An investigation of the formation and line properties of MgH in 3D hydrodynamical model stellar atmospheres

Abstract

Studies of the isotopic composition of magnesium in cool stars have so far relied upon the use of one-dimensional (1D) model atmospheres. Since the isotopic ratios derived are based on asymmetries of optical MgH lines, it is important to test the impact from other effects affecting line asymmetries, like stellar convection. Here, we present a theoretical investigation of the effects of including self-consistent modeling of convection. Using spectral syntheses based on 3D hydrodynamical CO${}^5$BOLD models of dwarfs (4000K$\lesssim T_{\mathrm{eff}}\lesssim 5160K$, $4.0\le$log(g)$\le 4.5$, $-3.0\le [Fe/H]\le -1.0$) and giants ($T_{\mathrm{eff}}\sim 4000$K, log(g)$=1.5$, $-3.0\le [Fe/H]\le -1.0$), we perform a detailed analysis comparing 3D and 1D syntheses. We describe the impact on the formation and behavior of MgH lines from using 3D models, and perform a qualitative assessment of the systematics introduced by the use of 1D syntheses. Using 3D model atmospheres significantly affect the strength of the MgH lines, especially in dwarfs, with 1D syntheses requiring an abundance correction of up to +0.69 dex largest for our 5000K models. The corrections are correlated with $T_{\mathrm{eff}}$ and are also affected by the metallicity. The shape of the strong ${}^{24}$MgH component in the 3D syntheses is poorly reproduced in 1D. This results in 1D syntheses underestimating ${}^{25}$MgH by up to $\sim 5$ percentage points and overestimating ${}^{24}$MgH by a similar amount for dwarfs. This discrepancy increases with decreasing metallicity. ${}^{26}$MgH is recovered relatively well, with the largest difference being $\sim 2$ percentage points. The use of 3D for giants has less impact, due to smaller differences in the atmospheric structure and a better reproduction of the line shape in 1D.

20 pages, 15 figures, accepted for publication in ApJ

References in corpus (12)

• The Radial Velocity Experiment (RAVE): first data release
• The GALAH Survey: Scientific Motivation
• CH in stellar atmospheres: an extensive linelist
• 3D Hydrodynamical Simulations of Surface Convection in Red Giant Stars. Impact on spectral line formation and abundance analysis
• Atomic and Molecular Data for Optical Stellar Spectroscopy
• Line shift, line asymmetry, and the 6Li/7Li isotopic ratio determination
• The chemical compositions of the extreme halo stars HE0107-5240 and HE1327-2326 inferred from 3D hydrodynamical model atmospheres
• The forbidden 1082 nm line of sulphur: the photospheric abundance of sulphur in the Sun and 3D effects
• Nucleosynthesis in a Primordial Supernova: Carbon and Oxygen Abundances in SMSS J031300.36-670839.31
• Barium even-to-odd isotope abundance ratios in thick disk and thin disk stars
• 3D hydrodynamical CO5BOLD model atmospheres of red giant stars: I. Atmospheric structure of a giant located near the RGB tip
• A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD140283

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