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Astron. Astrophys. 354, L41-L44 (2000)


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Letter to the Editor

The collision strength of the [Ne v] infrared fine-structure lines *

P.A.M. van Hoof 1,2, D.A. Beintema 3, D.A. Verner 1 and G.J. Ferland 1

1 University of Kentucky, Dept. of Physics & Astronomy, 177 CP Building, Lexington, KY 40506-0055, USA
2 Canadian Institute for Theoretical Astrophysics, McLennan Labs, 60 St. George Street, Toronto, ON M5S 3H8, Canada
3 SRON Laboratory for Space Research, P.O. Box 800, 9700 AV Groningen, The Netherlands

Received 30 November 1999 / Accepted 11 December 1999

Abstract

The calculation of accurate collision strengths for atomic transitions has been a long standing problem in quantitative spectroscopy. Most modern calculations are based on the R-matrix method and problems pertaining to the use of this method have led to a discussion of the accuracy of these results. More in particular, based on an analysis of the spectra of NGC 3918 and NGC 6302, Clegg et al. (1987) and Oliva et al. (1996) have questioned R-matrix calculations for the infrared [Ne V ] fine-structure transitions. Using improved flux measurements for the [Ne V ] lines, we show that the conclusion that these collision strengths would be too high, is not correct. The discrepancies found by Clegg et al. (1987) can be explained by the inaccuracy of the [Ne V ] 342.6 nm flux they adopted. The discrepancies found by Oliva et al. (1996) can be explained by the inaccuracy of the LRS flux for the [Ne V ] 14.32 µm line. Based on the data presented in this paper there is no reason to assume that there are any problems with the R-matrix calculations for Ne[FORMULA] of Lennon & Burke (1994). We show that the data are accurate at the 30 % level or better. This confirms the validity of the close coupling method.

Key words: atomic data – plasmas – ISM: planetary nebulae: individual: NGC 3918 – ISM: planetary nebulae: individual: NGC 6302 – ISM: planetary nebulae: individual: NGC 7027 – infrared: ISM: lines and bands

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA

Send offprint requests to: P.A.M. van Hoof at the Toronto address

© European Southern Observatory (ESO) 2000

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