AAS 201st Meeting, January, 2003
Session 89. Planetary Nebulae and Dusty Clouds
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[89.04] [Ne V] 14.3/24.3 micron Flux Ratio as a Test of Collision Strengths

R.H. Rubin, S.W.J. Colgan, A.R. Daane (NASA/Ames), R.J. Dufour (Rice)

In an earlier study of planetary nebulae (PNs) with ISO observations, we found evidence that the useful electron density (N_e) diagnostic [Ne V] 14.3/24.3 micron line flux ratio was out of range of theoretical predictions using current atomic data (Rubin et al. 2001 in ASP Conf. Ser. 247, 479). In particular, NGC 6818 with a measured flux ratio of 0.71 was significantly out of bounds in the low N_e limit. Thus N_e could not be derived; we concluded that perhaps the calculations of the effective collision strengths for these lines should be revisited. We have extended the work to include all PNs in the ISO archive that have both lines well measured. Of this sample of 22 PNs, 10 are found to have measured ratios below the theoretical predicted limit. Like NGC 6818, they are off scale in the low-N_e limit. While there might be systematic errors affecting the ISO data, we note that the observed aperture sizes match for this line pair. Such IR astronomical data serve to provide important tests of atomic data, collision strengths in this case. In principle, well-calibrated measurements of the [Ne V] 14.3/24.3 flux ratio could improve upon the existing atomic data.

RR acknowledges support from the NASA Long-Term Space Astrophysics program. We are grateful to the NASA Undergraduate Research Program (USRP) for summer support to AD.

The author(s) of this abstract have provided an email address for comments about the abstract: rubin@cygnus.arc.nasa.gov

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