vendredi 19 septembre 2008

Hercules 6

Beta Herculis (Beta Her / β Herculis / β Her), which also has the name Kornephoros, is the brightest star in the constellation of Hercules. It has an apparent visual magnitude which varies between 2.76 and 2.81.
Although β Herculis appears to the naked eye to be a single star, W. W. Campbell discovered in July 1899 from spectroscopic measurements that its radial velocity towards the Sun varies, and concluded that it is a binary system of two stars. An orbit for the binary was computed in 1908 from additional spectroscopic measurements.
At Palomar Observatory, Antoine Labeyrie and others used speckle interferometry with the Hale Telescope to resolve the system in 1977. The Hipparcos satellite observed the orbital motion of the primary relative to other stars, and an orbit was computed in 2005 using spectroscopic data together with these measurements. The period of the system is around 410 days. β Herculis has the names Kornephoros, a Greek word meaning "club bearer", and Rutilicus, a corruption of the Latin word titillicus, meaning "armpit".
Zeta Herculis (ζ Her, ζ Herculis) is a binary star system in the constellation Hercules. The primary star is a sub-giant that is somewhat larger than the Sun and has just begun to evolve away from the main sequence. It is orbited by a smaller and fainter star that is separated from the primary by just over 1 arcsec. The stars orbit each other with a period of 34.5 years and a semi-major axis of 1.36". Stars A & B are separated each other by an average separation of 14.65 AUs and swing as close as 8 AUs and as far away as 21.3 AUs.
This system forms part of the Zeta Herculis moving group of stars. This group includes: δ Trianguli, φ2 Pavonis, ζ Reticuli, 1 Hydrae, Gl 456, Gl 678, and Gl 9079.
Delta Herculis (δ Her / δ Herculis) is a star in the constellation Hercules. It also has the traditional name Sarin.
Alpha Herculis (α Her / α Herculis) is a multiple star in the constellation Hercules. It also has the traditional name Ras Algethi or Rasalgethi (Arabic: رأس الجاثي ra's al-jaθiyy Head of the Kneeler), and the Flamsteed designation 64 Herculis.
When viewed through a telescope, this system is resolved into two components designated α1 and α2. These two components are more than 500 astronomical units apart, with an estimated orbital period of approximately 3600 years. α1 is a relatively massive red bright giant. α2 is actually a double star system with a primary yellow giant star and a secondary, yellow-white dwarf star. (These components are sometimes designated α Herculis A, Ba and Bb, respectively.)
The angular diameter of the red giant α1 has been measured with an interferometer as 34 ± 0.8 milli-arcseconds, or 0.034 arcseconds. At an estimated distance of 120 parsecs, this corresponds to a radius of about 300 million kilometers (or 188 million miles), or 400 times the size of the Sun. It has a total of about 14 solar masses, and has emitted a sparse, gaseous envelope that extends at least 90 astronomical units.
The star is located at the bottom of the constellation. The traditional name "Head" comes from the fact that in the antiquity Hercules was depicted upside down on the constellation maps.
Mu Herculis is a nearest star system about 27.4 light years from Earth in the constellation Hercules. Its main star, Mu Herculis A (possibly a binary) is fairly similar to the Sun although more highly evolved. Its mass is about 1.1 times that of the Sun, and it is beginning to expand to become a giant. Mu Herculis A and the binary itself pair B-C are separated by 286 AUs. On the other hand stars B-C are separated by 11.4 AUs. Their orbit is quite elliptic (e=0.18) and both stars swing each other between 9.4 and 13.5 AUs.
Xi Herculis is a star located within the constellation of Hercules. Its Declination is 29° 15', Right Ascension is 17h 58m, and Magnitude is 3.7. Xi Herculis is about 160 light-years from Earth. Baraka

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