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We present a series of systematic abundance measurements for 89 hydrogenatmosphere (DA-type) white dwarfs with temperatures spanning 16000-77000K drawnfrom the FUSE spectral archive. This is the largest study to date of whitedwarfs where radiative forces are significant, exceeding our earlier work,based mainly on IUE and HST data, by a factor three. Using heavy elementblanketed non-LTE stellar atmosphere calculations, we have addressed the heavyelement abundance patterns making completely objective measurements ofabundance values and their error ranges using a \c{hi}2 fitting technique. Weare able to establish the broad range of abundances seen in a given temperaturerange and establish the incidence of stars which appear, in the optical, to beatmospherically devoid of any material other than H. We compare the observedabundances to predictions of radiative levitation calculations, revealinglittle agreement. We propose that the supply of heavy elements is accreted fromexternal sources rather than being intrinsic to the star. These elements arethen retained in the white dwarf atmospheres by radiative levitation, a modelthat can explain both the diversity of measured abundances for stars of similartemperature and gravity, including cases with apparently pure H envelopes, andthe presence of photospheric metals at temperatures where radiative levitationis no longer effective.

Evidence for an external origin of heavy elements in hot DA white dwarfs