Two-dimensional non-LTE \ion{O}{I} 777\,nm line formation in radiation hydrodynamics simulations of Cepheid atmospheres

Abstract

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.

9 pages, 10 figures; Published in Astronomy and Astrophysics

References in corpus (6)

• The NumPy array: a structure for efficient numerical computation
• The GALAH Survey: Scientific Motivation
• Oxygen Abundances in Nearby Stars. Clues to the formation and evolution of the Galactic disk
• Galactic abundance gradients from Cepheids : On the iron abundance gradient around 10-12 kpc
• Oxygen abundance distribution in Galactic disc
• Spectroscopic properties of a two-dimensional time-dependent Cepheid model I. Description and validation of the model

Cited by in corpus (3)

• Tracing the Milky Way warp and spiral arms with classical Cepheids
• Atmospheric parameters of Cepheids from flux ratios with ATHOS: I. The temperature scale
• The MAGIC project. III. Radial and azimuthal Galactic abundance gradients using classical Cepheids