vendredi 19 septembre 2008

Canis Major 3

Epsilon Canis Majoris

Distance (Light Years) 431 ± 32
Visual Magnitude 1.5
Color (B-V) -0.21

Names For This Star

The name of this star may also be written as "Adara".
The name comes from the Arabic. The Arabs designated four stars Epsilon, Delta, Eta, and Omicron Canis Majoris as Al `Adhara, meaning The Virgins. In modern astronomy the Arabic phrase has been abbreviated to "Adhara" (or "Adara") and applied to the Epsilon star only.

Description of the Star

Adhara is a blue B2II bright giant approximately 11 times the diameter of the sun.
Burnham gives the luminosity as 9000 times that of the sun. According to Burnham there is an eighth magnitude companion. At the distance of Adhara, the companion would lie at least 1000 AU away from the primary, but no change in the relative position of the two stars has been observed in more than a century.

Burnham lists Adhara as the twenty-second brightest star in the sky.

Eta Canis Majoris

Distance (Light Years) 3200 ± 1800
Visual Magnitude 2.45
Color (B-V) -0.08

Names For This Star

The name Aludra is derived from the Arabic Al 'Adhra the singular form of Al 'Adhara, "The Virgins." See Adhara.
Description of the Star

Aludra is a blue B5Ia supergiant star. The diameter of the star is very approximately 100 times the solar diameter. The luminosity would be on the order of 100,000 times that of the sun.
An A0V companion appears at a separation of 169 arc seconds, but according to Burnham the companion is probably not physically associated with the star.

Beta Canis Majoris

Distance (Light Years) 500 ± 50
Visual Magnitude 1.98
Color (B-V) -0.23

Names For This Star

Other names for this star ar Murzim or Mirza. The names derive from the Arabic name Al Murzim, "The Announcer."
The name may refer to the fact that Mirzam is situated to the east of Sirius, which is the brightest star of the nighttime sky. Thus Mirzam rises before that star. So the rising of Mirzam prefigures or announces the rising of Sirius

Description of the Star

Mirzam is a hot, blue B1II-III subgiant or giant star having about 8 times the diameter of the sun and 3200 times the luminosity.
Beta Canis Majoris is the prototype star for a certain class of oscillating, variable stars characterized by a multiplicity of periods. Burnham says that there is relation between period and luminosity as with the better known Cepheid variables.

The principle period of oscillation for Mirzam is about 6 hours.

Alpha Canis Majoris

Distance (Light Years) 8.60 ± 0.04
Visual Magnitude -1.44
Color (B-V) 0

Names For This Star

Sirius comes from the Greek. According to Allen the etymology and meaning of the name is uncertain. Sirius is also called the Dog Star by virtue of the name of the constellation in which it lies.
Other names for Sirius are Canicula - which is Latin and means "The Little Dog" - and Aschere which derives from the Arabic Al Shira or Al Sira. The Arabic name is again of uncertain derivation and meaning; it may be related to the Greek name Sirius for the star.

Description of the Star

Sirius is a white A1Vm main sequence star having 22 times the luminosity of the sun and 1.6 times the sun's diameter. The spectral type implies an effective temperature of 9600 K and a mass about twice that of the sun.
Sirius is one of the nearest stars. See this German site for a nice three-dimensional representation of our nearby neighbor stars.

Sirius B or The Pup

Sirius is a double star. The companion, Sirius B, is also known as "The Pup," since it is the companion to the The Dog Star. Sirius B has a Visual Magnitude of 8.49, corresponding to a luminosity 1/400 times that of the sun.
Sirius B reveals with a 50 year period in an orbit with a separation of about 20 AU between the two stars. This distance is approximate the same as the distance between the sun and Uranus.

According to Burnham the dynamics of the orbit indicates that the mass of the A star is 2.35 times the mass of the sun, while the B star has 98% of the mass of the sun.

A White Dwarf Star

According to the The Bright Star Catalog Sirius B has an effective temperature of about 32,000 K making it much hotter than the sun so that the star emits about 900 times more radiant energy per square meter of surface than the sun does. The very small luminosity of the star then must mean that the star has a very small surface area, that is, that the star is quite small in size. This type of star is known as a white dwarf.
Sirius B must be a star having almost the mass of the sun packed into a volume smaller than that of the earth. The density of Sirius B must correspond to about 5000 tons per cubic inch.

A white dwarf star like Sirius B is a stellar corpse that is very slowly cooling by the radiation of heat.

More on white dwarf stars.

Delta Canis Majoris

Distance (Light Years) 1790 ± 550
Visual Magnitude 1.83
Color (B-V) 0.68

Names For This Star

Other names for this star are Alwazn, Wesen, or Al Wazor.
These names derive from the Arabic name Al Wazn, "The Weight."

Description of the Star

Wezen is a yellowish F8Ia supergiant having a luminosity of almost 50,000 times that of the sun and about 200 times the sun's diameter.

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