Photoionization-driven Absorption Lines Variability in Balmer Absorption
  Line Quasar LBQS 1206+1052
  In this paper we present an analysis of absorption line variability in
mini-BAL quasar LBQS 1206+1052. The SDSS spectrum demonstrates that the
absorption troughs can be divided into two components of blueshift velocities
of $\sim$700 km s$^{-1}$ and $\sim$1400 km s$^{-1}$ relative to the quasar
rest-frame. The former component shows rare Balmer absorption, which is an
indicator of high density absorbing gas, thus the quasar is worth follow-up
spectroscopic observations. Our follow-up optical and near-infrared spectra
using MMT, YFOSC, TripleSpec and DBSP reveal that the strengths of the
absorption lines vary for both of the two components, while the velocities do
not change. We reproduce all of the spectral data by assuming that only the
ionization state of the absorbing gas is variable and that all other physical
properties are invariable. The variation of ionization is consistent with the
variation of optical continuum from the V-band light-curve. Additionally, we
can not interpret the data by assuming that the variability is due to a
movement of the absorbing gas. Therefore, our analysis strongly indicates that
the absorption line variability in LBQS 1206+1052 is photoionization-driven. As
shown from photo-ionization simulations, the absorbing gas with blueshift
velocity of $\sim$700 km s$^{-1}$ has a density in the range of $10^9$ to
$10^{10}$ cm$^{-3}$ and a distance of $\sim$1 pc, and the gas with blueshift
velocity of $\sim$1400 km s$^{-1}$ has a density of $10^3$ cm$^{-3}$ and a
distance of $\sim$1 kpc.
