Star that varies in brightness repeatedly but sporadically, sometimes by more than one magnitude, within a few minutes. The cause is thought to be the eruption of flares like those observed on the Sun but much larger (see solar flare). Proxima Centauri, in Alpha Centauri, the closest star to the Sun, is a flare star.

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A flare star is a variable star which can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to magnetic reconnection in the atmospheres of the stars. The brightness increase is across the spectrum, from X rays to radio waves. The first known flare stars (V1396 Cygni and AT Microscopii) were discovered in 1924. However, the best-known flare star (UV Ceti) was discovered in 1948, and today flare stars are sometimes known as UV Ceti variables.

Most flare stars are dim red dwarfs, although recent research indicates that less massive brown dwarfs might also be capable of flaring. The more massive RS Canum Venaticorum variables (RS CVn) are also known to flare, but it is understood that these flares are induced by a companion star in a binary system which causes the magnetic field to become tangled. Additionally, nine stars similar to the Sun have also been seen to undergo flare events. It has been proposed that the mechanism for this is similar to that of the RS CVn variables in that the flares are being induced by a companion, namely an unseen Jupiter like planet in a close orbit .

Nearby flare stars

The Sun's nearest stellar neighbor Proxima Centauri is a flare star, as is another near neighbor; Wolf 359. Barnard's Star, the second nearest star system, is also suspected of being a flare star. Flare stars are intrinsically faint, but have been found to distances of 1000 light years from Earth .

References

External links

• www.aavso.org/
• Stellar Flares - D. Montes, UCM.
• Definition of a flare star