We present a model-atmosphere analysis of the ultraviolet echelle spectra of KPD 0005+5106 taken with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope .
The star is the hottest known pre-white dwarf ( T \mathrm { \hskip { -1.72 pt } { } _ { eff } } = 200 000 \pm 20 000 K , \log g = 6.7 \pm 0.3 ( cm/s ^ { 2 } ) .
Its atmosphere is composed of helium with trace amounts of metals .
It is of the so-called O ( He ) spectral type that comprises very hot helium-rich pre-white dwarfs whose origin is debated .
From neon and silicon ionisation balances , we derive tighter constraints on the effective temperature ( 195 000 \pm 15 000 K ) and improve previous abundance determinations of these elements .
We confirm the idea that KPD 0005+5106 is the descendant of an R Coronae Borealis ( RCB ) star , so is the outcome of a binary-white-dwarf merger .
We discuss the relation of KPD 0005+5106 to other O ( He ) and RCB stars .