Deep 24 micron Imaging of Nearby Debris Disks around A Stars

Details Deep 24 micron Imaging of Nearby Debris Disks around A Stars Deep 24 micron Imaging of Nearby Debris Disks around A Stars

Jun 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20296s&link_type=abstract

Spitzer Proposal ID #20296

Mathematics

Logic

Scientific paper

Although it is the prototypical debris disk, Spitzer observations of Vega show that its disk behaves in a very unexpected way. To low surface brightness, it has a diameter of 3.5 arcmin, about 1600 AU. We have modeled this disk and shown that the large size is due to small grains, of order 10 microns or even less, being ejected from the system by radiation pressure. The mass loss rate is so large that it is very unlikely that the current situation has persisted for the life of the star (about 350 million years). Instead, we believe that a major event within roughly the last million years, perhaps a collision involving an object of 1000 km diameter, has produced a huge cloud of very fine dust that is now being ejected from the system. We have found a second star, HD 69830, where a different train of logic arrives at a similar conclusion: a major event in the planetary system around the star during the past million years or so has produced large amounts of dust that are dominating the system's radiometric properties. These stars suggest a major shift in the way we model, or even think about, debris systems. It is probable that a significant fraction of them are dominated by the consequences of recent major events. To understand the prevalence of this behavior, we propose to obtain deep 24 micron imaging of 15 A stars with large excesses. These stars are selected to be close enough that we could detect Vega-like behavior; they are virtually the entire sample of A stars where such behavior can be detected with Spitzer. We will use theoretical tools developed on Vega to model the observations, either to explain the implications of any detected extended emission or to set robust upper limits to the rate of debris mass loss in systems that are point-like. Including Vega, beta Pic, and Fomalhaut (of which the first two have very extended debris) the total sample of 18 stars will provide a new picture of the behavior of exoplanetary systems.

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