16263

Two new comma potentially causally correlated comma observational phenomena have recently been discovered in spatially resolved imagery of debris disksdoublePoint outward moving features traveling at super-Keplerian velocities and changes in the color of the AU Mic debris disk. To date comma these are the only moving structures and the only observed color change seen in spatially resolved debris disks. We propose to use the only observational facility capable of yielding high fidelity optical coronagraphic spectroscopy of AU Mic.s disk comma HST-STIS comma to obtain second epoch G750L and first epoch G430L spectroscopy. These data will enable us todoublePoint a) quantify color changes in the disk over a 2x greater time baseline (16 yrs) than previously achieved b) determine whether the disk.s color between 30-45 au continues to change as additional fast moving features pass by c) better quantify the size of dust grains whose spatial distribution has changed and d) confirm and better quantify whether small grains populate small (10-30 au) stellocentric distances. Derived grain size distributions will be linked to dynamical models proposed for the origin of fast moving features in this system.