configurations, the flux calibration based on the direct observed line profile should have low confidence level. As discussed in detail in the section 2 of Dietrich et al. (1998), some further procedures have been applied to complete the flux calibration. The spectra are firstly photometrically calibrated by comparison with the broadband photometric measurements (being convolved with the spectral response curve of the Johnson V and R), and then scaled by multiplicative factors to achieve the same total flux ratio as the intercalibrated photometric measurements in V and R bands. After that, the spectra have to be intercalibrated to a common flux level, in order to correct the effects for different wavelength shifts, and different spectral resolutions in different spectra. All the procedures have been successfully done by Dietrich et al. (1998), so that we directly collect the line fluxes ($f_1$) and corresponding uncertainties of broad H$\alpha$ listed in Dietrich et al. (1998). Moreover, in spite of the effects from different flux scales for the observed spectra, those directly measured line fluxes of the double-peaked broad H$\alpha$ ($f_0$, no corrections being considered) are also listed in Table 1.

Before the end of the subsection, there are two points we should note. 