28 research outputs found
Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments
Seismology of stars is strongly developing. To address this question we have
formed an international collaboration OPAC to perform specific experimental
measurements, compare opacity calculations and improve the opacity calculations
in the stellar codes [1]. We consider the following opacity codes: SCO,
CASSANDRA, STA, OPAS, LEDCOP, OP, SCO-RCG. Their comparison has shown large
differences for Fe and Ni in equivalent conditions of envelopes of type II
supernova precursors, temperatures between 15 and 40 eV and densities of a few
mg/cm3 [2, 3, 4]. LEDCOP, OPAS, SCO-RCG structure codes and STA give similar
results and differ from OP ones for the lower temperatures and for spectral
interval values [3]. In this work we discuss the role of Configuration
Interaction (CI) and the influence of the number of used configurations. We
present and include in the opacity code comparisons new HULLAC-v9 calculations
[5, 6] that include full CI. To illustrate the importance of this effect we
compare different CI approximations (modes) available in HULLAC-v9 [7]. These
results are compared to previous predictions and to experimental data.
Differences with OP results are discussed.Comment: 4 pages, 3 figures, conference Inertial Fusion Sciences and
Applications, Bordeaux, 12th to 16th September 2011; EPJ web of Conferences
201
Radiative properties of stellar plasmas and open challenges
The lifetime of solar-like stars, the envelope structure of more massive
stars, and stellar acoustic frequencies largely depend on the radiative
properties of the stellar plasma. Up to now, these complex quantities have been
estimated only theoretically. The development of the powerful tools of helio-
and astero- seismology has made it possible to gain insights on the interiors
of stars. Consequently, increased emphasis is now placed on knowledge of the
monochromatic opacity coefficients. Here we review how these radiative
properties play a role, and where they are most important. We then concentrate
specifically on the envelopes of Cephei variable stars. We discuss the
dispersion of eight different theoretical estimates of the monochromatic
opacity spectrum and the challenges we need to face to check these calculations
experimentally.Comment: 6 pages, 5 figures, in press (conference HEDLA 2010
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Los Alamos opacity web page
The Los Alamos opacity data base is now available on the World Wide Web at http://t4.lanl.gov. The data base contains both the original Astrophysical Opacity Library distributed worldwide in the 1980`s (for historical reference) and the new improved opacities from the Light Element Detailed Configuration OPacity (LEDCOP) code. Users can access the opacity data using the multigroup opacity code TOPS to obtain Rosseland and Planck gray opacities, group mean opacities over selected energy ranges, the monochromatic absorption coefficients and the average ionization over a wide range of temperatures and densities. As described in this paper, these quantities are available for all of the elements presently on the data base and TOPS will provide the same quantities for any arbitrary mixture of these elements
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Electron excitation collision strengths for positive atomic ions: a collection of theoretical data
This report contains data on theoretical and experimental cross sections for electron impact excitation of positive atomic ions. It is an updated and corrected version of a preliminary manuscript which was used during an Atomic Data Workshop on Electron Excitation of Ions held at Los Alamos in November 1978. The current status of quantitative knowledge of collisional excitation collision strengths is shown for highly stripped ions where configuration mixing, relativistic and resonance effects may be important. The results show a reasonably satisfactory state for first-row isoelectronic ions and indicate that a considerable amount of work remains to be done for second-row and heavier ions
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Progress in LTE and non-LTE transport calculations
The physical processes in ionized gases are reviewed along with recent calculations of particular processes. Ongoing opacity calculations at Los Alamos are described. Some of the open issues in the calculation of physical processes relevant to opacities are discussed. 39 refs., 7 figs
Interaction of configuration in spectral opacity calculations for stellar physics
We discuss the role of Configuration Interaction (CI) and the influence of the number of
configurations taken into account in the calculations of nickel and iron spectral
opacities provided by the OPAC international collaboration, including statistical
approaches (SCO, CASSANDRA, STA), detailed accounting (OPAS, LEDCOP, OP, HULLAC-v9) or
hybrid method (SCO-RCG). Opacity calculations are presented for a temperature T of 27.3 eV
and a density of 3.4 mg/cm3, conditions relevant for pulsating stellar
envelopes
Radiative properties of stellar envelopes: Comparison of asteroseismic results to opacity calculations and measurements for iron and nickel
International audienceThe international OPAC consortium consists of astrophysicists, plasma physicists and experimentalists who examine opacity calculations used in stellar physics that appear questionable and perform new calculations and laser experiments to understand the differences and improve the calculations. We report on iron and nickel opacities for envelopes of stars from 2 to and deliver our first conclusions concerning the reliability of the used calculations by illustrating the importance of the configuration interaction and of the completeness of the calculations for temperatures around 15–27 eV