Continuum Polarization Research Articles

Interstellar extinction and polarization in the infrared

view Abstract Citations (292) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar Extinction and Polarization in the Infrared Martin, P. G. ; Whittet, D. C. B. Abstract The wavelength dependences of interstellar continuum extinction and polarization in the range 0.35-5 microns are examined. The existence of a universal extinction curve with power law index of about 1.8 extending from the near-IR to at least 5 microns appears to be established for both diffuse and dense cloud dust. The polarization yields evidence for some degree of universality in the 1.6-5 micron regime which may be represented by a power law with index 1.5-2.0, encompassing that for extinction. The form of the polarization curve in the IR seems independent of the wavelength at which the degree of polarization peaks in the optical, implying that variations in that wavelength are caused by changes in the optical properties of the particle at blue-visible rather than IR wavelengths. It is argued that the more significant alterations of the grain size distribution from one environment to another occur for the smaller particles. Publication: The Astrophysical Journal Pub Date: July 1990 DOI: 10.1086/168896 Bibcode: 1990ApJ...357..113M Keywords: Cosmic Dust; Interstellar Extinction; Interstellar Matter; Molecular Clouds; Near Infrared Radiation; Energy Distribution; Particle Size Distribution; Stellar Mass; Astrophysics; INFRARED: GENERAL; INTERSTELLAR: GRAINS; INTERSTELLAR: MATTER; POLARIZATION; SPECTROPHOTOMETRY full text sources ADS | data products SIMBAD (10)

Linearly Polarised Radio Emission from M83 (NGC 5236) and NGC 891

Recent VLA 20 cm radio continuum observations of the southern face-on barred spiral M83 reveal that the magnetic field is very highly aligned at the outer regions (~12 kpc radius) and totally disrupted in the inner regions (<6 kpc) of the galaxy. The RM variation suggests an axisymmetric morphology for the magnetic field. VLA 6 cm continuum polarization observations of the edge-on spiral NGC 891 reveal ordered magnetic fields at large Z-distances (~3 kpc) from the galactic plane, probably emanating from the disk through instabilities.

Spectropolarimetry of Cygnus A and the scattering model for the extended continuum

Previous work on the peculiar double radio galaxy Cyg A has shown that the blue optical continuum in this object is extended over a region about 3 kpc in size. Spectropolarimetry of Cyg A is presented in order to test the hypothesis that this extended continuum source represents light scattered from an otherwise hidden active nucleus. The observed continuum polarization of 1.58 percent at position angle 13 deg is quite low, probably indicating that an explanation in terms of scattering is untenable. Instead, it is proposed that the blue continuum seen in the optical is light from hot stars, essentially unrelated to the active nucleus. The nucleus itself is still presumed to be hidden from direct view, either by an intervening dust lane or by an obscuring torus surrounding the nucleus. 14 refs.

The optical and near-infrared continuum polarization of five magnetic white dwarf stars - New observations and considerations regarding its origin

Linear and circular broadband continuum polarization measurements throughout the 0.35-1.65-micron spectral region were obtained for GrW +70 deg 8247, GD 229, G240-72, G227-35, and LP 790-29. The continuum is found to be characterized by significant Coulomb modification of the Landau-type autoionization thresholds. The spectral characteristics of continuum polarization originating from a centered dipole field distribution are predicted. The magnetobremsstrahlung model can describe several characteristics of the polarization of Grw + 70 deg 8247, suggesting that plasma eigenmodes draw the resultant continuum polarization away from a photoionization edge. 86 refs.

The origin of the optical polarizations of Seyfert 1 galaxies

A statistical study of the optical continuum polarizations of a sample of 68 optically selected Seyfert 1 galaxies is reported. The polarizations correlate with narrow H-alpha/H-beta, the 12 micron and 25 micron nuclear luminosities, with the nuclear 25/60 color and possibly the 112/60 and the 60/100 colors. They do not correlate with four broad-line reddening indicators, measures of asymmmetry in forbidden O III 5007, the 3.5 micron, 60 micron, and 100 micron luminosities, and the 12/3.5 and 12/25 nuclear colors. The only correlations found are with the properties of dust in the narrow-line region, and this indicates strongly that the polarization arises from scattering and extinction by dust that is outside or mixed with the narrow-line clouds. This same dust produces much of the 12 micron and 25 micron power of Seyfert 1s. 80 refs.

Polarization variablity among Wolf-Rayet stars. IV - A complete lack of circular polarization in the optical continuum

Quasi-simultaneous blue and red, broadband optical monitoring in linear and circular polarization and in intensity has been carried out over an interval of three weeks for several Wolf-Rayet stars that show relatively large Delta P variations in linear polarization. No significant varying Delta V component of circular polarization is detected in any of these stars. The lower upper limit Delta V/Delta P implies that the intrinsic linearly polarized light which does vary cannot be produced by electrons gyrating in a magnetic field, unless they are ultrarelativistic - a rather unlikely situation. The low mean circular polarization typically observed is probably interstellar in origin. Lack of periodicity in the observed variations of linear polarization implies that even weak magnetic field loops are unlikely to be involved in confining pockets of wind plasma. The observed linear polarization variations are related mainly to electron scattering. 25 refs.

Spectropolarimetry of 'narrow-line' Seyfert 1 galaxies

Spectropolarimetry is used here to investigate the properties of 'narrow-line' Seyfert 1 galaxies. In general, continuum polarization arising to the blue and/or the lack of significant broadening of the polarized emission lines points to dust reflection as the primary polarigenic mechanism. There is some evidence that the dust is associated with the forbidden O III-emitting region. Where line polarizations can be compared, H-beta is found to be more highly polarized than the forbidden O III 4959, 5007 A lines A, demonstrating that these lines come from spatially distinct within the nucleus. Simultaneous spectrophotometry obtained by the spectropolarimetry is used to demonstrate that X-ray selected Seyfert 1s show significantly smaller H-beta equivalent widths than a sample of optically selected narrow-line 1s and Seyfert 2s. 51 refs.

G70.7+1.2: A nonthermal bubble in a globule - Nova, supernova remnant, or outflow?

Millimeter-wave, near-IR, and 21 cm observations of the radio source G70.7 + 1.2 , which has been proposed to be a recent SNR developing inside a molecular cloud, are presented. A small molecular cloud with properties similar to a large dark cloud or globule is interacting with the nonthermal radio continuum source. The molecular cloud has a lumpy structure with its highest column density portion lying just outside the brightest portion of the radio continuum shell. If the radio source was produced by a supernova explosion, its kinetic energy was several orders of magnitude less than that of most observed supernovae. An OB star wind with certain characteristics is sufficient to drive the bubble, but the high radio continuum nonthermal surface brightness and polarization of the object is not explained by this model. 23 references.

Optical-Infrared Continuum Spectra and Polarization of Quasars: An Outburst in 3C 279 During 1987–88

We have observed a period of rapid and intense optical-infrared brightness and polarization variability in the quasar 3C 279. The observations were obtained as part of an ongoing study of the optical-infrared continuum evolution in a sample of optically violent variable (OVV) quasars and BL Lacertae objects. Simultaneous broadband UBVRI photometric and polarimetric observations are used to study the optical continuum spectral evolution and wavelength dependent linear polarization and to search for broad near-ultraviolet continuum spectral components.

Linear and Circular Polarization in the Diffuse Interstellar Medium

A brief introduction is provided to the origin of interstellar polarization, grain model calculations, and alignment. The characteristics of the observed linear and circular continuum polarization are described, with an emphasis on various constraints that might be placed on the nature of the polarizing grains and what additional observations would be of value. Complementary information can be obtained from polarization structure at spectral features in the extinction curve. Interstellar polarization has been measured in some other galaxies, indicating an interesting frontier for further research.

Formation of solid-liquid interface in ferroelectric particle dispersion and its effect on the dispersion stability

A model has been proposed for the formation of the ferroelectric solid-liquid interface in the non-electrolyte dispersion system. Bulk properties as well as the surface properties of the dispersing solid could be a factor which was associated with various characters of the dispersion state. A qualitative investigation was carried out to see whether the continuum polarization process in solid-liquid interface due to the inhomogeneous field from the polar solid might affect the powder dispersion. The development of the polarized solid-liquid interface might depend on the polarity of solid particle and of liquid medium, shapes, mobility, and solubility of the molecules in the liquid phase, and temperature. Two possible effects of polarized solid-liquid interface on the dispersion stability have been discussed. Lastly, this model was applied to interpreting some experimental results of adhesion.

Mass loss in a B2 IIIe star - Omega Orionis 1978-1984

A combination of long-term optical polarimetric, photometric, spectrometric, and UV spectral data has confirmed that all the observed portions of Omega Ori's outer atmosphere are variable on a variety of time scales. The shortest confirmed variations are detectable over a few hours, and the longest changes are observed on time scales of years. A straightforward interpretation of the available data is that the continuum polarization, continuum-magnitude changes, and color changes produced are in a presumably equatorial disk close to the stellar photosphere.

Simultaneous Spectroscopy and Polarimetry of Be Stars

Evidence is now accumulating that many Be stars display photospheric line profile variations on timescales of days or less that are probably caused by nonradial pulsations (Baade 1984; Penrod 1986). In some circumstances these pulsations can promote mass loss into the circumstellar envelope, and consequently the conditions in the inner part of the envelope may vary on similar timescales. Changes in the envelope could produce variations in the polarization and emission line profiles, and observers have reported rapid variability in both. We describe here an initial attempt to search for simultaneous variations in continuum polarization, Hα emission, and the He I λ6678 photospheric absorption line in order to investigate correlated changes on short timescales.

Polarimetry in the Mg ii h and k lines

The Ultraviolet Spectrometer and Polarimeter (UVSP) on the SMM satellite has been used to record the linear polarization profile across the Mgii h and k lines, including its center-to-limb variation. Linear polarization with an orientation of the electric vector parallel to the solar limb is detected in the line wings on the short wavelength side of the k line and on the long wavelength side of the h line, in agreement with theoretical predictions of Auer et al. (1980). The predicted negative polarization (electric vector perpendicular to the limb) between the h and k lines is however not confirmed by the observations. Instead values close to zero are indicated there, although the statistical significance of the results is marginal. We have examined possible explanations of such a discrepancy between theory and observations. After having rejected other alternatives (e.g., opacity effects, different continuum polarization, or deviations from a plane-parallel stratification), it is suggested that the solution may be found in a treatment of partial redistribution of the polarized radiation with the quantum-mechanical interference between the two scattering transitions being included as an integral part of the redistribution problem.

Continuum polarization transfer in 500 MeV proton scattering and pionic collectivity in nuclei.

A complete set of polarization transfer observables was measured for inclusive 500 MeV proton scattering from $^{2}\mathrm{H}$, Ca(nat.), and Pb(nat.) at ${\mathrm{theta}}_{\mathrm{lab}}$=18.5\ifmmode^\circ\else\textdegree\fi{} (q=1.75 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$). The excitation energy ranged over the entire quasielastic peak from 20 to 100 MeV. Longitudinal and transverse spin-flip probabilities were extracted from the data. These have simple model-dependent connections to the spin-longitudinal and transverse response functions for the heavy targets. Detailed analysis of the data reveals no evidence for collective enhancement in the spin-longitudinal response function. The relation of this analysis to the interpretation of the European Muon Collaboration effect in terms of excess pions is discussed in detail.

High precision spectropolarimetry of stars and planets – III. The wavelength dependence of interstellar polarization

The interstellar polarization curve has been measured for three stars at a resolution of 50 Å. Low amplitude structure is present in each case. For Zeta Ophiuchi, the star studied in greatest detail (3100–7600 Å), the structure includes an oscillation in the degree of polarization at λ ≳ λmax and a feature about 200 Å wide near 4100 Å. 55 Cygni shows a feature of similar width and amplitude (about 3 per cent of the continuum polarization) but at 4400 Å. The rotation of position angle across the spectrum seen in all three stars may be interpreted in terms of two or more dust clouds along the line-of-sight. These clouds must differ in grain size and grain size distribution as well as in the direction of grain alignment. We argue that the structure in Zeta Ophiuchi beyond λmax may be due to magnetite impurities in silicate grains.

Spectropolarimetry of comets Austin and Churyumov-Gerasimenko

Spectropolarimetric observations from 5000 to 8000 Å have been obtained for comets P/Austin (1982g) and P/Churyumov-Gerasimenko (1982f). The observations were spaced over phase angles of 50–125° for comet Austin and 10–40° for comet Churyumov-Gerasimenko. The use of spectropolarimetry allowed an evaluation of continuum polarization without molecular line contamination. Especially for comet Churyumov-Gerasimenko, the curve of polarization versus phase angle resembles curves for asteroids, where the polarization is negative (electric vector maximum parallel to the scattering plane) for phase angles less than 20° and the most negative polarization is from −1 to −2%. The negative polarization at backscattering angles may be due to multiple scattering in agglomerated grains, as assumed for asteroids, or to Mie scattering by small dielectric particles. If multiple scattering is important in comet dust, polarization measurements may imply a low albedo, less than 0.08. The polarization of comet Austin remained steady during a large change in the dust production rate. Both comets increased continuum flux by a factor of 2 near perihelion. The continuum of comet Churyumov-Gerasimenko had the shape of the solar spectrum with derivations less than 5%. The equivalent width of spectral features of C 2, NH 2, and O varied as r −2.

Study of energy release in flares

Recent advances in the study of energy release in Flares are reviewed. Progress has been made in modelling coronal X-ray emission and the chromospheric response to energy imput. These advances are based on theoretical studies and on the comparison of complementary data obtained from spacecraft and ground-based observatories. We first review the modelling of the coronal flare derived from radio, X-ray and XUV observations. Then we summarize results on the chromospheric response to various energy imput. Observations of X-ray continuum intensity and polarization, transition zone lines and chromospheric lines do not show evidence of particle trapping by a turbulent front. Although they might be in agreement with trapping and partial precipitation. White light flares appear to result from energy deposited above the photosphere. They are probably due to electron bombardment. The implication of these results on the primary energy release process are discussed and prospects for new research are presented.

Evidence for a highly polarized continuum in the nucleus of NGC 1068

view Abstract Citations (155) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evidence for a highly polarized continuum in the nucleus of NGC 1068. Miller, J. S. ; Antonucci, R. R. J. Abstract Spectropolarimetric observations of the nucleus of the Seyfert galaxy NGC 1068 are presented. The data indicate a substantial correction must be made for dilution of the featureless continuum by unpolarized starlight. After correction p is found to be 16 percent + or - 2 percent and wavelength independent. The permitted lines have considerably lower polarization than the continuum, but have the same position angle, 95 deg. The continuum polarization most likely results either from a synchrotron emission origin or from electron scattering, but dust scattering may also be important. The position angle of continuum polarization is perpendicular to the axis of radio emission proposed by Wilson and Ulvestad (1982) on the basis of VLA observations. The data are discussed in terms of a disk model for the nucleus. Publication: The Astrophysical Journal Pub Date: August 1983 DOI: 10.1086/184082 Bibcode: 1983ApJ...271L...7M Keywords: Continuous Spectra; Galactic Nuclei; Seyfert Galaxies; Accretion Disks; Electron Scattering; Polarimetry; Polarization (Waves); Spectral Energy Distribution; Synchrotron Radiation; Astrophysics full text sources ADS | data products SIMBAD (2) NED (2)

Direct reaction analysis of continuum spectra and polarizations in the 48Ti( 16O, 16O′) reaction

The multi-step direct reaction approach is used to calculate continuum cross sections and polarizations for the reaction 48Ti( 16O, 16O′) at E lab = 100 MeV. The dynamical part of the calculations is done fully quantum mechanically, and includes one- and two-step inelastic excitations. The spectroscopic amplitudes are obtained from correlated particle-hole response functions. A good description of the experimental data up to about 20 MeV energy loss is achieved this way.