Nonthermal phenomena in stellar coronae: Evidence from radio observations

  • George A. Dulk
Nonthermal Phenomena in Stellar Coronae
Part of the Lecture Notes in Physics book series (LNP, volume 291)


In the past few years a number of different kinds of stars have been detected at radio wavelengths, the majority of them cool stars. In most cases the radio emission is indicative of high energy, nonthermal processes: acceleration of electrons to some 10's of keV or, in some circumstances, several MeV or more. These electrons then emit radio waves by the incoherent processes of gyroresonance and gyrosynchrotron radiation, and the coherent processes of cyclotron maser and plasma radiation.

The source of energy for the electron acceleration in single stars and some binaries is probably the generation of strong magnetic fields in the stars' interiors (aided, in close binaries, by rapid rotation enforced by synchronous rotation), their emergence above the photospheres, and their subsequent dissipation. For some stars, RS CVn's and cataclysmic variables, interactions between the magnetic fields of two close companions may also be important. For evolved binaries the energy probably is mainly gravitational, coming from the transfer of matter onto a compact star.

Whatever the basic energy source, some energy appears in the form of fast electrons that are capable of generating intense radio waves. If the energy of the electrons is greater than ∼ 1 keV they may emit gyroresonance radiation of brightness temperature T B ∼ 107 K, and if ≿ 100 keV they may emit gyrosynchrotron radiation with T B ≿ 108 K (maximum so far observed: a few ×1010 K). For the coherent radiation mechanisms of cyclotron maser and plasma radiation, the electrons need not be more energetic than ∼ 10 keV, but they must have free energy, probably in the form of a loss cone distribution (for the cyclotron maser) or a bump-in-the-tail distribution (for plasma radiation). Then they are able to emit radiation with T B greater than the maximum so far observed, ∼ 1015 K.


Radio Emission Plasma Radiation Single Star Radio Flux Radio Luminosity 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Abbott, D.C.: 1985, see Hjellming and Gibson, p. 61.Google Scholar
  2. André, P., Montmerle, T. and Feigelson, E.D.: 1987, Astron. J., 93, 1182.Google Scholar
  3. Bastian, T.S.: 1987, Ph.D. Thesis, University of Colorado.Google Scholar
  4. Bastian, T.S. and Bookbinder, J.A.: 1987, Nature, 326, 678.Google Scholar
  5. Bastian, T.S., Dulk, G.A. and Chanmugam, G.: 1987, Astrophys. J., in press.Google Scholar
  6. Beiging, J.H., Cohen, M. and Schwartz, P.R.: 1985, see Hjellming and Gibson, p. 103.Google Scholar
  7. Bookbinder, J.A., Stencel, R.E., Drake, S.A., Simon, T., Linsky, J.L., and Florkowski, D.: 1987, this volume.Google Scholar
  8. Brown, R.L. and Crane, P.C.: 1978, Astron. J., 83, 1504.Google Scholar
  9. Davis, R.J., Lovell, B., Palmer, H.P. and Spencer, R.E.: 1978, Nature, 273, 644.Google Scholar
  10. Drake, S.A. and Linsky, J.L.: 1986, Astron. J., 91, 602.Google Scholar
  11. Drake, S.A., Abbott, D.C., Bastian, T.S., Beiging, J.H., Churchwell, E., Dulk, G.A. and Linsky, J.L.: 1987, Astrophys. J., in press.Google Scholar
  12. Dulk, G.A. and Gary, D.E.: 1983, Astron. Astrophys., 124, 103.Google Scholar
  13. Dulk, G.A.: 1985, Ann. Rev. Astron. Astrophys., 23, 169.Google Scholar
  14. Dulk, G.A.: 1987, Adv. Space Res., 6, 95.Google Scholar
  15. Feigelson, E.D. and Montmerle, T.: 1985, see Hjellming and Gibson, p. 335.Google Scholar
  16. Fu, Q., Jin, S., Zhao, R., Zheng, L., Liu, Y., Li, X., Wang, S., Chen, Z. and Hu, C.: 1986, in Rapid Fluctuations in Solar Flares, (eds. B.R. Dennis, L.C. Orwig and A.L. Kiplinger), NASA Conf. Proc. 2449, p. 237.Google Scholar
  17. Gary, D.E.: 1985, see Hjellming and Gibson, p. 185.Google Scholar
  18. Gibson, D.M.: 1985, see Hjellming and Gibson, p. 213.Google Scholar
  19. Hjellming, R.M. and Gibson, D.M., eds.: 1985, Radio Stars: Proc. of a Workshop on Stellar Radio Astronomy, (Dordrecht: Reidel), 411 pp.Google Scholar
  20. Hjellming, R.M.: 1985, see Hjellming and Gibson, p. 151.Google Scholar
  21. Hjellming, R. and Johnston, K.J.: 1985, see Hjellming and Gibson, p. 309.Google Scholar
  22. Hogg, D.E.: 1985, see Hjellming and Gibson, p. 117.Google Scholar
  23. Jackson, P.D., Kundu, M.R. and White, S.M.: 1987, this volume.Google Scholar
  24. Lang, K.R., Bookbinder, J., Golub, L. and Davis, M.: 1983, Astrophys. J. (Lett.); 272, L15.Google Scholar
  25. Lestrade, J.-F., Mutel, R.L., Preston, R.A. and Phillips, R.B.: 1987, Astrophys. J., in press.Google Scholar
  26. Linsky, J.L. and Gary, D.E.: 1983, Astrophys. J., 274, 776.Google Scholar
  27. McLean, D.J. and Labrum, N.R.: 1985, Solar Radiophysics, Cambridge Univ. Press, 516 pp.Google Scholar
  28. Melrose, D.B.: 1987, this volume.Google Scholar
  29. Morris, D.H. and Mutel, R.L.: 1987, this volume.Google Scholar
  30. Mutel, R.L. and Weisberg, J.M.: 1978, Astron. J., 83, 1499.Google Scholar
  31. Mutel, R.L. and Lestrade, J.F.: 1985, Astron. J., 90, 493.Google Scholar
  32. Mutel, R.L., Lestrade, J.F., Preston, R.A. and Phillips, R.B.: 1985, Astrophys. J., 289, 262.Google Scholar
  33. Seaquist, E.R., Taylor, A.R. and Button, S.: Astrophys. J., 284, 202.Google Scholar
  34. Simon, T., Fekel, F.C. Jr. and Gibson, D.M.: 1985, Astrophys. J., 295, 153.Google Scholar
  35. Slee, O.B., Nelson, G.J., Stewart, R.T., Wright, A.E., Innis, J.L., Ryan, S.G. and Vaughan, A.E.: 1987, M.N.R.A.S., submitted.Google Scholar
  36. Spangler, S.R., Rankin, J.M. and Shawhan, S.D.: 1974, Astrophys. J. (Lett.), 194, L43.Google Scholar
  37. Taylor, A.R. and Seaquist, E.R.: 1985a, see Hjellming and Gibson, p. 147.Google Scholar
  38. Taylor, A.R. and Seaquist, E.R.: 1985b, Astron. J., 90, 2049.Google Scholar
  39. White, R.L.: 1985, Astrophys. J., 289, 698.Google Scholar

Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • George A. Dulk
    • 1
  1. 1.Department of Astrophysical, Planetary and Atmospheric SciencesUniversity of ColoradoBoulderUSA

Personalised recommendations