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AB Aurigae disk rotates sub-Keplerian inside 60 au, lagging by up to 12 degrees over four years

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2026-07-01 16:07 UTC pith:XGE54FU7

load-bearing objection 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. the 3 major comments →

arxiv 2605.27084 v1 pith:XGE54FU7 submitted 2026-05-26 astro-ph.EP

Destructuring the disk of AB Aurigae: Dynamics and accretion

Anthony Boccaletti , Emmanuel Di Folco , Anne Dutrey , Tang Ya-Wen , Stephane Guilloteau , Thomas Collin-Dufresne , Anne-Marie Lagrange , Eric Pantin
show 18 more authors
Jeffrey S. Bary Nuria Hu\'elamo J\'ozsef Varga Julien Milli Tracy Beck Vincent Pi\'etu William Danchi Bin Ren Cl\'ement Baruteau Mickael Bonnefoy Maud Langlois Sylvestre Lacour Bruno Lopez Alexis Matter Julien Woillez Florentin Millour Matthis Houll\'e Philippe Berio
This is my paper
classification astro-ph.EP
keywords AB Aurigaeprotoplanetary diskKeplerian rotationsub-Keplerian motionprotoplanetspolarized imagingH-alpha accretion
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

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.

Core claim

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.

What carries the argument

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

Load-bearing premise

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.

What would settle it

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.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • 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.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • 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.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

3 major / 2 minor

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).

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 (3)
  1. [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.
  2. [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.
  3. [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.
minor comments (2)
  1. [Hα analysis] 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.
  2. [Throughout] 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.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive and detailed report. We address each major comment below and indicate the revisions that will be incorporated.

read point-by-point responses

  1. Referee: [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.

    Authors: 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: yes

  2. Referee: [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.

    Authors: 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: partial

  3. Referee: [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.

    Authors: 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: yes

Circularity Check

0 steps flagged

No significant circularity; claims rest on direct multi-epoch imaging measurements

full rationale

The paper's central results are derived from direct position tracking of disk features across three SPHERE/IRDIS epochs spanning 3.85 years and single-epoch ZIMPOL Halpha imaging. Angular deviations from Keplerian rotation are computed from observed displacements at specific radii (e.g., ~25 au showing ~12 deg shift), without any fitted parameter being renamed as a prediction or any load-bearing step reducing to a self-citation chain. The protoplanet-interaction interpretation is explicitly labeled as a posit without quantitative dynamical modeling that would create circularity. All reported quantities (fluxes, inclinations, deviations) trace to raw image data rather than internal definitions or ansatze.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 1 invented entities

The central claims rest on standard assumptions about Keplerian motion in protoplanetary disks and on two common accretion models; the planet-interaction interpretation is introduced to explain the observed deviations.

axioms (1)
  • domain assumption Disk rotation can be compared directly to a Keplerian model set by the central star's mass
    Used when quantifying the ~12 deg deviation at 25 au
invented entities (1)
  • Multiple protoplanets on inclined elliptical orbits no independent evidence
    purpose: To account for the observed sub-Keplerian rotation and spiral dynamics
    Postulated on the basis of the dynamical deviations; no independent detection (e.g., direct imaging or radial-velocity signal) is reported in the abstract

pith-pipeline@v0.9.1-grok · 6021 in / 1415 out tokens · 56428 ms · 2026-07-01T16:07:02.868061+00:00 · methodology

0 comments
read the original abstract

In this paper, we present near-IR polarized images of the AB Aur disk at three epochs spanning 3.85 years with SPHERE/IRDIS, as well as Halpha images obtained with SPHERE/ZIMPOL at a single epoch. The purpose of this study is to analyze the dynamics of the entire disk and of the various structures in near-IR polarimetry, and to identify sources of Halpha emission to derive constraints on their mass accretion rate. The dynamical study in the near-IR shows that 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 two bright spirals within the millimeter cavity have different dynamic trends, and we discuss their possible link with the identified planet candidates. We also discuss the implications of the non-Keplerian behavior, and we posit that it could be related to interactions with multiple protoplanets orbiting out of the disk plane on elliptical orbits. Furthermore, the orbital analysis of the compact sources (labeled f1, f2, and f3) suggests that their orbital planes are significantly inclined with respect to the disk plane by several tens of degrees. The variability of the shadows suggests that they are produced by optically thick regions located within ~60au. For the photometric analysis in Halpha, we derive a flux of about 8.22x10^{-15} erg/s/cm^2 for the entire feature f1, but only 6.46x10^{-16} erg/s/cm^2 at the location of AB Aur b, consistent with non-detection. If f1 were a point source and the accretion remained constant for 1Myr, it would correspond to ~5-20 Jupiter masses according to the magnetospheric accretion model or ~6-10 Jupiter masses according to the boundary layer accretion model.

Figures

Figures reproduced from arXiv: 2605.27084 by Alexis Matter, Anne Dutrey, Anne-Marie Lagrange, Anthony Boccaletti, Bin Ren, Bruno Lopez, Cl\'ement Baruteau, Emmanuel Di Folco, Eric Pantin, Florentin Millour, Jeffrey S. Bary, J\'ozsef Varga, Julien Milli, Julien Woillez, Matthis Houll\'e, Maud Langlois, Mickael Bonnefoy, Nuria Hu\'elamo, Philippe Berio, Stephane Guilloteau, Sylvestre Lacour, Tang Ya-Wen, Thomas Collin-Dufresne, Tracy Beck, Vincent Pi\'etu, William Danchi.

Figure 1
Figure 1. Figure 1: H-band images of AB Aur Qϕ in a 3′′ × 3 ′′ field of view at three epochs (December 2019, November 2021, and October 2023). The top row is displayed in logarithmic scale, while the bottom row is a high-pass filtered version in linear scale. The color bar shows the contrast obtained by normalizing with the out-of-mask point spread function image. North is up and east is left. three bands. The top rows are di… view at source ↗
Figure 2
Figure 2. Figure 2: H-band images of AB Aur (October 2023), showing the main structures. Top panel: Scattered light features. Bottom panel: Millimet￾ric features (yellow: dust ring; white: 12CO spirals S1 and S2 from Tang et al. (2017); green: SO ring and SO peak from Dutrey et al. (2024); blue: C18O ring from Dutrey et al. (2024) and pink: out of plane spirals (or streamers) St1, St2, and St3 from Speedie et al. (2025)). The… view at source ↗
Figure 3
Figure 3. Figure 3: H-band images of AB Aur at three epochs in a 1′′ × 1 ′′ field of view. The rightmost panel displays the contours of epoch 1 (dashed line) and epoch 3 (solid line) superimposed on the image from epoch 3. Images are spatially filtered. North is up and east is left. quadratic difference. Before the minimization, the Qϕ images were high-pass filtered by subtracting a blurred boxcar image (width 12 pixels; 1 pi… view at source ↗
Figure 6
Figure 6. Figure 6: Some are consistent across epochs but show measurable [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
Figure 4
Figure 4. Figure 4: Disk rotation as a function of radius for each pair of epochs. The data points are shown in red, while the blue line represents the expected Keplerian rotation in the disk plane (solid) and for inclinations of 20◦ , 30◦ , 40◦ , and 50◦ (darkest to lightest lines). The residuals between the data and the Keplerian are shown below each plot. From top to bottom: Epoch 2 vs. epoch 1, epoch 3 vs. epoch 2, and ep… view at source ↗
Figure 5
Figure 5. Figure 5: Rotation of the main disk features for two epoch pairs (2021 vs. 2019 in blue and 2023 vs. 2019 in red). The symbols correspond to f1 (circle), f2 (diamond), f3 (square), and the bridge (triangle). Each curve shows the expected Keplerian rotation using the same color cod￾ing as the symbols. The left panel shows the results from the optimiza￾tion method, while the right panel shows results from Gaussian fit… view at source ↗
Figure 6
Figure 6. Figure 6: Deprojected H-band images of AB Aur for the three epochs. Dotted lines approximately trace the main shadow patterns identified at each epoch. Images are multiplied by r 2 and spatially filtered. The blue, green, and pink circles trace the potential location of clumps that could be casting the shadows. 200 100 0 100 200 distance in au 200 100 0 100 200 distance in au sh1 sh2 sh3 sh4 sh5 sh6 sh7 H band PC #0… view at source ↗
Figure 7
Figure 7. Figure 7: Principal component analysis (PCA) of the three images shown in [PITH_FULL_IMAGE:figures/full_fig_p008_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Principal component analysis (PCA) reduction in ADI using ZIMPOL for the two filters CntHα (left) and N_Hα (middle and right). The rectangle indicates the aperture used for photometry. Structures oriented along the diagonal of the images at about 0.35′′ from the star are produced by the SPHERE deformable mirror (DM). The right subpanel shows the IRDIS DPI J-band contours overlaid on the ZIMPOL NHα PCA imag… view at source ↗
Figure 9
Figure 9. Figure 9: Images in NHα (left), with a fake planet (FP) injected at the flux of AB Aur b (middle) and with twice the flux (right). Labels indicate the position of the candidate planet. The dashed circles trace the region contaminated by the AO correction radius, while the pink cross represents the companion candidate reported in Kozdon et al. (2026) in 12CO ro-vibrational transitions. The yellow circle at ρ = 0.35′′… view at source ↗
Figure 10
Figure 10. Figure 10: GaiaPMEX analysis for AB Aur showing the solutions (green shades) at 1, 2 and 3 σ in a mass/semi-major axis (sma) diagram. – The disk morphology observed over three epochs shows strong consistency, both in large-scale structures and small-scale structures. This high level of stability is an important asset for dual polarimetry observations with SPHERE/IRDIS, enabling detailed and robust dynamical analyses… view at source ↗

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Reference graph

Works this paper leans on

4 extracted references · 4 canonical work pages

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