  We report the discovery of narrow Fe XXV and Fe XXVI K alpha X-ray absorption
lines at 6.65 and 6.95 keV in the persistent emission of the dipping low-mass
X-ray binary (LMXB) XB 1916-053 during an XMM-Newton observation performed in
September 2002. In addition, there is marginal evidence for absorption features
at 1.48 keV, 2.67 kev, 7.82 keV and 8.29 keV consistent with Mg XII, S XVI, Ni
XXVII K alpha and Fe XXVI K beta transitions, respectively. Such absorption
lines from highly ionized ions are now observed in a number of high inclination
(ie. close to edge-on) LMXBs, such as XB 1916-053, where the inclination is
estimated to be between 60-80 degrees. This, together with the lack of any
orbital phase dependence of the features (except during dips), suggests that
the highly ionized plasma responsible for the absorption lines is located in a
cylindrical geometry around the compact object. Using the ratio of Fe XXV and
Fe XXVI column densities, we estimate the photo-ionization parameter of the
absorbing material to be 10^{3.92} erg cm s^{-1}. Only the Fe XXV line is
observed during dipping intervals and the upper-limits to the Fe XXVI column
density are consistent with a decrease in the amount of ionization during
dipping intervals. This implies the presence of cooler material in the line of
sight during dipping. We also report the discovery of a 0.98 keV absorption
edge in the persistent emission spectrum. The edge energy decreases to 0.87 keV
during deep dipping intervals. The detected feature may result from edges of
moderately ionized Ne and/or Fe with the average ionization level decreasing
from persistent emission to deep dipping. This is again consistent with the
presence of cooler material in the line of sight during dipping.
