vendredi 12 septembre 2008

Corona Borealis 3

Alpha Coronae Borealis

Distance (Light Years) 74.7 ± 1.4
Visual Magnitude 2.22
Color (B-V) -0.02

Names For This Star

Other names for this star are Alphekka, Alphacca, Gemma, Gnosia, The Jewel, Gnosia Stella Coronae, or Ashtaroth.
Gemma is Latin, perhaps meaning a bud. This might be connected with the idea of Corona Borealis as a floral crown. Gnosia Stella Coronae is the Latin name applied to the star by the Roman poet Virgil in his Georgics composed in the first century C. E.

Ashtaroth was a middle-eastern goddess, also known as Astarte, who may be equated perhaps with the Greek love goddess Aphrodite. The names Alphecca, Alphekka, or Alphacca derive from the Arabic phrase Al Na`ir al Fakkah meaning "The Bright One of the Dish."

Description of the Star

Alphecca is an eclipsing binary. The brighter star of the pair is a white A0V main sequence star. This spectral type corresponds to an effective temperature of 9900 K. The star diameter must be about 2.5 times the sun's diameter. The star must be 50 times as luminous as the sun with maybe 3 times the mass.
The dimmer companion is a G5V main sequence dwarf having 90% of the sun's diameter, a slightly cooler temperature than the sun - 5500 K, 70% of the solar luminosity, and 90% of the solar mass.

The orbital period of the two stars about their common center of mass is 17.4 days. The apparent magnitude of the two stars dims by about 0.1 magnitude when the smaller star passes in front of the larger one.

Burnham gives the mean separation between the two stars as 17 million miles. Correcting this figure for the distance to the star system measured by Hipparcos Catalogue gives a mean separation of 40 million miles or about 0.4 AU. This is approximately the distance between the sun and planet Mercury.

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