5 Comparison with V652 Her and BX Cir

The observed radial velocity and luminosity curves for V652 Her and BX Cir are shown in Fig. 7. The measured velocity and luminosity ($\Delta$log $L/\mbox{$L_{\odot}$ }$) amplitudes are respectively 94   $\mbox{km}~\mbox{s}^{-1}$ and 0.240 for V652 Her and 56   $\mbox{km}~\mbox{s}^{-1}$ and 0.096 for BX Cir.

The observed radial velocities have been transformed into the stellar rest frame by multiplying the projection factor for helium-rich early-type stars, p=-1.402 (Montañés Rodríguez & Jeffery 2001). Observational data have been taken from Jeffery et al. (2001: V652 Her) and Woolf & Jeffery (2000: BX Cir).

Figure 7 also shows two models for each case, which fit quite well to the observed velocity and light curves, having not only a closer chemical composition to that observed but also similar parameters. For V652 Her these models have 0.62  $\mbox{$M_{\odot}$ }$ and 22 900 K and 0.70  $\mbox{$M_{\odot}$ }$ and 23 400 K. The second (model 20) shows the best fit and has a radius closer to that given by observations, although a bigger mass.

Figure 6: Velocity and luminosity curves for models indicated into brackets. Next to the model number: log $\mbox{~\em$T_{\rm eff}$ }$, stellar mass ( $\mbox{$M_{\odot}$ }$), iron abundance ( $\mbox{$n_{\rm Fe}$ }$) and total abundance of metals ( $\mbox{$n_{\rm Z}$ }$) appear respectively.

For BX Cir, model 25 with $0.50~\mbox{$M_{\odot}$ }$ and 22 400 K presents a good fit reproducing not only the measured velocity and luminosity amplitudes but also the observed shapes, except for the flattening observed in the light curve which has not been reproduced in any case for this composition. Model 23 with a smaller mass, $0.38~\mbox{$M_{\odot}$ }$, and higher temperature, 24 000 K, is also quite close to the observations for BX Cir. The velocity and luminosity curves of these two models are in remarkably good agreement with the observed ones. We emphasize that, after the pulsation period, they are the most directly and reliably measured properties of BX Cir.

Figure 7: Velocity and luminosity curves for four selected models with mixtures n2 and c2. Next to the model number: log $\mbox{~\em$T_{\rm eff}$ }$, stellar mass ( $\mbox{$M_{\odot}$ }$ ), iron abundance ( $\mbox{$n_{\rm Fe}$ }$) and total abundance of metals ( $\mbox{$n_{\rm Z}$ }$) appear respectively.