The He Fowler lines and the O and N Bowen fluorescence lines in the symbiotic nova RR Telescopii

¹ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy e-mail: selvelli@ts.astro.it
² CIFIST Marie Curie Excellence Team
³ Observatoire de Paris, GEPI, 5 place Jules Janssen, 92195 Meudon, France

Received: 3 August 2006
Accepted: 17 December 2006

Abstract

Aims.A detailed study of the and Bowen lines in the spectrum of RR Tel.

Methods.Absolute intensities for the , , and  emission lines have been obtained from STIS, UVES, FEROS and IUE data, after re-calibration of UVES and FEROS on the STIS scale.

Results.A new measure of reddening ( ~ 0.00) has been obtained from the comparison between the observed and the theoretical intensity decrement for 20 emission lines of the  Fowler (n  3) series. This value has been confirmed by the STIS and IUE continuum distribution, and by the value of n_H from the damped profile of the IS H Ly-α line. We have obtained very accurate measurements for about thirty Bowen lines of and a precise determination of the efficiency in the O1 and O3 excitation channels (18% and 0.7%, respectively). The relative  intensities are in good agreement with the predictions by Froese Fischer (1994). A detailed study of the decays from all levels involved in the Bowen mechanism has lead to the detection of two new  Bowen lines near λ 2190. High resolution IUE data have shown a nearly linear decline with time, from 1978 to 1995, in the efficiency of the O1 and O3 processes, with a steeper slope for the O3 channel. A detailed study of the  λ 4640 lines and of their excitation mechanism has shown that, recombination and continuum fluorescence being ruled out, line fluorescence remains the only viable mechanism to pump the 3d  and 3d  levels of . We point out the important role of multiple scattering in the resonance lines of  and  near λ 374 and show that the observed  line ratios and intensities can be explained in terms of line fluorescence by the three resonance lines of  at λλ 374.432, 374.162 and 374.073 under optically thick conditions.