Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2011-11-17
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
14 pages, 10 figures, typos fixed, discussion extended. Accepted by Astrophysical Journal
Scientific paper
We study the acceleration of charged grains by magnetohydrodynamics (MHD) turbulence in the interstellar medium (ISM). We begin with revisiting gyroresonance acceleration by taking into account the fluctuations of grain guiding center along a uniform magnetic field (i.e. nonlinear theory--NLT). We calculate grain velocities due to gyroresonance by fast MHD modes using the NLT for different phases of the ISM, and compare with results obtained using quasi-linear theory (QLT). We find for the parameters applicable to the typical ISM phases that the fluctuations of grain guiding center reduce grain velocities by less than 15 percent, but they can be important for more special circumstances. We confirm that large grains can be accelerated to super-Alfvenic velocities through gyroresonance. For such super-Alfvenic grains, we investigate the effect of further acceleration via transit time damping (TTD) by fast modes. We find that due to the broadening of resonance condition in the NLT, the TTD acceleration is not only important for the cosines of grain pitch angle relative to the magnetic field mu>V_{A}/v, but also for mu
Hoang Thiem
Lazarian Alex
Schlickeiser Reinhard
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