arXiv subjects

Simon Casassus

Publications and source records attributed to Simon Casassus.

At least 19 recordsLinked to original sources

arXiv2026

Substructures in Planet-Forming Disks with the SKAO

Disks of gas and dust orbiting young stars are the arenas and material reservoirs for planet formation. Over the past decade, multiwavelength observations, from infrared to radio, have resolved the spatial distribution of hundreds of protoplanetary disks in nearby star-forming regions, revealing a diverse zoo of substructures. These substructures are morphological features such as rings, gaps, spirals, vortices, asymmetries, warps, or clumps that trace variations in density, temperature, or composition relative to an otherwise smooth distribution of gas and dust. Many unknowns persist as to the origin of these substructures, their role in planet assembly, and their true properties. SKA-Mid Band 5b continuum observations, offering angular resolutions of $\sim 0.05''$ ($\sim 0.15''$) with AA4 (AA*) at $12.5$ GHz / $2.4$ cm, will enable new progress at this frontier. In this chapter, we outline the open questions in the field of disk substructure that SKA-Mid is uniquely poised to address, with a lens on dust thermal emission.

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arXiv2026

Hourly radio variability of PDS70c from time-differential photometry

The radio emission mechanisms from accreting protoplanets, and their variability, link observations and physical properties. We revisit the variability of the ~343GHz (ALMA Band7) flux density from PDS70c (F_B7). The subtraction of the extended time-averaged signal may enable the measurement of the flux density from variable and embedded point sources. Visibility alignment and self-calibration yields close to thermal residuals in each execution block (EB) of ALMA observations, allowing the time-differential photometry of point-source in the visibility domain. The variability of PDS70c is checked against synthetic control point sources. In images of the 2017 ALMA dataset, with three ~1h EBs, PDS70c was detected only on 6 Dec. 2017, where F_B7 rose by 228%+-69% (3.3sigma). Time-differential photometry confirms a rise by 170%+-46% (3.7sigma). An application to ~2h EBs from the 2023 dataset resulted in constant flux densities, within a scatter of ~15%. However, F_B7(t) shows some scatter when splitting the deep 2023 EBs in 20min intervals, with a chi2 test significant at 2.6sigma, and an intrinsic dispersion of 49%21%. The radio variability of PDS70c, observed over hours but averaged out on longer timescales, is indeed expected if the signal is due to HI free-free from an accretion shock on a circum-planetary disk surface. A planet-to-environment mass ratio <1E-4 is required to avoid smoothing by radiative diffusion if the signal is due to thermal emission from the environment.

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arXiv2026

The Ophiuchus DIsc Survey Employing ALMA (ODISEA). Substructures as a function of SED Class and disc mass in 100 systems

Current high-resolution studies of protoplanetary discs are biased toward small samples of the brightest (flux > 50 mJy at 225 GHz) and largest systems. We present a complete flux-limited high-resolution study of about 100 discs from the Ophiuchus Disc Survey Employing ALMA (ODISEA), spanning fluxes of about 4-400 mJy at 225 GHz. We investigate substructures as a function of SED Class and disc mass using ALMA Band 8 continuum observations (410 GHz, 0.7 mm). The survey extends to faint discs containing as little as about 2 Earth masses of dust. Given the flux-size relation, sources with flux >= 20 mJy were observed at about 20 au resolution, while fainter sources were observed at three times higher resolution. We used the Frankenstein code to fit non-parametric models to the visibilities, achieving sub-beam resolution. We classify substructures into an evolutionary sequence linking morphology with stages of giant planet formation, from featureless discs (Stage 0) to inflection-point discs, gap-ring systems, and discs with central cavities. Despite higher optical depths, Band 8 efficiently traces substructures and recovers gaps and cavities seen at longer wavelengths with shorter integration times. Discs with dust masses above about 10 Earth masses show structures consistent with this sequence, even at modest resolution. The fraction of evolved substructures increases from 23 percent (6 of 26) in Class I sources to at least 53 percent (17 of 32) in Class II objects. In contrast, lower-mass discs rarely show such features, likely due to the steep flux-size relation and limited resolution. These results support a link between substructures in discs above about 10 Earth masses and giant planet formation, and highlight Band 8 as a powerful probe of disc substructures.

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arXiv2026

ALMA Band1 observations of the rhoOphW filament I. Enhanced power from excess microwave emission at high spatial frequencies

The rhoOphW photo-dissociation region (PDR) is an example source of bright excess microwave emission (EME), over synchrotron, free-free, and the Rayleigh-Jeans tail of the sub-millimetre (sub-mm) dust continuum. Its filamentary morphology follows roughly that of the IR poly-cyclic aromatic hydrocarbon (PAHs) bands. The EME signal in rhoOphW drops abruptly above ~30GHz and its spectrum can be interpreted in terms of electric-dipole radiation from spinning dust grains, or ``spinning dust''. Deep and high-fidelity imaging and spectroscopy of rhoOphW may reveal the detailed morphology of the EME signal, free from imaging priors, while also enabling a search for fine structure in its spectrum. The same observations may constrain the spectral index of the high-frequency drop. An ALMA Band1 mosaic yields a deep deconvolved image of the filament at 36-44GHz, which we use as template for the extraction of a spectrum via cross-correlation in the uv-plane. Simulations and cross-correlations on near-infrared ancillary data yield estimates of flux-loss and biases. The spectrum is a power law, with no detectable fine structure. It follows a spectral index alpha=-0.78+-0.05, in frequency, with some variations along the filament. Interestingly, the Band1 power at high spatial frequencies increases relative to that of the IR signal, with a factor of two more power in Band1 at ~20'' than at ~100'' (relative to IRAC3.6um). An extreme of such radio-only structures is a compact EME source, without IR counterpart. It is embedded in strong and filamentary Band1 signal, while the IRAC maps are smooth in the same region. We provide multi-frequency intensity estimates for spectral modelling.

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arXiv2026

Impact of embedded circumplanetary winds on the circumstellar disk: I. Reshaping the local accretion environment

The existence of winds is among the uncertainties related to the growth of giant planets. Such circumplanetary outflows have been proposed to explain kinematic and chemical structures in protoplanetary disks. We investigate the immediate impact of circumplanetary outflows on the circumstellar disk environment, the planetary vicinity, and planetary growth. We performed three-dimensional hydrodynamic simulations using \texttt{FARGO3D}, implementing a parametric wind launched from the vicinity of an embedded planet. Although the imposed configurations for the outflows do not significantly alter the global structure of the disk, they do substantially redistribute material in the vicinity of the embedded planet. In particular, the wind redirects accretion flows from polar to equatorial latitudes, resulting in variable accretion patterns over time. Although the mass accretion rate variations depend on the efficiency of the outflows, their presence diminishes the accretion rate over time and the total mass reservoir within the Hill sphere and the planet's direct vicinity, potentially slowing or limiting planetary growth.

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arXiv2026

ALMA 873 $μ$m Polarization Observations of the PDS~70 Disk

At a 112.4 pc distance, the PDS70 protoplanetary disk is a rare case that has been confirmed to host two accreting planets. This makes it the most important laboratory for studying dust growth in the context of planet formation. Here we present the first deep, full polarization observations at 873 $μ$m wavelength. We detected $\sim$1%-2.5% linear polarization over the bulk of the $\sim$55-100 AU (sub)millimeter ring. The polarization position angles align preferentially with the projected minor axis of the disk. The standard interpretation is that the observed polarization is caused by dust self-scattering, with a maximum dust grain size of $\sim$100 $μ$m. On $\gtrsim$10 AU scales, which can be resolved by the presented 873-3075 $μ$m observations, the ring is marginally optical thick at 873 $μ$m wavelength. Using Monte Carlo radiative transfer simulations, we found that an azimuthally asymmetric, marginally optically thick ring with a maximum dust grain size of $\sim$87 $μ$m can reproduce the observed 873 $μ$m polarization position angles and percentages. This study indicates that the coagulation of ice-coated dust in the protoplanetary disk may be limited by fragmentation or bouncing.

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arXiv2026

Polycyclic aromatic hydrocarbon (PAH) abundances in the disk around T Chamaeleontis (T Cha): PAH sizes, ionization fraction, and mass during JWST observations

The T Tauri star T Cha is known to have a protoplanetary disk with a dust gap separating the inner and outer disk regions. The mid-infrared JWST spectrum of T Cha shows multiple prominent aromatic infrared bands (AIBs) around 6.2, 8.1, and 11.3 $μ$m. AIBs are commonly accepted as the emission stemming from PAH molecules. We aim to characterize the PAHs giving rise to the AIBs observed in the JWST spectrum of T Cha. Our objective is to estimate the PAH abundances, in terms of their sizes, ionization fraction, and mass, in the disk of T Cha. We perform spectral fitting of the observed AIBs to identify the possible underlying PAH emission components. We transfer the stellar radiation through a parametric disk model in order to reproduce the mid-IR spectrum, optical photometric fluxes, and mm continuum band fluxes of T Cha. We include PAH dust grains, which are stochastically heated, in our model calculations to simulate the AIBs. Thus, we estimate the PAH abundances from our modelling. We use the results from previous observations and modelling efforts to reduce our model degeneracies. The overall disk morphology - an inner and an outer disk separated by a dust gap - derived in this work is consistent with the previous results from Spitzer, VLT, and ALMA observations. PAHs are located within the outer disk in our model. Given our best fiducial model, we estimate a population of small PAHs of <26 C atoms, with an ionized PAH fraction of $\sim0.15$. We also obtain a PAH-to-dust mass ratio of ~7$\times$10$^{-3}$, which amounts to ~17% of the PAH-to-dust mass ratio observed in the ISM. We predict the outer disk to have a frontal wall with smaller dust grains, sizes limited up to $μ$m-order, in order to properly fit the continuum slope within 14-25 $μ$m. We propose a possibility of sub-micron dust grains within the gap to justify an observed plateau around ~10 $μ$m in the JWST spectrum.

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arXiv2025

Multi-frequency observations of PDS 70c: Radio emission mechanisms in the circum-planetary environment

PDS 70c is a source of Ha emission and variable sub-mm signal. Understanding its emission mechanisms may enable observations of accretion rates and physical conditions in the circum-planetary environment. We report ALMA observations of PDS 70 at 145 GHz (Band 4), 343.5 GHz (Band 7) and 671 GHz (Band 9) and compare with data at 97.5 GHz (Band 3), taken within two months. The radio spectrum (SED) is analyzed with an analytical circumplanetary disk (CPD) model. In a novel approach including the free-free continuum from H I, metals (e.g. K I) and H-. New detections in Bands 3 (tentative at 2.6sigma), 4 (5sigma), and 7 (re-detected at 9sigma) are consistent with optically thick thermal emission from PDS 70c (spectral index 2+-0.2). However, a Band 9 non-detection lies 2.6sigma below an optically thick extrapolation. A viscous dusty disk is inconsistent with the data, even with the inclusion of ionised jets. Interestingly, the central temperatures in such CPD models are high enough to ionise H I, with huge emission measures and an optically thick spectrum that marginally accounts for the SED (within 3sigma of Band 9). By contrast, uniform-slab models suggest much lower emission measures to account for the Band 9 drop, with ionisation fractions ~1e-7, and an outer radius ~0.1 au. Such conditions are recovered if the CPD interacts with a planetary magnetic field, leading to a radially variable viscosity alpha(R)<~1 and midplane temperatures ~1e3 K that regulate metal ionisation. However, the H- opacity still results in an optically thick SED, overshooting Band 9. We find that the optically thin turnover at ~600 GHz is only recovered if a thin shocked layer is present at the CPD surface, as suggested by simulations. A photospheric shock or accretion funnels are ruled out as radio emission sources because their small solid angles would require T~1e6 K, which is unrealistic for planetary accretion.

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arXiv2025

The Ophiuchus DIsk Survey Employing ALMA (ODISEA): A Unified Evolutionary Sequence of Planet-Driven Substructures Explaining the Diversity of Disk Morphologies

Understanding the origin of substructures in protoplanetary disks and their connection to planet formation is currently one of the main challenges in astrophysics. While some disks appear smooth, most exhibit diverse substructures such as gaps, rings, or inner cavities, with varying brightness and depth. As part of the Ophiuchus Disk Survey Employing ALMA (ODISEA), we previously proposed an evolutionary sequence to unify this diversity, driven by the formation of giant planets through core accretion and subsequent planet-disk interactions. By combining the disk evolution and planet formation code PLANETALP with the radiative transfer code RADMC-3D, we have now reproduced the key aspects of the proposed evolutionary sequence. Starting with a smooth disk (like e.g., WLY 2-63), we modeled the evolution of a fiducial disk with a 1 Jupiter-mass planet at 57 au. Within a few hundreds of orbits, a narrow gap forms, resembling ISO-Oph 17. By $\sim$0.1 Myr, the gap widens, and dust accumulates at the cavity edge, producing a structure similar to Elias 2-24. At $\sim$0.4 Myr, the disk evolves further into a morphology akin to DoAr 44, characterized by a smaller inner disk and a brighter inner rim. By $\sim$1 Myr, the system transitions to a single narrow ring, resembling RXJ1633.9-2442. This line of work strongly supports the planetary origin of substructures and enables the possibility of identifying a population of planets that is currently beyond the reach of more direct detection techniques.

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arXiv2025

The Ophiuchus DIsk Survey Employing ALMA (ODISEA): Complete Size Distributions for the 100 Brightest Disks Across Multiplicity and SED Classes

The size of a protoplanetary disk is a fundamental property, yet most remain unresolved, even in nearby star-forming regions (d $\sim$ 140-200 pc). We present the complete continuum size distribution for the $105$ brightest protoplanetary disks (M$_{\text{dust}}$ $\gtrsim$ 2 M$_{\oplus}$) in the Ophiuchus cloud, obtained from ALMA Band 8 (410 GHz) observations at 0.05$^{\prime\prime}$ (7 au) to 0.15$^{\prime\prime}$ (21 au) resolution. This sample includes 54 Class II and 51 Class I and Flat Spectrum sources, providing a comprehensive distribution across evolutionary stages. We measure the Half Width at Half Maximum (HWHM) and the radius encircling $68\%$ of the flux ($R_{68\%}$) for most non-binary disks, yielding the largest flux-limited sample of resolved disks in any star-forming region. The distribution is log-normal with a median value of $\sim$14 au and a logarithmic standard deviation $σ_{\log} = 0.46$ (factor of 2.9 in linear scale). Disks in close binary systems ($<$ 200 au separation) have smaller radii, with median value of $\sim$5 au, indicating efficient radial drift as predicted by dust evolution models. The size distribution for young embedded objects (SED Class I and Flat Spectrum, age $\lesssim$ 1 Myr) is similar to that of Class II objects (age $\sim$ a few Myr), implying that pressure bumps must be common at early disk stages to prevent mm-sized particle migration at au scales.

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arXiv2024

Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): Dynamical Evidence of a Spiral-Arm-Driving and Gap-Opening Protoplanet from SAO 206462 Spiral Motion

In the early stages of planetary system formation, young exoplanets gravitationally interact with their surrounding environments and leave observable signatures on protoplanetary disks. Among these structures, a pair of nearly symmetric spiral arms can be driven by a giant protoplanet. For the double-spiraled SAO 206462 protoplanetary disk, we obtained three epochs of observations spanning 7 yr using the Very Large Telescope's SPHERE instrument in near-infrared $J$-band polarized light. By jointly measuring the motion of the two spirals at three epochs, we obtained a rotation rate of $-0.85^\circ\pm0.05^\circ~{\rm yr}^{-1}$. This rate corresponds to a protoplanet at $66\pm3$ au on a circular orbit dynamically driving both spirals. The derived location agrees with the gap in ALMA dust-continuum observations, indicating that the spiral driver may also carve the observed gap. What is more, a dust filament at $\sim$63 au observed by ALMA coincides with the predicted orbit of the spiral-arm-driving protoplanet. This double-spiraled system is an ideal target for protoplanet imaging.

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arXiv2024

First JVLA Radio Observation on PDS70

PDS~70 is a protoplanetary system that hosts two actively accreting gas giants, namely PDS~70b and PDS~70c. The system has a $\sim$60--100 au dusty ring that has been resolved by ALMA, along with circumplanetary disks around the two gas giants. Here we report the first JVLA Q (40--48 GHz), Ka (29--37 GHz), K (18--26 GHz), and X (8--12 GHz) bands continuum observations, and the complementary ALMA Bands 3 ($\sim$98 GHz) and 4 ($\sim$145 GHz) observations towards PDS~70. The dusty ring appears azimuthally asymmetric in our ALMA images. We obtained firm detections at Ka and K bands without spatially resolving the source; we obtained a marginal detection at Q band, and no detection at X band. The spectral indices ($α$) are 5$\pm$1 at 33--44 GHz and 0.6$\pm$0.2 at 22--33 GHz. At 10--22 GHz, the conservative lower limit of $α$ is 1.7. The 33--44 GHz flux density is likely dominated by the optically thin thermal emission of grown dust with $\gtrsim$1 mm maximum grain sizes, which may be associated with the azimuthally asymmetric substructure induced by planet-disk interaction. Since PDS~70 was not detected at X band, we found it hard to explain the low spectral index at 22--33 GHz only with free-free emission. Hence, we attribute the dominant emission at 22--33 GHz to the emission of spinning nanometer-sized dust particles, while free-free emission may partly contribute to emission at this frequency range. In some protoplanetary disks, the emission of spinning nanometer-sized dust particles may resemble the 20--50 GHz excess in the spectra of millimeter-sized dust. The finding of strong continuum emission of spinning nanometer-sized particles can complicate the procedure of constraining the properties of grown dust. Future high-resolution, multi-frequency JVLA/ngVLA and SKA observations may shed light on this issue.

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arXiv2023

Radio-continuum decrements associated to shadowing from the central warp in transition disc DoAr44

Warps have often been used to explain disc properties, but well characterised examples are important due to their role in disc evolution. Scattered light images of discs with central gaps have revealed sharp warps, such that the outer rings are shadowed by tilted inner discs. The near-IR intensity drops along the ring around TTauri star DoAr44 have been interpreted in terms of a central warp. We report new ALMA observations of DoAr44 in the continuum at 230 GHz and 350 GHz (at ~10 au), along with a new epoch of SPHERE/IRDIS differential polarised imaging taken during excellent weather conditions. The ALMA observations resolve the ring and confirm the decrements proposed from deconvolution of coarse 336 GHz data. The scattered light image constrains the dips, which correspond to a misaligned inner disc with a relative inclination $ξ$ = 21.4 $^{+6.7}_{-8.3}$ deg. The SPHERE intensity profile shows a morphological change compared to a previous epoch that may be interpreted as a variable orientation of the inner disc, from $ξ$ ~30 deg to $ξ$ ~20 deg. The intensity dips probably correspond to temperature decrements, as their mm-spectral index, $α^{230 GHz}_{350 GHz}$ ~2.0 $\pm$ 0.1, is indicative of optically thick emission. The azimuth of the two temperature decrements are leading clockwise relative to the IR-dips, by $η$ = 14.95 deg and $η$ = 7.92 deg. For a retrograde disc, such shifts are expected from a thermal lag and imply gas surface densities of $Σ_g$ = 117 $\pm$ 10 g/cm$^2$ and $Σ_g$ = 48 $\pm$ 10 g/cm$^2$. A lopsided disc, with contrast ratio $f_r$=2.4 $\pm$ 0.5, is also consistent with the large continuum crescent.

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arXiv2023

Azimuthal temperature variations in ISO-Oph2 from multi-frequency ALMA observations

Environmental effects, such as stellar fly-bys and external irradiation, are thought to affect the evolution of protoplanetary disks in clustered star formation. Previous ALMA images at 225 GHz of the ISO-Oph 2 binary revealed a peculiar morphology in the disk of the primary, perhaps due to a possible fly-by with the secondary. Here we report on new ALMA continuum observations of this system at 97.5 GHz, 145 GHz and 405 GHz, which reveal strong morphological variations. Multi-frequency positional alignment allows to interpret these spectral variations in terms of underlying physical conditions. ISO-Oph 2A is remarkably offset from the centroid of its ring, at all frequencies, and the disk is lopsided, pointing at gravitational interactions. However, the dust temperature also varies in azimuth, with two peaks whose direction connects with HD 147889, the earliest-type star in the Ophiuchus complex, suggesting that it is the dominant heat source. The stellar environment of ISO-Oph 2 appears to drive both its density structure and its thermal balance.Simon Casassus, Lucas Cieza, Miguel Cárcamo, Álvaro Ribas, Valentin Christiaens, Abigali Rodríguez-Jiménez, Carla Arce-Tord, Trisha Bhowmik, Prachi Chavan, Camilo González-Ruilova, Rafael Martínez-Brunner, Valeria Guidotti, Mauricio Leiva

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arXiv2023

Resolving the Binary Components of the Outbursting Protostar HBC 494 with ALMA

Episodic accretion is a low-mass pre-main sequence phenomenon characterized by sudden outbursts of enhanced accretion. These objects are classified into two: protostars with elevated levels of accretion that lasts for decades or more, called FUors, and protostars with shorter and repetitive bursts, called EXors. HBC 494 is a FUor object embedded in the Orion Molecular Cloud. Earlier Atacama Large (sub-)Millimeter Array (ALMA) continuum observations showed an asymmetry in the disk at 0.''2 resolution. Here, we present follow-up observations at ~0.''03, resolving the system into two components: HBC 494 N (primary) and HBC 494 S (secondary). No circumbinary disk was detected. Both disks are resolved with a projected separation of ~0.''18 (75 au). Their projected dimensions are 84+/-1.8 x 66.9+/-1.5 mas for HBC 494 N and 64.6+/-2.5 x 46.0+/-1.9 mas for HBC 494 S. The disks are almost aligned and with similar inclinations. The observations show that the primary is ~5 times brighter/more massive and ~2 times bigger than the secondary. We notice that the northern component has a similar mass to the FUors, while the southern has to EXors. The HBC 494 disks show individual sizes that are smaller than single eruptive YSOs. In this work, we also report 12CO, 13CO, and C18O molecular line observations. At large scale, the 12CO emission shows bipolar outflows, while the 13CO and C18O maps show a rotating and infalling envelope around the system. At a smaller scale, the 12CO and 13CO moment zero maps show cavities within the continuum disks' area, which may indicate continuum over-subtraction or slow-moving jets and chemical destruction along the line-of-sight.

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arXiv2023

Gas distribution in ODISEA sources from ALMA long-baseline observations in $^{12}$CO(2-1)

The $^{12}$CO rotational lines in protoplanetary discs are good tracers of the total spatial extension of the gas component, and potentially planet-disc interactions. We present ALMA long baseline observations of the $^{12}$CO(2-1) line of ten protoplanetary discs from the Ophiuchus DIsc Survey Employing ALMA (ODISEA) project, aiming to set constraints on the gas distribution of these sources. The position angle of the gaseous disc can be inferred for five sources using high-velocity channels, which trace the gas in the inner part of the disc. We compare the high-velocity PAs to the orientations inferred from the continuum, representative of the orientation over $\sim$ 53 to 256 au in these resolved discs. We find a significant difference in orientation for DoAr 44, which is evidence of a tilted inner disc. Eight discs show evidence of gas inside inner dust cavities or gaps, and the disc of ISO-Oph 196 is not detected in $^{12}$CO(2-1), except for the compact signal located inside its dust cavity. Our observations also point out a possible outflow in WLY 2-63.

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arXiv2022

Discovery of a brown dwarf with quasi-spherical mass-loss

We report the serendipitous discovery of an elliptical shell of CO associated with the faint stellar object SSTc2d J163134.1-24006 as part of the "Ophiuchus Disk Survey Employing ALMA" (ODISEA), a project aiming to study the entire population of protoplanetary disks in the Ophiuchus Molecular Cloud from 230 GHz continuum emission and $^{12}$CO (J=2-1), $^{13}$CO (J=2-1) and C$^{18}$CO (J=2-1) lines readable in Band-6. Remarkably, we detect a bright $^{12}$CO elliptical shape emission of $\sim$ 3$^{"}$ $\times$ 4$^{"}$ towards SSTc2d J163134.1-24006 without a 230 GHz continuum detection. Based on the observed near-IR spectrum taken with the Very Large Telescope (KMOS), the brightness of the source, its 3-dimensional motion, and Galactic dynamic arguments, we conclude that the source is not a giant star in the distant background ($>$5 - 10 kpc) and is most likely to be a young brown dwarf in the Ophiuchus cloud, at a distance of just $\sim$139 pc. This is the first report of quasi-spherical mass loss in a young brown dwarf. We suggest that the observed shell could be associated with a thermal pulse produced by the fusion of deuterium, which is not yet well understood, but for a sub-stellar object is expected to occur during a short period of time at an age of a few Myr, in agreement with the ages of the objects in the region. Other more exotic scenarios, such as a merger with planetary companions, cannot be ruled out from the current observations.

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arXiv2022

The Doppler-flip in HD100546 as a disk eruption: the elephant in the room of kinematic protoplanet searches

The interpretation of molecular-line data in terms of hydro dynamical simulations of planet-disk interactions fosters new hopes for the indirect detection of protoplanets. In a model-independent approach, embedded protoplanets should be found at the roots of abrupt Doppler flips in velocity centroid maps. However, the largest velocity perturbation known for an unwarped disk, in the disk of HD100546, leads to a conspicuous Doppler flip that coincides with a thick dust ring, in contradiction with an interpretation in terms of a >~ 1Mjup body. Here we present new ALMA observations of the 12CO(2-1) kinematics in HD\,100546, with a factor of two finer angular resolutions. We find that the disk rotation curve is consistent with a central mass 2.1 < M* /Msun < 2.3, and that the blue-shifted side of the Doppler flip is due to vertical motions, reminiscent of the disk wind proposed previously from blue-shifted SO lines. We tentatively propose a qualitative interpretation in terms of a surface disturbance to the Keplerian flow, i.e. a disk eruption, driven by an embedded outflow launched by a ~10Mearth body. Another interpretation involves a disk-mass-loading hot-spot at the convergence of an envelope accretion streamer.

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