Alexander KRIVOV : University of Jena, Germany

TWO SCENARIOS OF STRUCTURE FORMATION

Alexander Krivov (1), Martina Queck (1), Torsten Loehne (1), and Miodrag Sremcevic (2)

(1) Astrophysical Institute und University Observatory Friedrich Schiller University Jena Schillergaesschen 2-3, 07745 Jena, Germany

(2) LASP, University of Colorado, Boulder, USA

Substructure observed in some debris disks, exemplified by epsilon Eridani, is usually attributed to the presence of planet(s) that may capture dust particles in exterior mean-motion resonances, resulting in formation of "clumps". In this scenario, the Poynting-Robertson (P-R) force is responsible for the dust delivery from outer regions of the disk to resonance locations. However, both P-R timescale and timescale of resonant feature development are much longer than that of catastrophic grain-grain collisions, even at moderate optical depths, casting doubt on the conventional scenario. Alternatively, Wyatt (2003, 2006) proposed that the observed features may stem from clumps of planetesimals which have been captured in resonances with the planet, such as Plutinos and Trojans in the solar system. A large fraction of dust produced by these bodies would stay locked in the same resonance, creating the observed structures. We constructing simple analytic models for both scenarios to compare their efficiency in different systems. In particular, we show that the first scenario works well for low optical depths, and is somewhat more efficient for more luminous/massive stars and close-in planets. For higher optical depths, the second scenario is more efficient. A planetesimal family with a total mass of ~ 0.01 to 0.1 Earth masses appears to be sufficient to account for the observed clumps. Like the first scenario, the second one is more efficient for smaller orbital radii of the planet, but here a lower stellar luminosity is preferable. Besides, it is more sensitive to the planet mass than the first one.