Mid-infrared imaging of candidate Vega-like systems

We have conducted deep mid-infrared imaging of a relatively nearby sample o f candidate Vega-like stars using the OSCIR instrument on the Cerro Tololo Inter-American Observatory 4 m and Keck II 10 m telescopes. Our discovery o f a spatially resolved disk around HR 4796A has already been reported in 19 98 by Jayawardhana et al. Here we present imaging observations of the other members of the sample, including the discovery that only the primary in th e HD 35187 binary system appears to harbor a substantial circumstellar disk and the possible detection of extended disk emission around 49 Ceti. We de rive global properties of the dust disks, place constraints on their sizes, and discuss several interesting cases in detail. Although our targets are believed to be main-sequence stars, we note that several have large infrare d excesses compared with prototype Vega-like systems and may therefore be s omewhat younger. The disk size constraints we derive, in many cases, imply emission from relatively large (greater than or similar to 10 mum) particle s at mid-infrared wavelengths.