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Delta Centauri
Delta Centauri (δ Cen, δ Centauri) is a star in the southern constellation of Centaurus. The apparent visual magnitude of this star is +2.57,〔 making it readily visible to the naked eye. Based upon parallax measurements, it is located at a distance of about from the Earth.〔
==Properties==
Delta Centauri is a variable star with a brightness varies from magnitude +2.51 to +2.65. This variability can be successfully modeled as a Gamma Cassiopeiae type variable,〔 also known as a shell star. The energy from this star is being radiated at an effective temperature of over 22,000 K from the outer envelope, giving it the blue-white hue of a B-type star.〔 It has a radius of 5.9 times the radius of the Sun〔 and 8.6 times the Sun's mass.〔
The stellar classification of this star is B2 IVne,〔 with the luminosity class of IV indicating that this is a subgiant star that has exhausted the hydrogen at its core and begun to evolve away from the main sequence. The star is spinning rapidly, with the resulting Doppler effect giving its spectrum broad absorption lines as indicated by the 'n'. The suffix 'e' means this is a classical Be star, which is a type of hot star that has not yet evolved into a supergiant and is surrounded by circumstellar gas. The presence of this gas creates an excess emission of infrared, along with emission lines in the star's spectrum. Most of it is concentrated around the equator, forming a disk.〔
Some of the variation in this star may be explained by assuming it is a binary star system. This proposed secondary star would need to have about 4–7 times the Sun's mass and be orbiting with a period of at least 4.6 years at a minimum separation of 6.9 Astronomical Units.〔 Delta Centauri shares a common proper motion with the nearby stars HD 105382 and HD 105383, so they may form a small cluster or perhaps a triple star system.〔 It is a proper motion member of the Lower-Centaurus Crux sub-group in the Scorpius-Centaurus OB association, the nearest such of association of co-moving massive stars to the Sun.〔
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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