Time Evolution of the Altitude of an Observed Coronal Wave

Abstract

The nature of coronal wave fronts is deeply debated. They are observed in several wavelength bandpasses in spectra, and are frequently interpreted as magnetosonic waves propagating in the lower solar atmosphere. However, they can be attributed to the line of sight projection of the edges of coronal mass ejections. Therefore, the altitude estimation of these features is crucial to discriminate in favor of one of these two interpretations. We take advantage of a set of observations obtained from two different points of view by EUVI/SECCHI/STEREO on December, 7th 2007 to derive the time evolution of the altitude of a coronal wave front. We develop a new technique to compute the altitude. We find that the observed brightness has an increasing altitude during 5 minutes, then the altitude decreases slightly back to the low corona. We interpret the evolution of the altitude as following: the increase of altitude of the wave front is linked to the rise of a bubble like structure whether it is a magnetosonic wave front or a CME in the first phase. During the second phase, the observed brightness is mixed with the brightening of the underlying magnetic structures as the emission of the plasma of the wave front fades due to the plasma dilution with the altitude.