Resonance-enhanced two-photon ionization (RETPI) of Si II and an anomalous, variable intensity of the λ1892 Si III line in the Weigelt blobs of η Carinae

Abstract

Context. The Si III] 1892 A 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] λ1892 line. Methods. The possible intensity enhancement of the λ1892 line is investigated as regards quasi-resonant intermediate energy levels of Si II. Results. The RETPI mechanism is effective on Si II in the radiation-rich Weigelt blobs where the two excitation steps are provided by the two intense hydrogen lines Lya and Lyy. © ESO 2006.