Peculiar surface composition of DAZ white dwarfs: evidence of the demise of ancient planetary systems?

The surface composition of white dwarf stars shows obvious scarring due to the traumatic post-AGB episode which left exposed hydrogen or helium envelopes, or in some extreme cases, an exposed carbon core. Subsequent turmoils in the immediate environment of the white dwarf may lead to further surface chemical evolution. I examine the role played by accretion of circumstellar material, left over debris or companion mass loss, in altering the surface composition of white dwarfs.
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