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Using White Dwarfs to Study Extrasolar Asteroids and Planets

Presenter: Michael Jura, University of California, Los Angeles
When: October 24, 2005 11AM PDT

White dwarfs cooler than 20000 K have very thin atmospheres. Consequently,
in these high gravity stars, heavy elements sink and become undetectable on
a time scale of less than 1000 years. While 75% of cool white dwarfs have
calcium abundances less than 10^-6 of the Sun’s, about 25% of these stars
have at least some detectable calcium. One model is that white dwarfs with
metals are accreting them from the interstellar medium. Alternatively, the
white dwarfs could be accreting from the dust produced by the disintegration
of comets and the destruction of asteroids. Accretion rates as low as 3
106 g s^-1, the rate at which dust is manufactured to produce the zodiacal
cloud in the Solar System are detectable. Infrared emission from the dust
around white dwarfs can be used to study their circumstellar matter. We
describe how the previous detection of an infrared excess around the white
dwarf G29-38 and our recent detection of an infrared excess around GD 362
can be used to investigate systems of asteroids and planets around these
stars.

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