Emission lines of [Cl II] in the optical spectra of gaseous nebulae

Francis Keenan, Don Pollacco, K.M. Exter, L.H. Aller, S. Hyung

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Abstract

Recent R-matrix calculations of electron impact excitation rates among the 3s(2)3p(4) levels of Cl II are used to derive the nebular emission-line intensity ratios R-1=I(6161.8 Angstrom)/I(8578.7 Angstrom) and R-2=I(6161.8 Angstrom)/I(9123.6 Angstrom) as a function of electron temperature (T-e) and density (N-e). The ratios are found to be very sensitive to changes in T-e but not N-e for densities lower than 10(5) cm(-3). Hence, they should, in principle, provide excellent optical T-e diagnostics for planetary nebulae. The observed values of R-1 and R-2 for the planetary nebulae NGC 6741 and IC 5117, measured from spectra obtained with the Hamilton echelle spectrograph on the 3 m Shane Telescope, imply temperatures in excellent agreement with those derived from other diagnostic lines formed in the same region of the nebula as [Cl II]. This provides some observational support for the accuracy of the [Cl II] line ratio calculations and hence the atomic data on which they are based. The [Cl II] 8578.7 and 9123.6 Angstrom lines are identified for the first time (to our knowledge) in 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. However, the 6161.8 Angstrom feature is unfortunately too weak to be identified in the RR Telescopii observations, consistent with its predicted line strength.
Original languageEnglish
Pages (from-to)385-389
Number of pages5
JournalAstrophysical Journal
Volume584
Issue number1 I
Publication statusPublished - 10 Feb 2003

ASJC Scopus subject areas

  • Space and Planetary Science

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    Keenan, F., Pollacco, D., Exter, K. M., Aller, L. H., & Hyung, S. (2003). Emission lines of [Cl II] in the optical spectra of gaseous nebulae. Astrophysical Journal, 584(1 I), 385-389.