{"id":"2d68abc6-aa32-4ebb-90da-ef0db3b32cb2","arxiv_id":"2605.27084","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Multi-epoch SPHERE observations of the AB Aurigae disk show sub-Keplerian rotation inside ~60 au and Halpha emission from feature f1 consistent with accretion onto a several-Jupiter-mass protoplanet candidate.","lead":"The paper reports multi-epoch near-IR polarized images and single-epoch Halpha imaging of the AB Aurigae protoplanetary disk, finding mostly Keplerian rotation with clear sub-Keplerian deviations inside 60 au and Halpha flux from a compact feature. A smart generalist might read it to see how repeated imaging can reveal dynamical signatures potentially linked to forming planets and accretion.","discovery_kind":"extension","skeptic_critique":{"model":"grok-4.3","headline":"Attribution of observed sub-Keplerian deviation at <60 au to inclined protoplanets is the least secure step in the central claim","rationale":"The reader's weakest_assumption directly matches the load-bearing concern. The observational report of a deviation may be robust once full methods are examined, but the causal attribution to inclined protoplanets lacks the quantitative support needed to elevate the claim above UNVERDICTED. No adjustment to the reader's verdict is warranted on this basis.","tokens_in":1901,"tokens_out":343,"duration_ms":35427,"concrete_test":"Re-track the two bright spirals and any other features at the three epochs using an independent image registration (e.g., cross-correlation on the outer disk rather than the central star) and recompute the angular displacement at 25 au; if the deviation falls below ~6 deg or changes sign, the sub-Keplerian claim and its dynamical interpretation are sensitive to alignment choices.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The strongest claim is that the disk is globally Keplerian but shows a ~12 deg departure from Keplerian rotation at ~25 au over 3.85 yr, interpreted as sub-Keplerian motion caused by dynamical interactions with multiple protoplanets on elliptical orbits inclined to the disk plane. The abstract presents this as a positing (\"we posit\") without quantitative dynamical modeling, exclusion of disk warping, or assessment of systematics in multi-epoch feature tracking in the SPHERE/IRDIS polarized images. The reported orbital inclinations of compact sources f1–f3 are noted separately but not linked via explicit calculation to the measured angular deviation.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The manuscript presents three-epoch SPHERE/IRDIS polarized near-IR images (spanning 3.85 yr) and single-epoch ZIMPOL Hα imaging of the AB Aurigae transition disk. It reports that the disk follows Keplerian rotation at most radii but shows a departure from Keplerian motion inside ~60 au, reaching a ~12° angular deviation at ~25 au that is interpreted as sub-Keplerian rotation. The authors posit that this deviation arises from dynamical interactions with multiple protoplanets on inclined elliptical orbits, analyze the orbits and inclinations of compact sources f1–f3, discuss spiral structures and shadows, and derive Hα-based accretion-rate constraints on f1 (yielding mass estimates of ~5–20 M_Jup or ~6–10 M_Jup depending on the accretion prescription).","tokens_in":2056,"tokens_out":749,"duration_ms":27024,"significance":"If the angular-deviation measurement is shown to be robust against systematics and if the protoplanet interpretation can be supported by explicit dynamical modeling, the work would supply a rare direct observational constraint on non-Keplerian kinematics inside the millimeter cavity of a transition disk. The multi-epoch feature tracking and the two-model accretion analysis are useful data products, but the current lack of error budgets and quantitative linkage between the observed deviation and the posited planets limits the immediate impact.","major_comments":[{"comment":"Abstract and dynamical-analysis section: the central claim of a ~12° deviation from Keplerian rotation at ~25 au over 3.85 yr is presented without reported uncertainties, a description of the position-tracking method across epochs, or a quantitative residual map relative to a fitted Keplerian velocity field. This measurement is load-bearing for the sub-Keplerian interpretation.","section":"Abstract / dynamical study"},{"comment":"Section discussing non-Keplerian behavior and protoplanet interpretation: the attribution of the observed departure to “interactions with multiple protoplanets orbiting out of the disk plane on elliptical orbits” is introduced as a posit (“we posit”) without dynamical simulations, N-body tests, or explicit exclusion of alternatives (disk warping, shadowing-induced apparent motion, or unaccounted systematics in multi-epoch feature registration). The separately reported inclinations of f1–f3 are not connected by calculation to the 12° deviation.","section":"Implications of non-Keplerian behavior"},{"comment":"Hα photometric section: the mass estimates (~5–20 M_Jup or ~6–10 M_Jup) rest on the assumption that accretion remains constant for 1 Myr; no sensitivity analysis or justification for this timescale is given, and the two standard prescriptions are presented without discussion of which is preferred for this source or how the derived masses would change under different assumptions.","section":"Photometric analysis in Hα"}],"minor_comments":[{"comment":"The abstract states specific flux values (8.22×10^{-15} and 6.46×10^{-16} erg s^{-1} cm^{-2}) but does not indicate whether these are aperture-integrated or peak values; the corresponding section should clarify the extraction aperture and any background subtraction.","section":"Hα analysis"},{"comment":"Figure captions and text should explicitly state the assumed distance, inclination, and position angle used to deproject the disk when comparing observed angular motions to Keplerian expectations.","section":"Throughout"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for the constructive and detailed report. We address each major comment below and indicate the revisions that will be incorporated.","responses":[{"response":"We agree that the robustness of the 12° deviation requires explicit support. In the revised manuscript we will (i) describe the multi-epoch feature-tracking procedure and registration method in the methods section, (ii) report the astrometric uncertainties derived from the three-epoch data, and (iii) add a residual map (observed minus best-fit Keplerian) either in the main text or as supplementary material. These additions will allow direct assessment of the measurement.","revision_made":"yes","referee_comment":"[Abstract / dynamical study] Abstract and dynamical-analysis section: the central claim of a ~12° deviation from Keplerian rotation at ~25 au over 3.85 yr is presented without reported uncertainties, a description of the position-tracking method across epochs, or a quantitative residual map relative to a fitted Keplerian velocity field. This measurement is load-bearing for the sub-Keplerian interpretation."},{"response":"We will expand the discussion to (a) quantitatively link the measured inclinations of f1–f3 to the observed angular deviation via a simple geometric estimate and (b) explicitly address alternative explanations (warping, shadowing, registration systematics) with the available data. Full N-body simulations lie outside the scope of this primarily observational study; we will therefore frame the protoplanet interpretation as a motivated hypothesis rather than a demonstrated conclusion and note the need for future dynamical modeling.","revision_made":"partial","referee_comment":"[Implications of non-Keplerian behavior] Section discussing non-Keplerian behavior and protoplanet interpretation: the attribution of the observed departure to “interactions with multiple protoplanets orbiting out of the disk plane on elliptical orbits” is introduced as a posit (“we posit”) without dynamical simulations, N-body tests, or explicit exclusion of alternatives (disk warping, shadowing-induced apparent motion, or unaccounted systematics in multi-epoch feature registration). The separately reported inclinations of f1–f3 are not connected by calculation to the 12° deviation."},{"response":"We will add a short sensitivity analysis exploring accretion timescales from 0.5–2 Myr and justify the fiducial 1 Myr choice by reference to typical protoplanet growth timescales in the literature. We will also indicate which of the two accretion prescriptions is more appropriate for AB Aurigae on the basis of the source’s spectral type and disk properties, and tabulate the resulting mass ranges under each assumption.","revision_made":"yes","referee_comment":"[Photometric analysis in Hα] Hα photometric section: the mass estimates (~5–20 M_Jup or ~6–10 M_Jup) rest on the assumption that accretion remains constant for 1 Myr; no sensitivity analysis or justification for this timescale is given, and the two standard prescriptions are presented without discussion of which is preferred for this source or how the derived masses would change under different assumptions."}],"tokens_in":1768,"tokens_out":664,"duration_ms":27552,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The main thing to know is that this paper adds three-epoch SPHERE/IRDIS polarized images spanning 3.85 years plus one-epoch ZIMPOL Halpha data, and reports a clear departure from Keplerian rotation inside ~60 au that reaches ~12 deg at the smallest tracked radius of ~25 au.\n\nWhat is actually new is the repeated position measurements of disk structures and the compact sources f1–f3, plus the specific Halpha flux values (8.22e-15 erg/s/cm2 for f1 overall, much lower at the AB Aur b location). The global Keplerian behavior outside the inner zone lines up with earlier work on this target, and the direct imaging constraints on orbital inclinations for the compact sources are straightforward results from the data.\n\nThe soft spot is the dynamical interpretation. The abstract states that the inner deviation could come from multiple protoplanets on inclined elliptical orbits, but this is presented as a positing with no quantitative simulations shown, no error budget on the angular measurements, and no explicit test ruling out disk warping or tracking systematics. The reported inclinations are noted separately but not tied by calculation to the observed 12 deg shift.\n\nThis paper is for people who follow detailed kinematics in individual transition disks. Readers who want fresh position time series or Halpha photometry on AB Aur will find usable numbers; the planet-formation angle is more speculative. It should go to peer review because the observations are new and the claims rest on measurable quantities that referees can check against the methods and alternatives.","headline":"New multi-epoch tracking shows a ~12 deg sub-Keplerian shift at 25 au in AB Aur, but the inclined-protoplanet explanation is only posited without modeling.","tokens_in":2649,"tokens_out":395,"would_cite":false,"duration_ms":30625,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"AB Aurigae disk rotates sub-Keplerian inside 60 au, lagging by up to 12 degrees over four years","keywords":["AB Aurigae","protoplanetary disk","Keplerian rotation","sub-Keplerian motion","protoplanets","polarized imaging","H-alpha accretion"],"falsifier":"New observations at the same inner radius showing motion that matches Keplerian rotation to within a few degrees over a comparable time baseline would falsify the sub-Keplerian claim.","tokens_in":2822,"feed_emoji":"🪐","tokens_out":786,"duration_ms":25334,"temperature":0.7,"pith_summary":"The paper presents multi-epoch near-infrared polarized images of the AB Aurigae protoplanetary disk spanning 3.85 years along with single-epoch H-alpha imaging. It establishes that the disk follows Keplerian rotation at larger radii but shows clear departures at radii smaller than about 60 au. At the innermost tracked radius of 25 au the observed motion falls short of Keplerian expectations by as much as 12 degrees. The authors attribute the sub-Keplerian behavior to gravitational interactions with multiple protoplanets on elliptical orbits that are inclined relative to the disk plane. Photometric analysis of H-alpha emission from compact sources yields accretion-rate constraints under two different models.","feed_headline":"AB Aurigae inner disk lags Keplerian rotation by 12 degrees","feed_subtitle":"Multi-epoch imaging shows sub-Keplerian motion inside 60 au, interpreted as gravitational influence from inclined protoplanets.","key_machinery":"Multi-epoch polarimetric imaging that tracks the angular displacement of disk features and compact sources over 3.85 years to compare observed motion against Keplerian predictions","core_discovery":"The disk globally follows Keplerian rotation, but we observe a departure from this behavior at radii smaller than ~60au. At the smallest radius of ~25au, we measure a deviation from Keplerian rotation as large as ~12deg over 3.85 years, demonstrating sub-Keplerian rotation. The non-Keplerian behavior could be related to interactions with multiple protoplanets orbiting out of the disk plane on elliptical orbits. The orbital analysis of the compact sources suggests that their orbital planes are significantly inclined with respect to the disk plane by several tens of degrees.","pith_inferences":["Inclined protoplanet orbits could produce the misalignments seen in other young planetary systems during the embedded phase.","High-resolution spectroscopy of the inner disk could distinguish between true sub-Keplerian flow and line-of-sight effects from a warp.","Comparable time-baseline imaging of other transition disks might reveal similar sub-Keplerian signatures as a general signature of embedded planets."],"forward_implications":["The two bright spirals inside the millimeter cavity follow distinct dynamic trends that may connect to the identified planet candidates.","Shadows cast across the disk vary because they are produced by optically thick material located within ~60 au.","The H-alpha flux measured for compact source f1, if interpreted as steady accretion over 1 Myr, corresponds to a forming planet of roughly 5-20 Jupiter masses under magnetospheric accretion or 6-10 Jupiter masses under the boundary-layer model.","The orbital planes of compact sources f1, f2, and f3 lie at inclinations of several tens of degrees relative to the disk plane."],"fun_headline_variants":["AB Aurigae disk lags Keplerian by 12 degrees at 25 au","12 degree sub-Keplerian lag in AB Aurigae inner disk","AB Aurigae non-Keplerian motion inside 60 au","AB Aurigae disk rotation deviates by 12 degrees from Keplerian"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"The observed sub-Keplerian motion at small radii arises from dynamical interactions with multiple protoplanets on inclined elliptical orbits rather than from disk warping or measurement artifacts.","fun_headline_variants_meta":{"raw":{"variants":["AB Aurigae disk lags Keplerian by 12 degrees at 25 au","12 degree sub-Keplerian lag in AB Aurigae inner disk","AB Aurigae non-Keplerian motion inside 60 au","AB Aurigae disk rotation deviates by 12 degrees from Keplerian"]},"model":"grok-4.3","cost_usd":0.008525,"raw_usage":{"total_tokens":3953,"prompt_tokens":871,"num_sources_used":0,"completion_tokens":80,"cost_in_usd_ticks":85249500,"prompt_tokens_details":{"text_tokens":871,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":3002,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":871,"tokens_out":80,"duration_ms":22703,"temperature":1.0,"reasoning_tokens":3002,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-01T16:07:02.868061+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"New observations at the same inner radius showing motion that matches Keplerian rotation to within a few degrees over a comparable time baseline would falsify the sub-Keplerian claim.","supporting_citations":[],"review_version":1}