gaussian prior centered at 33.1 d and never tests the 30.3 d alternative, so the period is not independently established.","rationale":"The reader's verdict CONDITIONAL is appropriate. The strongest claim is the detection of planet e at 4.9σ. The load-bearing assumption is that the 33.11 d peak is the true planet period rather than an alias of a signal at 30.3 d (or a window-function artifact). The paper acknowledges the 30.3 d alias (Fig. 5) but does not test it as an alternative model. Because the MCMC uses a Gaussian prior centered at 33.1 d (Table 1), the data are never allowed to prefer 30.3 d, so the reported period and significance are partly prior-driven. The stacked periodogram (Fig. 6) is computed from RVs filtered using the adopted 33.1 d model, so it does not provide an independent period search. This concern is concrete and testable: a uniform-prior fit or an explicit model comparison against 30.3 d would settle whether the peak is unique. No other issue undermines the b/c mass estimates or the magnetic-field evolution. Therefore the verdict remains CONDITIONAL, pending the alias test.","tokens_in":51417,"tokens_out":7392,"duration_ms":81005,"concrete_test":"Re-run the full MCMC of §5 with a uniform prior on Pe over 20–50 d (and no Keplerian at 33.1 d in the filtering), then compare the marginal likelihood of the best-fit Pe against a model with Pe fixed at 30.3 d. If the 30.3 d model is within Δlog LM < 5 of the 33.1 d model, the alias hypothesis is not ruled out and the confirmation of candidate e should be downgraded. Additionally, compute the window function of the actual RV sampling and verify the alias relationship by injecting a synthetic 30.3 d signal into the real observing times; if it produces a 33.1 d peak of comparable amplitude, the detection is ambiguous.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The confirmation of candidate e rests on a 33.11±0.06 d periodicity in the SPIRou RVs (§5, Table 1). This period is separated from the 1-yr alias at 30.3 d, which the authors identify in Fig. 5, by only 2.8 d. The MCMC fit of Pe uses a Gaussian prior centered at 33.1 d with width 1.0 d (Table 1), so the prior strongly penalizes 30.3 d (2.8σ away) and effectively selects the 33.1 d solution. The 'filtered RVs' used for the stacked periodogram (Fig. 6) are generated from the model that already includes the Keplerian at Pe≈33.1 d, so the strengthening peak is not an independent period search but a projection of the adopted model. No alternative model with Pe=30.3 d (or another alias) is compared. If the true signal were at 30.3 d, the analysis would still report 33.1 d due to the prior, yielding an apparently stable 4.9σ detection. The 29.5 d lunar window peak adds further periodogram power in the same region. Thus the planetary interpretation of the 33.11 d peak is not uniquely established by the data.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper extends the SPIRou monitoring of the young M dwarf AU Mic from 2019 to 2024 (2041 d, 382 spectra) and combines activity modeling, Zeeman-Doppler imaging (ZDI), and radial-velocity (RV) analysis. The authors report that the large-scale magnetic field is mostly poloidal with a dominant dipole of 1.1–1.4 kG that weakened until 2022 and then strengthened, while the small-scale field inferred from ZDI agrees with independent ZeeTurbo line-broadening measurements. They derive updated masses for the transiting planets b and c (6.3 and 11.6 M⊕), a 90% upper limit of 4.9 M⊕ for the putative planet d, and a 4.9σ RV detection of candidate planet e at P = 33.11 ± 0.06 d with M = 21.1 M⊕, which they interpret as a third planet.","tokens_in":51656,"tokens_out":7347,"duration_ms":95284,"significance":"If the planet-e detection holds, this is one of the few multi-planet systems around a pre-main-sequence star and would strengthen the case for early outer-planet formation. The six-year magnetic monitoring is also valuable: it places a lower bound on the magnetic cycle length of a rapidly rotating M dwarf and combines Stokes I and V constraints on both large- and small-scale fields. The paper is careful in several respects: it includes null-spectrum checks, MCMC posteriors with explicit priors, Bayesian model comparisons via marginal likelihoods, and a stacked periodogram showing that the 33-d signal grows as data accumulate. These are genuine strengths. The main caveats are that the RV detection of planet e rests on a restrictive period prior in the presence of a nearby yearly alias, and that the ZDI small-scale field agreement is partly set by the fixed filling-factor ratio fI/fV = 4.5.","major_comments":[{"comment":"The confirmation of candidate e rests on the posterior Pe = 33.11 ± 0.06 d, but the MCMC uses a Gaussian prior centered at 33.1 d with width 1.0 d (Table 1), while the 30.3 d one-year alias is explicitly identified in Fig. 5. Because 30.3 d lies about 2.8σ from the prior center, the prior strongly suppresses the alias before the data are evaluated. The paper should repeat the b+c+e fit with a uniform prior on Pe (or a much wider prior) and also report the marginal likelihood of a model with Pe fixed at 30.3 d, to show that the 33.1 d solution is selected by the data rather than by the prior. The periodogram evidence in Figs. 5 and 6 makes the detection plausible, but those periodograms do not by themselves eliminate the prior-induced selection concern, especially given the 29.5 d lunar window peak in the same region.","section":"Sec. 5, Table 1, Fig. 5"},{"comment":"The claimed agreement between the ZDI-derived small-scale field <Bs> and the ZeeTurbo <B> measurements is partially built into the model through the fixed filling-factor ratio fI/fV = 4.5 (fI = 0.9, fV = 0.2) and the fixed Doppler width vD = 3.5 km/s. The manuscript should state explicitly how fI/fV was chosen (e.g., inherited from Donati et al. 2023a or tuned to the present data) and should include a sensitivity test varying fI/fV and vD over plausible ranges, showing that the epoch-to-epoch trend and the rotational modulation amplitude of <Bs> remain compatible with <B> without re-tuning. As written, the statement in Sec. 7 that the ZDI modeling 'agrees' with <B> overstates what is partly a consistency check with fixed parameters rather than an independent prediction.","section":"Sec. 4, Table C.1, Sec. 7"},{"comment":"The large-scale field strength reconstructed here is about twice that of the previous study, attributed to a much tighter fit to the Stokes I profiles, yet the quoted internal uncertainties on the field values are only about 10 percent (Table C.1 note). Because this factor-of-two change is a central magnetic result, the paper should quantify the systematic uncertainty from the modeling assumptions: the chosen fI, fV, vD, the inclination (i = 80°), and the spherical-harmonic truncation at ℓ = 10. A small grid of inversions with varied settings would show whether the dipole strength of 1.1–1.4 kG is robust or whether the reported values are model-dependent.","section":"Sec. 4, Table C.1"}],"minor_comments":[{"comment":"The sentence 'we respectively fit zero, two (Kb, Kc), five (all but Kd) or all six from the RV data' is confusing because the four cases are listed in the opposite order in Table 1; consider reordering to match the table.","section":"Sec. 5, Table 1"},{"comment":"Column 4 would be easier to read if the header explicitly indicated 'time-averaged value / full-amplitude variation' rather than leaving this to the table note.","section":"Table C.1"},{"comment":"The stacked periodogram would be more useful if the color scale were accompanied by FAP contours for each stack, so that the reader can judge when the 33-d peak first becomes significant rather than only seeing the color change.","section":"Fig. 6"},{"comment":"There is a small grammatical issue in the sentence about convergence: 'verifying that the burn-in and main phase are more than 10 × longer than the autocorrelation lengths of all parameters..' has a doubled period and should be rephrased.","section":"Sec. 3"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a strong observational study and is well within the scope of A&A. My main substantive concern is the period prior for candidate e: the paper should demonstrate that the 33.1 d signal is preferred over the 30.3 d alias under a less restrictive prior. The ZDI small-scale agreement also needs a clearer statement of how fI/fV was fixed and a sensitivity analysis. These are fixable with additional analysis rather than fundamental flaws, so I recommend major revision rather than rejection."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague — This is a solid, workmanlike extension of the SPIRou monitoring. The new 2023–2024 spectra add 157 RVs and push the baseline past five years. The ZDI re-analysis across 11 subsets is careful, and the long-term magnetic field evolution — dipole weakening from 1.4 to 1.1 kG then recovering, with the small-scale field tracking it — is the kind of result that will get cited. The revised masses for b and c (6.3 and 11.6 Earth masses) and the density contrast between them are a real step forward, and the 90% upper limit on d is useful. The paper is honest about model choices, gives MCMC posteriors, checks null spectra, and tests a multi-dimensional GP. So the core of the paper deserves serious referee time.\n\nThe soft spots are where the reader and the stress test point. Candidate e is not yet nailed. The 33.11 d period is 2.8 d from the 1-yr alias at 30.3 d, and the MCMC uses a Gaussian prior centered at 33.1 d with width 1.0 d. The filtered RVs for the stacked periodogram come from a model that already contains a Keplerian at 33.1 d, so the strengthening peak is not an independent period search. The paper never fits a model with the period fixed at 30.3 d, or with a flat prior over the alias range. The signal is also 4.9 sigma, below the conventional threshold. That doesn't make e false — the phase coverage and the FAP are suggestive — but the period is not independently established, and the paper's wording ('confirm our claim') overstates it.\n\nThe ZDI small-scale field consistency is also partly by construction: fI/fV is fixed at 4.5 to reproduce the ZeeTurbo <B> scale, so the agreement between <Bs> and <B> is not an independent check. The doubled field strengths relative to the 2023 study stem from a tighter Stokes I fit; that may be right, but it should be presented as a modeling choice, not as a measurement.\n\nMinor: the 2023–2024 spectra are not yet public. Fine for a large program, but note it.\n\nBottom line: the magnetic evolution and b/c mass results are strong; the e confirmation should be softened to 'consistent with a planet at 33.1 d, but the 30.3 d alias remains viable.' Worth reviewing. I'd accept it with requested revisions.","headline":"A genuinely useful extended re-analysis of AU Mic, but the 33 d candidate planet is not yet separated from its 30.3 d yearly alias.","tokens_in":52367,"tokens_out":2684,"would_cite":true,"duration_ms":32802,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The 33.11-day radial-velocity signal of candidate planet e around AU Mic is real: after 2041 days of SPIRou monitoring it reaches 4.9 sigma and keeps strengthening as data accumulate.","keywords":["AU Mic","M dwarf","radial velocity","exoplanet detection","Gaussian process regression","Zeeman-Doppler imaging","magnetic activity","young planetary systems"],"falsifier":"Re-run the published radial velocities with the GP evolution timescale freed to exceed 300 days and with the 30.3-day one-year alias modeled explicitly: if the 33.11-day peak falls below roughly 3 sigma, the detection was an artifact of the activity model. A second, empirical test is to continue the campaign: two more seasons should show the stacked periodogram peak either holding phase and growing, or dissolving into alias structure.","tokens_in":51156,"feed_emoji":"🪐","tokens_out":9614,"duration_ms":96174,"temperature":0.7,"pith_summary":"Six years of SPIRou monitoring of the young M dwarf AU Mic produce a case for a third planet. The paper argues that the radial-velocity signal of candidate planet e, at a period of 33.11 ± 0.06 days, is a genuine Keplerian rather than an artifact of stellar activity: it is detected at 4.9 sigma with a semi-amplitude of about 5.9 m/s, implying a mass near 21 Earth masses, and it grows stronger in stacked periodograms as more spectra are added. If true, AU Mic hosts at least three planets, making it a rare benchmark for how planetary architectures settle within the first 20 million years of a star's life. The same analysis sharpens the masses of the two transiting planets, reveals a strong density contrast between them, and places a new upper limit on a fourth candidate.","feed_headline":"Six-year SPIRou campaign confirms a third planet at AU Mic","feed_subtitle":"A 33.1-day signal at 4.9 sigma puts planet e at 21 Earth masses, reshaping the young system.","key_machinery":"The load-bearing machinery is a quasi-periodic Gaussian process (GP), a statistical model of the stellar activity signal in the radial velocities, with a covariance that recurs near the 4.865-day stellar rotation period and evolves on a timescale of about 167 days. The GP is meant to absorb the spin-modulated activity jitter so the residuals behave like white noise; the planets are then fitted as circular Keplerians, with the periods of b and c fixed from photometry while the period and phase of candidate e are searched. The diagnostic that carries the confirmation is a stacked periodogram of the activity-filtered velocities: the 33.11-day peak deepening as data are added is presented as the signature that distinguishes a real planet from a transient activity artifact.","core_discovery":"On the paper's own terms, the central discovery is that candidate planet e, first proposed in the earlier SPIRou analysis, survives a fivefold-longer baseline. Fitting the 344 radial velocities with a quasi-periodic Gaussian process for activity plus circular Keplerians for planets b and c leaves a residual peak at $P_e = 33.11 \\pm 0.06$ d with a false-alarm probability near $2 \\times 10^{-9}$, a semi-amplitude $K_e = 5.9^{+1.5}_{-1.2}$ m/s, and a mass $M_e = 21.1^{+5.4}_{-4.3}$ $M_\\oplus$. The stacked periodogram shows the peak deepening as data accumulate, and the Bayesian evidence for the three-planet model over the two-planet model is $\\Delta\\log L \\approx 11.5$. The paper also derives updated masses for b and c, a 90% upper limit of 4.9 Earth masses for candidate d, and a six-year magnetic-field evolution in which the dipole weakens from about 1.4 to 1.1 kG before rising again.","pith_inferences":["The stacked-periodogram growth criterion demonstrated here could serve as a general validation protocol for RV planet candidates around active stars: a signal that strengthens monotonically as seasons accrue is far more likely to be planetary, while one that oscillates in power is likely activity.","If e is real and non-transiting, its orbital inclination must be below about 88.7 degrees; a future measurement of the mutual inclination between e and the transiting planets would test whether the system formed coplanar or was scattered.","Three to five more years of monitoring would distinguish between a very long magnetic cycle and non-periodic evolution: a polarity switch in the dipole would align AU Mic with less active M dwarfs that show Sun-like cycles, whereas continued drift would support the non-periodic interpretation.","The closeness of the 30.3-day one-year alias and the 29.5-day lunar window peak to the claimed 33.11-day period means independent sampling from a different observatory is the cheapest decisive check; if the signal phase-coheres across two observatories, activity-model concerns are largely retired."],"forward_implications":["AU Mic would join the small set of sub-20-Myr stars with a confirmed multi-planet system, giving formation and migration models a concrete outer-planet constraint at 0.17 au.","The density contrast between b (about 0.32 g/cm3) and c (about 2.9 g/cm3) implies the two transiting planets have very different structures or evolutionary states, with b still inflated.","The lower semi-amplitude of 5.9 m/s explains why optical RV surveys with a 10 m/s upper limit missed the signal; future joint optical-infrared fits should recover it.","With a circular orbit for e, the three-planet configuration is dynamically stable on Gyr timescales, so the architecture is long-lived rather than a snapshot of a transient arrangement.","Candidate planet d, if it causes the observed transit-timing variations, must be lighter than about 4.9 Earth masses, keeping the inner system compact and consistent with the TTV interpretation."],"supporting_citations":[{"why":"the prior SPIRou analysis that first proposed candidate planet e and set up the GP activity modeling this study extends.","marker":"Donati et al. 2023a"},{"why":"the optical-wavelength study that challenged planet e; its 10 m/s upper limit frames the new, lower semi-amplitude.","marker":"Mallorquín et al. 2024"},{"why":"supplies the quasi-periodic Gaussian-process regression framework used to subtract stellar activity from the RVs.","marker":"Haywood et al. 2014"},{"why":"the multi-dimensional GP formalism tested as a cross-check that yields consistent planet parameters.","marker":"Rajpaul et al. 2015"},{"why":"the line-by-line technique that extracts meter-per-second radial velocities from SPIRou spectra.","marker":"Artigau et al. 2022"},{"why":"the APERO reduction pipeline that produces the spectra from which the line-by-line RVs are derived.","marker":"Cook et al. 2022"},{"why":"the discovery of the two transiting planets b and c that anchor the Keplerian model.","marker":"Plavchan et al. 2020"},{"why":"the transit-timing analysis motivating candidate planet d, whose RV upper limit is derived here.","marker":"Wittrock et al. 2023"}],"fun_headline_variants":["SPIRou confirms 33-day planet around young AU Mic","Long SPIRou campaign locks in AU Mic's third world","Six-year SPIRou data solidify planet e at AU Mic","AU Mic's planet e confirmed after 6-year monitoring","Third planet at AU Mic nailed by six-year SPIRou run"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The confirmation of planet e rests on the quasi-periodic Gaussian process absorbing all stellar activity and leaving white noise; if that model underfits long-term magnetic evolution, or if the 30.3-day one-year alias and the 29.5-day lunar window peak leak into the 33.11-day period, the residual signal could be nonplanetary.","fun_headline_variants_meta":{"raw":{"variants":["SPIRou confirms 33-day planet around young AU Mic","Long SPIRou campaign locks in AU Mic's third world","Six-year SPIRou data solidify planet e at AU Mic","AU Mic's planet e confirmed after 6-year monitoring","Third planet at AU Mic nailed by six-year SPIRou run"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000599,"raw_usage":{"total_tokens":2943,"prompt_tokens":1228,"completion_tokens":1715,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":844,"completion_tokens_details":{"reasoning_tokens":1629}},"tokens_in":844,"tokens_out":1715,"duration_ms":12669,"temperature":1.0,"reasoning_tokens":1629,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T20:44:56.854145+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Re-run the published radial velocities with the GP evolution timescale freed to exceed 300 days and with the 30.3-day one-year alias modeled explicitly: if the 33.11-day peak falls below roughly 3 sigma, the detection was an artifact of the activity model. A second, empirical test is to continue the campaign: two more seasons should show the stacked periodogram peak either holding phase and growing, or dissolving into alias structure.","supporting_citations":[],"review_version":1}