Intensity ImageAt right is a normal intensity
image of the comet at K. Note how the
combination of the jet activity and the rotation of the comet creates a clear
'sprinkler hose' pattern on the side of the nucleus facing the Sun (SW). If you
look carefully, you will see three jet arcs, each one rotation of the nucleus
apart from the other. Also note that the jet is not a very high contrast
feature in the intensity image, sticking up only 20-30% above the underlying
continuum of the coma. |
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Edge FilteredThis is the same image run
through a Sobel edge filter. The filter just
takes the derivative of the image and is brightest where the slope in the
intensity is greatest. The bright arcs to the SW are at the leading edges of
the jets. |
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Percent PolarizationHere is the percent
polarization image. The brightest spots in the
second jet arc are about 11% at 2.2 microns. The darkest areas to the NW are
about 7%. The polarization for the whole comet and the nucles is about 9.5%. If
all of the grains in the coma were the same everywhere, then the polarization
would be the same everywhere as well. The clear presence of the jet in the
polarization image indicates that the grain population in the jet material is
different is some ways than the general grain population lifting off of the
nucleus. Most likely the grains in the jet are significantly smaller than the
grains in the rest of the coma. |
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Polarization vs. PhaseNormally, the
polarization characterisitcs of comets as a function of
phase (scattering) angle are similar to asteroids. They show a 'negative'
branch (polarization in the plane of scattering) at small phase angles. In
asteroids, this is interpreted as due to a rough surface. In comets this is
usually attributed to large fluffy aggregates of small grains. At 2.2 microns,
Hale-Bopp shows a polarization that lies somewhat in between the normal
behavior of comets in the visual and pure Rayleigh scattering. This is probably
due either to 1) a smaller grain population size in Hale-Bopp than in most
comets 2) the effects of observing at a much longer wavelength where the fluffy
aggregates are begining to become comparable to the wavelength or 3) a
combination of the two. |
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