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 η Carinae

Abstract

Context. The Si III] 1892 angstrom 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 Si II in the radiation-richWeigelt blobs where the two excitation steps are provided by the two intense hydrogen lines Ly alpha and Ly gamma. (Less)