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\n Aims. Coronal mass ejections or CMEs are large dynamical solar-corona events.\nThe mass balance and kinematics of a fast limb CME, including its\nprominence progenitor and the associated flare, will be compared\nwith computed magnetic structures to look for their origin and\neffect.\n Methods. Multi-wavelength ground-based and spaceborne observations are used to study\na fast W-limb CME event of December 2, 2003, taking into account\nboth on and off disk observations. Its erupting prominence is\nmeasured at high cadence with the Pic du Midi full Hα\nline-flux imaging coronagraph. EUV images from SOHO/EIT and\nCORONAS-F/SPIRIT space instruments are processed including\ndifference imaging. SOHO/LASCO images are used to study the mass\nexcess and motions. Computed coronal structures from extrapolated\nsurface magnetic fields are compared to observations.\n Results. A fast bright expanding coronal loop is identified in the region recorded\n slightly later by GOES as a C7.2 flare, followed by a brightening and an\n acceleration phase of the erupting material with both cool and hot components.\nThe total coronal radiative flux dropped by ~7% in the 19.5 nm channel and\n by 4% in the 17.5 nm channel, revealing a large dimming effect at and above the limb\nover a 2 h interval. The typical 3-part structure observed 1 h later\nby the Lasco C2 and C3 coronagraphs shows a core shaped similarly\n to the eruptive filament/prominence. The total measured mass of the escaping CME\n (~1.5$\\times$1016 g from C2 LASCO observations) definitely exceeds the estimated\n mass of the escaping cool prominence material although assumptions made to\n analyze the Hα erupting prominence, as well as the\n corresponding EUV darkening of the filament observed several days before, made\n this evaluation uncertain by a factor of 2. This mass budget suggests that the event\n is not confined to the eruption region alone. From the current free extrapolation\nwe discuss the shape of the magnetic neutral surface and a possible\n scenario leading to an instability, including the small scale dynamics inside and\n around the filament.\n