Unveiling Dust Aggregate Structure in Protoplanetary Disks by Millimeter-wave Scattering Polarization

Tazaki, Ryo; Tanaka, Hidekazu; Kataoka, Akimasa; Okuzumi, Satoshi; Muto, Takayuki

doi:10.3847/1538-4357/ab45f0

Cited by 52 publications

(67 citation statements)

References 118 publications

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“…The interpretation of the aforementioned observational data is hampered by the difficulty of the available light scattering codes in dealing with broad size distributions of realistic particle shapes. Great effort is being made to compute the scattering pattern of irregular cosmic dust particles (see, e.g., Min et al 2003Min et al , 2010Muinonen et al 2009;Zubko et al 2013;Merikallio et al 2015;Pohl et al 2016;Kolokolova et al 2018;Moreno et al 2018;Tazaki et al 2016Tazaki et al , 2019Kirchslager & Bertrang 2020), even though computational simulations of the scattering pattern of cosmic dust grains are still constrained to certain size ranges and/or simplified shapes. Therefore, it is important to know the effects of the adopted particle shape model on the retrieved dust parameters such as dust grain and the refractive index.…”

Section: Introductionmentioning

confidence: 99%

Retrieving Dust Grain Sizes from Photopolarimetry: An Experimental Approach

Muñoz

Frattin

Jardiel

et al. 2021

ApJS

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We present the experimental phase function, degree of linear polarization (DLP), and linear depolarization (δ L ) curves of a set of forsterite samples representative of low-absorbing cosmic dust particles. The samples are prepared using state-of-the-art size-segregating techniques to obtain narrow size distributions spanning a broad range of the scattering size parameter domain. We conclude that the behavior of the phase function at the side-and back-scattering regions provides information on the size regime, the position and magnitude of the maximum of the DLP curve are strongly dependent on particle size, the negative polarization branch is mainly produced by particles with size parameters in the ∼6 to ∼20 range, and the δ L is strongly dependent on particle size at all measured phase angles except for the exact backward direction. From a direct comparison of the experimental data with computations for spherical particles, it becomes clear that the use of the spherical model for simulating the phase function and DLP curves of irregular dust produces dramatic errors in the retrieved composition and size of the scattering particles: The experimental phase functions are reproduced by assuming unrealistically high values of the imaginary part of the refractive index. The spherical model does not reproduce the bell-shaped DLP curve of dust particles with sizes in the resonance and/or geometric optics size domain. Thus, the use of the Mie model for analyzing polarimetric observations might prevent locating dust particles with sizes of the order of or larger than the wavelength of the incident light.

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Section: Introductionmentioning

confidence: 99%

Retrieving Dust Grain Sizes from Photopolarimetry: An Experimental Approach

Muñoz

Frattin

Jardiel

et al. 2021

ApJS

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“…Such fluffly grains, which are naturally expected to form, were also proposed by Kataoka et al (2013) as a method to avoid the radial drift barrier. If dust grains are fluffly, the Mie theory is no longer valid (see the methods developed in Tazaki et al (2016) for fractal dust aggregates), and dust scattering opacity can be neglected, since most of the photons are forward scattered (Tazaki et al 2019). However, observations of the polarization pattern due to dust self scattering mentioned above (e.g.…”

Section: Introductionmentioning

confidence: 99%

Effects of Scattering, Temperature Gradients, and Settling on the Derived Dust Properties of Observed Protoplanetary Disks

Sierra¹,

Lizano²

2020

ApJ

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It is known that the millimeter dust thermal emission of protoplanetary disks is affected by scattering, such that for optically thick disks the emission decreases with respect to the pure absorption case and the spectral indices can reach values below 2. The latter can also be obtained with temperature gradients. Using simple analytical models of radiative transfer in thin slabs, we quantify the effect of scattering, vertical temperature gradients, and dust settling on the emission and spectral indices of geometrically thin face-on accretion disks around young stars. We find that in vertically isothermal disks with large albedo (ω ν 0.6), the emergent intensity can increase at optical depths between 10 −2 and 10 −1 . We show that dust settling has important effects on the spectral indices in the optically thick regime, since the disk emission mainly traces small dust grains in the upper layers of the disk. The λ = 870 µm emission of these small grains can hide large grains at the disk mid plane when the dust surface density is larger than ∼ 3.21 g cm −2 . Finally, because of the change of the shape of the spectral energy distribution, optically thick disks at 1.3 mm and grains with sizes between 300 µm < a max < 1 mm have a 7 mm flux ∼ 60% higher than the extrapolation from higher millimeter frequencies, assumed when scattering is neglected. This effect could provide an explanation to the excess emission at λ = 7 mm reported in several disks.

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“…This approach is therefore also applied in many studies concerning scattering at (sub-)mm wavelengths to explore the parameter space of dust composition and maximum grain size in the size distribution with regard to the expected degree of polarisation (e.g. Kataoka et al 2015;Tazaki et al 2019;Kirchschlager & Bertrang 2020;Brunngräber & Wolf 2020).…”

Section: Porosity and The General Effect On Polarised Scattered Radiationmentioning

confidence: 99%

“…It is the most commonly used quantity to describe and predict the scattering polarisation of different dust grains (e.g. Kataoka et al 2015;Tazaki et al 2019;Kirchschlager & Bertrang 2020;Brunngräber & Wolf 2020). For spherical grains, the thermal re-emission of the dust is unpolarised and the highest contribution to the net, that is, observable, polarised flux is indeed given by single-scattering events.…”

Section: Optical Quantitiesmentioning

confidence: 99%

“…A particularly frequently proposed solution for the discrepancy of the degree of polarisation is the use of porous dust grains because the polarisation after single scattering increases with Article number, page 1 of 14 arXiv:2103.04819v1 [astro-ph.SR] 8 Mar 2021 increasing porosity (e.g. Tazaki et al 2019;Brunngräber & Wolf 2020). Theoretical and laboratory studies of dust growth and evolution both suggest low filling factors Φ, that is, highly porous grains, and/or fractal geometries (Blum et al 2000;Blum & Wurm 2008;Kothe et al 2013;Garcia & Gonzalez 2020).…”

Section: Introductionmentioning

confidence: 99%

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Self-scattering in protoplanetary disks with dust settling

Brunngräber

Wolf²

2020

A&A

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Scattering of re-emitted flux is considered to be at least partially responsible for the observed polarisation in the (sub-)millimetre wavelength range of several protoplanetary disks. Although the degree of polarisation produced by scattering is highly dependent on the dust model, early studies investigating this mechanism relied on the assumption of single grain sizes and simple density distribution of the dust. However, in the dense inner regions where this mechanism is usually most efficient, the existence of dust grains with sizes ranging from nanometres to millimetres has been confirmed. Additionally, the presence of gas forces larger grains to migrate vertically towards the disk midplane, introducing a dust segregation in the vertical direction. Using polarisation radiative transfer simulations, we analyse the dependence of the resulting scattered light polarisation at 350 μm, 850 μm, 1.3 mm, and 2 mm on various parameters describing protoplanetary disks, including the effect of dust grain settling. We find that the different disk parameters change the degree of polarisation mostly by affecting the anisotropy of the radiation field, the optical depth, or both. It is therefore very challenging to deduce certain disk parameter values directly from polarisation measurements alone. However, assuming a high dust albedo, it is possible to trace the transition from optically thick to optically thin disk regions. The degree of polarisation in most of the considered disk configurations is lower than what is found observationally, implying the necessity to revisit models that describe the dust properties and disk structure.

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Unveiling Dust Aggregate Structure in Protoplanetary Disks by Millimeter-wave Scattering Polarization

Cited by 52 publications

References 118 publications

Retrieving Dust Grain Sizes from Photopolarimetry: An Experimental Approach

Retrieving Dust Grain Sizes from Photopolarimetry: An Experimental Approach

Effects of Scattering, Temperature Gradients, and Settling on the Derived Dust Properties of Observed Protoplanetary Disks

Self-scattering in protoplanetary disks with dust settling

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