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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Measurement of temperature and density fluctuations in turbulence using an ultraviolet laser

Noninvasive measurement of density and temperature fluctuations in turbulent air flow was examined. The approach used fluorescence of oxygen molecules which are selectively excited by a tunable vacuum ultraviolet laser beam. The strength of the fluorescence signal and its dependence on laser wavelength vary with the density and temperature of the air in the laser beam. Because fluorescence can be detected at 90 degrees from the beam propagation direction, spatial resolution in three dimensions, rather than path-integrated measurements can be achieved. With spatial resolutions of the order of a millimeter and at supersonic air velocities it is necessary to perform each measurement in a time of the order of a microsecond; this is possible by by using laser pulses of ten nanosecond duration. In this method atmospheric O2 is excited by the emission of a tunable ArF excimer laser, and the fluorescence, which spans the 210 to 420 range, is detected by an ultraviolet phototube.

Massey, G. A.↗
NASA NTRS1980

The abundance of CO in diffuse interstellar clouds - An ultraviolet survey

CO was detected in 17 directions and its upper limits were estimated in 21 directions by a UV survey carried out with the Copernicus satellite in the C-X 1088 A and E-X 1076 A lines toward 48 bright stars. The CO column densities range from 10 to the 12th to 10 to the 17th/sq cm and correlate with C I and H2. The tendency of the C I/CO ratio to be about 10 follows the ratio of particular atomic and molecular cross-sections and the physical parameters of interstellar clouds. Finally, the connection between UV observations in diffuse clouds and radio observations of (C-13)O in dark clouds is discussed.

Federman, S. R.↗
NASA NTRS1987

Observations of molecules in comets

Ultraviolet and visible spectroscopy of comets has identified a large number of species in the coma, most of which appear to be the photodissociation and photoionization products of the 'parent' molecules evaporated directly from the cometary nucleus. Analyses of cometary spectra support the icy conglomerate model of the nucleus with H2O as the dominant ice species. Two molecules detected in the ultraviolet, CO and S2, are of particular interest to the study of the cosmogonic evolution of cometary grains. CO appears to be a highly variable constituent from comet to comet, while S2, first observed in comet IRAS-Araki-Alcock in 1983, is found in no other celestial source. Both of these molecules appear to be parent molecules.

Feldman, P. D.↗
NASA NTRS1995

A duty cycle hypothesis for the central engines of LINERs

A recent ultraviolet snaphsot imaging survey of the nuclei of nearby galaxies detected a compact nuclear ultraviolet source in only five of the 26 LINERs (low-ionization nuclear emission-line regions) included in the observed sample. Motivated by this observational result, we examine the possibility that all LINERs are powered by photoionization from a nuclear source, which is, however, active only for 20% of the time. We show that decay times of low-ionization species can be of the order of one to a few centuries, and we demonstrate through time-dependent photoionization calculations that if the nuclear ionizing source is active for only a fraction of the time, this would not be readily noticeable in the emission-line spectrum. We suggest that the activity cycle is related to episodic accretion events which are associated with the tidal disruption of stars by a central black hole. The time interval between tidal disruptions is of the same order as the emission-line decay time, with the accretion episode following each disruption lasting a few decades. These estimates appear to support the duty cycle hypothesis. Some observational consequences of the proposed scenario are also discussed.

Eracleous, Michael↗
NASA NTRS1974

Two new physical processes in the far-ultraviolet spectrum of zeta Tauri

We have detected absorption features in the far-ultraviolet spectrum of zeta Tau (B3pe), one of which corresponds to a new transition involving quasi-H/-/, and the other to a transition involving quasi-H2/+/. The former transition produces a broad absorption feature on the red wing of L-alpha. It is the result of the absorption of a photon by a ground-state hydrogen atom and colliding electron, and it leads to the excitation of both electrons to the 2p2 3Pe state of H/-/.

Heap, S. R.↗
NASA NTRS1980

Far-ultraviolet studies. VIII - Apollo 17 search for zodiacal light

The analysis in a previous paper of a large quantity of far-ultraviolet spectrometer data from the Apollo 17 mission is reexamined with the intent of searching for zodiacal light. An upper limit at somewhat longer wavelengths than before is set. Spectrometer scannings were made from 1180 to 1680 A every 12 sec. Little evidence for a dependence of the residuals (calculated by subtracting the star catalog integration from the observed signal at 1558 to 1669 A for two portions of the sky) on an ecliptic parameter is shown. The present data do not show any detection of far ultraviolet zodiacal light or indeed of any light at all, but merely reflect the limitations of the star catalog integration.

Henry, R. C.↗
NASA NTRS2024

A Rapid Sequence of Solar Energetic Particle Events Associated with a Series of Extreme-ultraviolet Jets: Solar Orbiter, STEREO-A, and Near-Earth Spacecraft Observations

A series of solar energetic electron (SEE) events was observed from 2022 November 9 to November 15 by Solar Orbiter, STEREO-A, and near-Earth spacecraft. At least 32 SEE intensity enhancements at energies >10 keV were clearly distinguishable in Solar Orbiter particle data, with 13 of them occurring on November 11. Several of these events were accompanied by 10 MeV proton and 2MeV nucleon−1 heavy-ion intensity enhancements. By combining remote-sensing and in situ data from the three viewpoints (Solar Orbiter and STEREO-A were ∼20° and ∼15° east of Earth, respectively), we determine that the origin of this rapid succession of events was a series of brightenings and jetlike eruptions detected in extreme ultraviolet (EUV) observations from the vicinity of two active regions. We find a close association between these EUV phenomena, the occurrence of hard X-ray flares, type III radio bursts, and the release of SEEs. For the most intense events, usually associated with extended EUV jets, the distance between the site of these solar eruptions and the estimated magnetic connectivity regions of each spacecraft with the Sun did not prevent the arrival of electrons at the three locations. The capability of jets to drive coronal fronts does not necessarily imply the observation of an SEE event. Two peculiar SEE events on November 9 and 14, observed only at electron energies 50 keV but rich in 1MeV nucleon−1 heavy ions, originated from slow-rising confined EUV emissions, for which the process resulting in energetic particle release to interplanetary space is unclear.

D Lario↗
NASA NTRS1993

Goddard high-resolution spectrograph observations of narrow discrete stellar wind absorption features in the ultraviolet spectrum of the O7.5 III star Xi Persei

We report the observation of transient narrow absorption components (NACs) in the stellar wind of the O giant Xi Per. Two sets of GHRS observations of the Si IV ultraviolet resonance doublet have been obtained. These features are extremely weak, with column densities of approximately 10 exp 12/sq cm and optical depths of order 0.1. The features are narrow, less than 30 km/s, and seem to occur in groups. If the NACs are due to the 1393 A component, they represent previously undetected low-velocity discrete absorption components at V(rad) below -600 km/s. If they are high-velocity features on the 1402 A doublet component, they may represent the decay phase of the discrete absorption components at the terminal velocity. In either case, they are a new aspect of the NAC phenomenon that could not have been detected with previous ultraviolet spectrographs.

Shore, Steven N.↗
NASA NTRS1994

Ultraviolet observations of galaxies with the FAUST experiment

We have used the set of point sources detected by the Far Ultraviolet Space Telescope (FAUST) instrument to identify galaxies and study the total galaxy flux in a 250 A wide band peaking at 1650 A. A sample of 144 galaxies has been obtained after cross-reference with the RC3 catalog, elimination of objects confused with stars and various corrections for the photometry. The UV-B color dispersion is found to increase while the galaxies get redder from late to early types. The irregular galaxies appear on average redder and the Sbc galaxies bluer than indicated by the spectral energy distributions currently used for the calculations of K-corrections. Various arguments lead us to make the assumption of a constant dust extinction within each galaxy. The UV flux per unit area decreases on average from late to early type spirals. We find a weak correlation between the UV and far infra-red emission while the infra-red to UV flux ratio gets lower when galaxies get bluer (as measured by the UV to B flux ratio). The UV flux per unit area correlates with the HI gas surface density and the total gas surface density when this quantity is available. The correlation with the molecular gas alone is weak. In the Virgo cluster, the UV flux per unit area does not decrease in direct proportion to the HI deficiency. Galaxy counts per square degree and per magnitude interval have been obtained at high-galactic latitudes. Combined with data at fainter magnitudes, they show a variation as a function of magnitude with a near-euclidean slope over a range of 8 magnitudes.

Deharveng, J.-M.↗
NASA NTRS1966

Hydrogen Fire Detection System Features Sharp Discrimination

Hydrogen fire detection system discovers fires by detecting the flickering ultraviolet radiation emitted by the OH molecule, a short-lived intermediate combustion product found in hydrogen-air flames. In a space application, the system discriminates against false signals from sunlight and rocket engine exhaust plume radiation.

Bright, C. S.↗
NASA NTRS1978

A model of carbon production in a cometary coma

A model of the cometary ionosphere is developed in order to account for the large population of metastable C(D-1) atoms detected via the ultraviolet spectrum of Comet West (1976 VI). Dissociative recombination of CO(plus) ions and electrons is shown to be the dominant source of carbon atoms rather than photodissociation of CO so that the derived carbon production rate is only a lower limit to the evaporation rate of the carbon bearing mother molecule.

Feldman, P. D.↗
NASA NTRS1995

The origin of N III lambda 990 and C III lambda 977 emission in AGN narrow-line region gas

We discuss implications of Hopkins Ultraviolet Telescope (HUT) detections of C III lambda 977 and N III lambda 990 emission from the narrow-line region of the Seyfert 2 galaxy NGC 1068. In their discovery paper Kriss et al. showed that the unexpectedly great strength of these lines implies that the emitting gas must be shock-heated if the lines are collisionally excited. Here we investigate other processes which excite these lines in photoionization equilibrium. Recombination, mainly dielectronic, and continuum fluorescence are strong contributors to the line. The resulting intensities are sensitive to the velocity field of the emitting gas and require that the turbulence be of the same order of magnitude as the observed line width. We propose optical observations that will decide whether the gas is collisionally or radiatively heated.

Ferguson, J. W.↗
NASA NTRS1995

Selected highlights from the Extreme Ultraviolet Explorer

We present a few scientific highlights from the Extreme Ultraviolet Explorer (EUVE) all-sky and deep surveys, from the EUVE Righ Angle Program, and from the EUVE Guest Observer Program. The First EUVE Source Catalog includes 410 extreme ultraviolet (EUV) sources detected in the initial processing of the EUVE all-sky data. A program of optical identification indicates that counterparts include cool star coronae, flare stars, hot white dwarfs, central stars of planetary nebulae, B star photospheres and winds, an X-ray binary, extragalactic objects (active galactic nuclei, BL Lacertae), solar system objects (Moon, Mars, Io,), supernova remnants, and two novae.

Bowyer, S.↗
NASA NTRS1995

Vibrationally excited H2, HCl, and NO(+) in the diffuse clouds toward Zeta Ophiuchi

Absorption lines from vibrationally excited H2 and from HCl were detected in the ultraviolet spectrum of Zeta Oph with the Hubble Space Telescope (HST). Improved upper limits on NO(+) absorption were obtained as well. The data were analyzed with an updated version of a chemical model for diffuse clouds (van Dishoeck & Black 1986) as a guide to understanding this gaseous environment. The comparisons suggest that the flux of ultraviolet radiation impinging on the cloud surface is approximately 1-2 times the average interstellar radiation field, which is lower than once believed.

Federman, S. R.↗
NASA NTRS1995

Are Unidentified Extreme-Ultraviolet Sources the Closest Neutron Stars?

Unidentified extreme-ultraviolet (EUV) sources, detected in the EUVE and ROSAT WFC all-sky surveys, could be isolated old neutron stars, accreting material from the interstellar medium (ISM). The closest neutron stars, which are located in the local ISM bubble of unusually low density, are faint and cool (L approximately 10(exp 27) erg/s, T approximately < 6 eV). The extreme-UV spectrum of these sources is very sensitive to the H I column density, since a large fraction of the energy is emitted just below the hydrogen Lyman edge. The EUVE sources with large count rates in the long-wavelength bandpass (600 A) seem to be the most promising candidates. These sources should have low H I column density (N(sub H I) approximately < 10(exp 18) sq cm), constraining their distances to a few tens of parsecs. Otherwise, their spectra would be significantly modified by ISM absorption, and inevitably they would appear stronger in the short-wavelength (100 A, 200 A) EUVE bandpasses. If these unidentified objects are familiar EUV sources rather than neutron stars, i.e. white dwarfs, late-type stars or cataclysmic variables, they are expected to be identifiable, and generally brighter than V approximately 14.

Shemi, A.↗
NASA NTRS2001

Titan Orbiter Aerorover Mission

We propose a combined Titan orbiter and Titan Aerorover mission with an emphasis on both in situ and remote sensing measurements of Titan's surface, atmosphere, ionosphere, and magnetospheric interaction. The biological aspect of the Titan environment will be emphasized by the mission (i.e., search for organic materials which may include simple organics to 'amono' analogues of amino acids and possibly more complex, lightening detection and infrared, ultraviolet, and charged particle interactions with Titan's surface and atmosphere). An international mission is assumed to control costs. NASA will provide the orbiter, launch vehicle, DSN coverage and operations, while international partners will provide the Aerorover and up to 30% of the cost for the scientific instruments through collaborative efforts. To further reduce costs we propose a single PI for orbiter science instruments and a single PI for Aerorover science instruments. This approach will provide single command/data and power interface between spacecraft and orbiter instruments that will have redundant central DPU and power converter for their instruments. A similar approach could be used for the Aerorover. The mission profile will be constructed to minimize conflicts between Aerorover science, orbiter radar science, orbiter radio science, orbiter imaging science, and orbiter fields and particles (FP) science. Additional information is contained in the original extended abstract.

Sittler Jr., E. C.↗
NASA NTRS2009

Estimate of the Impact of Absorbing Aerosol Over Cloud on the MODIS Retrievals of Cloud Optical Thickness and Effective Radius Using Two Independent Retrievals of Liquid Water Path

Two independent satellite retrievals of cloud liquid water path (LWP) from the NASA Aqua satellite are used to diagnose the impact of absorbing biomass burning aerosol overlaying boundary-layer marine water clouds on the Moderate Resolution Imaging Spectrometer (MODIS) retrievals of cloud optical thickness (tau) and cloud droplet effective radius (r(sub e)). In the MODIS retrieval over oceans, cloud reflectance in the 0.86-micrometer and 2.13-micrometer bands is used to simultaneously retrieve tau and r(sub e). A low bias in the MODIS tau retrieval may result from reductions in the 0.86-micrometer reflectance, which is only very weakly absorbed by clouds, owing to absorption by aerosols in cases where biomass burning aerosols occur above water clouds. MODIS LWP, derived from the product of the retrieved tau and r(sub e), is compared with LWP ocean retrievals from the Advanced Microwave Scanning Radiometer-EOS (AMSR-E), determined from cloud microwave emission that is transparent to aerosols. For the coastal Atlantic southern African region investigated in this study, a systematic difference between AMSR-E and MODIS LWP retrievals is found for stratocumulus clouds over three biomass burning months in 2005 and 2006 that is consistent with above-cloud absorbing aerosols. Biomass burning aerosol is detected using the ultraviolet aerosol index from the Ozone Monitoring Instrument (OMI) on the Aura satellite. The LWP difference (AMSR-E minus MODIS) increases both with increasing tau and increasing OMI aerosol index. During the biomass burning season the mean LWP difference is 14 g per square meters, which is within the 15-20 g per square meter range of estimated uncertainties in instantaneous LWP retrievals. For samples with only low amounts of overlaying smoke (OMI AI less than or equal to 1) the difference is 9.4, suggesting that the impact of smoke aerosols on the mean MODIS LWP is 5.6 g per square meter. Only for scenes with OMI aerosol index greater than 2 does the average LWP difference and the estimated bias in MODIS cloud optical thickness attributable to the impact of overlaying biomass burning aerosol exceed the instantaneous uncertainty in the retrievals.

Wilcox, Eric M.↗