Radiative torques alignment in the presence of pinwheel torques

Abstract

We study the alignment of grains subject to both radiative torques and pinwheel torques while accounting for thermal flipping of grains. By pinwheel torques we refer to all systematic torques that are fixed in grain body axes, including the radiative torques arising from scattering and absorption of isotropic radiation. We discuss new types of pinwheel torques, which are systematic torques arising from infrared emission and torques arising from the interaction of grains with ions and electrons in hot plasma. We show that both types of torques are long-lived, i.e. may exist longer than gaseous damping time. We compare these torques with the torques introduced by E. Purcell, namely, torques due to H${}_2$ formation, the variation of accommodation coefficient for gaseous collisions and photoelectric emission. Furthermore, we revise the Lazarian & Draine model for grain thermal flipping. We calculate mean flipping timescale induced by Barnett and nuclear relaxation for both paramagnetic and superparamagnetic grains, in the presence of stochastic torques associated with pinwheel torques, e.g. the stochastic torques arising from H${}_2$ formation, and gas bombardment. We show that the combined effect of internal relaxation and stochastic torques can result in fast flipping for sufficiently small grains and, because of this, they get thermally trapped, i.e. rotate thermally in spite of the presence of pinwheel torques. For sufficiently large grains, we show that the pinwheel torques can increase the degree of grain alignment achievable with the radiative torques by increasing the magnitude of the angular momentum of low attractor points and/or by driving grains to new high attractor points.

23 pages and 15 figures emulated ApJ style. Thermal flipping and trapping revised; paper accepted to ApJ

References in corpus (12)

• Radiative torques: Analytical Model and Basic Properties
• Tracing Magnetic Fields with Aligned Grains
• Studies of regular and random magnetic fields in the ISM: statistics of polarization vectors and the Chandrasekhar-Fermi technique
• Radiative torque alignment: Essential Physical Processes
• The Efficiency of Grain Alignment in Dense Interstellar Clouds: A Reassessment of Constraints from Near Infrared Polarization
• Subsonic Mechanical Alignment of Irregular Grains
• Grain Alignment and Polarized Emission from Magnetized T Tauri Disks
• User Guide for the Discrete Dipole Approximation Code DDSCAT.6.0
• Alignment of Dust with Magnetic Inclusions: Radiative Torques and Superparamagnetic Barnett and Nuclear Relaxation
• Infrared and X-Ray Evidence for Circumstellar Grain Destruction by the Blast Wave of Supernova 1987A
• Simulations of polarized dust emission
• Thermal Flipping of Interstellar Grains

Cited by in corpus (18)

• Grain Alignment by Radiative Torques in Special Conditions and Implications
• Grain Alignment in Starless Cores
• On Internal and External Alignment of Dust Grains in Protostellar Environments
• Modeling Grain Alignment by Radiative Torques and Hydrogen Formation Torques in Reflection Nebula
• Effects of grain alignment with magnetic fields on grain growth and the structure of dust aggregates
• Multi-wavelength Stellar Polarimetry of the Filamentary Cloud IC5146: I. Dust Properties
• Constraining the magnetic field properties of Bok globule B335 using SOFIA/HAWC+
• The Mechanical Alignment of Dust (MAD) I: On the spin-up process of fractal grains by a gas-dust drift
• Variation of dust properties with cosmic time implied by radiative torque disruption
• Magnetic field structure of OMC-3 in the far infrared revealed by SOFIA/HAWC+
• The origin of dust polarization in the Orion Bar
• The radiative torque spin-up efficiency of ballistic dust grain aggregates
• Barnett relaxation in non-symmetric grains
• Evolution of Dust and Water Ice in Cometary Comae by Radiative Torques
• The alignment of interstellar dust grains: thermal flipping and the Davis-Greenstein mechanism
• Wavelength-dependent far-infrared polarization of HL Tau observed with SOFIA/HAWC+
• Diagnosing Turbulence in the Neutral and Molecular Interstellar Medium of Galaxies
• Effect of dust rotational disruption by radiative torques on radiation pressure feedback from massive protostars