X-ray emission from isolated hot white dwarfs

Hot white dwarfs are objects that copiously emit in the Extreme Ultraviolet and soft X-ray range. They are the brightest sources seen in the Low Energy Telescope of EXOSAT, with countrates up to 25 cnts/s. in contrast to their optical and UV spectrum the total flux and spectral distribution at soft X-ray energies are highly sensitive to the effective temperature, structure and elemental composition of the dwarf's atmosphere. The imaging soft X-ray experiments onboard EXOSAT cover with large sensitivity the spectral region where the peak of emission of hot white dwarfs is expected to occur.I here review some of the (preliminary) results obtained so far with broadband X-ray photometry on a dozen or so white dwarfs, and some of the high-resolution spectra obtained for three white dwarfs with the grating spectrometers.