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The problem of radiation diffusion in the atmosphere of a planet illuminated by solar rays was examined. The basic equations of the problem were obtained and the solution was found for the case when the absorption coefficient in the atmosphere is constant. The assumption was introduced of exponential variation of absorptivity with altitude, and a first approximation solution was proposed.
Results are reported for observations of diffuse radiation in the spectral bands from 114 to 150 A and from 44 to 120 A, which were made with rocket-borne proportional counters in areas of the sky near galactic coordinates 150 deg longitude, -15 deg latitude and 189 deg longitude, 3 deg latitude. The observed fluxes are 0.125 photon per sq cm/s/sr/eV at 180 eV, which is consistent with previous measurements, and 3.2 photons per sq cm/s/sr/eV at 100 eV, which indicates a steeply rising spectrum. It is noted that these fluxes are significantly smaller than those detected by Yentis et al. (1972), and the differences are attributed to either a terrestrial origin of the fluxes or the direction of observation. Constraints are placed on the parameters of simple emission models of celestial origin, and a rigorous upper limit is determined for the space density of white dwarfs at a blackbody temperature of at least 100,000 K.
Energetic (exceeding 35 MeV) gamma-rays have been observed from the direction of Cygnus X-3 with the SAS-2 gamma-ray telescope. The statistical significance of the excess above the galactic and diffuse radiation is approximately 4.5 sigma. In addition, the gamma-ray flux is modulated at the 4.8-hr period observed in the X-ray and infrared regions, and within the statistical error is in phase with this emission. The flux above 100 MeV has an average value of about 4.4 millionths photon/sq cm per sec. If the distance to Cygnus X-3 is 10 kpc, this flux implies a luminosity of more than 10 to the 37th power erg/s if the radiation is isotropic and about 10 to the 36th power erg/s if the radiation is restricted to a cone of 1 steradian, as it might be in a pulsar. Upper limits are presented for the gamma-ray flux from other known or suspected periodic X-ray sources.
Results are reported for measurements of cosmic diffuse gamma rays performed with a double Compton scatter gamma-ray telescope flows aboard a balloon at 3.5-g/sq cm residual atmosphere. The operation and calibration of the telescope are briefly reviewed, unwanted backgrounds are identified, and the only significant background for the telescope used is shown to arise from the interaction of albedo neutrons with hydrogen and carbon in one of the liquid scintillators. The fluxes of cosmic diffuse gamma rays with energies of 2 to 3, 3 to 5, 5 to 7, 7.5 to 10 MeV are listed, and upper limits are provided for energies of 10 to 15 and 15 to 25 MeV. These data are compared with numerous previous measurements, and no indication is found that the diffuse radiation is statistically different from isotropic. Upper limits are placed on the gamma-ray fluxes (mainly 3 to 25 MeV) from various localized sources.
Using the HEAO 1 soft X-ray sky survey, a search was conducted for X-ray emission from 18 stars in the spectral range B5-A7. The detection of 0.25 keV X-ray sources consistent with the positions of Pi Ceti, a normal B7 V star, and Phi Herculis, a classic Ap star was reported. The detection of these stars argues for large mass motions in the upper layers of stars in this spectral range, and argues against radiative diffusion as the source of abundance anomalies in Ap stars.
Observations and limiting values for the flux of 1-20 MeV gamma rays from the Crab, the Seyfert galaxy NGC 4151, the black hole candidate Cyg X-1, Cyg X-3 and the two nearest quasars CG 135+1 and 3C 273 are reported. Measurements of the energy and scatter angle of gamma rays at zenith angles between 10 and 30 deg were obtained by a balloon-borne double-scatter gamma-ray telescope. The flux from the Crab from 1.2 to 10 MeV is found to be 0.0039 + or - 0.0020 photons/sq cm per sec, and the energy distribution of the flux from 1.2 to 20 MeV is determined. Two-standard-deviation upper limits to the gamma-ray flux in the intervals 1.2-3, 3-5, 5-10 and 10-20 MeV of 0.0003, 0.0002, 0.00006 and 0.00004 photons/sq cm/sec are found for NGC 4151, Cyg X-1 and Cyg X-3, while those of 0.0005, 0.0003, 0.0001 and 0.00004 photons/sq cm per sec are determined for both quasars. These upper limits are interpreted as restricting confirmed gamma-ray sources to the Crab and NP 0532, and as evidence against Seyfert galaxies as the source of cosmic diffuse radiation.
The helium-flash model for X-ray burst sources, in which matter is presumed to accrete onto the surface of a neutron star, is discussed. Attention is given to the accretion process, nuclear burning, X-ray emission, and the energy released by convection as well as by radiative diffusion near the surface. The rise times of observed bursts, their spectral evolution, and the properties of the spectrally soft X-ray transients are considered. Problems in interpreting the continuum spectra are discussed, along with problems in the detection and measurement of line features in the spectra. Also considered are the ratio of time-averaged persistent luminosity to time-averaged burst luminosity, peak burst luminosities, and the possibility of detecting binary membership for burst sources.
The diffuse radiation field in the UV (900-3,000 A) affects the structure of galactic molecular clouds and conveys important information concerning the physical characteristics and spatial distribution of gas and dust in the universe. Continuum emission in this range is probably dominated by interstellar dust scattering in our galaxy. For view directions and angular resolutions allowing observations in the rifts between galactic dust clouds, the background due to the integrated light of spiral galaxies may be detected, providing important information on their structure and evolution. The redshifted emission from an intergalactic medium may be observable in the regions between nearby bright galaxies. Present observations provide weak constraints on the radiation field required to ionize the intergalactic medium at the level required by the Gunn-Peterson test.
The approaches of three computer flow field codes (HYVIS, COLTS, and RASLE), used to determine the Galileo Probe aerothermal environment and its effect on the design of the thermal protection system, are analyzed in order to resolve differences in their predicted results. All three codes account for the hypersonic, massively blown, radiation shock layers, characteristic of Jupiter entry. Significant differences, however, are evident in their solution procedures: the governing conservation equations, the numerical differencing methods, the governing physics (chemical, radiation, diffusion, and turbulence models), and the basic physical data (thermodynamic, transport, chemical, and spectral properties for atomic and molecular species). Solutions are compared for two near peak heating entry conditions for a Galileo Probe baseline configuration, having an initial mass of 242 kg and simulating entry into the Orton nominal atmosphere. The modern numerical methodology of COLTS and RASLE appear to provide an improved capability for coupled flow-field solutions.
Past hard X-ray and lower energy satellite instruments are reviewed and it is shown that observation above 20 keV and up to hundreds of keV can provide much valuable information on the astrophysics of cosmic sources. To calculate possible sensitivities of future arrays, the efficiencies of a one-atmosphere inch gas counter (the HEAO-1 A-2 xenon filled HED3) and a 3 mm phoswich scintillator (the HEAO-1 A-4 Na1 LED1) were compared. Above 15 keV, the scintillator was more efficient. In a similar comparison, the sensitivity of germanium detectors did not differ much from that of the scintillators, except at high energies where the sensitivity would remain flat and not rise with loss of efficiency. Questions to be addressed concerning the physics of active galaxies and the diffuse radiation background, black holes, radio pulsars, X-ray pulsars, and galactic clusters are examined.
The Auger ionization model is used to estimate the X-ray luminosities of supergiants of spectral types from B1.5 to B9. It is found that the ion N+4 is not useful in the B spectral range, while the C IV and Si IV line strengths are excellent diagnostics of X-ray luminosity, being only slightly affected by the diffuse radiation field. For the ion abundance calculations, the X-ray radiation field was assumed to be like that observed in early B supergiants and mass loss rates were estimated using an extrapolation of radio observations of earlier OB supergiants. X-ray luminosities were derived that are consistent with Einstein observatory results. Derived X-ray luminosities show a general bolometric magnitude decrease from early to late B supergiants.
The Gamma Ray Observatory (GRO) is an approved NASA mission, programmed for launch in 1988. Its complement of four detectors has established goals: (1) to study the nature of compact gamma-ray sources such as neutron stars and black holes, or objects whose nature is yet to be understood; (2) to search for evidence of nucleosynthesis especially in the regions of supernovae; (3) to study structural features and dynamical properties of the Galaxy; (4) to explore other galaxies, especially the extraordinary types such as radio, Seyferts, and quasars; and (5) to study cosmological effects by examining the diffuse radiation in detail. This paper discusses the design, objectives, and expected scientific results of each of the GRO instruments in view of the GRO mission goals.
The distribution of solar wind implanted noble gases in lunar samples depends on implantation energy, fluence, diffusion, radiation damage and erosion. It is known that at least the lighter rare gases are fractionated after implantation, but the redistribution processes, which mainly drive the losses, are not well understood. Some information about this one can get by looking at the concentration profiles of solar wind implanted He-4 measured by the Gas Ion Probe in single lunar grains. The observed profiles were divided in three groups. These groups are illustrated and briefly discussed.
The Caltech one-dimensional photochemical model is used to analyze important questions concerning the upper stratospheric O3 and the key HO(x), NO(x), and ClO(x) free radicals. The model is described and first order effects of the inclusion of diffuse radiation in a spherical rather than plane parallel atmosphere at solar zenith angles close to 90 deg are assessed. A comparison is made between photochemical theory and observations for upper stratospheric O3, where local photochemistry rather than dynamics should control the O3 abundance. The photochemical equilibrium relation for odd oxygen is studied, including the important radicals involves. It is concluded that a significant model ozone deficit exists in the upper stratosphere. Possible causes for such a discrepancy are investigated in light of current model and experimental uncertainties. In particular, the observational ratio of atomic oxygen to zone appears to disagree with the model results.
A simple realistic biosphere model for calculating the transfer of energy, mass and momentum between the atmosphere and the vegetated surface of the earth has been developed for use in atmospheric general circulation models. The vegetation in each terrestrial model grid is represented by an upper level, representing the perennial canopy of trees and shrubs, and a lower level, representing the annual cover of grasses and other heraceous species. The vegetation morphology and the physical and physiological properties of the vegetation layers determine such properties as: the reflection, transmission, absorption and emission of direct and diffuse radiation; the infiltration, drainage, and storage of the residual rainfall in the soil; and the control over the stomatal functioning. The model, with prescribed vegetation parameters and soil interactive soil moisture, can be used for prediction of the atmospheric circulation and precipitaion fields for short periods of up to a few weeks.
High energy gamma ray astronomy has evolved with the space age. Nonexistent twenty-five years ago, there is now a general sketch of the gamma ray sky which should develop into a detailed picture with the results expected to be forthcoming over the next decade. The galactic plane is the dominant feature of the gamma ray sky, the longitude and latitude distribution being generally correlated with galactic structural features including the spiral arms. Two molecular clouds were already seen. Two of the three strongest gamma ray sources are pulsars. The highly variable X-ray source Cygnus X-3 was seen at one time, but not another in the 100 MeV region, and it was also observed at very high energies. Beyond the Milky Way Galaxy, there is seen a diffuse radiation, whose origin remains uncertain, as well as at least one quasar, 3C 273. Looking to the future, the satellite opportunities for high energy gamma ray astronomy in the near term are the GAMMA-I planned to be launched in late 1987 and the Gamma Ray Observatory, scheduled for launch in 1990. The Gamma Ray Observatory will carry a total of four instruments covering the entire energy range from 30,000 eV to 3 x 10 to the 10th eV with over an order of magnitude increase in sensitivity relative to previous satellite instruments.
New NIR and FIR maps and J = 1-0 CO spectroscopy of the Magellanic irregular galaxy NGC 4449 are presented. The brighter 150-micron emission is concentrated along the central visual ridge of the galaxy, although there is lower intensity extended emission throughout the visible extent of the object. The maximum FIR emission is coincident, within the uncertainties, with the visual and NIR maxima, identified as the galactic nucleus. It is estimated that the IR luminosity of the 1-kpc-diameter central region in NGC 4449 is comparable to that for a similar-sized region at the center of the Galaxy. A large fraction of the 150-micron emission may arise from warm dust distributed throughout the galaxy and heated by the diffuse radiation field. Active star formation follows the NIR emission in part of the galaxy, but no coincidence is found in another region.
Some of the basic mechanisms of heating molecular clouds and their surfaces are reviewed, including cosmic rays, ambipolar diffusion, radiation, and shock waves. Cooling by fine structure transitions of atoms and ions as well as by vibrational and rotational transitions of interstellar molecules is discussed. A theoretical application of these processes is made to the observations of warm CO and vibrationally excited H2.