Synoptic Measurements of Electron Temperature and Speed in the Solar Corona with Next Generation White-Light Coronagraph

Abstract

Current white-light coronagraphs measure polarized brightness (pB) of the solar corona using a single bandpass filter to measure the density of electrons. However, future coronagraphs can be modified to take pB images through four bandpass filters to measure density, temperature and speed of electrons. In this article, we use a spherical three dimensional coronal model of the Bastille Day coronal mass ejection to synthetically measure pB through four bandpass filters along lines of sight originating from two observers located diametrically in front (1 AU, 0, 0) and behind (-1 AU, 0, 0) the plane of the sky on the xy-ecliptic plane. The lines of sight pass through 81 positions on a straight line parallel to the solar north–south z-direction in the yz-plane and this line intersects the ecliptic at (0, $1.25~\mbox{R}_{\odot}$ , 0) from Sun center. The 81 data points are separated in intervals of $0.05~\mbox{R}_{\odot}$ and points extend from (0, $1.25~\mbox{R}_{\odot}$ , - $2.0~\mbox{R}_{\odot}$ ) to (0, $1.25~\mbox{R}_{\odot}$ , $2.0~\mbox{R}_{\odot}$ ). The measured pB ratios are used to measure temperature and speed, then we compare with true temperature and speed in the plane of the sky, and quantify the difference, which is a systematic error associated with using modeled pB ratios, based on a symmetric corona, to compare with measured pB ratios, on an asymmetric corona. This understanding is reached by allowing the coronal model to rotate a full circle in intervals of $1^{\circ}$ and illuminating the lines of sight with both symmetric and asymmetric coronal atmospheres about the plane of the sky.