vendredi 12 septembre 2008

Corona Borealis 6

Alpha Coronae Borealis (α CrB / α Coronae Borealis) is a binary star in the constellation Corona Borealis. It also has the traditional names Gemma or Alphekka or Alphecca.
α CrB is an eclipsing binary system similar to Algol (β Per). Its period is 17.36 days, with magnitude varying from +2.21 to +2.32, which is hardly noticeable to the unaided eye.
α CrB is believed to be a stream star member of the Ursa Major Moving Group.
A large disc of dust and material has been shown to exist around Alphecca, prompting speculation of a similar planetary/proto-planetary system to that currently assumed around Vega. How the binary-star dynamic would affect such a system is the subject of intense debate.
The name Gemma is Latin for "jewel". The other traditional name comes from Arabic al-fakkah, "the broken" (ring of stars), from فكّ fakk "unsealed"). الفكه

النسقانBeta Coronae Borealis (Beta CrB / β Coronae Borealis / β CrB), which also has the traditional name Nusakan, is the second brightest star in the constellation of Corona Borealis. Although it appears to the naked eye to be a single star, it is actually a binary system of two stars. It is approximately 114 light-years away and has an apparent visual magnitude which varies between 3.65 and 3.72.
β Coronae Borealis was first announced to be a binary star in 1907, based on spectroscopic observations at Lick Observatory;[9] J. B. Cannon published an orbit in 1914, finding a period of 40.9 days. Later spectroscopic investigations by F. J. Neubauer at Lick, published in 1944, found a period of 10.5 years, with no evidence for the 41-day periodicity. Antoine Labeyrie and his coworkers resolved the pair by speckle interferometry in 1973 and found that the two stars were separated by about 0.25 arcseconds; this work was published in 1974. The pair was also observed visually by Coteau in 1973. A number of orbits were subsequently published using visual and speckle-interferometric observations, both alone and in conjunction with spectroscopic data. In 1999, Söderhjelm published an orbit using speckle-interferometric data together with Hipparcos observations.
Neubauer's 1944 work found a small variation in the radial velocity of β Coronae Borealis with a periodicity of 320 days, suggesting the presence of a third, lighter, body in the system. A 1999 study of the system by long-baseline infrared interferometry performed at Palomar Observatory found no evidence for this, and showed that any tertiary companion with this period must have mass 10 Jupiter masses or below. This study also found very weak evidence for the presence of a companion with a shorter, 21-day, period, but the data was insufficient to draw a positive conclusion.

κ CrB یک سیاره دارد

η CrB ستاره دوتایی

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