Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0817c&link_type=abstract
American Astronomical Society, DPS meeting #28, #08.17; Bulletin of the American Astronomical Society, Vol. 28, p.1086
Astronomy and Astrophysics
Astronomy
1
Scientific paper
The structure of a CNC formed by dusty ice sublimation from a nucleus is computed using a multifluid dusty gasdynamic model with parameters adjusted to fit existing P/Wirtanen observations. Four alternative assumptions are made: 1. a spherical and homogeneous; nucleus; 2. a spherical nucleus, but with several active areas separated by a weak background; 3. a homogeneous, but aspherical nucleus with the shape of a `weakly concave bean'; 4. a homogeneous nucleus with the shape of a `markedly concave bean'. In all four cases, it is observed that: 1. Most of the sunward CNC is in fluid regime out to about 2.5 AU. 2. A large mass range of dust grains can be ejected by gas drag up to 3 AU at least. 3. The ejection velocities are strongly dependent upon position on the nucleus and heliocentric distance. Except in the highly peculiar and non-representative case of the spherical homogeneous nucleus, the following properties are observed: 1. the gas and dust do not always flow vertically upwards; 2. their density does not always decrease radially outwards near to the surface; 3. their velocity is not a function of distance to the surface only, but depends effectively upon the three spatial coordinates; 4. the vicinity of the surface is subdivided into regions of subsonic gas flow, and regions of supersonic gas flow, by standing shock structures; the geometry of these shocks cannot be guessed intuitively, but must be discovered by tridimensional shock-capturing gasdynamic modelling; 5. to the regions of shocked gas with enhanced density correspond narrow regions of enhanced dust density; 6. owing to projection effects, these dust structures will appear on images as dust pseudo-jets; 7. The gas inhomogeneities tend to be smoothed-out with increasing distance to the surface, whereas, due to the fast uncoupling between gas and dust, the dust `pseudo jets' are preserved far out in the coma; 8. during a modest (<= 45(0) ) rotation of the nucleus, the gas shocks and dust pseudo-jets appear to approximately co-rotate (with distortion), whereas the bulk of the CNC appears approximately fixed (but also with distortion) in a plane defined by the comet-to-Sun axis and the normal to the orbital plane.
Crifo Jean-François
Rodionov Alexander V.
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