Abundances Of Planetary Nebulae Research Articles

Chemical abundances and metallicity of Planetary Nebulae

Confrontations of the dredge-up theory with observed patterns of chemical abundances of planetary nebulae (PNs) have been carried out by many authors (see, e.g., Kaler & Jacoby 1990, 1991; Stasińska & Tylenda 1990). Although these studies suggest that the observational abundance ratios of PNs can qualitatively be explained by the current dredge-up theory, scatters around the theoretical predictions in their diagrams are always large. This has led Ratag (1991) to conclude that there is no correlation at all between the nebular abundances and the core mass of CSPNs (see also Pottasch 1993).

Physical parameters and chemical abundances of Planetary Nebulae in the large Magellanic Cloud

In the present work we have computed the physical parameters and chemical abundances for 45 planetary nebulae (PN) in the Large Magellanic Cloud (LMC) using the photoionization code CLOUDY, developed by Ferland (1993). CLOUDY is used as a subroutine in the code DIANA, developed by Elizalde & Steiner (1996), which minimises indices that measures the difference between the calculated and real nebula.

A New Look at Carbon Abundances in Planetary Nebulae. I. PB 6, HU 2--1, K648, and H4--1

view Abstract Citations (34) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A New Look at Carbon Abundances in Planetary Nebulae. I. PB 6, HU 2--1, K648, and H4--1 Henry, R. B. C. ; Kwitter, K. B. ; Howard, J. W. Abstract We introduce and describe a new long-term project whose goal is to employ final archived lUE spectra to study carbon abundances in a sample of planetary nebulae representing a broad range in progenitor mass and metallicity In this paper we report on initial results for PB 6, Hu 2-1, K648, and H4-1. Our UV line strengths for H4-1 are the first such data to be published for this object. By combining our measured UV line strengths with optical line strengths found in the literature for each object, we have determined values for the abundance ratios He/H, 0/H, C/O, N/O, and Ne/O using a combined atomic level-balancing-photoionization model approach. Eventually, the abundances from this and subsequent studies will be analyzed using a newly improved stellar evolution code for intermediate-mass stars with the goal of determining carbon yields for stars of this mass range. Publication: The Astrophysical Journal Pub Date: February 1996 DOI: 10.1086/176804 Bibcode: 1996ApJ...458..215H Keywords: ISM: ABUNDANCES; ISM: PLANETARY NEBULAE: GENERAL; STARS: EVOLUTION full text sources ADS | data products SIMBAD (22) MAST (1) INES (1) Related Materials (3) Part 2: 1996ApJ...473..304K Part 3: 1998ApJ...493..247K Part 4: 2000ApJ...531..928H

Temperature Fluctuations in Photoionized Nebulae

Recombination lines in gaseous nebulae frequently yield parent4on abundances that are several times larger than abundances derived from forbidden lines. One possible explanation for this discrepancy is the presence of temperature fluctuations. We examine temperature fluctuations in model nebulae by utilizing Peimbert's t<SUP>2</SUP> parameter. We have run large grids of models, varying the stellar temperature and the total hydrogen density. We consider two abundance sets: The first uses "typical" planetary nebulae abundances, while the second examines the effect of increasing the metals and grains by a factor of 3. We also consider both a constant density distribution and one which varies sinusoidally with radius. We examine the method of deriving t<SUP>2</SUP> observationally, which uses measured [O III] and Balmer temperatures. We find that this derived t<SUP>2</SUP> shows no correlation with the t<SUP>2</SUP> based on the integral definition. We discuss the reasons for this discrepancy, which include nonvalidity of some of the basic assumptions and theoretical and observational difficulties with the Balmer temperature. We find that, in high-metallicity objects especially, noncollisional contributions to [O III] λ4363 can significantly affect the derived temperature. We argue that while temperature fluctuations may result in non-negligible abundance corrections in some objects, they are insufficient to resolve the abundance discrepancy.

Ionic processes in astrophysics

Ions are ubiquitous in astrophysical environments. Knowledge of the cross sections and rates for the atomic and molecular processes which create ions and which destroy them is an important part of any detailed model of an astronomical object. Ions and ionic collisions in two very different environments, the early Universe and planetary nebulae, are explored in this paper. Electron-ion recombination leading to the eventual formation of primordial molecules is described. Collisions of ions with electrons and atoms, central to the interpretation of emission lines in astrophysical plasmas, are discussed. Recent work in predicting element abundances in planetary nebulae is highlighted.

Element abundances in planetary nebulae from recombination line spectra

Element abundances in planetary nebulae from recombination line spectra

Determination of Element Abundances in Planetary Nebulae from Recombination Line Spectra

Carbon, nitrogen and oxygen abundances have been found from the recombination lines for 63 planetary nebulae.

PN Abundances in Different Galactic Systems

Developments in the measurement of abundances in planetary nebulae since IAU Symposium 131 are reviewed. Present uncertainties and outstanding problems in the interpretation of emission-line measurements are discussed. Results for different samples of PN are reviewed, in terms of the galactic site. Results for the Galactic disk, Galactic Bulge, Galactic Halo, LMC &amp; SMC, Fornax Dwarf galaxy and M31 are discussed. Attention is drawn to the importance of Magellanic Cloud samples for testing dredge-up theory, and to the strong variation of PN C/O ratios with the local site's metallicity and age. New results for carbon in Cloud PNs are presented. Important problems in the interpretation of the metallicity of Bulge PNs are highlighted. Attention is drawn to the idea that metal-rich stellar populations do not produce PNs, such stars leaving the lower AGB early.

Chemical Abundances of Planetary Nebulae in the LMC

We report new spectroscopic data on a sample constituted of 21 well observed planetary nebulae in the LMC. The observations were performed at the National Laboratory for Astrophysics (Brazópolis — Brasil) using the 1.6m telescope and a CCD detector. Extinction, electron temperature and densities were derived for all the planetaries and a comparison is made with results obtained by other surveys, including common objects. Chemical abundances of helium, nitrogen, oxygen, sulphur and argon were also derived for all sample objects. Enrichment of the progenitor stars in He and N due to mixing episodes as well as the relation with the chemical evolution of the LMC are discussed in terms of our data and other observations.

Chemical Composition of Planetary Nebulae: A New Determination

A new method of the determination of planetary nebulae abundances is proposed. Unobserved ionization stages are taken into account with aid of the correlations between relative abundances of various ions which had been obtained from the grid of the photoionization models of planetary nebulae luminescence calculated by us. Simple approximative expressions for the determination of He/H, C/H, N/H, O/H, Ne/H, Mg/H, Si/H, S/H, and Ar/H are found. The chemical composition of 130 galactic planetary nebulae is revised. The observational data were compiled from 73 papers of many authors published in 1972–1991. Our mean abundances of C, N, O, Ne, S, Ar are 0.1–0.3 dex lower than the mean abundances of these elements found previously by other authors. Such a discrepancy may be due to an overestimation of “empirical” ionization correction factors in previous works. It is shown that the abundance of oxygen in massive stars-precursors may be reduced by 0.2 dex on average due to the ON-cycle, but the abundance of neon remains practically unchanged. A comparative analysis of the abundances in the galactic disk, bulge and halo nebulae is carried out. We found that helium is enhanced in the galactic bulge nebulae relative to the disk ones, but the mean nitrogen abundance and mean ratio N/O are lower in the bulge. Our data suggest that the second dredge-up did not take place in the stars-precursors of the bulge planetaries, and the helium and nitrogen enhancement in these nebulae is due to other mixing processes. The mean abundances of O, Ne, S, Ar in the galactic disk and galactic bulge nebulae are quite similar, and we must conclude that the stars-precursors of the bulge planetaries had been formed during the same burst of star formation as the stars-precursors of the disk nebulae, while the halo nebulae correspond to the previous burst.

THE CNO NUCLEOSYNTHESIS TRIAD IN PLANETARY NEBULAE

ABSTRACT The variations of CNO abundances in planetary nebulae showing significant nucleosynthesis effects are studied. The group of PN include 17 Galactic Type I, 4 halo, 6 SMC, and 6 LMC objects for which accurate C and N abunances were determined based on ultraviolet lines observed with the IUE satellite, coupled with extensive ground-based spectrophotometry for detailed diagnostics of physical conditions. Correlations between C, N, O, and He are studied using a variety of diagrams. The results suggest that C + N is approximately constant in the PN, and this is independent of the initial composition of the progenitors.

Chemical abundances in planetary nebulae - Basic data and correlations between elements

view Abstract Citations (105) References (103) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Chemical Abundances in Planetary Nebulae: Basic Data and Correlations between Elements Perinotto, M. Abstract To form a critical compilation of the abundances of He, C, N, O and Ne, all the individual determinations of chemical abundances in PN obtained with linear detectors have been considered. The data cover all observations of the Galactic PN made in the 20 years up to the end of 1989. Average chemicql abundances have been evaluated separately for nebulae of type I and of types II-III of Peimbert. For the first, they are He/H = 0.137, C/H = 8.72, N/H = 8.60, O/H = 8.66, and Ne/H = 8.05. For the second they are He/H = 0.103, C/H= 8.82, N/H = 8.07, O/H = 8.66, and Ne/H = 7.99, in the usual units. The data analysis suggests that the enrichment of nitrogen in type I PNs is due mostly to the ON cycle, while that in PNs of type II-III is due mostly to the CN cycle. Publication: The Astrophysical Journal Supplement Series Pub Date: June 1991 DOI: 10.1086/191578 Bibcode: 1991ApJS...76..687P Keywords: Abundance; Data Correlation; Planetary Nebulae; Carbon; Chemical Composition; Helium; Neon; Nitrogen; Oxygen; Stellar Evolution; Astrophysics; ABUNDANCES; NEBULAE: PLANETARY; STARS: EVOLUTION full text sources ADS | data products SIMBAD (211) MAST (1)

Abundances in Magellanic Cloud planetary nebulae

The enhanced nitrogen abundances in planetary nebulae (PN) show the effects of CN-cycle processing at the time of the first dredge-up, while their very enhanced carbon abundances show the effects of the third dredge-up. The efficiency of both the first and third dredge-ups increases with decreasing initial metallicity. ON-cycle depletion of oxygen via the second dredge-up does not appear to have been significant in LMC Type I planetary nebulae (those with N/O &gt; 0.5) – these nebulae have experienced the third dredge-up and envelope-burning, giving enhanced C+N abundances. The LMC Type I PN show enhanced Ne/O ratios. Enrichment rates in nitrogen and carbon by PN are estimated for the ISM s of the Magellanic Clouds.

Stellar Mixing from Galactic and Magellanic Cloud Planetary Nebulae Abundances

The mixing and nucleosynthetic processes which occur in the main-sequence and red giant stages of evolution and which can affect measured PN abundances are discussed. It is suggested that samples of planetary nebulae contain a sufficient range of progenitor stars' initial metallicities, angular momenta, binarity, etc. so as to explain the large scatter always seen in abundance diagrams for PN samples. CNO abundances in the Galactic disk and in the Magellanic Clouds are reviewed. New results for nebular abundances and central star properties in the Clouds are given. The current red giant population in the Clouds mix out more 12C per star than their Galactic disk counterparts.

The oxygen and neon abundances in planetary nebulae: implications for stellar nucleosynthesis

Les abondances en oxygene et en neon de 171 nebuleuses planetaires de notre galaxie, des 2 nuages de Magellan et de M31 sont determinees. Le rapport [Ne/H] en fonction du rapport [O.H] est compare pour chaque galaxie

Abundances in Planetary Nebulae

Good progress has been made since the last Symposium on the determination of planetary nebulae (PN) abundances. Notable features for modern abundance determinations include the availability of good collision strengths and transition probabilities (reviewed by C. Mendoza (1983) at the last meeting - IAU Symp.103), the use of the IUE &amp; IRAS satellites to obtain UV &amp; IR line fluxes, and the availability of modern sensitive detectors enabling measurements both of faint extra galactic nebulae and of very weak abundance-indicator lines in nearby bright nebulae. The impact of IUE on PN studies was described by Köppen &amp; Aller (1987).

N/O Abundances in Planetary Nebulae from Far-Infrared Line Observations

Measurements of the [O III] 52, 88 μm and [N III] 57 μm fine-structure emission lines have been obtained for nine planetary nebulae, using the facility far-infrared array spectrometer on NASA's Kuiper Airborne Observatory. The N++/O++ ratios determined from these observations range by more than an order of magnitude among the sample. Using recent improved values for the atomic parameters, we find that the N++/O++ ratios agree fairly well with values of N+/O+ determined from optical lines in the same objects. The highest N++/O++ values, found for the extreme “Type I” nebulae NGC 2440 and NGC 6302, are approximately unity. These results imply that the synthesis and mixing of nitrogen must be extremely efficient in the progenitor stars of some planetary nebulae, and that these nebulae are significant sources of nitrogen to the interstellar medium. The local electron densities derived from the intensity ratios of the two [O III] lines are generally lower than values in the literature determined from small-beam optical observations of other ions, such as [O II]. This effect can be understood in terms of the presence of clumpy structure in the nebula, since the far-infrared lines have fairly low critical densities for collisional de-excitation and therefore are preferentially emitted from low-density gas.

Magnesium Abundances in Planetary Nebulae and Interstellar Absorption of Mg II λ2800 A

SummaryHigh-resolution IUE images have provided line profiles of emission cut by interstellar absorption in the magnesium II lines λλ2795, 2802 A in nine objects. The underlying emission has been reconstructed in seven of these by fitting Gaussian profiles to the remaining line wings. Estimates of the ratio of intrinsic to observed emission ranging from 1.5 to 23 have been obtained. Photo-ionization models of IC 418, IC 4997 and NGC 2440 have been used to obtain Mg/H ratios from the corrected Mg II line strengths. The logarithmic magnesium abundances obtained were 7.6±0.12, 6.96±0.3 and 6.5±0.3 respectively. These results indicate that depletion of Mg into grains is less than previously thought and reduce the observed gradient in the magnesium abundance. The Mg depletion may be related to the C/O ratio within the nebula; carbon-rich planetary nebulae may have less magnesium depletion than those with C/0 &lt; 1.

Helium Abundances in Gaseous Nebulae

New collision strengths, from a 19-state quantum calculation for He I, are used to derive revised He/H ratios in planetary nebulae (PN). Empirical formulae are given, for the correction of He I recombination line fluxes for collisional effects, and for the calculation of the population of metastable helium (He I 23S) in gaseous nebulae. The revised He abundances for PN, for four samples of published line fluxes, show a mean ratio He/H = 0.100 ±0.007 if nebulae with neutral He and Type I PN are excluded. The mean reduction due to collisional effects is only 10% for Galactic PN. It is shown that the hypothesis, that He/H should be independent of nebular temperature and density, is better satisfied when collisional effects are allowed for. The new He abundances indicate that there is very little He enrichment in Galactic PN of Types II, III, and IV, and that the enhancement of Type I PN in He over H II regions is reduced from earlier values by one third.

Magnesium abundances in planetary nebulae and interstellar absorption of MG II 2800 A

High-resolution IUE images have provided line profiles of emission cut by interstellar absorption in the magnesium II lines λλ2795, 2802 A in nine objects. The underlying emission has been reconstructed in seven of these by fitting Gaussian profiles to the remaining line wings. Estimates of the ratio of intrinsic to observed emission ranging from 1.5 to 23 have been obtained. Photo-ionization models of IC 4l8, IC 4997 and NGC 2440 have been used to obtain Mg/H ratios from the corrected Mg II line strengths. The logarithmic magnesium abundances obtained vere 7.6±0.12, 6.96±0.3 and 6.5±0.3 respectively. These results indicate that depletion of Mg into grains is less than previously thought and reduce the observed gradient in the magnesium abundance. The Mg depletion may be related to the C/0 ratio within the nebula; carbonrich planetary nebulae may have less magnesium depletion than those with C/0 < 1.