Nebular observations and stellar coronae

Copernicus UV observations of O VI in early-type stars are used to infer the existence of coronae or hot stellar winds. Attention is given to the optical doublet of O VI at wavelengths 3811 and 3834, which is seen in the spectra of some central stars in planetary nebulae, and taken to be evidence of a coronal wind. It is noted (from observations of NGC 6751) that hot gas in the coronal model produces radiation at energies above 54 eV, which can affect He II Zanstra temperatures. He(+) ionizing radiation in population I early-type stars is also taken as an indication of hot winds.