We conducted an experiment in conjunction with the total solar eclipse of 29 March 2006 in Libya that measured the coronal intensity through two filters centered at 3850 Å and 4100 Å with bandwidths of ≈ 40 Å. The purpose of these measurements was to obtain the intensity ratio through these two filters to determine the electron temperature. The instrument, Imaging Spectrograph of Coronal Electrons (ISCORE), consisted of an eight inch, f/10 Schmidt Cassegrain telescope with a thermoelectrically-cooled CCD camera at the focal plane. Results show electron temperatures of 10 5 K close to the limb to 3 × 10 6 K at 1.3R . We describe this novel technique, and we compare our results to other relevant measurements. This technique could be easily implemented on a space-based platform using a coronagraph to produce global maps of the electron temperature of the solar corona.

COR1 is the innermost coronagraph of the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument suite aboard the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft. The paired COR1 telescopes observe the whitelight K-corona from 1.4 to 4 solar radii in a waveband 22.5 nm wide centered on the Hα line at 656 nm. An internal polarizer allows the measurement of both total and polarized brightness. The co-alignment of the two COR1 telescopes is derived from the star λ Aquarii for the Ahead spacecraft, and from an occultation of the Sun by the Moon for Behind. Observations of the planet Jupiter are used to establish absolute photometric calibrations for each telescope. The intercalibration of the two COR1 telescopes are compared using coronal mass ejection observations made early in the mission, when the spacecraft were close together. Comparisons are also made with the Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) C2 and Mauna Loa Solar Observatory Mk4 coronagraphs.

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"Replacing the polarizer wheel with a polarization camera to increase the temporal resolution and reduce the overall complexity of a solar coronagraph," J. Astron. Telesc. Instrum. Syst. 3(1), 014001 (2017), doi: 10.1117/1.JATIS.3.1.014001. Abstract. Experiments that require linearly polarized brightness measurements, traditionally have obtained three successive images through a linear polarizer that is rotated through three well-defined angles and the images are combined to get the linearly polarized brightness. This technique requires a mechanism to hold the linear polarizer in place and to precisely turn it through the three angles. Obviously, the temporal resolution is lost in such a scenario, since the three images that are used to derive the linearly polarized brightness are taken at three different times. Specifically, in a dynamic corona that is in constant reshaping of its structures, the linearly polarized brightness image produced in this manner may not yield true values all around the corona. In this regard, with the advent of the polarization camera, the linearly polarized brightness can be measured from a single image. This also eliminates the need for a linear polarizer and the associated rotator mechanisms and can contribute toward lower weight, size, power requirements, overall risk of the instrument, and most importantly, increase the temporal resolution. We evaluate the capabilities of a selected polarization camera and how these capabilities could be tested in a ground experiment conducted in conjunction with a total solar eclipse. The ground experiment requires the measurement of the linearly polarized brightness, also known as K-corona, in a corona that also contains unpolarized brightness, known as F-corona, in order to measure three important physical properties pertaining to coronal electrons, namely, the electron density, electron temperature, and the electron speed.

An experiment was conducted in conjunction with the total solar eclipse on 29 March 2006 in Libya to measure both the electron temperature and its flow speed simultaneously at multiple locations in the low solar corona by measuring the visible K-coronal spectrum. Coronal model spectra incorporating the effects of electron temperature and its flow speed were matched with the measured K-coronal spectra to interpret the observations. Results show electron temperatures of (1.10 ± 0.05) MK, (0.70 ± 0.08) MK, and (0.98 ± 0.12) MK, at 1.1 R from Sun center in the solar north, east and west, respectively, and (0.93 ± 0.12) MK, at 1.2 R from Sun center in the solar west. The corresponding outflow speeds obtained from the spectral fit are (103 ± 92) km s −1 , (0 + 10) km s −1 , (0 + 10) km s −1 , and (0 + 10) km s −1 . Since the observations were taken only at 1.1 R and 1.2 R from Sun center, these speeds, consistent with zero outflow, are in agreement with expectations and provide additional confirmation that the spectral fitting method is working. The electron temperature at 1.1 R from Sun center is larger at the north (polar region) than the east and west (equatorial region).

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