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Evaporation and Accretion of Extrasolar Comets Following White Dwarf Kicks
Several lines of observational evidence suggest that white dwarfs receive
small birth kicks due to anisotropic mass loss. If other stars possess
extrasolar analogues to the Solar Oort cloud, the orbits of comets in such
clouds will be scrambled by white dwarf natal kicks. Although most comets will
be unbound, some will be placed on low angular momentum orbits vulnerable to
sublimation or tidal disruption. The dusty debris from these comets will
manifest itself as an IR excess temporarily visible around newborn white
dwarfs; examples of such disks may already have been seen in the Helix Nebula,
and around several other young white dwarfs. Future observations with the James
Webb Space Telescope may distinguish this hypothesis from alternatives such as
a dynamically excited Kuiper Belt analogue. Although competing hypotheses
exist, the observation that of young white dwarfs possess such
disks, if interpreted as indeed being cometary in origin, provides indirect
evidence that low mass gas giants (thought necessary to produce an Oort cloud)
are common in the outer regions of extrasolar planetary systems. Hydrogen
abundances in the atmospheres of older white dwarfs can, if sufficiently low,
also be used to place constraints on the joint parameter space of natal kicks
and exo-Oort cloud models.Comment: 22 pages, 13 figures, published in MNRAS. Changes made to match
published versio
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