  We present an X-ray absorption line spectroscopic study of the large-scale
hot interstellar medium (HISM) in the Galaxy. We detect Ne IX K$_\alpha$
absorption lines in the {\sl Chandra} grating spectra of seven Galactic
low-mass X-ray binaries. Three of these sources also show absorption of O VII
K$_\alpha$, O VII K$_\beta$, and/or O VIII K$_\alpha$. Both centroid and width
of the lines are consistent with a Galactic HISM origin of the absorption. By
jointly fitting the multiple lines, accounting for line saturation and assuming
the collisional ionization equilibrium, we estimate the average absorbing gas
temperature as $\sim 2.4\pm0.3\times10^6$ K (90% confidence errors). We further
characterize the spatial density distribution of the gas as ${\rm
6.4_{-1.7}^{+2.4} exp(-|z|/1.2_{-0.5}^{+1.0} kpc) \times10^{-3}{\rm cm^{-3}}} $
(a disk morphology) or ${\rm 6.2_{-2.1}^{+3.8} [ 1 + (R/2.3_{-1.1}^{+1.6}
kpc)^2]^{-1} \times10^{-3} {\rm cm^{-3}}}$ (a sphere morphology), where $z$ and
$R$ are the distances from the Galactic plane and Galactic center (GC)
respectively. Since nearly all the sight-lines with significant absorption
lines detected are somewhat toward GC and at low Galactic latitudes, these
results could be severely biased. More observations toward off-GC sight-lines
and at high latitudes are urgently needed to further the study. Nevertheless,
the results demonstrate the excellent potential of X-ray absorption line
spectroscopy in the study of the HISM.
