High-Resolution Imaging of the Dust Disk around 49 Ceti

Subarcsecond scale Keck images of the young A1 V star, 49 Ceti, resolve emission at lambda = 12.5 and 17.9 mu m from a disk with long axis at position angle (P.A.) 125 degree plus or minus 10 degree and inclination phi = 60 degree plus or minus 15 degree . At 17.9 mu m, the emission is brighter and more extended toward the northwest (NW) than the southeast (SE). Modeling of the mid-infrared images combined with flux densities from the literature indicate that the bulk of the mid-infrared emission comes from very small grains (a similar to 0,1 mu m) confined between 30 and 60 AU from the star. This population of dust grains contributes negligibly to the significant excess observed in the spectral energy distribution. Most of the nonphotospheric energy is radiated at longer wavelengths by an outer disk of larger grains (a similar to 15 mu m), inner radius similar to 60 AU, and outer radius similar to 900 AU. Global properties of the 49 Cet disk show more affinity with the beta Pic and HR 4796A disks than with other debris disks. This may be because they are all very young (t < 20 Myr), adding strength to the argument that they are transitional objects between Herbig Ae and "Vega-like" A stars with more tenuous circumstellar disks.