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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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NASA NTRS1975

G2.4 + 1.4, a supernova remnant or ring nebula around a peculiar star

G2.4 + 1.4 is a probable nonthermal radio source and an optical nebula which appears to be a supernova remnant (SNR). It also contains an O VI sequence star of great excitation. We present new radiofrequency-continuum and (nil) H 92 alpha observations, optical spectroscopy, and Fabry-Perot scanner observations of the nebula. The object distance (possibly 5 kpc), origin of gas kinematics (possibly SNR expansion), and mode of excitation of the gas (possibly photoexcitation and/or shock wave) remain uncertain. We discuss the possible roles of the O VI star as 'runaway' in an SNR, as a source of photoexcitation, and as an ejector of a 'counterfeit' SNR.

Johnson, H. M.↗

NASA NTRS1975

CO, CS, and HCN in a clustering of reflection nebulae in Monoceros

Observations are reported of the 2.6-mm line of CO from an extended region in Monoceros containing a complex of dust clouds as well as a group of reflection nebulae (Mon R2) and where a source of relatively strong millimeter emission from CS and HCN has been found. Lower limits are obtained for the CO and H2 column densities in this region, and five CO emission peaks are identified, each of which is approximately coincident with at least one reflection nebula. Around the position of the strongest peak, extended emission is observed from CS and HCN, suggesting the existence of a rotating core with an H2 density which corresponds to a mass of 5500 solar masses. The CO profiles in the direction of the strongest peak appear to show self-absorption, which may indicate a collapsing cloud.

Kutner, M. L.↗

NASA NTRS1975

An unusual nebula near UOA 27

Near-infrared plates of a region in Cygnus show an extremely red nebula, about 25 arc seconds in diameter, which is displaced by about 18 arc seconds from UOA 27, an object with infrared and microwave properties similar to those of the Becklin-Neugebauer point source in Orion. This nebula may be reflecting light from the same obscured star which is the energy source for UOA 27, and could therefore provide a unique, though indirect, means of investigating the nature of stars which heat the BN point source and related objects.

Kleinmann, S. G.↗

NASA NTRS1976

Formation of iron sulphide in solar nebula

Noting that the iron sulfide in the Orgueil carbonaceous meteorite is an Fe-deficient monosulfide (pyrrhotite), it is suggested that such mineral chemistry is inconsistent with equilibrium condensation of the solar nebula and that the course of condensation may have been modified by kinetic effects. The effect of Ni on the reaction between Fe and S to produce FeS is examined, and possible reasons are considered for the fact that the cited meteorite differs in both crystal structure and Ni content from the predictions of equilibrium condensation. It is proposed that sulfide formation in the solar nebula may have been inhibited by sluggish diffusion, so that sulfur began to react with previously condensed troilite to form pyrrhotite. On this basis, observations of the Orgueil sulfides are shown to suggest that the course of solar-system condensation was modified by kinetic effects below about 700 K and that equilibrium may not have been achieved.

Kerridge, J. F.↗

NASA NTRS1976

Observations of the Gum Nebula with a Fabry-Perot spectrometer

Scans have been made of H-alpha, 6584-A forbidden N II, 5007-A forbidden O III, and 5876-A He I emissions in selected directions in the Gum Nebula. Analyses of the line profiles and line intensities indicate that much of the emitting gas in the Gum Nebula is confined to an expanding shell which has a radius of about 125 pc, an expansion velocity of approximately 20 km/s, an emission measure which ranges from about 15 units to about 500 units, and a temperature near 11,000 K. The ultraviolet flux from zeta Pup and gamma-2 Vel appears to be capable of producing most of the observed ionization, although the origin of the shell structure and high expansion velocity is not certain.-

Reynolds, R. J.↗

NASA NTRS1976

Far-ultraviolet brightness of nebulae in Cygnus

A far-ultraviolet electrographic Schmidt camera was operated on the lunar surface during the Apollo 16 mission. Among the results obtained were imagery in the 1050-1600-A and 1250-1600-A wavelength ranges of a 20-deg-diameter field in Cygnus containing the Cygnus Loop nebula, the North America nebula (NGC 7000), and the H II region of the O8 star 68 Cygni. The maximum intensity in the Cygnus Loop was 100 R in the 1250-1600-A range and 130 R in the 1050-1600-A range. The maximum brightnesses in the 1250-1600-A range of the 68 Cyg H II region and of NGC 7000 were about 60 and more than 80 R, respectively, but require relatively large corrections for interstellar extinction.

Carruthers, G. R.↗

NASA NTRS1976

Spectra and Fabry-Perot interferometry of AG Carinae and the nebula

Observations of the variable P Cygni-type supergiant and the unique ring nebula around it were made in 1974. Line identifications are tabulated, and an estimated electron density of 1700 per cu cm is combined with a radio flux density to derive a nebular mass of 0.18 (plus or minus 0.04) solar mass on the basis of a distance of 2 kpc. From the data, some ideas of the age and kinematics of the nebula are offered, tracing the evolution of P Cygni supergiants from the youthful prototype past the nebular stage of AG Carinae into more typical, relative old age without recognizable nebular envelopes.

Johnson, H. M.↗

NASA NTRS1976

Direct photography of the Gum Nebula

The paper discusses a series of wide-angle photographs taken of the Gum Nebula in the traditional region including H-alpha with the aid of a 40-cm and an 80-cm lens in both the red and the green. The photographs support the large dimensions (75 deg in galactic longitude by 40 deg in galactic latitude) of the Gum Nebula suggested earlier, and the appearance is consistent with an origin due to photons from a supernova outburst. The relatively high-density gas has cooled and is visible on the red plates. The low-density gas has remained at a high temperature and may be visible as diffuse emission on the green plates.

Brandt, J. C.↗

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 NTRS1976

Meter-wavelength VLBI. IV - Temporal and spatial scattering of the Crab Nebula pulsar's radiation

The spatial and temporal phenomena observed in the Crab Nebula pulsar's radiation are reviewed, with emphasis on the recent VLBI observations of the apparent angular size and the ratio of pulsing to total power. Three models for scattering (single thin screen, two screen, and extended medium) are discussed and shown to be deficient, under the usual assumption of a uniform scattering medium, in explaining the observed combination of temporal and angular broadening. A new model is proposed, in which the temporal broadening is dominated by scattering in the small filament which lies in the nebula in front of the pulsar, while the extended interstellar medium causes the angular broadening. This model explains the otherwise discordant angular and temporal effects and also the lack of an apparent source-size expansion with pulse phase.

Vandenberg, N. R.↗

NASA NTRS1977

Spectrum of the Kleinmann-Low nebula from 29 to 125 micrometers

The infrared spectrum of the Kleinmann-Low nebula in M42 has been measured from 80 to 350 kaysers (approximately 29 to 125 microns) with a Michelson interferometer aboard the NASA Kuiper Airborne Observatory. The frequency spectrum peaks at about 185 kaysers. A simple model of the emission implies that the temperature is in the range 70-95 K and that the optical depth is at least 0.2 at the peak frequency. A possible absorption is seen at about 176 kaysers. Thermal emission by dust at a temperature of 71 K, with the absorption cross section proportional to frequency, provides a good fit to the data. Other thermal-emission models can also fit the spectrum. The data are compared with previous broad-band measurements. Upper limits are placed on expected line emission from the surrounding H II region at the position of the nebula.

Erickson, E. F.↗

NASA NTRS1977

Search for thermal X-ray line emission from the Crab Nebula

Observations of the Crab Nebula from 1.85 to 8 keV obtained with the large-area graphite crystal spectrometer on OSO-8 show a smooth featureless continuum with an absence of X-ray emission lines from highly ionized Si and S. Upper limits on the line emission are used to derive an upper limit to the emission measure for a thermal source associated with the Crab Nebula. Existing evidence for an extended thermal source is discussed, and it is shown that the evidence is not contradicted by the upper limits set with the spectrometer data.

Kestenbaum, H. L.↗

NASA NTRS1977

Chemical fractionation in the solar nebula

The sequence of condensation of minerals from a cooling gas of solar composition has been calculated from thermodynamic data over the pressure range 0.001-0.00001 atm, assuming that complete chemical equilibrium is maintained. The results suggest that the Ca-Al-rich inclusions Allende and other carbonaceous chondrites are aggregates of the highest temperature condensates. Complete condensation of these elements is followed, 100 deg later, by the onset of the crystallization of nickel-iron, forsterite and enstatite. Transport of Ca-Al-rich refractory condensates from one part of the nebula to another before the condensation of these lower-temperature phases may have been responsible for the refractory element fractionations between the different classes of chondrites and possibly for the inferred refractory element enrichment of the Moon. The temperature gap between the condensation temperatures of nickel-iron and forsterite increases with increasing total pressure. Because pressure and temperature probably increased with decreasing heliocentric distance in the solar nebula, Mercury may have accreted from a condensate assemblage having a higher metal/silicate ratio than Venus or Earth which may, in turn, have formed from less oxidized material than Mars.

Grossman, L.↗

NASA NTRS1978

Carbon recombination-line mapping of the Orion Nebula

The distribution of the C75-alpha line in the Orion Nebula has been mapped with a spatial resolution of 1.3 arcmin over a field of view of 4 by 8 arcmin. It is found that ionized carbon is more extended than the radio continuum distribution, particularly to the northeast, and possibly also beyond the ionization front in the southeast. However, the emission falls off across the ionization front northwest of the nebula. The emission is generally consistent with a model in which the line is formed in a thin sheet in the molecular cloud immediately adjacent to the H II region. However, the spatial extent of the emission does suggest that some of the emitting gas may be cooler and less dense than has previously been assumed.

Kuiper, T. B. H.↗

NASA NTRS1978

The rocket-ultraviolet spectrum and models of the planetary nebula NGC 7662

Ultraviolet spectral analysis of NGC 7662 has revealed a Balmer line distribution indicating a C/O ratio of unity. This abundance of carbon is characteristic of mixing between the central star and the outer envelope of the planetary nebula. A continuum spectrum is observed from the star and the nebula, radiating its energy via the two photon process through neutral hydrogen. Spectral lines were fitted to apply to the predictions of three models of the nebular structure. UV observations were compared with visible, IR, and radio observations.

Bohlin, R. C.↗

NASA NTRS1978

Observation of the 63 micron (0 1) emission line in the Orion and Omega Nebulae

The 63 micron fine structure transition P4 : 3Pl yields 3P2 for neutral atomic oxygen was obtained during a series of flights at an altitude of approximately 13.7 km. In the Orion Nebula (M42), the observed line strength was 8 x 10 to the minus 15 power watt cm/2 which is estimated to be approximately 0.3 o/o of the energy radiated at all wavelengths. For the Omega Nebulae (M17), the line strength was 2.4 x 10 to the minus 15 power watt cm/2, and the fraction of the total radiated power was slightly higher. These figures refer to a 4' x 6' field of view centered on the peak for infrared emission from each source. The uncertainty in the line strength is approximately 50% and is caused by variable water vapor absorption along the flight path of the airplane. The line position estimate is 63.2 micron (+0.1, -0.2) micron. The prime uncertainty is due to the uncertain position of the (0 I) emitting regions in the field of view.

Melnick, G.↗

NASA NTRS1978

Magnetic field in the primitive solar nebula

Carbonaceous chondrites have apparently been magnetized in their early history in magnetic fields with intensities of 0.1 to 10 G, but the origin of the magnetizing field has remained obscured. It is suggested that the magnetic field recorded in the remanence of carbonaceous chondrites may have been produced by a self-excited hydromagnetic dynamo in the gaseous preplanetary nebula from which the solar system is thought to have formed. Recently computed models for the evolution of the preplanetary nebula, consisting of turbulent and differentially rotating gaseous disks with characteristic radial scales of several AU, are used to demonstrate the feasibility of this hypothesis. The maximum field intensity that might be realized by the dynamo production process is estimated to be as high as 1 to 10 G, taking into account two dynamical mechanisms that limit the strength of the field (the Coriolis force and ambipolar diffusion).

Levy, E. H.↗

NASA NTRS1978

Far-infrared polarization of the Kleinmann-Low Nebula in Orion

Polarization observed in the Kleinmann-Low Nebula is described. The observations were obtained by the Kuiper Airborne Observatory at an altitude of 12 km and in wavelength ranges 16-26, 28-48, 44-72, and 71-115 microns. Beyond 28 microns, the 2% polarization detected is consistent with zero polarization, while the upper limit in the 16-26 micron range is 7% polarization. It is suggested that the smallness of the detected polarization restricts nebula models for explaining the observations.

Gull, G. E.↗