Abstract
X-ray observations of the solar corona show that it is comprised of three-dimensional magnetic structures which appear to be primarily in the form of fluxtubes or loops. Imaging the X-ray corona has led to a greater understanding of the dynamical behaviour of and the energy distribution in these magnetic structures. However, imaging observations, by their very nature, integrate along the line of sight resulting in a two-dimensional representation of the actual three-dimensional distribution. The optically thin nature of the solar corona to X-ray radiation makes the integrated images particularly difficult to interpret. The analysis of the two-dimensional observations must, therefore, inlcude the effect of the orientation of the coronal structure to the line-of-sight direction; a fact which is almost always ignored. In this paper we discuss the effect of loop orientation on the two-dimensional representation and argue that these effects may lead to a misinterpretation of the physics occurring in the structures observed. In particular, we discuss observations taken by the Soft X-ray Telescope (SXT) on board the Yohkoh satellite, taking account of the instrumental thermal response, spatial resolution, and point-spread-function.
We test the effect of geometry on the determination of the loop pressure by considering equatorial loops at various longitudes and discuss the implications of this for studies of coronal soft X-ray loops.
Similar content being viewed by others
References
Acton, L. W.: 1994, in V. Rušin, P. Heinzel, and J.-C. Vial (eds.), ‘Solar Coronal Structures’, IAU Colloq. 144, 69.
Bachelor, D. A. and Schmahl, E. J.: 1994, Proc. of 3rd SOHO Workshop, Solar Dynamic Phenomena and Solar Wind Consequences, ESA SP-373, p. 203.
Collins-Petersen, C., Bruner, M., Acton, L. W., and Ogawara, Y.: 1993, Sky Teles. 86, No. 3, 20.
Dixon, W. W., Klimchuk, J. A., Sturrock, P. A., and Lemen, J. R.: 1991, in Y. Uchida, R. C. Canfield, T. Watanabe, and E. Hiei (eds.), Flare Physics in Solar Activity Maximum 22, Springer-Verlag, New York, p. 297.
Hiei, E.: 1994, in V. Rušin, P. Heinzel, and J.-C. Vial (eds.), ‘Solar Coronal Structures’, IAU Colloq. 144, 163.
Kano, R. and Tsuneta, S.: 1995, Astrophys. J. 454, 934.
Martens, P. C., Acton, L. W., and Lemen, J. R.: 1995, Solar Phys. 157, 141.
Porter, L. J. and Klimchuk, J. A.: 1995, Astrophys. J. 435, 520.
Rosner, R., Tucker, W. H., and Vaiana, G. S.: 1978, Astrophys. J. 220, 643.
Tsuneta, S. et al.: 1991, Solar Phys. 136, 37.
Vaiana, G. S.: 1973, Astrophys. J. 185, L47.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Alexander, D., Katsev, S. Geometrical considerations in imaging the solar corona. Sol Phys 167, 153–166 (1996). https://doi.org/10.1007/BF00146334
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00146334