@article{discovery10096154, volume = {273}, month = {March}, publisher = {BLACKWELL SCIENCE LTD}, note = {This version is the version of record. For information on re-use, please refer to the publisher's terms and conditions.}, pages = {47--58}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {1}, year = {1995}, title = {Neutral carbon far-red forbidden line emission from planetary nubulae}, issn = {0035-8711}, keywords = {line formation, planetary nebulae: general}, url = {https://doi.org/10.1093/mnras/273.1.47}, abstract = {The temperature-sensitive neutral carbon forbidden lines at 8727, 9824 and 9850 ? have been measured simultaneously for the first time from a planetary nebula. The nebulae NGC 2346, NGC 2440, NGC 3132 and IC 4406 were observed. Accurate rest wavelengths of these lines are obtained. The observed line ratios I({\ensuremath{\lambda}}9824+{\ensuremath{\lambda}}9850)/I({\ensuremath{\lambda}}8727) are consistent with collisional excitation by electron impacts. It is demonstrated that radiative recombination and stellar continuum fluorescence are unimportant in exciting the observed [CI] lines, with the possible exception of NGC 2440 where a contribution from the former process cannot be ruled out. For NGC 2346, NGC 3132 and IC 4406, the observed [C I]line ratios yield electron temperatures between 7400 and 8000 K, about 1800 to 2800 K lower than those deduced from the [N II], [S III] and [O III] line ratios that we also measured. Electron densities are derived from the observed [N I], [S II] and [Cl III] doublet ratios.}, author = {LIU, XW and BARLOW, MJ and DANZIGER, IJ and CLEGG, RES} }