TY - JOUR EP - 886 AV - public Y1 - 2004/12// TI - A reexamination of electron density diagnostics for ionized gaseous nebulae KW - atomic data KW - ISM : lines and bands KW - ISM : planetary nebulae : general PB - EDP SCIENCES S A ID - discovery10095999 N2 - We present a comparison of electron densities derived from optical forbidden line diagnostic ratios for a sample of over a hundred nebulae. We consider four density indicators, the [O II] ?3729/?3726, [S II] ?6716/?6731, [Cl III] ?5517/?5537 and [Ar IV] ?4711/?4740 doublet ratios. Except for a few H II regions for which data from the literature were used, diagnostic line ratios were derived from our own high quality spectra. For the [O II] ?3729/?3726 doublet ratio, we find that our default atomic data set, consisting of transition probabilities from Zeippen (1982) and collision strengths from Pradhan (1976), fit the observations well, although at high electron densities, the [O II] doublet ratio yields densities systematically lower than those given by the [S II] ?6716/?6731 doublet ratio, suggesting that the ratio of transition probabilities of the [O II] doublet, A(?3729)/A(?3726), given by Zeippen (1982) may need to be revised upwards by approximately 6 per cent. Our analysis also shows that the more recent calculations of [O II] transition probabilities by Zeippen (1987) and collision strengths by McLaughlin & Bell (1998) are inconsistent with the observations at the high and low density limits, respectively, and can therefore be ruled out. We confirm the earlier result of Copetti & Writzl (2002) that the [O II] transition probabilities calculated by Wiese et al. (1996) yield electron densities systematically lower than those deduced from the [S II] ?6716/?6731 doublet ratio and that the discrepancy is most likely caused by errors in the transition probabilities calculated by Wiese et al. (1996). Using our default atomic data set for [O II], we find that Ne([O II]) < Ne ([S II]) ? Ne ([Cl III]) < Ne ([Ar IV]). N1 - This version is the version of record. For information on re-use, please refer to the publisher's terms and conditions. IS - 3 SP - 873 VL - 427 A1 - Wang, W A1 - Liu, XW A1 - Zhang, Y A1 - Barlow, MJ JF - Astronomy & Astrophysics UR - https://doi.org/10.1051/0004-6361:20041470 ER -