Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-25T15:46:30.450Z Has data issue: false hasContentIssue false

Solar Activity Observed in X-Rays and the EUV from OSO 7

Published online by Cambridge University Press:  14 August 2015

Roger J. Thomas*
Affiliation:
Laboratory for Solar Physics and Astrophysics, NASA-Goddard Space Flight Center, Greenbelt, Md., U.S.A.

Abstract

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.

Since 1971 the Goddard X-ray and EUV spectroheliograph aboard OSO 7 has been measuring the spatial distribution and time-variations of localized temperature and density features in solar active centers and flares. In some cases the sizes, shapes, orientations and locations of emitting plasmas at temperatures ranging from 104 K (Hα) to as high as 2 × 107 K (Fe xxv) have now been measured simultaneously. Our observations of active regions are consistent with the coronal structure being made up of nested systems of arches with footpoints in areas of opposite magnetic polarity. Temperatures seem to increase for arches nearer the center and also towards the top of any given magnetic arch, the innermost loops having the highest temperature gradients. There is also some evidence for electric current flow along such loops. Radiative cooling is significant for the region's hot central core which therefore must be maintained by a more or less continuous injection of energy.

A nested arch structure is also indicated for XUV flares of the two-component type, which likewise may require continuous energy input since conduction cooling should otherwise be very rapid. Multiple spikes during the impulsive phase seem to represent the consecutive triggering of different sources within the region and may occur outside of any detectable pre-existing coronal feature. Comparison of spatial distributions at several wavelengths during various stages of flare events provides information on interactions between the wide range of atmospheric levels involved. We have evidence for polarization of about 20% in a number of X-ray bursts, continuing throughout the decay phase. At least for some flares, our measurements seem to contradict the model of electron beams being radially injected into the chromosphere.

Type
Part 1: General Solar Activity, Coronal Holes and Bright Points
Copyright
Copyright © Reidel 1975 

References

Angel, J. R. P.: 1969, Astrophys. J. 158, 219.Google Scholar
Beigman, I. L.: 1974, Preprint No. 68, Lebedev Physical Institute, Moscow.Google Scholar
Blake, R. L., Chubb, T. A., Friedman, H., and Unzicker, A. E.: 1964, Space Res. IV, 785.Google Scholar
Brown, J. C., McClymont, A. N., and McLean, I. S.: 1974, Nature 247, 448.Google Scholar
Chupp, E. L., Forrest, D. J., and Suri, A. N.: 1973, in Ramaty, R. and Stone, R. G. (eds.), High Energy Phenomena on the Sun, NASA SP-342, p. 285.Google Scholar
Cox, D. P. and Tucker, W. H.: 1969, Astrophys. J. 157, 1157.Google Scholar
Culhane, J. L., Vesecky, J. F., and Phillips, K. J. H.: 1970, Solar Phys. 15, 394.Google Scholar
Datlowe, D. W. and Hudson, H. S.: 1975, This volume, p. 209.CrossRefGoogle Scholar
De Jager, C.: 1965, Ann. Astrophys. 28, 125.Google Scholar
De Jager, C. and Kundu, M. R.: 1963, Space Res. III, 836.Google Scholar
Donnelly, R. F.: 1967, J. Geophys. Res. 72, 5247.Google Scholar
Donnelly, R. F.: 1969, Astrophys. J. 158, L165.Google Scholar
Donnelly, R. F., Wood, A. T., and Noyes, R. W.: 1973, Solar Phys. 29, 107.Google Scholar
Elwert, G.: 1968, in Kiepenheuer, K. O. (ed.), ‘Structure and Development of Solar Active Regions’, IAU Symp. 35, 444.Google Scholar
Frost, K. J.: 1969, Astrophys. J. 158, L159.Google Scholar
Jordan, C.: 1975, This volume, p. 109.Google 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. 157, L139.Google Scholar
Kane, S. R. and Donnelly, R. F.: 1971, Astrophys. J. 164, 151.CrossRefGoogle Scholar
Korchak, A. A.: 1967, Soviet Phys. – Dokl. 12, 192.Google Scholar
Nakada, M. P., Neupert, W. M., and Thomas, R. J.: 1974, Solar Phys. 37, 429.Google Scholar
Nakagawa, Y.: 1974, Private Communication.Google Scholar
Neupert, W. M., Thomas, R. J., and Chapman, R. D.: 1974, Solar Phys. 34, 349.Google Scholar
Noyes, R. W., Withbroe, G. L., and Kirshner, R. P.: 1970, Solar Phys. 11, 388.Google Scholar
Pounds, K. A. and Russell, P. C.: 1966, Space Res. VII, 38.Google Scholar
Reidy, W. P., Vaiana, G. S., Zehnpfennig, T., and Giacconi, R.: 1968, Astrophys. J. 151, 333.Google Scholar
Rust, D. M.: 1974, Private communication.Google Scholar
Tandberg-Hanssen, E.: 1973, Earth Extraterrestrial Sci. 2, 89.Google Scholar
Tindo, I. P., Ivanov, V. D., Mandelstam, S. L., and Shuryghin, A. I.: 1970, Solar Phys. 14, 204.CrossRefGoogle Scholar
Tindo, I. P., Ivanov, V. D., Mandelstam, S. L., and Shuryghin, A. I.: 1972a, Solar Phys. 24, 429.Google Scholar
Tindo, I. P., Ivanov, V. D., Valnicek, B., and Livshits, M. A.: 1972b, Solar Phys. 27, 426.CrossRefGoogle Scholar
Tucker, W. H.: 1973, Astrophys. J. 186, 285.Google Scholar
Underwood, J. H. and Neupert, W. M.: 1974, Solar Phys. 35, 241.Google Scholar
Vaiana, G. S., Reidy, W. P., Zehnpfennig, T., Van Speybroeck, L., and Giacconi, R.: 1968, Science 161, 564.CrossRefGoogle Scholar
Vorpahl, J. and Zirin, H.: 1970, Solar Phys. 11, 285.CrossRefGoogle Scholar
Widing, K. G.: 1975, This volume, p. 153.Google Scholar