Bibcode
Shchukina, N. G.; Sukhorukov, A. V.; Trujillo Bueno, J.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 603, id.A98, 16 pp.
Fecha de publicación:
7
2017
Revista
Número de citas
19
Número de citas referidas
18
Descripción
Aims: The Si i 10 827 Å line is commonly used for
spectropolarimetric diagnostics of the solar atmosphere. First, we aim
at quantifying the sensitivity of the Stokes profiles of this line to
non-local thermodynamic equilibrium (NLTE) effects. Second, we aim at
facilitating NLTE diagnostics of the Si i 10 827 Å line. To this
end, we propose the use of a relatively simple silicon model atom, which
allows a fast and accurate computation of Stokes profiles. The NLTE
Stokes profiles calculated using this simple model atom are very similar
to those obtained via the use of a very comprehensive silicon model
atom. Methods: We investigate the impact of the NLTE effects on
the Si i 10 827 Å line by means of multilevel radiative transfer
calculations in a three-dimensional (3D) model atmosphere taken from a
state-of-the-art magneto-convection simulation with small-scale dynamo
action. We calculate the emergent Stokes profiles for this line at the
solar disk center and for every vertical column of the 3D snapshot
model, neglecting the effects of horizontal radiative transfer.
Results: We find significant departures from LTE in the Si i 10 827
Å line, not only in the intensity but also in the linearly and
circularly polarized profiles. At wavelengths around 0.1 Å, where
most of the Stokes Q, U, and V peaks of the Si i 10 827 Å line
occur, the differences between the NLTE and LTE profiles are comparable
with the Stokes amplitudes themselves. The deviations from LTE increase
with increasing Stokes Q, U, and V signals. Concerning the Stokes V
profiles, the NLTE effects correlate with the magnetic field strength in
the layers where such circular polarization signals are formed.
Conclusions: The NLTE effects should be taken into account when
diagnosing the emergent Stokes I profiles as well as the Stokes Q, U,
and V profiles of the Si i 10 827 Å line. The sixteen-level
silicon model atom proposed here, with six radiative bound-bound
transitions, is suitable to account for the physics of formation of the
Si i 10 827 Å line and for modeling and inverting its Stokes
profiles without assuming LTE.
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