The non-LTE line formation of neutral carbon in late-type stars

Abstract

Aims. We investigate the non-Local Thermodynamic Equilibrium (non-LTE) line formation of neutral carbon in late-type stars in order to remove some of the potential systematic errors in stellar abundance analyses employing C i features.Methods. The statistical equilibrium code MULTI was used on a grid of plane-parallel 1D MARCS atmospheric models.Results. Within the parameter space explored, the high-excitation C i lines studied are stronger in non-LTE due to the combined effect of line source function drop and increased line opacity due to overpopulation of the lower level for the transitions considered; the relative importance of the two effects depends on the particular combination of T eff , log g,

Carbon abundances of reference late-type stars from 1D analysis of atomic C i and molecular CH lines

“…At [M/H] = −2 our ∆NLTEs are consistent with that of Takeda & Honda (2005), but they are 0.08 dex smaller in absolute value compared with that of Fabbian et al (2006). We computed smaller NLTE abundance corrections for the [M/H] = −3 model atmospheres than the corresponding values in Takeda & Honda (2005) and Fabbian et al (2006). This is not due to applying the Reid (1994) data.…”

“…A We compared our calculations with the NLTE results of Takeda & Honda (2005) and Fabbian et al (2006). To be as close as possible to the NLTE method of Fabbian et al (2006), we employed the same collisional recipe as Fabbian et al (2006) and SH = 1.…”

“…Hayek et al (2011) updated the Collet et al (2007) Thus, the discrepancy between the C I and CH-based abundances found by Tomkin et al (1992) in the classical 1D analysis is expected to be larger in 3D. The NLTE methods for C I were developed by Vernazza et al (1981), Shchukina & Shcherbina (1990), Stuerenburg & Holweger (1990), Takeda (1992), Przybilla et al (2001), Fabbian et al (2006), and Lyubimkov et al (2015). Stuerenburg & Holweger (1990) showed that NLTE removes a discrepancy between visible and near-IR lines of C I in the Sun, while the difference in LTE abundances between individual lines can be up to 0.37 dex, for example between C I 9111Å and 5380Å.…”

“…[Fe/H] −0.7 metallicity range, while close-to-solar C/Fe ratios were obtained by Fabbian et al (2006) after correcting these data for the NLTE effects. The Lyubimkov et al (2015) studied the NLTE effects for C I in the galactic A-, F-and G-type supergiants and bright giants.…”

SYSTEMATIC NON-LTE STUDY OF THE −2.6 ≤ [Fe/H] ≤ 0.2 F AND G DWARFS IN THE SOLAR NEIGHBORHOOD. II. ABUNDANCE PATTERNS FROM Li TO Eu*

“…principles of non-LTE (NLTE) line formation and codes capable of such calculations have been around for a long time but have only been explored in a more systematic fashion for a wide range of stellar parameters over the past decade or so (e.g., Zhao et al 1998;Zhao & Gehren 2000;Mashonkina & Gehren 2001;Takeda et al 2002;Gehren et al 2004;Fabbian et al 2006;Mashonkina & Zhao 2006;Zhang et al 2006b;Mashonkina et al 2007aMashonkina et al , 2008Bergemann & Gehren 2008;Zhang et al 2008;Lind et al 2009;Shi et al 2009;Andrievsky et al 2010;Bergemann & Cescutti 2010;Spite et al 2011Spite et al , 2012Yan et al 2015). Before the observations are used to give constraints to the GCE models, we need to take into account the analysis errors of the stellar abundances, such as the departures from LTE and uncertainties in the atmospheric parameters.…”