scholarly journals Master equation theory applied to the redistribution of polarized radiation in the weak radiation field limit

2020 ◽  
Vol 644 ◽  
pp. A65
Author(s):  
Véronique Bommier
Keyword(s):  
Linear Polarization ◽  
Computing Time ◽  
Solar Spectrum ◽  
Polarization Degree ◽  
Line Center ◽  
Present Calculation ◽  
Thermodynamical Equilibrium ◽  
Numerical Application ◽  
Instrumental Polarization ◽  
Polarization Profiles

Context. This paper presents a numerical application of a self-consistent theory of partial redistribution in nonlocal thermodynamical equilibrium conditions, developed in previous papers of the series. Aims. The code was described in IV of this series. However, in that previous paper, the numerical results were unrealistic. The present paper presents an approximation able to restore the reliability of the outgoing polarization profiles. Methods. The convergence of the results is also proved. It is demonstrated that the step increment decreases like 1/Nα, with α >  1. Results. Thanks to these additions, the results series behaves like a Riemann series, which is absolutely convergent. However, convergence is not fully reached in line wings within the allocated computing time. Development of efficient acceleration methods would be desirable for future work. Conclusions. Agreement between the computed and observed linear polarization profiles remains qualitative only. The discrepancy is assigned to the plane parallel atmosphere model, which is insufficient to describe the chromosphere, where these lines are formed. As all the integrals are numerical in the code, it could probably be adapted to more realistic and higher dimensional model atmospheres. However, this is time consuming for lines with a hyperfine structure, as in the Na I D lines. The net linear polarization observed in Na I D1 with the Zürich Imaging Polarimeter ZIMPOL mounted on the McMath-Pierce telescope at Kitt Peak is not confirmed by the present calculations and could be an artefact of instrumental polarization. The presence of instrumental polarization could be confirmed by the higher linear polarization degree observed by this instrument in the Na I D2 line center with respect to the present calculation result where the magnetic field is not accounted for. At this precise point, the Hanle effect acts as a depolarizing effect in the second solar spectrum. The observed linear polarization excess is found to be of the same order of magnitude in both line centers, namely 0.1%, which is also comparable to the instrumental polarization compensation level of this experiment.

Comparison of linear polarization degree in healthy and wounded rat skin

2001 ◽  
Author(s):  
Martha S. Ribeiro ◽  
Anderson Z. Freitas ◽  
Daniela F. Silva ◽  
Denise M. Zezell ◽  
Cleusa M. R. Pellegrini ◽  
...  
Keyword(s):  
Linear Polarization ◽  
Polarization Degree ◽  
Rat Skin

scholarly journals The solar-like ‘Second Spectrum’ and polarized metal lines in the emission of the post-AGB binary 89 Herculis

2018 ◽  
Vol 480 (2) ◽  
pp. 1656-1665 ◽  
Author(s):  
F Leone ◽  
M Gangi ◽  
M Giarrusso ◽  
C Scalia ◽  
M Cecconi ◽  
...  
Keyword(s):  
High Resolution ◽  
Linear Polarization ◽  
Hot Spots ◽  
Optical Pumping ◽  
Solar Spectrum ◽  
Free Electrons ◽  
Emission Profile ◽  
Secondary Star ◽  
Two Jets ◽  
Rule Out

ABSTRACT We studied the polarized spectrum of the post-AGB binary system 89 Herculis on the basis of data collected with the high-resolution Catania Astrophysical Observatory Spectropolarimeter, HArps-North POlarimeter and Echelle SpectroPolarimetric Device for the Observation of Stars. We find the existence of linear polarization in the strongest metal lines in absorption and with low excitation potentials. Signals are characterized by complex Q and U morphologies varying with the orbital period. We rule out magnetic fields, continuum depolarization due to pulsations and hot spots as the possible origin of this ‘Second Solar Spectrum’-like behaviour. The linear polarization we detected in the Caii 8662-Å line is clear evidence of optical pumping polarization and rules out scattering polarization from free electrons of the circumbinary environment. In the framework of optical pumping due to the secondary star, the observed periodic properties of the spectral line polarization can be justified by two jets, with a flow velocity of a few tens of km s−1, at the basis of that hourglass structure characterizing 89 Herculis. We also discovered linear polarization across the emission profile of metal lines. Numerical simulations show that these polarized profiles could be formed in an undisrupted circumbinary disc rotating at ≤10 km s−1 and with an orientation in the sky in agreement with optical and radio interferometric results. We conclude that the study of aspherical envelopes, the origin of which is not yet completely understood, of PNe and already present in post-AGBs can benefit from high-resolution spectropolarimetry and that this technique can shape envelopes still too far away for interferometry.

scholarly journals Polarization in Pulsar Radio Emission

1992 ◽  
Vol 128 ◽  
pp. 384-386
Author(s):  
D. M. GOULD
Keyword(s):  
Radio Emission ◽  
Circular Polarization ◽  
Linear Polarization ◽  
Large Data ◽  
Position Angle ◽  
Published Data ◽  
Data Set ◽  
Pulsar Radio ◽  
Polarization Profiles ◽  
Pulsar Radio Emission

Polarimetric observations of over 300 pulsars have been carried out between 21 December 1988 and 22 January 1990 at 606, 610, 925, and 1408 MHz using the Lovell Telescope at Jodrell Bank. Many of these pulsars have no previously published polarization profiles and will be published shortly (Gould and Lyne 1990). This large data set along with previously published data from various sources, has been used to test the correlation found by Radhakrishnan and Rankin (1990) between sense reversing circular polarization signatures and the accompanying sense of rotation of the linear polarization position angle.

scholarly journals A revisit to model the Cr i triplet at 5204-5208 Å and the Ba ii D2 line at 4554 Å in the Second Solar Spectrum

2014 ◽  
Vol 10 (S305) ◽  
pp. 372-376
Author(s):  
H. N. Smitha ◽  
K. N. Nagendra ◽  
J. O. Stenflo ◽  
M. Bianda ◽  
M. Sampoorna ◽  
...  
Keyword(s):  
Standard Model ◽  
Solar Spectrum ◽  
Central Peak ◽  
Model Atmosphere ◽  
Previous Attempt ◽  
Line Profiles ◽  
Polarization Profiles

AbstractIn our previous attempt to model the Stokes profiles of the Cr i triplet at 5204-5208 Å and the Ba ii D2 at 4554 Å, we found it necessary to slightly modify the standard FAL model atmospheres to fit the observed polarization profiles. In the case of Cr i triplet, this modification was done to reduce the theoretical continuum polarization, and in the case of Ba ii D2, it was needed to reproduce the central peak in Q/I. In this work, we revisit both these cases using different standard model atmospheres whose temperature structures closely resemble those of the modified FAL models, and explore the possibility of synthesizing the line profiles without the need for small modifications of the model atmosphere.

Empirical Polarization Distribution Models for CLARREO-Imager Intercalibration

2016 ◽  
Vol 33 (3) ◽  
pp. 439-451 ◽  
Author(s):  
D. Goldin ◽  
C. Lukashin
Keyword(s):  
Linear Polarization ◽  
Infrared Imaging ◽  
Solar Spectrum ◽  
National Research Council ◽  
Real Data ◽  
Radiative Transfer Model ◽  
Degree Of Polarization ◽  
Transfer Model ◽  
Distribution Models ◽  
Polarization Distribution

AbstractPolarization effects bias the performance of various existing passive spaceborne instruments, such as MODIS and the Visible Infrared Imaging Radiometer Suite (VIIRS), as well as geostationary imagers. It is essential to evaluate and correct for these effects in order to achieve the required accuracy of the total reflectance at the top of the atmosphere.In addition to performing highly accurate decadal climate change observations, one of the objectives of the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission recommended by the National Research Council for launch by NASA is to provide the on-orbit intercalibration with the imagers over a range of parameters, including polarization. Whenever the on-orbit coincident measurements are not possible, CLARREO will provide the polarization distributions constructed using the adding–doubling radiative transfer model (ADRTM), which will cover the entire reflected solar spectrum. These ADRTM results need to be validated using real data. To this end the empirical polarization distribution models (PDMs) based on the measurements taken by the Polarization and Anisotropy of Reflectances for Atmospheric Sciences Coupled with Observations from a Lidar (PARASOL) mission were developed. Examples of such PDMs for the degree of polarization and the angle of linear polarization for the cloudless ocean scenes are shown here. These PDMs are compared across the three available PARASOL polarization bands, and the effect of aerosols on them is examined. The PDM-derived dependence of the reflectance uncertainty on the degree of polarization for imagers, such as MODIS or VIIRS, after their intercalibration with the CLARREO instrument is evaluated. The influence of the aerosols on the reflectance uncertainty is examined. Finally, the PDMs for the angle of linear polarization is cross-checked against the single-scattering approximation.

scholarly journals The Radio Lobes of Virgo A

1996 ◽  
Vol 175 ◽  
pp. 343-344
Author(s):  
H. Rottmann ◽  
K.-H. Mack ◽  
U. Klein ◽  
R. Wielebinski ◽  
N. Kassim ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Linear Polarization ◽  
Dynamic Range ◽  
Low Frequency ◽  
Spectral Indices ◽  
Frequency Data ◽  
Polarization Effects ◽  
Instrumental Polarization

In the framework of our multi-frequency study of Virgo A we have performed observations of Vir A at 10.55 GHz with the Effelsberg 100-m telescope. Using our improved CLEAN procedure for single dish data we have increased the dynamic range to some 40 dB.By applying our newly developed polarization CLEANing technique we are able to diminish instrumental polarization effects. Since Faraday rotation is negligible at λ2.8 cm the measured linear polarization is a direct trace of the projected magnetic field in Vir A. In combination with low-frequency data obtained with the VLA it is possible to determine parameters like spectral indices, break frequencies, and spectral ages.

scholarly journals Polarimetric imaging mode of VLT/SPHERE/IRDIS

2020 ◽  
Vol 633 ◽  
pp. A64 ◽  
Author(s):  
R. G. van Holstein ◽  
J. H. Girard ◽  
J. de Boer ◽  
F. Snik ◽  
J. Milli ◽  
...  
Keyword(s):  
Linear Polarization ◽  
Data Reduction ◽  
Near Infrared ◽  
Circumstellar Disks ◽  
Correction Method ◽  
Polarization Effects ◽  
Very Large Telescope ◽  
Instrumental Polarization ◽  
Imaging Polarimetry ◽  
Data Reduction Method

Context. Circumstellar disks and self-luminous giant exoplanets or companion brown dwarfs can be characterized through direct-imaging polarimetry at near-infrared wavelengths. SPHERE/IRDIS at the Very Large Telescope has the capabilities to perform such measurements, but uncalibrated instrumental polarization effects limit the attainable polarimetric accuracy. Aims. We aim to characterize and correct the instrumental polarization effects of the complete optical system, that is, the telescope and SPHERE/IRDIS. Methods. We created a detailed Mueller matrix model in the broadband filters Y, J, H, and Ks and calibrated the model using measurements with SPHERE’s internal light source and observations of two unpolarized stars. We developed a data-reduction method that uses the model to correct for the instrumental polarization effects, and applied it to observations of the circumstellar disk of T Cha. Results. The instrumental polarization is almost exclusively produced by the telescope and SPHERE’s first mirror and varies with telescope altitude angle. The crosstalk primarily originates from the image derotator (K-mirror). At some orientations, the derotator causes severe loss of signal (> 90% loss in the H- and Ks-band) and strongly offsets the angle of linear polarization. With our correction method we reach, in all filters, a total polarimetric accuracy of ≲0.1% in the degree of linear polarization and an accuracy of a few degrees in angle of linear polarization. Conclusions. The correction method enables us to accurately measure the polarized intensity and angle of linear polarization of circumstellar disks, and is a vital tool for detecting spatially unresolved (inner) disks and measuring the polarization of substellar companions. We have incorporated the correction method in a highly-automated end-to-end data-reduction pipeline called IRDAP, which we made publicly available online.

3mm POLARIZATION PROPERTIES OF OPTICAL AND γ-RAY CLASSES OF BLAZARS

2010 ◽  
Vol 19 (06) ◽  
pp. 923-929
Author(s):  
I. AGUDO ◽  
C. THUM ◽  
H. WIESEMEYER ◽  
T. P. KRICHBAUM
Keyword(s):  
Linear Polarization ◽  
Position Angle ◽  
Polarization Degree ◽  
Polarization Angle ◽  
Marginal Effect ◽  
Bl Lacertae ◽  
All Optical ◽  
Linearly Polarized ◽  
Γ Ray ◽  
The One

We have performed the first 3.5 mm polarimetric survey of radio loud active galactic nuclei (AGN) with the IRAM 30 m Telescope. Unlike radio wavelengths, millimeter observations allow us to measure the intrinsic linearly polarized emission from AGN, thanks to the marginal effect of Faraday rotation and depolarization at mm wavelengths. The sample contains 145 sources, and it essentially consists of all flat-spectrum AGN with declinations accessible to the 30 m Telescope (Dec. ( J 2000.0) > -30°), and with 3 mm flux density ≳ 1 Jy, as measured from 1978 to 1994. LBAS quasars in our sample show larger luminosity than non-LBAS ones, which is consistent with previous work claiming larger Doppler factors for brighter γ-ray blazars. This effect cannot be claimed for BL Lacertae objects in our sample, which suggests that only quasars contribute to distribute LBAS blazars towards larger luminosities. We find a systematic 3.5 mm linear polarization degree excess by a factor of ~ 2 with regard to the one at 2 cm for all optical and γ-ray classes of sources considered here. Our sample shows a significant trend to increase the luminosity of their jets for decreasing linear polarization fraction. Unlike previous studies in the radio spectral range, we do not find a clear relation between the linear polarization angle and the jet structural position angle of any source class in our sample. This is interpreted as a markedly non-axisymmetric character of the 3 mm emitting region of radio loud AGN jets.

Parametric Study of Molecular Line Polarization in the Solar Atmosphere

2000 ◽  
Vol 179 ◽  
pp. 269
Author(s):  
K. E. Rangarajan ◽  
D. Mohan Rao
Keyword(s):  
Solar Atmosphere ◽  
Linear Polarization ◽  
Parametric Study ◽  
Elastic Collision ◽  
The Other ◽  
Strong Line ◽  
Molecular Line ◽  
Physical Constraints ◽  
Molecular Lines ◽  
Polarization Profiles

Extended AbstractThe polarimetric observations of the quiet sun show linear polarization in molecular lines of C2, MgH, etc. The molecular lines are very faint in the intensity spectrum. Q branch transitions of MgH are considered in this study. Using radiative transfer calculations, we find that the intensity and polarization profiles of MgH lines can be matched for a range of inelastic collisional rates (ΓI) and depolarizing elastic collision rates (D(2)) of the transitions in solar atmosphere. It is shown that the physical constraints imposed on these parameters can be used to estimate them. This procedure also allows us to get the oscillator strength (f). It is found for the strong line 5156.652 Å,f= 0.12, ΓI, = 5.59 × l07sec−1andD(2)= 1.29 × 108sec−1. Most of the other lines observed are weak by a factor of 3 in intensity compared to the 5156.652 Å line but show a polarization value of the order of 0.08%. One such typical line is 5156.997 Å. This line can be fitted for the parametersf= 0.04, ΓI, = 1.22 × 107sec−1andD(2)= 2.95 × 107sec−1.

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