Wavelength Dependence Of Linear Polarization Research Articles

Wavelength dependence of linear polarization in the visible and near infrared domain for large levitating grains (PROGRA2 instruments)

Remote sensing measurements of light scattered by dust in solar system objects can provide clues on their physical properties. Databases obtained in the laboratory with numerous samples are necessary to interpret these measurements. We present here first studies of the wavelength dependence of the linear polarization between 545nm and 1.5μm, using the imaging polarimeters PROGRA2 for large levitating compact grains (PROGRA2-VIS in the visible domain, and the new instrument PROGRA2-IR in the near infrared). The measurements are conducted in microgravity conditions during parabolic flights for glass beads, quartz, sands, silicon carbides, anthracite, and lunar and Martian simulants. Comparison between measurements on glass beads and Mie calculations with glass spheres provides an assessment of the quality of the instruments. The dependence of the polarization on the wavelength is related to the complex refractive index of the particles, i.e. to their composition and to the size of the grains. More laboratory measurements will be necessary, in particular with smaller grains in aggregates, to better reproduce the remote sensing observations of solar system bodies.

Polarization of Saturn’s moon Iapetus

Context. The surface properties of atmosphereless solar system objects can be constrained by investigating the nature of the polarized light scattered from their surfaces. Aims. We provide new and precise measurements of the phase angle and the wavelength dependence of linear polarization on the leading side of Iapetus over the maximum phase angle range accessible from Earth (∼0.5−6.0 ◦ ) and over a broad spectral range (400–800 nm), thereby identifying the polarimetric characteristics of its dark material. Moreover, we provide circular spectral polarization measurement of the same side of Iapetus at one phase angle, which was performed aiming at detection of chiral signatures on its surface. We also compare our new polarization measurements with those of the trailing hemisphere of Iapetus which were obtained in our previous work. Methods. Using the FORS2 instrument of the ESO VLT, we performed spectro-polarimetric observations of Iapetus’ leading side. Results. While the linear polarization measurements of Iapetus’ leading side show an opposite trend in phase angle dependence to that of its trailing hemisphere, the polarization values measured for the two hemispheres around similar phase angles (in the range ∼3.0−6.0 ◦ )d iffer by a factor of three. Besides this, the degree of negative linear polarization of Iapetus’ leading hemisphere shows a slight dependence on the wavelengths of observations. Furthermore, like that of its trailing hemisphere, the circular polarization measurement of Iapetus’ leading side indicates no evidence of a significant amount of optically active (chiral) molecules on its surface.

Ultraviolet interstellar polarization observed with the Hubble Space Telescope

We have used the Faint Object Spectrograph of the Hubble Space Telescope to observe interstellar linear polarization from 1300 to 3300 A in two stars with well-studied interstellar polarization at visible wavelenths. The wavelength dependence of linear polarization declines smoothly with decreasing wavelength and is devoid of structure associated with the prominent 2175 A absorption bump in the interstellar extinction curve. The data for one star (HD 161056) are consistent with an extrapolation based on the Serkowski formula of a fit to the ground-based polariztion; the other star (HD 7252) shows excess (super-Serkowski) polarization relative to the extrapolation. Out of a total of 10 stars now studied by means of spectropolarimetry in the satellite ultraviolet, including eight obseved with the Wisconsin Ultraviolet Photopolarimeter, five (those of longest lambda (sub max)) show Serkowski behavior, and four others show super-Serkowski behavior; only one (HD 197770) shows evidence for polarization associated with the 2175 A bump. These results place important constraints on the nature of the bump feature.

The wavelength dependence of interstellar circular polarization - an exception

view Abstract Citations (4) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The wavelength dependence of interstellar circular polarization. Michalsky, J. J. ; Schuster, G. J. Abstract Certain features have characterized the wavelength dependence of linear and circular polarization due to interstellar material. At visible wavelengths, a two-parameter empirical relation fits the wavelength dependence of the linear polarization. This polarization exhibits a maximum in the visible. The circular polarization changes handedness at or near the maximum in linear polarization. The circular polarization of HD 183143 does not follow this pattern. There is no evidence for intrinsic circular polarization in this star. Existing calculations do not fit the observed wavelength dependence. Ad hoc models invoking a peculiar index of refraction may provide an explanation of the observations, but detailed scattering calculations are needed. Publication: The Astrophysical Journal Pub Date: July 1979 DOI: 10.1086/157164 Bibcode: 1979ApJ...231...73M Keywords: Circular Polarization; Interstellar Matter; Polarized Radiation; Wavelengths; Grains; Linear Polarization; Astrophysics; Interstellar Matter:Polarization; Polarization:Stars full text sources ADS | data products SIMBAD (1)

Polarization observations of the T Tauri stars by Tauri, T Tauri, and V866 Scorpii

view Abstract Citations (54) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Polarization observations of the T Tauri stars RY Tauri, T Tauri, and V866 Scorpii. Bastien, P. ; Landstreet, J. D. Abstract Observations of the wavelength dependence of linear polarization of the T Tauri stars RY Tauri, T Tauri, and V866 Scorpii are presented. These observations show that most of the polarization of these stars arises in extended circumstellar dust envelopes which lie outside the high-temperature gas-emitting regions. The distribution of this matter around the stars has no fixed axis of symmetry, such as is usually found in Be stars. Strong variations in the wavelength dependence of polarization are observed, which suggest large variations in the grain size in the dust scattering regions. Publication: The Astrophysical Journal Pub Date: May 1979 DOI: 10.1086/182947 Bibcode: 1979ApJ...229L.137B Keywords: Linear Polarization; Polarimetry; Stellar Envelopes; T Tauri Stars; Variable Stars; Interstellar Matter; Main Sequence Stars; Particle Size Distribution; Thomson Scattering; Astrophysics; Circumstellar Envelopes:T Tauri Stars; Polarization:T Tauri Stars full text sources ADS | data products SIMBAD (3)

Theoretical wavelength dependence of polarization in early-type stars

view Abstract Citations (21) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Theoretical wavelength dependence of polarization in early-type stars. Haisch, B. M. ; Cassinelli, J. P. Abstract The wavelength dependence of linear polarization produced by electron scattering and modified by an absorptive opacity in the extended, distorted atmospheres of early-type stars is examined theoretically. When we use an iterative scheme, the equation of radiative transfer for plane polarized light is solved numerically for four model atmospheres representing a Wolf-Rayet star and three types of Be star. The extended, but heretofore spherically symmetric, atmosphere models are now assumed to have the shapes of either a rigidly rotating star (called a Roche model) or a truncated disk. The asymmetry provides polarization in the net observable flux. The amount of this polarization and its wavelength dependence are investigated and compared to observations. It is found that only a highly flattened disk can provide polarization in excess of 1 percent as is sometimes observed. The wavelength dependence of the models agrees with the observed shape of the polarization curve between the Paschen and Balmer edges, but does not predict an increase in polarization longward of the Paschen continuum nor as sharp a decrease shortward of the Balmer continuum as is observed. Publication: The Astrophysical Journal Pub Date: August 1976 DOI: 10.1086/154602 Bibcode: 1976ApJ...208..253H Keywords: Atmospheric Optics; Early Stars; Polarization Characteristics; Stellar Atmospheres; Wavelengths; B Stars; Hot Stars; Paschen Series; Radiative Transfer; Stellar Rotation; Wolf-Rayet Stars; Astrophysics full text sources ADS |

Theoretical Wavelength Dependence of Polarization in Early-Type Stars

We have examined the theoretical wavelength dependence of linear polarization produced by electron scattering and modified by an absorptive opacity in the extended, distorted atmospheres of Be and Wolf-Rayet stars. A model atmosphere representing a Wolf-Rayet star recently calculated by Cassinelli and Hartmann was used. This model takes into consideration the subsonic portions of a radial, steady-state flow together with the requirement of radiative equilibrium. The model was then scaled down in temperature to approximate the cooler Be stars, again assuming radiative equilibrium. There were four models altogether, one WR star, and three Be models. All the atmospheres are quite extended by radiation pressure.

Linear polarization of H alpha in Be stars.

view Abstract Citations (38) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Linear polarization of Halpha in Be stars. Poeckert, R. Abstract The wavelength dependence of linear polarization across Ha has been measured in 12 Be stars with 2 A resolution. Shell stars like Tau exhibit a decrease in polarization which is proportional to the strength of the emission component of Ha. Stars considered "pole-on" have no such significant variations in polarization through the emission component. Some stars have substantial interstellar polarization which is indicated by a variation in position angle as well as in percent polarization. The results of this study show that the emission in Ha is unpolarized and therefore must arise in a region of the circumstellar envelope such that the optical depth in electron scattering from that region to the observer is much less than 1. Subject headings: Be stars - circumstellar shells - polarization Publication: The Astrophysical Journal Pub Date: March 1975 DOI: 10.1086/153468 Bibcode: 1975ApJ...196..777P full text sources ADS | data products SIMBAD (19)

The wavelength dependence of linear and circular polarized radiation from the magnetic white dwarf GRW +70 8247.

ABS>The wavelength dependence of linear polarization from the magnetic white dwarf Grw +70 deg 8247 is investigated. The gray-body magnetoemissive linear polarization is corrected for radiative transfer by the use of a model white-dwarf atmosphere. The wavelength dependence found by this method does not fit the wavelength dependence of the observed linear polarization. Also the wavelength dependence of the circular polarization from Grw +70 deg 8247 is reexamined in the light of new observations. (auth)

A Stochastic Theory for the Wavelength Dependence of Linear Polarization of Radio Sources

A Stochastic Theory for the Wavelength Dependence of Linear Polarization of Radio Sources

A Stochastic Theory for the Wavelength Dependence of Linear Polarization of Radio Sources.

The following model is proposed: The source contains n elementary radiators or cells of equal power output which have perfect linear polarization independent of frequency. Some cells m have identical polarization angles, while the remaining n-m cells have polarization angles which are independent random variables with a uniform probability density function over the range 0 to 2ir. Between each cell and the observer is a medium which produces Faraday rotation of the polarization angles. The Faraday rotations are independent Gaussian random variables with a standard deviation of R rad/m2. The fractional polarization is the expected value of the sum of the polarization vectors divided by n, and is given by the formula u(N) = [(2n)-'+m(m- 1)n-0 exp(-R2N4)j1, where N is the wavelength in meters. The model fits the observations of many radio galaxies and quasi-stellar sources including 3C33, MSH 23-64, 3C196, and Her A; but it fails to fit the observations of Cyg A and Tan A. The source Cyg A has an increase in fractional polarization with wavelength near 1 cm, but the model can give only constant or decreasing fractional polarization with wavelength. Extensions of the model which could describe Cyg A and Tan A seem feasible. The average rotation measure of the source (a measurable quantity) is independent of the fractional polarization in the present theory. Burn and Sciama (Monthly Not~ces Roy. Astron. Soc. 133, 5,1966) have described a theory based on a Fourier transform relation between the fractional polarization and a function which distributes the radiated power with Faraday depth. (At a certain Faraday depth, the number of rotations to the observer is constant.) The Burn and Sciama theory requires that the average polarization angle of each Faraday depth is identical, but no such assumption is required in the present theory.