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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Chemical compositions of planetary nebulae

The chemical compositions of 41 planetary nebulae are established on the basis of an analysis of image tube scanner measurements, supplemented by IUE data. An attempt is made to calculate a theoretical model that gives satisfactory values of the observed intensities, as well as a number of excitation-sensitive ratios, in order to obtain ionization correction factors applicable to the ionic concentrations that will lead to total abundance values. The quality of individual nebular analyses varies, depending on the completeness and accuracy of the observational data and the complexity of the nebular structure. Quality estimates are assigned for each element in each nebula, and an overall reliability index is given to each object. It is concluded that the confidence with which one can speak of the chemical composition of a nebula varies significantly.

Aller, L. H.↗
NASA NTRS1985

Ultraviolet spectra of the central stars of large planetary nebulae

The ultraviolet spectra of 32 planetary nebula nuclei have been examined with the IUE. Ultraviolet and UV-to-optical flux ratios are derived, from which color temperatures are derived. The distribution of the latter ranges from rough agreement with the Zanstra temperatures upward to infinite values. The high-luminosity stars have generally lower, determinable color temperatures; the infinite or indeterminable color temperatures are contained by the set of lower luminosity stars. About half the stars exhibit a mixture of line features, most commonly He II 1640 A and C IV 1550 A in emission or absorption. Three display clear P Cygni lines, while a fourth appears to display a remarkably broad C IV 1550 A P Cygni profile. The other half of the stars have no perceptible line features.

Kaler, J. B.↗
NASA NTRS1981

A far-infrared emission feature in carbon-rich stars and planetary nebulae

The 16-30 micron spectra of several carbon stars and the planetary nebulae IC 418 and NGC 6572 have been obtained using the NASA C-141 Kuiper Airborne Observatory. A newly observed emission feature appears in the spectrum of IRC +10216 and several other carbon stars at wavelengths greater than 24 microns. The feature is interpreted as resulting from a solid-state resonance in the dust grains which have condensed around these stars. A similar feature appears in the spectra of IC 418 and NGC 6572, implying that the same type of dust is present. Since the dust probably condensed from a carbon-rich gas, this indicates an evolutionary link between carbon stars and these planetary nebulae. No identification for the grain material has been found, but some clues are apparent which could aid in the identification.

Forrest, W. J.↗
NASA NTRS1975

Infrared forbidden lines in H II regions and planetary nebulae

Emissivity coefficients are calculated as functions of electron density and temperature for the IR forbidden lines between 2 and 300 microns of the elements and ionization stages most abundant in H II regions and planetary nebulae. The effect of self-absorption is investigated, and a method is presented for estimating when self-absorption may be important. The IR line spectrum of the Orion Nebula is predicted using the emissivity coefficients, and ionic abundances are derived for the Ar III, S IV, and Ne II forbidden lines in a number of planetary nebulae. The sulfur abundance and sulfur/oxygen ratio are discussed for H II regions and planetary nebulae. The average sulfur/oxygen ratio is found to be about 0.05 for gaseous nebulae.

Simpson, J. P.↗
DOE OSTI2022

Pre-planetary nebulae: a context for principles, progress, and questions on how binaries and magnetic fields produce jets

Astrophysical outflows treated initially as spherically symmetric often show evidence for asymmetry once seen at higher resolution. The preponderance of aspherical and multipolar planetary nebulae (PN) and pre-planetary nebulae (PPN) was evident after many observations from the Hubble Space Telescope. Binary interactions have long been thought to be essential for shaping asymmetric PN/PPN, but how? PPN are the more kinematically demanding of the two, and warrant particular focus. I address how progress from observation and theory suggests two broad classes of accretion driven PPN jets: one for wider binaries (PPN-W) where the companion is outside the outer radius of the giant and accretes via Roche lobe overflow, and the other which occurs in the later stages of CE for close binaries (PPN-C). Furthermore, the physics within these scenarios connects to progress and open questions about the role and origin of magnetic fields in the engines and in astrophysical jets more generally.

(ISM:) planetary nebulae: general↗
DOE OSTI2020

Bipolar planetary nebulae from outflow collimation by common envelope evolution

ABSTRACT The morphology of bipolar planetary nebulae (PNe) can be attributed to interactions between a fast wind from the central engine and the dense toroidal-shaped ejecta left over from common envelope (CE) evolution. Here we use the 3D hydrodynamic adaptive mesh refinement (AMR) code AstroBEAR to study the possibility that bipolar PN outflows can emerge collimated even from an uncollimated spherical wind in the aftermath of a CE event. The output of a single CE simulation via the smoothed particle hydrodynamics (SPH) code phantom serves as the initial conditions. Four cases of winds, all with high enough momenta to account for observed high momenta pre-PN outflows, are injected spherically from the region of the CE binary remnant into the ejecta. We compare cases with two different momenta and cases with no radiative cooling versus application of optically thin emission via a cooling curve to the outflow. Our simulations show that in all cases highly collimated bipolar outflows result from deflection of the spherical wind via the interaction with the CE ejecta. Significant asymmetries between the top and bottom lobes are seen in all cases. The asymmetry is strongest for the lower momentum case with radiative cooling. While real post-CE winds may be aspherical, our models show that collimation via ‘inertial confinement’ will be strong enough to create jet-like outflows even beginning with maximally uncollimated drivers. Our simulations reveal detailed shock structures in the shock-focused inertial confinement (SFIC) model and develop a lens-shaped inner shock that is a new feature of SFIC-driven bipolar lobes.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

The ionization structure of planetary nebulae. IV - NGC 6853

Upgraded UV and IR data were taken of the planetary nebula NGC 6853 in the same region as previous optical data to improve the data base on various ionized species in the nebula. The spectral range 1400-9600 A was scanned, and good agreement was obtained between UV and optical ionization abundance data, although the 4267 A C II line yielded a C(2+) abundance larger than indicated by the UV data. The discrepancy concentrated around the central star. Ionization abundances were determined for He, O, N, NC, C, Ar, and S relative to H, and the causes of discrepancies in the abundances compared to those of previous investigators are discussed. It is noted that, as in the planetary nebula NGC 6720, lighter element abundances are higher than solar values, which suggests mixing of processed materials in the envelope of the two nebulae.

Barker, T.↗
NASA NTRS1984

Evidence for an infrared disk in the core of the extraordinary planetary nebula Abell 30

High spatial resolution infrared maps of the core of the evolved planetary nebula Abell 30, which has been shown to be composed of heavily processed material, are presented. These maps reveal an elongated, disklike structure that is not evident on optical pictures. Multicolor photometry at several positions in this disk shows that this emission is due to dust, some of which is near the evaporation temperature of graphite. Lyman-alpha trapping is shown to be inadequate as a heating source for these grains, but direct absorption of stellar photons is sufficient. In view of the unusual chemical composition, A30 represents a late stage in the evolution of a planetary nebula progenitor. The observed infrared structure may provide clues to the ejection mechanism at this stage of development.

Lester, D. F.↗
NASA NTRS2000

ISO Spectroscopy of Proto-Planetary Nebulae

The goal of this program was to determine the chemical properties of the dust shells around protoplanetary nebulae (PPNs) through a study of their short-wavelength (6-45 micron) infrared spectra. PPNs are evolved stars in transition from the asymptotic giant branch to the planetary nebula stages. Spectral features in the 10 to 20 gm region indicate the chemical nature (oxygen- or carbon-rich), and the strengths of the features relate to the physical properties of the shells. A few bright carbon-rich PPNs have been observed to show PAH features and an unidentified 21 micron emission feature. We used the Infrared Space Observatory (ISO) to observe a sample of IRAS sources that have the expected properties of PPNs and for which we have accurate positions. Some of these have optical counterparts (proposal SWSPPN01) and some do not (SWSPPN02). We had previously observed these from the ground with near-infrared photometry and, for those with visible counterparts, visible photometry and spectroscopy, which we have combined with these new ISO data in the interpretation of the spectra. We have completed a study of the unidentified emission feature at 21 micron in eight sources. We find the shape of the feature to be the same in all of the sources, with no evidence of any substructure. The ratio of the emission peak to continuum ranges from 0.13 to 1.30. We have completed a study of seven PPNs and two other carbon-rich objects for which we had obtained ISO 2-45 micron observations. The unidentified emission features at 21 and 30 micron were detected in six sources, including four new detections of the 30 micron feature. This previously unresolved 30 micron feature was resolved and found to consist of a broad feature peaking at 27.2 micron (the "30 micron" feature) and a narrower feature peaking at 25.5 micron (the "26 micron" feature). This new 26 micron feature is detected in eight sources and is particularly strong in IRAS Z02229+6208 and 16594-4656. The unidentified features at 3.3, 6,2, 7.7, and 11.3 micron, which are commonly observed in planetary nebulae and HII regions, are also seen in these PPNs. However, their strengths relative to the continuum plateaus at 8 and 12 micron are weaker than in planetary nebulae. The 6.9 micron feature, seen almost exclusively in PPNs, is strong. The spectral energy distributions of these PPNs were fitted with a radiative-transfer model, taking into account the emission features at 21, 26, and 30 micron. A significant fraction of the total energy output is emitted in these features: as high as 20% in the 30 micron feature and 8% in the 21 micron feature. The fact that so much energy is carried in these features suggests that the material responsible for this feature must be made of abundant elements, and most likely involves carbon. The change in the in feature strengths from stronger aliphatic bonds in PPNs to stronger aromatic bonds in PNs suggests a chemical and physical evolution in the carbonaceous circumstellar dust during this transition time scale of a few thousand years.

Hrivnak, Bruce J.↗
NASA NTRS1984

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.

Shure, M. A.↗
NASA NTRS2009

Astrometry With the Hubble Space Telescope: Trigonometric Parallaxes of Planetary Nebula Nuclei NGC 6853, NGC 7293, ABELL 31, and DeHt 5

We present absolute parallaxes and relative proper motions for the central stars of the planetary nebulae NGC 6853 (The Dumbbell), NGC 7293 (The Helix), Abell 31, and DeHt 5. This paper details our reduction and analysis using DeHt 5 as an example. We obtain these planetary nebula nuclei (PNNi) parallaxes with astrometric data from Fine Guidance Sensors FGS 1r and FGS 3, white-light interferometers on the Hubble Space Telescope. Proper motions, spectral classifications and VJHKT2M and DDO51 photometry of the stars comprising the astrometric reference frames provide spectrophotometric estimates of reference star absolute parallaxes. Introducing these into our model as observations with error, we determine absolute parallaxes for each PNN. Weighted averaging with previous independent parallax measurements yields an average parallax precision, sigma (sub pi)/ pi = 5%. Derived distances are: d(sub NGC6853) = 405(exp +28 sub -25) pc, d(sub NGC7293) = 216(exp +14 sub -12) pc, d(sub Abell31) = 621(exp +91 sub -70) pc, and d(sub DeHt5) = 345(exp +19 sub -17) pc. These PNNi distances are all smaller than previously derived from spectroscopic analyses of the central stars. To obtain absolute magnitudes from these distances requires estimates of interstellar extinction. We average extinction measurements culled from the literature, from reddening based on PNNi intrinsic colors derived from model SEDs, and an assumption that each PNN experiences the same rate of extinction as a function of distance as do the reference stars nearest (in angular separation) to each central star. We also apply Lutz-Kelker bias corrections. The absolute magnitudes and effective temperatures permit estimates of PNNi radii through both the Stefan-Boltzmann relation and Eddington fluxes. Comparing absolute magnitudes with post-AGB models provides mass estimates. Masses cluster around 0.57 solar Mass, close to the peak of the white dwarf mass distribution. Adding a few more PNNi with well-determined distances and masses, we compare all the PNNi with cooler white dwarfs of similar mass, and confirm, as expected, that PNNi have larger radii than white dwarfs that have reached their final cooling tracks.

STARS↗
NASA NTRS1993

International Ultraviolet Explorer observations of the white dwarf nucleus of the very old, diffuse planetary nebula, IW-2

UV low-dispersion spectra of the central star of the faint planetary nebula, IW-2, were obtained with the IUE. The apparent large diameter of the very diffuse nebula, about half that of the moon, as seen on the Palomar Sky Survey plates by Ishida and Weinberger (1987), indicates this object to be potentially quite evolved, and nearby. The IUE spectra clearly reveal a hot stellar continuum extending over the entire wavelength range of the short-wavelength prime camera (1200-2000 A). This object with V = 17.7 +/- 0.4 is definitely one of the faintest stars ever successfully observed with the IUE. Comparisons of the IUE observed fluxes with those from white dwarf model atmospheres suggest extinction near E(B - V) = 0.45 for a white dwarf of T(eff) roughly 100,000 K. Constraints from estimates of the nebular emission measure and observed visual magnitude also argue for a white dwarf of T(eff) roughly 100,000 K at a distance of 300 to 350 pc. The nucleus of IW-2 is one of the most evolved stars to be identified with a planetary nebula.

Bruhweiler, F. C.↗
NASA NTRS1982

E/B - V/ extinction values for 24 planetary nebulae derived from IUE data

Excellent agreement was found for E(B - V) values for nine planetary nebulae observed in common by IUE and ANS, derived from a strong 2200A absorption feature. E(B - V) values for seven additional objects with moderately strong 2200A absorption were determined. A third group of eight planetary nebulae for which the 2200A absorption feature is marginal or absent had E(B - V) extinctions determined from the observed He II I(1640A)/I(4686A) ratio. A comparison with optical and radio data is included.

Feibelman, W. A.↗
NASA NTRS1988

Spectroscopic observations of the high-ionization planetary nebula NGC 2242 and the H II region K4-45

New optical spectra of two suspected planetary nebulae, K4-45 and NGC 2242, are presented. It is shown that K4-45 (PK 96 + 1) is a reddened H II region with approximately solar abundances, excited by an early B type star. NGC 2242 (PK 170 + 15) is a planetary nebula of exceptionally high ionization, exhibiting He II, and forbidden Ne V, Ar V, Ne III, and O III emission lines. The lack of He I emission and the presence of strong forbidden Ne V and He II emission indicate an optically thin nebula that is ionized by a central star with an effective temperature greater than 100,000 K.

Garnett, Donald R.↗