Grain Alignment by Radiative Torques in Special Conditions and
  Implications
  Grain alignment by radiative torques (RATs) has been extensively studied for
various environment conditions, including interstellar medium, dense molecular
clouds, and accretion disks, thanks to significant progress in observational,
theoretical and numerical studies. In this paper, we explore the alignment by
RATs and provide quantitative predictions of dust polarization for a set of
astrophysical environments that can be tested observationally. We first
consider the alignment of grains in the local interstellar medium and compare
predictions for linear polarization by aligned grains with recent observational
data for nearby stars. We then revisit the problem of grain alignment in
accretions disks by taking into account the dependence of RAT alignment
efficiency on the anisotropic direction of radiation fields relative to
magnetic fields. Moreover, we study the grain alignment in interplanetary
medium, including diffuse Zodiacal cloud and cometary comae, and calculate the
degree of circular polarization (CP) of scattered light arising from single
scattering by aligned grains. We also discuss a new type of grain alignment,
namely the alignment with respect to the ambient electric field instead of the
alignment with the magnetic field. We show that this type of alignment can
allow us to reproduce the systematic features of CP observed across a cometary
coma. Our findings suggest that polarized Zodiacal dust emission may be an
important polarized foreground component, which should be treated carefully in
cosmic microwave background experiments.
