Neutral carbon far-red forbidden line emission from planetary nubulae
Abstract
The temperature-sensitive neutral carbon forbidden lines at 8727, 9824 and 9850 A 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(lambda9824+lambda9850)/I(lambda8727) 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 1995
- DOI:
- 10.1093/mnras/273.1.47
- Bibcode:
- 1995MNRAS.273...47L
- Keywords:
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- LINE FORMATION;
- PLANETARY NEBULAE: GENERAL