Resonance-Enhanced Two-Photon Ionization of Ions by Lyman alpha Radiation in Gaseous Nebulae
One of the mysteries of nebulae in the vicinity of bright stars is theappearance of bright emission spectral lines of ions, which imply fairlyhigh excitation temperatures. We suggest that an ion formationmechanism, based on resonance-enhanced two-photon ionization (RETPI) byintense H Lyman alpha radiation (wavelength of 1215 angstroms) trappedinside optically thick nebulae, can produce these spect