Radiative Torques of Irregular Grains : Describing the Alignment of a Grain Ensemble

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http://hdl.handle.net/10138/304626

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Herranen , J , Lazarian , A & Hoang , T 2019 , ' Radiative Torques of Irregular Grains : Describing the Alignment of a Grain Ensemble ' , Astrophysical Journal , vol. 878 , no. 2 , 96 . https://doi.org/10.3847/1538-4357/ab1eb3

Title: Radiative Torques of Irregular Grains : Describing the Alignment of a Grain Ensemble
Author: Herranen, Joonas; Lazarian, A.; Hoang, Thiem
Contributor: University of Helsinki, Planetary-system research
Date: 2019-06-20
Language: eng
Number of pages: 13
Belongs to series: Astrophysical Journal
ISSN: 0004-637X
URI: http://hdl.handle.net/10138/304626
Abstract: The radiative torque (RAT) mechanism is the most promising way of explaining observed polarization arising from aligned grains. We explore the efficiency of the grain alignment by an anisotropic radiation flow for an extensive ensemble of grain shapes, grain sizes (a), and wavelength (lambda). We calculate the distribution of the ratios of the amplitudes of the two major components of the RATs, which is an essential parameter that is used in the theory of RAT alignment in Lazarian & Hoang. While this distribution is different for the different classes of grain shapes that we considered, the most probable values of the parameter are centered in the range of q(max) similar to 0.5-1.5. The functional form from the calculated RATs is in good agreement with the analytical model. We find that the RAT efficiency scales as (lambda/a)(-2.6) for lambda greater than or similar to 1.8a, which has a slightly shallower slope than previously found in LH07. This increases the power of predictions obtained with the RAT theory. We also confirm that superparamagnetic inclusions are necessary for achieving high degrees of alignment, and constrain the parameter space describing the requirements for achieving these alignment degrees.
Subject: dust, extinction
methods: numerical
polarization
radiation: dynamics
INTERSTELLAR GRAINS
OPTICAL-PROPERTIES
MECHANICAL ALIGNMENT
DUST
RELAXATION
SCATTERING
DYNAMICS
FE
AL
TI
115 Astronomy, Space science
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