Non‐LTE line formation of Fe in late‐type stars – I. Standard stars with 1D and 〈3D〉 model atmospheres

By M. Bergemann, K. Lind, R. Collet, Z. Magic, Martin Asplund. 2012

254 citations recorded by the source corpus.

We investigate departures from LTE in the line formation of Fe for a number of well-studied late-type stars in different evolutionary stages. A new model of Fe atom was constructed from the most up-to-date theoretical and experimental atomic data available so far. Non-local thermodynamic equilibrium (NLTE) line formation calculations for Fe were performed using 1D hydrostatic MARCS and MAFAGS-OS model atmospheres, as wellas the spatial and temporal average stratifications from full 3D hydrodynamical s imulations of stellar convection computed using the Stagger code. It is shown that the Fe I/Fe II ionization balance can be well established with the 1D and mean 3D models under NLTE including calibrated inelastic collisions with H I calculated from the Drawin’s (1969) form ulae. Strong low-excitation Fe I lines are very sensitive to the atmospheric structure; clas sical 1D models fail to provide consistent excitation balance, particularly so for cool metal-po or stars. A better agreement between Fe I lines spanning a range of excitation potentials is obtai ned with the mean 3D models. Mean NLTE metallicities determined for the standard stars using the 1D and mean 3D models are fully consistent. Also, the NLTE spectroscopic effective temperatures and gravities from ionization balance agree with that determined by other methods, e.g., infrared flux method and parallaxes, if one of the stellar parameters is constrai ned independently.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/86877c51d2f92319fae6d1825f6bfd4a8078b99a

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Citations in the corpus

The Gaia-ESO Survey : radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk (2014, background): “As shown by Bergemann et al. (2012) and Lind et al. (2012), non-local thermodynamic equilibrium (NLTE) effects change surface gravities and metallicities of stars, in a way such that logg and [Fe/H] obtained from Fe lines are systematically higher.”
The Stagger-grid: A grid of 3D stellar atmosphere models - I. Methods and general properties (2013, background): “In addition, the grid also includes the Sun with its non-solar metallicity analogs, and four additional stand rd stars, namely HD 84937, HD 140283, HD 122563 and G 64-12 that are presented in Bergemann et al. (2012).”
The elemental composition of the Sun - I. The intermediate mass elements Na to Ca (2014, methodology): “Such 〈3D〉 spectrum modelling has started to be used in the analyses of observed stellar spectra (e.g. Bergemann et al. 2012).”
Gaia FGK benchmark stars: Effective temperatures and surface gravities (2015, methodology): “Some recent publications using Procyon as a calibration or test object are Porto de Mello et al. (2014), Doyle et al. (2013), Bergemann et al. (2012a), Worley et al. (2012), Lobel (2011), Mashonkina et al. (2011), Quirion et al. (2010), Bruntt et al. (2010), Gebran et al. (2010).”
Gaia FGK benchmark stars: Metallicity (2013, methodology): “For an extensive dis- cussion on this issue for five of our Benchmark Stars (the Sun, Procyon, HD122563, HD140283, HD84937 and HD122563) see also Bergemann et al. (2012).”
OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO (2013, unknown): “We refer the reader to the recent works by Bergemann et al. (2012) and Lind et al. (2012) for a detailed investigation of these issues.”
The Gaia-ESO Survey: the analysis of high-resolution UVES spectra of FGK-type stars (2014, result): “Gravity values for metal-poor stars are known to be affected by NLTE effects (see e.g. Bergemann et al. 2012), therefore it is no surprise that the results of LTE-based analyses shown here are discrepant when compared to the reference values, since the latter are independent from spectroscopy.”
The elemental composition of the Sun: II. The iron group elements Sc to Ni (2014, methodology): “Mashonkina et al. (2011) and Bergemann et al. (2012) carried out NLTE calculations of Fe line formation, using the most up-to-date theoretical and experimental atomic data to construct their model atoms.”
THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, background): “…although we recognize the magnitude of such efforts currently underway (e.g., Andrievsky et al. 2008, 2011; Collet et al. 2011; Bergemann & Gehren 2008; Bergemann et al. 2010; Bergemann 2011; Bergemann et al. 2012; Dobrovolskas et al. 2012; Lind et al. 2009a, 2011, 2012; Spite et al. 2012).”
SPECTRAL PROPERTIES OF COOL STARS: EXTENDED ABUNDANCE ANALYSIS OF 1,617 PLANET-SEARCH STARS (2016, methodology): “We obtained corrections for lines in common with our line list of oxygen (Amarsi et al. 2015), sodium (Lind et al. 2011), magnesium (Osorio et al. 2015), titanium (Bergemann 2011), and iron (Bergemann et al. 2012; Lind et al. 2012).”