We have performed soft X-ray spectroscopy of two hot white dwarfs with the Chandra observatory using the Low Energy Transmission Grating .
The first target is the hot DA white dwarf LB1919 ( T _ { eff } =69 000 K ) .
This star is representative of a small group of hot DAs whose metallicities lie well below predictions from radiative levitation theory .
The Chandra spectrum shows a rich absorption line spectrum which may allow to find the origin of the low-metallicity nature of these DAs .
The second target is PG 1520+525 , a very hot non-pulsating PG1159 star .
We find that it is hotter ( T _ { eff } =150 000 K ) than the pulsating prototype PG 1159 - 035 ( T _ { eff } = 140 000 K ) and conclude that both stars confine the blue edge of the GW Vir instability strip .