eso9638 — Communiqué de presse photo
Seven Jets in Comet Hale-Bopp
20 septembre 1996
This heavily processed image of C/1995 O1 (Hale-Bopp) is based on a CCD frame that was obtained on August 18, 1996, by Nick Thomas (Max-Planck-Institut fuer Aeronomie, Germany) and Heike Rauer (Observatoire de Paris, France), observing with the DFOSC multi-mode instrument on the Danish 1.54-m telescope at La Silla. The frame was taken at 04:20 UT through an R filter (to show the dust around the cometary nucleus) and the integration time was 20 s.
The subsequent image processing was perfomed by Hermann Boehnhardt (Universitaets-Sternwarte, Munchen, Germany). It involved bias subtraction and flat-fielding, followed by extraction of a subframe centered on the nucleus (the area corresponds to 797 x 797 pixels = 320 x 320 arcsec), logarithmic transformation and finally the application of a Laplace filter with a width of 15 pixels.
This procedure suppresses the smooth structure of the coma and enhances the visibility of the complex, non-symmetrical dust jet structure. No less than seven jets can be clearly seen, emanating from the nucleus. They are caused by the reflected sunlight in dust grains which are emitted from vents on the surface, due to the pressure of outstreaming gas.
At the time of these observations, Comet Hale-Bopp was 2.761 AU from the Earth and 3.392 AU from the Sun. The appearance of the dust jet structures changed very little over a period of 3 nights, suggesting a long rotation period.