Bowen excitation of N III lines in symbiotic stars

¹ University College of Kalmar, 391 82 Kalmar, Sweden
² Atomic Astrophysics, Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden
³ INAF, Osservatorio Astronomico di Padova, Sede di Asiago, 36012 Asiago (VI), Italy

Received: 14 October 2004
Accepted: 3 December 2004

Abstract

We present a semi-empirical equation for prediction of the strengths of those N III lines that are generated by the Bowen mechanism and observed in spectra of symbiotic stars. The equation assumes that the Bowen mechanism is the only source populating the 3d state in N III, and comparisons with observations of the 3s–3p and 3p–3d transitions serve as a test of this assumption. In an ongoing study of symbiotic stars the equation has been applied to two symbiotic novae, RR Tel and AG Peg, by comparing the predicted N III line strengths to observed line intensities. It is clear that besides the Bowen mechanism there is another process, most likely radiative recombination, that contributes to the N III 3d population in AG Peg and is the main population process of this state in RR Tel. It is also clear that a second, not previously considered, N III channel, 2p ²P_1/2–3d ²D_3/2 at 374.198 Å, is pumped by O III in both RR Tel and AG Peg.