Electron-Temperature Maps of the Low Solar Corona: ISCORE Results from the Total Solar Eclipse of 29 March 2006 in Libya

Abstract

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.

Replacing the polarizer wheel with a polarization camera to increase the temporal resolution and reduce the overall complexity of a solar coronagraph

“…1, from Phillips,7 that shows the K and F brightness profiles measured from the sun center to the earth's orbit in solar radii, it is evident that the K component overwhelms the F component by orders of magnitude at coronal heights below 1.5 R ⊙ from the sun center. Therefore, the ISCORE experimental results from Reginald et al 4 that did not use a linear polarizer but restricted its observations to coronal heights below 1.5 R ⊙ from the sun center are reasonable.…”

“…12 and it is apparent that tB MR is a function of both the polarized I λ p and unpolarized I λ u light, but is not a function of the extinction ratios E λ PA . Figure 6 by Reginald et al 4 shows the "theoretically" modeled "temperature sensitive intensity ratio" (TSIR) plotted against electron temperature (T) in the corona based on photospheric light passing through the two color filters centered at 410.0 and 385.0 nm. TSIR, as defined in Eq.…”

“…Therefore, in the past ISCORE experiments, we limited our observations to low coronal regions close to the solar limb and assumed our measurements to satisfy the conditions to obtain TSIR and we interpreted the "measured" TSIR for electron temperature using Fig. 6 by Reginald et al 4 Here, we wish to note that tB MR cannot be used to determine the electron temperature since it also contains I λ u and will need a separate I λ u model or experimental results to correct tB MR . On the other hand, TSIR, if limited to low solar coronal regions, is not subject to any systematic errors associated with E λ PA of the micropolarizer array in the polarization camera:…”

“…4. In the ISCORE instrumental concept, the electron temperature and flow speed are measured by taking four consecutive coronal images of the solar corona using a linear polarizer with a mechanism to turn through three well-defined angles for each of four filters centered at 385.0, 398.7, 410.0, and 423.3 nm with a bandpass of ∼5 nm.…”

“…To test the potential of the polarization camera, the ISCORE instrument described by Reginald et al 4 was reconfigured to accommodate a polarization camera together with a filter wheel that housed four filters centered at 385.0, 398.7, 410.0, and 423.3 nm to measure both the electron temperature and speed in conjunction with the total solar eclipse of March 9, 2016, in Maba, Indonesia. Unfortunately, we were clouded out.…”