Shock wave effects?

In their recent study, FGB have shown that three main shock waves are propagating in the atmosphere of $\delta$Cephei during each pulsation period. These shocks cross the FeI line formation region at different phase intervals and with different intensities. The shock s1 is approximately in the FeI layer between phases 0.74 and 0.77 with a maximum shock amplitude u₂-u₁=16km/s at $\varphi=0.77$ (see Fig.5 of FGB). s2 occurs between $\varphi=0.87$ and 0.94 with a maximum amplitude of 19km/s while s3 is visible from 0.52 to 0.54 with a maximum amplitude of 9km/s only. The shock amplitude at the beginning of the shock visibility was assumed equal to the sound velocity around 8km/s. Thus the maximum Mach number of these shocks are not larger than 2.4, 2.0 and 1.1 respectively. This means that these shocks have a relatively weak intensity in the FeI line formation region and consequently, we must not expect large effects on the FWHM, RF and EW curves.

Within the above estimated phase intervals, no particular features can be associated to shocks s1, s2 and s3 in the FWHM curve. For the EW curve, we only remark that EW begins to decrease at the same phase $\varphi=0.74$ that s1 enters in the FeI layer. Note that, in the previous subsection, we have not well understood why ionizations were suddenly initiated largely after the beginning of the compression and why EW continues to strongly decreases after the minimum radius. We also note that the ``strongest'' shock s2 crosses the FeI layer at this time. Thus, although the radius is increasing, ionization seems still efficient until s2 leaves the FeI layer. This is consistent with the fact that the EW decrease ceases just after the s2 escape.

For the RF curve, nothing can be connected with s1 and s3. The stillstand occurs at phase 0.87 i.e., when s2 enters in the FeI layer. Nevertheless, the additional ionization effect induced by s2 cannot explain this stillstand because ionization decreases RF. Thus there are not clear shock signatures within the RF curve.

Finally, we conclude that shock effects are not perceptible in the FWHM and RF curves. Alone, a contribution of s1 and s2 is perharps present in the EW curve due to ionization.