Auroral and nebular emission lines of forbidden S II in the optical spectra of planetary nebulae

• Published in: Monthly notices of the Royal Astronomical Society 1996-08, Vol.281 (3), p.1073-1080
• Main Authors: Keenan, F P, Aller, L H, Bell, K L, Hyung, S, McKenna, F C, Ramsbottom, C A
• Format: Article
• Language: English
• ISSN: 0035-8711

R-matrix calculations of electron impact excitation rates among the 3s2 3p3 levels of S II are presented, which are found to be up to a factor about 2 different from those of Cai and Pradhan (1993). The present results are subsequently used to calculate emission-line ratio-ratio diagrams involving the 4068-, 4076-, 6717- and 6730-A transitions, for a range of electron temperatures and electron densities appropriate to gaseous nebulae. These diagrams should, in principle, allow the simultaneous determination of T(e) and N(e) from measurements of the S II forbidden lines in a spectrum. Plasma parameters deduced for a sample of planetary nebulae, using observational data obtained with the Hamilton Echelle spectrograph on the 3-m Shane Telescope at Lick Observatory, are found to show excellent internal consistency, and to be in generally good agreement with the values of T(e) and N(e) estimated from other line ratios in the echelle spectra. These results provide observational support for the accuracy of the theoretical ratios, and hence the atomic data adopted in their derivation. (Author)