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The Solar Flare Plasma: Observation and Interpretation

Published online by Cambridge University Press:  12 April 2016

G. A. Doschek
G. A. Doschek*
Affiliation:
E. O. Hulburt Center for Space Research, Naval Research Laboratory, Washington, D.C. 20390, U.S.A.

Abstract

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In the past several years, X-ray observations of the Sun made from rockets and satellites have demonstrated the existence of high temperature (~20 × 106 – ~100 × 106 K), low density plasmas associated with solar flare phenomena. In the hard X-ray range (λ≲ 1 Å), spectra of the flaring plasma have been obtained using proportional and scintillation counter detectors. It is possible from these data to determine the evolution of the hard X-ray flare spectrum as the burst progresses; and by assuming either a non-thermal or thermal (Maxwellian) electron distribution function, characteristic plasma parameters such as emission measure and temperature (for a thermal interpretation) can be determined. Thermal interpretations of hard X-ray data require temperatures of ~100 × 106 K.

Incontrasi, the soft X-ray flare spectrum (1 Å<λ<30Å) exhibits line emission from hydrogenlike and helium-like ions, e.g. Ne, Mg, Al, Si, … Fe, that indicates electron energies more characteristic of temperatures of ~20 × 106 K. Furthermore, line intensity ratios obtained during the course of an event show that the flare plasma can only be described satisfactorily by assuming a source composed of several different temperature regions; and that the emission measures and temperatures of these regions appear to change as the flare evolves. Temperatures are determined from line ratios of hydrogen-like to helium-like ions for a number of different elements, e.g., S, Si, and Mg, and from the slope of the X-ray continuum which is assumed to be due to free-free and free-bound emission. There is no obvious indication in soft X-ray flare spectra of non-thermal processes, although accurate continuum measurements are difficult with the data obtained to date because of higher order diffraction effects due to the use of crystal spectrometers.

Soft X-ray flare spectra also show satellite lines of the hydrogen-like and helium-like ions, notably the 1s22s2S-1s2s2p2P transition of the lithium-like ion, and support the contention that in low density plasmas these lines are formed by dielectronic recombination to the helium-like ion. Also, series of allowed transitions of hydrogen-like and helium-like ions are strong, e.g., the Lyman series of S up to Lyman-ε, and ratios of the higher member lines to the Lyman-α line can be compared with theoretical calculations of the relative line strengths obtained by assuming various processes of line formation.

This review will discuss the X-ray spectrum of solar flares from ~250 keV to ~0.4 keV, but will be primarily concerned with the soft X-ray spectrum and the interpretation of emission lines and continuum features that lie in this spectral range.

Type
Section V / The Solar Flare Plasma
Information
International Astronomical Union Colloquium , Volume 14: Special Issue: Ultraviolet and X-Ray Spectroscopy of Astrophysical and Laboratory Plasmas , November 1972 , pp. 765 - 821
Copyright
Copyright © Reidel 1972

References

Allen, J. W. and Dupree, A. K.: 1969, Astrophys. J. 155, 27.Google Scholar
Beigman, I. L., Vainshtein, L. A., and Urnov, A. M.: 1971a, Preprint.Google Scholar
Beigman, I. L., Vainshtein, L. A., Vacilev, B. N., Zitnik, I. A. Ivanov, V. D., Korneev, V. V., Krutov, V. V., Mandelshtam, S. L., Tindo, I. P., and Shuryghin, A. I.: 1971b, Preprint.Google Scholar
Beigman, I. L., Grineva, Yu. I., Mandelshtam, S. L., Vainshtein, L. A., and Zitnik, I. A.; 1969, Solar Phys. 9, 160.Google Scholar
Blake, R. L.: 1968a, private communication.Google Scholar
Blake, R. L.: 1968b, unpublished Ph.D. Thesis, University of Colorado and High Altitude Observatory, NCAR, Boulder, Colorado.Google Scholar
Blake, R. L. and House, L. L.: 1971, Astrophys. J. 166, 423.Google Scholar
Burgess, A.: 1964a, Astrophys. J. Letters 139, 776.CrossRefGoogle Scholar
Burgess, A.: 1964b, Mem. Roy. Astron. Soc. 69, Part 1.Google Scholar
Burgess, A.: 1965, Astrophys. J.Letters 141, 1588.CrossRefGoogle Scholar
Burgess, A. and Seaton, M. J.: 1964, Monthly Notices Roy. Astron. Soc. 127, 355.Google Scholar
Burton, W. M. and Wilson, R.: 1961, Proc. Phys. Soc. 78, 1416.Google Scholar
Chubb, T. A.: 1972, in Dyer, E. R. (ed.), Solar Terrestrial Physics, 1970, Part I, D. Reidel Publ. Co., Dordrecht, Holland, pp. 99–118.Google Scholar
Cohen, L., Feldman, U., Swartz, M., and Underwood, J. H.: 1968, J. Opt. Soc. Amer. 58, 843.Google Scholar
Cowan, R. D.: 1971, private communication.Google Scholar
Culhane, J. L.: 1969, Monthly Notices Roy. Astron. Soc. 144, 375.Google Scholar
Culhane, J. L. and Phillips, K. J. H.: 1970a, Astrophys. J. 160, 309.Google Scholar
Culhane, J. L. and Phillips, K. J. H.: 1970b, Solar Phys. 11, 117.CrossRefGoogle Scholar
Culhane, J. L., Sanford, P. W., Shaw, M. L., Phillips, K. J. H., Willmore, A. P., Bowen, P. J., Pounds, K. A., and Smith, D. G.: 1969, Monthly Notices Roy. Astron. Soc. 145, 435.Google Scholar
Culhane, J. L., Vesecky, J. F., and Phillips, K. J. H.: 1970, Solar Phys. 15, 394.Google Scholar
Doschek, G. A. and Meekins, J. F.: 1970, Solar Phys. 13, 220.Google Scholar
Doschek, G. A., Meekins, J. F., Kreplin, R. W., Chubb, T. A., and Friedman, H.: 1971a, Astrophys. J. 170, 573.CrossRefGoogle Scholar
Doschek, G. A., Meekins, J. F., Kreplin, R. W., Chubb, T. A., and Friedman, H.: 1971b, Astrophys. J. 164, 165.Google Scholar
Drake, J. F.: 1971, Solar Phys. 16, 152.CrossRefGoogle Scholar
Duwez, P.: 1965, Technical Report No. 32 submitted to: U.S. Atm. Energy Commission Contract No. AT(04-3)-221.Google Scholar
Elwert, G. and Haug, E.: 1970, Solar Phys. 15, 234.Google Scholar
Evans, K., Pounds, K. A., and Culhane, J. L.: 1967, Nature 214, 41.CrossRefGoogle Scholar
De Feiter, L. D.: 1972, this issue, p. 827.CrossRefGoogle Scholar
Flamberg, H.: 1942, Arkiv. Mat. Astron. Fys. 28A, 18.Google Scholar
Freeman, F. F., Gabriel, A. H., Jones, B. B., and Jordan, C.: 1971, Phil. Trans. Roy. Soc. London A270, 127.Google Scholar
Fritz, G., Kreplin, R. W., Meekins, J. F., Unzicker, A. E., and Friedman, H.: 1967, Astrophys. J. 148, L133.Google Scholar
Frost, K. J. and Dennis, B. R.: 1971, Astrophys. J. 165, 655.Google Scholar
Gabriel, A. H.: 1970, private communication.Google Scholar
Gabriel, A. H.: 1971, private communication.Google Scholar
Gabriel, A. H.: 1972, this issue, p. 655.CrossRefGoogle Scholar
Gabriel, A. H. and Jordan, C.: 1969a, Nature 221, 947.Google Scholar
Gabriel, A. H. and Jordan, C.: 1969b, Monthly Notices Roy. Astron. Soc. 145, 241.Google Scholar
Garcia, J. D. and Mack, J. E.: 1965, J. Opt. Soc. Amer. 55, 654.Google Scholar
Hauge, O. and Engvold, O.: 1970, preprint, Institute of Theoretical Astrophysics, University of Oslo, Oslo, Norway.Google Scholar
Holt, S. S. and Ramaty, R.: 1969, Solar Phys. 8, 119.Google Scholar
Horan, D. M.: 1971, Solar Phys. 21, 188.Google Scholar
House, L. L.: 1964, Astrophys. J. Suppl. 8, 307.Google Scholar
House, L. L.: 1969, Astrophys. J. Suppl. 18, 21.CrossRefGoogle Scholar
Hudson, H. S. and Ohki, K.: 1971, Preprint.Google Scholar
De Jager, C.: 1968, Solar Flares and Space Research, Proc. XICOSPAR Symp. Solar Flares, Tokyo, p. 1.Google Scholar
Jordan, C.: 1969, Monthly Notices Roy. Astron Soc. 142, 501.Google Scholar
Kahler, S. W.: 1971, Astrophys. J. 164, 365.Google Scholar
Kahler, S. W. and Kreplin, R. W.: 1971, Astrophys. J. 168, 531.CrossRefGoogle Scholar
Kahler, S. W., Meekins, J. F., Kreplin, R. W., and Bowyer, C. S.: 1970, Astrophys. J. 162, 293.Google Scholar
Kane, S. R.: 1969, Astrophys. J. Letters 157, L139.Google Scholar
Kane, S. R. and Anderson, K. A.: 1970, Astrophys. J. 162, 1003.Google Scholar
Kane, S. R. and Donnelly, R. F.: 1971, Astrophys. J. 164, 151.Google Scholar
Kreplin, R. W.: 1961, Ann. Geophys. 17, 151.Google Scholar
Kreplin, R. W.: 1970, International Symposium on Solar-Terrestrial Physics, Leningrad, USSR, 1970 May 11-20.Google Scholar
Landini, M. and Monsignori Fossi, B. C.: 1970, Astron. Astrophys. 6, 468.Google Scholar
Lie, T. N. and Elton, R. C.: 1971, Phys. Rev. A3, 865.CrossRefGoogle Scholar
Lin, R. P. and Hudson, H. S.: 1971, Solar Phys. 17, 412.Google Scholar
Meekins, J. F. and Doschek, G. A.: 1970, Solar Phys. 13, 213.Google Scholar
Meekins, J. F., Doschek, G. A., Friedman, H., Chubb, T. A., and Kreplin, R. W.: 1970, Solar Phys. 13, 198.Google Scholar
Neupert, W. M.: 1964, Astrophys. J. 139, 935.CrossRefGoogle Scholar
Neupert, W. M.: 1970, in Macris, C. J. (ed.), Physics of the Solar Corona, D. Reidel. Publ. Co., Dordrecht, Holland, p. 237.Google Scholar
Neupert, W. M.: 1971a, Solar Phys. 18, 474.Google Scholar
Neupert, W. M.: 1971b, private communication.Google Scholar
Neupert, W. M. and Swartz, M.: 1970, Astrophys. J. Letters 160, L189.Google Scholar
Neupert, W. M., Gates, W., Swartz, M., and Young, R.: 1967, Astrophys. J. Letters 149, L79.Google Scholar
Neupert, W. M., White, W. A., Gates, W. J., Swartz, M., and Young, R. M.: 1969, Solar Phys. 6, 183.Google Scholar
Phillips, K. J. H. and Culhane, J. L.: 1971, Solar Phys. 16, 469.Google Scholar
Pottasch, S. R.: 1964, Space Sci, Rev. 3, 816.CrossRefGoogle Scholar
Rugge, H. R. and Walker, A. B. C. Jr.: 1968, Space Res. VIII North-Holland Publ. Co., Amsterdam, p. 439.Google Scholar
Seaton, M. J.: 1959, Monthly Notices Roy. Astron. Soc. 119, 81.Google Scholar
Spitzer, L. Jr.: 1967, Physics of Fully Ionized Gases, Interscience Publishers, New York.Google Scholar
Švestka, Z.: 1970, Solar Phys. 13, 471.Google Scholar
Teske, R. G. and Thomas, R. J.: 1969, Solar Phys. 8, 348.Google Scholar
Thomas, R. J. and Neupert, W. M.: 1971, Bull. AAS 3, No. 1, Part 1, 7.Google Scholar
Thomas, R. J. and Teske, R. G.: 1971, Solar Phys. 16, 431.Google Scholar
Tindo, I. P., Ivanov, V. D., Mandelshtam, S. L., and Shuryghin, A. I.: 1970, Solar Phys. 14, 204.Google Scholar
Tindo, I. P., Ivanov, V. D., Mandelshtam, S. L., and Shuryghin, A. I.: 1971, XIVth Plenary Meeting of COSPAR, Seattle, Washington, U.S.A., 1971.Google Scholar
Tomblin, F. F.: 1971a, private communication.Google Scholar
Tomblin, F. F.: 1971b, Astrophys. J. 171, 377.Google Scholar
Unzicker, A. E.: 1971, private communication.Google Scholar
Vaiana, G. S., Reidy, W. P., Zehnpfennig, T., Van Speybroeck, L., and Giacconi, R.: 1968, Science 161, 564.Google Scholar
Van Regemorter, H.: 1962, Astrophys. 136, 906.Google Scholar
Vasiljev, B. N., Grineva, Yu. I., Zitnik, I. A., Karev, V. I., Korneev, V. V., Krutov, V. V., and Mandelshtam, S. L.: 1971, XIVth Plenary Meeting of COSPAR, Seattle, Washington, U.S.A., 1971.Google Scholar
Walker, A. B. C. Jr. and Rugge, H. R.: 1969, Solar Flares and Space Research, North-Holland Publ. Co., Amsterdam, p. 102.Google Scholar
Walker, A. B. C. Jr. and Rugge, H. R.: 1970, Astron Astrophys. 5, 4.Google Scholar
Walker, A. B. C. Jr. and Rugge, H. R.: 1971, Astrophys. J. 164, 181.Google Scholar
Wooley, R. v. d. R. and Allen, C. W.: 1948, Monthly Notices Roy. Astron. Soc. 108, 292.Google Scholar
Zirin, H.: 1971, Goddard Space Flight Center Colloquium.Google Scholar