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Radio Emission from Flares in Single Late-type Stars

Published online by Cambridge University Press:  12 April 2016

Arnold O. Benz
Arnold O. Benz*
Affiliation:
Institute of Astronomy, ETH-Zentrum, CH-8092 Zürich, Switzerland

Abstract

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Radio observations provide the most direct information on non-thermal electrons in stellar flares and in the coronae of late-type stars. Radio emissions of single main-sequence F, G, and of many K stars have recently been discovered, in addition to the well-known dwarf M stars. Their long-duration radio flares with low circular polarization, slow variations and broad bandwidth can be attributed to gyrosynchrotron emission of mildly relativistic electrons. The same holds for the low-level (‘quiescent’) radio emission. On the other hand, highly polarized radio flares of M stars have been interpreted by coherent emissions from loss-cone instabilities of magnetically trapped electrons. These conjectures are consistent with recent VLBI observations. The identification of the radio emission process allows to estimate the high-energy component of the flare and compare it to the total flare energy. The weakly polarized radio emission may serve as a proxy for hard X-ray signatures of relativistic electrons. The fraction of primary energy released into energetic electrons then appears to be large and similar to solar flares.

Type
Flares in Late-type Stars: Radio and Optical
Information
International Astronomical Union Colloquium , Volume 151: Flares and Flashes , 1995 , pp. 22 - 31
Copyright
Copyright © Springer-Verlag 1995

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