Polarization Of Thermal Emission Research Articles

Probing 3D Magnetic Fields Using Thermal Dust Polarization and Grain Alignment Theory

Magnetic fields are ubiquitous in the Universe and are thought to play an important role in various astrophysical processes. Polarization of thermal emission from dust grains aligned with the magnetic field is widely used to measure the 2D magnetic field projected onto the plane of the sky, but its component along the line of sight is not yet constrained. Here, we introduce a new method to infer 3D magnetic fields using thermal dust polarization and grain alignment physics. We first develop a physical model of thermal dust polarization using the modern grain alignment theory based on the magnetically enhanced radiative torque alignment theory. We then test this model with synthetic observations of magnetohydrodynamic simulations of a filamentary cloud with our updated POLARIS code. Combining the tested physical polarization model with synthetic polarization, we show that the B-field inclination angles can be accurately constrained by the polarization degree from synthetic observations. Compared to the true 3D magnetic fields, our method based on grain alignment physics is more accurate than the previous methods that assume uniform grain alignment. This new technique paves the way for tracing 3D B-fields using thermal dust polarization and grain alignment theory and for constraining dust properties and grain alignment physics.

Polarization oscillations of near-field thermal emission

We consider the polarization of thermal emission in the near field of various materials, including dielectrics and metallic systems with resonant surface modes. We find that, at thermal equilibrium, the degree of polarization exhibits spatial oscillations with a period of approximately half the optical wavelength, independent of material composition. This result contrasts with that of Setala et al. [Phys. Rev. Lett.88, 123902 (2002)PRLTAO0031-900710.1103/PhysRevLett.88.123902], who find monotonic decay of the degree of polarization for systems in local thermal equilibrium.

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.

Polarization of thermal emission from aspherical dust grains in an anisotropic radiation field

Polarization of thermal emission from aspherical dust grains in an anisotropic radiation field

Polarization of Thermal Emission from Venus.

Abstract : Thermal emission from a specific locale on a planetary surface is, in general, polarized, because the emissivities parallel and perpendicular to the plane of incidence are unequal. A radio telescope unable to resolve the planet will observe a net polarization in the thermal emission for appropriate asymmetries in the surface distribution of temperature, T, or dielectric constant, epsilon. Illustrative calculations indicate that the integrated polarization of the 3-cm radiation from Venus is probably between 0.35 and 2 per cent, which is close to or slightly below the capability of existing radio telescopes. A possibly more promising method of determining the polarization of Venus radio emission is provided by interferometry. Under certain, probably valid, approximations, a complete set of observations with one-dimensional resolution across the planetary disk can obtain the two-dimensional distribution of epsilon and T across the disk, and the obliquity of the axis of rotation. The observed integrated brightness-temperature phase effect requires a surface temperature difference between subsolar and antisolar point approximately 400 K. An analysis is made of the incomplete set of interferometric observations of Venus obtained at Owens Valley Radio Observatory by Clark and Spencer. These observations are shown to be consistent with the radar reflectivity and microwave phase effect of Venus if the surface temperature varies markedly (approximately 500 K) between the subsolar point and the pole. (Author)

Polarization of Thermal Emission from Venus.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Polarization of Thermal Emission from Venus. Pollack, J. B. ; Sagan, C. Abstract Thermal emission from a specific locale on a planetary surface is, in general, polarized, because the emissivities parallel to and perpendicular to the plane of incidence are unequal. A radio telescope unable to resolve the planet will observe a net polarization in the thermal emission for appropriate asymmetries in the surface distribution of temperature T or dielectric constant ~. Illustrative calculations indicate that the integrated polarization of the 3-cm radiation from Venus is probably between 0.35% and 2%, which s close to or slightly below the capability of existing radio telescopes. A possibly more promising method of determining the polarization of Venus radio emission is provided by interferometry. Under certain, probably valid, approximations, a complete set of observations with one-dimensional resolution across the planetary disk can obtain the two-dimensional distribution of E and T across the disk, and the obliquity of the axis of rotation. The observed integrated brightness temperature phase effect requires a surface temperature difference between subsolar and antisolar point 400 K0. An analysis is made of the incomplete set of interferometric observations of Venus obtained at Owens Valley Radio Observatory by Clark and Spencer (1963). These observations are shown to be consistent with the radar reflectivity and microwave phase effect of Venus if the surface temperature varies markedly (=500 K0) between the subsolar point and the pole. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109586 Bibcode: 1965AJ.....70R.146P full text sources ADS |