A resolved millimeter emission belt in the AU mic debris disk

Abstract

Imaging debris disks at millimeter wavelengths is important, because emission at these long wavelengths is dominated by large grains with dynamics similar to the population of dust-producing planetesimals. We have used the SMA and ALMA to make 1.3 millimeter observations of the debris disk surrounding the nearby (9.9 pc), ~10 Myr-old, M-type flare star AU Microscopii. We characterize the disk by implementing Markov Chain Monte Carlo methods to fit parametric models to the visibilities. The millimeter observations reveal a belt of dust emission that peaks at a radius of 40 AU. This outer size scale agrees with predictions for a reservoir of planetesimals (a "birth ring") based on the shape of the midplane scattered light profile. We do not find any significant asymmetries in the structure or the centroid position of the emission belt. The ALMA observations with a resolution of 0.6 arcsec (6 AU) also reveal a previously unknown central emission peak, ~6 times brighter than the stellar photosphere at these wavelengths. This central component remains unresolved and could be explained by stellar activity or an inner planetesimal belt located ≲ 3 AU from the star and containing roughly 1% the mass of the outer belt. Future observations with higher angular resolution will be able to distinguish between these possibilities. Copyright © 2013, International Astronomical Union.