2008ApJ...673.1106L

We present an analysis of the gas-poor circumstellar material in the HD 113766 binary system (F3/F5, 10-16 Myr), recently observed by the Spitzer Space Telescope. For our study we have used the IR mineralogical model derived from observations of the Deep Impact experiment. We find the dust dominated by warm, fine (∼1 µm) particles, abundant in Mg-rich olivine, crystalline pyroxenes, amorphous silicates, Fe-rich sulfides, amorphous carbon, and colder water ice. The warm dust material mix is akin to an inner main-belt asteroid of S-type composition. The ∼440 K effective temperature of the warm dust implies that the bulk of the observed material is in a narrow belt ∼1.8 AU from the 4.4 L_☉ central source, in the terrestrial planet-forming region and habitable zone of the system (equivalent to 0.9 AU in the solar system). The icy dust lies in two belts, located at 4-9 and 30-80 AU. The lower bound of warm dust mass in 0.1-20 µm, dn/da∼a^–3.5 particles is very large, at least 3x10²⁰ kg, equivalent to a 320 km radius asteroid of 2.5 g/cm3 density. Assuming 10 m particles are the largest present, the lower bound of warm dust mass is at least 0.5 M_Mars. Neither primordial nor mature, the dust around HD 113766A originates from catastrophic disruption of terrestrial planet embryo(s) and subsequent grinding of the fragments or from collisions in a young, extremely dense asteroid belt undergoing planetary aggregation. The persistence of the strong IR excess over the last two decades argues for a mechanism to provide replenishment of the circumstellar material on yearly timescales.