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Gamma Crucis
Gamma Crucis (γ Cru, γ Crucis), often called Gacrux, is the nearest red giant star to the Sun.〔 The distance to Gacrux has been determined using parallax measurements made during the Hipparcos mission, which yielded a value of away from Earth.〔 With an apparent visual magnitude of +1.63,〔 this is the third-brightest star in the southern circumpolar constellation of Crux, the Southern Cross, and one of the brightest stars in the night sky. Among Portuguese-speaking peoples it is also named "Rubídea" (or Ruby-like), in reference to its color. A line from the two "Pointers", Alpha Centauri through Beta Centauri, leads to within a few degrees of this star.
== Physical properties ==
Gacrux has a stellar classification M3.5 III.〔 It has evolved off of the main sequence to become a red giant star, but is most likely on the red giant branch rather than the asymptotic giant branch.〔 Although only 30% more massive than the Sun,〔 at this stage the star has expanded to 84〔 times the Sun's radius. It is radiating 1,500〔 times the luminosity of the Sun from its expanded outer envelope. With an effective temperature of 3,626 K,〔 the colour of Gamma Crucis is a prominent reddish-orange, well in keeping with its spectral classification. It is a semi-regular variable with multiple periods.〔 (See table at left.)
The atmosphere of this star is enriched with barium, which is usually explained by the transfer of material from a more evolved companion. Typically this companion will subsequently become a white dwarf.〔 However, no such companion has yet been detected. A +6.4 magnitude companion star lies about 2 arcminutes away at a position angle of 128° from the main star, and can be observed with binoculars. But it is only an optical companion,〔 which is about 400 light years distant from Earth.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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