%P 47-58 %D 1995 %T Neutral carbon far-red forbidden line emission from planetary nubulae %A XW LIU %A MJ BARLOW %A IJ DANZIGER %A RES CLEGG %V 273 %N 1 %X The temperature-sensitive neutral carbon forbidden lines at 8727, 9824 and 9850 Å 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(λ9824+λ9850)/I(λ8727) 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. %O This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. %I BLACKWELL SCIENCE LTD %K line formation, planetary nebulae: general %J Monthly Notices of the Royal Astronomical Society %L discovery10096154