ISOPHOT observations of dust disks around main sequence (Vega-like) stars

The photometer (ISOPHOT) on the Infrared Space Observatory (ISO) has proved to be invaluable for investigating the dust around main sequence stars (bo th prototypes and candidate Vega-like stars). The long wavelength camera (a t 60 and 90 mu m) has been used to map the area around the stars to establi sh whether the dust disk is extended. Low-resolution spectra between 5.8 an d 11.6 mu m show whether the dust is composed of silicate grains, and wheth er molecular features are present. The four prototype Vega-like stars (Vega , beta Pie, Fomalhaut, epsilon Eri) are studied, as well as eight other sta rs, which are main sequence stars with cool dust associated with them. We f ind that the spectra of beta Pie, 49 Get, HD98800, and HD135344 show excess emission from the cool dust around the star, HD144432 and HD139614 show si licate dust emission, HD169142 and HD34700 show emission features from carb on-rich molecules (possibly PAHs, polycyclic aromatic hydrocarbon molecules ), and HD142666 shows emission features from both carbon-rich molecules and silicate dust. Up to 11.6 mu m, the emission from Vega, Fomalhaut, and eps ilon Eri is dominated by the stellar photosphere. At 60 and 90 mu m, the ex tended dust emission is mapped, and the disk resolved in eight cases. The d ust mass in the disks is found to range from around 10(-9) to 10(-4) M.. Si nce several of the stars are younger than the Sun, and the disks have suffi cient material of the type found in the Solar System, these disks could be in the early stages of planet formation. (C) 2000 Academic Press.