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ISO observations of dust around Vega-like stars
Helen J Walker (RAL)
The photometer (ISOPHOT) on the Infrared Space Observatory (ISO) has
proved to be an instrument well suited to the study of the dust around
main sequence stars. Low resolution spectra (from 5.8 to 11.6 microns)
show the composition of the dust, whether it is composed of silicate
grains, whether molecular features are present, or whether the cool
thermal continuum dominates the emission. Photometry between 60 and 200
microns is used to estimate the temperature and grain emissivity of the
dust, which leads to an estimate of the dust mass of the material around
the stars. Small maps at 60 and 90 microns can show whether the dust disc
is resolved, allowing an estimate of the physical size of the disc to be
made. ISOPHOT was used to study the four prototype Vega-like stars
(Vega, Beta Pic, Fomalhaut, Epsilon Eri) and several candidate main
sequence stars. The discs around the four prototypes and four candidates
are resolved using the mapping mode. The dust temperatures are cool,
usually below 100K, and the dust masses are in the range 0.03 to 2200
times the mass of the moon.
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