About a dozen hot white dwarfs with effective temperatures T \mathrm { \hskip { -1.72 pt } { } _ { eff } } = 65 000 K – 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 10 ^ { 6 } K. 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 .