Abundances of planetary nebulae NGC 7662 and NGC 6741

Abstract

Abstract. The ISO and IUE spectra of the elliptical nebulae NGC 7662 and NGC 6741 are presented. These spectra are combined with the spectra in the visual wavelength region to obtain a complete, extinction corrected, spectrum. The chemical composition of the nebulae is then calculated and compared to previous determinations. The abundances found are compared to determinations made in other nebulae using ISO data. A discussion is given to see if possible evolutionary effects can be found from the abundance differences. IntroductionIncluding the ISO SWS spectra of planetary nebulae with spectra of the nebula in other spectral regions allows an abundance determination which has several important advantages. These have been discussed in earlier papers (e.g. see Pottasch & Beintema (1999), Pottasch et al. (2000), or Bernard Salas et al. (2001. The most important advantage is that the infrared lines originate from very low energy levels and thus give an abundance which is not sensitive to the temperature in the nebula, nor to possible temperature fluctuations. Furthermore, when a line originating from a high-lying energy level in the same ion is observed, it is possible to determine an effective temperature at which the lines in that particular ion are formed. When the effective temperature for many ions can be determined, it is possible to make a plot of effective temperature against ionization potential, which can be used to determine the effective temperature for ions for which only lines originating from a high energy level are observed. Use of an effective electron temperature takes into account the fact that ions are formed in different regions of the nebula. At the same time possible temperature fluctuations are taken into account.Use of the ISO spectra have further advantages. One of them is that the number of observed ions used in the Send offprint requests to: S. R. Pottasch, e-mail: pottasch@astro.rug.nl 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 UK) and with the participation of ISAS and NASA.abundance analysis is approximately doubled, which removes the need for using large "Ionization Correction Factors", thus substantially lowering the uncertainty in the abundance. A further advantage is that the extinction in the infrared is almost negligible, eliminating the need to include large correction factors.In much of the previously published analysis of PN using ISO spectra the nebulae involved had a bipolar morphology. In this paper we discuss two nebulae classified as "elliptical": NGC 7662 and NGC 6741. Their abundances will be compared to the other nebulae in the final section. The spectrum of NGC 7662 ISO observationsThe ISO SWS observations were made with the SWS02 observing template which gives good spectral resolution for a limited number of lines. This was supplemented by an SWS01 observation. The intensity of the lines found in the spectrum is shown in Table 1. The uncertainty of ...

Abundances in planetary nebulae: NGC 6826

“…The reasons for this have been discussed in earlier papers (e.g. see Pottasch & Beintema 1999;Pottasch et al 2006Pottasch et al , 2001Bernard Salas et al 2001), and can be summarized as follows.…”

Abundances in planetary nebulae: Hb 5

“…The reasons for this have been discussed in earlier papers (e.g. see Pottasch & Beintema 1999;Pottasch et al 2000Pottasch et al , 2001Bernard Salas et al 2001), and can be summarized as follows.…”

Abundances of planetary nebulae NGC 40 and NGC 6153

“…The reasons for this have been discussed in earlier papers (e.g. see Pottasch & Beintema 1999;Pottasch et al 2000Pottasch et al , 2001Bernard Salas et al 2001), and can be summarized as follows.…”