Other
Scientific paper
Jul 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007hst..prop11150g&link_type=abstract
HST Proposal ID #11150. Cycle 16
Other
Scientific paper
Debris disk stars host transient dust grains that comprise a collisional cascade with sizes ranging from planetesimals to the sub-micron. In addition to the gravity of the host star and any planets present, these grains are subject to size-dependent non-gravitational forces, e.g., corpuscular drag and radiation pressure. When a steep spectrum of grain sizes prevails, such as the Dohnanyi distribution, scattered light images preferentially trace grains with dimensionless size parameter of order unity. Thus images in scattered starlight provide unique windows on the balance of forces acting on grains at a specific size. Therefore, in an A star system such as beta Pic, the near-IR is dominated by grains close to the blow out size and therefore NICMOS traces dust on hyperbolic orbits. Scattering is fundamentally polarization sensitive, and measurements that record intensity literally see only half the picture. If linear polarization is measured then the elements of the complex scattering matrix can be reconstructed. These matrix elements provide fundamental constraints on the size, composition and structure of the scatterers. Notably, polarimetry can be used to break the degeneracy between scattering asymmetry, g, and the radial dust gradient, which are otherwise covariant in an edge-on disk. Thus, we can use polarimetry to localize the parent bodies in the beta Pic disk. In beta Pic, dust is thought to originate mainly from the sublimation of cometary bodies near periastron. The irradiation of cometary material leads to sublimation and photodissociation of ices forming porous grains consisting of a matrix of refractory material. Such grains have a characteristic scattering signature in polarized light that can be distinguished from compact grains that arise from collisional erosion of asteroidal material.;
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