Detailed Opacity Comparison for an Improved Stellar Modeling of the Envelopes of Massive Stars

Abstract

Seismic observations have led to doubts or ambiguities concerning the opacity calculations used in stellar physics. Here, we concentrate on the iron-group opacity peak, due to iron, nickel, and chromium, located around T = 200,000 K for densities from , which creates some convective layers in stellar radiative envelopes for masses between 3 and 18 . These conditions were extensively studied in the 1980s. More recently, inconsistencies between OP and OPAL opacity calculations have complicated the interpretation of seismic observations as the iron-group opacity peak excites acoustic and gravity modes in SPB, β Cephei, and sdB stars. We investigate the reliability of the theoretical opacity calculations using the modern opacity codes ATOMIC and SCO-RCG. We show their temperature and density dependence for conditions that are achievable in the laboratory and equivalent to astrophysical conditions. We also compare new theoretical opacity spectra with OP spectra and quantify how different approximations impact the Rosseland mean calculations.This detailed study estimates new ATOMIC and SCO-RCG Rosseland mean values for astrophysical conditions which we compare to OP values. Some puzzling questions are still under investigation for iron, but we find a strong increase in the Rosseland mean nickel opacity of a factor between 2 and 6 compared to OP. This appears to be due to the use of extrapolated atomic data for the Ni opacity within the OP calculations. A study on chromium is also shown.

Detailed Opacity Calculations for Astrophysical Applications

“…One observes that ATOMIC "full" and ATOMIC n5 agree within 20% and that, in all cases, ATOMIC n5 values are smaller than those of ATOMIC "full". SCO-RCG, which is not limited to n ≤ 5, is generally closer to ATOMIC "full" than to ATOMIC n5 (see Figure 7, left and right, as well as Tables 1 and 2) [41], which is consistent with the fact that configuration interaction plays a less important role than state completeness in the present case. The values of OP (Opacity Project) [42,43], are usually lower.…”

“…Figure 7. Comparison between SCO-RCG and ATOMIC "full" (left) and "n5" (right) computations [39][40][41] of iron opacity at T = 23 eV and ρ = 2 mg/cm 3 . The ATOMIC calculations were kindly provided by J. Colgan.…”

Computation of Atomic Astrophysical Opacities

“…For the former, it has been shown [19] that CI effects on the RMO are not as conspicuous as those of Fe: they manifest themselves mainly at lower photon energies (50-60 eV), but the spectral features are distinctively different from those of the OP; the latter are believed to be faulty as they were determined by extrapolation procedures. A similar diagnostic has been put forward for Cr, and both are supported by recent transmission measurements in the XUV [31]; moreover, comparisons with data from the ATOMIC code apparently lead to discrepancies with the OP Ni RMO of a factor of 6.…”

“…The importance of CI is also brought out in comparisons of the OP and OPAL monochromatic opacities with old transmission measurements, namely spectral energy displacements [19]. However, a further comparison [31] with recent results at T = 15.3 eV and ρ = 5.48 mg cm −3 obtained with the ATOMIC modeling code, results that include contributions from transitions with n ≤ 5, shows significantly higher monochromatic opacities than OP for photon energies greater than 100 eV and almost a factor of 2 increase in the RMO; it is pointed out therein that this is due to limited M-shell configuration expansions in OP for ions such as Fe VIII. A more controversial situation involves the recently measured Fe monochromatic opacities that proved to be higher that expected in conditions similar to the solar CZB [33]. Such a result came indeed as a surprise since previous comparisons of transmission measurements at T = 156 ± 6 eV and N e = (6.9 ± 1.7) × 10 21 cm −3 with opacity models-namely ATOMIC, MUTA, OPAL, PRISMSPECT, and TOPAZ-showed satisfying line-by-line agreement [32,88,89].…”

On Variations of Pre-Supernova Model Properties

“…One should bear in mind the limitations of our studies: our neglect of rotation and magnetic fields; ambiguous fidelity to the underlying 3D physics in the MESA 1D models: the treatment of convective (Trampedach et al 2014), semiconvective (Moore & Garaud 2016), and overshoot (Kitiashvili et al 2016) mixing; the parameterization of mass loss (e.g., Šurlan et al 2012;Madura et al 2013); potentially underestimated contributions from iron in the opacity (Blancard et al 2012;Krief et al 2016b,a;Turck-Chièze et al 2016;Colgan et al 2016); and unaccounted for uncertainties in the nuclear reaction rates (e.g., Sallaska et al 2013;Fields et al 2016). Software: MESA (Paxton et al 2011(Paxton et al , 2015, Python python.org, matplotlib (Hunter 2007), NumPy (van der Walt et al 2011) Facilities: Arizona State University Research Computing Saguaro and Ocotillo Systems.…”