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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 NTRS1979

A high-sensitivity X-ray survey using the Einstein Observatory and the discrete source contribution to the extragalactic X-ray background

Surveys of two fields have been carried out utilizing the X-ray imaging instruments of the Einstein Observatory to a limiting flux of 1.3 x 10 to the -14th ergs/sq cm s in the 1-3 keV band, a several hundred-fold increase in sensitivity with respect to previous surveys. Forty-three objects are observed with positional accuracies varying from 5 to 60 arcsec. Optical and radio studies of candidate counterparts are described. The number-intensity relationship for extragalactic sources is evaluated, and the consequences of the findings are discussed with particular emphasis on the discrete source contribution to the extragalactic X-ray background. It is concluded that a large fraction of the background is due to previously unresolved discrete sources.

Giacconi, R.↗
NASA NTRS1980

Quasi-stellar objects in the intergalactic medium - Source for the cosmic X-ray background

Current estimates of QSO luminosity, number density, evolution, and spectral index are used to study whether the diffuse cosmic ray background is (1) entirely due to thermal bremmstrahlung of the intergalactic medium (IGM), (2) completely supplied by QSO X-rays, or (3) a combination of both. The upper limits on an IGM fractional density with respect to closure are Omega = 0.26, 0.24, and 0.21 for pure collisional, photo/collisional, and pure photoionization, respectively. These calculations give emission spectra, Compton distortion of the microwave background, and optical depths to distant QSOs for comparison with relevant data.

Sherman, R. D.↗
NASA NTRS1981

Precursor active galaxies and the cosmic X-ray background

It is argued that the cosmic X-ray background (CXB) is not dominated by sources that are usual active galaxies or quasars. A comparable number of objects, young galaxies at z approximately 4 containing massive black holes surrounded by hot optically thin accretion disks, constitute the precursor active galaxies (PAG) postulated here for producing the thermal type spectrum required for the CXB. An evolutionary track for such PAG objects is described which would lead to the active galaxies observed as individual nonthermal sources. Unresolved emission from active galaxies at z 1 could then readily account for most of the nonthermal background observed in the gamma ray band.

Boldt, E. A.↗
NASA NTRS1981

Effect of display update interval, update type, and background on perception of aircraft separation on a cockpit display on traffic information

The concept of a cockpit display of traffic information (CDTI) includes the integration of air traffic, navigation, and other pertinent information in a single electronic display in the cockpit. Concise display symbology was developed for use in later full-mission simulator evaluations of the CDTI concept. Experimental variables used included the update interval motion of the aircraft, the update type, (that is, whether the two aircraft were updated at the same update interval or not), the background (grid pattern or no background), and encounter type (straight or curved). Only the type of encounter affected performance.

Jago, S.↗
NASA NTRS1980

Galactic and extragalactic contributions to the far-ultraviolet background

Data from the 1350-1550 A bandpass channel of the 2.5-deg angular resolution extreme-ultraviolet telescope on the Apollo-Soyuz mission have been analyzed for stellar and airglow radiation contributions for the galactic latitude range above 30 deg. At intermediate latitudes, the resulting diffuse background is found to be correlated with the neutral hydrogen column density as determined by 21 cm radio data. This result, together with the observed anisotropy and mean intensity of the radiation field, is consistent with the hypothesis that scattering of galactic-plane starlight off dust grains having an albedo of 0.5 and a phase function coefficient of 0.5 is the primary source of the observed radiation field at the intermediate latitudes. The background intensity near the poles is, however, higher than expected from the H I column density and extinction measurements.

Paresce, F.↗
NASA NTRS1980

The diffuse gamma-ray background in the Hoyle-Narlikar cosmology

The paper analyzes the contributions of QSOs, BL-Lac objects and Seyfert galaxies to the diffuse gamma-ray background within the framework of the Hoyle-Narlikar theory. It is shown that the inconsistency reported in standard theory, namely that the evolutionary function needed to explain the gamma-ray data is very different from the one derived from the optical part of the spectrum, is no longer present. It is also shown that the contribution of a variable gravitational 'constant' to the expression for the diffuse background is the same as that of a density evolution function.

Canuto, V. M.↗
NASA NTRS1981

Interstellar hot plasma contributions to the diffuse ultraviolet background

The intensity of the diffuse background emission in the far ultraviolet from hot coronal gas present in the plane and halo of the galaxy is calculated. The main emission lines expected are those of C III, IV, N III, IV and Si III, IV at 1909, 1549, 1749, 1487, 1207 and 1398 A respectively. Unless the gas is unusually clumped or has extremely depleted abundances, this source is not of sufficient intensity to influence current broadband measurements of the diffuse continuous ultraviolet background. However, future observations at higher sensitivity and resolution might have to take this effect into account.

Jakobsen, P.↗
NASA NTRS1981

Latitudinal anisotropy of the solar far ultraviolet flux - Effect on the Lyman alpha sky background

An estimate is given for the anisotropy of the solar full disk flux in the far ultraviolet, as it would be observed for lines of sight within and above the ecliptic plane through the predominant influence of plages at low heliocentric latitudes. The flux anisotropy for Lyman alpha, at a level of solar activity with a sunspot number of roughly 160, is approximately 0.88 for the integrated flux over the Lyman alpha profile and 0.83 for the flux at line center. The effect of this Lyman alpha flux anisotropy on the Lyman alpha sky background intensity, resonantly backscattered from the local interstellar medium that is streaming through the solar system, is examined. It is concluded that the solar Lyman alpha anisotropy should be included in models of the interplanetary background during periods of moderate to high solar activity.

Cook, J. W.↗
NASA NTRS1981

The transport of photochemical pollutants to the background troposphere

The considered investigation is concerned with the phenomena occurring as a chemically reacting plume, with specific initial concentrations of NO, NO2, O3, and hydrocarbons, emerges from an urban area and is advected to the background troposphere. A better understanding of the global NOx and hydrocarbon budgets can be realized by determining the fractions of NOx and hydrocarbons that are transported to distances far enough to be considered background. The investigation makes use of a 56-step, lumped kinetic mechanism for photochemical smog, which includes current information on pertinent chemical reactions and rate constants for the reactions.

Bazzell, C. C.↗
NASA NTRS1981

Pressure broadening of oxygen and its implications for cosmic background measurements

The pressure broadening of oxygen transitions at 119 and 425 GHz have been measured in the laboratory for nitrogen and oxygen broadening as a function of temperature. The measured values are significantly different from estimates used by Woody and Richards to obtain a secondary calibration in their cosmic background measurements. The effect of the new determination is to move the calibrated cosmic background further from a Planck function.

Pickett, H. M.↗
NASA NTRS1982

Measurement of speech levels in the presence of time varying background noise

Short-term speech level measurements which could be used to note changes in vocal effort in a time varying noise environment were studied. Knowing the changes in speech level would in turn allow prediction of intelligibility in the presence of aircraft flyover noise. Tests indicated that it is possible to use two second samples of speech to estimate long term root mean square speech levels. Other tests were also performed in which people read out loud during aircraft flyover noise. Results of these tests indicate that people do indeed raise their voice during flyovers at a rate of about 3-1/2 dB for each 10 dB increase in background level. This finding is in agreement with other tests of speech levels in the presence of steady state background noise.

Pearsons, K. S.↗
NASA NTRS1981

Quasar reddening, intergalactic dust, and the microwave background

Quasar reddening and distortion of the microwave background are calculated, assuming that dust in intervening galaxies and any possible intergalactic dust follow the extinction curve for dust in the Galaxy. Quasar reddening implies that the average line of sight has a visual extinction of 0.85 + or - 0.51 at z = 3; and this amount of dust is enough to distort the microwave background (given a very bright initial population of stars), but not enough to thermalize the added energy at wavelengths greater than 3 cm.

Wright, E. L.↗
NASA NTRS1982

Inhomogeneous cosmology - Gravitational radiation in Bianchi backgrounds

An exact formalism is developed for describing cosmological models with strong, long wavelength gravitational waves of general polarization, propagating over backgrounds corresponding to Bianchi types I through VII. A new metric which exhibits the appropriate symmetries of two equivalent independent polarizations of gravitational waves is introduced and discussed. The formalism is applied to an empty type I cosmology, and it is shown how the original z-dependent chaotic singularity structure transforms itself into gravitational radiation propagating along the z-axis in a Bianchi I background.

Adams, P. J.↗
NASA NTRS1982

On syntheses of the X-ray background with power-law sources

The conditions under which the combined emission from power-law sources can mimic the X-ray background (XRB) spectrum in the 3-50 keV range are considered in view of HEAO 1 A-2 experiment measurements, and it is confirmed that a good fit may be obtained. The required spectral properties of the component sources differ, however, from those observed for local active galactic nuclei. Constraints are deduced for both the low-luminosity extension and evolution of such local objects, and it is shown that any other class of sources contributing to the X-ray background must be characterized by an energy spectral index lower than about 0.4, which is the mean index of the XRB, and exhibit steeper spectra at higher energies.

De Zotti, G.↗
NASA NTRS1982

Thermalization of starlight by elongated grains - Could the microwave background have been produced by stars

The possibility of the microwave background being produced by stars after the big bang is considered. The critical problem for this hypothesis is the source of the long-wavelength opacity for observed wavelengths greater than 10 cm. It is shown that free-free opacity cannot thermalize the background. Spherical dust grains also fail, but needle-shaped conducting grains can provide sufficient opacity to produce the observed spectrum with a metal abundance Z approximately equal to 10 to the -7th.

Wright, E. L.↗
NASA NTRS1982

On the origin of the 1 keV diffuse X-ray background

Soft X-ray sky survey data for high galactic latitudes are used to constrain simple geometric models for the source of the diffuse X-ray background at 1 keV. The intensity maps show two extended and enhanced features, in Eridanus and in the direction of the galactic center, with a relatively uniform sky away from these features and an observed degree of isotropy consistent with a model in which the 0.5-1.2 keV background consists of an isotropic extragalactic component and a thick disk galactic component. A temperature of 2-3 million K and an emission pressure of 0.004 per cm to the 6th pc are derived for the galactic component from an assumed spectrum of 11E to the -1.4 power photons/sq cm s sr keV. While consistent with the data, a local, isotropically distributed source model is shown to pose physical difficulties.

Nousek, J. A.↗
NASA NTRS1981

Ultraviolet background radiation and the search for decaying neutrinos

The spectrum of the observed far-ultraviolet background at high galactic latitudes is studied in order to find evidence of radiation from neutrino decay. It is concluded that at latitudes above about 20 degrees, the limit on any light scattered from interstellar dust or the limit on light from any source other than stars is of order 300 photons/sq cm sec ster A. Superficial evidence for radiation from decaying neutrinos is provided by an examination of the spectrum of the observed background at the highest galactic latitudes, although the spectrum is so uncertain that conclusions are not possible.

Henry, R. C.↗
NASA NTRS1981

Anisotropy of the cosmic microwave background radiation

Theoretical predictions of the angular anisotropy in the cosmic microwave background radiation on both small and large angular scales are presented, and the effect of massive neutrinos on both the background radiation anisotropy and on the galaxy correlation function over very large scales is reviewed. Current observations show that the quadrupole anisotropy provides the greatest constraint on theory, and the values for the gravitational potential fluctuations indicate that small amplitude but sufficiently large-scale density fluctuations, both at the present epoch and on the surface of last scattering, can produce significant large angular scale variations in the radiation temperature. Most importantly, it is proposed that the quadrupole moment is most simply and elegantly interpreted in terms of the density fluctuations on very large scales whose presence is inferred from the requirement that an initial fluctuation spectrum is required in order for structure to develop.

Silk, J.↗