UVCS Observations of a Helical CME Structure

A helical structure in the coronal mass ejection (CME) of 12 September 2000 was observed by the Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) at heliocentric distances of 3.5 and 6 R_⊙. A difference of 300 km sec^-1 in line-of-sight velocities for two segments of the helix obtained from Doppler measurements implies expansion and allows one to distinguish which segment was closest to the observer. The tilt of the segment then determines the handedness. Observed Ly α and C III line emissions indicate that the helix was threaded with filament plasma of varying density. While the helix constituted the bright core of filament plasma, the helix itself was most likely not the pre-existing filament structure.