  X-ray observations have revealed that many microquasars and low-mass X-ray
binaries (LMXBs) exhibit narrow absorption features identified with resonant
absorption from Fe XXV and Fe XXVI and other abundant ions. In many well
studied systems there is evidence for blue-shifts, indicating outflowing
plasmas. We succesfully model the changes in both the X-ray continuum and the
Fe absorption features during dips from all the bright dipping LMXBs observed
by XMM-Newton (EXO 0748-676, XB 1254-690, X 1624-490, MXB 1659-298, 4U 1746-371
and XB 1916-053) as resulting primarily from an increase in column density and
a decrease in the ionization state of a highly-ionized absorber in a similar
way as was done for 4U 1323-62. This implies that the complex spectral changes
in the X-ray continua observed from the dip sources as a class can be most
simply explained primarily by changes in the highly ionized absorbers present
in these systems. There is no need to invoke unusual abundances or partial
covering of extended emission regions. Outside of the dips, the absorption line
properties do not vary strongly with orbital phase. This implies that the
ionized plasma has a cylindrical geometry with a maximum column density close
to the plane of the accretion disk. Since dipping sources are simply normal
LMXBs viewed from close to the orbital plane this implies that ionized plasmas
are a common feature of LMXBs.
