  We have detected an ionized nebula around the hot DO white dwarf KPD
0005+5106, and used the [OIII]/H-alpha ratios and nebular velocities to
separate this nebula from the background HII region of AO Cas. The angular size
of the [OIII] nebula of KPD 0005+5106 is ~3 deg. The velocity of this nebula is
similar to those of the local interstellar HI gas and the
interstellar/circumstellar absorption lines in UV spectra of KPD 0005+5106, but
has a large offset from those of the stellar photospheric lines. The mass of
the ionized nebula, ~70 Msun, indicates that it consists of interstellar
material and that the velocity offset between the star and the ambient medium
should not be interpreted as a wind outflow. We have also analyzed the ROSAT
PSPC observation of KPD 0005+5106 to determine its hard X-ray luminosity. Using
the L_X/L_bol relation for late-type stars and the lack of obvious near-IR
excess of KPD 0005+5106, we exclude the possible existence of a binary
companion with coronal activity. Without a wind outflow, the presence of
stellar OVIII emission requires that X-rays at energies greater than 0.871 keV
are present in the vicinity of KPD 0005+5106. This hard X-ray emission is most
puzzling as neither photospheric emission at such high energies nor a
high-temperature corona is expected from current stellar atmospheric models of
KPD 0005+5106. X-ray observations with high angular resolution and sensitivity
are needed to confirm the positional coincidence and to enable X-ray spectral
analyses for constraining the physical origin of the hard X-ray emission from
KPD 0005+5106.
