1997 December 12 helical coronal mass ejection. II. Density, energy estimates, and hydrodynamics

We use Ultraviolet Coronagraph and Spectrometer (UVCS) spectra to investigate the density range of the plasma ejected during the coronal mass ejection (CME) on 1997 December 12. Time-dependent ionization states for several phenomenological models, with the boundary conditions derived from the EUV Imaging Telescope (EIT) and UVCS observations, were computed and constraints on the density and temperature of the plasma at the early stage of the ejection are obtained. The role of physical mechanisms such as thermal conduction, radiation, and heating is also studied with a two-dimensional hydrodynamics simulation. The kinetic, thermal, and gravitational energies are estimated as well as the plasma heating. Whenever the ejected plasma has a density greater than or equal to 10(9)cm(-3), a continuous supply of heat is required to meet the conditions observed at 1.7 R.. Moreover heating mechanisms that release energy gradually during the outward motion of the plasma seem to be more appropriate than those that dump most of the energy when the plasma is lower in the corona. Our simulations also indicate that a. three-dimensional self-similar expansion does not fit the UVCS observations. Comparisons with some CME models from the dynamical and energetics points of view are discussed.