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NASA NTRS1990

A large-scale cosmic microwave background anisotropy measurement at millimeter and submillimeter wavelengths

A balloon-borne experiment to measure the anisotropy of the cosmic microwave background radiation at angular scales of 4 deg or greater is reported. The instrument simultaneously measures in four spectral bands centered on 5.6, 8.7, 15.8, and 22.5/cm. Three results are presented: (1) the 95-percent confidence limit for monochromatic anisotropies is 0.0001 or less on angular scales of 10 deg; (2) the Galactic plane dust emission at l = 42 deg is consistent with a nu-squared emissivity law at frequencies above 15/cm, with excess emission below 15/cm; and (3) atmospheric ozone at an altitude of 35 km may form clumps as large as Delta emissivity/emissivity = 0.002.

Page, Lyman A.↗

NASA NTRS1989

The cosmic microwave background

Recent observational and theoretical investigations of the cosmic microwave background radiation (CMBR) are reviewed. Particular attention is given to spectral distortions and CMBR temperature anisotropies at large, intermediate, and small angular scales. The implications of the observations for inflationary cosmological models with curvature fluctuation are explored, and it is shown that the limits determined for intermediate-scale CMBR anisotropy almost rule out a baryon-dominated cosmology.

Silk, Joseph↗

NASA NTRS1991

X ray absorption by dark nebulae (HEAO-2 guest investigator program)

A study is described of data obtained from the Imaging Proportional Counter (IPC) x ray detector aboard the HEAO-2 satellite (Einstein Observatory). The research project involved a search for absorption of diffuse low energy x ray background emission by galactic dark nebulae. The commonly accepted picture that the bulk of the C band emission originates locally, closer that a few hundred parsec, and the bulk of the M band emission originates farther away than a few hundred parsec, was tested. The idea was to look for evidence of absorption of the diffuse background radiation by nearby interstellar clouds.

Sanders, W. T.↗

NASA NTRS1991

Statistical mechanics of soft-boson phase transitions

The existence of structure on large (100 Mpc) scales, and limits to anisotropies in the cosmic microwave background radiation (CMBR), have imperiled models of structure formation based solely upon the standard cold dark matter scenario. Novel scenarios, which may be compatible with large scale structure and small CMBR anisotropies, invoke nonlinear fluctuations in the density appearing after recombination, accomplished via the use of late time phase transitions involving ultralow mass scalar bosons. Herein, the statistical mechanics are studied of such phase transitions in several models involving naturally ultralow mass pseudo-Nambu-Goldstone bosons (pNGB's). These models can exhibit several interesting effects at high temperature, which is believed to be the most general possibilities for pNGB's.

Gupta, Arun K.↗

NASA NTRS1990

Consequences of relativistic proton injection in active galactic nuclei

The processes are analyzed by which extremely relativistic protons lose energy under the conditions thought to apply in the central engines of active galactic nuclei. Analytic formulae are derived which permit the consequences of relativistic proton injection under a variety of conditions to be predicted. Different proton cooling mechanisms are compared for a power-law proton injection function and two types of background radiation spectra: power-law and power-law plus blackbody. The kinetic equations for neutrons and protons are examined, and it is shown how to calculate the energy distributions of primary gamma rays and escaping neutrons and neutrinos.

Begelman, Mitchell C.↗

NASA NTRS1991

Thermal design of the Cosmic Background Explorer cryogenic optical assembly

The Cosmic Background Explorer (COBE) is a satellite which is designed to study the 3-K cosmic background radiation. Two cryogenic instruments and a common support structure comprise the Cryogenic Optical Assembly (COA). In order to make definitive measurements of the low-energy FIR radiation, the temperature of the COA must be maintained below 3 K. Temperature control of the COA elements is achieved by the use of a superfluid helium dewar. The thermal design also minimizes power dissipation, transient operational effects, and thermal gradients within the COA. This is accomplished by isolating selected components and heat-sinking others to various locations on the cryogen tank. The thermal design was developed primarily through analysis. Analytical models were created to perform parametric design studies. Ground testing was performed to correlate the thermal models and validate the thermal design. Both test and flight data confirmed that all design requirements were either met or exceeded.

Mosier, Carol L.↗

NASA NTRS1991

Electron densities and the excitation of CN in molecular clouds

In molecular clouds of modest density and relatively high fractional ionization, the rotational excitation of CN is controlled by a competition among electron impact, neutral impact and the interaction with the cosmic background radiation. The degree of excitation can be measured through optical absorption lines and millimeter-wave emission lines. The available, accurate data on CN in diffuse and translucent molecular clouds are assembled and used to determine electron densities. The derived values, n(e) = roughly 0.02 - 0.5/cu cm, imply modest neutral densities, which generally agree well with determinations by other techniques. The absorption- and emission-line measurements of CN both exclude densities higher than n(H2) = roughly 10 exp 3.5/cu cm on scales varying from 0.001 to 60 arcsec in these clouds.

Black, John H.↗

NASA NTRS1991

Zodiacal emission. II - Dust near ecliptic

The location and brightness of the peak zodiacal emission are derived from IRAS observations of the diffuse infrared background radiation. A uniform ellipsoid geometrical model is fitted to the latitudes of peak brightness, from which the orientation of the surface of maximum dust density near the earth's orbit is derived. Deviations from the uniform ellipsoid indicate that this surface bends toward the invariable plane of the solar system beyond 2.5 AU from the sun. The variations of the peak zodiacal emission brightness with solar elongation and observation date allow two independent determinations of the gradient of the volume emissivity of interplanetary dust. Combined with theoretical calculations of the infrared emission from silicate and graphite grains heated by the sun, the gradient of the dust density is found to be n proportional to r exp (-1.1 + or - 0.2). Systematic brightness variations with ecliptic longitude reveal two potential asymmetries in the dust complex: excess emission following the earth in its orbit, and excess emission along lines of sight with ecliptic longitude lambda = 190 + or - 20 deg and solar lambda about 100 deg.

Reach, William T.↗

NASA NTRS1991

A measurement of the large-scale cosmic microwave background anisotropy at 1.8 millimeter wavelength

This measurement of the large-scale cosmic microwave background radiation (CMBR) anisotropy places the most stringent constraints to date on fluctuations in the CMBR on angular scales greater than about 4 deg. Using a four-channel bolometric radiometer operating at 1.8, 1.1, 0.63, and 0.44 mm, the diffuse sky brightness over half of the northern hemisphere has been mapped with an angular resolution of 3.8 deg. Analysis of the sky map at the longest wavelength for Galactic latitudes of 15 deg or more yields a 95-percent confidence level upper limit on fluctuations of the CMBR at Delta T/T of 1.6 x 10 to the -5th with a statistical power of 92 percent for Gaussian fluctuations at a correlation angle of 13 deg. Between 3 deg and 22 deg, the upper limit of fluctuations is 4.0 x 10 to the -5th . An anisotropy is detected in the map, but it cannot yet be attributed to primordial sources. The ultimate sensitivity for this experiment is 7 x 10 to the -6th over this angular range for Gaussian fluctuations.

Meyer, Stephan S.↗

NASA NTRS1991

Formation of cosmic structure by Doppler instability

A new mechanism is described which can create an instability in homogeneous gaseous matter at very low density. When an isotropic background radiation field has, near an electronic resonance, a spectral feature for which photon occupation number increases with frequency, moving atoms increase their speed by taking energy from the photon distribution. In a cosmological setting, a sufficiently intense spectral feature can interact with neutral atomic gas, after recombination, to generate protogalactic perturbations of the scale and magnitude needed to explain large-scale cosmic structure.

Hogan, Craig J.↗

NASA NTRS1990

The intergalactic medium - Initial and boundary conditions for galaxy and primeval star formation

New detailed numerical calculations are presented of the evolution of the intergalactic medium (IGM) in a post recombination Friedmann universe, including a solution of the nonequilibrium rate equations for the ionization and recombination of H and He, the energy equation, and the equation of radiative transfer. The implications of this study for the characteristic mass scale and the epoch of gravitational collapse for the average 'first' star-forming clouds are discussed. The star-formation rate and associated metallicity generation implied if the IGM is fully ionized by starlight by redshift greater than 4 as suggested by recent interpretations of the Gunn-Peterson effect are examined. It is shown that the relative strengths of metal lines from a quasar absorption-line Lyman limit system cloud at z = 3 photoionized by the present intergalactic UV radiation background are compatible with the observations, at least for background sources of either AGN-type or star-forming galaxy spectra.

Giroux, Mark L.↗

NASA NTRS1990

Physics of the outer heliosphere; Proceedings of the 1st COSPAR Colloquium, Warsaw, Poland, Sept. 19-22, 1989

This volume includes chapters on spectroscopic data on the local interstellar medium and the related XUV radiation background; solar UV backscatter on neutral Galactic gases; entry and dynamics of Galactic and anomalous cosmic rays in the heliosphere; distant solar wind plasma, magnetic field, and solar energetic particles; the interaction of solar wind with the interstellar medium; and deep-space missions. Papers are on the characteristics and the velocity structure of the local interstellar medium, the scattering of solar UV on local neutral gases, solar effects on underground muons at 570 hg/sq cm, and cosmic rays and magnetosonic instabilities of solar wind flow near the heliospheric shock wave. Consideration is also given to the shock heating of the solar wind plasma, solar wind vortex flow in the outer heliosphere, the signature of a viscous interaction at the heliopause, the expected beams of energetic neutral atoms in the outer heliosphere, and the Pioneers 10 and 11 deep-space missions.

Grzedzielski, S.↗

NASA NTRS1992

Fields Of View Of X-Ray-Telescope Collimator Tubes

Results of theoretical analysis conducted to determine fields of view and irradiation patterns of collimator tubes of various shapes indicates, while background flux incident on surface at outlet of tube determined by ratio between diameter and length, shape of tube important in screening out background radiation.

Safren, Harvey G.↗

NASA NTRS1992

Scientific objectives and first results from COMPTEL

The imaging Compton telescope (COMPTEL) is the first imaging telescope in space to explore the MeV gamma ray range. At present it is performing a complete sky survey. In later phases of the mission, selected celestial objects will be studied in more detail. Targets of special interest in the COMPTEL energy range are radio pulsars, X-ray binaries, novae, supernova remnants, molecular clouds, and the interstellar medium within the Milky Way, as well as the nuclei of active galaxies, supernovae, and the diffuse cosmic background radiation in extragalactic space. The first four months of operation demonstrated that COMPTEL basically performs as expected. The Crab is clearly seen at its proper position in the first images of the anticenter region of the Galaxy. The Crab pulsar lightcurve was measured with unprecedented accuracy. The quasar 3C273 was seen for the first time at MeV-energies. Several cosmic bursts within the COMPTEL field of view could be located to an accuracy of about 1 degree. On June 9, 11, and 15, 1991 COMPTEL observed gamma ray (continuum and line) emission from three solar flares. Neutrons were also detected from the June 9 flare. At the present state of analysis, COMPTEL achieves the prelaunch predictions of its sensitivity within a factor of 2. Based on the present performance of COMPTEL, the team is confident that COMPTEL will fulfill its primary mission of surveying and exploring the MeV sky.

Schoenfelder, V.↗

NASA NTRS1990

Research and technology, 1990: Goddard Space Flight Center

Goddard celebrates 1990 as a banner year in space based astronomy. From above the Earth's obscuring atmosphere, four major orbiting observatories examined the heavens at wavelengths that spanned the electromagnetic spectrum. In the infrared and microwave, the Cosmic Background Explorer (COBE), measured the spectrum and angular distribution of the cosmic background radiation to extraordinary precision. In the optical and UV, the Hubble Space Telescope has returned spectacular high resolution images and spectra of a wealth of astronomical objects. The Goddard High Resolution Spectrograph has resolved dozens of UV spectral lines which are as yet unidentified because they have never before been seen in any astronomical spectrum. In x rays, the Roentgen Satellite has begun returning equally spectacular images of high energy objects within our own and other galaxies.

Source record↗

NASA NTRS1991

Microwave background anisotropies implied by large-scale galaxy correlations - The minimum of C(0) and cosmological parameters

Data from a recent APM survey are used to show that large-scale galaxy correlations found there imply the existence of measurable microwave background radiation (MBR) anisotropies on scales greater than several degrees. It is shown that sq rt C(0) is not less than 3.5 x 10 exp -5 if the APM data are used at Theta-0 = 20 deg, or sq rt C(0) is not less than 2.8 x 10 exp -5 if Theta-0 = 10 deg is used. These numbers are almost independent of the cosmological parameters Omega, Lambda, and the redshift of the last scattering surface. For finite-beamwidth experiments the minimal fluctuations depend on the cosmological parameters. The minimal anisotropies are smaller in a low-Omega universe.

Kashlinsky, A.↗

NASA NTRS1992

A hydrodynamic approach to cosmology - Methodology

The present study describes an accurate and efficient hydrodynamic code for evolving self-gravitating cosmological systems. The hydrodynamic code is a flux-based mesh code originally designed for engineering hydrodynamical applications. A variety of checks were performed which indicate that the resolution of the code is a few cells, providing accuracy for integral energy quantities in the present simulations of 1-3 percent over the whole runs. Six species (H I, H II, He I, He II, He III) are tracked separately, and relevant ionization and recombination processes, as well as line and continuum heating and cooling, are computed. The background radiation field is simultaneously determined in the range 1 eV to 100 keV, allowing for absorption, emission, and cosmological effects. It is shown how the inevitable numerical inaccuracies can be estimated and to some extent overcome.

Cen, Renyue↗

NASA NTRS1992

The Jodrell bank 'C' pulsar survey - A survey of the northern Galactic plane for rapidly rotating pulsars

Nearly 1500 sq deg of the northern Galactic plane were surveyed for rapidly rotating pulsars using the 76-m Lovell telescope. The sampling rate was such that there was sufficient nominal sensitivity to detect pulsars with periods as short as 0.6 ms. To overcome the effects of dispersion, scattering, and galactic background radiation, the high frequency of 1420 MHz was used to survey the inner Galaxy, while lower frequencies of 928 and 610 MHz were used for regions further from the Galactic center. PSR 1937 + 21 was detected in the survey, but no new pulsars were discovered. This is consistent with the results of other recent surveys and suggests that rapidly rotating, high-luminosity pulsars are not very common in the Galactic disk.

Biggs, J. D.↗