Super-Keplerian Motions in the AU Mic Circumstellar Debris System
Abstract
We found enigmatic, few-au-scale features in spatially resolved near-IR scattered light observations of the AU Mic debris disk system obtained with VLT/SPHERE in 2014. We recovered these structures in re-analysis of HST/STIS imagery from 2010/2011, and discovered that they are moving away from the star at super-Keplerian speeds, possibly escaping the system. To-date, these are the only moving features seen in resolved imagery of debris disks. To help diagnose the origin of this phenomenon and in concert with multi-wavelength diagnostics being pursued with other facilities, we propose to use 12 orbits of HST/STIS to re-image the AU Mic scattered light disk from 0.2 (2 au) to 13 (130 au) 8 years after the previous epoch of HST/STIS imagery. HST/STIS provides the only means to trace the motion of structures that have already moved outside the FOV of ground-based extreme-AO imagers, the best means to accurately diagnose the morphological and kinematic evolution of these moving features, and the best means to trace the evolution of small grains in the system. Our optical STIS coronagraphy observations are critically needed to establish the locations and shapes of the blobs, establish their optical fluxes at high photometric fidelity, and therefore enable (IR - optical) colors of disk features to be measured in JWST's cycle-1, using NIRCAM's and MIRI's coronagraphs. These data will constrain the grain size distribution, hence mass, of the moving features and by extension the magnitude of the force that is expelling the features, enabling us to test whether mechanisms like the stellar wind or coronal-mass ejections are responsible for the newly observed phenomenon.
- Publication:
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HST Proposal
- Pub Date:
- August 2017
- Bibcode:
- 2017hst..prop15219W