NLTE model calculations for the solar atmosphere with an iterative treatment of opacity distribution functions

Context. Modeling the variability of the solar spectral irradiance is a key factor in understanding the Sun’s influence on the climate of the Earth. Aims. As a first step toward calculating the solar spectral irradiance variations, we reproduce the solar spectrum for the quiet Sun over a broad wavelength range with an emphasis on the UV. Methods. We introduce the radiative transfer code COSI, which calculates solar synthetic spectra under conditions of non-local thermodynamic equilibrium (NLTE). A self-consistent simultaneous solution of the radiative transfer and the statistical equation for the level populations guarantees that the correct physics is considered for wavelength regions where the assumption of local thermodynamic equilibrium (LTE) breaks down. The new concept of iterated opacity distribution functions (NLTE-ODFs) is presented, through which all line opacities are included in the NLTE radiative transfer calculation. Results. We show that it is essential to include the line opacities in the radiative transfer to reproduce the solar spectrum in the UV. Conclusions. Through the implemented scheme of NLTE-ODFs, the COSI code is successful in reproducing the spectral energy distribution of the quiet Sun.

[1]  D. F. Gray,et al.  The Observation and Analysis of Stellar Photospheres , 2021 .

[2]  E. Avrett,et al.  Models of the Solar Chromosphere and Transition Region from SUMER and HRTS Observations: Formation of the Extreme-Ultraviolet Spectrum of Hydrogen, Carbon, and Oxygen , 2008 .

[3]  L. Koesterke,et al.  Center-to-Limb Variation of Solar Three-dimensional Hydrodynamical Simulations , 2008, 0802.2177.

[4]  Alexander G. Kosovichev,et al.  Solving the Discrepancy between the Seismic and Photospheric Solar Radius , 2007, 0711.2392.

[5]  Mike Lockwood,et al.  Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature , 2007, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[6]  J. Harder,et al.  Semiempirical Models of the Solar Atmosphere. II. The Quiet-Sun Low Chromosphere at Moderate Resolution , 2007 .

[7]  T. Egorova,et al.  Simulation of the stratospheric ozone and temperature response to the solar irradiance variability during sun rotation cycle , 2006 .

[8]  S. K. Solanki,et al.  Reconstruction of solar irradiance variations in cycles 21-23 based on surface magnetic fields , 2006 .

[9]  C. Keller,et al.  Solar Carbon Monoxide, Thermal Profiling, and the Abundances of C, O, and Their Isotopes , 2006, astro-ph/0606153.

[10]  M. Asplund,et al.  Effects of line-blocking on the non-LTE Fe I spectral line formation , 2005, astro-ph/0507375.

[11]  P. Storey,et al.  Atomic data from the IRON project - LVIII. Electron impact excitation of Fe XII , 2005 .

[12]  S. Solanki,et al.  Can surface magnetic fields reproduce solar irradiance variations in cycles 22 and 23 , 2005 .

[13]  J. Haigh,et al.  The impact of solar variability on the middle atmosphere in present-day and pre-industrial atmospheres , 2005 .

[14]  C. Prieto,et al.  Line formation in solar granulation VI. [Cl], Cl, CH and C2 lines and the photospheric C abundance , 2004, astro-ph/0410681.

[15]  P. H. Hauschildt,et al.  A Non-LTE Line-Blanketed Model of a Solar-Type Star , 2004, astro-ph/0409693.

[16]  E. Manzini,et al.  Chemical and dynamical response to the 11‐year variability of the solar irradiance simulated with a chemistry‐climate model , 2004 .

[17]  G. Schmidt,et al.  Volcanic and Solar Forcing of Climate Change during the Preindustrial Era , 2003 .

[18]  D. Lambert,et al.  Non-LTE Model Atmospheres for Late-Type Stars. II. Restricted Non-LTE Calculations for a Solar-like Atmosphere , 2003, astro-ph/0303560.

[19]  D. Lambert,et al.  Non-LTE Model Atmospheres for Late-Type Stars. I. A Collection of Data for Light Neutral and Singly Ionized Atoms , 2003, astro-ph/0303559.

[20]  Han Uitenbroek,et al.  The Effect of Coherent Scattering on Radiative Losses in the Solar Ca II K Line , 2002 .

[21]  A. Peraiah,et al.  An Introduction to Radiative Transfer: Methods and Applications in Astrophysics , 2001 .

[22]  A. Waple,et al.  Solar Forcing of Regional Climate Change During the Maunder Minimum , 2001, Science.

[23]  Han Uitenbroek,et al.  Multilevel Radiative Transfer with Partial Frequency Redistribution , 2001 .

[24]  J. Worden,et al.  Improved solar Lyman α irradiance modeling from 1947 through 1999 based on UARS observations , 2000 .

[25]  Eugene H. Avrett,et al.  Calculation of Solar Irradiances. I. Synthesis of the Solar Spectrum , 1999 .

[26]  Atomic data from the Iron Project - XXVI. Photoionization cross sections and oscillator strengths for Fe IV , 1997 .

[27]  M. A. Bautista.  Atomic data from the IRON Project XX. Photoionization cross sections and oscillator strengths for Fe I , 1997 .

[28]  I. Hubeny,et al.  Partial redistribution in multilevel atoms. I. Method and application to the solar hydrogen line formation , 1995 .

[29]  Ivan Hubeny,et al.  Non-LTE line-blanketed model atmospheres of hot stars. 1: Hybrid complete linearization/accelerated lambda iteration method , 1995 .

[30]  M. Seaton,et al.  Opacities for stellar envelopes , 1994 .

[31]  Gary J. Rottman,et al.  Solar‐Stellar Irradiance Comparison Experiment 1: 1. Instrument design and operation , 1993 .

[32]  Gary J. Rottman,et al.  Solar‐Stellar Irradiance Comparison Experiment 1: 2. Instrument calibrations , 1993 .

[33]  C. Leitherer,et al.  Non-LTE analysis of the Ofpe/WN9 star HDE 269227 (R84) , 1991 .

[34]  R. Athay,et al.  Model solar chromosphere with prescribed heating , 1989 .

[35]  L. Anderson.  Line blanketing without local thermodynamic equilibrium. II - A solar-type model in radiative equilibrium , 1989 .

[36]  Ivan Hubeny,et al.  A computer program for calculating non-LTE model stellar atmospheres , 1988 .

[37]  Eugene H. Avrett,et al.  Structure of the solar chromosphere. III. Models of the EUV brightness components of the quiet sun , 1981 .

[38]  A. Irwin.  Polynomial partition function approximations of 344 atomic and molecular species. , 1981 .

[39]  D. Lambert,et al.  The Dissociation Equilibrium of H– in Stellar Atmospheres , 1968 .

[40]  R. Latter,et al.  Electron Radiative Transitions in a Coulomb Field , 1961 .

[41]  J. M. Berger.  Absorption Coefficients for Free-Free Transitions in a Hydrogen Plasma. , 1956 .

[42]  M. Montuori,et al.  Memorie della Società Astronomica Italiana Supplementi - Vol. 1 Computational Astrophysics in Italy: Methods and Tools Prima Riunione Nazionale , 2008 .

[43]  K. Labitzke.  On the solar cycle–QBO relationship: a summary , 2005 .

[44]  S. Solanki,et al.  Reconstruction of solar UV irradiance , 2005 .

[45]  O. White,et al.  Solar irradiance variability – comparison of models and observations , 2004 .

[46]  M. Haberreiter,et al.  Reconstruction of the solar UV irradiance back to 1974 , 2004 .

[47]  John T. Jefferies,et al.  Spectral line formation , 1968 .

[48]  D. Mihalas.  STATISTICAL-EQUILIBRIUM MODEL ATMOSPHERES FOR EARLY-TYPE STARS. I. HYDROGEN CONTINUA. , 1967 .

[49]  S. Strom,et al.  Abundance Analysis of the A Stars α Lyr, γ Gem, 63, 64, and 68 Tau. , 1966 .

[50]  R. Kurucz,et al.  Statistical Procedure for Computing Line-Blanketed Model Stellar Atmospheres. , 1966 .

[51]  B. Baschek,et al.  Tabellen fur die Berechnung von Zustandssummen , 1966 .

[52]  ScienceDirect.  Journal of Atmospheric and Terrestrial Physics , 1950, Nature.