Issue |
A&A
Volume 690, October 2024
|
|
---|---|---|
Article Number | A213 | |
Number of page(s) | 11 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/202449722 | |
Published online | 09 October 2024 |
Full non-LTE spectral line formation
III. The case of a two-level atom with broadened upper level
1
Indian Institute of Astrophysics,
Koramangala,
Bengaluru
560034,
India
2
Université de Toulouse, UPS-Observatoire Midi-Pyrénées, Cnrs, Cnes, Irap,
Toulouse,
France
3
Cnrs, Institut de Recherche en Astrophysique et Planétologie,
14 av. E. Belin,
31400
Toulouse,
France
4
LESIA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CNRS,
Meudon,
France
★ Corresponding author; sampoorna@iiap.res.in
Received:
24
February
2024
Accepted:
10
August
2024
In the present paper we consider the full nonlocal thermodynamic equilibrium (non-LTE) radiation transfer problem. This formalism allows us to account for deviation from equilibrium distribution of both the radiation field and the massive particles. In the present study, two-level atoms with broadened upper level represent the massive particles. In the absence of velocity-changing collisions, we demonstrate the analytic equivalence of the full non-LTE source function with the corresponding standard non-LTE partial frequency redistribution (PFR) model. We present an iterative method based on operator splitting techniques that can be used to numerically solve the problem at hand. We benchmark it against the standard non-LTE transfer problem for a two-level atom with PFR. We illustrate the deviation of the velocity distribution function of excited atoms from the equilibrium distribution. We also discuss the dependence of the emission profile and the velocity distribution function on elastic collisions and velocity-changing collisions.
Key words: line: formation / line: profiles / radiation mechanisms: general / radiative transfer / methods: numerical / stars: atmospheres
© The Authors 2024
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