Author:

Keywords:

circumstellar matter, stars: individual (AU Mic), Science & Technology, Physical Sciences, Astronomy & Astrophysics, PICTORIS MOVING GROUP, LOW-MASS STARS, SPITZER-SPACE-TELESCOPE, CIRCLE-DOT STARS, CIRCUMSTELLAR DISK, DUST DISK, COLLISIONAL CASCADES, SCORPIUS-CENTAURUS, PLANET FORMATION, SUPER-EARTHS, astro-ph.SR, 0201 Astronomical and Space Sciences, 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics, 0306 Physical Chemistry (incl. Structural), 5101 Astronomical sciences, 5107 Particle and high energy physics, 5109 Space sciences

Abstract:

We present far-infrared and submillimeter maps from the Herschel Space Observatory and the James Clerk Maxwell Telescope of the debris disk host star AU Microscopii. Disk emission is detected at 70, 160, 250, 350, 450, 500, and 850 μm. The disk is resolved at 70, 160, and 450 μm. In addition to the planetesimal belt, we detect thermal emission from AU Mic’s halo for the first time. In contrast to the scattered light images, no asymmetries are evident in the disk. The fractional luminosity of the disk is 3.9× {10}-4 and its milimeter-grain dust mass is 0.01 {M}\oplus (±20%). We create a simple spatial model that reconciles the disk spectral energy distribution as a blackbody of 53 ± 2 K (a composite of 39 and 50 K components) and the presence of small (non-blackbody) grains which populate the extended halo. The best-fit model is consistent with the “birth ring” model explored in earlier works, i.e., an edge-on dust belt extending from 8.8 to 40 AU, but with an additional halo component with an {r}-1.5 surface density profile extending to the limits of sensitivity (140 AU). We confirm that AU Mic does not exert enough radiation force to blow out grains. For stellar mass-loss rates of 10-100 times solar, compact (zero porosity) grains can only be removed if they are very small; consistently with previous work, if the porosity is 0.9, then grains approaching 0.1 μm can be removed via corpuscular forces (i.e., the stellar wind).