Improving spectroscopic lithium abundances. Fitting functions for 3D non-LTE corrections in FGK stars of different metallicity

Abstract

Accurate spectroscopic lithium abundances are essential in addressing a variety of open questions, such as the origin of a uniform lithium content in the atmospheres of metal-poor stars (Spite plateau) or the existence of a correlation between the properties of extra-solar planetary systems and the lithium abundance of their host stars. We have developed a tool that allows the user to improve the accuracy of standard lithium abundance determinations based on 1D model atmospheres and the assumption of Local Thermodynamic Equilibrium (LTE) by applying corrections that account for hydrodynamic (3D) and non-LTE (NLTE) effects in FGK stars of different metallicity. Based on a grid of CO5BOLD 3D models and associated 1D hydrostatic atmospheres, we computed three libraries of synthetic spectra of the lithium line at 670.8 nm for a wide range of lithium abundances, accounting for detailed line formation in 3D NLTE, 1D NLTE, and 1D LTE, respectively. The resulting curves-of-growth were then used to derive 3D NLTE and 1D NLTE lithium abundance corrections. We demonstrate that 3D and NLTE effects are small for metal-poor stars on the Spite plateau, leading to errors of at most +/-0.05 dex if ignored. The largest corrections are found at the coolest effective temperature, Teff=5000 K, where they can reach -0.4 dex for the strongest lines. We present analytical functions for evaluating the corrections and for directly converting a given lithium abundance into an equivalent width, or vice versa, a given equivalent width (EW) into a lithium abundance. For convenience, a Python script is made available that evaluates all fitting functions for given Teff, log g, [Fe/H], and A(Li) or EW. By means of the fitting functions, the results of complex 3D and NLTE calculations are made readily accessible and quickly applicable to large samples of stars across a wide range of metallicities.

arXiv comment28 pages 16 + 6 figures, accepted by Astronomy & Astrophysics

References in corpus (32)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Planck 2013 results. XVI. Cosmological parameters
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Lithium isotopic abundances in metal-poor halo stars
• Departures from LTE for neutral Li in late-type stars
• A probable stellar solution to the cosmological lithium discrepancy
• A consistent explanation for ${}^{12}$C/${}^{13}$C, ${}^7$Li, and ${}^3$He anomalies in red giant stars
• The Spite Lithium Plateau: Ultra-Thin but Post-Primordial
• Implications of WMAP observations on Li abundance and stellar evolution models
• The metal-poor end of the Spite plateau. 1: Stellar parameters, metallicities and lithium abundances
• First stars VII. Lithium in extremely metal poor dwarfs
• Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
• Enhanced lithium depletion in Sun-like stars with orbiting planets
• Lithium Abundances of Extremely Metal-Poor Turn-off Stars
• Lithium depletion in solar-like stars: no planet connection
• Observational evidence for a broken Li Spite plateau and mass-dependent Li depletion
• The photospheric solar oxygen project: IV. 3D-NLTE investigation of the 777 nm triplet lines
• Systematic NLTE study of the -2.6 < [Fe/H] < 0.2 F and G dwarfs in the solar neighbourhood. I. Stellar atmosphere parameters
• Consistent metallicity scale for cool dwarfs and giants. A benchmark test using the Hyades
• TOPoS: IV. Chemical abundances from high-resolution observations of seven EMP stars
• The formation of the Milky Way halo and its dwarf satellites, a NLTE-1D abundance analysis. I. Homogeneous set of atmospheric parameters
• Lithium in the Globular Cluster NGC 6397: Evidence for dependence on evolutionary status
• Atomic Diffusion and Mixing in Old Stars. III. Analysis of NGC 6397 Stars under New Constraints
• Back to the Lithium Plateau with J0023+0307 with [Fe/H]<-6
• Measurements of the Isotopic Ratio 6Li/7Li in Stars with Planets
• First Stars XI. Chemical composition of the extremely metal-poor dwarfs in the binary CS 22876--032
• Atomic diffusion and mixing in old stars VI: The lithium content of M30
• Sulphur abundances from the SI near-infrared triplet at 1045 nm
• Lithium abundance and 6Li/7Li ratio in the active giant HD123351 I. A comparative analysis of 3D and 1D NLTE line-profile fits
• High-resolution spectroscopy of extremely metal-poor stars from SDSS/SEGUE. III. Unevolved Stars with $[Fe/H]\lesssim -3.5$
• 3D non-LTE corrections for Li abundance and 6Li/7Li isotopic ratio in solar-type stars I. Application to HD 207129 and HD 95456
• A detailed study of Lithium in 107 CHEPS dwarf stars

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