3D non-LTE Ca II line formation in metal-poor FGK stars. I. Abundance corrections, radial velocity corrections, and synthetic spectra

Abstract

The Ca II resonance doublet (HK) and the near-infrared triplet (CaT) are among the strongest features in stellar spectra of FGK-type stars. These spectral lines remain prominent down to extremely low metallicities and are thus useful for providing stellar parameters via ionisation balance and as radial velocity diagnostics. However, the majority of studies that model these lines in late-type stars still rely on one dimensional (1D) hydrostatic model atmospheres and the assumption of local thermodynamic equilibrium (LTE). We present 3D non-LTE radiative transfer calculations of the CaT and HK lines in an extended grid of 3D model atmospheres of metal-poor FGK-type. We investigate the impact of 3D non-LTE effects on abundances, line bisectors and radial velocities. We used a subset of 3D model atmospheres from the recently published STAGGER-grid to synthesize spectra in 3D (non-)LTE. For comparison, similar calculations were performed in 1D (non-)LTE using models from the MARCS grid. Abundance corrections for the CaT lines relative to 1D LTE range from +0.1 to -1.0 dex, with more severe corrections for strong lines in giants. With fixed line strength, the abundance corrections become more negative with increasing effective temperature and decreasing surface gravity. Radial velocity corrections relative to 1D LTE based on cross-correlation of the whole line profile range from -0.2 km/s to +1.5 km/s, with more severe corrections where the CaT lines are strongest. The corrections are even more severe if the line core alone is used to infer the radial velocity. The line strengths and shapes, and consequently the abundance and radial velocity corrections, are strongly affected by the chosen radiative transfer assumption, 1/3D (non)-LTE. We release grids of theoretical spectra that can be used to improve the accuracy of stellar spectroscopic analyses based on the Ca II triplet lines.

References in corpus (87)

• The chemical composition of the Sun
• Modules for Experiments in Stellar Astrophysics (MESA)
• Gaia Data Release 3: Summary of the content and survey properties
• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• MESA Isochrones and Stellar Tracks (MIST) 0: Methods for the construction of stellar isochrones
• The PLATO 2.0 Mission
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• Co-formation of the Galactic disc and the stellar halo
• The chemical make-up of the Sun: A 2020 vision
• SkyMapper and the Southern Sky Survey
• Near-Field Cosmology with Metal-Poor Stars
• Simulations of stellar convection with CO5BOLD
• Non-LTE calculations for neutral Na in late-type stars using improved atomic data
• A single low-energy, iron-poor supernova as the source of metals in the star SMSS J 031300.36-670839.3
• In disguise or out of reach: first clues about in-situ and accreted stars in the stellar halo of the Milky Way from Gaia DR2
• Gaia Data Release 3 Properties and validation of the radial velocities
• Supernova Nucleosynthesis in Population III 13 -- 50 $M_{\odot }$ Stars and Abundance Patterns of Extremely Metal-Poor Stars
• The Pristine survey I: Mining the Galaxy for the most metal-poor stars
• Gaia Radial Velocity Spectrometer
• HE 0557-4840 - Ultra-Metal-Poor and Carbon-Rich
• The NIR Ca II triplet at low metallicity - Searching for extremely low-metallicity stars in classical dwarf galaxies
• HE1327-2326, an unevolved star with [Fe/H]<-5.0. I. A Comprehensive Abundance Analysis
• A non-LTE study of neutral and singly-ionized calcium in late-type stars
• The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars
• Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars
• HE 1327-2326, an unevolved star with [Fe/H]<-5.0. II. New 3D-1D corrected abundances from a VLT/UVES spectrum
• The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- I: Survey Description, Spectra and Radial Velocities
• Carbon, oxygen, and iron abundances in disk and halo stars. Implications of 3D non-LTE spectral line formation
• The lithium isotopic ratio in very metal-poor stars
• Non-LTE oxygen line formation in 3D hydrodynamic model stellar atmospheres
• Deriving Stellar Effective Temperatures of Metal-Poor Stars with the Excitation Potential Method
• The Southern Stellar Stream Spectroscopic Survey ($S^5$): Overview, Target Selection, Data Reduction, Validation, and Early Science
• A primordial star in the heart of the Lion
• Accurate abundance analysis of late-type stars: advances in atomic physics
• Constraining the primordial initial mass function with stellar archaeology
• The chemical compositions of the extreme halo stars HE0107-5240 and HE1327-2326 inferred from 3D hydrodynamical model atmospheres
• The GALAH Survey: Non-LTE departure coefficients for large spectroscopic surveys
• Spectroscopic survey of the Galaxy with Gaia I. Design and performance of the Radial Velocity Spectrometer
• Three-dimensional non-LTE radiative transfer computation of the Ca 8542 infrared line from a radiation-MHD simulation
• The solar silicon abundance based on 3D non-LTE calculations
• 3D NLTE spectral line formation of lithium in late-type stars
• The origin of the reversed granulation in the solar photosphere
• Metal-Poor Stars Observed with the Magellan Telescope. III. New Extremely and Ultra Metal-Poor Stars from SDSS/SEGUE and Insights on the Formation of Ultra Metal-Poor Stars
• 3D NLTE analysis of the most iron-deficient star, SMSS0313-6708
• Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation
• Spectropolarimetric capabilities of Ca II 8542 A line
• Three-dimensional modeling of the Ca II H&K lines in the solar atmosphere
• Non-LTE analysis of K I in late-type stars
• NLTE for APOGEE: Simultaneous Multi-Element NLTE Radiative Transfer
• The Stagger-grid: A grid of 3D stellar atmosphere models V. Synthetic stellar spectra and broad-band photometry
• Back to the Lithium Plateau with J0023+0307 with [Fe/H]<-6
• A grid of NLTE corrections for magnesium and calcium in late-type giant and supergiant stars: application to Gaia
• Influence of inelastic collisions with hydrogen atoms on the non-LTE modelling of Ca I and Ca II lines in late-type stars
• NLTE determination of the calcium abundance and 3D corrections in extremely metal-poor stars
• Chemical Abundance Signature of J0023+0307 -- A Second-Generation Main-Sequence Star with [Fe/H]<-6
• Atomic data from the Iron Project. LXIV. Radiative transition rates and collision strengths for Ca II
• Solar velocity references from 3D HD photospheric models
• Isotopic anomaly and stratification of Ca in magnetic Ap stars
• Convective H-He Interactions in Massive Population III Stellar Evolution Models
• Convective line shifts for the Gaia RVS from the CIFIST 3D model atmosphere grid
• Emergence of granular-sized magnetic bubbles through the solar atmosphere. II. Non-LTE chromospheric diagnostics and inversions
• Measurement of ${}^{19}$F($p$,$\gamma$)${}^{20}$Ne reaction suggests CNO break-out in first stars
• 3D non-LTE iron abundances in FG-type dwarfs
• The benchmark halo giant HD 122563: CNO abundances revisited with three-dimensional hydrodynamic model stellar atmospheres
• The effect of isotopic splitting on the bisector and inversions of the solar Ca II 854.2 nm line
• The solar gravitational redshift from HARPS-LFC Moon spectra. A test of the General Theory of Relativity
• Ca line formation in late-type stellar atmospheres: I. The model atom
• HE 1327-2326, an unevolved star with [Fe/H] < -5.0 III. Does Its Atmosphere Reflect Its Natal Composition?
• Heavy Calcium in CP Stars
• Titans metal-poor reference stars. I. Accurate effective temperatures and surface gravities for dwarfs and subgiants from 3D non-LTE H$\alpha$ profiles and Gaia parallaxes
• The calcium isotopic anomaly in magnetic CP stars
• Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars VI. First chromosphere model of a late-type giant
• Raising the observed metallicity floor with a 3D non-LTE analysis of SDSS J102915.14+172927.9
• 1D non-LTE corrections for chemical abundance analyses of very metal-poor stars
• Improving spectroscopic lithium abundances. Fitting functions for 3D non-LTE corrections in FGK stars of different metallicity
• An extended and refined grid of 3D STAGGER model atmospheres. Processed snapshots for stellar spectroscopy
• Spatially resolved spectroscopy across stellar surfaces. IV. F, G, & K-stars: Synthetic 3D spectra at hyper-high resolution
• Titans metal-poor reference stars II. Red giants and CEMP stars
• The Stagger-grid - A Grid of 3D Stellar Atmosphere Models
• Detailed abundances in a sample of very metal poor stars
• A distinct halo population revealed from 3D non-LTE magnesium abundances
• Probing Na in giant exoplanets with ESPRESSO and 3D NLTE stellar spectra
• Accurate Metallicities for Very Metal-Poor Stars from the Ca~II Infrared Triplet
• Interpolation of spectra from 3D model atmospheres

Cited by in corpus (2)

• The R-Process Alliance: Exploring the cosmic scatter among ten r-process sites with stellar abundances
• Investigating non-LTE abundances of Neodymium (Nd) in metal-poor FGK stars