3D non-LTE line formation of neutral carbon in the Sun. (arXiv:1903.08838v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Amarsi_A/0/1/0/all/0/1">A. M. Amarsi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barklem_P/0/1/0/all/0/1">P. S. Barklem</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Collet_R/0/1/0/all/0/1">R. Collet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Grevesse_N/0/1/0/all/0/1">N. Grevesse</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Asplund_M/0/1/0/all/0/1">M. Asplund</a>

Carbon abundances in late-type stars are important in a variety of
astrophysical contexts. However C i lines, one of the main abundance
diagnostics, are sensitive to departures from local thermodynamic equilibrium
(LTE). We present a model atom for non-LTE analyses of C i lines, that uses a
new, physically-motivated recipe for the rates of neutral hydrogen impact
excitation. We analyse C i lines in the solar spectrum, employing a
three-dimensional (3D) hydrodynamic model solar atmosphere and 3D non-LTE
radiative transfer. We find negative non-LTE abundance corrections for C i
lines in the solar photosphere, in accordance with previous studies, reaching
up to around 0.1 dex in the disk-integrated flux. We also present the first
fully consistent 3D non-LTE solar carbon abundance determination: we infer log
$epsilon_{text{C}}$ = $8.44pm0.02$, in good agreement with the current
standard value. Our models reproduce the observed solar centre-to-limb
variations of various C i lines, without any adjustments to the rates of
neutral hydrogen impact excitation, suggesting that the proposed recipe may be
a solution to the long-standing problem of how to reliably model inelastic
collisions with neutral hydrogen in late-type stellar atmospheres.

Carbon abundances in late-type stars are important in a variety of
astrophysical contexts. However C i lines, one of the main abundance
diagnostics, are sensitive to departures from local thermodynamic equilibrium
(LTE). We present a model atom for non-LTE analyses of C i lines, that uses a
new, physically-motivated recipe for the rates of neutral hydrogen impact
excitation. We analyse C i lines in the solar spectrum, employing a
three-dimensional (3D) hydrodynamic model solar atmosphere and 3D non-LTE
radiative transfer. We find negative non-LTE abundance corrections for C i
lines in the solar photosphere, in accordance with previous studies, reaching
up to around 0.1 dex in the disk-integrated flux. We also present the first
fully consistent 3D non-LTE solar carbon abundance determination: we infer log
$epsilon_{text{C}}$ = $8.44pm0.02$, in good agreement with the current
standard value. Our models reproduce the observed solar centre-to-limb
variations of various C i lines, without any adjustments to the rates of
neutral hydrogen impact excitation, suggesting that the proposed recipe may be
a solution to the long-standing problem of how to reliably model inelastic
collisions with neutral hydrogen in late-type stellar atmospheres.

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