Drag forces on porous aggregates in protoplanetary disks

Schneider, Niclas; Wurm, Gerhard

doi:10.1051/0004-6361/202141582

Cited by 7 publications

(2 citation statements)

References 49 publications

(59 reference statements)

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“…Dust grains close to the inner dusty disc edge are hot and sticky (Pillich et al 2023), which leads to the creation of porous fluffy aggregates. This enhances the radiation pressure force effect (Tazaki & Nomura 2015) as well as the gas drag force (Schneider & Wurm 2021). We address this only marginally by using a smaller bulk density of big grains.…”

Section: Discussionmentioning

confidence: 99%

Inner dusty regions of protoplanetary discs – II. Dust dynamics driven by radiation pressure and disc winds

Vinković¹,

Čemeljić

2020

Monthly Notices of the Royal Astronomical Society

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We explore dust flow in the hottest parts of protoplanetary discs using the forces of gravity, gas drag and radiation pressure. Our main focus is on the optically thin regions of dusty disc, where the dust is exposed to the most extreme heating conditions and dynamical perturbations: the surface of optically thick disc and the inner dust sublimation zone. We utilise results from two numerically strenuous fields of research. The first is the quasi-stationary solutions on gas velocity and density distributions from mangetohydrodynamical (MHD) simulations of accretion discs. This is critical for implementing a more realistic gas drag impact on dust movements. The second is the optical depth structure from a high-resolution dust radiation transfer. This step is critical for a better understanding of dust distribution within the disc. We describe a numerical method that incorporates these solutions into the dust dynamics equations. We use this to integrate dust trajectories under different disc wind models and show how grains end up trapped in flows that range from simple accretion onto the star to outflows into outer disc regions. We demonstrate how the radiation pressure force plays one of the key roles in this process and cannot be ignored. It erodes the dusty disc surface, reduces its height, resists dust accretion onto the star, and helps the disc wind in pushing grains outwards. The changes in grain size and porosity significantly affect the results, with smaller and porous grains being influenced more strongly by the disc wind and radiation pressure.

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Section: Discussionmentioning

confidence: 99%

Inner dusty regions of protoplanetary discs – II. Dust dynamics driven by radiation pressure and disc winds

Vinković¹,

Čemeljić

2020

Monthly Notices of the Royal Astronomical Society

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“…fragmentation, bouncing, and hit-and-stick; Güttler et al 2010). In addition, porous particles are subject to increasingly large drag forces (Schneider & Wurm 2021).…”

Section: Porositymentioning

confidence: 99%

Mineral snowflakes on exoplanets and brown dwarfs

Samra

Helling

Birnstiel

2022

A&A

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Context. Brown dwarfs and exoplanets provide unique atmospheric regimes that hold information about their formation routes and evolutionary states. Cloud particles form through nucleation, condensation, evaporation, and collisions, which affect the distribution of cloud particles in size and throughout these atmospheres. Cloud modelling plays a decisive role in understanding these regimes. Aims. Modelling mineral cloud particle formation in the atmospheres of brown dwarfs and exoplanets is a key element in preparing for missions and instruments like CRIRES+, JWST, and ARIEL, as well as possible polarimetry missions like PolStar. The aim is to support the increasingly detailed observations that demand greater understanding of the microphysical cloud processes. Methods. We extend our kinetic cloud formation model that treats nucleation, condensation, evaporation, and settling of mixed material cloud particles to consistently model cloud particle-particle collisions. The new hybrid code Hybrid moments (Ls) and Size (HyLandS) is then applied to a grid of Drift-Phoenix (Tgas, pgas) profiles. Effective medium theory and Mie theory are used to investigate the optical properties. Results. Turbulence proves to be the main driving process of particle-particle collisions, with collisions becoming the dominant process in the lower atmosphere (p > 10−4 bar) at the cloud base. Particle-particle collisions produce one of three outcomes for brown dwarf and gas-giant atmospheres: fragmenting atmospheres (log10(g[cms−2])=3.0) coagulating atmospheres (log10(g)=5.0), Teff ≤1800K) or condensational growth dominated atmospheres (log10(g) = 5.0, Teff > 1800 K). Cloud particle opacity slope at optical wavelengths (Hubble) is increased with fragmentation, as are the silicate features at JWST NIRSpec, JWST MIRI, and ARIEL AIRS wavelengths. Conclusions. The hybrid moment-bin method HyLandS demonstrates the feasibility of combining a moment and a bin method for cloud modelling, whilst assuring element conservation. It provides a powerful and fast tool for capturing general trends of particle collisions, consistently with other microphysical growth processes. Collisions are an important process in exoplanet and brown dwarf atmospheres, but cannot be assumed to be hit-and-stick only. The spectral effects of cloud particle collisions in both optical and mid-infrared wavelengths complicate inferences of cloud particle size and material composition from observational data.

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Forbidden planetesimals

Schönau

Teiser

Demirci

et al. 2023

A&A

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Planetesimals are born fragile and are subject to destruction by wind erosion as they move through the gas of a protoplanetary disk. In microgravity experiments, we determined the shear stress necessary for erosion of a surface consisting of 1 mm dust pebbles down to 1 Pa ambient pressure. This is directly applicable to protoplanetary disks. Even pebble pile planetesimals with low eccentricities of 0.1 cannot survive inside of 1 au in a minimum-mass solar nebula, and safe zones for planetesimals with higher eccentricities are located even farther out.

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Drag forces on porous aggregates in protoplanetary disks

Cited by 7 publications

References 49 publications

Inner dusty regions of protoplanetary discs – II. Dust dynamics driven by radiation pressure and disc winds

Inner dusty regions of protoplanetary discs – II. Dust dynamics driven by radiation pressure and disc winds

Mineral snowflakes on exoplanets and brown dwarfs

Forbidden planetesimals

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