Variability in Low Ionization Broad Absorption Line Outflows
  We present results of our time variability studies of Mg II and Al III
absorption lines in a sample of 22 Low Ionization Broad Absorption Line QSOs
(LoBAL QSOs) at 0.2 <= zem <= 2.1 using the 2m telescope at IUCAA Girawali
Observatory over a time-scale of 10 days to 7.69 years in the QSO's rest frame.
Spectra are analysed in conjunction with photometric light curves from Catalina
Real-Time Transient Survey. Long time-scale (i.e >= 1 year) absorption line
variability is seen in 8 cases (36% systems) while only 4 of them (i.e 18%
systems) show variability over short time-scales (i.e < 1 year). We notice a
tendency of highly variable LoBAL QSOs to have high ejection velocity, low
equivalent width and low redshift. The detection rate of variability in LoBAL
QSOs showing Fe fine-structure lines (FeLoBAL QSOs) is less than that seen in
non-Fe LoBAL QSOs. Absorption line variability is more frequently detected in
QSOs having continuum dominated by Fe emission lines compared to rest of the
QSOs. Confirming these trends with a bigger sample will give vital clues for
understanding the physical distinction between different BAL QSO sub-classes.
We correlate the absorption line variability with various parameters derived
from continuum light curves and find no clear correlation between continuum
flux and absorption line variabilities. However, sources with large absorption
line variability also show large variability in their light curves. We also see
appearance/disappearance of absorption components in 2 cases and clear
indications for profile variations in 4 cases. The observed variability can be
best explained by a combination of process driven by continuum variations and
clouds transiting across the line of sight.
