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Author Chiang, Eugene ♦ Fung, Jeffrey
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ASTROPHYSICS, COSMOLOGY AND ASTRONOMY ♦ CHAIN REACTIONS ♦ CLOUDS ♦ COLLISIONS ♦ COSMIC DUST ♦ DISTANCE ♦ DWARF STARS ♦ LIMIT CYCLE ♦ LORENTZ FORCE ♦ MAGNETIC FIELDS ♦ MASS TRANSFER ♦ PARTURITION ♦ PERIODICITY ♦ PROTOPLANETS ♦ ROTATION ♦ STARS ♦ STELLAR WINDS ♦ VELOCITY
Abstract We explain the fast-moving, ripple-like features in the edge-on debris disk orbiting the young M dwarf AU Mic. The bright features are clouds of submicron dust repelled by the host star’s wind. The clouds are produced by avalanches: radial outflows of dust that gain exponentially more mass as they shatter background disk particles in collisional chain reactions. The avalanches are triggered from a region a few au across—the “avalanche zone”—located on AU Mic’s primary “birth” ring at a true distance of ∼35 au from the star but at a projected distance more than a factor of 10 smaller: the avalanche zone sits directly along the line of sight to the star, on the side of the ring nearest Earth, launching clouds that disk rotation sends wholly to the southeast, as observed. The avalanche zone marks where the primary ring intersects a secondary ring of debris left by the catastrophic disruption of a progenitor up to Varuna in size, less than tens of thousands of years ago. Only where the rings intersect are particle collisions sufficiently violent to spawn the submicron dust needed to seed the avalanches. We show that this picture works quantitatively, reproducing the masses, sizes, and velocities of the observed escaping clouds. The Lorentz force exerted by the wind’s magnetic field, whose polarity reverses periodically according to the stellar magnetic cycle, promises to explain the observed vertical undulations. The timescale between avalanches, about 10 yr, might be set by time variability of the wind mass loss rate or, more speculatively, by some self-regulating limit cycle.
ISSN 0004637X
Educational Use Research
Learning Resource Type Article
Publisher Date 2017-10-10
Publisher Place United States
Journal Astrophysical Journal
Volume Number 848
Issue Number 1


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