The spectrum of NGC 7027

Keyes, C. D.; Aller, L. H.; Feibelman, W. A.

doi:10.1086/132607

Cited by 62 publications

(58 citation statements)

References 23 publications

(33 reference statements)

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“…The data used were taken from the electronic emissionline catalogue for planetary nebulae by Kaler et al (1997), from Kingsburgh & English (1992) and from the spectral survey of high surface brightness planetaries by Hyung, Aller, Feibelman and collaborators (Aller & Hyung 1995;Aller et al 1996;Feibelman et al 1994Feibelman et al , 1996Hyung 1994;Hyung & Aller 1995a,b, 1996, 1997a,b, 1998Hyung et al 1993Hyung et al , 1994aHyung et al ,b,c, 1995Hyung et al , 1997Hyung et al , 1999aHyung et al ,b, 2000Hyung et al , 2001Keyes et al 1990). Instead of comparing directly the derived densities, as has been done by other authors, what implies in discarding all line ratios close or beyond the saturation limits at low and high densities, we have compared the line ratios themselves with one another.…”

Section: Discussionmentioning

confidence: 99%

Study of electron density in planetary nebulae

Copetti

Writzl

2002

A&A

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Abstract. We present a comparison of electron density estimates for planetary nebulae based on different emissionline ratios. We have considered the density indicators. The observational data were extracted from the literature. We have found systematic deviations from the density homogeneous models, in the sense that:We argue that the lower [O ii] density estimates are likely due to errors in the atomic parameters used.

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Section: Discussionmentioning

confidence: 99%

Study of electron density in planetary nebulae

Copetti

Writzl

2002

A&A

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“…(9) at electron temperatures of T e ϭ 10,000 K (solid line) and 20,000 K (dashed-dotted line), plus those derived by using the atomic data of Butler et al (10) at T e ϭ 10,000 K (dashed line). F transitions is detected in the spectrum of NGC 7027 (19), so that the measured [K V] line ratio for this object should be secure. Indeed, our results indicate that the [K V] lines may be used as a reliable density diagnostic, but only for objects that do not show a strong Fe II emission line spectrum.…”

Section: Resultsmentioning

confidence: 98%

“…Emission line intensities in the NGC 7027 spectrum have been corrected for interstellar extinction by using the extinction curve of Seaton (21), in conjunction with the interstellar extinction coefficient C ϭ 1.47E(B Ϫ V) ϭ 1.37 (19). In Figs.…”

Section: Resultsmentioning

confidence: 99%

Emission lines of [K v ] in the optical spectra of gaseous nebulae

Keenan¹,

Aller²,

Espey³

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

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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 10 3 to 10 6 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. D 5/2 lines, which can provide an excellent electron density (N e ) diagnostic for the emitting plasma by means of their intensity ratio (3). However, to calculate reliable theoretical line ratios, accurate atomic data must be used, especially for electron impact excitation rates (4).Previously, we have derived theoretical ratios for P-like [S II] (5), [Cl III] (6), and [Ar IV] (7) applicable to the spectra of gaseous nebulae, by using electron impact excitation rates calculated with the R-matrix code (8). Very recently, Wilson and Bell (9) have extended this work by performing R-matrix calculations for P-like K V, which are a significant improvement over the earlier results of Butler et al. (10), because of the inclusion of more levels and the delineation of additional resonances in the collision cross sections (see ref. 9 for more details).In this paper we use the Wilson and Bell (9) atomic data for K V to derive density-sensitive line ratios for this ion involving the nebular transitions at 4122.6 Å and 4163.3 Å. These data are subsequently compared with high-resolution optical observations to investigate the usefulness of the [K V] line ratio as a density diagnostic. We note that the [K V] nebular ratio is potentially a very important density indicator. As the [K V] lines arise in a region where K IV is ionized, and the ionization potential (IP) of this species is 60.9 eV (1 eV ϭ 1.602 ϫ 10 Ϫ19 J), the [K V] emission zone will lie in a very high-excitation part of a nebula. Most density diagnostic line ratios for highexcitation regions of nebulae lie at UV or infrared wavelengths, such as those for [Ne IV] (11) and [O IV] (12). Some highexcitation species, including Fe VII and Ar IV, have emission lines in the optical, but their intensity ratios are sensitive to both density and temperature (7, 13). Hence, if reliable values of N e could be derived from [K V], this would mean that densities could be determined for the high-excitation zones of nebulae on the basis of optical observations alone. Adopted Atomic Data and Theoretical Line RatiosThe model ion for K V consisted of the three LS states within the 3s 2 3p 3 ground configuration, namely 4 S, 2 D, and 2 P, making a total of five fine-structure levels. Energies of all these levels were taken from Sugar and Corliss (14). Test calculations, including the higher-lying 3s3p 4 terms, were found to have a negligible effect on the 3s 2 3p 3 level populations at the electron temperatures and densities typical of gaseous nebulae, and hence these states were not included in the analysis.Electron impact...

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“…The spectra of some bright, well studied planetary nebulae, such as NGC 7027, NGC 7662, NGC 2022 (Peimbert et al 1987;Keyes et al 1990), were used in order to correct the S-distortion, inherent to the image tube, and to level out the wavelength dependence of the instrumental response. The precision of intensities is about 10-15% for moderate and strong emission lines.…”

Section: Observationsmentioning

confidence: 99%