High-excitation Planetary Nebula Research Articles

The temperatures of the nuclei of high-excitation planetary nebulae

An empirical relationship between the ratio of the intensities of emission lines in spectra of planetary nebulae, 4686 Heii/Hβ andN1+N2[Oiii]/4868 Heii, is established (see Equation (1), curve in Figure 1). A new statistical temperature scale based on this empirical relationship is proposed for the determination of lower limits of the temperatures of the nuclei of planetary nebulae. The well-known method 4686 Heii/Hβ gives the upper level of the temperature of the nucleus. A simultaneous application of both methods has been carried out for 97 planetary nebulae, in order to determine both the upper and lower limits of the temperature of their nuclei (last two columns in Table I). A new quantitative system for the determination of excitation classes of nebulae is proposed (Tables IV and V).

Ultraviolet spectrum and probable chemical composition of the high-excitation planetary nebula M1-1

One of the highest excitation planetary nebulae known, M1-1, was studied with the image-tube scanner on the Shane 3-m telescope at Lick Observatory and with the International Ultraviolet Explorer. Large fractions of abundant elements such as C, N, O, S, and Ar exist in unobservable stages of ionization. Hence, it is difficult to establish the chemical composition of this nebula. The logarithmic abundance values of various elements compared with those of the Sun appear to be as follows: [Table: see text] Here log N(H) = 12. In contrast to NGC 6537, the composition of M1-1 does not appear to differ markedly from that of the Sun. N may be enhanced but there is no enhancement of He or C. In spite of its high excitation and its presumed origin from a relatively massive star, M1-1 shows no evidence for pronounced nuclear processing.

Far infrared emission from three new planetary nebulae

As dust emission in the far infrared (FIR) is a characteristic property of planetary nebulae we searched the Infrared Astronomical Satellite (IRAS) point-source catalogue for confirmatory evidence on the two new possible planetary nebulae S 68 and 248 - 5 identified by Fesen, Gull & Heckathorn (1983) and the high-excitation planetary nebula 76 + 36 detected by Sanduleak (1983). We identify the nebulae 248 - 5 and 76 + 36 with IRAS sources 07404 - 3240 and 17125 + 4919, respectively and have determined their dust temperature, total FIR emission and optical depth. We also set a lower limit ranging in value from 1.2 × 10-6 to 3.7 × 10-5 forMdust/Mbd of the nebula 248 - 5 depending on whether its grain material is silicate or graphite. S 68 could not be identified with an IRAS source.

Spectrum of the high-excitation planetary Nebula NGC 6741 (33-2 deg 1)

view Abstract Citations (42) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrum of the high-excitation planetary nebula NGC 6741 (33-2 1). Aller, L. H. ; Keyes, C. D. ; Czyzak, S. J. Abstract Image tube observations carried out at the Lick and Mount Wilson Observatories were combined with IUE and infrared observations to study the spectra of the high-excitation planetary nebula NGC 6741. Plasma diagnostics were carried out and ion concentrations were calculated for ions from He I to Ca4(+). The ion densities and plasma diagnostics data were compared with theoretical nebular models to interpret the spectra and to obtain ionization correction factors. It is shown that the exciting star in NGC 6741 has an effective temperature near 160,000 K. The predicted abundance ratios for the lines at 5876/4686 A, 3426/3868 A, and 3727/5007 A conformed well to the observations. The derived logarithmic abundances in NGC 6741 are given in a table. Publication: The Astrophysical Journal Pub Date: September 1985 DOI: 10.1086/163469 Bibcode: 1985ApJ...296..492A Keywords: Abundance; Astronomical Spectroscopy; Planetary Nebulae; Ultraviolet Astronomy; Astronomical Models; Ion Concentration; Line Spectra; Astrophysics full text sources ADS | data products SIMBAD (1) MAST (1) INES (1)

Spectrum and chemical composition of the remarkable planetary nebula NGC 6537

Observations with the image tube scanner at the Shane 3-m telescope are combined with data obtained with the International Ultraviolet Explorer to assess the spectrum of the remarkable high-excitation planetary nebula NGC 6537. We have analyzed the spectrum of this nitrogen-rich object with the aid of the theoretical nebular models. The models permit one to estimate the fraction of unobservable ions of abundant elements. On the scale log N(H) = 12, the logarithmic abundance values for He, C, N, and O are as follows: [Table: see text] The abundances of Ne S, Cl, and Ar appear to be essentially solar to within a factor of 2. Our interpretation is that the progenitor of NGC 6537 had a chemical composition not differing greatly from that of the Sun. In the course of its prenebular evolution, C and probably O were converted to N and much H was converted to helium.

Detection of the NE III 36 micron forbidden line in the planetary nebula NGC 6543

The first observation of the Ne III 36.02 micron forbidden line in a planetary nebula, NGC 6543, is presented. Since the dominant form of neon in medium-excitation to high-excitation planetary nebulae is Ne III, the abundance of this ion is important in determining the total neon abundance. Use of the 36 micron line for an abundance determination has the advantage of insensitivity to temperature uncertainties. However, current atomic parameters lead to a Ne III abundance in NGC 6543 which is 4.5 times the cosmic neon abundance and 2.6 times the abundance from optical line studies. Although such a high abundance cannot be ruled out immediately, inaccuracies in the infrared level collision strengths are suspected because resonances were neglected in their calculation. The 36 micron line is also useful as a temperature probe when combined with the Ne III 3868-A forbidden line. When compared to Ne III 15.56 micron forbidden line fluxes, a temperature-insensitive density estimate may be obtained. The utility of these line ratios depends upon the actual infrared level collision strengths, which will affect the density range over which they are sensitive.

A NEW, YOUNG PLANETARY NEBULA IN HERCULES.

ABSTRACT An objective prism survey at high galactic latitudes has detected a new, resolved, high-excitation planetary nebula containing a 14th magnitude O-type central star. The H-gamma, H-delta, and He absorptions have comparable equivalent widths of about 2 A. The equivalent width of H-beta absorption is about 1 A, a result of being partially filled in by weak nebular H-beta emission. He II absorption lines with equivalent widths of about 1 A are seen at wavelengths 5412, 4686, and 4541. A slightly weaker wavelength 4200 absorption line is also present. The nebula presents a very sharp-edged, stellarlike image which can easily be mistaken for a 13th magnitude star.

IUE observations of the perplexing bipolar planetary nebula NGC 2346

A preliminary analysis of International Ultraviolet Explorer (IUE) low-dispersion spectrograms of NGC 2346, obtained at various phases of the eclipsing nucleus, shows features typical of a high-excitation planetary nebula. Variations in line profiles, intensities, and stellar continuum are observed as a function of time. An orbital period of 16.0 days was determined from 1.8m(v) variations measured by the IUE Fine Error Sensor (FES) and agrees with the period derived from radial velocity measurements by Mendez.

On the O III/O II Problem in Medium and High Excitation Planetary Nebulae

Numerical models have been constructed for twelve ionization bounded, medium to high excitation planetary nebulae. In most objects the excitation sensitive line ratio (O III) λ 500.9 nm / (O II) λ 372.7 nm is predicted to be too low as compared to observations. A similar systematic discrepancy is observed for [S III] λ 953.2 nm / (S II) λ 672.0 nm. We investigated the following effects on the ionization structure of the nebulae: 0++ + HO → 0+ + H+ charge exchange reaction, energy distribution of ionizing radiation and density distribution of gas in the nebular shell. The results show that density distribution is the most important factor determining the 0 III/O II and S III/S II line intensity ratios. While a factor of ten decrease in the charge exchange coefficient is required to explain the systematic discrepancy, a reduction of nebular radius by a few percent - truncated nebula (quasi density bounded model, but nebula still optically thick to Lyman photons) - suffices to produce the correct 0 III/O II ratio. Also, a density gradient of n ∼ r−1 to r−2 yields much better agreement with observations. Realistic variations in stellar spectrum hardly affects the 0 III/O II line intensity ratio.

Spectroscopy of Extragalactic Planetary Nebulae in the Ultraviolet

Three high-excitation planetary nebulae in the Magellanic Clouds were successfully observed with the International Ultraviolet Explorer. Emission lines as well as nebular and stellar continua were detected. Fluxes in the lines 1550 C IV, 1640 He II, 1663 O III, and 1909 C III were measured in spectra of LMC P40, SMC N2, and SMC N5 obtained with the IUE short wavelength spectrograph; 2422 Ne IV was measured in P40 with the long wavelength spectrograph. The data were analyzed together with groundbased observations by Aller in order to derive ionization models and the nebular abundances of He, C, N, O, S, Ar. The C abundances are as large as those typically found in galactic planetaries, although the interstellar media of the Clouds are notably deficient in C. Thus, the C was synthesized in the progenitor stars and presumably was lifted to the stellar envelopes by convection prior to the ejection of the nebulae. Other planetary nebulae in the Clouds, as well as the planetary nebula in the Fornax galaxy, may be observable with IUE.

High Oxygen Abundance in a Bright Filament of the Crab Nebula

Detailed stationary photoionization models with homogeneous chemical composition were constructed for a bright filament of the Crab Nebula centered ~42″ W-SW of the pulsar. So far this filament is the only one which has been observed in the ultraviolet (Davidson et al, 1982), in the visual (Miller, 1978; Davidson et al, 1982) and in the near-infrared (Dennefeld and Péquignot, 1982), so that numerous constraints and meaningful tests of the models exist. On the other hand the computer program used in the calculations includes recently introduced atomic physics processes (charge exchange reactions and “low-temperature” di-electronic recombinations) and was tested and calibrated by means of models of the high-excitation planetary nebula NGC 7027 whose line spectrum shares some characteristics with that of the Crab Nebula.

Discovery of a Large High-Excitation Planetary Nebula

The discovery of a new planetary nebula from (O III) interference filter imagery is reported. The nebula, PN 136 + 5°1, is 15′ in diameter and asymmetric in appearance. Spectrophotometry of the central regions indicate it is of excitation class between 8 and 10. A single bright condensation within the nebula exhibits emission lines of much lower ionization with (S II) λλ 6717, 6731 line intensities indicating an electron density of about 350 ± 150 cm−3. Seeing limited (O III) imagery of this planetary nebula is also presented. (This article is appearing in Astron. Astrophys. in the near future).

Comparison of Planetary Nebulae and Symbiotic Star Emitting Regions

The spectra of symbiotic stars generally display many emission lines seen in moderate to high-excitation planetary nebulae, but are superposed upon a strong continuum characteristic of a cool star, typically of type M. Furthermore, the spatial distribution of symbiotics has been noted to resemble that of planetaries. These similarities suggest that the symbiotic stars and planetary nebulae might have some relationship (causal or otherwise) or that they might arise from similar progenitors.

The optical and ultraviolet spectra of the high excitation planetary nebula, CD -23 deg 12238 = ME 2-1

view Abstract Citations (32) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The optical and ultraviolet spectra of the high excitation planetary nebula, CD -23 12238 = ME 2-1. Aller, L. H. ; Keyes, C. D. ; Czyzak, S. J. Abstract Planetary nebula are now recognized as a penultimate stage in the evolution of many stars. Me 2-1 offers advantages meriting a detailed analysis. A description is presented of measurements regarding this object which have been conducted with a photoelectric scanner and a 3 m telescope Cassegrain image tube scanner. The chemical composition of Me 2-1 appears to fit well that of other planetaries. The values for N, O, and Ne fall slightly above those for an 'average' planetary, but Me 2-1 would not qualify as a nitrogen-rich object. When a comparison is made with the sun, there appears to be an enhancement of carbon, possibly slight enhancements of nitrogen and neon, but a slight reduction in oxygen. Publication: The Astrophysical Journal Pub Date: November 1981 DOI: 10.1086/159406 Bibcode: 1981ApJ...250..596A Keywords: Chemical Composition; Planetary Nebulae; Stellar Evolution; Stellar Models; Stellar Spectrophotometry; Ultraviolet Spectra; Abundance; Interstellar Extinction; Iue; Spectrum Analysis; Astrophysics full text sources ADS | data products SIMBAD (3) MAST (1) INES (1)

Large High Excitation Planetary Nebulae

Large High Excitation Planetary Nebulae

The optical and ultraviolet spectrum of the planetary nebula NGC 2440

New measurements of the optical and ultraviolet emission-line intensities of the high-excitation planetary nebula NGC 2440 in the wavelength range 1240-8578 A are analyzed with the aid of photoionization models. The observed O III and N II forbidden-line temperatures (13,800 K and 10,000 K, respectively) differ by more than the models predict. Inclusion of charge-transfer reactions at published rates improves agreement between calculated and observed abundances of many ions, but worsens the agreement for several highly ionized ions. Nitrogen shows a larger overabundance N(N)/N(O) approximately equal to 1.0, whereas ultraviolet lines give a carbon abundance close to the solar value. The refractory elements magnesium, calcium, and iron have similar gas-phase depletions of approximately 1.5 dex. The abundances of oxygen, neon, sodium, sulfur, chlorine, potassium, and argon are rougly solar.

IUE observations of the peculiar M giant HD 4174

view Abstract Citations (22) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS IUE observations of the peculiar M giant HD 4174. Stencel, R. E. ; Sahade, J. Abstract Ultraviolet spectra of the peculiar M giant HD 4174, which may possess a significant magnetic field, are shown to exhibit numerous high-excitation emission lines and no background continuum. Ionization equilibrium temperatures for species observed range from 6000 K (Mg II) up to 200,000 K (N v). Density diagnostics using line ratios indicate electron density of 3 x 10 to the 9th power per cu cm in the emission-line-forming region, which favorably compares with coronal model parameters previously suggested for this star. High-resolution Ca II and Mg II profiles suggest an enhanced chromospheric temperature rise. Comparison with symbiotic objects and a high-excitation planetary nebula reveals similarities among these objects. Publication: The Astrophysical Journal Pub Date: June 1980 DOI: 10.1086/158056 Bibcode: 1980ApJ...238..929S Keywords: Binary Stars; Giant Stars; Iue; Late Stars; M Stars; Magnetic Stars; Ultraviolet Spectra; Chromosphere; Emission Spectra; Line Spectra; Optical Emission Spectroscopy; Planetary Nebulae; Spectrum Analysis; Stellar Spectra; Stellar Temperature; Astrophysics full text sources ADS | data products SIMBAD (3) MAST (1) INES (1)

International Ultraviolet Explorer satellite observations of seven high-excitation planetary nebulae

Observations of seven high-excitation planetary nebulae secured with the International Ultraviolet Explorer (IUE) satellite were combined with extensive ground-based data to obtain electron densities, gas kinetic temperatures, and ionic concentrations. We then employed a network of theoretical model nebulae to estimate the factors by which observed ionic concentrations must be multiplied to obtain elemental abundances. Comparison with a large sample of nebulae for which extensive ground-based observations have been obtained shows nitrogen to be markedly enhanced in some of these objects. Possibly most, if not all, high-excitation nebulae evolve from stars that have higher masses than progenitors of nebulae of low-to-moderate excitation.

Search with Copernicus for ultraviolet emission lines in the planetary nebula NGC 3242

The high-excitation planetary nebula NGC 3242 has been observed with the ultraviolet telescope-spectrometer aboard Copernicus. Wavelength intervals corresponding to the emission lines of O VI at 1032 A, He II at 1085 A, Si III at 1206 A, and N V at 1239 A have been scanned. Upper limits to the observed fluxes are reported and compared with predicted emission-line fluxes from this object.

Gas-phase abundances of iron and carbon in planetary nebulae

Five high-excitation planetary nebulae are found to have order-of-magnitude deficiencies of iron in the gas phase, in agreement with an earlier result for NGC 7027. Most of the nebulae cluster in the range (Fe/O) = 1.2 +- 0.4. The results indicate that efficient condensation of iron into grains is characteristic of planetary nebulae. Carbon abundances are determined from recombination lines of C II, III, and IV. The nebulae all have carbon abundances larger than solar. Most of the total carbon may be in the gas phase, in contrast to the case for iron. Empirical collision strengths for (Fe III), (Fe V), and (Fe VI) are derived from line intensities of NGC 7027 and a detailed model of its ionization structure. 2 figures, 5 tables.