Bowen fluorescence lines in symbiotic stars - I. Observational data, line ratios and efficiency

Spectroscopic observations have been taken for eight type-D symbiotic syste ms in the spectral regions lambda lambda 3100-4100 and lambda lambda 3700-5 700. We show that the OIII. permitted lines formed by the O1 and O3 Bowen p rocesses are definitely present in these objects. In this paper the data ha ve been used to calculate ratios of lines arising from the same upper level . The results indicate that the intermediate-coupling radiative rates calcu lated by Froese Fischer are the most accurate for OIII Bowen fluorescence l ines. The efficiencies of the Bowen mechanism for both processes are derive d. In spite of the relatively small size of our sample, we find that the ef ficiencies increase with the fractional abundance of ionized helium and ele ctronic density, but decrease with electron temperature, confirming previou s results from studies of planetary nebulae.