Collaborative Research: Large Scale Structures and Solar Wind Origin from Eclipse Observations of Coronal Lines

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The solar wind is the key component of the solar system that shapes the interplanetary space and planetary atmospheres. Understanding the underlying physical processes controlling its expansion is key to understanding the coupling of the Sun to the solar system. The importance of this knowledge is becoming all the more critical with our increased reliance on access to space by manned and unmanned missions. Specifically, despite decades of observational and theoretical studies devoted to the solar wind, we are still far from a consensus on where and how the solar wind is accelerated. The solar wind is usually studied with two completely different techniques: in-situ measurements of local wind plasma properties in the heliosphere, and remote sensing (spectroscopy and imaging) of regions closer than roughly 1.5 solar radii to the solar surface. The region of the solar corona between 1.5 and 4 solar radii, where the solar wind continues to accelerate, however, is largely unexplored. Total solar eclipse events offer rare, unique opportunities to obtain observations of this crucial region of the solar corona. The basic idea behind this research collaboration is to utilize observations of the solar corona during recent and upcoming total solar eclipse events to obtain measurements of solar wind parameters for this region, many of which will be first of its kind. Total solar eclipses are unique astronomical events that capture people's imagination. The team has a successful record of public outreach and general education efforts that build on this easy fascination to raise public awareness of scientific research and engage young people's interest in science. A graduate student at the University of Hawaii Institute for Astronomy will be hired and trained to participate in this research and this work will constitute a significant part of that person's dissertation. Undergraduate student participation will be integrated into the research at the University of Michigan through the existing Undergraduate Research Opportunities Program there at no cost to this project. This research project is aimed at investigating the coronal region between 1.5 and 4 solar radii, where the solar wind continues to accelerate and its charge state composition freezes-in. In this region the evolution of heavy ions becomes a direct probe of solar wind heating and acceleration processes. This research uses eclipse observations of visible lines emitted by consecutive stages of ionization of iron to study the large-scale corona. Line-to-continuum and line-to-line intensity ratios will be used to build a map of the iron freeze-in location. Frozen in charge states will be measured and directly compared to in-situ measurements, linking remote sensing and in-situ observations. Diagnostics will couple the existing CHIANTI spectral code with user-defined velocity, temperature, and density of the solar wind. Predicted line intensities will be compared to eclipse observations, and the input plasma parameters will be modified until agreement is reached. The resulting empirical model of solar wind plasma parameters will be able to discriminate between different candidate wind source regions and will provide a constraint for solar wind heating and acceleration models.