Photospheric nickel in the hot DO white dwarf REJ0503-289

Nickel is often detected spectroscopically in the atmosphere of hot H-rich DA white dwarfs and is always found along with iron. However, it has not been detected in a helium-rich DO white dwarf until recently. Our HST/GHRS observation of REJ0503-289 presents the first evidence for the direct detection of Ni in the atmosphere of a He-rich object (Barstow et al. 2000, MNRAS, vol 314, p109). Intriguingly, Fe, which is observed to be more abundant than Ni in the hot DA stars, is not detected. The upper limit to the abundance of Fe in REJ0503 implies an Fe/Ni ratio a factor of 10 lower than seen in the H-rich objects.