Definition
Magnetic activity is a characteristic of low-mass stars, with the Sun as a prototype. Its most spectacular observational manifestation is in the form of stellar flares that can be seen in the optical domain, UV, and X-rays. These flares correspond to the release of magnetic energy, itself temporarily built up as a result of movements of the outer layers of these stars, which are convective (“dynamo” effect). During flares, the stellar luminosity is enhanced by a factor which depends on the energy domain, but which is maximum in X-rays (amplification by a factor of up to 10 or more). The whole phenomenon typically lasts a few hours and may be described by a rapid heating phase (minutes to tens of minutes), followed by a long cooling phase (a few hours).
History
The Sun is the first known celestial X-ray source. It was discovered by rocket observations in 1949 by a group of physicists in New Mexico, USA (Friedmann et al. 1951). Since EUV photons and X-rays cannot penetrate...
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References and Further Reading
Charles P, Seward FD (2010) Exploring the X-ray universe. Cambridge University Press
Feigelson ED, Montmerle T (1999) High-energy processes in young stellar objects. Annu Rev Astron Astrophys 37:363
Friedmann H, Lichtman S, Byram E (1951) Photon counter measurements of solar X-rays and extreme ultraviolet light. Phys Rev 83:1025
Güdel M (2007) The sun in time: activity and environment. Living Rev Sol Phys 4, #1, article id.3, 137 pp
Güdel M, Nazé Y (2009) X-ray spectroscopy of stars. Astron Astrophys Rev 17:309
Ilic N, Poppenhaeger K, Hosseini SM (2021) The star-planet connection, on-line workshop, October 25–28, id.34
Kochukhov O (2021) Magnetic fields of M dwarfs. Astron Astrophys Rev 29, #1, article id.1
Lanza AF (2009) Stellar coronal magnetic fields and star-planet interaction. Astron Astrophys 505:339
Ray TP, Ferreira J (2021) Jets from young stars. New Astron Rev 93:article id. 101615
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Montmerle, T. (2022). Activity, Magnetic. In: Gargaud, M., et al. Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-27833-4_28-4
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DOI: https://doi.org/10.1007/978-3-642-27833-4_28-4
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Activity, Magnetic- Published:
- 26 July 2022
DOI: https://doi.org/10.1007/978-3-642-27833-4_28-4
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Activity, Magnetic- Published:
- 29 April 2015
DOI: https://doi.org/10.1007/978-3-642-27833-4_28-3