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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

A shock-tube determination of the SiO /A 1 Pi - X 1 Sigma +/ transition moment

The sum of the squares of the electronic transition moments for the A 1 Pi - X 1 Sigma + band system of SiO has been determined from absorption measurements conducted in the reflected-shock region of a shock tube. The test gas was produced by shock-heating a mixture of N2O, SiCl4, and Ar, and the spectra were recorded photographically in the 260-290-nm wavelength range. The values of the sum as a function of internuclear distance between 2.8 and 3.3 Bohr were determined by comparing the measured absorption spectrum with that produced by a line-by-line synthetic-spectrum calculation which accounted for instrumental broadening. The value of the sum so deduced at an internuclear distance of 3.0 Bohr was 1.0 + or - 0.3 atomic units.

Park, C.↗
NASA NTRS1978

A shock-tube measurement of the SiO/E 1 Sigma + - X 1 Sigma +/ transition moment

The sum of the squares of the electronic transition moments for the (E 1 Sigma +) - (X 1 Sigma +) band system of SiO has been determined from absorption measurements conducted in the reflected-shock region of a shock tube. The test gas produced by shock-heating a mixture of SiCl4, N2O, and Ar, and the spectra were recorded photographically in the 150-230-nm wavelength range. The values of the sum of the squares were determined by comparing the measured absorption spectra with those produced by a line-by-line synthetic spectrum calculation. The value so deduced at an r-centroid value of 3.0 bohr was 0.86 + or - 0.10 atomic unit.

Park, C.↗
NASA NTRS1979

Shock tube spectroscopy of C3 + C2H mixture in the 140 to 700 nm range

Absorption spectroscopy has been performed in the reflected-shock region of a shock tube. Acetylene was shock-heated to produce a mixture, at around 4000 K, rich in C3 and C2H to simulate the ablation layer over the Jovian entry probe, and the spectral range from 140 to 700 nm was surveyed with an evacuable spectrograph. The observed spectra were dominated by those of C2 and C3 and an unknown band at wavelengths below 300 nm. The cross sections of the C3 Swings band in the 300 to 450 nm range agreed with previous measurements within a factor of 1.5. No absorption was observed in the wavelength range from 550 to 700 nm. The unknown broadband absorption with a peak cross section of 4 times 10 to the minus 17/sq cm at around 170 nm was attributed tentatively to the C2H radical. A preliminary calculation showed that the newly found absorption band would reduce the radiative heat flux to the stagnation point wall by about 12.5% in a typical flight condition.

Prakash, S. G.↗
NASA NTRS1979

The origin of metal clasts in the Bencubbin meteoritic breccia

The Bencubbin meteorite is a shock-welded breccia consisting of a diverse collection of metal and silicate clasts. Several types of evidence suggest that the metal clasts in Bencubbin retain chemical abundances that were established during condensation. The Cr, Ni, P and trace element abundances are consistent with condensation calculations and are much closer to the predicted compositions of metal condensates than the CM metal particles. In addition, petrographic and chemical evidence strongly suggest that the breccia components were incorporated as solid clasts within the breccia prior to a shock heating event of very short duration, which did not produce significant metamorphic effects.

Newsom, H. E.↗
NASA NTRS1979

Rb-Sr age of the Shergotty achondrite and implications for metamorphic resetting of isochron ages

The age of the Shergotty achondrite is determined by Rb-Sr isotope analysis and the metamorphic resetting of isochron ages, which is presumed to have occurred during a shock event in the history of the meteorite, is discussed. The isochron best fitting the Rb-Sr evolution diagram is found to correspond to an age of 165 million years, with an initial Sr-87/Sr-86 value of 0.72260. Different apparent ages obtained by the K-Ar and Sm-Nd methods are interpreted in terms of a model which quantifies the degree of resetting of internal isochron ages by low temperature solid state diffusion. On the basis of these considerations, it is concluded that Shergotty crystallized from a melt 650 million years ago, was shock heated to 300 to 400 C after its parent body was involved in a collision 165 million years ago, and was first exposed to cosmic rays two million years ago.

Nyquist, L. E.↗
NASA NTRS1979

Molecule formation and infrared emission in fast interstellar shocks. I Physical processes

The paper analyzes the structure of fast shocks incident upon interstellar gas of ambient density from 10 to the 7th per cu cm, while focusing on the problems of formation and destruction of molecules and infrared emission in the cooling, neutral post shock gas. It is noted that such fast shocks initially dissociate almost all preexisting molecules. Discussion covers the physical processes which determine the post shock structure between 10 to the 4 and 10 to the 2 K. It is shown that the chemistry of important molecular coolants H2, CO, OH, and H2O, as well as HD and CH, is reduced to a relatively small set of gas phase and grain surface reactions. Also, the chemistry follows the slow conversion of atomic hydrogen into H2, which primarily occurs on grain surfaces. The dependence of this H2 formation rate on grain and gas temperatures is examined and the survival of grains behind fast shocks is discussed. Post shock heating and cooling rates are calculated and an appropriate, analytic, universal cooling function is developed for molecules other than hydrogen which includes opacities from both the dust and the lines.

Hollenbach, D.↗
NASA NTRS1981

Cyclotron emission from AM Herculis

The cyclotron absorption coefficients in the ordinary and extraordinary modes are calculated for the shock heated region of AM Her. The equations of radiative transfer are solved and the intensity of the emitted UV radiation determined as a function of angle. The average spectrum is shown to have deviations from the previously predicted Rayleigh-Jeans spectrum and the magnetic field of AM Her is deduced to be roughly 5 x 10 to the 7th power gauss.

Chanmugam, G.↗
NASA NTRS1980

Diffuse X-ray emission from the jets of SS 433

The detection of large-scale diffuse X-ray jets from the variable-emission-line object SS 433 is reported. Observations were made with the high resolution imager and imaging proportional counter on board the Einstein X-ray Observatory. The two diffuse X-ray features discovered are found to be aligned with both the central source of SS 433 and with the bulges of the shell of the huge supernova remnant W 50 associated with SS 433, thus confirming the detection of jets related to SS 433 and the link between SS 433 and W 50, establishing a minimum age of 1000 years for the jet phenomenon and offering an explanation of the size of W 50. Processes by which two oppositely directed beams of material from the SS 433 source region may emit the diffuse X-rays are then considered, including shock heating by interactions with the ambient medium and synchrotron radiation. Similarities between the morphologies of the diffuse X-ray emission and those of radio galaxies are also noted.

Seward, F.↗
NASA NTRS1981

A 100 microsec, reliable, 10 Hz pulsed supersonic molecular beam source

A 10-Hz repetition rate, 100-microsec duration, reliable pulsed supersonic molecular beam source is described. Mechanical and electrical design of the pulsed valve are given in detail. Characteristics of the supersonic expansion obtained using coherent anti-Stokes Raman spectroscopy in acetylene are presented. They include pulse shape, gas rotational and translational cooling as a function of distance from the nozzle, clustering effects, and shock heating at the leading edge of the pulse.

Byer, R. L.↗
NASA NTRS1981

X-ray line emission from the Puppis A supernova remnant - Oxygen lines

Six prominent X-ray emission lines of O VII and O VIII have been detected from a portion of the Puppis A supernova remnant in observations with the Einstein Observatory Focal Plane Crystal Spectrometer. The lines are sufficiently well resolved to serve as diagnostics of the emitting plasma. From the relative intensities of the lines, it is inferred that the population of O VIII is about 1.5 times that of O VII, and that electron collisions are the dominant excitation mechanism in the plasma. A locus of allowed electron temperatures and interstellar-absorption column densities is derived: 1.5 x 10 to the 6th K, and (2-6) x 10 to the 21st per sq cm. The data are consistent with either a thin plasma source in equilibrium at a temperature of 2.2 x 10 to the 6th K with a column density of 4 x 10 to the 21st per sq cm, or with a nonequilibrium source in which the electrons have been shock-heated to a higher temperature and oxygen is underionized.

Winkler, P. F.↗
NASA NTRS1982

Plasma electron signature of magnetic connection to the earth's bow shock - ISEE 3

New observations of bowshock modified electron velocity distribution for upstreams are investigated using the Los Alamos ISEE 3 electron analyzer. Examples of two-dimensional electron distributions observed when ISEE 3 magnetically connected to the bowshock are presented, and the velocity moments are determined. The origin of the enhanced backstreaming electron fluxes and their likely effects on the upstream microturbulence spectrum are interpreted. A nearly isotropic component of back-streaming shock-heated electrons is found with energies at least as high as 1 keV. Phase-space density of the low energy parts of distributions measures well within the boundaries of accessibility and is observed to be depressed. Such distributions are likely to result from the direct sampling of electrons originating within the forward edge of the earth's bowshock, and may be unstable to whistler waves.

Feldman, W. C.↗
NASA NTRS1982

Absorptivity of water vapor for 10.6 micron radiation

Attention is called to recent measurements of the absorptivity of water vapor to 10.6-micron laser radiation made using shock-heated H2O/H2 and H2O/Ar mixtures and a probe CO2 laser. It is noted that these measurements give values about a factor of 2 lower than Ludwig's (1971) low resolution values. It is also argued that Fowler's (1981) high values are not likely to be caused by excited water molecules. It is shown that very intense laser radiation would be required to obtain any appreciable vibrational nonequilibrium. Within the narrow spectral range of 944-948/cm, no significant variation in absorption coefficient (suitably normalized) is observed as a function of laser line, water vapor concentration, total pressure, or diluent gas.

Pugh, E. R.↗
NASA NTRS1982

The effects of ejecta on the X-ray luminosities of supernova remnants

Because X-ray luminosities of most SNRs are dominated by emission from heavy elements, estimates of the X-ray emitting mass based on cosmic abundances may be incorrect. Here we investigate the apparent density evolution of a SNR when substantial amounts of processed material are ejected by the supernova. If this material is shock heated, it will dominate X-ray emission from the remnant long after the SNR has swept up the equivalent amount of interstellar matter (ISM). Emission from metal-rich ejecta may explain why ISM densities of young remnants far from the galactic plane, deduced from standard analysis, are higher than expected, as well as why larger SNRs appear to be lying in regions of lower ISM density. It should be included in detailed calculations of SNR surface brightness distributions, along with effects due to departures from ionization equilibrium and cloudlet evaporation in a multiphase ISM which may also contribute to the apparent evolution of density with radius.

Long, K. S.↗
NASA NTRS1982

Detection of interstellar NH sub 3 in the far-warm and dense gas in Orion-KL

The detection of the (J,K) = a(4,3) yields s(3,3) rotation inversion transition of ammonia at 124.6 microns toward the center of the Orion-KL region is reported. The line is in emission and has a FWHM or = to 30 km s 0.15. The far IR ammonia line emission probably comes mainly from the 'hot core', a compact region of warm, very dense gas previously identified by the radio inversion lines of NH3. The a(4,3) yields s(3,3) line is very optically thick, and since it is seen in emission, radiative excitation of the (4,3) NH3 level by far IR emission from dust within the source can be ruled out. Radiative excitation via the 10 microns of vibrational transitions of NH3 also seems unlikely. Hence, the (4,3) level is probably collisionally excited and the gas in the hot core region is warmer than the dust. Since the far IR line emission is highly trapped, densities of approximately 10 to the 7th power cu cm are high enough to explain the observations. Shock heating by the mass outflow from IRc2 may account for the high gas temperatures in the hot core region.

Townes, C. H.↗
NASA NTRS1982

Chemical studies of L chondrites. II - Shock-induced trace element mobilization

Data for 13 trace elements in 14 L4-6 chondrites of established shock history are reported and discussed. These data are combined with data for an additional 13 L4-6 chondrites to delineate the full extent of losses by shock. Trace element contents vary with petrologic type, S/Fe subgroup, and shock history, the last dominating strongly. Absolute abundances and interelement relationships for the six or seven most mobile elements vary with degree of shock-loading established from mineralogic and petrologic study. Shock-heating, previously known to have affected radiogenic Ar-40 and/or He-4 in meteorites but not other elements, apparently was at least as effective as other open-system processes in establishing mobile trace element contents of L chondrites and probably others.

Walsh, T. M.↗
NASA NTRS1983

The mass of Tycho's supernova remnant as determined from a high-resolution X-ray map

High resolution Einstein Observatory X ray images of Tycho's supernova remnant (SNR) are discussed. The object has features of a shock heated shell in the interstellar medium, accompanied by an inner shell with clumped ejecta. The measurements were made for 22 hr on Feb. 8, 1979, revealing a circular SNR, a thin emission shelf at the outer edge of the remnant, no emission in the central object, and most emissions concentrated in small, clumpy objects within a spherical shell. Three components of the X ray emission were identified, and calculations of the swept-up mass, the diffuse component of the ejecta shell, and the clumpy ejecta are reported to be 2.2, 1.2, and 0.7 solar mass, respectively. The SNR is concluded to be at an evolutionary stage between uniform expansion and adiabatic changes.

Seward, F.↗
NASA NTRS1983

Spatially extended narrow emission-line gas in the Seyfert galaxy NGC 4151

Details of the spatial structure of the narrow-line region (NLR) in NGC 4151 are presented, and the structure of the NLR is compared to that of the radio and X-ray emission. Results for the morphology and excitation of the NLR, the luminosity of the extranuclear features, and the kinematics are presented, citing published research. These results are used to test several models: the X-ray gas in pressure equilibrium with the adjacent NLR, the X-ray gas identified as shock-heated NLR clouds flowing supersonically through the ambient galactic interstellar medium, X-rays arising in SNR and massive X-ray binaries produced in bursts of star formation stimulated by nuclear outflow, and X-ray and line emission regions ionized indirectly by the radio jet.

Heckman, T. M.↗
NASA NTRS1983

Detection of interstellar NH3 in the far-infrared - Warm and dense gas in Orion-KL

Results of an investigation are presented which show the detection of the (J,K) = a(4,3)-s(3,3) rotation-inversion transition of ammonia at 124.6 microns toward the center of the Orion-KL region. The line is found to be in emission and has a FWHM greater than or equal to 30 km/s, while the far-IR ammonia line emission probably comes mainly from the 'hot core', a compact region of warm, very dense gas previously identified by the radio inversion lines of NH3. The a(4,3)-s(3,3) line is very optically thick and it is determined that radiative excitation of the (4,3) NH3 level by far-IR emission from dust within the source can be ruled out. It is concluded that the (4,3) level is probably collisionally excited and the gas in the hot core region is warmer than the dust. Densities of approximately 10 to the 7th/cu cm are high enough to explain the observations, while shock heating by the mass outflow from IRc2 may account for the high gas temperatures in the hot core region.

Townes, C. H.↗