Dust Dynamics, Surface Brightness Profiles, and Thermal Spectra of Debris Disks: The Case of AU Mic

摘要: AU Microscopii is a 12 Myr old M dwarf that harbors an optically thin, edge-on disk of dust. The scattered light surface brightness falls with projected distance b from the star as b^-a; within = 43 AU, 1-2, while outside 4-5. We devise theory to explain this profile. At stellocentric r r_BR we posit ring parent bodies on circular orbits: "birth ring," wherein micron-sized grains are born collisional attrition bodies. "inner disk" at comprises just large enough remain bound star, orbits rendered highly eccentric by stellar wind and radiation pressure. How vertical optical depth tau scales depends fraction migrate inward CPR drag without suffering collision. If large, inner birth share same depth, r^-5/2 in outer disk. By contrast, under collision-dominated conditions, empty, r^-3/2 outside. These scaling relations, which derive analytically confirm numerically, robust against uncertainties grain size distribution. simultaneously modeling thermal spectrum, break model degeneracies establish Mic system collision-dominated, its narrow contains lunar mass decimeter-sized devoid grains; < arises forward ring. Inside disk's V-H color should not vary b; outside, must become bluer ever smaller probed.