A model for the origin of the anomalous and very bright UV lines of Fe II in gaseous condensations of the star Carinae
Department of Physics, Lund University, PO Box 118, 22100 Lund, Sweden e-mail: Vladilen.Letokhov@fysik.lu.se
2 Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow region, 142190, Russia
Corresponding author: S. Johansson, email@example.com
Accepted: 19 July 2001
We present a qualitative physical model of the origin of two very bright UV lines of Fe II at 2507-2509 Å, present in high-resolution spectra of gaseous condensations (blobs) close to the central star of η Carinae. The spectra have been obtained with the Hubble Space Telescope (HST). The model is based on a type of Bowen mechanism with selective photoexcitation of Fe II by a broad HLyα profile, generated in the HII region and diffusely transferred to the optically thick HI region. The frequency distribution by large Doppler diffusion into the HI region provides a substantial broadening of HLyα, which makes it possible to selectively photo-excite short-lived (≈1 ns) states at 11.2 eV in Fe II. Within the frame of the present model the intense HLyα radiation induces a depletion of the lower, long-lived (≈1 ms) level of the strong UV lines by photoionization. The subsequent recombination of Fe III explains the appearance of the "forest" of narrow Fe II lines. The possibility of a cyclic process is also discussed, where HLyα induces depletion to bound states, which have fast decays in the far-UV to the lower state of the Bowen pumping channel.
Key words: atomic processes / line: formation / radiation mechanisms: non-thermal / stars: individual: η Carinae
© ESO, 2001