arXiv subjects

Jochen Stadler

Publications and source records attributed to Jochen Stadler.

At least 19 recordsLinked to original sources

arXiv2026

Planetary gas gaps and kinematic signatures in the planet forming disk around WISPIT 2

The giant planet formation process in disks of gas and dust surrounding young stars is observationally still poorly constrained. Direct detection of protoplanets within the disk remains limited with current facilities. Indirect observational evidence of protoplanets through substructures or deviations from Keplerian rotation in the gas remains ambiguous in absence of detected planets. The lack of the combined detection of substructures and their corresponding planets makes it challenging to connect the planet formation process to the host environment. Observations with the Atacama Large Millimeter Array (ALMA) reveal clear detections of gas gaps and kinematic signatures in the WISPIT 2 protoplanetary disk that are cospatial with the locations of previously detected giant protoplanets. The newly identified gas gaps, observed in both the 12CO integrated intensity map and its rotation curve, correspond with the previously identified gaps in scattered light. Their morphologies are shown to be consistent with eccentric gaps, as expected from planet-disk interaction models of massive planets. The lack of eccentricity in the outer disk can be explained if a third planet is present in the system. The observations of WISPIT 2 provide a long-sought empirical bridge between kinematic signatures, gas gaps and giant planet formation in disks.

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arXiv2026

The Circumbinary Disc of HD 34700A II. Analysis of a strong dust asymmetry

ALMA observations have shown that substructures are ubiquitous in protoplanetary discs. A sub-group, the transition discs, shows large cavities and rings in dust continuum. Among these, some present very high contrast asymmetries possibly due to the presence of vortices. HD 34700A is a binary system featuring a cavity, a ring, and multiple spiral arms detected in scattered light, a prominent crescent in the ALMA continuum and a complex gas morphology possibly connected with ongoing infall. We present new ALMA band 6 (1.3 mm) continuum images of the circumbinary disc around HD 34700A and compare them with two other systems showcasing high ($\gtrsim30$, measured as the peak-to-azimuthal-average ratio) contrast continuum asymmetries, IRS 48 and HD 142527. We aim to characterise the crescent morphology and discuss their possible origin. We perform visibility modelling of the new high resolution (0.''11x0.''09) ALMA band 6 continuum data of HD 34700A, together with improved visibility modelling of the other two targets. Our visibility model is in remarkable agreement with the HD 34700A data, featuring only localised residuals in the region of the disc corresponding to the tail of the asymmetry. We reproduce the double-peaked emission in HD 142527, and recover the crescent shape in IRS 48. We then run a hydrodynamic model of a vortex with different dust fluids, reproducing the general asymmetric crescent morphology observed in the HD 34700A and IRS 48 systems. With a combination of visibility, dust evolution and hydrodynamical models, we have constrained the morphology of the dust continuum emission of HD 34700A for the first time, and improved existing models for IRS 48 and HD 142527. The high azimuthal contrast of the asymmetries rules out the orbit clustering of eccentric cavities scenario, while the dust evolution models we consider suggest that the vortex scenario is a plausible option.

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arXiv2026

exoALMA XXII: A Two-dimensional Atlas of Deviations from Keplerian Disks

Protoplanetary disks are the birthplaces of planetary systems, and deviations from Keplerian rotation imprinted in disk gas kinematics serve as key tracers of physical processes and the presence of protoplanets within disks. Using the the CO (J=3-2) data from the exoALMA Large Program encompassing 15 disks, we constructed two-dimensional (2D) maps of centroid velocity, line width, and peak intensity, and extracted non-Keplerian deviations by subtracting smooth Keplerian models. This paper provides the first systematic and uniform overview of 2D gas substructures across the entire exoALMA sample. We find that all targets exhibit large-scale deviations from smooth Keplerian disks, displaying a variety of morphologies including spiral-like structures, arc- or ring-like features, and patterns indicative of variations in the emitting surface height. Non-axisymmetric spiral-arm features are detected or suggested in five disks (CQ Tau, MWC 758, HD 135344B, HD 34282, and SY Cha), and are preferentially found in Herbig Ae/Fe systems. In contrast, some other sources (J1852, PDS 66, and V4046 Sgr), despite exhibiting noticeable deviations, appear to be dynamically quieter. This 2D atlas suggests that kinematic substructures are ubiquitous in large ($\gtrsim$ 100 au) protoplanetary disks with ages of a few million years, based on the observations obtained with sufficient sensitivity at moderate-to-high spatial resolution of $\sim$20 au and high velocity resolution of $\sim$0.1 km s$^{-1}$.

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arXiv2026

exoALMA. XXIV. Formaldehyde Emission in Protoplanetary Disks of exoALMA Compared with Their Properties and Dynamical State

The presence of asymmetries and substructures in protoplanetary disks, revealed by both dust and gas emission, highlights the potential interplay and the broader connection between chemistry and dynamics in disk evolution. We explore multiple relationships using the nonparametric Kendall-$\tau$ correlation to examine formaldehyde (H$_2$CO) emission with relation to stellar and disk properties for a subset of disks from the exoALMA sample. We also retrieve the H$_2$CO column density and excitation temperature using four transitions, measured in radial bins of 100 au, and quantify the level of asymmetry in the resolved peak intensity of the H$_2$CO emission. From our correlation analysis, we find no correlations with sufficient statistical significance. However, we identify tentative relationships that can be tested with larger samples. In particular, we report a proposed correlation ($2.1\sigma$) between stellar effective temperature and the formaldehyde excitation conditions, suggesting that, to first order, the central star dominates the nature of the H$_2$CO emission over possible dynamical asymmetries traced by dust. Although a correlation with the stellar luminosity was also expected, a larger sample is required to confirm or refute this trend. A possible correlation with spectral type, together with the broad range of H$_2$CO excitation temperatures within the inner 100 au of the studied disks, hint at possible multiple chemical formation pathways for H$_2$CO, including both gas-phase reactions and ice-surface chemistry on dust grains.

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arXiv2026

exoALMA XXI: The Morphology and Dynamics of Vertical Flows

Vertical gas flows, such as winds and meridional circulations, are natural outcomes of protoplanetary disk processes and play a critical role in the earliest stages of planet formation. We analyze vertical gas motions in 14 disks as part of the exoALMA Large Program, focusing on the 12CO J=3-2 and 13CO J=3-2 emission lines. Using discminer to model the Keplerian velocity field, we extract line-of-sight velocity residuals and measure the radial and vertical components of the gas motion. Vertical motions are detected in most disks. Two types of patterns emerge: (1) oscillatory up/down flows, likely linked to instabilities, and (2) transitions from downward to upward motions that we interpret as the base of a disk wind. In most cases, the velocity amplitudes are of a few tens of m/s. Two disks, however, MWC758 and CQ Tau, show two spiral velocity features in their residual maps, red- and blue-shifted, which we interpret as vertical velocities reaching up to 350 m/s (0.7 Cs), consistent with gas motion in eccentric disks. Fast upward motions (up to 500 m/s; 1.8 Cs) is also detected in the outer disk of MWC758. Synthetic observations from (magneto)hydrodynamic simulations validate the reliability of our method. Although strong molecular winds appear to be relatively rare in 12CO and 13CO, our study shows that, when traced by deep high spectral resolution line data, protoplanetary disks exhibit ubiquitous vertical flows. However, their overall velocity structure is highly complex, preventing to identify a coherent, dominant physical mechanism driving the vertical motions across all disks, thus requiring further theoretical investigation.

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arXiv2026

exoALMA XXIII. Estimating Disk and Planet Properties from Dust Morphologies with DBNets2.0

The exoALMA large program provided an unprecedented view of the morphology and kinematics of 15 circumstellar disks, offering a biased but homogenous and well-characterized sample for population-level analysis. Continuum observations revealed numerous dust substructures, known to be potential signatures of embedded planets. We analyze the observed dust morphologies with the simulation-based inference tool DBNets2.0, assuming these are due to embedded planets at fixed locations, to infer the system properties. We estimate the putative planet mass, the disk $\alpha$-viscosity, scale-height, and dust Stokes number that would reproduce 19 substructures in 13 of the 15 exoALMA disks. We compare our results with literature estimates derived with different methods, and find good agreement in most cases. We further explore the implications of the inferred disk properties for accretion, showing that for the Herbig stars in our sample, the implied viscous accretion timescales are too long to account for their observed stellar accretion rates. Regarding planet migration, our results favor inward migration, with only three putative planets expected to migrate outward. Finally, we check for correlations of the inferred disk and planet properties with the disks' gas-to-dust mass ratio, non-axisymmetry index, and masses of the gas, dust, and host stars, finding no remarkable trend.

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arXiv2026

exoALMA XX: Tomographic Detection of Embedded Planets in Protoplanetary Disks

The exoALMA Large Program has revealed a wealth of substructures in the dust and molecular line emission of several protoplanetary discs, suggesting that planet formation may unfold within highly dynamic environments. Using synthetic observations of planet-disc interactions and disc instabilities, we demonstrate how the origin of these substructures can be investigated through a tomographic study of molecular lines, extending the scope of the analysis beyond line-centroid kinematics alone. Our results indicate that with only a few hours of ALMA integration at moderate angular resolution ($0.15''-0.30''$), it is possible to identify the key signatures driven by planets more massive than 0.1% of the stellar mass. These signatures manifest not only as deviations from Keplerian motion but also as localized line broadening, enabling accurate constraints on the orbital radius and azimuthal location of the planets. We further show that a diagnostic based on line skewness in spectrally resolved observations can help distinguish between planetary and instability-driven signatures, owing to the distinct degrees of velocity coherence associated with each mechanism. Finally, we apply this tomographic analysis to exoALMA CO line data for the discs of HD 135344B and MWC 758. In HD 135344B, we identify strongly localized velocity and line-width perturbations, suggesting the possibility of three massive planets embedded in the disc: one at $R=95$ au, exterior to the continuum substructures, and two within dust gaps at $R=41$ au and $R=73$ au. For MWC 758, the dominance of vertical-velocity spirals over localized signatures is consistent with predictions from models of moderate disc eccentricities or warps, potentially induced by a substellar companion in the inner regions of the system.

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arXiv2026

exoALMA XIX: Confirmation of Non-thermal Line Broadening in the DM Tau Protoplanetary Disk

Turbulence is expected to transport angular momentum and drive mass accretion in protoplanetary disks. One way to directly measure turbulent motion in disks is through molecular line broadening. DM Tau is one of only a few disks with claimed detection of nonthermal line broadening of 0.25cs-0.33cs, where cs is the sound speed. Using the radiative transfer code mcfost within a Bayesian inference framework that evaluates over five million disk models to efficiently sample the parameter space, we fit high-resolution (0.15", 28 m s-1) 12CO J = 3-2 observations of DM Tau from the exoALMA Large Program. This approach enables us to simultaneously constrain the disk structure and kinematics, revealing a significant nonthermal contribution to the line width of ~0.4cs, inconsistent with purely thermal motions. Using the CO-based disk structure as a starting point, we reproduce the CS J = 7-6 emission well, demonstrating that the CS (which is more sensitive to nonthermal motions than CO) agrees with the turbulence inferred from the CO fit. Establishing a well-constrained background disk model further allows us to identify residual structures in the moment maps that deviate from the expected emission, revealing localized perturbations that may trace forming planets. This framework provides a powerful general approach for extracting disk structure and nonthermal broadening directly from molecular line data and can be applied to other disks with high-quality observations.

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arXiv2026

Circumplanetary Disk Candidate in the Disk of HD 163296 Traced by Localized Emission from Simple Organics

Atacama Large Millimeter/submillimeter Array observations suggest that the disc of HD 163296 is being actively shaped by embedded, yet unseen protoplanets, as indicated by numerous gas and dust substructures consistent with planet-disc interaction models. We report the first detection of simple organic molecules, HCN and C2H, tracing a candidate circumplanetary disc (CPD) in the HD 163296 system, located at an orbital radius of $R=88\pm7$ au and azimuth $\phi=46\pm3^\circ$ (or $R=0.75''$, $\rm{{PA}}=350^\circ$ in projected sky coordinates), and originating near the midplane of the circumstellar disc. The signature is localised but spectrally resolved, and it overlaps with a previously reported planet candidate, P94, identified through kinematic perturbations traced by CO lines. We propose a scenario in which the observed chemical anomalies arise from increased heating driven by the forming planet and ongoing accretion through its CPD, facilitating the thermal desorption of species that would otherwise remain frozen out in the disc midplane, and potentially triggering the activation barriers of chemical reactions that lead to enhanced molecular production. Based on a first-order dynamical analysis of the HCN spectrum from the CPD--isolated with a 7$\sigma$ significance--we infer an upper limit on the planet mass of 1.8 $M_{\rm Jup}$, consistent with predictions from CO kinematics and constraints from direct imaging studies. By comparing the CPD sizes derived from our models with theoretical expectations where the CPD radius corresponds to roughly one-third of the planet's Hill radius, we favor CPD gas temperatures $T > 150$ K, planet masses $M_{\rm p} < 1.0$ $M_{\rm Jup}$, and CPD radii $R_{\rm CPD} < 2$ au.

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arXiv2025

exoALMA. XVIII. Interpreting large scale kinematic structures as moderate warping

The exoALMA program gave an unprecedented view of the complex kinematics of protoplanetary disks, revealing diverse structures that remain poorly understood. We show that moderate disk warps ($\sim 0.5-2^\circ$) can naturally explain many of the observed large-scale velocity features with azimuthal wavenumber $m = 1$. Using a simple model, we interpret line-of-sight velocity variations as changes in the projected Keplerian rotation caused by warping of the disk. While not a unique explanation, this interpretation aligns with growing observational evidence that warps are common. We demonstrate that such warps can also produce spiral structures in scattered light and CO brightness temperature, with $\sim 10$ K variations in MWC 758. Within the exoALMA sample, warp properties correlate with stellar accretion rates, suggesting a link between the inner disc and outer disc kinematics. If warps cause large-scale kinematic structure, this has far reaching implications for turbulence, angular momentum transport, and planet formation.

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arXiv2025

SO emission in the dynamically perturbed protoplanetary disks around CQ Tau and MWC 758

We report the serendipitous detection of the SO $J_N=6_5-5_4$ (219.949 GHz) rotational transition in archival Atacama Large Millimeter/submillimeter Array (ALMA) observations of the spiral hosting protoplanetary disks around CQ Tau (with $\approx4.9\sigma$ significance) and MWC 758 (with $\approx3.4\sigma$ significance). In the former, the SO emission comes in the shape of a ring, arises from the edge of the continuum cavity, and is qualitatively consistent, at the currently available spectral resolution, with being in Keplerian rotation. In the latter, instead, while arising primarily from inside the continuum cavity, the SO emission also extends to the continuum ring(s), and its morphology and kinematics are less clear. We put these sources in the context of the other protoplanetary disks where SO detections have been previously reported in the literature and discuss the possible origins of SO in terms of (thermal) desorption or formation in the gas phase. We argue that these processes might be fostered by dynamical perturbations caused by unseen embedded massive companions, shadows, or late-time infall, thus suggesting a possible link between perturbed dynamics and SO emission in (these) protoplanetary disks. If confirmed, our interpretation would imply that chemical evolution timescales could be significantly shorter in these systems than is commonly assumed, indicating that dynamical perturbations might influence the composition of newborn (proto-)planets by altering the volatile makeup of their formation environment.

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arXiv2025

exoALMA XIV. Gas Surface Densities in the RX J1604.3-2130 A Disk from Pressure-broadened CO Line Wings

The gas surface density is one of the most relevant physical quantities in protoplanetary disks. However, its precise measurement remains highly challenging due to the lack of a direct tracer. In this study, we report the spatially-resolved detection of pressure-broadened line wings in the CO $J=3-2$ line in the RX J1604.3-2130 A transition disk as part of the exoALMA large program. Since pressure-broadened line wings are sensitive to the total gas volume density, we robustly constrain the radial dependence of the gas surface density and midplane pressure in the region located $50-110$ au from the central star, which encompasses the dust ring of the system. The peak radius of the midplane pressure profile matches the dust ring radial location, directly proving radial dust trapping at a gas pressure maximum. The peak gas surface density is $18-44\ {\rm g\ cm^{-2}}$} and decreases at radii interior to and exterior of the dust ring. A comparison of the gas and dust surface densities suggests that the disk turbulence is as low as $\alpha_{\rm turb} \sim 2\times10^{-4}$. Despite dust trapping, the gas-to-dust surface density ratio at the ring peak is { $70-400$}, which implies already-formed protoplanets and/or less efficient dust trapping. The gas surface density drop at radii interior to the ring is consistent with a gas gap induced by a Jupiter-mass planet. The total gas mass within $50 < r < 110$ au is estimated to be $\sim 0.05-0.1\ M_\odot$ ($50-100\ {M_{\rm Jup}}$), suggesting that planetary system formation is possible.

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arXiv2025

exoALMA. XVI. Predicting Signatures of Large-scale Turbulence in Protoplanetary Disks

Turbulent gas motions drive planet formation and protoplanetary disk evolution. However, empirical constraints on turbulence are scarce, halting our understanding of its nature. Resolving signatures of the large-scale perturbations driven by disk instabilities may reveal clues on the origin of turbulence in the outer regions of planet-forming disks. We aim to predict the observational signatures of such large-scale flows, as they would appear in high-resolution Atacama Large Millimeter/submillimeter Array observations of CO rotational lines, such as those conducted by the exoALMA Large Program. Post-processing 3D numerical simulations, we explored the observational signatures produced by three candidate (magneto-)hydrodynamical instabilities to operate in the outer regions of protoplanetary disks: the vertical shear instability (VSI), the magneto-rotational instability (MRI), and the gravitational instability (GI). We found that exoALMA-quality observations should capture signatures of the large-scale motions induced by these instabilities. Mainly, flows with ring, arc, and spiral morphologies are apparent in the residuals of synthetic velocity centroid maps. A qualitative comparison between our predictions and the perturbations recovered from exoALMA data suggests the presence of two laminar disks and a scarcity of ring- and arc-like VSI signatures within the sample. Spiral features produced by the MRI or the GI are still plausible in explaining observed disk perturbations. Supporting these scenarios requires further methodically comparing the predicted perturbations and the observed disks' complex dynamic structure.

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arXiv2025

exoALMA XI: ALMA Observations and Hydrodynamic Models of LkCa 15: Implications for Planetary Mass Companions in the Dust Continuum Cavity

In the past decade, the Atacama Large Millimeter/submillimeter Array (ALMA) has revealed a plethora of substructures in the disks surrounding young stars. These substructures have several proposed formation mechanisms, with one leading theory being the interaction between the disk and newly formed planets. In this Letter, we present high angular resolution ALMA observations of LkCa~15's disk that reveal a striking difference in dust and CO emission morphology. The dust continuum emission shows a ring-like structure characterized by a dust-depleted inner region of $\sim$40 au in radius. Conversely, the CO emission is radially smoother and shows no sign of gas depletion within the dust cavity. We compare the observations with models for the disk-planet interaction, including radiative transfer calculation in the dust and CO emission. This source is particularly interesting as the presence of massive planets within the dust cavity has been suggested based on previous NIR observations. We find that the level of CO emission observed within the dust cavity is inconsistent with the presence of planets more massive than Jupiter orbiting between 10-40 au. Instead, we argue that the LkCa~15 innermost dust cavity might be created either by a chain of low-mass planets, or by other processes that do not require the presence of planets.

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arXiv2025

exoALMA II: Data Calibration and Imaging Pipeline

The exoALMA Large Program was designed to search for subtle kinematic deviations from Keplerian motion, indicative of embedded planets, in high angular and spectral resolution Band 7 observations of $^{12}$CO, $^{13}$CO and CS emission from protoplanetary disks. This paper summarizes the calibration and imaging pipelines used by the exoALMA collaboration. With sources ranging in diameter from 2.4" to 13.8" when probed by $^{12}$CO, multiple antennae configurations were required to maximally recover all spatial information (including the ACA for 7 sources). Combining these datasets warranted particular care in their alignment during calibration and prior to imaging, so as not to introduce spurious features that might resemble the kinematic deviations being investigated. Phase decoherence was found in several datasets, which was corrected by an iterative self-calibration procedure, and we explored the effects of the order of operations of spatial alignment, flux scaling, and self-calibration. A number of different imaging sets were produced for the continuum and line emission, employing an iterative masking procedure that minimizes bias due to non-Keplerian motions in the disk.

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arXiv2025

exoALMA. VI. Rotating under Pressure: Rotation curves, azimuthal velocity substructures, and pressure variations

The bulk motion of the gas in protoplanetary disks around newborn stars is nearly Keplerian. By leveraging the high angular and spectral resolution of ALMA, we can detect small-scale velocity perturbations in molecular line observations caused by local gas pressure variations in the disk, possibly induced by embedded protoplanets. This paper presents the azimuthally averaged rotational velocity and its deviations from Keplerian rotation ($\delta\upsilon_{\phi}$) for the exoALMA sample, as measured in the $^{12}$CO and $^{13}$CO emission lines. The rotation signatures show evidence for vertically stratified disks, in which $^{13}$CO rotates faster than $^{12}$CO due to a distinct thermal gas pressure gradient at their emitting heights. We find $\delta\upsilon_{\phi}$-substructures in the sample on both small ($\sim$10 au) and large ($\sim$100 au) radial scales, reaching deviations up to 15% from background Keplerian velocity in the most extreme cases. More than 75% of the rings and 80% of the gaps in the dust continuum emission resolved in $\delta\upsilon_{\phi}$ are co-located with gas pressure maxima and minima, respectively. Additionally, gas pressure substructures are observed far beyond the dust continuum emission. For the first time, we determined the gas pressure derivative at the midplane from observations and found it to align well with the dust substructures within the given uncertainties. Based on our findings, we conclude that gas pressure variations are likely the dominant mechanism for ring and gap formation in the dust continuum.

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arXiv2025

exoALMA. XVII. Characterizing the Gas Dynamics around Dust Asymmetries

The key planet-formation processes in protoplanetary disks remain an active matter of research. One promising mechanism to radially and azimuthally trap millimeter-emitting dust grains, enabling them to concentrate and grow into planetesimals, is anticyclonic vortices. While dust observations have revealed crescent structures in several disks, observations of their kinematic signatures are still lacking. Studying the gas dynamics is, however, essential to confirm the presence of a vortex and understand its dust trapping properties. In this work, we make use of the high-resolution and sensitivity observations conducted by the exoALMA large program to search for such signatures in the $^{12}$CO and $^{13}$CO molecular line emission of four disks with azimuthal dust asymmetries: HD 135344B, HD 143006, HD 34282, and MWC 758. To assess the vortex features, we constructed an analytical vortex model and performed hydrodynamical simulations. For the latter, we assumed two scenarios: a vortex triggered at the edge of a dead zone and of a gap created by a massive embedded planet. These models reveal a complex kinematical morphology of the vortex. When compared to the data, we find that none of the sources show a distinctive vortex signature around the dust crescents in the kinematics.

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arXiv2025

exoALMA XV: Interpreting the height of CO emission layer

The availability of exquisite data and the development of new analysis techniques have enabled the study of emitting heights in proto-planetary disks. In this paper we introduce a simple model linking the emitting height of CO to the disk surface density and temperature structure. We then apply the model to measurements of the emitting height and disk temperature conducted as part of exoALMA, integrated with additional legacy measurements from the MAPS Large Programme, to derive CO column densities and surface density profiles (assuming a CO abundance) for a total of 14 disks. A unique feature of the method we introduce to measure surface densities is that it can be applied to optically thick observations, rather than optically thin as conventionally done. While we use our method on a sample of well studied disks where temperature structures have been derived using two emission lines, we show that reasonably accurate estimates can be obtained also when only one molecular transition is available. With our method we obtain independent constraints from $^{12}$CO and $^{13}$CO and we find they are in general good agreement using the standard $^{12}$C/$^{13}$C isotopic ratio. The masses derived from our method are systematically lower compared with the values derived dynamically from the rotation curve if using an ISM CO abundance, implying that CO is depleted by a median factor $\sim$20 with respect to the ISM value, in line with other works that find that CO is depleted in proto-planetary disks.

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