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  • 1.
    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.

  • 2. Feltzing, S
    et al.
    Eriksson, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Kleyna, J
    Wilkinson, I
    Evidence of enrichment by individual SN from elemental abundance ratios in the very metal-poor dSph galaxy Bootes I2009In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 508, no 1, p. L1-L4Article in journal (Refereed)
    Abstract [en]

    Aims. We establish the mean metallicity from high-resolution spectroscopy for the recently found dwarf spheroidal galaxy Bootes I and test whether it is a common feature for ultra-faint dwarf spheroidal galaxies to show signs of inhomogeneous chemical evolution (e. g. as found in the Hercules dwarf spheroidal galaxy). Methods. We analyse high-resolution, moderate signal-to-noise spectra for seven red giant stars in the Bootes I dSph galaxy using standard abundance analysis techniques. In particular, we assume local thermodynamic equilibrium and employ spherical model atmospheres and codes that take the sphericity of the star into account when calculating the elemental abundances. Results. We confirm previous determinations of the mean metallicity of the Bootes I dwarf spheroidal galaxy to be -2.3 dex. Whilst five stars are clustered around this metallicity, one is significantly more metal-poor, at -2.9 dex, and one is more metal-rich at, -1.9 dex. Additionally, we find that one of the stars, Boo-127, shows an atypically high [Mg/Ca] ratio, indicative of stochastic enrichment processes within the dSph galaxy. Similar results have previously only been found in the Hercules and Draco dSph galaxies and appear, so far, to be unique to this type of galaxy.

  • 3.
    Heiter, Ulrike
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Barklem, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Fossati, L.
    Kildiyarova, R.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Kupka, F.
    Obbrugger, M.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Plez, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ryabchikova, T.
    Stempels, H. C.
    Stütz, C.
    Weiss, W. W.
    VALD — an atomic and molecular database for astrophysics2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 130, p. 012011-Article in journal (Refereed)
    Abstract [en]

    The VALD database of atomic and molecular data aims to ensure a robust and consistent analysis of astrophysical spectra. We offer a convenient e-mail and web-based user interface to a vast collection of spectral line parameters for all chemical elements and in the future also for molecules. An international team is working on the following tasks: collecting line parameters from relevant theoretical and experimental publications, computing line parameters, evaluating the data quality by comparison of similar data from different sources and by comparison with astrophysical observations, and incorporating the data into VALD. A unique feature of VALD is its capability to provide the most comprehensive spectral line lists for specific astrophysical plasma conditions defined by the user.

  • 4.
    Höfner, Susanne
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Dust Formation and Winds around Evolved Stars The Good, the Bad and the Ugly Cases2009In: COSMIC DUST - NEAR AND FAR / [ed] Henning T, Grun E, Steinacker J, 2009, Vol. 414, p. 3-21Conference paper (Refereed)
    Abstract [en]

    Cool luminous giants, in particular asymptotic giant branch stars, are among the most important sources of cosmic dust Their extended dynamical atmospheres are places where grains form and initiate outflows driven by radiation pressure, leading to considerable stellar mass loss and the enrichment of the interstellar medium with newly-produced elements This review summarizes the current understanding of dust formation and winds in such stars, sketching a system of criteria for identifying crucial types of dust grains in the range of possible condensates Starting with an overview of the specific conditions for dust formation in cool dynamic atmospheres, the role of grains as wind drivers, as well as their influence on observable properties of cool giants and the circum-stellar environment is discussed in some detail Regarding the literature, special attention is given to current developments, e g, the debate concerning the Fe-content and size of silicate grains in M-type AGB stars which are critical issues for the wind mechanism, or recent advances in spatially resolved observations and 3D modeling of giants and their dusty envelopes

  • 5.
    Karlsson, Ola
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Lagerkvist, Claes-Ingvar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Davidsson, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    (U)BVRI photometry of Trojan L5 asteroids2009In: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 199, no 1, p. 106-118Article in journal (Refereed)
  • 6.
    Korn, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    NLTE line formation2008In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T133, p. 014009-Article in journal (Refereed)
    Abstract [en]

    I review some of the present achievements and future challenges of non-local thermodynamicequilibrium (NLTE) line-formation calculations for solar-type stars. It is concluded that thefull potential of NLTE still remains to be tapped, in particular in view of the current transitionfrom one-dimensional (1D) hydrostatic to 3D hydrodynamic model atmospheres.

  • 7.
    Lyra, Wladimir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Johansen, Anders
    Klahr, Hubert
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Global magnetohydrodynamical models of turbulence in protoplanetary disks: I. A cylindrical potential on a Cartesian grid and transport of solids2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 479, p. 883-901Article in journal (Refereed)
    Abstract [en]

    Aims.We present global 3D MHD simulations of disks of gas and solids, aiming at developing models that can be used to study various scenarios of planet formation and planet-disk interaction in turbulent accretion disks. A second goal is to demonstrate that Cartesian codes are comparable to cylindrical and spherical ones in handling the magnetohydrodynamics of the disk simulations while offering advantages, such as the absence of a grid singularity, for certain applications, e.g., circumbinary disks and disk-jet simulations. Methods: We employ the Pencil Code, a 3D high-order finite-difference MHD code using Cartesian coordinates. We solve the equations of ideal MHD with a local isothermal equation of state. Planets and stars are treated as particles evolved with an N-body scheme. Solid boulders are treated as individual superparticles that couple to the gas through a drag force that is linear in the local relative velocity between gas and particle. Results: We find that Cartesian grids are well-suited for accretion disk problems. The disk-in-a-box models based on Cartesian grids presented here develop and sustain MHD turbulence, in good agreement with published results achieved with cylindrical codes. Models without an inner boundary do not show the spurious build-up of magnetic pressure and Reynolds stress seen in the models with boundaries, but the global stresses and alpha viscosities are similar in the two cases. We investigate the dependence of the magnetorotational instability on disk scale height, finding evidence that the turbulence generated by the magnetorotational instability grows with thermal pressure. The turbulent stresses depend on the thermal pressure obeying a power law of 0.24 ± 0.03, compatible with the value of 0.25 found in shearing box calculations. The ratio of Maxwell to Reynolds stresses decreases with increasing temperature, dropping from 5 to 1 when the sound speed was raised by a factor 4, maintaing the same field strength. We also study the dynamics of solid boulders in the hydromagnetic turbulence, by making use of 106 Lagrangian particles embedded in the Eulerian grid. The effective diffusion provided by the turbulence prevents settling of the solids in a infinitesimally thin layer, forming instead a layer of solids of finite vertical thickness. The measured scale height of this diffusion-supported layer of solids implies turbulent vertical diffusion coefficients with globally averaged Schmidt numbers of 1.0 ± 0.2 for a model with α≈10-3 and 0.78 ± 0.06 for a model with α≈10-1. That is, the vertical turbulent diffusion acting on the solids phase is comparable to the turbulent viscosity acting on the gas phase. The average bulk density of solids in the turbulent flow is quite low (ρp = 6.0×10-11 kg m-3), but in the high pressure regions, significant overdensities are observed, where the solid-to-gas ratio reached values as great as 85, corresponding to 4 orders of magnitude higher than the initial interstellar value of 0.01

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