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The predictions of a two-phase accretion model is compared with all the observations currently available on the metal-line phenomenon in cool white dwarfs. The model is based on a simplified picture of the interstellar medium, but makes specific predictions as to the presence of metals in the photospheres of these stars. The gross observed metal abundance patterns are found to be very well accounted for within the framework of the model. For many individual stars, it is also possible to infer directly the accretion rates necessary to maintain photospheric metal abundances. The question of traces of hydrogen in these stars is discussed. It is found that hydrogen, like the metals, must be accreted. However, hydrogen accretion must be reduced by factors of 10 exp 2 to 10 exp 7 with respect to metal accretion to account for the observations.
Dupuis et al. (Thu,) studied this question.