Dust Grain Dynamics in Debris Discs

Dust Grain Dynamics in Debris Discs

Debris discs are the dusty aftermath of planet formation, and are composed of planetesimal belts containing asteroids and comets that produce dust grains in mutual collisions. Non-gravitational forces acting upon the smallest of these grains can drive them onto eccentric orbits, spreading them far from their point of original production in the planetesimal belt. This thesis focuses on the understanding of the structure and composition of debris discs through observational and dynamical modelling. The initial model explored radiative transfer models that assumed a fixed number density of dust grains at any location in the belt, irrespective of their size, for debris discs surrounding Sunlike stars HD 105211 and HD 48682. This work established a robust set of analytical techniques, including a deconvolution method, that was used to determine dust properties for spatially resolved debris disc systems observed by Herschel. This was followed by the creation of a 1-D collision-less model to ascertain grain location through orbital dynamics driven by radiation pressure and gravitational forces combined with the physical and chemical properties of the grains to predict the continuum emission of the debris disc. This new model compared standard models of density distribution of the grains and radiative transfer codes in the literature by estimating the emission. It found that sub-micron sized grains close to the blowout limit will alter the disc’s emission. The difference was clear at mid-infrared wavelengths where the emission was lower for radiation pressure affected grains. Resultant thermal emission will change according to the disc structure due to non-gravitational forces transporting grains of different sizes along different trajectories.

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