flare stars


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flare stars

(UV Ceti stars) Intrinsically faint cool red dwarf stars that undergo intense outbursts of energy from localized areas of the surface, causing transient but appreciable increases in the brightness of the star. The brightness can change by two magnitudes or more in several seconds, decreasing to its normal minimum in about 10 to 60 minutes; the output usually peaks in the near-ultraviolet. There are also radio and X-ray flares, not always coincident with optical flares. Flare stars are of spectral type M or sometimes K with spectral emission lines of hydrogen and ionized calcium, i.e. they are Me stars. They have unusually strong magnetic fields (typically 10–4 tesla), suggesting a similar mechanism to solar flares. Most flare stars are either young (found in associations) or are a component of a close binary star: the fast rotation due to youth or to tidal effects, respectively, is probably responsible for the strong magnetism. The nearby binary UV Ceti (M6e V) is a typical flare star.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Flare Stars

 

stars that flare up for periods ranging from several minutes to several hours; the intervals between outbursts vary from several hours to several dozens of hours. During the most intense outbursts, the apparent brightness of the stars increases dozens of times. The outbursts are accompanied by changes in the stellar spectra and by radiation in the radio frequency range.

There are two types of flare stars. The first type includes some of the red dwarfs, which are widely distributed throughout the galaxy. A typical representative of this type is UV Ceti, which is 35,000 times weaker than the sun, 30 times smaller in mass, and 17 times smaller in diameter. Because of their poor luminosity, this type of flare star can be seen only in the immediate vicinity of the sun. The second type is found in groupings of young stars. These are also dwarfs, but they are larger and brighter than the flare stars of the first type. The outbursts are caused by the sudden transition of a yet unknown form of energy into heat and radiation energy, which apparently occurs in the external layers of the stellar atmosphere. In this respect the outbursts are related to solar flares, but they generate thousands of times more luminous energy and hundreds of thousands of times more radio-frequency radiation than the solar flares.

REFERENCE

Gershberg, R. E. Vspyshki krasnykh karlikovykh zvezd. Moscow, 1970.

P. F. CHUGAINOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

flare stars

[′fler ‚stärz]
(astronomy)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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The earth's two nearest neighbors, Proxima Centauri and Barnard's Star, are flare stars.
In analyzing their discovery, the observers rule out possible foreground objects in our own galaxy, such as flare stars, asteroids and dwarf novas, on grounds that the object, though variable, does not vary quickly enough for a flare star.
In 1960, at the suggestion of the Commonwealth Scientific and Industrial Research Organization, the Australian government's scientific agency, the ASNSW launched a program to monitor flare stars. The professional astronomers were studying the stars' outbursts at radio wavelengths and wanted society members to detect the outbursts' optical counterparts.
In the October 1st Astrophysical Journal Letters Woodgate and his coauthors write, "We are not able at present to determine whether the observed proton beam provides the dominant energy in this flare." They hope to settle that question with observations of more powerful outbursts on AU Microscopium and other flare stars. They cannot seek proton beams on the Sun, of course, because Hubble's instruments would be destroyed by sunlight.
If Proxima indeed orbits Alpha - and therefore probably arose from the same stellar nursery at the same time -- then researchers will have to reconsider certain important theoretical issues, Matthews and Gilmore say, Proxima is a flare star, given to periodic and dramatic surface brightenings.