Center-to-Limb Variation of Solar Line Profiles as a Test of NLTE Line Formation Calculations

Abstract

We present new observations of the center-to-limb variation of spectral lines in the quiet Sun. Our long-slit spectra are corrected for scattered light, which amounts to 4-8 % of the continuum intensity, by comparison with a Fourier transform spectrum of the disk center. We examine the effect of inelastic collisions with neutral hydrogen in NLTE line formation calculations of the oxygen infrared triplet, and the Na I 6160.8 A line. Adopting a classical one-dimensional theoretical model atmosphere, we find that the sodium transition, formed in higher layers, is much more effectively thermalized by hydrogen collisions than the high-excitation oxygen lines. This result appears as a simple consequence of the decrease of the ratio NH/Ne with depth in the solar photosphere. The center-to-limb variation of the selected lines is studied both under LTE and NLTE conditions. In the NLTE analysis, inelastic collisions with hydrogen atoms are considered with a simple approximation or neglected, in an attempt to test the validity of such approximation. For the sodium line studied, the best agreement between theory and observation happens when NLTE is considered and inelastic collisions with hydrogen are neglected in the rate equations. The analysis of the oxygen triplet benefits from a very detailed calculation using an LTE three-dimensional model atmosphere and NLTE line formation. The chi**2 statistics favors including hydrogen collisions with the approximation adopted, but the oxygen abundance derived in that case is significantly higher than the value derived from OH infrared transitions.

arXiv comment10 pages, 8 figures, to appear in A&A

References in corpus (8)

• Line formation in solar granulation: IV. [O I], OI and OH lines and the photospheric O abundance
• O/Fe in metal-poor main sequence and subgiant stars
• Inelastic H+Li and H^-+Li^+ collisions and non-LTE Li I line formation in stellar atmospheres
• Kinetic equilibrium of iron in the atmospheres of cool stars III. The ionization equilibrium of selected reference stars
• Oxygen Line Formation in Late-F through Early-K Disk/Halo Stars: Infrared O I Triplet and [O I] Lines
• Non-LTE Model Atmospheres for Late-Type Stars I. A Collection of Atomic Data for Light Neutral and Singly-Ionized Atoms
• A catalogue of accurate wavelengths in the optical spectrum of the Sun
• Non-LTE Model Atmospheres for Late-Type Stars II. Restricted NLTE Calculations for a Solar-Like Atmosphere

Cited by in corpus (63)

• The chemical composition of the Sun
• Helioseismology and Solar Abundances
• The photospheric solar oxygen project: I. Abundance analysis of atomic lines and influence of atmospheric models
• A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars
• Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo
• Oxygen Abundances in Nearby Stars. Clues to the formation and evolution of the Galactic disk
• Carbon, oxygen, and iron abundances in disk and halo stars. Implications of 3D non-LTE spectral line formation
• The Solar Heavy Element Abundances: I. Constraints from Stellar Interiors
• Center-to-Limb Variation of Solar 3-D Hydrodynamical Simulations
• Accurate abundance analysis of late-type stars: advances in atomic physics
• The C/O ratio at low metallicity: constraints on early chemical evolution from observations of Galactic halo stars
• Open clusters as key tracers of Galactic chemical evolution. III. Element abundances in Berkeley 20, Berkeley 29, Collinder 261, and Melotte 66
• The GALAH Survey: Non-LTE departure coefficients for large spectroscopic surveys
• The photospheric solar oxygen project: IV. 3D-NLTE investigation of the 777 nm triplet lines
• Neutral oxygen spectral line formation revisited with new collisional data: large departures from LTE at low metallicity
• The effect of the stellar absorption line centre-to-limb variation on exoplanet transmission spectrum observations
• Oxygen lines in solar granulation. II. Centre-to-limb variation, NLTE line formation, blends and the solar oxygen abundance
• Inelastic O+H collisions and the OI 777nm solar centre-to-limb variation
• On the maximum value of the cosmic abundance of oxygen and the oxygen yield
• Electron-impact excitation of neutral oxygen
• Astrophysical tests of atomic data important for stellar Mg abundance determinations
• The formation of sunspot penumbra. I. Magnetic field properties
• Permitted Oxygen Abundances and the Temperature Scale of Metal-Poor Turn-Off Stars
• 3D non-LTE line formation of neutral carbon in the Sun
• The GREGOR Fabry-Pérot Interferometer
• 3-D non-LTE radiative transfer effects in Fe I lines: II. Line formation in 3-D radiation hydrodynamic simulations
• Another forbidden solar oxygen abundance: the [O I] 5577 A line
• Is the solar spectrum latitude dependent? An investigation with SST/TRIPPEL
• Oxygen lines in solar granulation. I. Testing 3D models against new observations with high spatial and spectral resolution
• Stray-light contamination and spatial deconvolution of slit-spectrograph observations
• Deep probing of the photospheric sunspot penumbra: no evidence for magnetic field-free gaps
• Temporal evolution of the Evershed flow in sunspots. I. Observational characterization of Evershed clouds
• The centre-to-limb variations of solar Fraunhofer lines imprinted upon lunar eclipse spectra - Implications for exoplanet transit observations
• A Low Solar Oxygen Abundance from the First Overtone OH Lines
• Spectropolarimetric analysis of an active region filament. I. Magnetic and dynamical properties from single component inversions
• Solar and Stellar Photospheric Abundances
• A new MHD-assisted Stokes inversion technique
• Application of speckle and (multi-object) multi-frame blind deconvolution techniques on imaging and imaging spectropolarimetric data
• The IAG spectral atlas of the spatially resolved Sun: Centre-to-limb observations
• The energy of waves in the photosphere and lower chromosphere: IV. Inversion results of Ca II H spectra
• Magnetic fields of opposite polarity in sunspot penumbrae
• Fundamental Parameters and Abundances of Metal-Poor Stars: The SDSS Standard BD +17 4708
• Inference of magnetic fields in the very quiet Sun
• How different are the Liège and Hamburg atlases of the solar spectrum?
• On the role of magnetic fields in abundance determinations
• A three-dimensional view of the thermal structure in a super-penumbral canopy
• Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen
• Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations
• Combined analysis of stellar and planetary absorption lines via global forward-transit simulations
• Magnetic topology of the north solar pole
• The Solar Heavy Element Abundances: II. Constraints from Stellar Atmospheres
• Solar Center--Limb Variation of the Strengths of Spectral Lines: Classification and Interpretation of Observed Trends
• Fitting peculiar spectral profiles in He I 10830 Å absorption features
• Influence of Inelastic Collisions with Hydrogen Atoms on Non-LTE Oxygen Abundance Determination in the Sun and late-type stars
• Hanle effect for stellar dipoles and quadrupoles
• Eclipses observed by LYRA - a sensitive tool to test the models for the solar irradiance
• A NLTE analysis of boron abundances in metal-poor stars
• High-resolution spectroscopy and spectropolarimetry of the total lunar eclipse January 2019
• Probing 3D and NLTE models using APOGEE observations of globular cluster stars
• NIRPS detection of delayed atmospheric escape from the warm and misaligned Saturn-mass exoplanet WASP-69b
• Full-disk Synoptic Observations of the Chromosphere Using H${}_{\alpha }$ Telescope at the Kodaikanal Observatory
• Empirical Investigation on the Impact of Hydrogen Collisions for the Formation of CI 1.07 mu~m Lines Based on the Solar Center-to-Limb Variation
• Old open clusters as key tracers of Galactic chemical evolution. I. Fe abundances in NGC 2660, NGC 3960, and Berkeley 32