Variation Of Linear Polarization Research Articles

High-precision broadband linear polarimetry of early-type binaries

Aims. DH Cephei is a well-known massive O+O-type binary system on the northern sky, situated at the center of young open cluster NGC 7380. Our high-precision multi-band polarimetry clearly reveals that variations of linear polarization in this system are synchronous with the phase of the orbital period. We used the observed variations of Stokes parameters q and u to derive the orbital inclination i, orientation Ω, and the direction of rotation. Moreover, in order to obtain a rough estimation of the interstellar polarization in the vicinity of DH Cep, we observed polarization arising from the neighboring stars in the cluster. Methods. We used the Dipo1–2 polarimeter in combination with the remotely controlled 60 cm Tohoku T60 telescope to obtain linear polarization measurements of DH Cep in the B, V, and R passbands at the accuracy level of ~0.003%. To obtain an estimation of interstellar polarization of DH Cep, we observed more than a dozen field stars identified as members of NGC 7380 and in the close proximity to DH Cep. A Lomb-Scargle period search was applied to the acquired polarization data to reveal the dominating frequency in polarization variations. We used a standard analytical method based on a two-harmonics Fourier fit to derive the inclination, orientation, and the direction of rotation of the binary orbit. Results. The variations of Stokes parameters in all three B, V, and R passbands clearly suggest an unambiguous periodic signal at 1.055 d with an amplitude of variations of ~0.2%, which corresponds to half of the known orbital period of 2.11 d. This type of polarization variability is expected for a binary system with light-scattering material distributed symmetrically with respect to the orbital plane. In addition to the regular polarization variability, there is a nonperiodic component, which is strongest in the B passband. In the V passband, we obtained our most reliable values for the orbital inclination i = 46° + 11°/ − 46° and an orientation of the orbit on the sky of Ω = 105° ± 55°, with 1σ confidence intervals. Using our best estimate of i and the polametric amplitude in the V passband, we estimated that the mass loss from the system is ~3.4 × 10−7 M⊙ yr−1. The direction of the binary system rotation on the plane of the sky is clockwise. Our polarimetric observations of neighboring stars of DH Cep in NGC 7380 reveal that the polarization of the cluster stars is most likley due to aligned interstellar dust in the foreground.

Long-lasting activity of asteroid (248370) 2005 QN173

ABSTRACT We present the results of observations of asteroid (248370) QN173 obtained during July 2021–January 2022 with three telescopes. Our analysis revealed the presence of the dust tail for about half of a year. The direct images of the asteroid were obtained with broad-band filters. No emissions were revealed in the spectra, and the spectrum of the asteroid closely matched that of a C-type asteroid. Created colour and linear polarization variations along the tail were analysed. The asteroid demonstrated a redder colour compared to the Sun. Dramatic changes in dust productivity obtained in different filters were not detected. The g − r colour changes from 0.2m to 0.7m over the coma, and the linear polarization degree varies from about 1.2 per cent to 0.2 per cent and from −0.2 per cent to −1.5 per cent at the phase angle of 23.2° and 8.16°. The total dust mass ejected until the latest observation on October 10 is 4.2 × 107 kg, with a maximum rate of 2.6 kg s−1 based on the Monte Carlo modelling of the dust tail. The estimated asteroid size is 1.3 km. It is shown that large particles are concentrated around the nucleus, whereas smaller ones dominate in the tail. The evolution of (248370) QN173 orbit and the orbits of the sample of the 464 short-periodic comets were followed. Ten of them approached the asteroid’s orbit. These objects are not genetically related, despite very close distance of their orbits for a relatively long time.

ARE INTERNETWORK MAGNETIC FIELDS IN THE SOLAR PHOTOSPHERE HORIZONTAL OR VERTICAL?

ABSTRACT Using many observations obtained during 2007 with the Spectro-Polarimeter of the Hinode Solar Optical Telescope, we explore the angular distribution of magnetic fields in the quiet internetwork regions of the solar photosphere. Our work follows from the insight of Stenflo, who examined only linear polarization signals in photospheric lines, thereby avoiding complications of the analysis arising from the differing responses to linear and circular polarization. We identify and isolate regions of a strong polarization signal that occupy only a few percent of the observed quiet Sun area yet contribute most to the net linear polarization signal. The center-to-limb variation of the orientation of linear polarization in these strong signal regions indicates that the associated magnetic fields have a dominant vertical orientation. In contrast, the great majority of the solar disk is occupied by much weaker linear polarization signals. The orientation of the linear polarization in these regions demonstrates that the field orientation is dominantly horizontal throughout the photosphere. We also apply our analysis to Stokes profiles synthesized from the numerical MHD simulations of Rempel as viewed at various oblique angles. The analysis of the synthetic data closely follows that of the observations, lending confidence to using the simulations as a guide for understanding the physical origins of the center-to-limb variation of linear polarization in the quiet Sun area.

POLARIZATION IN EXOPLANETARY SYSTEMS CAUSED BY TRANSITS, GRAZING TRANSITS, AND STARSPOTS

We present results of numerical simulations of flux and linear polarization variations in transiting exoplanetary systems, caused by the host star disk symmetry breaking. We consider different configurations of planetary transits depending on orbital parameters. Starspot contribution to the polarized signal is also estimated. Applying the method to known systems and simulating observational conditions, a number of targets is selected where transit polarization effects could be detected. We investigate several principal benefits of the transit polarimetry, particularly, for determining orbital spatial orientation and distinguishing between grazing and near-grazing planets. Simulations show that polarization parameters are also sensitive to starspots, and they can be used to determine spot positions and sizes.

The intra-hour variable quasar J1819+3845: 13-year evolution, jet polarization structure, and interstellar scattering screen properties

We examine the long-term evolution of the intra-hour variable quasar, J1819+3845, whose variations have been attributed to interstellar scintillation by extremely local turbulent plasma, located only 1-3pc from Earth. The variations in this source ceased some time between June 2006 and February 2007. The evolution of the source spectrum and the long-term lightcurve, and the persistent compactness of the source VLBI structure indicates that the cessation of rapid variability was associated with the passage of the scattering material out of the line of sight to the quasar. We present an analysis of the linear polarization variations and their relation to total intensity variations. The proper motion of polarized features in the quasar jet is found to be subluminal. Systematic time delays between Stokes I, Q and U, in combination with the structure of the source obtained from 8.4GHz VLBI data, confirm the estimate of the screen distance: 1-2pc, making the screen one of the nearest objects to the Solar System. We determine the physical properties of this scattering material. The electron density in the scattering region is extremely high with respect to the warm ionized ISM, with an estimated density of $n_e \sim 97 \, l_0^{1/3} {\Delta L}_{100}^{-1/2}$cm$^{-3}$, where $l_0$ is the outer scale of the turbulence in AU and $\Delta L = 100 \Delta L_{100}$ AU is the depth of the scattering region. If this plasma is in pressure balance with the local magnetic field, one expects a ~2 rad/m^2 rotation measure change associated with the passage of this material past the quasar. We examine the rotation measures of sources and the diffuse polarized emission in the surrounding region. We place a limit of 10 rad/m^2 on the RM change. The variability of sources near J1819+3845 is used to deduce that the screen must therefore be either very small (~100 AU) or patchy.

Linear spectropolarimetry: a new diagnostic tool for the classification and characterization of asteroids

Abstract We explore the use of spectropolarimetry as a remote sensing tool for asteroids in addition to traditional reflectance measurements. In particular, we are interested in possible relationships between the wavelength-dependent variation of linear polarization and the properties of the surfaces, including albedo and composition. We have obtained optical spectropolarimetric measurements of a dozen asteroids of different albedo and taxonomic classes and of two small regions at the limb of the Moon. We found that objects with marginally different relative reflectance spectra (in the optical) may have totally different polarization spectra. This suggests that spectropolarimetry may be used to refine the classification of asteroids. We also found that in some cases the Umov law may be violated, that is, in contrast to what is expected from basic physical considerations, the fraction of linear polarization and the reflectance may be positively correlated. In agreement with a few previous studies based on multicolour broad-band polarimetry, we found that the variation of linear polarization with wavelength and with phase-angle is correlated with the albedo and taxonomic class of the objects. Finally, we have serendipitously discovered that spinel-rich asteroid (599) Luisa, located very close to the Watsonia family, is a member of the rare class of Barbarian asteroids. We suggest that future modelling attempts of the surface structure of asteroids should be aimed at explaining both reflectance and polarization spectra.

Polarimetric observations of comet 67P/Churyumov-Gerasimenko during its 2008–2009 apparition

Remote observations of the light scattered by comet 67P/Churyumov-Gerasimenko dust coma are of major importance for determining the physical properties of the particles and prepare the rendezvous with the ESA/Rosetta spacecraft in 2014. Aims. Light scattering and especially linear polarization observations allow comparison between different coma regions and different comets, including comets that have been studied by space probes. Our aim is to retrieve physical properties of the dust particles and to characterize their evolution around perihelion passage. Methods. Recent imaging polarimetric observations were conducted at the Haute-Provence observatory (France) on 2009 March 17-19 at 35° phase angle and at IUCAA Girawali observatory (India) on 2008 December 25-27 at 36° phase angle and on 2009 April 30-May 1 at 29° phase angle. With the imaging technique, the intensity and linear polarization variations are studied through the various coma regions. These observations are compared to other cometary data (e.g. Jupiter family comets) and to numerical and experimental simulations. Results. The decrease in intensity as a function of the distance to nucleus in log-log scale is on average close to -1, although important variations with values down to -1.5 are noticed, in agreement with previous observations in 1982-83 and 1995-96. The intensity along the tailward direction decreases with a slope between -1.2 two months before perihelion (2009 February 28) to -1.0 two months after perihelion, and the decrease is more pronounced in the sunward direction. Before perihelion, aperture polarization values are comparable to polarization values measured on other comets at similar phase angles. The sharp decrease in intensity and the feature in the tailward direction, without any difference in polarization in the coma before perihelion, could suggest the presence of large dark particles. The post-perihelion increase in intensity and in polarization suggests that an outburst has occurred. The freshly ejected dust polarizes more the scattered light and is more sensitive to the solar radiation pressure, suggesting small micron- or submicron-sized grains. Conclusions. Polarization and intensity variations in the coma of 67P/Churyumov-Gerasimenko are reminiscent of those noticed for some comets such as comet 81P/Wild 2 and comet 9P/Tempel 1. The presence of rather large particles can thus be suggested before and just after perihelion and the ejection of post-perihelion smaller grains, eventually in fluffy aggregates. A strong seasonal effect related to the obliquity of the comet suggests that the different grains originate in different hemispheres of the nucleus.

UBIQUITOUS Hα-POLARIZED LINE PROFILES: ABSORPTIVE SPECTROPOLARIMETRIC EFFECTS AND TEMPORAL VARIABILITY IN POST-AGB, HERBIG Ae/Be, AND OTHER STELLAR TYPES

We show here that the absorptive H-alpha polarized line profile previously seen in many Herbig Ae/Be (HAeBe) stars is a nearly ubiquitous feature of other types of embedded or obscured stars. This characteristic 1% linear polarization variation across the absorptive part of the H-alpha line is seen in Post-AGB stars as well as RV-Tau, Delta-Scuti, and other types. Each of these stars shows evidence of obscuration by intervening circumstellar hydrogen gas and the polarization effect is in the absorptive component, consistent with an optical pumping model. We present ESPaDOnS spectropolarimetric observations of 9 post-AGB and RV-Tau types in addition to many multi-epoch HiVIS observations of these targets. We find significant polarization changes across the H-alpha line in 8/9 stars with polarization amplitudes of 0.5% to over 3% (5/6 Post-AGB and 3/3 RV-Tau). In all but one of these, the polarization change is dominated by the absorptive component of the line profile. There is no evidence that subclasses of obscured stars showing stellar pulsations (RV-Tau for Post-AGB stars and Delta-Scuti for Herbig Ae/Be stars) show significant spectropolarimetric differences from the main class. Significant temporal variability is evident from both HiVIS and ESPaDOnS data for several stars presented here: 89 Her, AC Her, SS Lep, MWC 120, AB Aurigae and HD144668. The morphologies and temporal variability are comparable to existing large samples of Herbig Ae/Be and Be type stars. Since Post-AGB stars have circumstellar gas that is very different from Be stars, we discuss these observations in the context of their differing environments.

“The photopolarimetric activity and circumstellar environment of the T tauri star CO ORI”

We present the results of simultaneous UBVRI photometry and polarimetry of the classical T Tauri star CO Ori carried out at the Crimean Astrophysical Observatory during the 18 years between 1986 and 2004. We show that the variations of linear polarization accompanying the star’s brightness variations follow the law characteristic of UX Ori stars. This suggests that the brightness variations of the star are mainly due to changes of the circumstellar extinction due to non-uniform structure of the circumstellar environment, and to an “optimal” orientation of the circumstellar gas and dust disk relative to the observer, whose line of sight crosses the gas and dust atmosphere of the disk. We determine the star’s intrinsic polarization due to scattering of light in the circumstellar disk. The polarization position angle indicates the orientation of the disk’s symmetry axis in the plane of the sky. Our analysis of an archival light curve for CO Ori confirms the existence of a many-year cycle of photometric activity, suspected by us earlier. The refined period of this cycle is 12.4 years. The existence of such activity cycles of UX Ori stars testifies to considerable deviations of their circumstellar disks from axial symmetry, a reflection of either stellar binarity or the commencement of the process of planetary formation.

Fading of light maximum and linear polarization variation in the carbon Mira R Leporis

Polarimetry of R Lep obtained over the years 1991-2002 is presented. During this period the star underwent an episode of fading of the brightness at light maximum, after an interval of about 35 yr. An analysis of the data shows that the percentage linear polarization increased as the fading progressed, attained a maximum of slightly over 3 per cent in the V band close to the epoch of minimum, and remained more or less at the same level during and well after the recovery to normal brightness. The polarization, apparently, originated from the circumstellar envelope above the region where the dust that caused the fading in the star condensed. The physical mechanism that causes the rather large polarization during fadings is perhaps selective extinction by aligned foreground grains produced by the passage of shocks through the circumstellar envelope. The small-amplitude, short-term fluctuations in polarization observed in R Lep, which appear to be superposed on the fading-related large-amplitude variation, are probably pulsation-related and arise from the inner zones of the circumstellar envelope.

Anomalous Behavior of the Linear Polarization of the Herbig Ae Star WW Vul during the 1997 Minimum

In the course of photopolarimetric monitoring of the Herbig Ae star WW Vul, an unusual variation of linear polarization upon energence from a deep minimum was recorded, which cannot be explained by the standard mechanism for such objects (UX Ori stars): a variable contribution of radiation scattered by circumstellar dust. An analysis of possible causes of the anomalous behavior of polarization shows that it was most likely due to the presence of aligned, aspherical dust grains in the dust cloud crossing the line of sight at that time.

Nature of Eclipsing Pulsars

We present a model for pulsar radio eclipses in some binary systems, and test this model for PSRs B1957+20 and J2051-0827. We suggest that in these binaries the companion stars are degenerate dwarfs with strong surface magnetic fields. The magnetospheres of these stars are permanently infused by the relativistic particles of the pulsar wind. We argue that the radio waves emitted by the pulsar split into the eigenmodes of the electron-positron plasma as they enter the companion's magnetosphere and are then strongly damped due to cyclotron resonance with the ambient plasma particles. Our model explains in a natural way the anomalous duration and behavior of radio eclipses observed in such systems. In particular, it provides stable, continuous, and frequency-dependent eclipses, in agreement with the observations. We predict a significant variation of linear polarization both at eclipse ingress and egress. In this paper we also suggest several possible mechanisms of generation of the optical and $X$-ray emission observed from these binary systems.

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.

Polarimetry of Stellar Active Regions and Flares

AbstractObservations of regular and irregular polarimetric variability in late-type stars are reviewed, and the related physical and geometrical effects are discussed. There are indications that the irregular part of the variability could be caused by transient events, possibly associated with flares. Polarimetric observations during flares are reviewed, and preliminary results of new observations of a well-known flare star, YY Geminorum, are presented. The results show that the small flare in YY Gem did not cause any significant variations in linear polarization, while the binary eclipse evidently causes an enhancement in the polarization. The reasons for the difficulties in stellar flare polarimetry are discussed. Finally, future prospects for the observations of flaring stars and for the utilization of linear polarimetry as a complementary method to other techniques of surface imaging of stellar activity and flares are presented.

Variation of linear polarization in R Aquarii system

R Aquarii is a very interesting symbiotic system. There is an emission nebulosity close to the star which extends in North-South direction and a “jet” feature of about 6″ with a position angle of 29° has also been observed (Sopka et al. 1982; Mauron et al. 1985; Kafatos et al. 1983). Polarization measurements are important to understand the peculiar geometry of the circumstellar material around the central objects. Wavelength and time dependence of polarization can be used to put constraints on the geometry of the object and to identify the mechanism(s) responsible for polarization. In view of this linear polarization measurements of R Aquarii were carried out by us in UBVRI bands. Observations were made during November-December 1984 on 1 meter telescope of Indian Institute of Astrophysics, Bangalore, with a dual channel photo polarimeter discussed elsewhere (Deshpande et al. 1985). Measured values of percent polarization and position angle at different phases alongwith the earlier observations of Serkowski (1974) and Ladbeck (1985) are plotted in Figure 1.

Polarimetric observations of the WN7 binary CQ Cephei

view Abstract Citations (37) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Polarimetic Observations of the WN7 Binary CQ Cephei Drissen, L. ; Moffat, A. F. J. ; Bastien, P. ; Lamontagne, R. ; Tapia, S. Abstract Linear polarization variations in the Wolf-Rayet eclipsing binary CQ Cep are reported. These variations describe a double wave with orbital phase, which is consistent with electron scattering in a binary system. The amplitude of the polarization variations in CQ Cep appears to be the largest found among binary stars, excluding the special case of magnetic white dwarfs in close binaries. This may be a consequence of a dense W-R wind in the shortest period binary W-R system known. The orbital inclination derived from the polarimetric data is roughly 78 deg, only slightly different from the value of about 70 deg derived from photometric data. Combining the value of the orbital inclination with the mass function and the mass ratio, masses of 42 and 30 solar masses are found for the WN7 star and the unseen O star companion, respectively. Publication: The Astrophysical Journal Pub Date: July 1986 DOI: 10.1086/164333 Bibcode: 1986ApJ...306..215D Keywords: Eclipsing Binary Stars; Linear Polarization; O Stars; Polarimetry; Stellar Mass; Wolf-Rayet Stars; Electron Scattering; Orbital Elements; Stellar Winds; Astrophysics; POLARIZATION; STARS: ECLIPSING BINARIES; STARS: INDIVIDUAL CONSTELLATION NAME: CQ CEPHEI; STARS: WOLF-RAYET full text sources ADS | data products SIMBAD (5)

Circular and linear polarization variations of compact radio sources

For 22 compact extragalactic sources, 5-GHz measurements of all four Stokes parameters were made at Parkes at quarterly intervals from 1976 December to 1982 March. Circular polarization significant at the 4σ level or greater was measured in 16 of these sources. The fractional variability of the circularly polarized flux density was found to be greater than that of the linearly polarized flux density, which in turn was greater than that of the total flux density. Attributing the observed large changes in circularly polarized flux density accompanied by only small changes in total flux density to the appearance of new components would require such a high degree of polarization for the new components as to argue against the circular polarization being the intrinsic polarization of synchrotron radiation. In an alternative model the circular polarization is the intrinsic polarization of the synchrotron emission, not of a new component but of an existing, non-uniform, partly optically-thick source in which some of the parameters vary. In another alternative model, the medium through which the radiation propagates converts a small fraction of the linear polarization to circular polarization, and it is assumed that the degree of conversion varies without the magnitude of the total emission being affected. There was little if any correlation between the fluctuations of the total intensity and the fluctuations of either the circularly or the linearly polarized components. For at least some of the sources the variations of linear polarization are consistent with a model comprising two components, approximately orthogonally polarized, for which the relative intensities of the two components vary with time.

The variable linear polarization of Cygnus X-1, 1974-1975 observations

view Abstract Citations (17) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The variable linear polarization of Cygnus X-1, 1974 - 1975 observations. Kemp, J. C. ; Southwick, R. G. ; Rudy, R. J. Abstract An interim report is given concerning a long-range UBV observational study of linear polarization variations in HDE 226868, the optical counterpart of Cyg X-1. The observed rms fluctuations per night for either of the Stokes parameters are found to be approximately 0.33% for the U filter and 0.28% for either the B or the V filter, indicating that real variability is present with overwhelming probability. Very accurate measures of the average polarization are made for each filter. A folding of the data from each color on the period of 5.600 days reveals no significant phase locking and no statistically significant Fourier components at either the fundamental or half period. Power spectra of the variations are shown to be very noisy in appearance and to exhibit marginal evidence for anisotropic concentrations of excess power around the fundamental and half periods. The suspected structure in the power spectra, which does not consist of simple peaks, is explained tentatively in terms of phase modulation of an otherwise phase-locked process. Correlation with variable circular polarization is briefly examined. Publication: The Astrophysical Journal Pub Date: November 1976 DOI: 10.1086/154823 Bibcode: 1976ApJ...210..239K Keywords: Optical Polarization; Power Spectra; Supergiant Stars; Ubv Spectra; X Ray Sources; Black Holes (Astronomy); Circular Polarization; Optical Filters; Tables (Data); Astrophysics full text sources ADS | data products SIMBAD (1)

Linear polarization variations modulo 5.6 days in HDE 226868

view Abstract Citations (19) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Linear polarization variations modulo 5.6 days in HDE 226868. Nolt, I. G. ; Kemp, J. C. ; Rudy, R. J. ; Southwick, R. G. ; Radostitz, J. V. ; Caroff, L. J. Abstract Results are reported for observations of variations in the linear polarization in HDE 226868 (the optical counterpart of Cyg X-1) made with a photoelastic polarimeter and a U-filter. The UV linear-polarization variations, as folded on the 5.6-day orbital period, are found to have amplitudes of 0.25% and position-angle changes of 2.7 deg. These results are shown to be consistent with the geometry and phasing required by the model of the binary system. Publication: The Astrophysical Journal Pub Date: July 1975 DOI: 10.1086/181841 Bibcode: 1975ApJ...199L..27N Keywords: Binary Stars; Polarization Characteristics; Ubv Spectra; Variable Stars; Light Curve; Optical Filters; Optical Polarization; Stellar Spectra; Astrophysics full text sources ADS | data products SIMBAD (1)

Variations of Linear Polarization in Extragalactic Radio Sources

SINCE mid-1965 the linear polarizations of the stronger extragalactic variable radio sources have been monitored at 8 GHz using the University of Michigan 85-foot paraboloid equipped with a rotating, linearly polarized feed horn. Strong thermal and non-thermal sources were measured each observing day to determine the stability of the instrumental polarization. Five sources, 3C 120, 3C 273, 30 279, 3C 345 and 3C 454.3, have exhibited significant changes in polarization, and three sources, 3C 84, NRAO 150 and 3C 446, are suspected of having variable polarizations. Preliminary observational results for several of these sources have been reported previously1–2.