arXiv subjects

Gaylor Wafflard-Fernandez

Publications and source records attributed to Gaylor Wafflard-Fernandez.

25 records · Page 2Linked to original sources

arXiv2025

exoALMA XII: Weighing and sizing exoALMA disks with rotation curve modelling

The exoALMA large program offers a unique opportunity to investigate the fundamental properties of protoplanetary disks, such as their masses and sizes, providing important insights in the mechanism responsible for the transport of angular momentum. In this work, we model the rotation curves of CO isotopologues $^{12}$CO and $^{13}$CO of ten sources within the exoALMA sample, and we constrain the stellar mass, the disk mass and the density scale radius through precise characterization of the pressure gradient and disk self gravity. We obtain dynamical disk masses for our sample measuring the self-gravitating contribution to the gravitational potential. We are able to parametrically describe their surface density, and all of them appear gravitationally stable. By combining dynamical disk masses with dust continuum emission data, we determine an averaged gas-to-dust ratio of approximately 400, not statistically consistent with the standard value of 100, assuming optically thin dust emission. In addition, the measurement of the dynamical scale radius allows for direct comparison with flux-based radii of gas and dust. This comparison suggests that substructures may influence the size of the dust disk, and that CO depletion might reconcile our measurements with thermochemical models. Finally, with the stellar mass, disk mass, scale radius, and accretion rate, and assuming self-similar evolution of the surface density, we constrain the effective $α_S$ for these systems. We find a broad range of $α_S$ values ranging between $10^{-5}$ and $10^{-2}$.

astro-ph.EP↗

arXiv2025

exoALMA IV: Substructures, Asymmetries, and the Faint Outer Disk in Continuum Emission

The exoALMA Large Program targeted a sample of 15 disks to study gas dynamics within these systems, and these observations simultaneously produced continuum data at 0.9 mm (331.6 GHz) with exceptional surface brightness sensitivity at high angular resolution. To provide a robust characterization of the observed substructures, we performed a visibility space analysis of the continuum emission from the exoALMA data, characterizing axisymmetric substructures and nonaxisymmetric residuals obtained by subtracting an axisymmetric model from the observed data. We defined a nonaxisymmetry index and found that the most asymmetric disks predominantly show an inner cavity and consistently present higher values of mass accretion rate and near-infrared excess. This suggests a connection between outer disk dust substructures and inner disk properties. The depth of the data allowed us to describe the azimuthally averaged continuum emission in the outer disk, revealing that larger disks (both in dust and gas) in our sample tend to be gradually tapered compared to the sharper outer edge of more compact sources. Additionally, the data quality revealed peculiar features in various sources, such as shadows, inner disk offsets, tentative external substructures, and a possible dust cavity wall.

astro-ph.EP↗

arXiv2025

Gone with the wind: the outward migration of eccentric giant planets in windy disks

Recent studies indicate that circumstellar disks exhibit weak turbulence, with their dynamics and evolution being primarily influenced by magnetic winds. However, most numerical studies have focused on planet-disk interactions in turbulent disk models. We aim to explore how wind-driven accretion affects the orbital and eccentricity evolution of a Jovian planet within a magnetized disk. Conversely, we seek to determine in what extent such a planet can modify the accretion behavior and the wind dynamics. We perform high-resolution 3D global non-ideal magneto-hydrodynamic (MHD) simulations of a massive gap-carving planet interacting with a wind-launching disk, using the accelerated code IDEFIX. We consider the influence of the gap shape on planet migration by restarting a "fixed-planet" simulation at three different times, from which the planet evolves freely in the disk. For a strong initial magnetization and a sufficiently deep planet gap, we find that the planet becomes moderately eccentric, and its migration is slow, unsteady and mostly outward. This migration pattern is due to the gap's radial asymmetry which enhances the inner Lindblad torque while reducing the outer Lindblad torque. We show that eccentricity can grow up to 6-8% and is likely driven by a finite-amplitude instability triggered by first-order external Lindblad resonances. These moderate eccentricity values periodically modulate the gap accretion rate and wind mass loss rate, possibly leading to the formation of discrete structures in CO outflows. Slow outward migration and eccentricity growth appear to be common outcomes of planet-disk-wind interactions, which may contribute significantly to both the long orbital periods and the moderate eccentricities of warm jupiters. Additionally, eccentric massive protoplanets embedded in circumstellar disks could play a role in generating structured outflows.

astro-ph.EP↗

arXiv2023

Planet-disk-wind interaction: the magnetized fate of protoplanets

Models of planet-disk interaction are mainly based on 2D and 3D viscous hydrodynamical simulations. Accretion is classically prescribed by an alpha parameter which characterizes the turbulent radial transport of angular momentum (AM) in the disk. This accretion scenario has been questioned for a few years and an alternative paradigm has been proposed that involves the vertical transport of AM by MHD winds. We revisit planet-disk interaction in such context, with a focus on the planet's ability to open a gap and produce meridional flows. Accretion, magnetic field and wind torque in the gap are also explored, as well as the gravitational torque exerted by the disk onto the planet. We carry out high-resolution 3D global non-ideal MHD simulations of a gaseous disk threaded by a large-scale vertical magnetic field harboring a planet in a fixed circular orbit using the GPU-accelerated code Idefix. We consider various planet masses and disk magnetizations. We find that gap-opening always occurs for sufficiently massive planets, with deeper gaps when the planet mass increases and when the initial magnetization decreases. We propose a gap opening criterion when accretion is dominated by MHD winds. We show that accretion is unsteady and comes from surface layers in the outer disk, bringing material directly towards the planet poles. A planet gap is a privileged region for magnetic field accumulation, leading to nearly sonic accretion stream through the gap. For massive planets, the wind torque induces an asymmetric gap, both in depth and in width, that gradually erodes the outer gap edge, reducing the outer Lindblad torque and potentially reversing the migration direction of Jovian planets in magnetized disks after a few hundreds of orbits. For low-mass planets, we find strongly fluctuating gravitational torques that are mostly positive on average, indicating a stochastic outward migration.

astro-ph.SR↗

arXiv2021

Observational signatures of eccentric Jupiters inside gas cavities in protoplanetary discs

Predicting how a young planet shapes the gas and dust emission of its parent disc is key to constraining the presence of unseen planets in protoplanetary disc observations. We investigate the case of a 2 Jupiter mass planet that becomes eccentric after migrating into a low-density gas cavity in its parent disc. Two-dimensional hydrodynamical simulations are performed and post-processed by three-dimensional radiative transfer calculations. In our disc model, the planet eccentricity reaches ~0.25, which induces strong asymmetries in the gas density inside the cavity. These asymmetries are enhanced by photodissociation and form large-scale asymmetries in 12CO J=3-2 integrated intensity maps. They are shown to be detectable for an angular resolution and a noise level similar to those achieved in ALMA observations. Furthermore, the planet eccentricity renders the gas inside the cavity eccentric, which manifests as a narrowing, stretching and twisting of iso-velocity contours in velocity maps of 12CO J=3-2. The planet eccentricity does not, however, give rise to detectable signatures in 13CO and C18O J=3-2 inside the cavity because of low column densities. Outside the cavity, the gas maintains near-circular orbits, and the vertically extended optically thick CO emission displays a four-lobed pattern in integrated intensity maps for disc inclinations > 30 degrees. The lack of large and small dust inside the cavity in our model further implies that synthetic images of the continuum emission in the sub-millimetre, and of polarized scattered light in the near-infrared, do not show significant differences when the planet is eccentric or still circular inside the cavity.

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arXiv2020

Intermittent planet migration and the formation of multiple dust rings and gaps in protoplanetary disks

A key challenge for protoplanetary disks and planet formation models is to be able to make a reliable connection between observed structures in the disks emission, like bright and dark rings or asymmetries, and the supposed existence of planets triggering these structures. The observation of N dark rings of emission is often interpreted as evidence for the presence of N planets which clear dust gaps around their orbit and form dust-trapping pressure maxima in the disk. The vast majority of the models that studied the impact of planets on the dynamics of dust and gas in a protoplanetary disk assumed planets on fixed orbits. Here we go a different route and examine how the large-scale inward migration of a single planet structures the dust content of a massive disk. In many circumstances, the migration of a partial gap-opening planet with a mass comparable to Saturn is found to run away intermittently. By means of 2D gas and dust hydrodynamical simulations, we show that intermittent runaway migration can form multiple dust rings and gaps across the disk. Each time migration slows down, a pressure maximum forms beyond the planet gap that traps the large dust. Post-processing of our simulations results with 3D dust radiative transfer calculations confirms that intermittent runaway migration can lead to the formation of multiple sets of bright and dark rings of continuum emission in the (sub)millimeter beyond the planet location.

astro-ph.EP↗

arXiv2017

A Comparison of Two Methods for Estimating Black Hole Spin in Active Galactic Nuclei

Angular momentum, or spin, is a fundamental property of black holes (BHs), yet it is much more difficult to estimate than mass or accretion rate (for actively accreting systems). In recent years, high-quality X-ray observations have allowed for detailed measurements of the Fe K$α$ emission line, where relativistic line broadening allows constraints on the spin parameter (the X-ray reflection method). Another technique uses accretion disk models to fit the AGN continuum emission (the continuum-fitting, or CF, method). Although each technique has model-dependent uncertainties, these are the best empirical tools currently available and should be vetted in systems where both techniques can be applied. A detailed comparison of the two methods is also useful because neither method can be applied to all AGN. The X-ray reflection technique targets mostly local (z $\lesssim$ 0.1) systems, while the CF method can be applied at higher redshift, up to and beyond the peak of AGN activity and growth. Here, we apply the CF method to two AGN with X-ray reflection measurements. For both the high-mass AGN, H1821+643, and the Seyfert 1, NGC 3783, we find a range in spin parameter consistent with the X-ray reflection measurements. However, the near-maximal spin favored by the reflection method for NGC 3783 is more probable if we add a disk wind to the model. Refinement of these techniques, together with improved X-ray measurements and tighter BH mass constraints, will permit this comparison in a larger sample of AGN and increase our confidence in these spin estimation techniques.

astro-ph.GA↗