C/1995 O1 (Hale-Bopp)
the 'Porcupine' Structure
of August 1996
|Field of View:||7.2' x 4.7'
||Receiver:||576 x 387 CCD
||Filter:||RX (red continuum)
Pik Terskol, Caucasus
||Observer:||T. Credner, K. Jockers
In 1996 the appearance of Comet Hale-Bopps shape was dominated
by the so called 'porcupine' structure. These jetlike features
in the dust tail remained very stable for months until about
November 96 and then changed more and more to the
shell like structures of spring 1997.
One scientific explanation of this 'porcupine' and the change to
the shell structure is the following:
On the cometary surface are active spots which shoot out collimated
beams of gas and dust. Due to the rotation of the nucleus, the
ejected material is distributed on a spiral that is lying on
a cone surface in space. If we see the nucleus rotation axis
edge on, we also see this cone edge on with brighter edges, that
are our 'porcupine' spikes above.
In 1997 the perspective changed more to a view ontop of the
rotation axis. So the cones vanished and due to the closer
geocentric distance the spiral structure could be resolved.
R-scaling is a very useful and easy processing for cometary
dust images to show the bright inner and the faint outer structures
simultaneously. Each pixel intensity is multiplied with
the radial distance r to the nucleus.
The idea is the following:
If you have an idealized sphere of expanding dust, then the
density and intensity drops with 1/r2. In the
two-dimensional projection, as in images, this becomes
a 1/r decrease of intensity. This can be used as
the most simple model for the radial dependence of the
dust distribution and removed by the R-scaling.
Some more informations can be found on the special project page of the
Max-Planck-Institut für Aeronomie.
© Copyright by the observers
Max-Planck-Institut für Aeronomie