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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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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The peculiar planetary nebula 75+35 deg 1

The high galactic latitude planetary nebula 75+35 deg 1 was observed in the low-dispersion mode of the IUE satellite. The UV spectrum is characterized by a strong continuum that matches the energy distribution of a blackbody curve of 90,000 K + or - 5000 K. The color temperature of 94,000 K + or - 4000 K is derived from the UV color indices. The spectral type mimics that of an O7.5 V star; a very strong N V 1240-A feature with a P Cygni profile is present, in addition to a very weak C IV P Cygni line. A very slight depression in the 2200-A region suggests very little interstellar absorption with an upper limit of E(B-V) = 0.025 mag, as would be expected for a high galactic latitude object. The ultraviolet observations, in context with the optical data, indicate that this object is not a typical planetary.

Feibelman, Walter A.↗
NASA NTRS1989

The peculiar planetary nebula in M22

The source discovered by the IRAS satellite near the center of the globular cluster M22, IRAS 18333-2357, has been studied using the IUE satellite and a ground-based optical telescope. The northern component of the close pair of stars is not a member of the cluster. The southern component is a hot star with T(eff) of about 50,000 K illuminating a small planetary nebula and is a member of M22. Both the planetary nebula and its central star are extremely hydrogen deficient. The luminosity of the central star is in good agreement with that expected on theoretical grounds and with the observed luminosity of the tip of the red giant branch.

Cohen, J. G.↗
NASA NTRS1986

IUE survey of planetary nebulae in the large and small magellanic clouds

Twelve planetary nebulae of the 15 surveyed by IUE in the Megellanic Clouds were analyzed. Chemical abundances and other nebular parameters were determined, along with masses for the central stars. The latter are clustered in the range 0.58 to 0.71 solar masses, contrary to preliminary finding for 3 of the stars. This difference is attributed to the adoption of stellar atmosphere models that better represent the emergent flux distributions below the Lyman limit.

Gull, T. R.↗
NASA NTRS1989

Terminal velocity of wind, mass loss, and absorption lines of the central star of the planetary nebula 75 + 35.1 deg

The high-galactic latitude planetary nebula 75 + 35.1 deg was observed in the high-dispersion mode of the International Ultraviolet Explorer (IUE) satellite in the wavelength range 1150-1950 A. The N V resonance doublet at 1240 A and O V subordinate line at 1371 A exhibit strong stellar P Cygni profiles with absorption extending to -2150 km/s and -1000 km/s, respectively. Application of the first moment method implies a mass-loss rate of M = (1-3) x 10 to the -8th solar mass/yr. The high ionization of the wind lines and the presence of strong Fe VI and Fe V lines in the stellar photosphere support that this object is quite hot. A Teff of 75,000 + or - 10,000 K was adopted, although Tc = 94,000 K was found previously from low-resolution IUE data.

Feibelman, Walter A.↗
NASA NTRS2002

An ISO and IUE Study of Planetary Nebula NGC 2440

The infrared and ultraviolet spectra of planetary nebula NGC 2440 is presented. The observations were made respectively by the Infrared Space Observatory (ISO) and International Ultraviolet Explorer (IUE) These data, in conjunction with published optical observations have been used to derive electron temperature and density. A trend of electron temperature with ionization potential is found. In particular the electron temperature increases from 11000 to 18000 K with increasing IBM. The electron density has a constant value of 4500/cu cm in agreement with previous determination. The chemical abundance has been derived for the following elements; helium, carbon, nitrogen, oxygen, neon, sulfur and argon. The ionization correction factor turns out to be very small (almost unnecessary) for all species except sulfur.

Salas, J. Bernard↗
NASA NTRS2007

Far-Ultraviolet Temperature Diagnostics for Hot Central Stars of Planetary Nebulae

The effective temperature of hot central stars of planetary nebulae is usually determined from the ratios of optical He II lines. However, far-ultraviolet spectra from the FUSE satellite of several hot (T(sub eff) > 70,000 K) hydrogen-rich central stars have stellar features that imply a significantly hotter effective temperature than that determined from He II. There are many stellar features in the long wavelength portion of the FUSE spectrum. These include O VI 1146-47, F VI 1039.5, FeVII 1118.6, 1141.4, FeVI 1120.9, 1131.5, and NiVI 1124.2, 1148.2. The strong FVI 1139.5 line is of interest because of the large overabundance (over 100X solar) of F in some PG1159 stars reported recently by Werner et al. (2005). Modeling these spectral features may provide an method for measuring the effective temperature of these stars independent of the He II lines. An example of HD 200516, the central star of NGC 7009 (T(sub eff)= 82000 K from He II vs 95000 K from Far-W metal lines) is presented.

Sonneborn, G.↗
DOE OSTI2021

Hunting for Planetary Nebulae toward the Galactic Center

We present near-infrared (IR) spectra of two planetary nebula (PN) candidates in close lines of sight toward the Galactic center (GC) using the Gemini Near-Infrared Spectrograph at Gemini North. High-resolution images from radio continuum and narrowband IR observations reveal ringlike or barrel-shaped morphologies of these objects, and their mid-IR spectra from the Spitzer Space Telescope exhibit rich emission lines from highly-excited species such as [S iv], [Ne iii], [Ne v], and [O iv]. We also derive elemental abundances using the Cloudy synthetic models, and find an excess amount of the s-process element krypton in both targets, which supports their nature as PNe. We estimate foreground extinction toward each object using near-IR hydrogen recombination lines, and find significant visual extinctions (A {sub V} > 20). The distances inferred from the size versus surface brightness relation of other PNe are 9.0 ± 1.6 kpc and 7.6 ± 1.6 kpc for SSTGC 580183 and SSTGC 588220, respectively. These observed properties along with the abundance patterns and close proximity to Sgr A* (projected distances ≲20 pc) make it highly probable that these objects are the first confirmed PN objects in the nuclear stellar disk. The apparent scarcity of such objects resembles the extremely low rate of PN formation in old stellar systems, but is in line with the current rate of sustained star formation activity in the Central Molecular Zone.

47 OTHER INSTRUMENTATION↗
NASA NTRS1976

Kinematics and spectra of planetary nebulae with O VI-sequence nuclei

Spectral features of NGC 5189 and NGC 6905 are tabulated. Fabry-Perot profiles around H alpha and O III lambda 5007 of NGC 5189, NGC 6905, NGC 246, and NGC 1535, are illustrated. The latter planetary nebula is a non-O VI-sequence, comparison object of high excitation. The kinematics of the four planetary nebulae are simply analyzed. Discussion of these data is motivated by the possibility of collisional excitation by high-speed ejecta from broad-lined O VI-sequence nuclei, and by the opportunity to make a comparison with conditions in the supernova remnant or ring nebula, G2.4 + 1.4, which contains an O VI-sequence nucleus of Population I.

Johnson, H. M.↗
NASA NTRS2005

Sculpting a Pre-Planetary Nebula with a Precessing Jet: IRAS 16342-3814

We have imaged the bipolar pre-planetary nebula IRAS 16342-3814 with the Keck adaptive optics (AO) system in four near-infrared bands in the 1.6-4.7 (micro)m range. The lobes, which showed smoothly varying brightness distributions in previous optical images taken with the Hubble Space Telescope, have a limb-brightened appearance in the AO images, with a remarkable corkscrew structure inscribed on the lobe walls. A well-collimated, precessing jet with a diameter less than or approximately equal to 100 AU and a precession period less than or approximately equal to 50 yr, interacting with ambient circumstellar material, is most likely responsible for the corkscrew structure and the lobes, as indicated by a detailed comparison of our observations with published numerical simulations. The very red colors of the lobes in the near-infrared, coupled with their visibility at optical wavelengths, require that at least half, but not all, of the light of the central star be trapped by a compact circumstellar dust cloud heated to approximately 600-700 K and reradiated in the infrared. The lobes are thus illuminated both by the infrared light from this dust cloud as well as by the optical light from the central star.

circumstellar matter↗
NASA NTRS1991

The carbon-rich proto-planetary nebula IRAS 22272 + 5435

Ground-based photometry and spectroscopy is presented for IRAS 22272 + 5435, a 9th mag star with a large infrared excess. The flux distribution is 'double-peaked', with a visible and near-infrared component due to the reddened photosphere and a far-infrared component presumably due to a detached dust shell. About equal amounts of energy are detected from each. The spectrum is that of a peculiar G supergiant, Gp Ia. In addition, strong molecular bands of C3 and C2 are observed. The flux distribution is modeled and, together with published molecular-line radio observations, allows the determination of basic parameters of the central star and the dust shell. The source has the characteristics one would expect of a proto-planetary nebula, an object in transition from the asymptotic giant branch to the planetary nebula phase.

Hrivnak, Bruce J.↗
NASA NTRS1969

Abundances in a halo planetary nebula.

Photoelectric measurements of emission line intensities for low density planetary nebula with moderate excitation located near north galactic pole, deriving abundances

Miller, J. S.↗
NASA NTRS1976

Reddening of planetary nebulae - NGC 2392

A method for finding the reddening of planetary nebulae is proposed which makes use of the fact that the color of a hot star is an insensitive function of its temperature. Spectrophotometric data of NGC 2392 are presented and used to compute its color excess by the present method as well as older methods; the present method appears to be viable. These results combined with previous measurements tend to support the idea that reddening is variable over the surface of the nebula.

Zipoy, D. M.↗
NASA NTRS1979

Reversal of the /O III/lambda 4363/H sub gamma lambda 4340 ratio in the planetary nebula IC 4997

Five image-tube spectrograms of the planetary nebula IC 4997 obtained during August 1977 show that the intensity forbidden ratio O III 4363 A/H-gamma 4340 A was equal to unity, but a sixth one obtained in April 1978 showed the ratio to be 0.91. These results represent a significant increase in the intensity ratio, which had been declining from 1895 to 1962 (when it was considerably less than unity), and is interpreted as resulting from a gradual increase in temperature of the nebula's central star accompanied by a transient event which led to a temporarily high value for the ratio in mid-1977.

Feibelman, W. A.↗
NASA NTRS1984

The remarkable ultraviolet spectrum of the planetary nebula Abell 30

Abell 30 has been identified as a planetary nebula in which the nucleus has experienced a final helium shell flash after ejection of the original, outer envelope. Around the central star of the nebula, four knots of material are observed. In view of the importance of the chemical composition of the ejected material for studies of advanced stages of stellar evolution, clarification of the physical conditions in the knots is vital. Data obtained of Abell 30 with the aid of the International Ultraviolet Explorer (IUE) satellite are discussed along with aspects of extinction, the He II flux, ionic abundances, the C II lambda 4267 line, questions regarding the existence of a carbon-rich core in the knot, the heating of the nebular gas, the central star, and heating by suprathermal particles from the stellar wind. The UV spectrum of the inner nebulosity of Abell 30 indicates that an extraordinary amount of energy is being deposited in the gas.

Harrington, J. P.↗
NASA NTRS1985

Wind distances for planetary nebulae

A new method for the determination of distances to planetary nebulae is presented. If a star has a strong wind that produces a P Cygni profile in its spectrum, an escape velocity may be inferred from the terminal velocity, which provides a relation involving stellar temperature, luminosity, and mass. The theory of stellar evolution provides a second relation among these three variables, so that once the star's temperature is known, it is possible to simultaneously derive its mass and luminosity, and hence its distance. The method is applied to several test cases that illustrate its viability and current limitations.

Kaler, J. B.↗