jeudi 18 septembre 2008

Eridanus 3

Theta1 Eridani

Distance (Light Years) 161 ± 4
Visual Magnitude 2.88(Combined)
Constellation Eridanus
Color (B-V) 0.14

Names For This Star

According to Allen, this star, Theta Eridani, was originally recognized as the end of the River Eridanus and therefore bore the name Achernar. This name now applies to Alpha Eridani instead.
According to Allen, the first usage of the name "Acamar" for this star was in the Alfonsine Tables published in Spain in 1252 under the patronage of King Alfonso X of Leon and Castile. However, Allen gives no information about the origin of the name.

Description of the Star

Acamar is a binary star system. The primary, Acamar A, is an A4III normal giant. This star is much hotter than the sun and white in color. Even though the smaller star is technically a dwarf, both stars are larger in mass and radius than our sun.

The smaller star is about one magnitude dimmer than the larger star and lies about 8.31 arc seconds away from it. At the distance of the star system from the earth, this separation corresponds to more than 5 times the diameter of the solar system out to Pluto.
According to Burnham a very slow orbital motion has been observed for the companion relative to the primay. This is consistent with the large separation between the stars.

Alpha Eridani

Distance (Light Years) 144 ± 4
Visual Magnitude 0.45
Color (B-V) -0.16

Names For This Star

The name "Achernar" from the Arabic name for this star: Al Ahir al Nahr, which means "the End of the River". The river to which the name refers is of course, the River Eridanus, which is the constellation to which this star belongs.
Description of the Star

Achernar is a very hot B3Vpe main sequence star blue in color, about 9 times the diameter of the sun and much more luminous. According to Burnham, the surface temperature is around 14,000 K. The temperature and diameter of the star imply a luminosity about 1300 times larger than that of the sun.
Spectral emission lines suggest an expanding shell of gas surrounding the star.

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