188 CIV BAL QSOs from SDSS DR7

Considering only the longest time-scale between epochs for each QSO, 73 variable regions in the CIV BAL troughs are detected for 43 BAL QSOs. The proportion of BAL QSOs showing variable regions increases with longer time-interval than about 1 yr in the rest frame.

The velocity width of variable regions is narrow compared to the BAL-trough outflow velocity. For 43 BAL QSOs with variable regions, it is found that there is a medium strong correlation between the variation of the continuum luminosity at 1500{AA} and the variation of the spectral index. With respect to the total 188 QSOs, a larger proportion of BAL QSOs with variable regions appears bluer during their brighter phases, which implies that the origin of BAL variable regions is related to the central accretion process.