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Debris Disks as Signposts for Planet Formation in Binary Star Systems

Wednesday, November 16, 2005
Stansberry (Steward Observatory, University of Arizona)

One of the key discoveries made using data from IRAS was excess far-infrared emission from main-sequence stars (the Vega phenomenon, Aumann et al., 1984). The infrared excess emission is attributed to thermal emission from dust warmed by the light of the star, typically to temperatures of 30 - 100 K. The infrared emission is dominantly from grains of order 10 um in size. Such dust grains (5 - 50 um) should be removed by PR drag, causing them to spiral onto the star. Grains smaller than 5 um are instead removed by radiation pressure, which blows them out of the system. The timescales for dust removal are of order 1000 yr, so the presence of dust around main-sequence stars requires a mechanism for replenishment. The most likely source for such dust is from collisions between larger bodies (from 100 um grains to 100 km asteroids) and dust production by comets. Thus circumstellar dust is a proxy for the presence of planetary debris, and presumably planets, around other stars.

A key science driver for the Spitzer space telescope was to study the occurrence of debris disks around other stars, as a way to gain insight into the fraction of stars which may harbor planets. I will discuss some key early results from such studies with Spitzer, and then go into more detail about the discovery that binary star systems have debris disks about as often as single stars do.

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