[Prev][Next][Index][Thread]
(meteorobs) NEW TYPE OF COMET TAIL
ISAAC NEWTON GROUP OF TELESCOPES (ING)
Press Release: ING 4/97
Contacts on La Palma: Dr. Gabrielle Cremonese
Padova Astronomical Observatory
Phone: +34-22-405655
Dr. Alan Fitzsimmons
Queen's University Belfast
Phone: +34-22-405655
Dr. Don Pollaco
Isaac Newton Group
Phone: +34-22-405655
EUROPEAN ASTRONOMERS DISCOVER NEW TYPE OF COMET TAIL
Santa Cruz de La Palma, 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.
THE IMAGE
The discovery image can be found at:
http://ing.iac.es/PR/Caption_ING397.html
Pictures of CoCAM camera are available on CoCAM home page:
http://ing.iac.es/HB/CoCAM.html
IMAGE CAPTION
The picture on the left is the discovery image of the sodium tail in Comet
Hale-Bopp taken on the 16th April 1997. The tail appears as a very straight
narrow feature extending from the head of the comet to the upper left. The
picture on the right is an image of Comet Hale-Bopp showing the ion and dust
tails of the comet, taken a few minutes before the discovery of the sodium
tail. The dust tail is the broad tail pointing straight upwards, while the
ion tail is the filamentary structure to the left. Comparison of the two images
shows how the sodium tail has a completely different appearance to the other
tails of the comet.
--------------------
The Isaac Newton Group of Telescopes is run by the United Kingdom's Particle
Physics and Astronomy Research Council (PPARC) and The Netherlands' National
Foundation for Research in Astronomy (NFRA). It consists of the William
Herschel (4.2 m), the Isaac Newton (2.5 m) and the Jacobus Kapteyn (1.0 m)
telescopes, all of them situated on the Roque de Los Muchachos Observatory,
La Palma, Spain.