STEREOSCOPIC RECONSTRUCTION FROMSTEREO/EUV IMAGERS DATA OF THE THREE-DIMENSIONAL SHAPE AND EXPANSION OF AN ERUPTING PROMINENCE

Abstract

On 2007 May 9, a prominence eruption was observed in the Heii λ304 filter by the two EUV Imagers (EUVI) telescopes aboard the STEREO A and B spacecrafts. The high spatial resolution (∼1. �� 5p ixel −1 ) EUVI images have been used to infer via triangulation the three-dimensional (3D) shape and orientation of the prominence � 12 minutes after the beginning (13:40 UT) of the eruption. At this time, the prominence has the shape of a “hook” with the base anchored at the Sun. The “hook” prominence is highly inclined southward with respect to the radial direction, has an average thickness of 0.061 R� , a length of 0.43 R� , and lies in first approximation on a plane inclined by ∼54. 5 with respect to the line of sight. Thanks to the very high temporal cadence (∼37 s) of EUVI observations it has been possible also to infer the 3D early eruption trajectory. In the following ∼20 minutes the prominence rotates westward, undergoing a strong latitudinal acceleration, ∼3 times larger than the radial acceleration. In this time interval, the prominence expands in a direction mainly parallel to the plane of the sky; the total volume occupied by the plasma increases by a factor of ∼8, while the prominence thickness increases only by ∼12%. This is related to the fact that the early prominence expansion is anisotropic and occurs mainly on a plane parallel to the plane of the sky. Even if the smallscale spatial distribution of the erupting material observed in the Heii EUVI images is quite complex, both the approximately planar shape and the successive planar expansion suggest that on larger spatial scales the prominence can be globally approximated as a two-dimensional “ribbon-like” feature, instead of a 3D twisted flux tube.