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  • 1. Allende Prieto, C
    et al.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Asplund, M
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Ruiz Cobo, B
    Chemical Abundances from Inversions of Stellar Spectra: Analysis of Solar-Type Stars with Homogeneous and Static Model Atmospheres2001In: ASTROPHYSICAL JOURNAL, Vol. 558, p. 830-851Article in journal (Other (popular scientific, debate etc.))
  • 2. Allende Prieto, C.
    et al.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Lambert, D.L
    Cunha, K.
    S4N: A Spectroscopic Survey of Stars in the Solar Neighborhood2004In: Astronomy and Astrophysics, Vol. 420, p. 183-205Article in journal (Refereed)
  • 3.
    Amarsi, A. M.
    et al.
    Australian Natl Univ, Res Sch Astron & Astrophys, Canberra, ACT 2611, Australia..
    Lind, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy. Max Planck Inst Astron, Konigstuhl 17, D-69117 Heidelberg, Germany..
    Asplund, M.
    Australian Natl Univ, Res Sch Astron & Astrophys, Canberra, ACT 2611, Australia..
    Barklem, Paul S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Collet, R.
    Aarhus Univ, Dept Phys & Astron, Stellar Astrophys Ctr, Ny Munkegade 120, DK-8000 Aarhus C, Denmark..
    Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 463, no 2, p. 1518-1533Article in journal (Refereed)
    Abstract [en]

    As one of the most important elements in astronomy, iron abundance determinations need to be as accurate as possible. We investigate the accuracy of spectroscopic iron abundance analyses using archetypal metal-poor stars. We perform detailed 3D non-LTE radiative transfer calculations based on 3D hydrodynamic STAGGER model atmospheres, and employ a new model atom that includes new quantum-mechanical neutral hydrogen collisional rate coefficients. With the exception of the red giant HD122563, we find that the 3D non-LTE models achieve Fe I/Fe II excitation and ionization balance as well as not having any trends with equivalent width to within modelling uncertainties of 0.05 dex, all without having to invoke any microturbulent broadening; for HD122563 we predict that the current best parallax-based surface gravity is overestimated by 0.5 dex. Using a 3D non-LTE analysis, we infer iron abundances from the 3D model atmospheres that are roughly 0.1 dex higher than corresponding abundances from 1D MARCS model atmospheres; these differences go in the same direction as the non-LTE effects themselves. We make available grids of departure coefficients, equivalent widths and abundance corrections, calculated on 1D MARCS model atmospheres and horizontally and temporally averaged 3D STAGGER model atmospheres.

  • 4. Aoki, W
    et al.
    Frebel, A
    Christlieb, Norbert
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Norris, J
    Beers, T
    Minezaki, T
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Honda, S
    Takada-Hidai, M
    Asplund, M
    Ryan, S
    Tsangarides, S
    Eriksson, Kjell
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    HE 1327-2326, an Unevolved Star with [Fe/H] < -5.0.: I. A Comprehensive Abundance Analysis2006In: The Astrophysical Journal, Vol. 639, p. 897-917Article in journal (Refereed)
  • 5.
    Barklem, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Electron-impact excitation of neutral oxygen2007In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 462, no 2, p. 781-788Article in journal (Refereed)
    Abstract [en]

    Aims.Our goal was to calculate transition rates from ground and excited states in neutral oxygen atoms due to electron collisions for non-LTE modelling of oxygen in late-type stellar atmospheres, thus enabling the reliable interpretation of oxygen lines in stellar spectra.Methods.A 38-state R-matrix calculation in LS-coupling has been performed. Basis orbitals from the literature are adopted, and a large set of configurations are included to obtain good representations of the target wave functions. Rate coefficients are calculated by averaging over a Maxwellian velocity distribution. Results.Estimates for the cross sections and rate coefficients are presented for transitions between the seven lowest LS states of neutral oxygen. The cross sections for excitation from the ground state compare well with existing experimental and recent theoretical results.

  • 6.
    Barklem, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 610, article id A57Article in journal (Refereed)
    Abstract [en]

    Excitation and charge transfer in low-energy O+H collisions is studied; it is a problem of importance for modelling stellar spectra and obtaining accurate oxygen abundances in late-type stars including the Sun. The collisions have been studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model. The method has been extended to include configurations involving excited states of hydrogen using an estimate for the two-electron transition coupling, but this extension was found to not lead to any remarkably high rates. Rate coefficients are calculated for temperatures in the range 1000-20000 K, and charge transfer and (de) excitation processes involving the first excited S-states, 4s.S-5(0) and 4s.S-3(0), are found to have the highest rates.

  • 7.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Self-broadening of Balmer Lines Using Asymptotic Potentials: Application to Stellar Spectroscopy2004In: 17th International Conference on Spectral Line Shapes, 2004Conference paper (Other scientific)
  • 8.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Aspelund-Johansson, Jenny
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    The broadening of Fe II lines by neutral hydrogen collisions2005In: Astronomy and Astrophysics, Vol. 435, p. 373-377Article in journal (Refereed)
  • 9.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Belyaev, A. K.
    Asplund, M.
    Inelastic H+Li and H-+Li+ collisions and non-LTE Li I line formation in stellar atmospheres2003In: Astronomy & Astrophysics, Vol. 409, p. L1-L4Article in journal (Refereed)
  • 10.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Belyaev, A. K.
    Dickinson, A. S.
    Gadea, F. X.
    Inelastic Na+H collision data for non-LTE applications in stellar atmospheres2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 519, p. A20-Article in journal (Refereed)
    Abstract [en]

    Rate coefficients for inelastic Na+H collisions are calculated for all transitions between the ten levels up to and including the ionic state (ion-pair production), namely Na(3s,3p,4s,3d,4p,5s,4d,4f,5p)+H(1s) and Na++H-. The calculations are based on recent full quantum scattering cross-section calculations. The data are needed for non-LTE applications in cool astrophysical environments, especially cool stellar atmospheres, and are presented for a temperature range of 500-8000 K. From consideration of the sensitivity of the cross-sections to input quantum chemical data and the results of different methods for the scattering calculations, a measure of the possible uncertainties in the rate coefficients is estimated.

  • 11.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Belyaev, A. K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Guitou, M.
    Feautrier, N.
    Gadea, F. X.
    Spielfiedel, A.
    On inelastic hydrogen atom collisions in stellar atmospheres2011In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 530, p. A94-Article in journal (Refereed)
    Abstract [en]

    The influence of inelastic hydrogen atom collisions on non-LTE spectral line formation has been, and remains to be, a significant source of uncertainty for stellar abundance analyses, due to the difficulty in obtaining accurate data for low-energy atomic collisions either experimentally or theoretically. For lack of a better alternative, the classical "Drawin formula" is often used. Over recent decades, our understanding of these collisions has improved markedly, predominantly through a number of detailed quantum mechanical calculations. In this paper, the Drawin formula is compared with the quantum mechanical calculations both in terms of the underlying physics and the resulting rate coefficients. It is shown that the Drawin formula does not contain the essential physics behind direct excitation by H atom collisions, the important physical mechanism being quantum mechanical in character. Quantitatively, the Drawin formula compares poorly with the results of the available quantum mechanical calculations, usually significantly overestimating the collision rates by amounts that vary markedly between transitions.

  • 12.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Belyaev, A. K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Spielfiedel, A.
    Guitou, M.
    Feautrier, N.
    Inelastic Mg plus H collision data for non-LTE applications in stellar atmospheres2012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 541, p. A80-Article in journal (Refereed)
    Abstract [en]

    Rate coefficients for inelastic Mg+H collisions are calculated for all transitions between the lowest seven levels and the ionic state (charge transfer), namely Mg(3s(2) S-1, 3s3p P-3, 3s3p P-1, 3s4s S-3, 3s4s S-1, 3s3d D-1, 3s4p P-3)+H(1s) and Mg+(3s S-2)+H-. The rate coefficients are based on cross-sections from full quantum scattering calculations, which are themselves based on detailed quantum chemical calculations for the MgH molecule. The data are needed for non-LTE applications in cool astrophysical environments, especially cool stellar atmospheres, and are presented for a temperature range of 500-8000 K. From consideration of the sensitivity of the cross-sections to various uncertainties in the calculations, most importantly input quantum chemical data and the numerical accuracy of the scattering calculations, a measure of the possible uncertainties in the rate coefficients is estimated.

  • 13.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Christlieb, Norbert
    Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Beers, T.C.
    Hill, V.
    Bessell, M.S.
    Holmberg, J.
    Marsteller, B.
    Rossi, S.
    Zickgraf, F.-J.
    Reimers, D.
    The Hamburg/ESO R-process Enhanced Star survey (HERES).: II. Spectroscopic analysis of the survey sample2005In: Astronomy and Astrophysics, Vol. 439, p. 129-151Article in journal (Refereed)
  • 14.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Christlieb, Norbert
    Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Beers, T.C.
    Hill, V
    Holmberg, J
    Marsteller, B
    Rossi, S
    Zickgraf, F.-J
    Bessell, M.S.
    The Hamburg/ESO R-process Enhanced Star survey (HERES).: Abundances2005In: From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution, IAU Symposium Proceedings of the international Astronomical Union 228, 2005, p. 439-443Conference paper (Other (popular scientific, debate etc.))
  • 15.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    O'Mara, B. J.
    Stempels, H. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Hydrogen Line Formation in Cool Stars2001In: 11th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun / [ed] Garcia Lopez, Ramon J.; Rebolo, Rafael; Zapaterio Osorio, Mario Rosa, San Francisco: Astronomical Society of the Pacific , 2001, p. 766-Conference paper (Other academic)
  • 16.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, BJ
    Broadening of lines of BeII, SrII and BaII by collisions with hydrogen atoms and the solar abundance of strontium2000In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, ISSN 0035-8711, Vol. 311, no 3, p. 535-540Article in journal (Refereed)
  • 17.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, B.J.
    Broadening of Spectral Lines of Singly Ionised Atoms by Collisions with Neutral Hydrogen Atoms2001In: 11th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun, ASP Conference Proceedings, Vol. 223., 2001, p. 772-Conference paper (Other (popular scientific, debate etc.))
  • 18.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, B.J.
    Comments on alternative calculations of the broadening of spectral lines of neutral sodium by H-atom collisions2001In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, Vol. 34, p. 4785-4799Article in journal (Refereed)
  • 19.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Osorio, Y.
    Instituto de Astrofísica de Canarias, vía Láctea.; Universidad de La Laguna, Departamento de Astrofísica.; Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg.
    Fursa, D. V.
    Curtin Institute for Computation, Kent Street.; Department of Physics, Astronomy and Medical Radiation Science, Kent Street.
    Bray, I.
    Curtin Institute for Computation, Kent Street.; Department of Physics, Astronomy and Medical Radiation Science, Kent Street.
    Zatsarinny, O.
    Drake University, Department of Physics and Astronomy.
    Bartschat, K.
    Drake University, Department of Physics and Astronomy.
    Jerkstrand, A.
    Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching.
    Inelastic e plus Mg collision data and its impact on modelling stellar and supernova spectra2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 606, article id A11Article in journal (Refereed)
    Abstract [en]

    Results of calculations for inelastic e+Mg effective collision strengths for the lowest 25 physical states of Mg I (up to 3s6p P-1), and thus 300 transitions, from the convergent close-coupling (CCC) and the B-spline R-matrix (BSR) methods are presented. At temperatures of interest, similar to 5000 K, the results of the two calculations differ on average by only 4%,with a scatter of 27%. As the methods are independent, this suggests that the calculations provide datasets for e+Mg collisions accurate to this level. Comparison with the commonly used dataset compiled by Mauas et al. (1988, ApJ, 330, 1008), covering 25 transitions among 12 states, suggests the Mauas et al. data are on average similar to 57% too low, and with a very large scatter of a factor of similar to 6.5. In particular the collision strength for the transition corresponding to the Mg I intercombination line at 457 nm is significantly underestimated by Mauas et al., which has consequences for models that employ this dataset. In giant stars the new data leads to a stronger line compared to previous non-LTE calculations, and thus a reduction in the non-LTE abundance correction by similar to 0.1 dex (similar to 25%). A non-LTE calculation in a supernova ejecta model shows this line becomes significantly stronger, by a factor of around two, alleviating the discrepancy where the 457 nm line in typical models with Mg/O ratios close to solar tended to be too weak compared to observations.

  • 20.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Hydrogen Balmer Lines as Probes of Stellar Atmospheres2003In: IAUS 210, Modelling of stellar atmospheres, 2003, p. E28-Conference paper (Other scientific)
  • 21.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, BJ
    A list of data for the broadening of metallic lines by neutral hydrogen collisions2000In: ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES, ISSN 0365-0138, Vol. 142, no 3, p. 467-473Article in journal (Refereed)
  • 22.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, BJ
    Self broadening of hydrogen lines: initial results2000In: ASTRONOMY AND ASTROPHYSICS, ISSN 0004-6361, Vol. 355, no 1, p. L5-L8Article in journal (Refereed)
  • 23.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, BJ
    Self-broadening in Balmer line wing formation in stellar atmospheres2000In: ASTRONOMY AND ASTROPHYSICS, ISSN 0004-6361, Vol. 363, no 3, p. 1091-1105Article in journal (Refereed)
  • 24.
    Barklem, Paul S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Accurate abundance analysis of late-type stars: advances in atomic physics2016In: The Astronomy and Astrophysics Review, ISSN 0935-4956, E-ISSN 1432-0754, Vol. 24, article id 9Article, review/survey (Refereed)
    Abstract [en]

    The measurement of stellar properties such as chemical compositions, masses and ages, through stellar spectra, is a fundamental problem in astrophysics. Progress in the understanding, calculation and measurement of atomic properties and processes relevant to the high-accuracy analysis of F-, G-, and K-type stellar spectra is reviewed, with particular emphasis on abundance analysis. This includes fundamental atomic data such as energy levels, wavelengths, and transition probabilities, as well as processes of photoionisation, collisional broadening and inelastic collisions. A recurring theme throughout the review is the interplay between theoretical atomic physics, laboratory measurements, and astrophysical modelling, all of which contribute to our understanding of atoms and atomic processes, as well as to modelling stellar spectra.

  • 25.
    Barklem, Paul S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Excitation and charge transfer in low-energy hydrogen-atom collisions with neutral atoms: Theory, comparisons, and application to Ca2016In: PHYSICAL REVIEW A, ISSN 2469-9926, Vol. 93, no 4, article id 042705Article in journal (Refereed)
    Abstract [en]

    A theoretical method is presented for the estimation of cross sections and rates for excitation and charge-transfer processes in low-energy hydrogen-atom collisions with neutral atoms, based on an asymptotic two-electron model of ionic-covalent interactions in the neutral atom-hydrogen-atom system. The calculation of potentials and nonadiabatic radial couplings using the method is demonstrated. The potentials are used together with the multichannel Landau-Zener model to calculate cross sections and rate coefficients. The main feature of the method is that it employs asymptotically exact atomic wave functions, which can be determined from known atomic parameters. The method is applied to Li + H, Na + H, and Mg + H collisions, and the results compare well with existing detailed full-quantum calculations. The method is applied to the astrophysically important problem of Ca + H collisions, and rate coefficients are calculated for temperatures in the range 1000-20 000 K.

  • 26.
    Barklem, Paul S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Hydrogen Atom Collision Processes in Cool Stellar Atmospheres: Effects on Spectral Line Strengths and Measured Chemical Abundances in Old Stars2012In: XXI INTERNATIONAL CONFERENCE ON SPECTRAL LINE SHAPES (ICSLS 2012), 2012, p. 012049-Conference paper (Refereed)
    Abstract [en]

    The precise measurement of the chemical composition of stars is a fundamental problem relevant to many areas of astrophysics. State-of-the-art approaches attempt to unite accurate descriptions of microphysics, non-local thermodynamic equilibrium (non-LTE) line formation and 3D hydrodynamical model atmospheres. In this paper I review progress in understanding inelastic collisions of hydrogen atoms with other species and their influence on spectral line formation and derived abundances in stellar atmospheres. These collisions are a major source of uncertainty in non-LTE modelling of spectral lines and abundance determinations, especially for old, metal-poor stars, which are unique tracers of the early evolution of our galaxy. Full quantum scattering calculations of direct excitation processes X(nl) + H <-> X(n'l') + H and charge transfer processes X(nl) + H <-> X+ + H- have been done for Li, Na and Mg [1,2,3] based on detailed quantum chemical data, e.g. [4]. Rate coefficients have been calculated and applied to non-LTE modelling of spectral lines in stellar atmospheres [5,6,7,8,9]. In all cases we find that charge transfer processes from the first excited S-state are very important, and the processes affect measured abundances for Li, Na and Mg in some stars by as much as 60%. Effects vary with stellar parameters (e.g. temperature, luminosity, metal content) and so these processes are important not only for accurate absolute abundances, but also for relative abundances among dissimilar stars.

  • 27.
    Barklem, Paul S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Hydrogen lines2008In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T133, p. 014023-Article in journal (Refereed)
    Abstract [en]

    Advances in modern detectors have allowed hydrogen Balmer lines to be used as high-precision diagnostics of effective temperature in F, G and K stars. Their precision as such a diagnostic is now to a large degree dependent on our understanding of their formation in stellar atmospheres. In this paper, I review the current status of Balmer lines as effective temperature diagnostics and in particular discuss two aspects of their line formation: (i) the question of whether the line wings form in Local Thermodynamic Equilibrium (LTE) or not and (ii) the broadening of the line wings by collisions.

  • 28.
    Barklem, Paul S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Collet, R.
    Australian Natl Univ, Res Sch Astron & Astrophys, Canberra, ACT 2611, Australia.;Aarhus Univ, Dept Phys & Astron, Stellar Astrophys Ctr, Ny Munkegade 120, DK-8000 Aarhus C, Denmark..
    Partition functions and equilibrium constants for diatomic molecules and atoms of astrophysical interest2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 588, article id A96Article in journal (Refereed)
    Abstract [en]

    Partition functions and dissociation equilibrium constants are presented for 291 diatomic molecules for temperatures in the range from near absolute zero to 10 000 K, thus providing data for many diatomic molecules of astrophysical interest at low temperature. The calculations are based on molecular spectroscopic data from the book of Huber & Herzberg (1979, Constants of Diatomic Molecules) with significant improvements from the literature, especially updated data for ground states of many of the most important molecules by Irikura (2007, J. Phys. Chem. Ref. Data, 36, 389). Dissociation energies are collated from compilations of experimental and theoretical values. Partition functions for 284 species of atoms for all elements from H to U are also presented based on data collected at NIST. The calculated data are expected to be useful for modelling a range of low density astrophysical environments, especially star-forming regions, protoplanetary disks, the interstellar medium, and planetary and cool stellar atmospheres. The input data, which will be made available electronically, also provides a possible foundation for future improvement by the community.

  • 29.
    Barklem, Paul S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Osorio, Yeisson Fabian Martinez
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Modelling the spectrum of Mg in cool stars2014In: XXII International Conference on Spectral Line Shapes (ICSLS 2014), 2014, p. 012001-, article id 012001Conference paper (Refereed)
    Abstract [en]

    The astrophysical importance of Mg, together with its unique range of spectral features in late-type stars, plus its relative simplicity from an atomic physics point of view, makes it a prime target and test bed for detailed ab initio non-local thermodynamic equilibrium (NLTE) modelling in stellar atmospheres. In this paper, we present example first results for calculations of NLTE Mg line based on a new model atom with significant improvements in the collision data for neutral Mg. We perform calculations for excitation of the lower-lying levels due to electron impacts using the R-matrix method. Recent data for excitation and charge transfer due to hydrogen atom impacts involving low-lying levels are now employed. Further, we have made efforts to use physically-motivated methods for calculating radiative and collisional data involving Rydberg states. The results are compared with observed spectra and the impact of the new calculations briefly explored.

  • 30.
    Barklem, Paul S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Tscherbul, Timur V.
    Univ Nevada, Dept Phys, Reno, NV 89557 USA..
    Inelastic processes in atomic, molecular and chemical physics (in honour of Andrey K. Belyaev)2015In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 462, p. 1-2Article in journal (Other academic)
  • 31.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Stempels, H.C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Allende Prieto, C.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    O'Mara, B.J.
    Detailed analysis of Balmer lines in cool dwarf stars2002In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 385, p. 951-Article in journal (Refereed)
  • 32.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Stempels, H.C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    O'Mara, J.B.
    Balmer lines and effective temperatures in cool stars2003In: 12th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, 2003, p. 1103-Conference paper (Other academic)
  • 33. Beers, T. C.
    et al.
    Christlieb, Norbert
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Bessell, M. S.
    Hill, V.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Korn, A.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Ryan, S. G.
    Rossi, S.
    Rhee, J.
    HERES: The Search for r-Process-Enhanced, Metal-Poor Stars2003In: Bulletin American Astronomical Society Meeting, 2003Conference paper (Other scientific)
  • 34. Beers, T. C.
    et al.
    Christlieb, Norbert
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Bessell, M. S.
    Hill, V.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Ryan, S. G.
    Rossi, S.
    Korn, A.
    Heres: the Search for R-Process Enhanced, Metal-Poor Stars2003In: Elemental Abundances in Old Stars and Damped Lyman-α Systems, 25th meeting of the IAU, Joint Discussion 15, 2003, p. p. 34-Conference paper (Other scientific)
  • 35. Beers, T.C.
    et al.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Christlieb, Norbert
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Hill, V.
    Efficient Searches for r-Process-Enhanced, Metal-Poor Stars2005In: Nuclear Physics A, Vol. 758, p. 595-598Article in journal (Other scientific)
  • 36. Beers, T.C.
    et al.
    Lucatello, S.
    Marsteller, B.
    Sivarani, T.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Christlieb, Norbert
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Rossi, Silvia
    The frequency of Carbon-enhanced stars in HERES and SDSS2006In: Proceedings of the International Symposium on Nuclear Astrophysics: Nuclei in the Cosmos - IX. 25-30 June 2006, CERN, 2006Conference paper (Other (popular scientific, debate etc.))
  • 37.
    Bellot Rubio, L. R.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Borrero, J. M.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    del Toro Iniesta, J. C.
    Accurate Atomic Parameters from the Solar Spectrum2003In: Frontiers of High Resolution Spectroscopy, 25th meeting of the IAU, Joint Discussion 20, 2003, p. p. 16-Conference paper (Other scientific)
  • 38. Belyaev, A
    et al.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Ab initio cross sections for low-energy inelastic H+Li collisions2003Conference paper (Other (popular scientific, debate etc.))
  • 39. Belyaev, A. K.
    et al.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Cross sections for low-energy inelastic H+Li collisions2003In: Physical Review A, Vol. 68, no 06, p. 2703-Article in journal (Refereed)
  • 40.
    Belyaev, Andrey K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Barklem, Paul S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Gadéa, F. X.
    Vlasov, D. V.
    Low-energy inelastic Na + H collisions2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 388, no 9, p. 092001-Article in journal (Refereed)
    Abstract [en]

    We report full quantum scattering calculations for near-threshold collision cross sections for excitation of Na by H. The calculations include contributions from transitions between all singlet states up to and including the ionic state (ion-pair production). The dynamics calculations are based on three sets of recent ab initio and pseudo-potential quantum-chemical calculations. Considerable sensitivity to the couplings employed is found.

  • 41.
    Belyaev, Andrey K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Barklem, Paul S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Guitou, M.
    Spielfiedel, A.
    Feautrier, N.
    Vlasov, D. V.
    Rodionov, D. S.
    Ab initio cross sections for low-energy inelastic Mg+H collisions2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 388, no 9, p. 092002-Article in journal (Refereed)
    Abstract [en]

    Full quantum scattering calculations of cross sections for low-energy near-threshold inelastic Mg + H collisions are reported, such processes being of interest for modelling of Mg spectral lines in stellar atmospheres. Nonadiabatic transions associated with radial couplings at avoided ionic crossings in the 2Σ+ molecular states are found to be the main mechanism for excitation and ion-pair production processes.

  • 42.
    Belyaev, Andrey K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Barklem, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Spielfiedel, A.
    Guitou, M.
    Feautrier, N.
    Rodionov, D. S.
    Vlasov, D. V.
    Cross sections for low-energy inelastic Mg + H and Mg+ + H- collisions2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 3, p. 032704-Article in journal (Refereed)
    Abstract [en]

    We report full quantum scattering calculations for low-energy near-threshold inelastic cross sections in Mg + H and Mg+ + H- collisions. The calculations include all transitions between the eight lowest adiabatic MgH((2)Sigma(+)) molecular states, with the uppermost of those diabatically extended to the ionic molecular state in the asymptotic region. This allows us to treat the excitation processes between the seven lowest atomic states of magnesium in collisions with hydrogen atoms, as well as the ion-pair production and the mutual neutralization processes. The collision energy range is from threshold up to 10 eV. These results are important for astrophysical modeling of spectra in stellar atmospheres. The processes in question are carefully examined and several process mechanisms are found. Some mechanisms are determined by interactions between ionic and covalent configurations at relatively large internuclear distances, while others are based on short-range nonadiabatic regions due to interactions between covalent configurations.

  • 43.
    Belyaev, Andrey K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Yakovleva, Svetlana A.
    Barklem, Paul S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Inelastic silicon-hydrogen collision data for non-LTE applications in stellar atmospheres2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 572, p. A103-Article in journal (Refereed)
    Abstract [en]

    Aims. Inelastic processes in low-energy Si + H and Si+ + H- collisions are treated for the states from the ground state up to the ionic state, in order to provide rate coefficients needed for non-LTE modeling of Si in cool stellar atmospheres. Methods. Electronic molecular structure is determined using a recently proposed model approach based on an asymptotic method in combination with available ab initio potentials. Nonadiabatic nuclear dynamics are treated by means of a combination of multichannel formulas and the branching-probability-current method, based on the Landau-Zener model for nonadiabatic transition probabilities. Results. Cross sections and rate coefficients for inelastic processes in Si + H and Si+ + H- collisions for all transitions between 26 low-lying states plus the ionic state are calculated. It is shown that the highest rate coefficient values correspond to the excitation, de-excitation, ion-pair formation, and mutual neutralization processes involving the Si(3p4p D-3), Si(3p3d F-3), Si(3p4p D-1), Si(3p3d P-3), Si(3p4p S-1), and the ionic Si+ + H- states. These processes are likely to be important in non-LTE modeling.

  • 44. Bikmaev, I.F.
    et al.
    Ryabchikova, T.C.
    Bruntt, H.
    Musaev, F.A.
    Mashonkina, L.I.
    Belyakova, E.V.
    Shimansky, V.V.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Galazutdinov, G.
    Abundance analysis of two late A-type stars HD 32115 and HD 375942002In: Astron. Astrophys., Vol. 389, p. 537-546Article in journal (Refereed)
  • 45. Borrero, J. M.
    et al.
    Bellot Rubio, L. R.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    del Toro Iniesta, J. C.
    Accurate atomic parameters for near-infrared spectral lines2003In: Astronomy & Astrophysics, Vol. 404, p. 749-762Article in journal (Refereed)
  • 46. Christlieb, N.
    et al.
    Beers, T.C.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Bessell, M.S.
    Hill, V.
    Holmberg, J.
    Korn, A.J.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Marsteller, B.J.
    Mashonkina, L.
    Qian, Y.-Z.
    Rossi, S.
    Wasserburg, G.J.
    et al,
    The Hamburg/ESO R-process Enhanced Star survey (HERES).: I. Project description, and discovery of two stars with strong enhancements of neutron-capture elements2004In: Astronomy and Astrophysics, Vol. 428, p. 1027-1037Article in journal (Refereed)
  • 47. Christlieb, N.
    et al.
    Bessell, M. S.
    Beers, T. C.
    Gustafsson, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Korn, A.
    Barklem, Paul
    Department of Astronomy and Space Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Karlsson, T
    Mizuno-Wiedner, M.
    Rossi, S.
    A stellar relic from the early Milky Way2002In: Nature, Vol. 419, p. 904-906Article in journal (Refereed)
  • 48. Christlieb, N.
    et al.
    Gustafsson, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Korn, A.J.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Beers, T.C.
    Bessell, M.S.
    Karlsson, T.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Mizuno-Wiedner, M.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    HE0107, A Chemically Ancient Star.: I. A Detailed Abundance Analysis2004In: The Astrophysical Journal, Vol. 603, p. 708-728Article in journal (Refereed)
  • 49. Derouich, M
    et al.
    Barklem, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Spin depolarizing effect in collisions with neutral hydrogen: II. Application to simple/complex ions in spherically symmetric states2007In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 462, no 3, p. 1171-1177Article in journal (Refereed)
    Abstract [en]

    Aims: We develop an accurate and general semi-classical formalism that deals with the definition and the calculation of the collisional depolarizing constants of the levels of simple and complex singly-ionized atoms in arbitrary s-states perturbed by collisions with hydrogen atoms. The case of ions with hyperfine structure is investigated fully. Methods: We obtain potential energy curves based on the MSMA exchange perturbation theory by employing the Unsöld approximation. These potentials enter the Schrödinger equation to determine the collisional T-matrix elements in a semi-classical description. We use the T-matrix elements for the calculation of the collisional depolarization rates of simple atoms. Then, we use these rates to calculate the collisional coefficients in cases of ions with hyperfine structure. Results: We evaluate the collisional depolarization and polarization transfer rates of the ground levels of the ionized alkaline earth metals Be II, Mg II, Ca II, Sr II, and Ba II. We study the variation of the collisional rates with effective principal quantum number n* characterizing an arbitrary s-state of a perturbed simple ion. We find that the collisional rates for simple ions obey simple power laws as a function of n^*. We present direct and indirect formulations of the problem of the calculation of the depolarization and polarization transfer rates of levels of complex atoms and hyperfine levels from those for simple atoms. In particular, the indirect method allows a quick and simple calculation with its simple power-law relations. For the state 4s ^2S{1/2} of Ca II, our computed rate of the destruction of orientation differs from existing quantum chemistry calculations by only 4% at T=5000 K.

  • 50. Derouich, M.
    et al.
    Barklem, Paul
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Sahal-Bréchot, S.
    Spin depolarizing effect in collisions of simple/complex atoms in spherically symmetric states with neutral hydrogen2005In: Astronomy and Astrophysics, Vol. 441, p. 395-406Article in journal (Refereed)
12 1 - 50 of 94
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