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Circumstellar Dust Created by Terrestrial Planet Formation in HD 113766
We present an analysis of the gas-poor circumstellar material in the HD113766 binary system (F3/F5, 10-16 Myr), recently observed by theSpitzer Space Telescope. For our study we have used the IR mineralogicalmodel derived from observations of the Deep Impact experiment. We findthe dust dominated by warm, fine (~1 ?m) particles, abundant inMg-rich olivine, crystalline pyroxenes, amorphous silicates, Fe-richsulfides, amorphous carbon, and colder water ice. The warm dust materialmix 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 ofthe observed material is in a narrow belt ~1.8 AU from the 4.4Lsolar central source, in the terrestrial planet-formingregion and habitable zone of the system (equivalent to 0.9 AU in thesolar system). The icy dust lies in two belts, located at 4-9 and 30-80AU. The lower bound of warm dust mass in 0.1-20 ?m,dn/da~a-3.5 particles is very large, at least3×1020 kg, equivalent to a 320 km radius asteroid of2.5 g cm-3 density. Assuming 10 m particles are the largestpresent, the lower bound of warm dust mass is at least 0.5MMars. Neither primordial nor mature, the dust around HD113766A originates from catastrophic disruption of terrestrial planetembryo(s) and subsequent grinding of the fragments or from collisions ina young, extremely dense asteroid belt undergoing planetary aggregation.The persistence of the strong IR excess over the last two decades arguesfor a mechanism to provide replenishment of the circumstellar materialon yearly timescales.
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