OBSERVATION OF BOWEN FLUORESCENCE AND OTHER PHENOMENA IN FIVE SYMBIOTIC STARS

Wavelength measurements and line identifications in the 3200 Å-3600 Å region are presented for AG Dra, HM Sge, V1016 Cyg, V1329 Cyg, Z And, and R Aqr. Except for R Aqr all of the systems showed high levels of ionization as exemplified by the presence of [Ne í] and [Fe vii]. The O iii lines that are excited by resonance lines of He ii (Bowen's mechanism) are analyzed in detail. A model based on an emitting sphere of uniform density yields impossibly large sizes and low densities. An alternative shell model yields much more reasonable dimensions, shell thicknesses of 10⁵ -10⁶ cm and electron densities as high as 10¹¹ -10¹² cm ¹. For the long-period systems (HM Sge, V1016 Cyg, and V1329 Cyg) these parameters are consistent with a colliding-wind model. For shorter-period systems (AG Dra and Z And) the derived parameters may suggest an accretion disk around the hot star. From [Ne v] and [Fe vii] lines the ratio of Ne/Fe is derived for five of the systems. For HM Sge and V1016 Cyg the Ne/Fe ratio is five and three times the solar ratio, indicating some depletion of iron onto dust. Both of these systems are of D-type, i.e., dusty, while the three systems of S-type do not show a high Ne/Fe ratio. Alternatively, a high neon abundance could be due to mass loss from an O-Ne-Mg white dwarf. Spectra in the blue region (4200 Å-4620 Å) are briefly described. For V1016 Cyg the measured radial velocity of Fe ii lines is 10 km s⁻¹ more negative than it was in the period 1981-85. By combining all the data for V1016 Cyg an orbital period of 20 years may be indicated.