Abstract
Maps of the brightness distribution of the ‘quiet Sun’ at 80 and 160 MHz reveal the presence of features both brighter and darker than average. The ‘dark’ regions are well correlated with dark regions on UV maps; we deduce that they result from ‘coronal holes’. The ‘bright’ regions are associated with quiescent filaments and not plages or bright regions on microwave or UV maps; we deduce that they result from ‘coronal helmets’.
When coronal holes appear near the centre of the disk we can estimate the density and kinetic temperature in the holes from the radio observations. For a hole observed on 1972 July 20–21, we find T ≈ 0.8 × 106 inside the hole and T ≈ 1.0 × 106 in average regions outside the hole. Inside the hole the density is estimated to be about one-quarter of that in Newkirk's model of the spherically symmetric corona.
Variations in brightness at a fixed height above the limb are generally well correlated with scans at a similar height made with a K-coronameter. Occasional differences may result from streamers protruding beyond the limb from the back of the Sun. These can be seen by the K-coronameter but, because of refraction of the radio rays, not by the radio-heliograph.
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References
Altschuler, M. D., Trotter, D. E., and Orrall, F. Q.: 1972, Solar Phys. 26, 354.
Aubier, M., Leblanc, Y., and Boischot, A.: 1971, Astron. Astrophys. 12, 435.
Avignon, Y. and Le Squeren-Malinge, A. M.: 1961, Compt. Rend. 253, 2859.
Axisa, F., Avignon, Y., Martres, M. J., Pick, M., and Simon, P.: 1971, Solar Phys. 19, 110.
Billings, D. E.: 1966, A Guide to the Solar Corona, Academic Press, N.Y., p. 65.
Conway, R. G., Kellermann, K. I., and Long, R. J.: 1963, Monthly Notices Roy. Astron. Soc. 125, 261.
Hansen, R. T., Garcia, C. J., Hansen, S. F., and Loomis, H. G.: 1969, Solar Phys. 7, 417.
Hansen, S. F., Hansen, R. T., and Garcia, C. J.: 1972, Solar Phys. 26, 202.
Hobbs, R. W., Jordan, S. D., and Webster, W. J. Jr.: 1973, Nature Phys. Sci. 243, 48.
Kundu, M. R.: 1971, Solar Phys. 21, 130.
Leblanc, Y.: 1970, Astron. Astrophys. 4, 315.
McAlister, K. R. and Labrum, N. R.: 1967, Proc. Inst. Radio Elec. Engrs. Australia 28, 291.
Munro, R. H. and Withbroe, G. L.: 1972, Astrophys. J. 176, 511.
Newkirk, G. Jr.: 1961, Astrophys. J. 133, 983.
Newkirk, G. Jr.: 1967, Ann. Rev. Astron. Astrophys. 5, 213.
Perry, R. M. and Altschuler, M. D.: 1973, Solar Phys. 28, 435.
Pneuman, G. W.: 1972, Astrophys. J. 177, 793.
Quarterly Bulletin Solar Activity: 1973, IAU, No. 179.
Saito, K. and Owaki, N.: 1967, Publ. Astron. Soc. Japan 19, 535.
Sheridan, K. V.: 1970, Proc. Astron. Soc. Austr. 1, 304.
Sheridan, K. V., Labrum, N. R., and Payten, W. J.: 1973, Proc. IEEE 61, 1312.
Smerd, S. F.: 1950, Austr. J. Sci. Res. Series A 3, 34.
Solar-Geophysical Data: 1972, IER-FB 337, Part 1, U.S. Dept. of Commerce, Boulder, Colo.
Vaiana, G. S., Davis, J. M., Giacconi, R., Krieger, A. S., Silk, J. K., Timothy, A. F., and Zombeck, M.: 1973a, Astrophys. J. Letters 185, L47.
Vaiana, G. S., Krieger, A. S., and Timothy, A. F.: 1973b, Solar Phys. 32, 81.
Withbroe, G. L.: 1972, Solar Phys. 25, 116.
Withbroe, G. L., Dupree, A. K., Goldberg, L., Huber, M. C. E., Noyes, R. W., Parkinson, W. H., and Reeves, E. M.: 1971, Solar Phys. 21, 272.
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Exchange visitor from the Dept. of Astro-Geophysics, Univ. of Colorado, Boulder, U.S.A.
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Dulk, G.A., Sheridan, K.V. The structure of the middle corona from observations at 80 and 160 MHz. Sol Phys 36, 191–202 (1974). https://doi.org/10.1007/BF00151560
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DOI: https://doi.org/10.1007/BF00151560