Speaker
Dr
Jean-Christophe Pain
(Commissariat a l'Energie Atomique (CEA))
Description
The opacities computed by different codes for astrophysical applications may show significant differences. In this work, we discuss some important issues, such as the number of configurations, levels and lines included in the calculations, the accounting for configuration interaction or the breakdown of statistical methods. 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 compared with results of the fine-structure atomic code SCO-RCG [1] and with MCDF (Multi-Configuration Dirac-Fock) calculations. A particular attention is paid to iron, which plays a crucial role in the understanding of astero-seismic observations of Beta-Cephei- and SPB- (Slowly Pulsating B) type stars, as well as in the Sun [2]. For instance, in Beta-Cephei type stars, the opacity peak of the iron group, at a temperature of about 200,000 K, excites acoustic modes by the "kappa mechanism". An analysis of the recent and unexplained iron opacity measurements performed on the Z machine of Sandia National Laboratory [3] in conditions close to the ones of the tachocline (boundary between the convective and radiative zones of the Sun) is presented. We comment on several theoretical aspects related to that experiment concerning the roles of collisional excitation and auto-ionization, the modeling of Stark broadening [4], the accounting for Rydberg states or the calculation of photo-ionization [5].
[1] J.-C. Pain and F. Gilleron, High Energy Density Phys. **15**, 30 (2015).
[2] S. Turck-Chièze et al., Ap. J. **823**, 78 (2016).
[3] J. Bailey et al., Nature 517, **56** (2015).
[4] J.-C. Pain, F. Gilleron and D. Gilles, J. Phys. Conf. Ser. **717**, 012074 (2016).
[5] S. N. Nahar and A. K. Pradhan, Phys. Rev. Lett. **116**, 235003 (2016).
Primary author
Dr
Jean-Christophe Pain
(Commissariat a l'Energie Atomique (CEA))
Co-authors
Dr
Franck GILLERON
(Commissariat à l'Energie Atomique (CEA))
Dr
Maxime COMET
(Commissariat à l'Energie Atomique (CEA))
