Distance, Energy, and Variability of Quasar Outflows: Two HST/COS epochs
  of LBQS 1206+1052
  We analyze new HST/COS spectra for two quasar absorption outflows seen in the
quasi-stellar object LBQS 1206+1052. These data cover, for the first time,
absorption troughs from $S_{IV}$, $Si_{II}$, and $P_V$. From the ratio of the
$S_{IV}$* to $S_{IV}$ column densities, we measure the electron number density
of the higher-velocity ($-1400$ km s$^{-1}$, v1400) outflow to be log($n_e$) =
$4.23^{+0.09}_{-0.09}$ cm$^{-3}$ and constrain the lower-velocity ($-730$ km
s$^{-1}$, v700) outflow to log($n_e$) $>$ $5.3$ cm$^{-3}$. The $n_e$ associated
with the higher-velocity outflow is an order of magnitude larger than reported
in prior work. We find that the previous measurement was unreliable since it
was based on density-sensitive absorption troughs that were likely saturated.
Using photoionization models, we determine the best $\chi^2$-minimization fit
for the ionization parameter and hydrogen column density of the higher-velocity
outflow: log($U_H$) = $-1.73^{+0.21}_{-0.12}$ and log($N_H$) =
$21.03^{+0.25}_{-0.15}$ cm$^{-2}$, respectively. We calculate from $U_H$ and
$n_e$ a distance of $500^{+100}_{-110}$ pc from the central source to the
outflow. Using an SED attenuated by the v700 outflow yields a two-phase
photoionization solution for the v1400 outflow, separated by a $\Delta U
\approxeq 0.7$. Otherwise, the resultant distance, mass flux, and kinetic
luminosity are similar to the unattenuated case. However, the attenuated
analysis has significant uncertainties due to a lack of constraints on the v700
outflow in 2017.
