Hostname: page-component-77c89778f8-5wvtr Total loading time: 0 Render date: 2024-07-20T08:04:27.670Z Has data issue: false hasContentIssue false

Flare stars at radio wavelengths

Published online by Cambridge University Press:  23 September 2016

Kenneth R. Lang*
Affiliation:
Department of Physics and Astronomy Tufts University Medford, MA 02155 U.S.A.

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The radio emission from dMe flare stars is discussed using Very Large Array and Arecibo observations as examples. Active flare stars emit weak, unpolarized, quiescent radio radiation that may be always present. Although thermal bremsstrahlung and/or thermal gyroresonance radiation account for the slowly-varying, quiescent radio radiation of solar active regions, these processes cannot account for the long-wavelength quiescent radiation observed from nearby dMe flare stars. It has been attributed to nonthermal gyrosynchrotron radiation, but some as yet unexplained mechanism must be continually producing the energetic electrons. Long-duration (hours), narrow-band (Δv/v < 0.1) radiation is also emitted from some nearby dMe stars at 20 cm wavelength. Such radiation may be attributed to coherent plasma radiation or to coherent electron-cyclotron masers. Impulsive stellar flares exhibit rapid variations (< 100 msec) that require radio sources that are smaller than the star in size, and high brightness temperatures TB > 1015 K that are also explained by coherent radiation processes. Quasi-periodic temporal fluctuations suggest pulsations during some radio flares. Evidence for frequency structure and positive or negative frequency drifts during radio flares from dMe stars is also presented.

Type
I Flare Stars Optical Observations and Flare Statistics
Copyright
Copyright © Kluwer 1990 

References

Bastian, T.S. and Bookbinder, J.A. (1987) ‘First dynamic spectra of stellar microwave flares’, Nature, 326, 678680.Google Scholar
Bastian, T.S., Bookbinder, J., Dulk, G.A. and Davis, M. (1990) ‘Dynamic spectra of radio bursts from flare stars’, Astrophysical Journal, April 10, 1990 issue.Google Scholar
Dulk, G.A. (1985), ‘Radio emission from the sun and stars’, Annual Review of Astronomy and Astrophysics 23, 169224.Google Scholar
Gary, D.E. (1985) ‘Quiescent stellar radio emission’, in Hjellming, R.M. and Gibson, D.M. (eds.), Radio Stars, D. Reidel, Boston, pp. 185196.Google Scholar
Güdel, M. and Benz, A.O. (1989) ‘Broad-band spectrum of dMe star radio emission’, Astronomy and Astrophysics Letters, 211, L5L8.Google Scholar
Güdel, M., Benz, A.O., Bastian, T.S., Fürst, E., Simnett, G.M. and Davis, R.J. (1989) ‘Broadband spectral observation of a dMe star radio flare’, Astronomy and Astrophysics Letters 220, L5L8.Google Scholar
Jackson, P.D., Kundu, M.R. and White, S.M., (1987) ‘Dynamic spectrum of a radio flare on UV Ceti’, Astrophysical Journal Letters 316, L85L90.Google Scholar
Jackson, P.D., Kundu, M.R. and White, S.M. (1989) ‘Quiescent and flaring radio emission from the flare stars AD Leonis, EQ Pegasi, UV Ceti, Wolf 630, YY Geminorum, and YZ Canis Minoris’, Astronomy and Astrophysics 210, 284294.Google Scholar
Kuijpers, J. (1989) ‘Radio emission from stellar flares’, Solar Physics 121, 163185.Google Scholar
Kundu, M.R., Jackson, P.D., White, S.M., and Melozzi, M. (1987) ‘Microwave observations of the flare stars UV Ceti, AT Microscopii, and AU Microscopii’, Astrophysical Journal 312, 822829.Google Scholar
Kundu, M.R., Pallavicini, R., White, S.M., and Jackson, P.D. (1985) ‘Co-ordinated VLA and EXOSAT observations of the flare stars UV Ceti, EQ Pegasi, YZ Canis Minoris and AD Leonis’, Astronomy and Astrophysics 195, 159171.Google Scholar
Kundu, M.R. and Shevgaonkar, R.K. (1988) ‘Detection of the dMe flare star YZ Canis Minoris simultaneously at 20 and 90 centimeter wavelengths’, Astrophysical Journal 334, 10011007.Google Scholar
Lang, K.R. (1986) ‘Radio wavelength observations of magnetic fields on active dwarf M, RS CVn and magnetic stars’, Advances in Space Research 6, No. 8, 109112.Google Scholar
Lang, K.R., Bookbinder, J., Golub, L. and Davis, M.M. (1983) ‘Bright, rapid, highly-polarized radio spikes from the M dwarf AD Leonis’, Astrophysical Journal (Letters) 272, L15L18.Google Scholar
Lang, K.R. and Willson, R.F. (1986a) ‘Narrow-band, slowly varying decimetric radiation from the dwarf M flare star YZ Canis Minoris’, Astrophysical Journal (Letters) 302, L17L21.Google Scholar
Lang, K.R. and Willson, R.F. (1986b) ‘Millisecond radio spikes from the dwarf M flare star AD Leonis’, Astrophysical Journal 305, 363368.Google Scholar
Lang, K.R. and Willson, R.F. (1988) ‘Narrow-band, slowly varying decimetric radiation from the dwarf M flare star YZ Canis Minoris II’, Astrophysical Journal 326, 300304.Google Scholar
Mullan, D.J. (1989) ‘Solar and stellar flares: questions and answers’, Solar Physics 121, 239259.Google Scholar
White, S.M., Jackson, P.D., and Kundu, M.R. (1989) ‘A VLA survey of nearby flare stars’, Astrophysical Journal Supplement, December 15, 1989.Google Scholar
White, S.M., Kundu, M.R., and Jackson, P.D. (1986) ‘Narrow-band radio flares from red dwarf stars’, Astrophysical Journal 311, 814818.Google Scholar
Willson, R.F., Lang, K.R., and Foster, P. (1988) ‘VLA observations of dwarf M flare stars and magnetic stars’, Astronomy and Astrophysics 199, 255261.Google Scholar