A Last Look at the Common, Moderately Polluted White Dwarfs

Details A Last Look at the Common, Moderately Polluted White Dwarfs A Last Look at the Common, Moderately Polluted White Dwarfs

Jun 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010sptz.prop70116f&link_type=abstract

Spitzer Proposal ID #70116

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Scientific paper

Our ongoing Spitzer work has been highly successful in the identification of metal-polluted white dwarfs with circumstellar dust. Both the orbiting material and the photospheric heavy element abundances are refractory-rich and volatile- poor, revealing these stars are polluted by rocky material. In this way we continue to build a target list on which to perform spectroscopy of extrasolar rocky planetesimals, via their heavy element signatures in white dwarf atmospheres. No other currently available technique can observe the bulk composition of extrasolar, terrestrial, planetary material -- this is the singular, enormous advantage offered by these metal-enriched stars. We propose IRAC imaging of the twelve remaining, moderately metal-rich white dwarfs that have not yet been searched for warm orbiting dust. The nature of their relativley common and moderate pollution is still somewhat uncertain. Our model invokes the tidal destruction of a single, large asteroid to produce circumstellar dust, while multiple, smaller asteroids are invoked to explain stars that are dust-poor. In the latter case, orbiting dust is readily destroyed via collisions and sputtering as additional asteroids enter a pre-existing, closely orbiting disk at slightly different inclinations, resulting in a gaseous disk. In both cases, the white dwarf accretes, and becomes polluted by, material which is rich in heavy elements. Thus, the presence of warm dust implies pollution by a single body, whose heavy element abundances should reflect an idiosyncratic pattern of an extrasolar analog to a large asteroid like Ceres. On the other hand, a lack of orbiting dust implies the metal abundance pattern reflects pollution by an ensemble of smaller extrasolar asteroids, and closer to an average chemical composition. Discriminating between these two cases is critical to the interpretation of optical and ultraviolet spectroscopy of the photospheric heavy elements seen in polluted white dwarfs.

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