1,252 research outputs found
Polarization of Thermal Emission from Aligned Dust Grains Under an Anisotropic Radiation Field
If aspherical dust grains are immersed in an anisotropic radiation field,
their temperature depends on the cross-sections projected in the direction of
the anisotropy.It was shown that the temperature difference produces polarized
thermal emission even without alignment, if the observer looks at the grains
from a direction different from the anisotropic radiation. When the dust grains
are aligned, the anisotropy in the radiation makes various effects on the
polarization of the thermal emission, depending on the relative angle between
the anisotropy and alignment directions. If the both directions are parallel,
the anisotropy produces a steep increase in the polarization degree at short
wavelengths. If they are perpendicular, the polarization reversal occurs at a
wavelength shorter than the emission peak. The effect of the anisotropic
radiation will make a change of more than a few % in the polarization degree
for short wavelengths and the effect must be taken into account in the
interpretation of the polarization in the thermal emission. The anisotropy in
the radiation field produces a strong spectral dependence of the polarization
degree and position angle, which is not seen under isotropic radiation. The
dependence changes with the grain shape to a detectable level and thus it will
provide a new tool to investigate the shape of dust grains. This paper presents
examples of numerical calculations of the effects and demonstrates the
importance of anisotropic radiation field on the polarized thermal emission.Comment: 13pages, 7figure
Information theory in the study of anisotropic radiation
Information theory is used to perform a thermodynamic study of non
equilibrium anisotropic radiation. We limit our analysis to a second-order
truncation of the moments, obtaining a distribution function which leads to a
natural closure of the hierarchy of radiative transfer equations in the
so-called variable Eddington factor scheme. Some Eddington factors appearing in
the literature can be recovered as particular cases of our two-parameter
Eddington factor. We focus our attention in the study of the thermodynamic
properties of such systems and relate it to recent nonequilibrium thermodynamic
theories. Finally we comment the possibility of introducing a nonequilibrium
chemical potential for photons.Comment: 1 eps figure upon request by e-mail, to appear in Journal of Physics
Anisotropic Dark Energy and the Generalized Second Law of Thermodynamics
We consider a Bianchi type model in which anisotropic dark energy is
interacting with dark matter and anisotropic radiation. With this scenario, we
investigate the validity of the generalized second law of thermodynamics. It is
concluded that the validity of this law depends on different parameters like
shear, skewness and equation of state.Comment: 12 pages, accepted for publication in Phys. Scr. arXiv admin note:
text overlap with arXiv:1008.0692 and arXiv:1106.241
Anisotropic radiation field and trapped photons around the Kerr black hole
Aims. In order to understand the anisotropic properties of local radiation
field in the curved spacetime around a rotating black hole, we investigate the
appearance of a black hole seen by an observer located near the black hole.
When the black hole is in front of a source of illumination the black hole cast
shadow in the illumination. Accordingly, the appearance of the black hole is
called the black hole shadow.
Methods. We first analytically describe the shape of the shadow in terms of
constants of motion for a photon seen by the observer in the locally
non-rotating reference frame (LNRF). Then, we newly derive the useful equation
for the solid angle of the shadow. In a third step, we can easily plot the
apparent image of the black hole shadow. Finally, we also calculate the ratio
of the photon trapped by the hole and the escape photon to the distant region
for photons emitted near the black hole.
Results. From the shape and the size of the black hole shadow, we can
understand the signatures of the curved spacetime; i.e., the mass and spin of
the black hole. Our equations for the solid angle of the shadow has technical
advantages in calculating the photon trapping ratio. That is, this equation is
computationally very easy, and gives extremely precise results. This is because
this equation is described by the one-parameter integration with given values
of the spin and location for the black hole considered. After this, the solid
angle can be obtained without numerical calculations of the null geodesics for
photons.Comment: Accepted for publication in A&
Dynamics of gas and dust clouds in active galactic nuclei
We analyse the motion of single optically thick clouds in the potential of a
central mass under the influence of an anisotropic radiation field
~|cos(\theta)|, a model applicable to the inner region of active galactic
nuclei. Resulting orbits are analytically soluble for constant cloud column
densities. All stable orbits are closed, although they have non-trivial shapes.
Furthermore, there exists a stability criterion in the form of a critical
inclination, which depends on the luminosity of the central source and the
column density of the cloud.Comment: 4 pages, 3 figures; language corrections, minor formatting change
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