{\it HST}/COS Observations of the Warm Ionized Gaseous Halo of NGC 891
  The metallicity of galactic gaseous halos provides insights into accretion
and feedback of galaxies. The nearby edge-on galaxy NGC 891 has a
multi-component gaseous halo and a background AGN (LQAC 035+042 003) projected
5 kpc above the disk near the minor axis. Against the UV continuum of this AGN,
we detect lines from 13 ions associated with NGC 891 in new {\it HST}/COS
spectra. Most of the absorption is from the warm ionized gas with $\log
T=4.22\pm0.04$, $\log n_{\rm H}=-1.26\pm0.51$, and $\log N_{\rm H}=20.81\pm
0.20$. The metallicity of volatile elements (i.e., C, N, and S) is about half
solar ($\rm[X/H] \approx -0.3\pm 0.3$), while Mg, Fe, and Ni show lower
metallicities of $\rm[X/H]\approx-0.9$. The absorption system shows the
depletion pattern seen for warm Galactic diffuse clouds, which is consistent
with a mixture of ejected solar metallicity disk gases and the hot X-ray
emitting halo ($Z=0.1-0.2Z_\odot$). The warm ionized gases are about 5 times
more massive than the cold \ion{H}{1} emitting gases around the galactic
center, which might lead to accretion with a mean rate of
$10^2~M_\odot\rm~yr^{-1}$ for a period of time. We also detect low metallicity
($\approx 0.1~Z_\odot$) gases toward LQAC 035+042 003 at $110\rm~km~s^{-1}$ (a
high velocity cloud) and toward another sight line (3C 66A; 108 kpc projected
from NGC 891) at $30\rm~km~s^{-1}$. This low metallicity material could be the
cold mode accretion from IGM or the tidal disruption of satellites in the NGC
891 halo.
