Investigating the Brightness of Coronal Rays with the Parker Solar Probe/WISPR Observations

The Parker Solar Probe (PSP), launched in 2018, has already accumulated seven years of observations with the Wide-Field Imager for Solar Probe (WISPR), offering numerous opportunities to study different coronal structures in visible light, such as streamers, dynamic outflows of blobs, and expanding coronal mass ejections (CMEs). Their brightness profiles are of interest because they depend on the position of these coronal structures with respect to the Thomson Sphere (TS), defined as the sphere with a radius equal to the distance between the Sun and the observer (i.e., PSP). The same feature moving in the observer's line of sight will appear brighter when it is in the vicinity of the TS because it is closer to the Sun, hence its density and brightness are higher. A study by Nisticò et al. (2020) demonstrated how the brightness profiles of ray tracing simulated blobs in WISPR change depending on their position relative to the TS and their speed. We apply the same theoretical approach to simulated and actual observations of coronal streamers in WISPR. Their brightness variations help us to infer the dynamics, scattering angle, velocity, extension, and electron density of these structures. To validate our results, we use multiple approaches, including MHD modeling and triangulation techniques to determine the location and dynamics of coronal structures.