Broadening processes

The integration of the radial velocity curve of the absorption line FeI5576.0883Å shows that the maximum and minimum radii occur at the pulsation phases $\varphi=0.37$ and 0.90 respectively. The projection effect over the stellar disk is maximum when the radial velocity is maximum i.e., at phases 0.0 and 0.80 (Fig.). It is minimum when the velocity is equal to zero ($\varphi=0.37$ and 0.90).

FWHM reaches its minimum value at phase 0.34 (Fig.). Then, during the following compressing phase, the FWHM increases more and more because all broadening mechanisms (thermal, turbulence and projection effect) are working to widen the line. For the same reason, RF and EW also increase (Fig.). Near phase 0.72, EW reaches its maximum value and begins to slowly decrease certainly because FeI ionizations take place. From phase 0.83, EW abruptly falls down until about half of its maximum value at the minimum radius ($\varphi=0.90$). During this phase interval, the temperature increases and consequently, ionizations must decrease EW like observed. Although, during the last part of the atmospheric contraction, the turbulence is increasing and must contribute to extend the EW, we conclude that it remains a secondary effect. Later, when the atmosphere begins to expand ($\varphi\gt.90$), EW continues to strongly decrease until ($\varphi=0.0$). During this period, the projection effect, which is minimum at $\varphi=0.90$ and maximum at $\varphi=0.0$, is certainly the dominant broadening mechanism. Indeed, turbulence, which is now decreasing (atmospheric expansion), has no reasons to stop its variation at $\varphi=0.0$. On the other hand, at the beginning of the expansion, recombinations, which must contribute to expand EW, are still too weak to play an appreciable role. Later, when recombinations become significant, EW continuously increases and does not seem affected by the variation of the projection effect which is minimum at the maximum radius ($\varphi=0.37$). After, when the contraction of the atmosphere begins, EW continues its linear increase. This is certainly the consequence of the turbulence broadening mechanism which must be the major contribution to the EW variation during the compression phase.

FWHM reaches its maximum value near phase 0.83 before a rapid decrease (Fig.). This is certainly the consequence of the fast reduction of the broadening projection effect between phases 0.83 and 0.90. The FWHM decrease becomes smaller and smaller after the minimum radius ($\varphi=0.90$) although the turbulence declines due to the atmospheric expansion. This means that the projection effect, which increases again until its second maximum ($\varphi=0.0$), is the dominant broadening process in this time interval. Finally, from the luminosity maximum ($\varphi=0.0$), where the projection effect begins again to decrease, FWHM regulary decreases until the maximum radius ($\varphi=0.37$). Thus the fast variations of the projection effect appears to be at the origin of the FWHM-stillstand at $\varphi=0.0$.

The RF curve presents a small stillstand around $\varphi=0.87$ (Fig.). Because, from phase 0.8 until the minimum radius ($\varphi=0.90$), the amplitude of the projection effect changes from its maximum to minimum values, the augmentation of RF decreases more and more and finally produces the observed stillstand. When the atmospheric expansion starts ($\varphi=0.90$), RF strongly increases due to the new augmentation of the projection effect in spite of the diminution of the temperature. RF only begins to decrease after the projection effect reaches its maximum value ($\varphi=0.0$). Then and until the maximum radius ($\varphi=0.37$), both the temperature decrease and the fading of the projection effect provoke the RF decrease. This also explains the FWHM drop after its stillstand ($\varphi=0.0$).