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We used the HIRES echelle spectrograph on the Keck telescope to search for metals in the 3700-5200 Å spectra of white dwarfs with hydrogen-rich photospheres. The most popular models that account for the presence of metals are interstellar accretion and comet impact. The data are not easily reconciled with either model, but binarity might play a role. We comment on the implications for Oort-like comet clouds and certain types of planets around main-sequence stars.
Zuckerman et al. (Thu,) studied this question.
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