White-Light Observations and Polarimetric Analysis of the Solar Corona During the Eclipse of 1 August 2008

Abstract

In order to study the solar corona during eclipses, a new telescope was constructed. Three coronal images were obtained simultaneously through a single objective of the telescope as the coronal radiation passed through three polarizers (whose transmission directions were turned 0°, 60°, and 120°in the chosen direction); one image was obtained without a polarizer. The telescope was used to observe the solar corona during the eclipse of 1 August 2008. We obtained the distributions of polarization brightness, K-corona brightness, the degree of K-corona polarization and the total polarization degree; the polarization direction, depending on the latitude and radius in the plane of the sky, was also obtained. We calculated the radial distributions of electron density depending on the latitude. The properties of all these distributions were compared for different coronal structures. We determined the temperature of the coronal plasma in different coronal structures assuming hydrostatic equilibrium.

Electron temperature maps of the low solar corona: ISCORE results from the total solar eclipse of 1 August 2008 in China

“…Hanaoka et al [] measured the brightness of the 1 August 2008 solar eclipse and concluded that the solar activity was the lowest in one hundred years, and the coronal brightness was very low. On the same eclipse Figure 5 in Skomorovsky et al [] indicates that at a distance of 1.2 R ⊙ from the Sun center the equator was ∼ 5 times brighter than at the equivalent distance in the pole. Lamy et al [] measured that the solar minimum during the solar cycle 23/24 (2008–2009) was 24% fainter than the minimum during the previous cycle 22/23 (1995–1996) and that the two hemispheres experienced different reductions, 17% for the north and 29% for the south.…”

“…For example, the task of simultaneous imaging was successfully accomplished by von Klüber [] as far back as the total solar eclipse of 25 February 1952 by splitting the beam to four identical cameras that were cross calibrated. A similar instrumental concept was used by Skomorovsky et al [] to characterize the solar corona in conjunction with the total solar eclipse of 1 August 2008. However, to create synoptic maps of the coronal electron temperature and bulk flow speed over a complete solar rotation, the use of a coronagraph is inevitable and we present the following ideas to create such maps.…”

“…Many other researchers conducted field experiments in conjunction with the total solar eclipse of 1 August 2008, and here we list some of their results. Skomorovsky et al [] conducted four simultaneous observations of the solar corona: three through polarizers oriented 120° apart and another without a polarizer to characterize the coronal environment in terms of the K‐coronal intensity, degree of polarization, and polarization angle. Here they report a representative plasma temperature of ∼1.7 MK at the base of the streamer in southeast and ∼1.2 MK in the polar region, based on the assumption of spherical symmetry, hydrostatic equilibrium, identical temperature for ions and electrons, and radial independence of plasma temperature.…”

“…If such a dependence is confirmed and not corrected then it will be one more factor contributing toward systematic error owing to its larger contribution to the 3850.0 Å band than the 4100.0 Å band. The importance of correcting for F‐coronal contamination is further signified by Figure 5 in Skomorovsky et al [] that shows at a distance of 1.2 R ⊙ from the Sun center the total brightness measured during the total solar eclipse of 1 August 2008 was ∼25% brighter than the K‐coronal brightness. Scattering within the telescope: The optical components used in this experiment were off the shelf components and we did have the means to quantify, if any, internal scattering. Only in the case of the two filters, the transmission profiles shown in Figure were exhaustively measured in the laboratory over a wide wavelength range extending from ultraviolet to near infrared for any leakage beyond the band pass of the individual filters.…”

Spectro-Imaging Polarimetry of the Local Corona During Solar Eclipse

“…Imaging-polarimetry during solar eclipses has a history of more than one hundred years. Most researchers detected highly polarized radiations from the corona and presented highly structured polarization maps (for instance, Ney et al, 1961;Eddy and McKim Malville, 1967;Blackwell and Petford, 1966;Hyder, Mauter, and Shutt, 1968;McDougal, 1971;Koutchmy and Schatten, 1971;Molodensky, 1973;Badalyan and Sýkora, 1997;Kulijanishvili and Kapanadze, 2005;Skomorovsky et al, 2012;Qu et al, 2013). More efficient, improved diagnostic methods (House, 1977;House, Querfeld, and Rees, 1982;Raouafi, Lemaire, and Sahal-Bréchot, 1999;Raouafi, Sahal-Bréchot, and Lemaire, 2002;Raouafi and Solanki, 2003;Raouafi, 2005) have been devised to reveal distributions of electron density, electron temperature, and especially the magnetic field, which is highly relevant here and cannot be accurately diagnosed by non-polarimetric measurements.…”