Abstract
The Wide-field Imager for Parker Solar Probe (WISPR) captures unprecedented white-light images of the solar corona and inner heliosphere. Thanks to the uniqueness of the Parker Solar Probe’s (PSP) orbit, WISPR is able to image “locally” coronal structures at high spatial and time resolutions. The observed plane of sky, however, rapidly changes because of the PSP’s high orbital speed. Therefore, the interpretation of the dynamics of the coronal structures recorded by WISPR is not straightforward. A first study, undertaken by Liewer et al. (Solar Phys.294, 93, 2019), shows how different coronal features (e.g., streamers, flux ropes) appear in the field-of-view of WISPR by means of raytracing simulations. In particular, they analyze the effects of the spatial resolution changes on both the images and the associated height–time maps, and introduce the fundamentals for geometric triangulation. In this follow-up paper, we focus on the study of the total brightness of a simple, spherical, plasma density structure, to understand how the analysis of Thomson-scattered emission by the electrons in a coronal feature can shed light into the determination of its kinematic properties. We investigate two cases: (i) a density sphere at a constant distance from the Sun for different heliographic longitudes; (ii) a density sphere moving outwardly with constant speed. The study allows us to characterize the effects of the varying heliocentric distance of the observer and scattering angle on the total brightness observed, which we exploit to contribute to a better determination of the position and speed of the coronal features observed by WISPR.
Highlights
The launch of Parker Solar Probe (PSP, Fox et al, 2016) has raised a lot of excitement and expectations in the science community
To the heliospheric imagers (Howard et al, 2008) aboard the Solar Terrestrial Relations Observatory (STEREO, Kaiser et al, 2008), Wide-field Imager for Parker Solar Probe (WISPR) consists of two cameras: the inner telescope with a field-of-view (FoV) of 40 deg and optical axis offset from the Sun centre by 33.5 deg; and the outer telescope with a FoV of 58 deg and optical axis offset by 79 deg
We investigate the total brightness profiles as a function of time for a coronal structure observed with WISPR, by creating synthetic images using the raytracing code distributed within the IDL/SolarSoftWare (SSW) library (Thernisien, Howard, and Vourlidas, 2006)
Summary
The launch of Parker Solar Probe (PSP, Fox et al, 2016) has raised a lot of excitement and expectations in the science community. WISPR is mounted on the spacecraft (S/C) ram direction, plasma structures are observed in advance and eventually crossed by PSP and measured in-situ by the other instruments Both imagers record the total brightness emission due to 1) Thomson-scattered light by free electrons in coronal features and solar wind (K-corona), and 2) scattered light by dust particles in orbit around the Sun (F-corona). If a feature moves with constant speed v, keeping its size and density constant, the total brightness would decrease according to Equation 1 via the variation of the radial distance r and the scattering angle χ , and to Equation 2 via the variation of ξ , which is directly measured from observations One of these equations could be used to infer the propagation speed of the structure. The quantification of the speed via photometric analysis could constrain
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