  About a dozen hot white dwarfs with effective temperatures Teff =
65,000-120,000 K exhibit unusual absorption features in their optical spectra.
These objects were tentatively identified as Rydberg lines of ultra-high
excited metals in ionization stages V-X, indicating line formation in a dense
environment with temperatures near one million Kelvin. Since some features show
blueward extensions, it was argued that they stem from a superionized wind. A
unique assignment of the lines to particular elements is not possible, although
they probably stem from C, N, O, and Ne. To further investigate this
phenomenon, we analyzed the ultraviolet spectra available from only three stars
of this group; that is, two helium-rich white dwarfs, HE 0504-2408 and HS
0713+3958 with spectral type DO, and a hydrogen-rich white dwarf, HS 2115+1148
with spectral type DAO. We identified light metals (C, N, O, Si, P, and S) with
generally subsolar abundances and heavy elements from the iron group (Cr, Mn,
Fe, Co, Ni) with solar or oversolar abundance. The abundance patterns are not
unusual for hot WDs and can be interpreted as the result of gravitational
settling and radiative levitation of elements. As to the origin of the
ultra-high ionized metals lines, we discuss the possible presence of a
multicomponent radiatively driven wind that is frictionally heated.
