TY - JOUR
T1 - Thermodynamics of Pickup Ions in the Heliosphere
AU - Livadiotis, G.
AU - McComas, D. J.
AU - Shrestha, Bishwas L.
N1 - Publisher Copyright:
© 2024. The Author(s). Published by the American Astronomical Society.
PY - 2024/6/1
Y1 - 2024/6/1
N2 - The paper shows the thermodynamic nature of the evolution of the pickup ion (PUI) distributions through their incorporation and subsequent expansion as the solar wind moves outward through the heliosphere. In particular, the PUI expansive cooling is connected to thermodynamic polytropic processes and the thermodynamic kappa parameter. Previously, the characterization of the cooling was phenomenologically given by a “cooling index” α, which is the exponent involved in the power-law relationship between PUI speed and position. Here, we develop the relationship between the cooling and polytropic indices. Then, we show the connection between the cooling index and the thermodynamic parameter kappa. Finally, we verify the derived thermodynamic relations with direct heliospheric observations over varying distances from the Sun. Going forward, we suggest that studies of PUIs seeking to understand the underlying physics of these important particles rely on the thermodynamic parameter of kappa, and its association with the polytropic index, and not on an ad hoc cooling index.
AB - The paper shows the thermodynamic nature of the evolution of the pickup ion (PUI) distributions through their incorporation and subsequent expansion as the solar wind moves outward through the heliosphere. In particular, the PUI expansive cooling is connected to thermodynamic polytropic processes and the thermodynamic kappa parameter. Previously, the characterization of the cooling was phenomenologically given by a “cooling index” α, which is the exponent involved in the power-law relationship between PUI speed and position. Here, we develop the relationship between the cooling and polytropic indices. Then, we show the connection between the cooling index and the thermodynamic parameter kappa. Finally, we verify the derived thermodynamic relations with direct heliospheric observations over varying distances from the Sun. Going forward, we suggest that studies of PUIs seeking to understand the underlying physics of these important particles rely on the thermodynamic parameter of kappa, and its association with the polytropic index, and not on an ad hoc cooling index.
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U2 - 10.3847/1538-4357/ad3e79
DO - 10.3847/1538-4357/ad3e79
M3 - Article
AN - SCOPUS:85196047368
SN - 0004-637X
VL - 968
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 66
ER -