Scattered disk objects

Figure 2.11 The HH-30 object, a young stellar object showing two thin jets flowing out from the central region of an accretion disk. The outflow velocity in the jets is 90-270 km s-1. The two bowl-shaped regions are starlight scattered by the dust in the uppermost layers of the disk. The dark lane in between is the accretion disk seen side-on. The radial optical depth in the disk is too high for starlight to penetrate in this direction. The radial extension of the disk is 425 AU. (Photo credit Hubble Space Telescope, NASA/ESA and STScI.)...

In Section 5.2.2 it was shown that at large q the intensity I(q) of scattering from a sphere decays as q A, from a thin disk as q 2, and from a thin rod as q l. The power-law exponent at large q is therefore seen to be related to the dimensionality of the scattering object. There are, however, many cases in which the intensity varies as an unexpected or even fractional power of q. In the case of a Gaussian model of a polymer chain, the intensity was seen to decrease as q 2 even though a chain obviously is a three-dimensional object. The inverse power-law exponents that differ from 1, 2, or 4 can be explained in terms of the concept of a fractal. 

In the case of a sphere, there is only one volume parameter the radius, R. But what about shapes that have more dimensions, such as a rod, disk, or parallelepiped In these cases, simple analysis can show that R is related to all the physical dimensions of the scattering object. For example, for a cylindrical rod of length L and... 

Echoes from the Moon, Mercury, Venus, and Mars are characterized by sharply peaked OC echo spectra (Fig. 11), Although these objects are collectively referred to as quasispecular radar targets, their echoes also contain a diffusely scattered component and have full-disk circular polarization ratios averaging about 0.07 for the Moon, Mercury, and Venus, but ranging from 0.1 to 0.4 for Mars, as discussed below. 

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