Intrinsic polarisation of elongated porous dust grains

Abstract

ALMA observations revealed recently polarised radiation of several protoplanetary disks in the (sub-)millimetre wavelength range. Besides self-scattering of large particles, thermal emission by elongated grains is a potential source for the detected polarisation signal. We calculate the wavelength dependent absorption and intrinsic polarisation of spheroidally shaped, micrometre and sub-millimetre sized dust grains using the discrete dipole approximation. In particular, we analyse the impact of dust grain porosity which appears to be present in disks when small grains coagulate to form larger aggregates. For the first time our results show that (a) the intrinsic polarisation decreases for increasing grain porosity and (b) the polarisation orientation flips by 90 degree for certain ratios of wavelength to grain size. We present a new method to constrain grain porosity and the grain size in protoplanetary disks using multi-wavelength polarisation observations in the far-infrared to millimetre wavelengths. Finally, we find that moderate grain porosities ($\mathcal{P}\lesssim 0.7$) potentially explain the observed polarisation fraction in the system HD 142527 while highly porous grains ($\mathcal{P}>0.7$) fail unless the grain's axis ratio is extraordinarily large.

10 pages, 10 figures

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Cited by in corpus (22)

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• Self-scattering of non-spherical dust grains
• Polarized emission by aligned grains in the Mie regime : application to protoplanetary disks observed by ALMA
• Modeling of the ALMA HL Tau Polarization by Mixture of Grain Alignment and Self-scattering
• Gravitoviscous Protoplanetary Discs with a Dust Component. IV. Disc Outer Edges, Spectral Indices, and Opacity Gaps
• The JCMT BISTRO Survey: Studying the Complex Magnetic Field of L43
• Polarization from Aligned Dust Grains in the $\beta$ Pic Debris Disk
• Thermal Emission and Scattering by Aligned Grains: Plane-Parallel Model and Application to Multiwavelength Polarization of the HL Tau Disk
• First L band detection of hot exozodiacal dust with VLTI/MATISSE
• Rotational Disruption of Porous Dust Aggregates due to Gas Flow in Protoplanetary Disks
• Probing the Temperature Structure of the Inner Region of a Protoplanetary Disk
• First BISTRO observations of the dark cloud Taurus L1495A-B10: the role of the magnetic field in the earliest stages of low-mass star formation
• The JCMT BISTRO-2 Survey: The Magnetic Field in the Center of the Rosette Molecular Cloud
• Dust mass in protoplanetary disks with porous dust opacities
• SOFIA/HAWC+ observations of the Crab Nebula: dust properties from polarised emission
• Synthetic Modelling of Polarized Dust Emission in Intermediate-Mass YSOs: I: Constraining the Role of Iron Inclusions and Inelastic Relaxation on Grain Alignment with ALMA Polarization
• How much large dust could be present in hot exozodiacal dust systems?
• Wavelength-dependent far-infrared polarization of HL Tau observed with SOFIA/HAWC+
• Far-infrared Polarization of the Supernova Remnant Cassiopeia A with SOFIA HAWC+
• Exploring Polarized Millimeter Emission from Protoplanetary Disks with Irregular Dust Grains