Physical Parameters of the 2000 February 11 Coronal Mass Ejection: Ultraviolet Spectra versus White‐Light Images

Abstract

We present spectra of a three-part coronal mass ejection (CME) observed by the Ultraviolet Coronagraph Spectrometer aboard SOHO on 2000 February 11. Images of the CME in different spectral lines show how the morphology depends on the temperature, density, and outflow speed of the ejected plasma. The H I Ly? is the line that best resembles the white-light data, although it can be rather different where the outflow speed severely dims its radiative component. We estimate the ranges of temperature and density in the front, prominence core, and void. We also estimate the outflow speed that is the true speed of the ejecta as obtained from the Doppler dimming technique, its component projected on the plane of the sky, and the line-of-sight speed for the three components of the CME. The plasma in the front was denser, cooler, and more depleted in O and Si than the ambient coronal streamer. These characteristics indicate that it originated in the closed field core of the pre-CME streamer. The leading edge was not the projection of a simple spherical shell onto the plane of the sky. The line profiles suggest a wide looplike structure, although a more complete shell that was brighter in some areas could also match the data. The prominence has a structure in temperature and density with the hotter top end emitting in the Mg X and Si XII lines while the bottom end was much cooler and visible only in the H I Lyman lines. Emission in the void was rather faint. The outflow speed obtained from Doppler dimming of the radiative lines, the line-of-sight speed measured from the Doppler shift of the lines, and the plane-of-the-sky speed estimated from the comparison of the images taken at 2.3 and 2.6 R? give speeds much lower than those estimated at greater heights (>4 R?) from LASCO and indicate a stronger acceleration at lower heights.