Article

Polarization and Physical Properties of the August 11, 1999 White-Light Corona

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Four series of coronal images have been obtained by the expedition of Abastumani Astrophysical Observatory during the August 11, 1999 total solar eclipse with the help of a photographic mirror–lens polarimeter (D = 100 mm, F = 1000 mm). Each series include three images corresponding to three positions of the polarization analyzer. The position of the solar disk center relative to the Moon's center has been determined beforehand. In addition, the background skylight polarization and intensity are calculated. All measurements are absolute given in units of the Sun's average surface brightness. A new technique for separation of the F- and K-coronae is used. It was found that in the equatorial regions the model of hydrostatic distribution of the density with T = constant is not quite accurate for the August 11, 1999 corona and there is a temperature gradient in this region. For r1 = 1.3R⊙ and r2 = 1.8R⊙ we derived T1 = 1.25×106 K and T2 = 1.07×106 K, respectively. The average polarization degree in the equatorial regions changes from 10 to 40%, while in the polar regions the maximum value reaches only 10%. The values of electron densities Ne(r) vary from 1.32×108 cm−3 (r = 1.1R⊙) to 2.0×106 cm−3 (r = 2.0R⊙). Our data are compared with previous measurements.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Total brightness values in the polar angles 0 • , 30 • , 60 • and 90 • are shown with black circles in Figure 8 compared to the minimum type coronal model (solid line) of Saito (1970) and seven eclipse observations made by various authors (Young, 1966;Saito, 1948;Ramberg, 1951;Saito, 1956;Klüber, 1958;Saito and Hata, 1964;Waldmeier, 1964). Each eclipse observation value is shown with a different symbol. ...
... This telescope can analyze the solar corona up to 1.4R . On the other hand, the same method was used for the solar eclipse of 11 August 1999, and the obtained I A+S value 0.63 × 10 −8Ī is in good agreement with the 0.5 × 10 −8Ī value of Kulijanishvili and Kapanadze (2005), who observed the same eclipse. Parameters obtained from the calibration images taken at the 1999 eclipse and a graph of the intensity calibration function are also given in Appendix A with explanations and tables. ...
Article
Full-text available
Determining the relative brightness of the solar corona is one of the most critical stages in solar eclipse studies. For this purpose, images taken with different exposures and polarization angles in white-light observations are used. The composite image of each polarization angle is produced by combining the images of different exposures. With the help of the intensity calibration function of these images, the relative intensity of the corona can be calculated. The total brightness of the solar corona is calculated using Stokes parameters obtained from intensity values of three polarization angles. In this study, two methods are presented: the first is used to obtain the intensity calibration function of the photographic material using calibration images, and the second is used to calculate the combined intensity values of images taken with different polarization angles.
... Deviations of the polarisation direction of the scattered signal from tangential have also been reported only seldomly. This may be due to the fact that a tangential polarisation is often firmly assumed and even used as a premise to separate F and K corona [Koutchmy, 1994] or to eliminate a polarisation bias due to seeing or instrumental effects [Kulijanishvili and Kapanadze, 2005]. Anomalous polarisation directions were reported by [Pepin, 1970, Park et al., 2001, Skomorovsky et al., 2012, Qu et al., 2013 while other studies found no deviation from tangential polarisation within the measurement error [Koutchmy et al., 1993, Kim et al., 1996, Kulijanishvili and Kapanadze, 2005. ...
... This may be due to the fact that a tangential polarisation is often firmly assumed and even used as a premise to separate F and K corona [Koutchmy, 1994] or to eliminate a polarisation bias due to seeing or instrumental effects [Kulijanishvili and Kapanadze, 2005]. Anomalous polarisation directions were reported by [Pepin, 1970, Park et al., 2001, Skomorovsky et al., 2012, Qu et al., 2013 while other studies found no deviation from tangential polarisation within the measurement error [Koutchmy et al., 1993, Kim et al., 1996, Kulijanishvili and Kapanadze, 2005. All of these studies were made during lunar eclpises and can at best represent a snapshot of the state of the corona. ...
Article
Full-text available
The fundaments of the application of Thomson scattering to the analysis of coronagraph images has been laid decades ago. Even though the basic formulation is undebated, a discussion has grown in recent years about the spatial distribution of Thomson scatter sensitivity in space. These notes are an attempt to clarify the understanding about this topic. We reformulate the classical calculations in a more transparent way using modern SI-compatible quantities and extend the scattering calculations to the case of relativistic electrons. Many mathematical and some basic physical ingredients are made explicit in several chapters of the appendix.
... These kinds of deviations have been reported only seldom in the literature (Pepin, 1970;Badalyan, 1988;Skomorovsky et al., 2012;Qu et al., 2013) and some results deduced from photographic films/plates are of limited precision and significance (Park et al., 2001;Kim and Popov, 2015), especially when radial neutral filters were not used. Other studies explicitly found no deviation from the tangential polarisation within the measurement error (Koutchmy et al., 1993;Filippov, Molodensky, and Koutchmy, 1994;Kim et al., 1996;Kulijanishvili and Kapanadze, 2005;Vorobiev et al., 2020). ...
Article
Full-text available
In this work we performed a polarimetric study of a fast and wide coronal mass ejection (CME) observed on 12 July 2012 by the COR1 and COR2 instruments onboard the Solar TErrestrial RElations Observatory (STEREO) mission. The CME source region was an X1.4 flare located at approximately S15W01 on the solar disk, as observed from the Earth’s perspective. The position of the CME as derived from the 3D Graduated Cylindrical Shell (GCS) reconstruction method was at around S18W00 at 2.5 solar radii and S07W00 at 5.7 solar radii, meaning that the CME was deflected towards the Equator while propagating outward in the corona. The projected speed of the leading edge of the CME also evolved from around 200 km s⁻¹ in the lower corona to around 1000 km s⁻¹ in the COR2 field of view. The degree of polarisation of the CME is around 65% but it can go as high as 80% in some CME regions. The CME showed deviation of the polarisation angle from the tangential in the range of 10 – 15∘ (or more). Our analysis showed that this is mostly due to the fact that the sequence of three polarised images from where the polarised parameters are derived is not taken simultaneously, but at a difference of a few seconds in time. In this interval of time, the CME moves by at least two pixels in the FOV of the instruments and this displacement results in uncertainties in the polarisation parameters (degree of polarisation, polarisation angle, etc.). We propose some steps forward to improve the derivation of the polarisation. This study is important for analysing the future data from instruments with polarisation capabilities.
... These kinds of deviations have been reported only seldom in the literature (Pepin, 1970;Badalyan, 1988;Skomorovsky et al., 2012;Qu et al., 2013) and some results deduced from photographic films/plates are of limited precision and significance (Park et al., 2001;Kim and Popov, 2015), especially when radial neutral filters were not used. Other studies explicitly found no deviation from the tangential polarisation within the measurement error (Koutchmy et al., 1993;Filippov, Molodensky, and Koutchmy, 1994;Kim et al., 1996;Kulijanishvili and Kapanadze, 2005;Vorobiev et al., 2020). ...
Preprint
Full-text available
In this work we performed a polarimetric study of a fast and wide coronal mass ejection (CME) observed on 12 July 2012 by the COR1 and COR2 instruments onboard Solar TErrestrial RElations Observatory (STEREO) mission. The CME source region was an X1.4 flare located at approximately S15W01 on the solar disk as observed from the Earth's perspective. The position of the CME as derived from the 3D Graduated Cylindrical Shell (GCS) reconstruction method was at around S18W00 at 2.5 solar radii and S07W00 at 5.7 solar radii, meaning that the CME was deflected towards the Equator while propagating outward in the corona. The projected speed of the leading edge of the CME also evolved from around 200 km s$^{-1}$ in the lower corona to around 1000 km s$^{-1}$ in the COR2 field of view. The degree of polarisation of the CME is around 65 % but it can go as high as 80 % in some CME regions. The CME showed deviation of the polarisation angle from the tangential in the range of 10$^\circ$ - 15$^\circ$ (or more). Our analysis showed that this is mostly due to the fact that the sequence of three polarised images from where the polarised parameters are derived is not taken simultaneously, but at a difference of few seconds in time. In this interval of time, the CME is moving by at least two pixels in the FOV of the instruments and this displacement results in uncertainties in the polarisation parameters (degree of polarisation, polarisation angle, etc.). We propose some steps forward to improve the derivation of the polarisation. This study is important for analysing the future data from instruments with polarisation capabilities.
... Získané matice údajov budú slúžiť ako podklad na určenie veľkosti intenzity polarizovanej zelenej koróny a stupňa polarizácie (Sýkora a Mogilevskij, 1977;Kulijanishvili a Kapanadze, 2005). ...
Article
Abstrakt Pozorovanie úplného zatmenia Slnka sa uskutočnilo 29.3. 2006 v stredomorskom turistickom stredisku Manavgat (obr.1) Turecko. Úplná fáza nastala okolo miestneho poludnia. Pozorovacie podmienky počas úplneho zatmenia boli čiastočne rušené jemnou vysokou oblačnosťou. Boli pripravené a úspešne vykonané dva experimenty: 1. polarizácia zelenej koróny (Lorenc), 2. identifikácia neutrálnej hmoty v koróne (Lukáč). Pri obidvoch experimentoch bol získaný hodnotný fotografický a digitálny obrazový materiál. ÚVOD Úplné zatmenie Slnka, ktoré nastalo dňa 29.3.2006 bolo v poradí 29-tym zatmením série Saros č. 139. Pás totality začínal na východnom pobreží Brazílie, prechádzal Atlantickým oceánom, saharskou Afrikou, kde na hranici Líbie a Cadu dĺžka totality dosiahla maximum 4m07s, východnou časťou Stredozemného mora, naprieč Tureckom, Čiernym morom a končil hlboko v centrálnej Ázii pri hraniciach Mongolska (obr.2). Vzhľadom na dostupnosť dopravnými prostriedkami a predpovedanú poveternostnú situáciu sa javilo, že najvýhodnejšie pre nás bude vybudovať pozorovacie stanovište na stredomorskom pobreží Turecka v oblasti Tureckej riviéry -veľmi tesne pri centrálnej línii pásu totality, kde dĺžka úplnej fázy zatmenia bola predpovedaná na cca 3m50s. Bolo možné uvažovať o experimentoch, ktoré vyžadujú dlhší expozičný čas. Bolo možné použiť aj objemnejšie a hmotnejšie astronomické a pomocné zariadenie, nakoľko bolo možné a výhodné sa dopraviť na pozorovacie stanovište mikrobusom. Vlastné stanovište bolo zriadené na kamienkovej terase hotela, ktorý sa nachádzal tesne pri morskom pobreží. Súradnice pozorovacieho stanovišťa: ϕ =36°49´03 =31°18´14adm.výška: 10m.
Article
Full-text available
We carried out the polarimetric observation of the white-light inner corona during the 2017 total solar eclipse in the United States. Degree of linear polarization (DLP) of the inner corona is obtained by the modulated polarized data. The electron density is inferred from the normalized white-light polarization brightness data. According to the observational results, we find that: (1) The DLP of the white-light corona increases with the height, peaking at approximately $1.3 \sim 1.35\, {\rm R}_{\odot }$ and then slightly decreases. In the coronal streamer region, DLP peaks at approximately 1.35 R⊙ and its value is about 40 per cent, whereas in the coronal hole region, DLP peaks at approximately 1.3 R⊙ and its value is about 35 per cent. (2) The azimuth angle of polarization sin (2χ) is symmetrical around the solar disk center. It can be easily found that the gradients of the angle of polarization, representing the direction of oscillations of the electric vector E, are tangential. Above the active region, the DLP distribution changes significantly, whereas the azimuth distribution is stable. This proves that the polarization of white-light corona is mainly caused by scattering polarization. (3) The electron density and the K-corona have similar distributions of properties. Electron density decreases from 6 × 107cm−3 to 2 × 106cm−3, whereas the height increases from $1.1\, {\rm R}_{\odot }$ to $1.85\, {\rm R}_{\odot }$. (4) An interesting finding is that, in the cavity region, there may be other polarization-induced mechanisms besides scattering, which can affect the value of the white-light DLP.
Article
Full-text available
Results are presented from spectro-imaging polarimetry of radiation from the local solar corona during the 2013 total solar eclipse in Gabon. This polarimetric observation was performed from 516.3 nm to 532.6 nm using a prototype Fiber Arrayed Solar Optical Telescope (FASOT). A polarimetric noise level on the order of \(10^{-3}\) results from a reduced polarimetric optical switching demodulation (RPOSD) procedure for data reduction. It is revealed that the modality of fractional linear polarization profiles of the green coronal line shows a diversity, which may indicate complex mechanisms. The polarization degree can approach 3.2 % above the continuum polarization level on a scale of 1500 km, and the nonuniform spatial distribution in amplitude and polarization direction is found even within a small field of view of 7500 km. All of this implies that the coronal polarization is highly structured and complex even on a small scale.
Article
We present results from imaging polarimetry (IP) of upper solar atmospheres during a total solar eclipse on 2012 November 13 and spectropolarimetry of an annular solar eclipse on 2010 January 15. This combination of techniques provides both the synoptic spatial distribution of polarization above the solar limb and spectral information on the physical mechanism producing the polarization. Using these techniques together we demonstrate that even in the transition region, the linear polarization increases with height and can exceed 20%. IP shows a relatively smooth background distribution in terms of the amplitude and direction modified by solar structures above the limb. A map of a new quantity that reflects direction departure from the background polarization supplies an effective technique to improve the contrast of this fine structure. Spectral polarimetry shows that the relative contribution to the integrated polarization over the observed passband from the spectral lines decreases with height while the contribution from the continuum increases as a general trend. We conclude that both imaging and spectral polarimetry obtained simultaneously over matched spatial and spectral domains will be fruitful for future eclipse observations.
Article
Measurements of white-light corona polarization, performed during three solar eclipses, are presented. Corresponding maps of polarization reflect the actual coronal structures far better than isophotes do. Analysis of the degree of polarization also allows us to say more about the density distribution along the line of sight. Unique green-line corona eclipse images were obtained on July 11, 1991. The distribution of polarization around the Sun is shown. We have found a reversed dependence (anticorrelation) between the degree of polarization and the green-line intensity. Polarization data contains new information about the relative role of electron collisions and photospheric radiation in the excitation of the Fe XIV 530.3 nm emission line. Eliminating the dependence of polarization on distance, the anticorrelation found distinctly splits into two branches. Different types of coronal structures are identified in the anticorrelation diagram.
Article
Thanks to the availability of a large radiative flux in the optical region, solar total eclipses are rare occasions offering the opportunity of using sophisticated methods to analyze all parts of the highly structured white light corona. Coronal absolute intensities and line emissions, including their polarization, are studied to analyze density and temperature inhomogeneities, velocities and magnetic fields. Detailed density distribution is directly extracted from fine coronal structures. During the 1991 eclipse, the large 3.6 m aperture CFH (Canada France Hawaii) optical telescope was used to analyze time sequences over small coronal fields and to reach the finest structure; results from this experiment are presented including the analysis of the faintest detected feature and small scale dynamical plasma processes. To prepare the SOHO (Solar and Heliospheric Observatory) mission on coronal physics, an overview of what is known on coronal structures from eclipse observations of the past solar cycles is given. The nonpotential nature of the coronal magnetic field is well illustrated by the large deviation of streamers from the radial direction as well as by the systematic occurrence of tangential discontinuities at edges of streamers.
Article
The Third Goddard Workshop on the Modeling and Physics of the Global Magnetosphere was held at NASA's Goddard Space Flight Center (GSFC) June 3-5, 1992. About twenty scientists discussed recent progress and ongoing work involving global field models and areas where such models were used.
Article
During the July 91 total solar eclipse, the polarized K corona was observed from two sites in Baja California (Mexico) using two techniques: photography with a 6 position polarizing filter (30 deg steps) and CCD (Charge Coupled Device) camera using 12 positions (15 deg steps). A total of 36 CCD images were combined to produce intensity and polarization maps of the corona from 1.1 to 3.0 solar radii with 10 inch spatial resolution. Several characteristics of the corona can already be deduced from those data, which are now processed to compute the global electron density distribution.
Article
At present data exist showing that in some regions of the corona the polarization degree has been found to be higher than the maximum possible value determined by Thomson scattering. Besides this, there exist regions where the direction of the prevailing vibration of the E-vector does not coincide with the tangential one. This may be caused by the velocity of scattered electrons. The theory of polarization taking the velocity into account is given, and the above-mentioned data are discussed. The direction of polarization turns out to be the sensitive detector of fact electrons (for energy of 5 keV, the deviation angle ≈ 10°). Very important data about accelerated electrons on the Sun may be received from precise measurements of the corona polarization.
  • C W Allen
  • C. W. Allen