Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994icar..111..237w&link_type=abstract
Icarus (ISSN 0019-1035), vol. 111, no. 1, p. 237-245
Astronomy and Astrophysics
Astronomy
7
Brightness, Comet Nuclei, Cometary Atmospheres, Comets, Dust, Emission Spectra, Particle Emission, Astronomical Photography, Computer Aided Mapping, Computerized Simulation, Hydrodynamics, Maximum Likelihood Estimates, Particle Size Distribution, Solar Orbits
Scientific paper
Four photographic exposures of the dust coma of Comet Wilson 1987 7 were obtained at heliocentric distances from 3.0 to 2.7 AU preperihelion. Digitally processed using the Ring Masking algorithm, brightness maps revealed a strong asymmetry in dust emission from the nucleus of the comet. Such a phenomenon was reported previously by both visible-light and IR observers (Debi Prasad et al. 1992; Campins et al. 1989) The possibility of reproducing the directional distribution of the dust production rate from the 2-D brightness profile was studied. The method of directional deconvolution based on the maximum likelihood approach was developed. Maps of the directional distribution of dust emission rate are presented. The most striking feature is the occurrence of a large, stable region of enhanced dust production located almost perpendicular to the comet-Sun direction. Its nucleocentric longitude was unchanged during the 1-month observations (October 1986) but the region shifted toward the 'north pole.' The possibilities of forming of such a stable active area located near the nucleus terminator are discussed. Furthermore, such parameters as the dust ejection velocity, the power index of the exponential dust size distribution, and the power index in the exponential dependence of the grain velocity upon the 1 - mu parameter were obtained. The dust ejection velocity (for 1 - mu = 1.0) rose from 0.04 km/sec at 3.0 AU to 0.09 km/sec at 2.7 AU. The dependence of grain ejection velocity upon 1 - mu parameter is described by a power index ranging from 0.17 to 0.32, which is a factor of two less than that predicted by the dusty gas hydrodynamical simulation of the cometary coma.
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