Hostname: page-component-cd9895bd7-dzt6s Total loading time: 0 Render date: 2024-12-13T10:32:41.815Z Has data issue: false hasContentIssue false
  • English
  • Français

Physical Processes During Impulsive Solar and Stellar Flares

Published online by Cambridge University Press:  12 April 2016

Maria Katsova  and
Moissei Livshits
Maria Katsova
Affiliation:
Sternberg State Astronomical Institute, Moscow State University, 119899 Moscow, Russia
Moissei Livshits
Affiliation:
Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, 142092 Troitsk, Moscow Region, Russia

Extract

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.

Investigations of impulsive flares on both the Sun and red dwarf stais during more than 30 years allow us to arrive at quite definite conclusions. Here we will consider impulsive events; on the Sun the impulsive phase of a flare is observed as a hard X-ray burst with the emission of photons with energies E > 30 keV up to the γ-ray range. At the same time microwave radio bursts, and sometimes UV and optical continuum bursts are registered. Typical durations of these processes are ∼l-3 min. In this time interval other kinds of flare emission like soft X-ray (2-10 keV) emission, meter radio bursts and Balmer line emission begin to rise, but their maxima occur later on, in the gradual (thermal) phase of the flare.

Impulsive stellar flares are often observed as a significant increase in optical continuum, especially in the U-band, of similar duration (1-3 min), and this time interval is, like in the solar case, the rise phase of the soft X-ray emission.

Modern observations demonstrate that both the impulsive phase of a flare or an impulsive flare develops in low-lying loops. Earlier only indirect evidence existed in optical and radio data. Recently, however, the heights of the hard X-ray sources in impulsive solar events were determined directly from YOHKOH’s HXT (Kosugi 1994, Masuda 1994) (Fig. 1a). Statistically, the height of the hard X-ray source in the 14-23 keV range is 9700 ± 2000 km above the photosphere, and this height reduces to 6500 km in the 53-93 keV range. Besides two hard X-ray sources in the loop footpoints, a third hard X-ray source exists at the top of the loop at least in some cases. The authors of this experiment suppose that the appearance of this loop-top source is due to reconnection in the impulsive phase. Note that the reconnection begins close to the apex of the loop, when this loop is filled by hot plasma that evaporated from both footpoints.

Type
Theory of Flares
Information
International Astronomical Union Colloquium , Volume 151: Flares and Flashes , 1995 , pp. 176 - 184
Copyright
Copyright © Springer-Verlag 1995

References

Alexander, D., Dunphy, P.P., MacKinnon, A.L., 1994, Solar Phys. 151, 147 Google Scholar
Antonucci, E., Gabriel, A., Acton, L., et al., 1982, Solar Phys. 78, 107 CrossRefGoogle Scholar
Belov, A.V., Eroshenko, E.A., 1995, Nuclear tracks and radiation measurements (in press)Google Scholar
Belov, A.V., Eroshenko, E.A., Livshits, M.A., 1994, Proc. 8th Int. Symp. on Solar-Terrestrial Physics, Sendai, Japan Pt. 1, 26 Google Scholar
Belov, A.V., Livshits, M.A., 1995, Sov. Astron. Lett. 21, 1 Google Scholar
Boiko, A.Ya., Livshits, M.A., 1995, Astron. Zh. 72, (in press)Google Scholar
Brown, J., 1971, Solar Phys. 18, 489 Google Scholar
Bruevich, E.A., 1995, Astron. Zh. 72, No. 1 Google Scholar
Fisher, G.H., 1986, Radiation Hydrodynamics in Stars and Compact Objects, Lect. Notes in Physics, 255, 53 Google Scholar
Gershberg, R.E., Pikel’ner, S.B., 1972, Comments Ap. Space Phys. 4, 113 Google Scholar
Hawley, S.L., Fisher, G.H., 1992, ApJS, 78, 565 Google Scholar
Katsova, M.M., Livshits, M.A., 1989, Sov. Astron. 33(2), 155 Google Scholar
Katsova, M.M., Livshits, M.A., 1991, Sov. Astron. 35(1), 65 Google Scholar
atsova, M.M., Boiko, A.Ya., Livshits, M.A., 1995, (in prep.)Google Scholar
Katsova, M.M., Kosovichev, A.G., Livshits, M.A., 1981, Astrofiz. 17, 285 Google Scholar
Kopp, R.A., Fisher, G.H., MacNice, P., et al., 1989, Energetic Phenomena on the Sun, Kundu, M.R., Woodgate, B., Schmahl, E.J. (eds.), Kluwer, Dordrecht, p. 601 Google Scholar
Korchak, A.A., 1976, Astron. Zh. 53, 370 Google Scholar
Kostyuk, N.D., Pikel’ner, S.B., 1975, Sov. Astron. 18, 590 Google Scholar
Kosugi, T., 1994, New Look at the Sun with Emphasis on Advanced Observations of Coronal Dynamics and Flares. Proc. of Kofu Symp. NRA Rep. No. 360, Enome, S. & Hirayama, T. (eds.), p. 11 Google Scholar
Livshits, M.A., Badalyan, O.G., Kosovichev, A.G., Katsova, M.M., 1981, Solar Phys. 73, 269 CrossRefGoogle Scholar
Masuda, S., 1994, PhD Thesis. Univ. of Tokyo Google Scholar
Melrose, D.B., 1994, New Look at the Sun with Emphasis on Advenced Observations of Coronal Dynamics and Flares, Proc. of Kofu Symp. NRA Rep. No. 360 eds. Enome, S. & Hirayama, T. (eds.), p. 235 Google Scholar
van den Oord, G.H.J., 1993, Advances Space Res. 13, No. 9, 143 Google Scholar
Ramaty, R., 1986, Physics of the Sun, Sturrock, P. et al. (eds.) Reidel, Dordrecht, Vol. 2, 291 Google Scholar
Spicer, D.S., Mariska, J.T., Boris, J.P., 1986, Physics of the Sun, Sturrock, P. et al. (eds.) Reidel, Dordrecht, Vol. 2, 181 Google Scholar
Stepanov, A.V., Zaitsev, V.V., 1992, Solar Phys. 139, 343 Google Scholar
Syrovatskij, S.I., Shmeleva, O.P., 1972, Astron. Zh. 49, 334 Google Scholar
Zirin, H., Wang, H., 1993a, Solar Phys. 144, 137 Google Scholar
Zirin, H., Wang, H., 1993b, Nature 363, 426 Google Scholar
Zhang, H., 1994, Solar Phys. 154, 207 Google Scholar