Since by definition the E.W. is computed from the $\rm H\alpha$ net flux normalized to the red continuum, it would result artificially reduced by a strong contribution of the bulge to the continuum. To assess this important point we investigate the correlation between the $\rm H\alpha$ E.W. and another SFR indicator, namely the $\rm H\alpha$ surface brightness ($\rm \Sigma~H\alpha$). The latter parameter is defined as the ratio of the $\rm H\alpha$ net line flux to the disk area (computed using $\rm a_{25}$, the diameter measured in the B band at the 25  isophote). The normalizing area is independent of the bulge properties, thus $\rm \Sigma~H\alpha$ should give a reliable estimate of the disk SFR. In Fig. 8 we plot (adopting the usual symbols coded according to the bulge-to-disk ratio) the two SFR parameters one against the other (panel a): the two quantities are linearly correlated and disks and bulges are nicely segregated along the diagonal line. Furthermore we show in Fig. 8b that the correlation between $\rm \Sigma~H\alpha$ and $\rm L_H$ is qualitatively similar to the one found between $\rm H\alpha$ E.W. and $\rm L_H$ (Fig. 5b). We conclude that $\rm H\alpha$ E.W. is marginally affected by the bulge contribution, 