TY - JOUR
T1 - A Reduced-order NLTE Kinetic Model for Radiating Plasmas of Outer Envelopes of Stellar Atmospheres
AU - Munafò, Alessandro
AU - Mansour, Nagi N.
AU - Panesi, Marco
N1 - Funding Information:
The research of A.M. was supported by the NASA Award grant NNX 14AN44G. The research of M.P. was supported by the NASA grant NNX15AQ57A. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of NASA. The authors gratefully acknowledge Dr. A Wray and Dr. D Hathaway at NASA Ames Research Center for the useful scientific discussions and suggestions while preparing the manuscript.
Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved.
PY - 2017/4/1
Y1 - 2017/4/1
N2 - The present work proposes a self-consistent reduced-order NLTE kinetic model for radiating plasmas found in the outer layers of stellar atmospheres. A detailed collisional-radiative kinetic mechanism is constructed by leveraging the most up-to-date set of ab initio and experimental data available in the literature. This constitutes the starting point for the derivation of a reduced-order model, obtained by lumping the bound energy states into groups. In order to determine the needed thermo-physical group properties, uniform and Maxwell-Boltzmann energy distributions are used to reconstruct the energy population of each group. Finally, the reduced set of governing equations for the material gas and the radiation field is obtained based on the moment method. Applications consider the steady flow across a shock wave in partially ionized hydrogen. The results clearly demonstrate that adopting a Maxwell-Boltzmann grouping allows, on the one hand, for a substantial reduction of the number of unknowns and, on the other, to maintain accuracy for both gas and radiation quantities. Also, it is observed that, when neglecting line radiation, the use of two groups already leads to a very accurate resolution of the photo-ionization precursor, internal relaxation, and radiative cooling regions. The inclusion of line radiation requires adopting just one additional group to account for optically thin losses in the α, β, and γ lines of the Balmer and Paschen series. This trend has been observed for a wide range of shock wave velocities.
AB - The present work proposes a self-consistent reduced-order NLTE kinetic model for radiating plasmas found in the outer layers of stellar atmospheres. A detailed collisional-radiative kinetic mechanism is constructed by leveraging the most up-to-date set of ab initio and experimental data available in the literature. This constitutes the starting point for the derivation of a reduced-order model, obtained by lumping the bound energy states into groups. In order to determine the needed thermo-physical group properties, uniform and Maxwell-Boltzmann energy distributions are used to reconstruct the energy population of each group. Finally, the reduced set of governing equations for the material gas and the radiation field is obtained based on the moment method. Applications consider the steady flow across a shock wave in partially ionized hydrogen. The results clearly demonstrate that adopting a Maxwell-Boltzmann grouping allows, on the one hand, for a substantial reduction of the number of unknowns and, on the other, to maintain accuracy for both gas and radiation quantities. Also, it is observed that, when neglecting line radiation, the use of two groups already leads to a very accurate resolution of the photo-ionization precursor, internal relaxation, and radiative cooling regions. The inclusion of line radiation requires adopting just one additional group to account for optically thin losses in the α, β, and γ lines of the Balmer and Paschen series. This trend has been observed for a wide range of shock wave velocities.
KW - atomic processes
KW - plasmas
KW - radiation mechanisms: non-thermal
KW - radiative transfer
KW - shock waves
KW - stars: atmospheres
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U2 - 10.3847/1538-4357/aa602e
DO - 10.3847/1538-4357/aa602e
M3 - Article
AN - SCOPUS:85017325168
VL - 838
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - 126
ER -