Light Absorption Study Of Broad Absorption Line Quasars

Broad-absorption-line quasars (BAL QSOs) exhibit broad, ultraviolet (UV) line absorption troughs. BAL troughs are thought to be the strongest observed signatures of QSO winds. Variability of BAL can provide information on the structure, location and dynamics of the outflow winds. Using a single BAL QSO, SDSS J022844.09+ 000217.0, (Z=2.719) which has 18 epoch observations and a sample which contains 188 QSOs (Z> 1.7) from Sloan Digital Sky Survey (SDSS)/Baryon Oscillation Spectroscopic Survey (BOSS), we investigate the spectral variability of BAL QSOs, as well as the relation with the central black hole accretion properties.(1) A single QSO, SDSS J022844.09+000217.0. Fitting a power-law continuum iteratively and the emission lines of C ? 1549, Si ? 1399, C ?] 1399, we find that there is a strong correlation between the BAL equivalent width (EW) and the spectral index and a weak negative correlation between the BAL-EW and the continuum luminosity. The strong correlation between the BAL EW and the spectral index for this particular QSO suggests that dust is intrinsic to outflows. The weak correlation between the BAL variability and the continuum luminosity for this particular QSO implies that the BAL-trough variation is not dominated by photoionization.(2) A sample of 118 BAL QSOs. This sample is consist of 428 spectra, covering a timescale of about 0.001-3 years in the rest frame. Through fitting a power-law continuum iteratively, the C ?1549 BAL EWs for 428 spectra are calculated, as well as the continuum luminosity at 1500A (Lisoo) and the spectral index (?).79 variable regions in the C ? BAL troughs are identified in 47 two-epoch different spectra. For 188 BAL QSOs, it is found that there is no significant correlation between ?EW and ?L1500 or ??, about 50%BAL QSOs appear bluer during their brighter phases. For a subsample of BAL QSOs with variable BAL-trough regions, it is found that there is a mediate correlation between the ?L1500 and ??, about 70% BAL QSOs appear bluer during their brighter phases. This larger proportion implies that the origin of variable BAL-trough regions is related to the central accretion process. There is a moderate negative correlation between|?EW| and the black hole masses, showing smaller variation of BAL trough in BAL QSOs with larger black hole masses. There is a moderate positive correlation between the maximum outflow velocity of varied region and the Eddington ratio, showing larger outflow velocity with larger Eddington ratio.