ar089.alexander04 Posted: 3-Feb-96 Updated: 20-Sep-96 Events specified: N/A
D. Alexander, D. Weston, G. Peres
The solar corona is a three-dimensional medium which is optically thin to X-rays. Imaging of this medium by the Soft X-ray Telescope (SXT) on the Yohkoh satellite necessarily involves the projection of the 3-D coronal structures on to a 2-D detector. Because of the optically thin nature of the corona the position of a soft X-ray loop on the solar disk becomes important for the determination of physical parameters from the observations. We are currently modelling the physical distributions in coronal loops in active regions and flares to take account of projection effects.
This work has many potential applications to studies using SXT data. A paper is currently being refereed ("Geometrical Considerations in Imaging the Solar Corona" - D. Alexander and S. Katsev) which outlines the basic methodology and which addresses the determination of coronal loop pressures as a function of position on the solar disk for active region loops. It was found that the usual assumption of uniform line of sight volume is not adequate when determining physical parameters from SXT data.
This work will be extended to the study of loop-top coronal sources in flares and will be applied to numerical flare models for a detailed comparison with SXT data.
Update 20-Sep-96
In the last few months we have completed re-vamped our geometry code to make it more generally useful. We have used this code to generate 3D loops representing the SXT emission resulting from the flare models of the Palermo code. The time sequence of these flare loops when viewed from various angles shows a range of behaviours, the most dramatic of which is the appearance of a strongly asymmetric loop resulting from a perfectly symmetric distribution of plasma parameters.