Ultraviolet Coronagraph Spectrometer observation of the 1996 December 23 coronal mass ejection

The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) observed a spectacular coronal mass ejection (CME) caused by a prominence eruption on 1996 December 23. The evolution of the ejected prominence material was followed for 1 hr and 50 minutes. The observation consists of a series of 5 minute exposures, at a fixed heliocentric distance of 1.5 R circle dot in several spectral ranges. The Lyman lines of hydrogen brighten more than 2 orders of magnitude during the CME. The C III 977.02 Angstrom line is very bright, and many other low-temperature lines have been detected. Line intensities and profiles provide important diagnostics for the physical and dynamical parameters of the ejected plasma. Lines widths show nonthermal line broadening due to a plasma expansion with velocity larger than 50 km s(-1). The Ly alpha inside the CME region shows red and blue shifts, up to 0.2 Angstrom (50 km s(-1)) and 0.8 Angstrom (200 km s(-1)), respectively. A preliminary estimate shows a flat emission measure distribution 3 or 4 orders of magnitude smaller than typical prominence emission measures. Essentially the same structure in space and velocity is seen in the Lyman lines, in C III (10(5) K) and in 0 VI (3 x 10(5) K).