Abstract
We analyze Ca ii K-line profiles of one flare and EUV continuum observations of two other flares in order to infer values for the temperature enhancements (over active region values) produced in the upper photosphere around and above the temperature minimum region. The results, obtained through a partial redistribution calculation of the Ca ii K-line profiles and an LTE approach to the continuum observations, show that the flare temperature minimum is depressed some two scale heights below its preflare level, and that substantial temperature enhancements are produced even at this depth. Estimates for the energy release in these photospheric layers are given, and are found to be comparable with that released in chromospheric Hα and Lα emission.
We then turn our attention to the investigation of possible heating mechanisms which might be responsible for the observed enhancements. Bombardment by both electrons and protons, and irradiation by soft X-rays, are each considered and found to be largely ineffective, due to the large attenuation of flux by photospheric depths, unless new ideas on the precise nature of these mechanisms are invoked, particularly if the same mechanism is also to explain the observed chromospheric emissions. We therefore conclude that it is most likely that some other mechanism must be advocated in order to explain the observed heating. Possibilities for this are (a) heating by EUV radiation, (b) proton beams with low dispersion energy spectra centered around 10–20 MeV, and (c) localized heating at temperature minimum levels.
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References
Allen, C. W.: 1973, Astrophysical Quantities 3rd ed., Athlone.
Ayres, T. R.: 1975, Astrophys. J. 201, 799.
Ayres, T. R.: 1977, Astrophys. J. 213, 296.
Ayres, T. R. and Linsky, J. L.: 1976, Astrophys. J. 205, 874.
Brault, J. and Testerman, L.: 1972, Kitt Peak Wavelength Atlas, unpublished.
Brown, J. C.: 1973, Solar Phys. 31, 143.
Brown, J. J. C., Canfield, R. C., and Robertson, M. N.: 1978, Solar Phys. 57, 399.
Canfield, R. C. and Athay, R. G.: 1974, Solar Phys. 34, 193.
Cheng, C.-C. and Moe, O. K.: 1978, Solar Phys., in press.
Cook, J. and Brueckner, G. E.: 1978, submitted to Astrophys. J.
Cox, D. P. and Tucker, W. H.: 1969, Astrophys. J. 156, 87.
Cruddance, R., Paresce, F., Bowyer, S., and Hampton, M.: 1974, Astrophys. J. 187, 497.
Culhane, J. L. and Acton, L. W.: 1970, Monthly Notices Roy. Astron. Soc. 151, 141.
Doschek, G. A., Feldman, U., and Rosenberg, F. D.: 1977, Astrophys. J. 215, 329.
Emslie, A. G.: 1978, Astrophys. J. 224.
Emslie, A. G., Brown, J. C., and Donnelly, R. F.: 1978, Solar Phys. 57, 175.
Feldman, U., Doschek, G. A., and Rosenberg, F. D.: 1977, Astrophys. J. 215, 652.
Gebbie, K. B. and Thomas, R. N.: 1970, Astrophys. J. 161, 229.
Henoux, J.-C. and Nakagawa, Y.: 1976, Astron. Astrophys. 57, 105.
Houtgast, J.: 1970, Solar Phys. 15, 273.
Kostyuk, N. D. and Pikel'ner, S. B.: 1975, Soviet Astron. A.J. 18, 590.
Lin, R. P. and Hudson, H. S.: 1976, Solar Phys. 50, 153.
Linsky, J. L. and Avrett, E. H.: 1970, Publ. Astron. Soc. Pacific 82, 169.
Linsky, J. L. and Ayres, T. R.: 1978, Astrophys. J. 220, 619.
Machado, M. E.: 1978, Solar Phys., in press.
Machado, M. E. and Linsky, J. L.: 1975, Solar Phys. 42, 395.
Machado, M. E. and Rust, D. M.: 1974, Solar Phys. 38, 499.
Praderie, F. and Thomas, R. N.: 1972, Astrophys. J. 172, 485.
Ramaty, R., Kozlovsky, B., and Lingenfelter, R. E.: 1974, GSFC Document X-660-74-368.
Raymond, J. C., Cox, D. P., and Smith, B.: 1976, Astrophys. J. 204, 290.
Shine, R. A.: 1973, Ph.D. Thesis, University of Colorado.
Shine, R. A. and Linsky, J. L.: 1972, Solar Phys. 25, 357.
Shine, R. A. and Linsky, J. L.: 1974, Solar Phys. 37, 145.
Shine, R. A., Milkey, R. W., and Mihalas, D.: 1975, Astrophys. J. 201, 222.
Somov, B. V.: 1975, Solar Phys. 42, 235.
Somov, B. V. and Syrovatskii, S. I.: 1976, Sou. Phys. Usp. 19, 813.
Smith, E. v. P.: 1960, Astrophys. J. 132, 202.
Smith, D. F.: 1970, Solar Phys. 15, 202.
Spitzer, L.: 1962, Physics of Fully Ionized Gases 2nd ed., Interscience.
Švestka, Z.: 1976, Solar Flares, D. Reidel Publ. Co., Dordrecht, Holland.
Syrovatskii, S. I. and Shmeleva, O. P.: 1972, Soviet Astron. A.J. 16, 273.
Thomas, R. N. and Athay, R. G.: 1961, Physics of the Solar Chromosphere, Interscience.
Ulmschneider, P.: 1971, Astron. Astrophys. 14, 275.
Van Beek, H. F., de Feiter, L. D., and de Jager, C.: 1974, Space Res. 14, 447.
Vernazza, J. E., Avrett, E. H., and Loeser, R.: 1976, Astrophys. J. Suppl. 30, 1.
Zirin, H. and Tanaka, K.: 1973, Solar Phys. 32, 173.
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On leave from: Department of Astronomy, The University, Glasgow G12 8QQ, Scotland, United Kingdom.
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Machado, M.E., Emslie, A.G. & Brown, J.C. The structure of the temperature minimum region in solar flares and its significance for flare heating mechanisms. Sol Phys 58, 363–387 (1978). https://doi.org/10.1007/BF00157282
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DOI: https://doi.org/10.1007/BF00157282