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Contacts on La Palma:
Dr. Gabriele Cremonese
Dr. Alan Fitzsimmons
Dr. Don Pollaco
Press Release: ING 4/97
Press Photo ING 3/97
Padova Astronomical Observatory
Phone: +34-22-405655
Queen's University Belfast
Phone: +34-22-405655
Isaac Newton Group
Phone: +34-22-405655
Santa Cruz de La Palma, the 18th of April 1997.- Observations carried
out in the past few days to study the distribution of sodium
atoms in Comet Hale-Bopp have led to the
discovery of a new type
of comet tail. Sodium atoms have previously been seen near the
centers of other comets, but these observations reveal for the first
time in Hale-Bopp a straight tail of sodium atoms 6 degrees long.
The discovery images were taken on the CoCAM wide-field CCD camera, built and operated by staff at the Isaac Newton Group on La Palma, set up next to the 2.5m Isaac Newton Telescope. At the instigation of Gabriele Cremonese of the Padova Astronomical Observatory Italy, a member of the European Comet Hale-Bopp Team, Don Pollacco of the Isaac Newton Group made several exposures of the comet through a narrow filter that isolates emission from sodium atoms.
To their great surprise the astronomers found that these atoms are distributed over an enormous region in and around the comet. Contrary to earlier observations of bright comets near the sun, the sodium was present not only in the region next to the cometary nucleus, there were also large amounts in the region of the cometary tails.
Following a careful analysis of the observed distribution of these atoms, the astronomers concluded that Comet Hale-Bopp displays a third type of tail never seen before and consisting of sodium atoms.
Whereas the well-known ion and dust tails so prominently displayed by Hale-Bopp show a large amount of structure, the new sodium tail has a completely different appearance. It takes the form of an approximately 600,000 km wide and 50 million km long tail, in a direction close but slightly different to that of the ion tail. While the electrically charged particles in the ion tail are accelerated to large velocities by the solar wind (very fast atomic particles emitted by the Sun), there is no obvious explanation at this moment of how the observed sodium tail is formed. Nevertheless, the astronomers in the team believe that the sodium atoms may be released in-situ from very small dust grains or molecules. These particles or molecules are emitted by the cometary nucleus and then transported into the tail at high velocity by at present unknown mechanisms.
The observations of the European Comet Hale-Bopp Team will continue during the next week. In addition to direct imaging of Hale-Bopp in many different spectral regions, they are also carrying out very detailed spectroscopic analyses on the various components of the comet and the motion of individual atoms and molecules.
Information on the European Comet Hale-Bopp Team can be found at http://www.iac.es/Hale-Bopp/hbitp.html.