Nuclear dust emission pattern of comet Wilson 1987 VII
Waclaw Waniak
Astronomical Observatory, Jagiellonian University, ul. Orla
171, Krakow, Poland
Four photographic exposures of the dust coma of comet Wilson 1987
VII obtained at heliocentric distances from 3.0 to 2.7 AU preperihelion
were digitally processed using the Ring Masking algorithm. Brightness
profiles revealed a strong asymmetry in dust emission from the
nucleus of the comet. The possibility of reproducing the directional
distribution of the dust production rate from the 2-D brightness
profile was studied and the method of directional deconvolution
basing 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 one-month observations but the region shifted towards
the "North Pole". The possibilities of forming of such
a stable active area 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 / s at 3.0 AU to 0.09 km / s at 2.7
AU. The power index in the dust size distribution was close to
3, which is in good agreement with the results of dust tail analysis
by Cremonese and Fulle (1990). 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.