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M. D. Silverstone (Univ. of Arizona)
Excess far-infrared emission from main-sequence stars, commonly referred to as "The Vega Phenomenon," is believed to be thermal emission from cold dust particles orbiting in a circumstellar disk. These particles are thought to be a signature of planet formation. This study sought to characterize the nature of The Vega Phenomenon around solar-type stars. The effects of age and stellar multiplicity were examined through sensitive far-infrared photometry of these systems, optical spectroscopy of the central stars, and multiplicity studies from the published literature.
A survey consisting of 146 target observations was performed with ISOPhot at 60 and 90 or 100 microns. Significant (greater than 2 sigma) excess emission was detected from 42 targets, above a typical noise level of about 20 mJy (1 sigma). Ages of stars in the sample were determined with optical high-resolution spectroscopy of the Ca II H and K lines, supplemented by published age estimates. The observations revealed that of 25 targets selected for previously measured far-infrared excess at 60 microns (by IRAS), 7 were confused probably by background cirrus, and thus the IRAS flux was not a measurement of circumstellar dust.
Results indicate a decrease of infrared excess with stellar age consistent with the dust disk mass decrease with about time-1.75, as determined for nearby open clusters with ages spanning 107 to 109 years. The results also suggest that stars with close binary companions have less dust than single stars or those in wide binary orbits.
This work is based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA. This work is part of the NASA ISO Key project DEBRIS, and was supported by the grant NASA/JPL 961592.
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