Electron Temperatures and Flow Speeds of the Low Solar Corona: MACS Results from the Total Solar Eclipse of 29 March 2006 in Libya

Abstract

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).

Origins of the Ambient Solar Wind: Implications for Space Weather

“…The electron temperatures at r > 1.5 R ⊙ are preliminary results from an empirical generalization of older hydrostatic scale-height techniques (see, e.g., Lemaire and Stegen 2016) using the UVCS visible-light and Lyα data as constraints. These estimates of T e generally agree with existing visible-light Thomson scattering results (Reginald et al 2011).…”

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

“…Although using the ISCORE instrument, both these electron parameters can be measured globally in the low solar corona; nevertheless, they cannot be measured simultaneously unless the incoming beam is split four ways to simultaneously image the corona through the four filters. On the other hand, an alternate technique to using filters is described in Reginald et al [] where a companion instrument to ISCORE called the Multi Aperture Coronal Spectrograph (MACS) is used to simultaneously measure both the electron temperature and bulk flow speed at multiple points of choice in the solar corona by measuring the K‐coronal intensity spectrum in white‐light extending from 3850.0 Å to 4450.0 Å. In MACS the modeled “K‐coronal intensity spectrum (KCIS)” is used to interpret measured KCIS where the shape and wavelength shift of the measured KCIS measure the electron temperature and bulk flow speed, respectively.…”

“…In this regard, Ichimoto et al [] used a slit‐based spectrograph during the total solar eclipse of 3 November 1994 in Chile to measure KCIS at two altitudes in a coronal hole and in a coronal streamer and used the shape based models by Cram [] to interpret for electron temperatures and speed differences over coronal heights. Reginald et al [] and Reginald et al [] used a fiber optic‐based spectrograph to measure KCIS at multiple locations in the solar corona and used shape and wavelength shift based models by Reginald and Davila [] to interpret for electron temperatures and speeds. However, in both the slit and fiber optic‐based techniques the theoretical models used for temperature and speed interpretation of the measured KCIS were based on modeled KCIS that assumed a symmetric corona devoid of any coronal structures.…”

The Balloon-Borne Investigation of Temperature and Speed of Electrons in the Corona (BITSE): Mission Description and Preliminary Results

“…Unlike traditional coronagraphs, the BITSE coronagraph (BITSE COR) has a single-stage optics and a polarization detector to obtain both the total and polarized brightness of the solar corona at four narrow passbands in the blue end of the K-corona spectrum. The BITSE mission is specifically built to demonstrate that the temperature and flow speed of the coronal electrons can be measured by quantifying the change in shape and red shift of the K-corona spectrum when the temperature and speed of the electrons change (Menzel and Pasachoff, 1968;Cram, 1976;Ichimoto et al, 1996Ichimoto et al, , 1997Takahashi, Yoneshima, and Hiei, 2000;Reginald and Davila, 2000;Reginald et al, 2003Reginald et al, , 2011. The temperature and flow speed of the electrons along with the density are key input parameters to models of solar wind acceleration.…”