37 research outputs found
Detailed Opacity Calculations for Stellar Models
Radiative opacity is an important quantity in the modeling of stellar
structure and evolution. In the present work we recall the role of opacity in
the interpretation of pulsations of different kinds of stars. The detailed
opacity code SCO-RCG for local-thermodynamic-equilibrium (LTE) plasmas is
described, as well as the OPAMCDF project dedicated to the spectroscopy of LTE
and non-LTE plasmas. Interpretations, with the latter codes, of several laser
and Z pinch experiments in conditions relevant to astrophysical applications
are also presented and our work in progress as concerns the internal solar
conditions is illustrated.Comment: submitted to ASP Conf. Se
Detailed opacity calculations for astrophysical applications
Nowadays, several opacity codes are able to provide data for stellar
structure models, but the computed opacities may show significant differences.
In this work, we present state-of-the-art precise spectral opacity
calculations, illustrated by stellar applications. The essential role of
laboratory experiments to check the quality of the computed data is underlined.
We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as
well as X-ray emission spectroscopy experiments involving hot dense plasmas
produced by ultra-high-intensity laser irradiation. The measured spectra are
systematically compared with the fine-structure opacity code SCO-RCG. Focus is
put on iron, due to its crucial role in understanding asteroseismic
observations of Cephei-type and Slowly Pulsating B stars, as well as of
the Sun. For instance, in Cephei-type stars, the iron-group opacity
peak excites acoustic modes through the "kappa-mechanism". A particular
attention is paid to the higher-than-predicted iron opacity measured at the
Sandia Z-machine at solar interior conditions. We discuss some theoretical
aspects such as density effects, photo-ionization, autoionization or the
"filling-the-gap" effect of highly excited states.Comment: submitted to "Atoms
Statistics of electric-quadrupole lines in atomic spectra
In hot plasmas, a temperature of a few tens of eV is sufficient for producing
highly stripped ions where multipole transitions become important. At low
density, the transitions from tightly bound inner shells lead to
electric-quadrupole (E2) lines which are comparable in strength with
electric-dipole ones. In this work, we propose analytical formulas for the
estimation of the number of E2 lines in a transition array. Such expressions
rely on statistical descriptions of electron states and J-levels. A generalized
'J-file' sum rule for E2 lines and the strength-weighted shift and variance of
the line energies of a transition array nl^N+1 \rightarrow nl^Nn'l' of
inter-configuration E2 lines are also presented.Comment: submitted to J. Phys. B: At. Mol. Opt. Phy