Most flare stars are dim red dwarfs, although recent research indicates that less massive brown dwarfs might also be capable of flaring.[citation needed] 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 had also been seen to undergo flare events[2] prior
to the flood of superflare data from the Kepler observatory.
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.[3]
Nearby flare stars
Flare stars are intrinsically faint, but have been found to distances of 1,000 light years from Earth.[4] On April 23, 2014, NASA's Swift satellite detected the strongest, hottest, and longest-lasting sequence of stellar flares ever seen from a nearby red dwarf, DG Canum Venaticorum. The initial blast from this record-setting series of explosions was as much as 10,000 times more powerful than the largest solar flare ever recorded.[5]
Proxima Centauri
The Sun's nearest stellar neighbor Proxima Centauri is a flare star that undergoes occasional increases in brightness because of magnetic activity.[6] The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun.[7]
Wolf 359
The flare star Wolf 359 is another near neighbor (2.39 ± 0.01 parsecs). This star, also known as Gliese 406 and CN Leo, is a red dwarf of spectral class M6.5 that emits X-rays.[8] It is a UV Ceti flare star,[9] and has a relatively high flare rate.
The mean magnetic field has a strength of about 2.2kG (0.2T), but this varies significantly on time scales as short as six hours.[10] By comparison, the magnetic field of the Sun averages 1G (100μT), although it can rise as high as 3kG (0.3T) in active sunspot regions.[11]
Barnard's Star
Barnard's Star is the fourth nearest star to the Sun. Given its age, at 7–12 billion years of age, Barnard's Star is considerably older than the Sun. It was long assumed to be quiescent in terms of stellar activity. However, in 1998, astronomers observed an intense stellar flare, showing that Barnard's Star is a flare star.[12][13]
EV Lacertae
EV Lacertae is located 16.5 light-years away, and is the nearest star in its constellation. It is a young star, about 300 million years old, and has a strong magnetic field. In 2008, it produced a record-setting flare that was thousands of times more powerful than the largest observed solar flare.[14]
TVLM513-46546
TVLM 513-46546 is a very low mass M9 flare star, at the boundary between red dwarfs and brown dwarfs. Data from Arecibo Observatory at radio wavelengths determined that the star flares every 7054 s with a precision of one one-hundredth of a second.[15]
2MASS J18352154-3123385 A
The more massive member of the binary star 2MASS J1835, an M6.5 star, has strong X-ray activity indicative of a flare star, although it has never been directly observed to flare.
Record-setting flares
The most powerful stellar flare detected, as of December 2005, may have come from the active binary II Peg.[16] Its observation by Swift suggested the presence of hard X-rays in the well-established Neupert effect as seen in solar flares.
See also
Solar flare– Eruption of electromagnetic radiation
Christian, Damian J.; Mathioudakis, Michail; Bloomfield, D. Shaun; Dupuis, Jean; Keenan, Francis P. (2004). "A Detailed Study of Opacity in the Upper Atmosphere of Proxima Centauri". Astrophysical Journal. 612 (2): 1140–6. Bibcode:2004ApJ...612.1140C. doi:10.1086/422803. hdl:10211.3/172067.
Wood, Brian E.; Linsky, Jeffrey L.; Müller, Hans-Reinhard; Zank, Gary P. (2001). "Observational Estimates for the Mass-Loss Rates of α Centauri and Proxima Centauri Using Hubble Space Telescope Lyα Spectra". Astrophysical Journal. 547 (1): L49–L52. arXiv:astro-ph/0011153. Bibcode:2001ApJ...547L..49W. doi:10.1086/318888. S2CID118537213.
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