Emission lines of [K V] in the optical spectra of gaseous nebulae
Abstract
Recent R-matrix calculations of electron impact excitation rates in K V are used to derive the nebular emission line ratio R = I(4122.6 Å)/I(4163.3 Å) as a function of electron density (Ne). This ratio is found to be very sensitive to changes in Ne over the density range 103 to 106 cm-3, but does not vary significantly with electron temperature, and hence in principle should provide an excellent optical Ne diagnostic for the high-excitation zones of nebulae. The observed value of R for the planetary nebula NGC 7027, measured from a spectrum obtained with the Hamilton Echelle spectrograph on the 3-m Shane Telescope, implies a density in excellent agreement with that derived from [Ne IV], formed in the same region of the nebula as [K V]. This observation provides observational support for the accuracy of the theoretical [K V] line ratios, and hence the atomic data on which they are based. However, the analysis of a high-resolution spectrum of the symbiotic star RR Telescopii, obtained with the University College London Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope, reveals that the [K V] 4122.6 Å line in this object is badly blended with Fe II 4122.6Å. Hence, the [K V] diagnostic may not be used for astrophysical sources that show a strong Fe II emission line spectrum.
- Publication:
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Proceedings of the National Academy of Science
- Pub Date:
- 2002
- DOI:
- 10.1073/pnas.062032299
- Bibcode:
- 2002PNAS...99.4152K
- Keywords:
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- Astronomy