Adaptive Optics Imaging of the AU Microscopii Circumstellar Disk: Evidence for Dynamical Evolution
We present an H-band image of the light scattered from circumstellar dust around the nearby (10 pc) young M star AU Microscopii (AU Mic, GJ 803, HD 197481), obtained with the Keck adaptive optics system. We resolve the disk both vertically and radially, tracing it over 17-60 AU from the star. Our high angular resolution (0.04 or 0.4 AU per resolution element) observations thus offer the opportunity to probe the morphology of the AU Mic debris disk on solar system scales. We identify substructures (dust clumps and gaps) in the disk that may point to the existence of orbiting planets. No planets are seen in our H-band image down to a limiting mass of 1M_J at >20 AU, although the existence of smaller planets cannot be excluded from the current data. Modeling of the disk surface brightness distribution at H band and R band, and of the optical to submillimeter spectral energy distribution, allows us to constrain the disk geometry and the dust grain properties. We confirm the nearly edge-on orientation of the disk inferred from previous observations and deduce that the disk may be clear inward of 1-10 AU. We find evidence for a lack of small grains at <50 AU, either as a result of grain growth or because of destruction by Poynting-Robertson and/or corpuscular drag. A change in the power-law index of the surface brightness profile is observed near 33 AU, similar to a feature known in the profile of the β Pic circumstellar debris disk. By comparing the timescales for interparticle collisions and Poynting-Robertson drag between the two systems, we argue that the breaks are linked to one or both of these processes.
© 2005 American Astronomical Society. Received 2004 September 22. Accepted 2004 December 6. We are grateful to Randy Campbell, Paola Amico, and David Le Mignant for their guidance in using Keck AO, Keith Matthews and Dave Thompson for advice on using NIRC2, and our telescope operator, Madeline Reed, at the Keck II telescope. We also thank the anonymous referee for his/her constructive comments, Scott Kenyon for a critical review of the draft manuscript, and Laird Close, Eugene Chiang, Ruth Murray-Clay, and Peter Plavchan for insightful discussions. This publication has made use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the IPAC/California Institute of Technology, funded by the NASA and the NSF, and of the SIMBAD database, operated at CDS, Strasbourg, France. Finally, the authors wish to extend special thanks to those of Hawaiian ancestry, on whose sacred mountain of Mauna Kea we are privileged to be guests. Without their generous hospitality, none of the observations presented herein would have been possible. J. A. E. acknowledges support from a Michelson Graduate Research Fellowship. S. W. was supported by the German Research Foundation (DFG) through the Emmy Noether grant WO 857/2–1.
Archival Material - 0412143.pdf
Published - Metchev_2005_ApJ_622_451.pdf