|NGC 6164, NGC 6165 - and the Wolf-Rayet Star HD 148 937 (SAO
|Description of object:
nebula NGC 6164/6165 surrounds the unusual massive (40 sun masses) star HD
148937. It is a very hot multiple star system (triple maybe quadruple). HD
148937 shines about 25.000 times as strong as the sun and rotates very fast. It
could be a Wolf-Rayet-Star which is about to
transition to a new development phase. The nebula itself consists of gas masses
which HD 148937 emitted during an eruptive phase. Now they are excited to emit
light because of the stars strong UV radiation. In the high-resolution
one can see a second further-out nebula shell towards the left edge of the
image, which might have been created by a prior active phase of the star. The
age of the brighter part of the nebula is estimated to be ca. 200.000
The distance to NGC 6164/6165 is 4200 light years. With an
apparent diameter of 3 x 6 arc minutes in the sky, the nebula extends to an
area of 4.2 light years in space. The two brightest nebula areas, lying
symmetrical to its central star, both received a separate NGC number
â so that the nebula now has this double identifier. The
image field of the linked
resolution picture corresponds to about the size of the half-moon area.
Wolf-Rayet-Stars are stars with a spectrum only containing
bright emission lines instead of the usual dark absorption lines. All lines are
very broad. They were discovered by the French astronomer Ch. Wolf and G. Rayet
in 1867. They are very rare stars. Wolf-Rayet stars are subdivided in two main
classes: the WN type mainly showing nitrogen lines and the WC type mainly
showing carbon lines. Many Wolf-Rayet stars are attached to big gas nebulas.
Some central stars of planetary nebulas are Wolf-Rayet stars, too
â like NGC 40 for example.
6164/65 is located in a quite colorful region within the constellation Norma.
The picture shows a mosaic of two fields. On the left side of the picture is
NGC 6193, a very compact open star cluster. Right of the vertical shock front
(NGC 6188) is an active star birth region. NGC 6164/65 is in the right upper
corner of the mosaic.
The picture was also taken at Rooisand in 2009.
The telescope used was a 6" APQ Refractor with AP Reducer at 900mm focal
the big picture (2000 x 1200 pixel). More information about the picture
The surface temperatures
are between 25.000 and 50.000 Kelvin, their masses are between 10 and 50 sun
masses and their luminosity is between 100.000 times and million times stronger
than our sun. The high temperature creates high radiation pressure leading to
strong stellar wind which causes a strong mass loss. It is estimated to be
about 3 sun masses per one million years on average (up to 1 sun mass per a few
thousand years in an extreme case). That is way Wolf-Rayet stars are often
times connected to nebulas. They are very young stars and their life expectancy
cannot be very long because of the strong mass loss â some
ten millions of years at max.
The Wolf-Rayet star HD 148 937 might
be at the transition from a WR-star to a new development phase; some stars in
IC 2984 (Carina) and in NGC 3606 (Carina) are Wolf-Rayet stars. The most famous
examples for observers at the northern hemisphere are NGC 6888 (Crescent
nebula) and NGC 2359 (Thors Helmet) in the constellation Canis Majoris. There
are just nearly 200 stars know overall and 23 of them are