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تسجيل مستخدم جديدRadiative properties of stellar plasmas and open challenges
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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 $beta$ 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.
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The knowledge of stellar evolution is evolving quickly thanks to an increased number of opportunities to scrutinize the stellar internal plasma properties by stellar seismology and by 1D and 3D simulations. These new tools help us to introduce the in
ternal dynamical phenomena in stellar modeling. A proper inclusion of these processes supposes a real confidence in the microscopic physics used, partly checked by solar or stellar acoustic modes. In the present paper we first recall which fundamental physics has been recently verified by helioseismology. Then we recall that opacity is an important ingredient of the secular evolution of stars and we point out why it is necessary to measure absorption coefficients and degrees of ionization in the laboratory for some well identified astrophysical conditions. We examine two specific experimental conditions which are accessible to large laser facilities and are suitable to solve some interesting questions of the stellar community: are the solar internal radiative interactions properly estimated and what is the proper role of the opacity in the excitation of the non radial modes in the envelop of the $beta$ Cephei and the Be stars ? At the end of the paper we point out the difficulties of the experimental approach that we need to overcome.
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ive to the optical and infra-red frequencies. A quantum mechanical equation for the frequency of collisions is developed by the use of Fermi-Dirac statistics and Rutherford scattering theory. The validity of the Rutherford scattering theory is discussed. The influence of many weak collisions is taken into account by a Coulomb logarithmic function. The present analysis might have implication to stellar plasmas with medium temperatures for which Fermi-Dirac statistics is used. The relations between the present analysis and the stabilities of stars plasmas are discussed. The ratio between the radius and mass of star plasmas with the present densities and that of a typical white dwarf are discussed.
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