What the awkward relatives tell us about planetary nebulae hosting binary systems

Relatives to Planetary Nebulae, such as barium stars or symbiotic systems, can shed light on the connection between Planetary Nebulae and binarity. Because of the observational selection effects against direct spectroscopic detection of binary PNe cores with orbital periods longer than a few dozen days, at present these "awkward relatives" are a critical source of our knowledge about the binary PNe population at longer periods. Below a few examples are discussed, posing constraints on the attempts to model nebula, ejection process in a binary. © 2006 International Astronomical Union.

Emission lines of [Cl II] in the optical spectra of gaseous nebulae

Recent R-matrix calculations of electron impact excitation rates among the 3s(2)3p(4) levels of Cl II are used to derive the nebular emission-line intensity ratios R-1=I(6161.8 Angstrom)/I(8578.7 Angstrom) and R-2=I(6161.8 Angstrom)/I(9123.6 Angstrom) as a function of electron temperature (T-e) and density (N-e). The ratios are found to be very sensitive to changes in T-e but not N-e for densities lower than 10(5) cm(-3). Hence, they should, in principle, provide excellent optical T-e diagnostics for planetary nebulae. The observed values of R-1 and R-2 for the planetary nebulae NGC 6741 and IC 5117, measured from spectra obtained with the Hamilton echelle spectrograph on the 3 m Shane Telescope, imply temperatures in excellent agreement with those derived from other diagnostic lines formed in the same region of the nebula as [Cl II]. This provides some observational support for the accuracy of the [Cl II] line ratio calculations and hence the atomic data on which they are based. The [Cl II] 8578.7 and 9123.6 Angstrom lines are identified for the first time (to our knowledge) in a high-resolution spectrum of the symbiotic star RR Telescopii, obtained with the University College London Echelle Spectrograph on the 3.9 m Anglo- Australian Telescope. However, the 6161.8 Angstrom feature is unfortunately too weak to be identified in the RR Telescopii observations, consistent with its predicted line strength.

Emission-line ratios for [N II] in gaseous nebulae and a comparison between theory and observation

R-matrix calculations of electron impact excitation rates among the 2s(2)2p(2) P-3, D-1, S-1, and 2s2p(3) S-5 levels of N II are presented. These results are used in conjunction with other recent calculations of electron impact excitation rates and Einstein A-coefficients for N II to derive the emission-line ratio: ratio diagrams and where (R-1, R-2) (R-1, R-3), where R-1 = I(5756.2 Angstrom)/I(6549.9 + 6585.2 Angstrom), R-2 = I(2143.5 Angstrom)/I(6549.9 + 6585.2 Angstrom), and R-3 = I(2139.7 Angstrom)/I(6549.9 + 658.2 Angstrom), for a range of electron temperatures (T-e = 5000-20,000 K) and electron densities (N-e = 10(2)-10(7) cm(-3)) appropriate to gaseous nebulae. These diagrams should, in principle, allow the simultaneous determination of T-e and N-e from measurements of the [N II] lines in a spectrum. Plasma parameters deduced for a sample of gaseous nebulae, using observational data obtained from ground-based telescopes plus the International Ultraviolet Explorer and Hubble Space Telescope satellites, are found to show generally excellent internal consistency and to be in good agreement with the values of T-e and N-e estimated from other line ratios. These results provide observational support for the accuracy of the theoretical ratios and hence the atomic data adopted in their derivation. Theoretical ratios are also presented for the infrared line pair R-4 = I(122 mum)/I(205 mum), and the usefulness of R-4 as an electron density diagnostic is briefly discussed.

Nebular and auroral emission lines of [Cl III] in the optical spectra of planetary nebulae

Electron impact excitation rates in Cl III, recently determined with the R-matrix code, are used to calculate electron temperature (T-e) and density (N-e) emission line ratios involving both the nebular (5517.7, 5537.9 Angstrom) and auroral (8433.9, 8480.9, 8500.0 Angstrom) transitions. A comparison of these results with observational data for a sample of planetary nebulae, obtained with the Hamilton Echelle Spectrograph on the 3-m Shane Telescope, reveals that the R-1 = /(5518 Angstrom)/I(5538 Angstrom) intensity ratio provides estimates of N-e in excellent agreement with the values derived from other line ratios in the echelle spectra. This agreement indicates that R-1 is a reliable density diagnostic for planetary nebulae, and it also provides observational support for the accuracy of the atomic data adopted in the line ratio calculations. However the [Cl III] 8433.9 Angstrom line is found to be frequently blended with a weak telluric emission feature, although in those instances when the [Cl III] intensity may be reliably measured, it provides accurate determinations of T-e when ratioed against the sum of the 5518 and 5538 Angstrom line fluxes. Similarly, the 8500.0 Angstrom line, previously believed to be free of contamination by the Earth's atmosphere, is also shown to be generally blended with a weak telluric emission feature. The [CI III] transition at 8480.9 Angstrom is found to be blended with the He I 8480.7 Angstrom line, except in planetary nebulae that show a relatively weak He I spectrum, where it also provides reliable estimates of T-e when ratioed against the nebular lines. Finally, the diagnostic potential of the near-UV [Cl III] lines at 3344 and 3354 Angstrom is briefly discussed.