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HR 5171, also known as HD 119796 and V766 Centauri, is a yellow hypergiant star in the constellation Centaurus. Its spectral type is variable around G8Ia+ - K3Ia+〔 and its brightness varies in an irregular fashion. It has a distant B-type companion and is in close contact with a cool companion.〔 It is around from Earth and is the largest known yellow hypergiant, most likely due to interactions with the close companion. This type of star has evolved from an initial mass of around 40 times the Sun to a red hypergiant and is now shedding its remaining outer layers in a series of dramatic explosions, progressively increasing in temperature. It may become a blue supergiant or luminous blue variable before declining in luminosity as a late type Wolf–Rayet star, but is expected to explode as a supernova before that point. The very high luminosity, extreme size, and mass exchange with the lower mass companion make this an unusual star within a very rare class of stars, but it has been relatively poorly studied until recently.〔 The Star was observed by the European Southern Observatory's (ESO) Very Large Telescope Interferometer (VLTI) and has been revealed to be the largest yellow star. This star has been determined to be more than 1,300 times the diameter of the Sun and part of a double star system, with the second component so close that it is in contact with the main star. If HR 5171 were to be put in the center of the Solar System, it would stretch to a distance of , between the orbits of Jupiter and Saturn. It has a volume approximately 2.274 billion times bigger than the Sun. Using ESO's VLTI, an international team of observers led by Olivier Chesneau from the Observatoire de la Côte d’Azur in Nice, France, have found that HR 5171 is much larger than was expected, making it the largest yellow star known. The star is 50 percent larger than the red supergiant Betelgeuse and about 1 million times brighter than the Sun.〔 The star has also been found to be getting larger in size over the time of its examination and is one of the very few stars that have been found to be changing their temperature with difference in size: HR 5171 is getting cooler as it grows. The astronomers concluded that the star is in a binary system by studying the data contributed by several observatories and determined the system as an eclipsing binary star system with the smaller companion star orbiting the larger HR 5171 once every 1300 days. ==Gallery== File:HR 5171A.jpg|Artist's impression of HR 5171 and its companion star File:HR 5171A - VLT.jpg|Field around HR 5171 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「HR 5171」の詳細全文を読む スポンサード リンク
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