A plea for reexamining heavy element opacities in stars

Abstract

It is shown that increasing the opacity due to heavy elements by a factor of 2-3 leads to classical Cepheid models which reproduce observed period ratios at evolutionary masses and luminosities. Thus the mass anomalies are removed in both the double-mode and bump Cepheid regimes. The proposed increases may also serve to energize {3 Cephei variables, thus solving yet another important problem in the theory of pulsating stars. We argue that opacity changes of this order are not implausible and urge further work in this important area.

Statistical line-by-line model for atomic spectra in intermediate coupling

“…Thus, the study of stellar pulsations provides indirect tests of opacities and has stimulated research. The "Z bump" is and important example, originally invoked to resolved mass discrepancies [26], soon after predicted by new opacity calculations [27,28], later corroborated by laboratory experiments [29] as well as pulsation studies [30], and now a standard feature in astrophysical opacities [31]. The Z bump is due to photon absorption by iron group elements.…”

Detailed Opacity Calculations for Astrophysical Applications

“…Figure 1 (left) shows that the spectrum can be interpreted with a rather high accuracy (except maybe as concerns the main feature around 1530 eV) using SCO-RCG at a single temperature and a single density. The spectrally-resolved transmission of aluminum was measured in the range of 70-280 eV at ρ = 0.01 g/cm 3 and T = 22 eV [28,29]. For this purpose, the iodine laser ASTERIX IV (200 J energy with pulse duration 0.4 ns at 400 nm) was focused into a spherical gold cavity with a diameter of 3 mm.…”

“…As can be seen in Figure 1 (right), the spectrum can be analyzed taking into account a temperature variation of 6 eV. [27] on HELEN laser facility in the United Kingdom and interpreted by SCO-RCG at T = 37 eV and ρ = 0.01 g/cm 3 . The areal mass is equal to 54 µg/cm 2 .…”

“…The areal mass is equal to 54 µg/cm 2 . Right: aluminum spectrum measured by Winhart et al [28,29] on ASTERIX IV laser facility in Germany and interpreted by SCO-RCG at ρ = 0.01 g/cm 3 and averaged over four temperatures (T = 18, 20, 22 and 24 eV) in order to simulate the gradients. The areal mass is equal to 30 µg/cm 2 .…”

“…The Cepheid stars (named after δ Cephei) are known to be used to estimate the stellar distances. They have been better understood after a revision by a factor two of the opacity for species of atomic number Z > 2 [3] confirmed by the first measurements of absorption coefficients [4]. The β Cephei-type stars (which should not be confused with Cepheid variables), also known as β Cepheids and named after β Cephei (or Alfirk) are now of primary interest due to the correlation between the frequencies of the excited modes and the mass of these stars for a given age.…”