Abstract
The basic assumptions of the NLTE approximation in stellar atmospheres are summarized. The assumptions of thermodynamic equilibrium, local thermodynamic equilibrium (LTE), and non-LTE (NLTE) are compared. It is emphasized that LTE is a poor approximation if radiative transitions dominate in stellar atmospheres. The equations of kinetic equilibrium and methods of their solution are discussed.
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Notes
- 1.
Note that sometimes \(n_iP_{il}\) is called the rate. Here we prefer to use the notation consistent with the textbook of Hubeny and Mihalas (2014).
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Acknowledgments
The author would like to thank Dr. Ewa Niemczura for inviting him to the Spring School of Spectroscopic Data Analyses in Wrocław. He is also grateful to both referees (Ivan Hubeny and the anonymous one) for their invaluable comments. This work was partly supported by the project 13-10589S of the Grant Agency of the Czech Republic (GA ČR).
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Kubát, J. (2014). Basics of the NLTE Physics. In: Niemczura, E., Smalley, B., Pych, W. (eds) Determination of Atmospheric Parameters of B-, A-, F- and G-Type Stars. GeoPlanet: Earth and Planetary Sciences. Springer, Cham. https://doi.org/10.1007/978-3-319-06956-2_14
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DOI: https://doi.org/10.1007/978-3-319-06956-2_14
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