TY - JOUR SP - 47 VL - 273 PB - BLACKWELL SCIENCE LTD A1 - LIU, XW A1 - BARLOW, MJ A1 - DANZIGER, IJ A1 - CLEGG, RES JF - Monthly Notices of the Royal Astronomical Society Y1 - 1995/03// UR - https://doi.org/10.1093/mnras/273.1.47 ID - discovery10096154 N2 - 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(?9824+?9850)/I(?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. N1 - This version is the version of record. For information on re-use, please refer to the publisher?s terms and conditions. KW - line formation KW - planetary nebulae: general AV - public TI - Neutral carbon far-red forbidden line emission from planetary nubulae SN - 0035-8711 EP - 58 IS - 1 ER -