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NGC 2359, "Thors Helmet" -a Wolf Rayet nebulae in the
constellation Canis Major |
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Short object description:NGC 2359 and Haffner 6
NGC 2359, also called "Thor's helmet"
because of its outer shape, is an emission nebula in the constellation of Canis
Major. It surrounds a massive and with 50.000 degrees Celsius very hot Wolf
Rayet star with the designation HD 56925 or WR 7. The star with a brightness of
11.5 magnitude is located a bit west (right in the image) of the center of the
bubble. NGC 2359 is located at a distance of about 15,000 light years from the
solar system, the central bubble has a diameter of about 20 light
years.
Wolf Rayet stars are typically characterized by the repulsion of
large amounts of material as so-called violent "stellar winds". The often
episodic loss of mass is enormous and when the wind encounters the general
interstellar matter in the star's surroundings, a fibre structure is formed -
similar to a supernova. The initial masses of young WR stars are between 10 and
250 solar masses. |
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In
later stages WR stars are the exposed cores of formerly massive stars. They are
not assigned to any of the usual spectral classes, but are classified in a
separate type. Another nebula with WR star in the southern night sky is the
bipolar nebula
NGC 6164/65 in the constellation Norma.
NGC 2359 was
discovered by William Herschel on January 31, 1785 and in 1877 a brighter
section was catalogued by Wilhelm Tempel as NGC 2361.
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comparison to the size of the moon. |
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Haffner 6
Besides the classic star clusters from the Messier,
NGC or IC catalogues, there are also special, mostly unknown catalogues like
Berkeley, Stock and also Haffner. The star clusters of these catalogs have
mostly been catalogued on the basis of photo plate surveys. Hans Haffner (1912
- 1977) was an astronomer at the Hamburg-Bergedorf observatory in the
mid-1950s, his catalogue contains 27 objects.
Haffner 6 is strongly concentrated and has a diameter
of approx. 5 arc minutes. The brightest stars have the 16th magnitude class,
the cluster is classified by Trumpler as type IV 2 r
n. The age of the star cluster is approximately 800 million years.
Berkeley
36
Berkeley 36 is an
open star cluster with an apparent diameter of 5 arc minutes. It consists of
about 40 stars with the brightest stars having only 17th magnitude. Its
distance to the solar system is given as 20 000 lightyears.
The Berkeley
catalogue includes 104 open star clusters, 88 of which were first discovered
and observed on photographic plates by astronomers from the "University of
California at Berkeley".
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