Comparison of Fe and Ni opacity calculations for a better understanding of pulsating stellar envelopes

Abstract

a b s t r a c tOpacity is an important ingredient of the evolution of stars. The calculation of opacity coefficients is complicated by the fact that the plasma contains partially ionized heavy ions that contribute to opacity dominated by H and He. Up to now, the astrophysical community has greatly benefited from the work of the contributions of Los Alamos [1], Livermore [2] and the Opacity Project (OP) [3]. However unexplained differences of up to 50% in the radiative forces and Rosseland mean values for Fe have been noticed for conditions corresponding to stellar envelopes. Such uncertainty has a real impact on the understanding of pulsating stellar envelopes, on the excitation of modes, and on the identification of the mode frequencies. Temperature and density conditions equivalent to those found in stars can now be produced in laboratory experiments for various atomic species. Recently the photo-absorption spectra of nickel and iron plasmas have been measured during the LULI 2010 campaign, for temperatures between 15 and 40 eV and densities of w3 mg/cm 3 . A large theoretical collaboration, the "OPAC", has been formed to prepare these experiments. We present here the set of opacity calculations performed by eight different groups for conditions relevant to the LULI 2010 experiment and to astrophysical stellar envelope conditions.

Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments

“…The temperatures are between 15 and 40 eV and densities of a few mg/cm 3 . The codes are based on different approaches: statistical (SCO, STA), detailed (OPAS, OP, LEDCOP) or mixed (SCO-RCG) [2][3][4]. These comparisons show some differences in the frequency-dependent spectra among all codes but at low temperature and in the spectral range of our comparisons, indicate a clearly distinct behavior of the OP spectra with a…”

“…In recent papers [2,3] we have compared a large number of opacity calculations for experimental conditions relevant for stellar envelope conditions of intermediate mass stars. The temperatures are between 15 and 40 eV and densities of a few mg/cm 3 .…”

“…The temperatures are between 15 and 40 eV and densities of a few mg/cm 3 . The codes are based on different approaches: statistical (SCO, STA), detailed (OPAS, OP, LEDCOP) or mixed (SCO-RCG) [2][3][4].…”

“…The temperatures are between 15 and 40 eV and densities of a few mg/cm 3 . The codes are based on different approaches: statistical (SCO, STA), detailed (OPAS, OP, LEDCOP) or mixed (SCO-RCG) [2][3][4]. These comparisons show some differences in the frequency-dependent spectra among all codes but at low temperature and in the spectral range of our comparisons, indicate a clearly distinct behavior of the OP spectra with a e-mail: dominique.gilles@cea.fr This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.…”

“…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/cm 3 [2-4]. 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.…”