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 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] 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 Lyα and Lyγ.