The ultraviolet and visible-light coronagraph of the Herschel experiment

The Herschel (HElium Resonant Scattering in the Corona and HELiosphere) experiment, to be flown on a sounding rocket, will investigate the helium coronal abundance and the solar wind acceleration from a range of solar source structures by obtaining the first simultaneous observations of the electron, proton and helium solar corona. The HERSCHEL payload consists of the EUV Imaging Telescope (EIT), that resembles the SOHO/EIT instrument, and the Ultraviolet and Visible Coronagraph (UVC).UVC is an imaging coronagraph that will image the solar corona from 1.4 to 4 solar radii in the EUV lines of HI 121.6 nm and the HeII 30.4 nm and in the visible broadband polarized brightness. The UVC coronagraph is externally occulted with a novel design as far as the stray light rejection is concerned. Therefore, HERSCHEL will also establish proof-of-principle for the Ultraviolet Coronagraph, which is in the ESA Solar Orbiter Mission baseline.The scientific objectives of the experiment will be discussed, togetherwith a description of the UVC coronagraph.