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

Abstract

Spectroscopic observations have been taken for eight type‐D symbiotic systems in the spectral regions λλ3100–4100 and λλ3700–5700. We show that the O iii permitted lines formed by the O1 and O3 Bowen processes are definitely present in these objects. In this paper the data have been used to calculate ratios of lines arising from the same upper level. The results indicate that the intermediate‐coupling radiative rates calculated by Froese Fischer are the most accurate for O iii Bowen fluorescence lines. The efficiencies of the Bowen mechanism for both processes are derived. In spite of the relatively small size of our sample, we find that the efficiencies increase with the fractional abundance of ionized helium and electronic density, but decrease with electron temperature, confirming previous results from studies of planetary nebulae.

The He$\rm_{II}$ Fowler lines and the O$\rm_{III}$ and N$\rm_{III}$ Bowen fluorescence lines in the symbiotic nova RR Telescopii

“…The same ratio was reported as =3.39 by Pereira et al (1999), in a study of Bowen fluorescence lines for a group of symbiotic stars, including RR Tel using ESO data with spectral resolution of ∼2.5 Å (FWHM). As mentioned in Sect.…”

“…The generally accepted E (B−V) values in the literature are in the range 0.08-0.10. Recently, Pereira et al (1999), using ESO data with spectral resolution of ∼2.5 Å (FWHM) have obtained E (B−V) = 0.04 from the relative ratios of H γ /H β , H δ /H β and He ii 3203/4686. Very recently, Young et al (2005) have derived E (B−V) ≤ 0.28 from a study of the Fe vii lines, based on the same STIS and UVES spectra of RR Tel as this work.…”

“…Figure 6 is complemented by Table 3 that includes the configuration and the energy (eV and cm −1 ) of the relevant levels. In most planetary nebulae and symbiotic stars, the "efficiency" of the Bowen mechanism, that is the fraction of He ii Ly-α photons that is converted into O iii Bowen lines (mostly a function of the He ii Ly-α optical depth) varies from object to object and covers almost the whole range of possible values (Liu & Danziger 1993;Pereira et al 1999). Therefore, the Bowen mechanism can have a major influence on the fate of the He ii Ly-α photons and consequently also on the photoionization equilibrium in the nebula.…”

Bowen excitation of N III lines in symbiotic stars

“…The O III Bowen excited lines have also been observed in symbiotic stars (Wallerstein et al 1991), and the mechanism behind their formation is discussed in detail by Pereira et al (1999). They show that the efficiency of the Bowen mechanism increases with electron density and fractional abundance of ionized helium.…”

A multi-epoch spectrophotometric atlas of symbiotic stars

“…Van Winckel et al (1993) surveyed emission line profiles for 59 objects and Ivison et al (1994) for 35. Pereira et al (1999) presented Bowen-fluorescence dominated blue spectra for 8 symbiotic stars and Schmid & Schild (1994) surveyed Ramanscatter dominated red spectra for 15 objects.…”