Prominence Eruption Observed in He II 304 Å up to >6 Solar Radii by EUI/FSI Aboard Solar Orbiter

On 15–16 February 2022, a large prominence eruption was observed in the 304 Å (He II) passband of the Extreme Ultraviolet Imager/Full Sun Imager telescope aboard the Solar Orbiter spacecraft. Observations from several viewpoints (Solar Orbiter, SOHO, STEREO, PROBA2, SDO, GOES-16) were analyzed to infer the kinematics of the prominence and its associated coronal mass ejection (CME) in three-dimensional space. The leading parts of the prominence and the corresponding CME are very fast, propagating at speeds of 1700 and 2200 km/s respectively, and the trailing parts of the prominence are slower, propagating at speeds around 500 km/s. Some parts of the prominence can be followed up to heights of over 6 solar radii. Observations taken in several EUV passbands allowed us to investigate the radiative properties of the prominence. The He II emission seems to be produced via the collisional excitation mechanism rather than via scattering of the incident radiation. This is the first prominence observed in the He II emission at 304 Å at such a great height (above 6 solar radii), and other similar events were observed since that time. This implies that helium may not be fully ionized at these heights, with such prominences potentially being a source of rare He+ ions in the solar wind.