Determination of the physical properties of an erupting prominence from SOHO/LASCO and UVCS observations

We studied the physical conditions of an erupting prominence observed in the core of a coronal mass ejection, using combination of SOHO/LASCO-C2 visible-light images and SOHO/UVCS ultraviolet data. Measured intensities and profiles of the neutral-hydrogen Lyman- α and Lyman- β lines and the 977 Å C III line were used together with the visible-light brightness to derive the geometrical and physical parameters of the prominence, such as the line-of-sight apparent thickness, electron column density, kinetic temperature, and microturbolent velocity. These parameters were used to constrain a non-LTE ( i.e., out of local thermodynamic equilibrium) radiative-transfer model of the prominence that provides the effective thickness, electron density, and flow velocity, in a sample of points selected along the prominence. The prominence can be described as a hot structure with low electron density and very low gas pressure compared to typical quiescent prominences. Intensities of the hydrogen lines were also used for a detailed determination of the plasma line-of-sight filling factor, in the two prominence points where simultaneous and cospatial LASCO-C2 and UVCS observations were available.