Two-dimensional non-LTE ion{O}{I} 777,nm line formation in radiation hydrodynamics simulations of Cepheid atmospheres. (arXiv:1903.02109v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Vasilyev_V/0/1/0/all/0/1">V. Vasilyev</a>, <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:+Ludwig_H/0/1/0/all/0/1">H.-G. Ludwig</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lemasle_B/0/1/0/all/0/1">B. Lemasle</a>
Oxygen abundance measurements are important for understanding stellar
structure and evolution. Measured in Cepheids, they further provide clues on
the metallicity gradient and chemo-dynamical evolution in the Galaxy. However,
most of the abundance analyses of Cepheids to date have been based on
one-dimensional (1D) hydrostatic model atmospheres. Here, we test the validity
of this approach for the key oxygen abundance diagnostic, the ion{O}{I}
$777,mathrm{nm}$~triplet lines. We carry out 2D non-LTE radiative transfer
clculations across two different 2D radiation hydrodynamics simulations of
Cepheid atmospheres, having stellar parameters of $T_mathrm{eff}= 5600$ K,
solar chemical compositions, and $log,g= 1.5$ and $2.0$, corresponding to
pulsation periods of 9 and 3 days, respectively. We find that the 2D non-LTE
versus 1D LTE abundance differences range from $-1.0$~dex to $-0.25$~dex
depending on pulsational phase. The 2D non-LTE versus 1D non-LTE abundance
differences range from $-0.2$~dex to $0.8$~dex. The abundance differences are
smallest when the Cepheid atmospheres are closest to hydrostatic equilibrium,
corresponding to phases of around $0.3$ to $0.8$, and we recommend these phases
for observers deriving the oxygen abundance from ion{O}{I} $777,mathrm{nm}$
triplet with 1D hydrostatic models.
Oxygen abundance measurements are important for understanding stellar
structure and evolution. Measured in Cepheids, they further provide clues on
the metallicity gradient and chemo-dynamical evolution in the Galaxy. However,
most of the abundance analyses of Cepheids to date have been based on
one-dimensional (1D) hydrostatic model atmospheres. Here, we test the validity
of this approach for the key oxygen abundance diagnostic, the ion{O}{I}
$777,mathrm{nm}$~triplet lines. We carry out 2D non-LTE radiative transfer
clculations across two different 2D radiation hydrodynamics simulations of
Cepheid atmospheres, having stellar parameters of $T_mathrm{eff}= 5600$ K,
solar chemical compositions, and $log,g= 1.5$ and $2.0$, corresponding to
pulsation periods of 9 and 3 days, respectively. We find that the 2D non-LTE
versus 1D LTE abundance differences range from $-1.0$~dex to $-0.25$~dex
depending on pulsational phase. The 2D non-LTE versus 1D non-LTE abundance
differences range from $-0.2$~dex to $0.8$~dex. The abundance differences are
smallest when the Cepheid atmospheres are closest to hydrostatic equilibrium,
corresponding to phases of around $0.3$ to $0.8$, and we recommend these phases
for observers deriving the oxygen abundance from ion{O}{I} $777,mathrm{nm}$
triplet with 1D hydrostatic models.
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