jeudi 4 septembre 2008

Auriga 4

Alpha Aurigae

Distance (Light Years) 42.2 ± 0.5
Visual Magnitude 0.08
Color (B-V) 0.8

Names For This Star

The name Capella is Latin and means "The Little She-goat."
The star is also known as Alhajoth, an Arabicization of the Greek name of the nymph Aige, who in some versions of the myths of Zeus, is named as one of the nursemaids who tended the infant god on the island of Crete, where he was being hidden from the threat of his monstrous Titan father, Cronos.

Description of the Star

Burnham describes Capella as the sixth brightest star in the sky, and the nearest star to the pole of the stars that are first magnitude or brighter.
A Pair of Giants

Capella is a quadruple system consisting of two giants and two dwarves. The A and B components are a close binary consisting of a yellow G5IIIe giant having 7.2 times the diameter of the sun 2.67 times the mass and a yellow G0III giant having 5.6 times the diameter of the sun and 2.55 times the mass.
The two stars individually have 80 and 50 times the luminosity of the sun. The data of the The Bright Star Catalog seem to indicate that the G5 star is the brighter of the pair.

The spectral types imply temperatures near that of the sun, 5600 K for the G0 star and 5000 K for the G5.

The two stars are separated by about 65 million miles and revolve with a period of 104 days.

The Red Dwarves

The remaining pair of stars in the system are two red dwarves of spectral type M1 and M5 designated as Capella H. These stars appear at Visual Magnitude 10.0 and 13.7 respectively. The separation between the stars is 2 sec of arc, corresponding to a projected distance of 26 A.
The pair of dwarves appear separated from the AB pair by 12 minutes of arc, a projected distance of at least 0.17 ly.

The dwarves are small stars having approximately 40% and 10% of the mass of the sun respectively with 60% and 30% of the sun's diameter. The stars have respective luminosities of about 1.4% of the sun and 0.05%.

Beta Aurigae

Distance (Light Years) 82.1 ± 1.6
Visual Magnitude 1.9
Color (B-V) 0.03

Names For This Star

This star is also known as Menkalina. The star name derives from the Arabic name Al Mankib dhi'l Inan, "The Shoulder of the One Who Holds the Reins," that is, "The Shoulder of the Charioteer."
Description of the Star

The Menkalinan spectrum is characteristic of a white A2IV subgiant star.
Menkalinan is actually a multiple star system. According to Burnham the A and B components are almost identical in size and spectrum and revolve with a period of 3.96 days. The orbit appears almost edge-on to the earth. So one of the two stars eclipses the other twice each revolution.

During an eclipse, about 25% of the diameter of one star is covered by the other, and the brightness of the pair of stars decreases by about 0.09 magnitudes.

According to Burnham, the diameter of each star is about 2.6 times that of the sun. One star is about 2.35 times as massive as the sun, while the other star contains about 2.25 solar masses.

There is a third component to the system, Menkalinan C, of Visual Magnitude 14.1. The C component is separated from A and B by 13 sec of arc which corresponds to a projected distance of 330 AU or more than 8 times the radius of the solar system out to Pluto.

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