Article

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

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## 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.

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... 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
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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. ...
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... 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). ...
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... 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). ...
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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). ...
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• C W Allen
• C. W. Allen