arXiv subjects

Michael L. Weber

Publications and source records attributed to Michael L. Weber.

9 recordsLinked to original sources

arXiv2026

Ionized gas emission in protoplanetary disks with the SKAO

Protoplanetary disks represent a crucial stage in the evolution of Young Stellar Objects towards the formation of fully formed planetary systems. While substantial progress has been made in the last decades in the characterization of the dust and molecular gas in these systems, the ionized component remains poorly understood. Ionized gas traces important processes such as photoevaporation, accretion, disk winds, and jets, and therefore is key to studying disk dynamics, evolution, and ultimately planet formation. In this paper, we investigate the capabilities of the forthcoming SKA telescope to probe this component in protoplanetary disks within nearby star forming regions. We present state-of-the-art simulations of photoevaporative, magneto-thermal, and magnetohydrodynamic winds, and generate theoretical predictions and synthetic SKAO observations to assess its potential in detecting and characterizing free-free emission and Hydrogen recombination lines. Finally, we discuss synergies with complementary facilities and how they will provide a comprehensive, multi-scale view of disk winds and offer critical insights on the mechanisms driving disk evolution and the onset of planet formation.

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arXiv2026

Can photoevaporation open gaps in protoplanetary discs?

We investigate whether photoevaporation alone can open and sustain gaps in protoplanetary discs by coupling the evolving disc structure with the photoevaporative flow in two dimensional radiation hydrodynamical simulations. Our results show that once a density depression forms, the local mass-loss rate decreases sharply, suppressing further gap deepening. Viscous inflow and radial mass transport along the disc surface act to partially refill the depleted region, preventing complete clearing. The resulting configuration is a persistent, partially depleted zone whose evolution is largely insensitive to the initial disc morphology. This behaviour challenges the standard paradigm that photoevaporation efficiently carves clean inner cavities and directly produces transition discs. However, the pressure maximum at the outer edge of the depression may still trap dust grains, giving rise to transition disc like observational signatures. We also present a first-order prescription to approximate this behaviour in one dimensional disc evolution models, suitable for use in planet formation and population synthesis studies. Although the prescription improves upon static mass-loss treatments, it remains approximate, underscoring the need for further multidimensional simulations and parameter-space exploration to derive robust recipes for global disc and planet population models.

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arXiv2025

From thermal to magnetic driving: spectral diagnostics of simulation-based magnetothermal disc wind models

Disc winds driven by thermal and magnetic processes are thought to play a critical role in protoplanetary disc evolution. However, the relative contribution of each mechanism remains uncertain, particularly in light of their observational signatures. We investigate whether spatially resolved emission and synthetic spectral line profiles can distinguish between thermally and magnetically driven winds in protoplanetary discs. We modelled three disc wind scenarios with different levels of magnetisation: a relatively strongly magnetised wind ($β$4), a rather weakly magnetised wind ($β$6), and a purely photoevaporative wind (PE). Using radiative transfer post-processing, we generated synthetic emission maps and line profiles for [OI] 6300 Å, [NeII] 12.81 $\mathrmμ$m, and o-H2 2.12 $\mathrmμ$m, and compared them with observations. The $β$4 model generally produces broader and more blueshifted low-velocity components across all tracers, consistent with compact emission regions and steep velocity gradients. The $β$6 and PE models yield narrower profiles with smaller blueshifts, in better agreement with most observed narrow low-velocity components (NLVCs). We also find that some line profile diagnostics, such as the inclination at maximum centroid velocity, are not robust discriminants. However, the overall blueshift and full-width at half-maximum (FWHM) of the low-velocity components provide reliable constraints. The $β$4 model reproduces the most extreme blueshifted NLVCs in observations, while most observed winds are more consistent with the $β$6 and PE models. Our findings reinforce previous conclusions that most observed NLVCs are compatible with weakly magnetised or purely photoevaporative flows. The combination of line kinematics and emission morphology offers meaningful constraints on wind-driving physics.

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arXiv2024

The interplay between forming planets and photoevaporating discs II: Wind-driven gas redistribution

Disc winds and planet-disc interactions are two crucial mechanisms that define the structure, evolution and dispersal of protoplanetary discs. While winds are capable of removing material from discs, eventually leading to their dispersal, massive planets can shape their disc by creating sub-structures such as gaps and spiral arms. We study the interplay between an X-ray photoevaporative disc wind and the substructures generated due to planet-disc interactions to determine how their mutual interactions affect the disc's and the planet's evolution. We perform three-dimensional hydrodynamic simulations of viscous ($α= 6.9\cdot10^{-4}$) discs that host a Jupiter-like planet and undergo X-ray photoevaporation. We trace the gas flows within the disc and wind and measure the accretion rate onto the planet, as well as the gravitational torque that is acting on it. Our results show that the planetary gap takes away the wind's pressure support, allowing wind material to fall back into the gap. This opens new pathways for material from the inner disc (and part of the outer disc) to be redistributed through the wind towards the gap. Consequently, the gap becomes shallower, and the flow of mass across the gap in both directions is significantly increased, as well as the planet's mass-accretion rate (by factors $\approx 5$ and $\approx 2$, respectively). Moreover, the wind-driven redistribution results in a denser inner disc and less dense outer disc, which, combined with the recycling of a significant portion of the inner wind, leads to longer lifetimes of the inner disc, contrary to the expectation in a planet-induced photoevaporation (PIPE) scenario that has been proposed in the past.

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arXiv2023

GIARPS High-resolution Observations of T Tauri stars (GHOST) V. New insights into disk winds from 3 km/s resolution observations

This paper aims at revisit the physical and dynamical properties of the warm atomic gas in the inner disk region of classical T Tauri stars (CTTs) and relate them to the properties of the outer dusty disk. We used the high resolution (R=115,000) spectra of 36 CTTs observed as part of the GHOsT project and analysed the profile and luminosity of the brightest optical forbidden lines, namely [OI]630 and 557nm, [SII]406 and 673nm, and [NII]658nm. We find that in about 40% of sources the so-called narrow low-velocity component (NLVC) display a peak velocity compatible with the stellar velocity. In these sources, that typically show lower mass accretion rates and the absence of a jet, the [OI]630nm profiles are well fitted by a simple Keplerian disk model, indicating that the emission from the disk is dominant with respect to the wind contribution. For transitional disks (TD), no correlation is found between $R_{kep}$, derived from the line HWHM, and the size of the dust cavity. We also see an anti-correlation between the [OI] 557/630 nm ratio and $R_{kep}$, which suggests that the [OI] emitting region expands as the gas cools and becomes less dense. We confirmed previous findings on the density and temperature ranges implied by the line ratios, and additionally constrained the ionisation fraction in the NLVC to be < 0.1. We however discuss the limits of applying this diagnostic to winds that are not spatially resolved. For the outflow component, we estimated the mass-loss for both the disk winds and jets and compared the results with X-ray photoevaporative models. We conclude that without better knowledge of the wind geometry, and given the limitation of the diagnostics, the mass-loss in the wind traced by the LVC cannot be constrained better than a factor of 100, with a mass-loss/mass-accretion ratio spanning between ~ 0.01 and more than 1.

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arXiv2022

The interplay between forming planets and photo-evaporating discs I: Forbidden line diagnostics

Disc winds and planet formation are considered to be two of the most important mechanisms that drive the evolution and dispersal of protoplanetary discs and in turn define the environment in which planets form and evolve. While both have been studied extensively in the past, we combine them into one model by performing three-dimensional radiation-hydrodynamic simulations of giant planet hosting discs that are undergoing X-ray photo-evaporation, with the goal to analyse the interactions between both mechanisms. In order to study the effect on observational diagnostics, we produce synthetic observations of commonly used wind-tracing forbidden emission lines with detailed radiative transfer and photo-ionisation calculations. We find that a sufficiently massive giant planet carves a gap in the gas disc that is deep enough to affect the structure and kinematics of the pressure-driven photo-evaporative wind significantly. This effect can be strong enough to be visible in the synthetic high-resolution observations of some of our wind diagnostic lines, such as the [OI] 6300 Å or [SII] 6730 Å lines. When the disc is observed at inclinations around 40° and higher, the spectral line profiles may exhibit a peak in the redshifted part of the spectrum, which cannot easily be explained by simple wind models alone. Moreover, massive planets can induce asymmetric substructures within the disc and the photo-evaporative wind, giving rise to temporal variations of the line profiles that can be strong enough to be observable on timescales of less than a quarter of the planet's orbital period.

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arXiv2020

The interpretation of protoplanetary disc wind diagnostic lines from X-ray photoevaporation and analytical MHD models

High resolution spectra of typical wind diagnostics ([OI] 6300 Å and other forbidden emission lines) can often be decomposed into multiple components: high-velocity components with blueshifts up to several 100 km/s are usually attributed to fast jets, while narrow (NLVC) and broad (BLVC) low-velocity components are believed to trace slower disc winds. Under the assumption that the line-broadening is dominated by Keplerian rotation, several studies have found that the BLVCs should trace gas launched between 0.05 and 0.5 au and correlations between the properties of BLVCs and NLVCs have been interpreted as evidence for the emission tracing an extended MHD wind and not a photoevaporative wind. We calculated synthetic line profiles obtained from detailed photoionisation calculations of an X-ray photoevaporation model and a simple MHD wind model and analyzed the emission regions of different diagnostic lines and the resulting spectral profiles. The photoevaporation model reproduces most of the observed NLVCs but not the BLVCs or HVCs. The MHD model is able to reproduce all components but produces Keplerian double peaks at average inclinations that are rarely observed. The combination of MHD and photoevaporative winds could solve this problem. Our results suggest that the Gaussian decomposition does not allow for a clear distinction of flux from different wind regions and that the line broadening is often dominated by the velocity gradient in the outflow rather than by Keplerian rotation. We show that observed correlations between BLVC and NLVC do not necessarily imply a common origin in an extended MHD wind.

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arXiv2019

The dispersal of protoplanetary discs I: A new generation of X-ray photoevaporation models

Photoevaporation of planet forming discs by high energy radiation from the central star is potentially a crucial mechanism for disc evolution and it may play an important role in the formation and evolution of planetary system. We present here a new generation of X-ray photoevaporation models for solar-type stars, based on a new set of hydrodynamical simulations, which account for stellar irradiation via a new, significantly improved, parameterisation of gas temperatures, based on detailed photoionisation and radiation transfer calculations. This is the first of a series of papers aiming at providing a library of models which cover the observed parameter space in stellar and disc mass, metallicity and stellar X-ray properties. We focus here on solar-type stars (0.7 M$_\odot$) with relatively low-mass discs (1% of the stellar mass) and explore the dependence of the wind mass loss rates on stellar X-ray luminosity. We model primordial discs as well as transition discs at various stages of evolution. Our 2D hydrodynamical models are then used to derive simple recipes for the mass loss rates that are suitable for inclusion in one-dimensional disc evolution and/or planet formation models typically employed for population synthesis studies. Line profiles from typical wind diagnostics ([OI] 6300 $\overset{\lower.5em\circ}{\mathrm{A}}$ and [NeII] 12.8 $μ$m) are also calculated for our models and found to be roughly in agreement with previous studies. Finally, we perform a population study of transition discs by means of one-dimensional viscous evolution models including our new photoevaporation prescription and find that roughly a half of observed transition discs cavities and accretion rates could be reproduced by our models.

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arXiv2017

Accreting Transition Discs with large cavities created by X-ray photoevaporation in C and O depleted discs

Circumstellar discs with large dust depleted cavities and vigorous accretion onto the central star are often considered signposts for (multiple) giant planet formation. In this letter we show that X-ray photoevaporation operating in discs with modest (factors 3-10) gas-phase depletion of Carbon and Oxygen at large radii (> 15 AU) yield the inner radius and accretion rates for most of the observed discs, without the need to invoke giant planet formation. We present one-dimensional viscous evolution models of discs affected by X-ray photoevaporation assuming moderate gas-phase depletion of Carbon and Oxygen, well within the range reported by recent observations. Our models use a simplified prescription for scaling the X-ray photoevaporation rates and profiles at different metallicity, and our quantitative result depends on this scaling. While more rigorous hydrodynamical modelling of mass loss profiles at low metallicities is required to constrain the observational parameter space that can be explained by our models, the general conclusion that metal sequestering at large radii may be responsible for the observed diversity of transition discs is shown to be robust. Gap opening by giant planet formation may still be responsible for a number of observed transition discs with large cavities and very high accretion rate.

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