Abstract
We analysed multifrequency 2-dimensional maps of the solar corona obtained with the Nançay radioheliograph during two solar rotations in 1986. We discuss the emission of the quiet Sun, coronal holes and local sources and its association with chromospheric and coronal features as well as with large-scale magnetic fields. The brightness temperature of the quiet Sun was 5 to 5.5 × 105 K at 164 MHz and 4.5 to 5 × 105 K at 408 MHz. A coronal hole, also detected in the 10830 Å He i line, had a brightness temperature of 4.5 × 105 at 164 and 2.5 × 105 at 408 MHz. We give statistics of source brightness temperatures (on the average 8% above the background at 164 MHz and 14% at 408 MHz), as well as distributions in longitude and latitude. Although we found no significant center-to-limb effect in the brightness temperature, the sources were not visible far from the central meridian (apparently a refraction effect). The brightest sources at 164 MHz were near, but not directly above active regions and had characteristics of faint type I continua. At 408 MHz some sources were observed directly above active regions and one was unambiguously a type I continuum. The majority of the fainter sources showed no association with chromospheric features seen on Hα synoptic charts, including filaments. Most of them were detected at one frequency only. Sources identified at three frequencies (164, 327, and 408 MHz) were located in regions of enhanced large-scale magnetic field, some of them at the same location as decayed active regions visible one rotation before on synoptic Hα charts. Multifrequency sources are associated with maxima of the green line corona. The comparison with K-corona synoptic charts shows a striking association of the radio sources with dense coronal regions, associated with the coronal neutral sheet. Furthermore, we detected an enhanced brightness region which surrounds the local sources and is stable over at least one solar rotation. We call this feature a coronal plateau and we identify it with the radio counterpart of the coronal neutral sheet.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Alissandrakis, C. E., Kundu, M. R., and Lantos, P.: 1980, Astron. Astrophys. 82, 30.
Alissandrakis, C. E., Lantos, P., and Nicolaidis, E.: 1985, Solar Phys. 97, 267.
Axisa, F., Avignon, Y., Martres, M. J., Pick, M., and Simon, P.: 1971, Solar Phys. 19, 110.
Baars, J. W. M. and Hartsuijker, A. P.: 1972, Astron. Astrophys. 17, 172.
Boischot, A.: 1958, Ann. Astrophys. 21, 273.
Boischot, A. and Moutot, M.: 1961, Ann. Astrophys. 24, 171.
Chiuderi-Drago, F., Avignon, Y., and Thomas, R. J.: 1977, Solar Phys. 51, 143.
Christiansen, W. N. and Mathewson, J. L.: 1959, in R. N. Bracewell (ed.), Paris Symposium on Radio Astronomy, Stanford University Press, Stanford, p. 108.
Christiansen, W. N., Warburton, J. A., and Davis, R. D.: 1957, Australian J. Phys. 10, 491.
Clavelier, B.: 1967, Ann. Astrophys. 30, 895.
Dulk, G. and Sheridan, K. V.: 1974, Solar Phys. 36, 191.
Dulk, G., Sheridan, K. V., Smerd, S. F., and Withbroe, G. L.: 1977, Solar Phys. 52, 349.
Dunn, R. B.: 1971, in C. J. Macris (ed.), Physics of the Solar Corona, D. Reidel Publ. Co., Dordrecht, Holland, p. 114.
Firor, J. W.: 1959, in R. N. Bracewell (ed.), Paris Symposium on Radio Astronomy, Stanford University Press, Stanford, p. 136.
Fort, B., Picat, J. P., Dantel, M., and Leroy, J. L.: 1973, Astron. Astrophys. 24, 267.
Hoeksema, J. T.: 1984, Thesis, Center for Space Science and Astrophysics, Stanford University.
Hundhausen, A. J.: 1977, in J. B. Zirker (ed.), Coronal Holes and High Speed Wind Streams, Colorado Associated University Press.
Jordan, C.: 1969, Monthly Notices Roy. Astron. Soc. 142, 501.
Lang, K. R., Willson, R. F., and Trottet, G.: 1988, Astron. Astrophys. 199, 325.
Lantos, P. and Avignon, Y.: 1975, Astron. Astrophys. 41, 137.
Lantos, P., Alissandrakis, C. E., Gergely, T., and Kundu, M. R.: 1987, Solar Phys. 112, 325.
Leblanc, Y.: 1970, Astron. Astrophys. 4, 315.
Leroy, J. L. and Noens, J. C.: 1983, Astron. Astrophys. 120, L1.
Loucif, M. L. and Koutchmy, S.: 1989, Astron. Astrophys. Suppl. Ser. 77, 45.
Martres, M. J., Simon, G., and Zlicaric, G.: 1988, Cartes synoptiques de la chromosphere solaire VII, No. 1, Paris Observatory.
Mercier, M.: 1978, Solar Phys. 57, 423.
Palagi, F. and Patriarchi, P.: 1980, Astron. Astrophys. Suppl. Ser. 41, 129.
Pneuman, G. W., Hansen, S. F., and Hansen, R. T.: 1978, Solar Phys. 59, 313.
Radioheliograph Group: 1977, Solar Phys. 55, 251.
Radioheliograph Group: 1983, Solar Phys. 88, 383.
Radioheliograph Group: 1989, Solar Phys. 120, 193.
Saito, K.: 1970, Ann. Tokyo Astron. Obs. XII, 2.
Saito, K.: 1972, Ann. Tokyo Astron. Obs. XIV, 93.
Sheridan, K. V.: 1970, Proc. Astron. Soc. Australia 1, 304.
Shevgaonkar, R. K., Kundu, M. R., and Jackson, P. D.: 1988, Astrophys. J. 329, 982.
Sime, D. G., Garcia, C., Yasukawa, E., Lundin, E., and Rock, K.: 1987, NCAR Technical Note 280.
Solar Geophysical Data: 1986, NOAA, Boulder.
Swarup, G. and Parthasarathy, R.: 1958, Australian J. Phys. 11, 338.
Trottet, G. and Lantos, P.: 1978, Astron. Astrophys. 70, 245.
Waldmeier, M.: 1958, Z. Astrophys. bf45, 155.
Waldmeier, M.: 1981, Solar Phys. 70, 251.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Lantos, P., Alissandrakis, C.E. & Rigaud, D. Quiet-Sun emission and local sources at meter and decimeter wavelengths and their relationship with the coronal neutral sheet. Sol Phys 137, 225–256 (1992). https://doi.org/10.1007/BF00161848
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00161848