Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars

Abstract

Aims. We investigate the role of convection in the formation of atomic and molecular lines in the atmosphere of a red giant star. For this purpose we study the formation properties of spectral lines that belong to a number of astrophysically important tracer elements, including neutral and singly ionized atoms (Li Ba ii, and Eu ii), and molecules (CH, CO, C 2 , NH, CN, and OH).Methods. We focus our investigation on a prototypical red giant located close to the red giant branch (RGB) tip (T eff = 3660 K, log g = 1.0, [M/H] = 0.0). We used two types of model atmospheres, 3D hydrodynamical and classical 1D, calculated with the CO 5 BOLD and LHD stellar atmosphere codes, respectively. Both codes share the same atmospheric parameters, chemical composition, equation of state, and opacities, which allowed us to make a strictly differential comparison between the line formation properties predicted in 3D and 1D. The influence of convection on the spectral line formation was assessed with the aid of 3D-1D abundance corrections, which measure the difference between the abundances of chemical species derived with the 3D hydrodynamical and 1D classical model atmospheres. Results. We find that convection plays a significant role in the spectral line formation in this particular red giant. The derived 3D-1D abundance corrections rarely exceed ±0.1 dex when lines of neutral atoms and molecules are considered, which is in line with the previous findings for solar-metallicity red giants located on the lower RGB. The situation is different with lines that belong to ionized atoms, or to neutral atoms with high ionization potential. In both cases, the corrections for high-excitation lines (χ > 8 eV) may amount to Δ 3D−1D ∼ −0.4 dex. The 3D-1D abundance corrections generally show a significant wavelength dependence; in most cases they are smaller in the near-infrared, at 1600-2500 nm.

The Stagger-grid: A grid of 3D stellar atmosphere models

“…This is, in particular, distinctive for low-excitation neutral iron lines as previously found by Asplund et al (1999) and Collet et al (2007). Kučinskas et al (2013) present similar findings for a solar-metallicity RG simulation as well, namely that neutral iron lines based on 1D MLT models are slightly closer to the full 3D lines compared to the 3D lines.…”

“…Since their effect is strongest in convective zone below the optical surface and the line formation region, the influence in terms of abundance is likely small; in fact, Kučinskas et al (2013) only found a very small effect < 0.02 dex for the reduction in α MLT from 1.5 to 1.2. However, for metal-poor giants the influence can be greater for lines with very high excitation potential.…”

A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD 140283

“…It has been established in previous works that deviations in line abundance exist between 3D and 1D analyses (Asplund et al 1999;Asplund & García Pérez 2001;Frebel et al 2008;Kučinskas et al 2013). The analysis done here likewise found abundance differences in the 3D analysis, relative to the 1D analysis in Paper I.…”

Spectroscopic analysis of DA white dwarfs with 3D model atmospheres

“…Kučinskas et al (2013) studied 3D vs. 3D effects for metal lines, but these results can not be applied to non-trace elements and saturated lines. In principle, the monochromatic flux would Fig.…”