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RCW 71 and the red carbon star RX
Crux |
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Description of object:
There is little information about RCW
71 - also cataloged as Gum 46 or GN
12.47.3 - because it is a little-known DeepSky object. It is a small,
with an apparent diameter of only 3 arcminutes, H-II region in the Southern
Cross constellation (located just south of NGC 4755, Herschel's jewel box). RCW
71, with coordinates (J 2000) RA: 12 h 50m 22s and -61 degrees 35 minutes and
00 seconds, lies directly in the Coal Sack, the large dark cloud between the
constellations Southern Cross (Crux), Centaur (Centaurus) surrounding it, and
the Fly (Musca).
The star ionizing the H-II region at the center of RCW
71 is HD 311 999 with spectral class O9.5V. It is the brightest star of a small
cluster [DBS 2003] 80 whose stars emit light mainly in the infrared spectrum.
However, HD 311 999 is clearly visible in our image as the brightest
star.
The distance of RCW 71 is given between 2000 and 2800 pc (1 pc =
3.26 light-years), which corresponds to 6500 to 9000 light-years, depending on
scientific investigations. Since the distance of the dark cloud Coal Sack is
only about 500 to 600 light years, RCW 71 stands much farther away and we are
thus looking through a transparent region of the large dark cloud of Coal
Sack.
The RCW catalog (Rodgers,
Cambell, and Whiteoak) is an extension of the Gum catalog of H-II
regions of the southern starry sky. More information about the catalogs
here. |
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Further information and links to RCW 71
can be found here. More
information about the star cluster in the center of RCW 71 [DBS 2003] 80
here.
« The annotated image shows the size comparison with the
moon
Furthermore our image
shows one of the rare red carbon stars, RX
Crux with the B-V color index of 4.5 magnitudes and spectral class
K. Carbon stars are very old giant stars, similar to red giant stars like
Antares in the constellation Scorpio or Betelgeuse in Orion. Carbon stars
contain in contrast to the "normal" red giant stars more carbon than oxygen.
The carbon forms different carbon molecules in the outer, cool layers
of the star, which absorb blue and yellow light and this causes the star to
appear in deep red color to the observer. |
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Carbon stars
are divided into 5 classes and like many giant red stars are variable. RX Crux
is irregularly variable with a period of one magnitude. More information about
carbon stars
can be
found here. |
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All Images und all Content are ©
by Franz Hofmann + Wolfgang Paech |