Line profile modelling

In the present analysis we use the hydrodynamic model RR41 from our previous study (Fokin & Gillet 1997), which reveals the strongest shocks among other models. Its parameters are: $T_{\mbox{\scriptsize eff}}=7175\,$K, $L\,=62$L$_{\odot}$,$M\,=0.578$M$_{\odot}$,\, X=0.7,\, Z=0.002$. The details of the numerical calculation and dynamical properties of this model can be found in the paper mentioned above. In the same paper we already estimated the general effect of the microturbulence on the line profiles. The sets of profiles of the FeII4923.921Å and BaII4934.076Å lines were calculated for two values of the microturbulent velocity, v_turb=0 and 5km/s. We found that the increase of v_turb leads to stronger and broader lines.

In order to study the variation of v_turb with the pulsation phase, we computed a large set of the FeII line profiles for different phases, using v_turb as a free parameter to get the best fit to the observed FWHM. The method of solution of the transfer equation is the same as in Fokin & Gillet (1997). We always adopt v_rot=0 and assume the microturbulent velocity constant at each moment within the whole the atmosphere.

  

Figure: Theoretical fit (solid curve) to the observed values obtained during 3 nights (black points: 3 August 1994; white circles: 4 August 1994; triangles: 5 August 1994) for the line FeII4923.921Å. The large dispersion of the observed values is probably due to dynamical variations from cycle-to-cycle, since the points represent three consecutive nights of observations. The theoretical curve was obtained by varying v_turb as a free parameter

  

Figure: Theoretical velocity curve measured from the minima of the FeII4923.921Å line