Broad absorption line symbiotic stars: highly ionized species in the
  fast outflow from MWC 560
  In symbiotic binaries, jets and disk winds may be integral to the physics of
accretion onto white dwarfs from cool giants. The persistent outflow from
symbiotic star MWC 560 (=V694 Mon) is known to manifest as broad absorption
lines (BALs), most prominently at the Balmer transitions. We report the
detection of high-ionization BALs from C IV, Si IV, N V, and He II in
International Ultraviolet Explorer spectra obtained on 1990 April 29-30, when
an optical outburst temporarily erased the obscuring 'iron curtain' of
absorption troughs from Fe II and similar ions. The C IV and Si IV BALs reached
maximum radial velocities at least 1000 km/s higher than contemporaneous Mg II
and He II BALs; the same behaviors occur in the winds of quasars and
cataclysmic variables. An iron curtain lifts to unveil high-ionization BALs
during the P Cygni phase observed in some novae, suggesting by analogy a
temporary switch in MWC 560 from persistent outflow to discrete mass ejection.
At least three more symbiotic stars exhibit broad absorption with blue edges
faster than 1500 km/s; high-ionization BALs have been reported in AS 304
(=V4018 Sgr), while transient Balmer BALs have been reported in Z And and CH
Cyg. These BAL-producing fast outflows can have wider opening angles than has
been previously supposed. BAL symbiotics are short-timescale laboratories for
their giga-scale analogs, broad absorption line quasars (BALQSOs), which
display a similarly wide range of ionization states in their winds.
