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Issue A&A
Volume 452, Number 1, June II 2006
Page(s) 253 - 256
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20054375



A&A 452, 253-256 (2006)
DOI: 10.1051/0004-6361:20054375

Resonance-enhanced two-photon ionization (RETPI) of Si II and an anomalous, variable intensity of the $\mathsf{\lambda}$1892 Si III] line in the Weigelt blobs of $\eta$ Carinae

S. Johansson1, H. Hartman1 and V. S. Letokhov2, 1

1  Lund Observatory, Lund University, PO Box 43, 22100, Lund, Sweden
    e-mail: sveneric.johansson@astro.lu.se
2  Institute of Spectroscopy, Russian Academy of Sciences, 142190 Troitsk, Moscow region, Russia

(Received 19 October 2005 / Accepted 21 February 2006 )

Abstract
Context.The Si III] 1892 Å intercombination line shows an anomalously high intensity in spectra of the radiation-rich Weigelt blobs in the vicinity of Eta Carinae. The line disappears during the 100 days long spectral events occurring every 5.5 years.
Aims.The aim is to investigate whether resonance-enhanced two-photon ionization (RETPI) is a plausible excitation mechanism for the Si III]  $\lambda$1892 line.
Methods.The possible intensity enhancement of the $\lambda$1892 line is investigated as regards quasi-resonant intermediate energy levels of Si II.
Results.The RETPI mechanism is effective on $\ion{Si}{ii}$ in the radiation-rich Weigelt blobs where the two excitation steps are provided by the two intense hydrogen lines Ly$\alpha$ and Ly$\gamma$.


Key words: atomic processes -- radiation mechanisms: non-thermal -- HII regions -- stars: individual: $\eta$ Carinae

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© ESO 2006


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