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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 235 records · Page 13
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NASA NTRS1983

Determinations of SIII, OIV and NeV abundances in planetary nebulae from IR lines

Airborne observations of the infrared forbidden lines (SIII) 18.71 microns, (NeV) 24.28 microns and (OIV) 25.87 microns were made for twelve planetary nebulae. One or more of the lines was detected in seven of these nebulae and ionic abundances were calculated. These results are insensitive to nebula temperatures, in contrast to the case for optical or UV lines. However, density estimates from optical and UV forbidden lines were required to obtain abundances. The NeV infrared line flux from NGC 7662 was combined with the 3426A flux to obtain a NeV electron temperature of 11,200 (+2000, - 1100) K, which overlaps OIII temperature measurements. Since the ionization potential of NeIV is much greater than that of OII, T sub e (NeV) would be expected to be much greater than T sub e (OIII). In fact, numerical models predict T sub e (NeV) (16-20) x 1000 K. This discrepancy may indicate inaccuracies in currently available atomic parameters for NeV.

Shure, M. A.↗
NASA NTRS1988

International ultraviolet explorer spectral atlas of planetary nebulae, central stars, and related objects

The International Ultraviolet Explorer (IUE) archives contain a wealth of information on high quality ultraviolet spectra of approximately 180 planetary nebulae, their central stars, and related objects. Selected are representative low-dispersion IUE spectra in the range 1200 to 3200 A for 177 objects arranged by Right Ascension (RA) for this atlas. For most entries, the combined short wavelength (SWP) (1200to 1900) and long wavelength (LWR) (or LWP, 1900 to 3200 A) regions are shown on 30 cm by 10 cm Calcomp plots on a uniform scale to facilitate intercomparison of the spectra. Each calibrated spectrum is also shown on an expanded vertical scale to bring out some of the weaker features.

Feibelman, Walter A.↗
NASA NTRS1999

Detection of O VII Lambda 1522 in IUE Spectra of Planetary Nebula Nuclei and Other Hot Stars

We present the first detection of O VII lambda 1522 emission or absorption from archival IUE spectra in 14 planetary nebula nuclei and three PG 1159-type stars. The n = 5 approaching 6 transition of O VII was determined by Kruk & Werner and observed by them in the spectrum of the very hot PG 1159-type star H1504+65 from data obtained with the Hopkins Ultraviolet Telescope (HUT). Emission-line fluxes or absorption equivalent widths as well as radial velocities for the program stars are presented. The precise rest wavelength for the 5 approaching 6 transition requires further investigation.

Feibelman, Walter A.↗
NASA NTRS1984

The ionization structure of planetary nebulae V NGC 3242

Spectrophotometric observations of emission line intensities over the spectral range 1400 A to 9600 A were made in five positions in the planetary nebula NGC 3242. In two of the positions, both the weakness of the 1548 A, 1550 A C IV resonance lines and the steepness of the Balmer decrement suggest the possibility of internal dust in the nebula. The measured electron temperature varies little from the average value of 11,100 K, which is in reasonably good agreement with the less accurate value of 12,900 K measured from the Balmer continuum. The 4267 A C II line implies a C(2+) abundance that is much higher than that determined from the 1906 A, 1908 A C III lines. This discrepancy decreases with increasing distance from the central star. Equations used to correct for the existence of elements in other than the optically-observable ionization stages give results that are consistent and in agreement with abundances calculated using ultraviolet lines. This discrepancy decreases with increasing distance from the central star. Equations used to correct for the existence of elements in other than the optically-observable ionization stages give results that are consistent and in agreement with abundances calculated using ultraviolet lines. The logarithmic abundances are He=10.96, 0=8.64, N=7.96, Ne=8.04, C=8.41, Ar=6.15, and S=6.51.

Barker, T.↗
NASA NTRS1985

The ionization structure of planetary nebulae. V - NGC 3242

Spectrophotometric observations of emission line intensities over the spectral range 1400 A to 9600 A were made in five positions in the planetary nebula NGC 3242. In two of the positions, both the weakness of the 1548 A, 1550 A C IV resonance lines and the steepness of the Balmer decrement suggest the possibility of internal dust in the nebula. The measured electron temperature varies little from the average value of 11,100 K, which is in reasonably good agreement with the less accurate value of 12,900 K measured from the Balmer continuum. The 4267 A C II line implies a C(2+) abundance that is much higher than that determined from the 1906 A, 1908 A C III lines. This discrepancy decreases with increasing distance from the central star. Equations used to correct for the existence of elements in other than the optically-observable ionization stages give results that are consistent and in agreement with abundances calculated using ultraviolet lines. This discrepancy decreases with increasing distance from the central star. Equations used to correct for the existence of elements in other than the optically-observable ionization stages give results that are consistent and in agreement with abundances calculated using ultraviolet lines. The logarithmic abundances are He = 10.96, O = 8.64, N = 7.96, Ne = 8.04, C = 8.41, Ar = 6.15, and S = 6.51.

Barker, T.↗
NASA NTRS1988

Radiation-driven winds of hot stars. V - Wind models for central stars of planetary nebulae

Wind models using the recent improvements of radiation driven wind theory by Pauldrach et al. (1986) and Pauldrach (1987) are presented for central stars of planetary nebulae. The models are computed along evolutionary tracks evolving with different stellar mass from the Asymptotic Giant Branch. We show that the calculated terminal wind velocities are in agreement with the observations and allow in principle an independent determination of stellar masses and radii. The computed mass-loss rates are in qualitative agreement with the occurrence of spectroscopic stellar wind features as a function of stellar effective temperature and gravity.

Pauldrach, A.↗
NASA NTRS1989

The ionization structure of planetary nebulae 10: NGC 2392

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in six positions in the planetary nebula NGC 2392. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give consistent results for the different positions that are in excellent agreement with abundances calculated using ultraviolet lines, and there is no evidence for any abundance gradient in the nebula. The logarithmic abundances agree well with determinations by Aller and Keyes.

Barker, Timothy↗
NASA NTRS1991

The ionization structure of planetary nebulae. X - NGC 2392

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in six positions in the planetary nebula NGC 2392. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give consistent results for the different positions that are in excellent agreement with abundances calculated using ultraviolet lines, and there is no evidence for any abundance gradient in the nebula. The logarithmic abundances agree well with determinations by Aller and Keyes.

Barker, Timothy↗
NASA NTRS1995

Recent chaqnges in the IUE spectrum of the very young planetary nebula He 3-1357 (=SAO 244567)

We obtained the first high-dispersion IUE spectrum, and an additional low-dispersion spectrum of the very young planetary nebula He 3-1357 and its central star SDAO 244567. In 1988, it showed a very strong C IV lambda-1549 P Cygni profile which diminished and has disappeared by 1994, but C IV absorptions are seen in a high-resolution spectrum. The electron density from the C III F(lambda 1907)/F(lambda 1909) emission ratio is log N(sub e) = 4.1/cc. The older IUE data were reprocessed, and emission-line fluxes vary greatly for the period 1988-1994. The high-dispersion data show a rich Fe V and Fe VI absorption spectrum.

Feibelman, Walter A.↗
NASA NTRS1985

The ionization structure of planetary nebulae. Part 4: NGC 7662

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in five positions in the planetary nebula NGC 7662. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages show a consistent and approximate agreement with abundances calculated using ultraviolet lines. The abundances of C and N indicate that some mixing of CNO-processed material into the nebular shell may have occurred in NGC 7662; the low He abundance, however, indicates that little or no He enrichment occurred. The Ar, Ne, and O and S abundances appear to be low. It is suggested that the progenitor to NGC 7662 may have formed out of somewhat metal-poor material.

Barker, T.↗
NASA NTRS1998

Investigating the Near-Infrared Properties of Planetary Nebulae II. Medium Resolution Spectra: Medium Resolution Spectra - 2

We present medium-resolution (R approximately 700) near-infrared (lambda = 1 - 2.5 micrometers) spectra of a sample of planetary nebulae (PNe). A narrow slit was used which sampled discrete locations within the nebulae; observations were obtained at one or more positions in the 41 objects included in the survey. The PN spectra fall into one of four general categories: H1 emission line-dominated PNe, H1 and H2 emission line PNe, H2 emission line-dominated PNe, and continuum-dominated PNe. These categories correlate with morphological type, with the elliptical PNe falling into the first group, and the bipolar PNe primarily in the H2 and continuum emission groups. The categories also correlate with C/O ratio, with the O-rich objects falling into the first group and the C-rich objects in the groups. Other spectral features were observed in all catagories, such as continuum emission from the central star, and warm dust continuum emission towards the long wavelength end of the spectra. H2 was detected in four PNe in this survey for the first time. An analysis was performed using the H2 line ratios in all of the PN spectra in the survey where a sufficient number of lines were observed to determine the ortho-to-para ratio and the rotational and vibrational excitation temperatures of the H-2 in those objects. One unexpected result from this analysis is that the H-2 is excited by absorption of ultraviolet photons in most of the PNe, although there are several PNe in which collisional excitation plays an important role. The correlation between bipolar morphology and H2 emission has been strengthened with the new detections of H2 in this survey.

Hora, Joseph L.↗
NASA NTRS1989

Electron temperatures in the high-excitation zones of planetary nebulae

Airborne infrared and ground-based UV observations of the forbidden Ne-V 24.3-micron and forbidden Ne-V 3426-A fine-structure lines of 17 planetary nebulae are discussed. Significantly higher Ne-V than O-IV temperatures are found for Hu 1-2 and NGC 2440, while IC 2165, NGC 6818, and NGC 7662 have similar Ne-V and O-IV temperatures. It is suggested that the Ne-V and O-IV temperature similarities may be due to the presence of large abundances of the dominant coolants (oxygen or neon) in the Ne-V zone.

Rowlands, N.↗
NASA NTRS1994

The spectrum of the planetary nebula IC 418

A detailed high-spectral-resolution study of the spectrum of IC 418 is made for the region 3650 to 10050 A, using the Hamilton echelle spectrograph of Lick Observatory, and of the UV spectral region with archival International Ultraviolet Explorer (IUE) data. From high-resolution images in both the near- and mid-infrared, Hora et al. (1993) showed that IC 418 probably has a compact shell interior to the detached, well-known, main shell emission. If one assumes a black body or Hubeny (or standard LTE) model atmosphere energy distribution, it does not appear possible to construct a fully satisfactory nebula model that will simultaneously represent the H-beta flux, the (O III) 5007/H-beta ratio, and the scale of this planetary nebula (PN). Fortunately, IUE and IR data supply information on ions in addition to those optically observed so that the chemical composition can be reasonably well established by summing over concentrations of observed ions. In spite of the fact that IC 418 is carbon rich in sense of having a C/O ratio exceeding the solar value, it is a 'metal-poor' object. Possibly it resembles IC 4997 but in a more advanced evolutionary phase. The central star is variable and has a strong wind.

Hyung, Siek↗
NASA NTRS1992

Imaging of four planetary nebulae in the Magellanic Clouds using the Hubble Space Telescope Faint Object Camera

Using the Faint Object Camera on-board the Hubble Space Telescope, we have obtained images of four planetary nebulae (PNe) in the Magellanic Clouds, namely N2 and N5 in the SMC and N66 and N201 in the LMC. Each nebula was imaged through two narrow-band filters isolating forbidden O III 5007 and H-beta, for a nominal exposure time of 1000 s in each filter. In forbidden O III, SMC N5 shows a circular ring structure, with a peak-to-peak diameter of 0.26 arcsec and a FWHM of 0.35 arcsec while SMC N2 shows an elliptical ring structure with a peak-to-peak diameter of 0.26 x 0.21. The expansion ages corresponding to the observed structures in SMC N2 and N5 are of the order of 3000 yr. LMC N201 is very compact, with a FWHM of 0.2 arcsec in H-beta. The Type I PN LMC N66 is a multipolar nebula, with the brightest part having an extent of about 2 arcsec and with fainter structures extending over 4 arcsec.

Blades, J. C.↗
NASA NTRS1983

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.

Feibelman, W. A.↗
NASA NTRS1992

Unusual 3 micron emission features in three proto-planetary nebulae

Medium-resolution 3-4 micron spectra have been obtained of three objects, IRAS 04296 + 3429, IRAS 22272 + 5435, and CRL 2688, which are in transition between the asymptotic red giant branch and the planetary nebula phase. All three show unusual 3-micron emission features. The two IRAS objects, already unusual in having 21 micron features, have remarkably strong 3.4-3.5 micron emission relative to the usually dominant 3.3-micron feature, with the spectrum of IRAS 04296 + 3429 being nearly identical to that of IRAS 05341 + 0852 (previously published). CRL 2688's spectrum bears some resemblance to those of the IRAS objects, but its 3.4-3.5 micron emission is not as strong. The relationships between the various emission features are discussed. CRL 2688 may be completing a transition between the '21-micron phase' and the 'normal phase', which is associated with dominant 3.3-micron emission, weak 3.4-3.6 micron features and plateau, and a lack of 21-micron emission.

Geballe, T. R.↗
NASA NTRS1981

The abundances of neon, sulfur, and argon in planetary nebulae

New infrared observations of Ne II, Ar III, and S IV are used in optical observations of other ionization states of the considered elements to evaluate the abundances of neon, argon, and sulfur in 18 planetary nebulae. Attention is also given to one or more of the infrared lines in 18 other nebulae. It is pointed out that S IV was detected in approximately 90% of the observed objects, while Ar III was found in about 80%, and Ne II in roughly one-third. It is noted that optical observations typically include only a limited region of the nebula, while the infrared measurements frequently involve integration over the entire nebular image.

Beck, S. C.↗