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Coronal Electron Temperature Inferred from the Strahl Electrons in the Inner Heliosphere: Parker Solar Probe and Helios Observations

Laura Berčič 1, 2 Davin Larson 3 Phyllis Whittlesey 3 Milan Maksimović 1 Samuel T. Badman 3 Simone Landi 2, 4 Lorenzo Matteini 1 Stuart. D. Bale 3, 5, 6 John W. Bonnell 3 Anthony W. Case 7 Thierry Dudok De Wit 8 Keith Goetz Peter R. Harvey 3 Justin C. Kasper 7, 9 Kelly E. Korreck 7 Roberto Livi 3 Robert J. Macdowall 10 David M. Malaspina 11 Marc Pulupa 3 Michael L. Stevens 7
1 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 Università degli Studi di Firenze = University of Florence [Firenze]
3 University of California [Berkeley]
4 OAA - INAF - Osservatorio Astrofisico di Arcetri
5 Imperial College London
6 QMUL - Queen Mary University of London
7 Smithsonian Astrophysical Observatory
8 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
9 University of Michigan [Ann Arbor]
10 GSFC Solar System Exploration Division
GSFC - NASA Goddard Space Flight Center
11 University of Colorado [Boulder]
Abstract : The shape of the electron velocity distribution function plays an important role in the dynamics of the solar wind acceleration. Electrons are normally modeled with three components, the core, the halo, and the strahl. We investigate how well the fast strahl electrons in the inner heliosphere preserve the information about the coronal electron temperature at their origin. We analyzed the data obtained by two missions, Helios, spanning the distances between 65 and 215 R S, and Parker Solar Probe (PSP), reaching down to 35 R S during its first two orbits around the Sun. The electron strahl was characterized with two parameters: pitch-angle width (PAW) and the strahl parallel temperature (T s∥). PSP observations confirm the already reported dependence of strahl PAW on core parallel plasma beta (${\beta }_{\mathrm{ec}\parallel }$). Most of the strahl measured by PSP appear narrow with PAW reaching down to 30°. The portion of the strahl velocity distribution function aligned with the magnetic field is for the measured energy range well described by a Maxwellian distribution function. T s∥ was found to be anticorrelated with the solar wind velocity and independent of radial distance. These observations imply that T s∥ carries the information about the coronal electron temperature. The obtained values are in agreement with coronal temperatures measured using spectroscopy, and the inferred solar wind source regions during the first orbit of PSP agree with the predictions using a PFSS model.
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https://hal.sorbonne-universite.fr/hal-02996324
Contributor : Gestionnaire Hal-Su <>
Submitted on : Monday, November 9, 2020 - 3:43:08 PM
Last modification on : Thursday, April 15, 2021 - 3:08:18 PM

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Laura Berčič, Davin Larson, Phyllis Whittlesey, Milan Maksimović, Samuel T. Badman, et al.. Coronal Electron Temperature Inferred from the Strahl Electrons in the Inner Heliosphere: Parker Solar Probe and Helios Observations. The Astrophysical Journal, American Astronomical Society, 2020, 892 (2), pp.88. ⟨10.3847/1538-4357/ab7b7a⟩. ⟨hal-02996324⟩

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