Infrared Space Observ at Ory Photometric Search of Main-sequence Stars for Vega-type Systems1

We obtained 3.6È20 km photometry of 38 bright [IRAS km)[ 0.7 Jy] main-sequence stars with Fl(12 the Infrared Space Observatory (ISO). Observations were conducted with the ISOPHOT instrument, in the single-pointing photometry mode, through Ðlters at 3.6, 11.5, and 20.0 km. We searched for excess (Vega-type) emission from dust at temperatures K, located at D1È60 AU from the stars. We thus Z100 sampled dust at warm, terrestrial material temperatures and at cool (D100 K) temperatures of possible Kuiper BeltÈtype regions in these systems. We detected 20 km excesses from D14% of our sources, but we did not detect 11.5 km excesses from any of them. We present single-temperature blackbody models of the location and density of dust emission around 10 stars, two of them (29 Cyg and Gl 816) with excesses newly reported here. We make a thorough comparison of ISO and IRAS data on our target stars and propose a new calibration procedure for ISOPHOT staring measurements at 3.6, 11.5, and 20 km. Subject headings : circumstellar matter È dust, extinction È infrared : stars