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  -