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Register a new userThe effect of dust composition and shape on radiation-pressure forces and blowout sizes of particles in debris disks
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The light scattered from dust grains in debris disks is typically modeled as compact spheres using Lorenz-Mie theory or as porous spheres by incorporating an effective medium theory. In this work we examine the effect of incorporating a more realistic particle morphology on estimated radiation-pressure blowout sizes. To calculate the scattering and absorption cross sections of irregularly shaped dust grains, we use the discrete dipole approximation. These cross sections are necessary to calculate the $beta$-ratio, which determines whether dust grains can remain gravitationally bound to their star. We calculate blowout sizes for a range of stellar spectral types corresponding with stars known to host debris disks. As with compact spheres, more luminous stars blow out larger irregularly shaped dust grains. We also find that dust grain composition influences blowout size such that absorptive grains are more readily removed from the disk. Moreover, the difference between blowout sizes calculated assuming spherical particles versus particle morphologies more representative of real dust particles is compositionally dependent as well, with blowout size estimates diverging further for transparent grains. We find that the blowout sizes calculated have a strong dependence on the particle model used, with differences in the blowout size calculated being as large as an order of magnitude for particles of similar porosities.
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Debris disks are tenuous, dust-dominated disks commonly observed around stars over a wide range of ages. Those around main sequence stars are analogous to the Solar Systems Kuiper Belt and Zodiacal light. The dust in debris disks is believed to be continuously regenerated, originating primarily with collisions of planetesimals. Observations of debris disks provide insight into the evolution of planetary systems; the composition of dust, comets, and planetesimals outside the Solar System; as well as placing constraints on the orbital architecture and potentially the masses of exoplanets that are not otherwise detectable. This review highlights recent advances in multiwavelength, high-resolution scattered light and thermal imaging that have revealed a complex and intricate diversity of structures in debris disks, and discusses how modeling methods are evolving with the breadth and depth of the available observations. Two rapidly advancing subfields highlighted in this review include observations of atomic and molecular gas around main sequence stars, and variations in emission from debris disks on very short (days to years) timescales, providing evidence of non-steady state collisional evolution particularly in young debris disks.
(Abridged) The radii of debris disks and the sizes of their dust grains are tracers of the formation mechanisms and physical processes operating in these systems. We use a sample of 34 debris disks spatially resolved in various Herschel programs to constrain them. While we modeled disks with both warm and cold components, we focus our analysis only on the cold outer disks, i.e. Kuiper-belt analogs. The disk radii derived from the resolved images reveal a large dispersion, but no significant trend with the stellar luminosity, which argues against ice lines as a dominant player in setting the debris disk sizes. Fixing the disk radii to those inferred from the resolved images, we model the spectral energy distributions to determine the dust temperatures and the grain size distributions. While the dust temperature systematically increases towards earlier spectral types, its ratio to the blackbody temperature at the disk radius decreases with the stellar luminosity. This is explained by an increase of typical grain sizes towards more luminous stars. The sizes are compared to the radiation pressure blowout limit $s_text{blow}$ that is proportional to the stellar luminosity-to-mass ratio and thus also increases towards earlier spectral classes. The grain sizes in the disks of G- to A-stars are inferred to be several times $s_text{blow}$ at all stellar luminosities, in agreement with collisional models of debris disks. The sizes, measured in the units of $s_text{blow}$, appear to decrease with the luminosity, which may be suggestive of the disks stirring level increasing towards earlier-type stars.
The connection between the nature of a protoplanetary disk and that of a debris disk is not well understood. Dust evolution, planet formation, and disk dissipation likely play a role in the processes involved. We aim to reconcile both manifestations of dusty circumstellar disks through a study of optically thin Class III disks and how they correlate to younger and older disks. In this work, we collect literature and ALMA archival millimeter fluxes for 85 disks (8%) of all Class III disks across nearby star-forming regions. We derive millimeter-dust masses $M_{text{dust}}$ and compare these with Class II and debris disk samples in the context of excess infrared luminosity, accretion rate, and age. The mean $M_{text{dust}}$ of Class III disks is $0.29 pm 0.19~M_{oplus}$. We propose a new evolutionary scenario wherein radial drift is very efficient for non-structured disks during the Class II phase resulting in a rapid decrease of $M_{text{dust}}$. However, we find long infrared protoplanetary disk timescales of ${sim}$8~Myr, which are consistent with overall slow disk evolution. In structured disks, the presence of dust traps allows for the formation of planetesimal belts at large radii, such as those observed in debris disks. We propose therefore that the planetesimal belts in debris disks are the result of dust traps in structured disks, whereas protoplanetary disks without dust traps decrease in dust mass through radial drift and are therefore undetectable as debris disks after the gas has dissipated. These results provide a hypothesis for a novel view of disk evolution.
Impacts of micrometeoroids on the surfaces of Nix and Hydra can produced dust particles and form a ring around Pluto. However, dissipative forces, such as the solar radiation pressure, can lead the particles into collisions in a very short period of time. In this work we investigate the orbital evolution of escaping ejecta under the effects of the radiation pressure force combined with the gravitational effects of Pluto,Charon, Nix and Hydra. The mass production rate from the surfaces of Nix and Hydra was obtained from analytical models. By comparing the lifetime of the survived particles, derived from our numerical simulations, and the mass of a putative ring mainly formed by the particles released from the surfaces of Nix and Hydra we could estimate the ring normal optical depth. The released particles, encompassing the orbits of Nix and Hydra, temporarily form a 16000 km wide ring. Collisions with the massive bodies, mainly due to the effects of the radiation pressure force, remove about 50% of the $1mu$m particles in 1 year. A tenuous ring with a normal optical depth of $6 times 10^{-11}$ can be maintained by the dust particles released from the surfaces of Nix and Hydra.
This proceeding summarises a talk given on the state-of-the-art of debris disc modelling. We first review the basics of debris disc physics, which is followed by a short overview of the state-of-the-art in terms of modelling dust and gas in debris disc systems.
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