3-DIMENSIONAL RECONSTRUCTION OF A CORONAL MASS EJECTION

We reconstruct the three-dimensional density distribution of a coronal mass ejection (CME) in the interplanetary medium from data provided b y the Hellos spacecraft zodiacal light photometers and by the Solwind coronagraph. Computer assisted tomography (CAT) techniques can be used to reconstruct an image from its projections whenever multiple views of optically thin objects are available. In this case Thomson scatteri ng of sunlight from electrons is the source of variations in observed brightness. Polarization measurements from the Helios spacecraft yield additional information about line of sight electron densities not nor mally present in usual CAT-scan techniques. The Hellos and coronagraph views are not simultaneous; the Hellos 16 degrees photometer observes to within 17 R., whereas the Solwind observations extend outward to o nly 10 R.. However, if we assume radial velocities for ejected materia l, and that as an approximation the velocity of outward-moving materia l at a given height is fixed for the ejection, we obtain a solution. T his solution is certified by the reconstruction of two test structures - a hollow sphere and two spheres of material analyzed by the same te chniques used to deconvolve the CME. The CAT solution shows that the d ense structure of the May 7, 1979 CME is distributed in two lobes exte nding over a quarter of a heliospheric hemisphere. We conclude from th e CAT analysis that the CME material must have accelerated from 100 km s(-1) in the Solwind field of view to 600 km s(-1) in the view from H elios.