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Wolf 359
Wolf 359 is a red dwarf that is located in the constellation Leo, near the ecliptic. At a distance of approximately 7.8 light years from Earth, it has an apparent magnitude of 13.5 and can only be seen with a large telescope. Wolf 359 is one of the nearest stars to the Sun; only the Alpha Centauri system (including Proxima Centauri), Barnard's Star and the brown dwarfs Luhman 16 and WISE 0855−0714 are known to be closer. Its proximity to Earth has led to its mention in several works of fiction.
Wolf 359 is one of the faintest and lowest-mass stars known. At the light-emitting layer called the photosphere, it has a temperature of about 2,800 K, which is low enough for chemical compounds to form and survive. The absorption lines of compounds such as water and titanium(II) oxide have been observed in the spectrum.〔 The surface has a magnetic field that is stronger than the average magnetic field on the Sun. As a result of magnetic activity caused by convection, Wolf 359 is a flare star that can undergo sudden increases in luminosity for several minutes. These flares emit strong bursts of X-ray and gamma ray radiation that have been observed by space telescopes. Wolf 359 is a relatively young star with an age of less than a billion years. No companions or disks of debris have been detected in orbit around it.
==Observation history and name==
Wolf 359 first came to the attention of astronomers because of the relatively high rate of transverse motion against the background, known as the proper motion. A high rate of proper motion can indicate that a star is located nearby, as more distant stars must move at higher velocities in order to achieve the same rate of angular travel across the celestial sphere. The proper motion of Wolf 359 was first measured in 1917 by German astronomer Max Wolf, with the aid of astrophotography. In 1919 he published a catalog of over one thousand stars with high proper motions, including this one, that are still identified by his name.〔 He listed this star as entry number 359, and the star has since been referred to as Wolf 359 in reference to Max Wolf's catalogue.〔
The first parallax measurement of Wolf 359 was reported in 1928 from the Mount Wilson Observatory, yielding an annual shift in the star's position of . From this position change, and the known size of the Earth's orbit, the distance to the star could be estimated. It was the lowest-mass and faintest star known until the discovery of VB 10 in 1944.〔〔 The infrared magnitude of the star was measured in 1957.〔 In 1969, a brief flare in the luminosity of Wolf 359 was observed, linking it to the class of variable stars known as flare stars.〔
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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