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  • ASTROPHYSICS  (1,826)
  • LUNAR AND PLANETARY EXPLORATION  (1,628)
  • 2005-2009
  • 1990-1994  (2,324)
  • 1980-1984  (1,130)
  • 1992  (2,324)
  • 1983  (1,130)
Collection
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  • 2005-2009
  • 1990-1994  (2,324)
  • 1980-1984  (1,130)
Year
  • 1
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    Supernovae as sources of interstellar diamonds (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Small hydrocarbon grains in the vicinity of a supernova could be annealed by the absorption of several far-ultraviolet photons to produce the tiny diamonds found in meteorites. These freshly-synthesized diamond grains would be bombarded by the heavy ions and neutrals in the supernovae outflow and would thereby acquire the distinctive noble-gas isotopic signature by which they were first isolated. Only diamonds formed relatively close to supernovae would acquire such a signature, since grains formed farther out would be subjected to a much diluted and less energetic plasma environment.
    Keywords: ASTROPHYSICS
    Type: Astrophysics and Space Science (ISSN 0004-640X); 196; 1; p. 117-123.
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  • 2
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    UV spectroscopy of Z Chamaeleontis. II - The 1988 January normal outburst (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: IUE observations taken during the 1988 January normal outburst of Z Cha are presented and a detailed comparison with the 1987 April superoutburst is made. The most important difference from the superoutburst is that the normal outburst continuum flux shows less than 10 percent orbital variation away from the eclipse, implying that there is no 'cool' bulge on the disk to occult the brighter inner disk periodically. The implications for the outburst mechanism in the types of outburst are discussed. The evolution of the continuum flux distribution and emission-line fluxes, the modulation of the continuum and line fluxes with orbital phase, and the behavior of the mideclipse spectral during normal outburst are investigated.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 259; 4; p. 593-603.
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  • 3
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    Search for periodic gamma-ray emission from Cygnus X-3 by the EGRET telescope on the Compton Gamma-Ray Observatory (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory observed the Cygnus region of the Galaxy during the periods 1991 May 30-June 8 and 1991 August 8-15. We report on a periodicity analysis of the gamma rays originating from the direction of Cygnus X-3. This analysis showed no evidence of periodic modulation during these observations of the gamma-ray emission at the approximately 4.8 hr period observed at X-ray wavelengths.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 401; 2; p. 724-727.
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  • 4
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    X-ray flares from runaway pair production in active galactic nuclei (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The hard X-ray spectrum of AGNs is nonthermal, probably arising from an electron-positron pair cascade, with some emission reflected off relatively cold matter. There has been interest in models on which protons are accelerated and create relativistic electrons on interaction with a local radiation field. It is shown here that a sufficient column density of protons can lead to runaway pair production: photons generated by the relativistic pairs are the targets for the protons to produce more pairs. This can produce X-ray fluxes with the characteristics observed in AGN. The model predicts the maximum ratio of luminosity to source size as well as their spectrum in the early phases. The same mechanism may also be able to create the knots of synchrotron-radiating pair plasma seen in sources such as 3C273.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 360; 6400; p. 135-137.
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  • 5
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    Scattering of infrared radiation by dust in NGC 7023 and NGC 2023 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The contribution of scattered light to the total nebular emission is determined on the basis of linear polarization measurements at 1.25, 1.65, and 2.2 microns of the visual reflection nebulae NGC 7023 and NGC 2023. The percentage polarization of NGC 7023 slowly increases from 0.3 to 1 micron, with peak polarizations of up to 26 percent at 1.25 micron, then rapidly decreases, with values of 4-7 percent at 2.2 microns. This is interpreted as implying that scattered starlight contributes most to the SW emission, while unpolarized emission from small grains or large molecules dominates at longer wavelengths. IR polarization and surface brightness measurements are combined to derive the intensity of scattered light, which is then compared with scattering models. While the near-IR emission of both NGC 2023 and NGC 7023 is dominated by small-grain or large-molecule emission, IR scattered light plays a larger role in NGC 2023 than in NGC 7023.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 400; 1; p. 238-247.
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  • 6
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    The X-ray variability of NGC 6814 - Power spectrum (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The existence of the periodic component seen in NGC 6814 with Exosat at 12,000 +/- 100 s is confirmed by a power spectrum and folded light curve analysis of unevenly sampled Ginga data. A comparison of the power spectra produced from simulated light curves with that observed enables the intrinsic shape of the power spectrum of the source to be determined despite the distortions introduced by the window function. The best estimate for the period is 12,132 +/- 3 s, where the error is that derived from simulations. An upper limit to the rate of change of period of about 10 exp -9 is inferred if the light curves are truly phase-coherent, but as this is not required by the data, the conservative upper limit is not greater than 5 x 10 exp -7. The large amount of power in the periodic component and its stability both suggest occultation of the source as its origin.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 400; 1; p. 138-152.
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  • 7
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    Cold dissipationless collapse of spherical systems - Sensitivity to the initial density law (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The collapse of cold, initially spherical systems with varying degrees of central condensation is investigated. The way in which the final shape of a collapsing system depends on the initial density law is examined. For an initial stellar number density rho varies as r exp -n, where n is in the range 0-2.5, the final, nearly prolate shape is given by a/c is approximately equal to 1.28(1 + 0.16 n), where a/c is the ratio of long to short axes of the inertia ellipsoid computed from the moment of inertia tensor of the most tightly bound 80 percent of the mass. The properties associated with the final states in the present computations are also studied. The collapsing systems develop an anisotropic halo dominated by radial orbits surrounding an isotropic core as predicted by Burkert (1990).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 400; 1; p. 58-64.
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  • 8
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    Pulsed high-energy gamma-rays from the radio pulsar PSR1706-44 (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Gamma radiation above 100 MeV in energy has been detected from the radio pulsar PSR1706-44. The gamma emission forms a single broad peak within the pulsar period of 102 ms, in contrast to the two narrow peaks seen in the other three known high-energy gamma-ray pulsars. The emission mechanism in all cases is probably the same, the differences arising from the geometry of the magnetic and rotation axes and the line of sight. Gamma-ray emission accounts for as much as 1 percent of the total neutron star spindown energy in these pulsars, much more than emerges at optical or radio frequencies. Thus, study of this emission is important in understanding pulsar emission and evolution.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 359; 6396; p. 615, 616.
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  • 9
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    Major outburst of periodic Comet Halley at a heliocentric distance of 14 AU (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The properties and evolution of the major outburst experienced by Comet Halley at 14 AU during February-March 1991 are studied. It is found that the observed halo is a segment of a conical surface populated by solid particles ejected from a localized, temporarily activated region on the sunlit hemisphere of the spinning nucleus. The total mass of the ejecta was at least 10 exp 12 g and CO was probably the prime driver, accelerating the smallest grains to a terminal velocity of about 45 m/s. The mass loading of the gas flow by particulate matter is enormous, with the mass production rate exceeding the expected production rate of CO by a factor of several tens.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 263; 1-2; p. 367-386.
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  • 10
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    Stratification of chemical elements in the atmosphere of the Ap star 53 Camelopardalis (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A detailed abundance analysis of Cr, Fe, Mn, Ca, and Ti in the Ap star 53 Cam from IUE high-resolution spectra has been performed. It is found that UV lines give significantly lower abundance than visible lines for Cr and Fe. Theoretical spectra of Cr II line calculated with the stratified chromium abundance distributions predicted a priori by the diffusion-mass loss model match well both visible and UV lines. The spectral shape of the Ca II K line and its variation are well accounted for by the diffusion model with mass loss. A spectrum synthesis with a stratified abundance well reproduces the observations. These findings provide convincing evidence for stratification in the photosphere of 53 Cam.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 263; 1-2; p. 232-240.
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  • 11
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    Modelling of IR emission of interstellar clouds. I - Emission of isolated clouds and dust abundance variations (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A model for the IR emission and extinction properties of small dust particles is used here to compute the IR emissions in the IRAS photometric bands for a set of isolated, spherical, and nonhomogeneous clouds heated by the local interstellar radiation field. It is predicted that the IR limb brightening (LB) in the IRAS photometric bands caused by selective absorption of UV photons of different energies in the cloud generally happens for central extinctions over 4 mag at 12 microns and greater than 10 mag at 100 microns and intermediate extinctions for the other IRAS bands. The surface brightness in the four IRAS bands is limited to about 0.4, 0.6, 3, and 10 MJy/sr at 12, 25, 60, and 100 microns respectively when no strong density discontinuity is present at the cloud edge.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 263; 1-2; p. 258-274.
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  • 12
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    A spatial domain Stokes flow model for the gravity and topography of the middle latitudes of Venus (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A novel modeling technique is developed and applied to the long-wavelength gravity, topography, and internal density structure of Venus. The focus of this study is to employ data on the gravity and topography of Venus, which are obtained from the Pioneer Venus Orbiter mission, to enhance understanding some key aspects of the internal structure of the planet. A modeling strategy utilizing 'stokeslets' or basic units of slow viscous flow (governed by the Stokes equations) to duplicate the observed gravity and topography is implemented.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E11; p. 18,285-18,294.
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  • 13
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    First-order inflation (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: I discuss the most recent model of inflation. In first-order inflation the inflationary epoch is associated with a first-order phase transition, with the most likely candidate being GUT symmetry breaking. The transition from the false-vacuum inflationary phase to the true-vacuum radiation-dominated phase proceeds through the nucleation and percolation of true-vacuum bubbles. The first successful and simplest model of first-order inflation, extended inflation, is discussed in some detail: evolution of the cosmic-scale factor, reheating, density perturbations, and the production of gravitational waves both from quantum fluctuations and bubble collisions. Particular attention is paid to the most critical issue in any model of first-order inflation: the requirements on the nucleation rate to ensure a graceful transition from the inflationary phase to the radiation-dominated phase.
    Keywords: ASTROPHYSICS
    Type: In: The infrared and submillimetre sky after COBE; Proceedings of the NATO Advanced Study Institute, Les Houches, France, Mar. 20-30, 1991 (A93-51701 22-90); p. 35-74.
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  • 14
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    An analysis of the focusing performance of Magellan SAR image data (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Synthetic aperture radar (SAR) focusing can be achieved either based on accurate ephemeris data or on an autofocusing process. For the Magellan project, such a decision must be made in the early phase of Magellan SAR system design. The analysis of the emphemeris requirement is complicated. The analysis given by the author leads to the conclusion that empheris data obtained from the Magellan navigation system provide sufficient accuracy to meet the Magellan image resolution requirement.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 610-613.
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  • 15
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    Local gravitomagnetic perturbations of the lunar orbit (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Using the metric in the local inertial frame of the Earth, we calculate relativistic effects on the lunar orbit with the synodic month period. It is shown that such perturbations arise entirely from the gravitomagnetic components of the local metric which exist because of the relative motion of the sun with respect to the Earth. In the case of general relativity, the net perturbation has an amplitude of 3 cm for the lunar range.
    Keywords: ASTROPHYSICS
    Type: Physical Review D - Particles and Fields, 3rd Series (ISSN 0556-2821); 46; 12; p. 5404-5406.
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  • 16
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    Accelerated complete-linearization method for calculating NLTE model stellar atmospheres (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Two approaches to accelerating the method of complete linearization for calculating NLTE model stellar atmospheres are suggested. The first one, the so-called Kantorovich variant of the Newton-Raphson method, consists of keeping the Jacobi matrix of the system fixed, which allows us to calculate the costly matrix inversions only a few times and then keep them fixed during the subsequent computations. The second method is an application of the Ng acceleration. Both methods are extremely easy to implement with any model atmosphere code based on complete linearization. It is demonstrated that both methods, and especially their combination, yield a rapidly and globally convergent algorithm, which takes 2 to 5 times less computer time, depending on the model at hand and the required accuracy, than the ordinary complete linearization. Generally, the time gain is more significant for more complicated models. The methods were tested for a broad range of atmospheric parameters, and in all cases they exhibited similar behavior. Ng acceleration applied on the Kantorovich variant thus offers a significant improvement of the standard complete-linearization method, and may now be used for calculating relatively involved NLTE model stellar atmospheres.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 262; 2; p. 501-514.
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  • 17
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    An IRAS study of pre-main sequence stars in B209 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We have constructed high resolution IRAS maps of the B209 star forming region in the Taurus complex. By combining survey scans with pointed observations using advanced techniques specially developed to handle IRAS data in crowded fields, we have constructed images that reveal two new premain-sequence (PMS) objects. One of these, IRAS 04114+2757G, has FIR colors close to those of typical T Tauri stars and is probably associated with a faint stellar object visible on the POSS prints. The other new PMS source, IRAS 04111+2800G, is a deeply embedded object not detected at 12 microns and not optically visible. The object is projected close to the center of an ammonia core. Our detection of compact blue and red shifted (C-12)O emission peaks around the position of IRAS 04111+2800G confirms the PMS nature and youth of this object. We have examined the reasons for the exclusion of IRAS 04111+2800G and IRAS 04114+2757G from the IRAS Point Source Catalog and estimated the incompleteness of the currently known sample of embedded PMS stars in Taurus. The implications for the determination of evolutionary time scales in low mass star formation are discussed.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 259; 2; p. 537-542.
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  • 18
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    A different view of plasma flow inside P/Halley (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Giotto spacecraft carried two different instruments - the JPA and the IMS - for the observation of hot ions in the coma of P/Halley. Although there are many similarities in the time and distance profiles of the plasma flow parameters (bulk velocity, number density, and temperature) computed from the two data sets, there are also some significant differences, especially at cometocentric distances less than 500,000 km. The principal discrepancies between the JPA results presented by Formisano et al. (1990) and the IMS observations are: (1) the IMS did not detect the levelling off of the speed and temperature profiles that Formisano et al. interpreted as flow stabilization; (2) the IMS detected differential north-south flow between the solar wind and cometary ions for only a brief interval when the magnetic field was oriented nearly southward, whereas Formisano et al. reported more extensive differential north-south flow that was independent of the direction of the field; (3) the JPA ion densities were factors of 2 to 4 higher than the IMS ion densities which, in turn, were an order of magnitude greater than theoretical values.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 258; 2; p. 549-554.
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  • 19
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    Theoretical profiles of Lyman-alpha satellites and application to synthetic spectra of DA white dwarfs (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present new theoretical calculations for the red wing of the Lyman-alpha profile. Close collisions with neutral and ionized hydrogen lead to the formation of the pseudomolecules H-H and H-H(+) with the appearance of satellite features near 1600 and 1400 A. The calculations include multiperturber effects, which are responsible for the formation of H3 and H3 with features near 1950 and 2600 A. The theoretical absorption profiles are included in stellar atmosphere codes and used to predict synthetic spectra for DA white dwarfs of intermediate temperatures (20,000 to 8000 K). These new calculations offer a unique opportunity to determine accurate effective temperatures and surface gravities for the variable ZZ Ceti stars.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 258; 2; p. 464-468.
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  • 20
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    Mass loss in main-sequence A-type stars? (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present new observations of the H-alpha line profile for five main-sequence A-type stars, where very high SNRs were achieved. A search for weak asymmetries was carried out to detect a stellar wind, but the many telluric absorption lines in this range prevent us from taking the full benefit of the high SNRs. This situation was improved by modeling the telluric absorptions to remove them from the observed spectra, but the H-alpha profiles were nevertheless found to be quite symmetric. We calculated the profile of the H-alpha line for a grid of model atmospheres of an A-type star including a weak wind, in order to assess an upper limit on the mass loss rate. The asymmetry is found to be sensitive to the velocity law and to the turbulent velocity of the wind, but its first moment depends much less on them. The upper limits deduced on the mass loss rate are between 1 and 2 x 10 exp -10 solar mass/yr. An improvement up to a factor 10 could be anticipated if new observations could be secured from a much drier location, achieving similar SNRs.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 257; 2; p. 663-670.
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  • 21
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    A study of the optical and ultraviolet spectral characteristics and of the circumstellar material around the new luminous blue variable WRA 751 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The LBV characteristics of the new LBV candidate WRA 751 suggested by Hu et al. (1990) are studied in greater detail. A comparison is made with observational characteristics of the well-known LBVs Ag Car and HR Car using photometric and spectroscopic data of Hu et al. supplemented with an IUE spectrum and direct CCD images in H-alpha, blue, and red. It is found that the spectra of WRA 751 and HR Car discussed in this paper are similar to the minimum-phase spectrum of AG Car and therefore resemble the Of/WN 9 spectral type. The characteristics of the optical, near- and far-UV (IUE) spectra of the Fe II spectrum in these wavelength regions is due to continuum fluorescence. The H, He I, Fe II and forbidden Fe II emission lines are formed in different parts of the stars' envelopes, corresponding to their expanding velocities. It is concluded that WRA 751 has properties which fit well the LBV properties at minimum-brightness phase, and possesses circumstellar material with observational properties similar to those of the known LBVs AG Car and HR Car.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 257; 2; p. 632-640.
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  • 22
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    Condensation of cosmic analog material in microgravity conditions - Preliminary analysis of a first set of flights (1992)
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    Publication Date: 2011-08-24
    Description: The first results of the STARDUST project, aimed at producing and analyzing cosmic-dust analog materials in microgravity conditions, are summarized. The discussion covers the purpose of the investigation, cosmic-dust formation and properties, previous simulations of cosmic-dust formation, the current approach, the microgravity experimental apparatus, and potential advantages of studying dust formation under microgravity conditions.
    Keywords: ASTROPHYSICS
    Type: Nuovo Cimento C, Serie 1 (ISSN 0390-5551); 15 C; 6; p. 1071-1076.
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  • 23
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    Observations of the 18.3-GHz transition of C3H2 towards Sgr B2 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Three molecular clouds of Sgr B2 have been mapped in the 1(10) - 1(01) orthotransition of C3H2 at 18.3 GHz. The distribution of C3H2 and the C3H2 optical depth of the three clouds, centered near 50, 65, and 80 km/s, are reported.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of Australia, Proceedings (ISSN 0066-9997); 10; 2; p. 113-117.
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  • 24
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    Of narrow lines and beaming in the strong-field SSC emission model (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The synchrotron self-Compton (SSC) emission model for gamma-ray bursts is capable of producing narrow line features for a variety of modelled field strengths, primary electron injection distributions and burst luminosities. Multiple resonant scattering with synchrotron continuum photons efficiently traps and cools pairs in the ground state to an average energy where the Compton energy loss rate is zero. Annihilation between pairs in these cooled distributions can be very efficient. For isotropic injection of primary electrons, there is an anti-correlation of the intensity of the angular-binned emission between the portions of the continuum spectrum below the cyclotron peak and above the annihilation line feature. Small-angle emission dominates the continuum above the annihilation line feature and is smooth through the line up to the pair production cut-off, which can be above several MeV for small enough angles. The angle-averaged annihilation line is made of components which can have peak emission centered at energies away from 511 keV, due to Doppler shifting. For beamed injection,the annihilation line breaks up into relatively narrow components in the angular emission, which sum into a broad feature in the angle-averaged emission.
    Keywords: ASTROPHYSICS
    Type: In: Gamma-ray bursts; Proceedings of the Workshop, Univ. of Alabama, Huntsville, Oct. 16-18, 1991 (A93-40051 16-93); p. 272-276.
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  • 25
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    Physical processes and diagnostics of gamma-ray burst emission (1992)
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    Publication Date: 2011-08-24
    Description: With improved data from BATSE and other instruments, it is important to develop a range of diagnostic tools to link gamma-ray burst observations with theory. I will review some of the physical processes which may take place to form the spectrum of gamma-ray burst sources, assuming that the bursts originate on strongly magnetized neutron stars. The important diagnostics that these processes provide to probe the emission region and how they might be used to interpret observed spectra will also be discussed.
    Keywords: ASTROPHYSICS
    Type: In: Gamma-ray bursts; Proceedings of the Workshop, Univ. of Alabama, Huntsville, Oct. 16-18, 1991 (A93-40051 16-93); p. 231-240.
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  • 26
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    Pickup ions observed at Comet Halley (1992)
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    Publication Date: 2011-08-24
    Description: Data on the velocity distributions of pickup ions in the vicinity of Comet Halley that were obtained by the Giotto spacecraft are presented. Combination of data from two different instruments allows a comparative study of the pitch-angle scattering rates and velocity diffusion rates of protons and water-group ions.
    Keywords: ASTROPHYSICS
    Type: In: Particle acceleration in cosmic plasmas; Proceedings of the Workshop, Bartol Research Inst., Newark, DE, Dec. 4-6, 1991 (A93-39976 16-93); p. 273-278.
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  • 27
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    The contribution of stars to the AGN line emission (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: It has been suggested that the presence of red giants in the vicinity of an active nucleus can contribute significantly to the line emission by the reprocessing of the continuum radiation onto the red giant's surface or in the stellar wind that usually accompanies these stars. We present herein the line profiles and the corresponding transfer functions for this model for the line emission, using a realistic phase space distribution function for the stars in the vicinity of the active nucleus.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 560-563.
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    High energy continuum measurements of active galactic nuclei (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We review recent hard X-ray and gamma-ray observations of Cen A, NGC 4151, 3C273, and 3C279. The new data showed remarkable variability of these objects in the high-energy gamma-ray regime. Recent observations by GRANAT show an unexpected sharp break at about 50 keV in the 1990 spectrum of NGC 4151. Recent observations by the Compton Observatory show intense GeV emission from 3C279 in June 1991. We present composite energy spectra of these objects from the radio to gamma-ray energies.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 348-355.
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    The high energy AGN continuum - Models without e+e- -pairs (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The general properties of the high energy AGN continuum are reviewed with particular emphasis on the connection between radio loud and radio quiet AGN in the broad context of the dynamics of accretion onto a black hole. Arguments are provided indicating the possibility that the emission from radio loud AGN originates at distances much larger than a few Schwarzschild radii from the black hole and hence the role of pairs in defining the observed spectrum is limited. A connection is made between the radio and high energy continuum of AGN.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 301-310.
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    The benefit of amateur observations for research in dwarf novae (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Contributions of amateur astronomers to research on dwarf novae, which are based on carefully monitoring the outburst behavior of these objects, are reviewed. These contributions range from scheduling of observations to the observational basis for research on the dwarf nova outburst mechanism. It is suggested, that, with better equipment, observations of orbital light variations in dwarf novae might be performed by amateur astronomers.
    Keywords: ASTROPHYSICS
    Type: In: Variable star research: An international perspective (A93-29397 10-89); p. 279-289.
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    Origin and use of Martian nomenclature (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The history and construction of Martian place names are examined. The 24 specific descriptor terms in use for Mars are defined. Informal names of individual rocks are discussed: the human fondness for informality is evident in the names attached to individual rocks at the Viking Lander sites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 1305-1314.
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    SAR data processing for the Magellan prime mission (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Magellan prime mission involves mapping the planet of Venus once around its rotational axis. The Magellan synthetic aperture radar (SAR) data processing facility processes all SAR data collected by the Magellan spacecraft into image data on an orbit-by-orbit basis. About 1700 million bits of radar data were collected. A complete description of the Magellan SAR Data Processing Facility is provided with emphasis on key design features of the data processors that satisfied the project data processing requirements. A summary of the attained data processing performance is included, as well as a brief discussion of some of the constraints and considerations regarding the applicability of the processors to meeting the data processing goals anticipated for the follow-on mission phases (i.e., cycles II, III, and beyond).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 606-609.
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    The (C-12)O/(C-13)O ratio toward Zeta Ophiuchi (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A tentative detection of the J = 1 - 0 emission line of (C-13)O has been obtained with SEST from a 24.4 hour integration. The velocity resolution used was 0.23 km/s and the FWHP beamwidth was 45 arcsec. If the (C-13)O line data are conservatively interpreted as an upper limit, the (C-12)O/(C-13)O ratio is not less than 60. Our result supports the previous determination of a large value of the isotope ratio in this cloud, made using radio emission lines with a 1.6-arcmin beam, and extends the ratio based on emission lines to a smaller region. When interpreted as a lower limit, our data is consistent with the ratio obtained from UV absorption line data for (C-12)O and (C-13)O.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 262; 1; p. 248-250.
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    The integrated radio continuum spectrum of M33 - Evidence for free-free absorption by cool ionized gas (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present measurements of the integrated radio continuum flux density of M33 at frequencies between 22 and 610 MHz and discuss the radio continuum spectrum of M33 between 22 MHz and 10 GHz. This spectrum has a turnover between 500 and 900 MHz, depending on the steepness of the high frequency radio spectrum of M33. Below 500 MHz the spectrum is relatively flat. We discuss possible mechanisms to explain this spectral shape and consider efficient free-free absorption of nonthermal emission by a cool (not greater than 1000 K) ionized gas to be a very likely possibility. The surface filling factor of both the nonthermal and the thermal material appears to be small (of order 0.001), which could be explained by magnetic field/density fluctuations in the M 33 interstellar medium. We briefly speculate on the possible presence of a nuclear radio source with a steep spectrum.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 261; 1; p. 47-56.
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    Warm neutral halos around molecular clouds. IV - H I and continuum: Aperture synthesis observations towards the molecular cloud B5 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present aperture synthesis observations of H I (21 cm) line radiation and continuum emission at 408 and 1420 MHz towards a field centered on the molecular cloud B5. The H I emission shows an extended atomic halo around the molecular cloud. The opacity of the halo is derived using H I absorption toward several background sources and a simple source model is presented. The model indicates that the halo is not gravitationally bound to the molecular cloud and that it is in fact expanding away from it. Approximately 350 solar masses are contained in the H I halo. Flux densities and spectral indices for the sources detected in both of the continuum bands are given.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 260; 1-2; p. 355-369.
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    Interferometric observations of Mira (Omicron Ceti) (1992)
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    Publication Date: 2011-08-24
    Description: The long-period variable Mira Omicron Ceti has been observed at 800 nm wavelength with the Mk III Optical Interferometer at photometric phases 0 = 0.96, 0.05, and 0.14 in 1990; some additional data were taken in 1989. The star is not spherically symmetric, and temporal variations of the size and the position angle of the asymmetry are detected. The visibility data can be represented by two uniform elliptical disks, which could correspond to different layers in Mira's atmosphere. If the size variations are interpreted in terms of physical motion of the emitting material, an infall velocity of about 15 km/s around phi = 0 is derived.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 259; 1; p. L19-L22.
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    Search for H2D(+) at 372 GHz in dense interstellar clouds (1992)
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    Publication Date: 2011-08-24
    Description: The 1(10)-1(11) transition of ortho-H2D(+) at 372 GHz has been sought in several dark clouds. The transition was not detected; the best upper limits obtained are about 0.3 K (3 sigma). We derive upper limits for the ortho-H2D(+) column density and briefly discuss their meaning in comparison with a simple chemical model we have developed (Pagani et al., 1992).
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 258; 2; p. 472-478.
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    The variable Herbig Ae Star HR 5999. X - Its photometric 'pulse-shaped' variability (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present additional photometric observations (Stromgren y filter) of the Herbig Ae Star HR 5999. This new set of data, composed of 282 data points covering April 1983 to August 1989, was used in conjunction with the 362 data points compiled by Baade and Stahl (1989). Our aim was to detect single or multiple periods in the integrated set of data spanning nearly 20 yr. Through the use of series analysis techniques, and by removing any linear component present in the raw data, we were able to detect weak peaks in the power spectra (in the order of intensity the strongest peaks are at 301 and 113 d) which were not self-evident in the phase diagrams. The overall picture of the data shows a small linear component, which is more noticeable in the new set of data, indicating that the recent maxima appear brighter. By a detailed analysis of the full light curve we were able to detect the presence of well-defined 'pulses' or bursts. Further Gaussian fits of these bursts indicated that the pulses are relatively rapid, of the order of 10 d, with some of them being closely spaced. No periodicity was found for the pulses. A possible explanation of these aperiodic outbursts is that they detect a flow of matter accompanied by magnetic field disturbances originated from the interior of the star, unlike those originating externally such as binary perturbations, which tend to be periodic.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 257; 1; p. 209-217.
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    EGRET detection of high energy gamma rays from the gamma-ray burst of 3 May 1991 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: On May 3, 1991, the Energetic Gamma Ray Experiment Telescope on the Compton Gamma Ray Observatory detected a gamma-ray burst both in the energy measurement subsystem and independently in the spark chamber assembly. Six individual photons were detected in the spark chamber, allowing a determination of the burst arrival direction which was l(II) = 171.9 deg +/- 1.3 deg, b(II) = 5.3 deg +/- 1.1 deg. Three energy spectra were measured from 1 to 200 MeV; they were measured during the first second after the Burst and Transient Sources Experiment trigger, the next two seconds, and the subsequent four seconds. The first two spectra exhibit a similar differential spectra index of about -2.2 with no apparent high-energy cut-off. By the time of the third spectrum, an additional soft component is evident.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 255; 1-2; p. L13-L16.
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    Geodesy and cartography of the Martian satellites (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The difficulties connected with conventional maps of Phobos and Deimos are largely overcome by producing maps in digital forms, i.e., by projecting Viking Orbiter images onto a global topographic model made from collections of radii derived by photogrammetry. The resulting digital mosaics are then formatted as arrays of body-centered latitudes, longitudes, radii, and brightness values of Viking Orbiter images. The Phobos mapping described was done with Viking Orbiter data. Significant new coverage was obtained by the Soviet Phobos mission. The mapping of Deimos is in progress, using the techniques developed for Phobos.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 1249-1256.
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    Physical and chemical weathering (1992)
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    Publication Date: 2011-08-24
    Description: Physical and chemical weathering processes that might be important on Mars are reviewed, and the limited observations, including relevant Viking results and laboratory simulations, are summarized. Physical weathering may have included rock splitting through growth of ice, salt or secondary silicate crystals in voids. Chemical weathering probably involved reactions of minerals with water, oxygen, and carbon dioxide, although predicted products vary sensitively with the abundance and physical form postulated for the water. On the basis of kinetics data for hydration of rock glass on earth, the fate of weathering-rind formation on glass-bearing Martian volcanic rocks is tentatively estimated to have been on the order of 0.1 to 4.5 cm/Gyr; lower rates would be expected for crystalline rocks.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 626-651.
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    Long-term orbital and spin dynamics of Mars (1992)
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    Publication Date: 2011-08-24
    Description: This review of the long-term dynamical behavior of Mars covers secular variations of the orbit, oscillations of the obliquity, and polar wandering. Calculations of the large-scale obliquity oscillations of Mars are updated using the most recent orbit theory and contrasted with the earth. The motion for Mars is characterized by about 100,000-yr oscillations driven by differential spin axis and orbit plane precession rates during which the obliquity may change by as much as about 20 deg. The possible role of spin-orbit secular resonances to the spin axis histories of the earth and Mars is also considered. Numerical integrations of the equations of motion indicate that Mars may have passed through resonance as little as 5 Myr ago and that obliquities approaching about 45 deg could have been achieved during such an event.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 298-320.
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    Stress and tectonics on Mars (1992)
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    Publication Date: 2011-08-24
    Description: Deformation of the Martian lithosphere and the various theoretical formulations used to model its behavior on local, regional, and global scales are studied. An overview of the various classes of tectonic features found on Mars is presented. The tectonic record on Mars, which provides the basic framework for interpreting theoretical thermomechanical models in terms of major tectonic events and provinces is summarized. The thickness of the elastic lithosphere is estimated using its response to local surface loads, and significant spatial variability is found, with values ranging from 20 to 300 km. A comparison of the major radial graben systems with theoretical stress models shows that more than one mechanism of lithospheric deformation is required to produce its enormous extent.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 249-297.
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    Gravity and topography (1992)
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    Publication Date: 2011-08-24
    Description: The paper summarizes the fundamental gravity field constants for Mars and a brief historical review of early determinations and current-day accurate estimates. These include the planetary gravitational constant, global figure, dynamical oblateness, mean density, and rotational period. Topographic results from data acquired from the 1967 opposition to the most recent, 1988, opposition are presented. Both global and selected local topographic variations and features are discussed. The inertia tensor and the nonhydrostatic component of Mars are examined in detail. The dimensionless moment of inertia about the rotational axis is 0.4 for a body of uniform density and 0.37621 if Mars were in hydrostatic equilibrium. By comparing models of both gravity and topography, inferences are made about the degree and depth of compensation in the interior and stresses in the lithosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 209-248.
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    Spacecraft exploration of Mars (1992)
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    Publication Date: 2011-08-24
    Description: Soviet and American spacecraft exploration of Mars over the past quarter century is reviewed. Data on the earliest Soviet attempts to send spacecraft to observe the planet are presented. Of the series of spacecraft that were announced (designated Mars 1 to Mars 7), none fulfilled all its scientific goals, but some good photographs and other important data were obtained. Of the six spacecraft in the Mariner series, two failed, but Mariner 4 first revealed the cratered surface of Mars, and Mariner 9 discovered all the major geologic features. The Viking mission, with its two Orbiters, two Landers, and its 6-yr duration, surpassed in quantity and variety of data all other missions combined. The Phobos mission ended in two failures, but the second of the two spacecraft acquired significant new data about Mars and Phobos. An appendix listing special issues of journals containing collections of papers about Mars is provided.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 71-119.
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    The planet Mars - From antiquity to the present (1992)
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    Publication Date: 2011-08-24
    Description: Telescopic observations of Mars, from those of Galileo in 1610 to the late 19th century, were summarized by Flammarion (1892, 1909). Major compilations of knowledge of Mars were produced by Antoniadi (1930) and de Vaucouleurs (1954). Polar cap composition was debated until the discovery by the Viking mission that the north and south perennial polar caps are composed of different materials. Spacecraft data indicate a rich and diverse geologic history as well as many unsolved puzzles. An annotated list of books about Mars is provided. Basic physical and chemical data on Mars are summarized in tabular form, and a guide to the Martian seasons is given.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 1-33.
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    SAR data processing adaptation for Magellan Cycle II (1992)
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    Publication Date: 2011-08-24
    Description: The authors describe the effort made at the Magellan SAR Data Processing Facility in adapting existing data processors to handle data collected from various imaging experiments. The different data processing requirements imposed by the various types of data are discussed, the tradeoffs and compromises made to work within the constraint of the existing systems are explained, and summary processing results obtained to date are given.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 100-103.
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    Remote radio observations of solar wind parameters upstream of planetary bow shocks (1992)
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    Publication Date: 2011-08-24
    Description: Radio emission is frequently produced at twice the electron plasma frequency 2fp in the foreshock region upstream of the terrestrial bow shock. Observations of this emission provide a remote diagnostic of solar wind parameters in the foreshock. Using ISEE-3 radio data, we present the first evidence that the radio intensity is proportional to the kinetic energy flux and to other parameters correlated with solar wind density. We provide a qualitative explanation of this intensity behavior and predict the detection of similar emission at Jupiter by the Ulysses spacecraft.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Solar Wind Seven; Proceedings of the 3rd COSPAR Colloquium, Goslar, Germany, Sept. 16-20, 1991 (A93-33554 13-92); p. 647-650.
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    Observational evidence for thin AGN disks (1992)
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    Publication Date: 2011-08-24
    Description: AGN spectrum and spectral features, polarization, inclination, and X-ray line and continuum reflection features are discussed in a critical way in order to determine the ones that are the least model-dependent. The sign and strength of absorption and emission edges are found to be model-dependent, and relativistic broadening and shifting makes them hard to detect. The presence or absence of the predicted Lyman edge polarization feature may be used as a decisive test for thin, bare AGN disks. Other good model-independent tests are several inclination-related line and continuum correlations in big AGN samples. It is shown that electron temperature near the surface of the disk can greatly exceed the disk equilibrium temperature, which causes deviations from LTE. This effect must be incorporated into realistic disk models.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 146-154.
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    Astrophysical bags - A new paradigm for active galactic nuclei? (1992)
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    Publication Date: 2011-08-24
    Description: Active galaxies are believed to consist of a compact nucleus, the standard model for which is a massive black hole or a cluster of black holes. A different paradigm is considered here, deriving from quark confinement theory in QCD. It is an 'astrophysical bag', modelled after the 'hadron bags' of particle physics which have already been studied in astrophysics as quark stars. Another interpretation of the cosmological constant in general relativity, and possibly a new quasar redshift formula, are introduced. As a highly-energetic object, this model may resolve the baryonic matter problem for fuelling AGN accretion processes which black hole paradigms cannot account for. Here, baryons, cosmic rays, and neutrinos are free.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 109-112.
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    Testing the AGN paradigm for our home Galaxy (1992)
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    Publication Date: 2011-08-24
    Description: Although there are some flaws in each of the methods to constrain the black hole mass, which are described in the above paper, all of them unambiguously indicate that the mass of a putative black hole at the Galactic center is much smaller than a widely quoted value, about 10 exp 6 M(solar). Possibly, the mass of the black hole, if any, does not exceed 100 M(solar) or so. Further work is needed in order to distinguish between such a modest-mass black hole and its potential rival such as a very massive star of about the same mass. Anyway, the Galactic nucleus seems to be a tracer of a past star burst rather than a remnant of a Seyfert galaxy activity.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 44-47.
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    Quasi-periodic climate change on Mars (1992)
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    Publication Date: 2011-08-24
    Description: The paper examines evidence that the Martian climate undergoes quasi-periodic variations, including the polar layered terrain, differences between the residual polar caps, and the current net southward flow of H2O. The driving functions for these variations are oscillations in the elements of the Martian orbit coupled with precession of the Martian spin axis. These 'astronomic variations' control the distribution of the insolation, which in turn influences the partition of volatiles between atmospheric and surface reservoirs. The major effects anticipated at low obliquity are growth of the polar caps, substantial decrease in surface pressure, cessation of duststorms, release of CO2 from the regolith, and poleward migration of H2O ground ice. At high obliquity, the mass of the perennial polar caps decreases and permanent CO2 frost disappears, CO2 desorbs from the regolith at high latitudes, the surface pressure may increase to several times its current value, and the atmospheric dust load increases.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 1180-1218.
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    Comparative aspects of the climate of Mars - An introduction to the current atmosphere (1992)
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    Publication Date: 2011-08-24
    Description: The study reviews the historical perspective of the Martian climate, beginning with the early view of inexorable climate change on an older, but otherwise very earthlike, planet and continuing through the period when earth-based spectroscopy and the Mariner 4, 6, and 7 flyby missions portrayed a moonlike body, heavily cratered and almost airless by comparison with earth. The most general features of the earth and Mars are discussed and compared, with consideration given to the standard atmospheres, atmospheric circulation, seasonal cycles of carbon dioxide, water, and dust, and coupling between cycles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 799-817.
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    Radar determination of Mars surface properties (1992)
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    Publication Date: 2011-08-24
    Description: Radar studies of Mars have provided measurements of surface texture on scales of centimeters to hundreds of meters and measurements of surface material properties. Texture (rms surface tilts and estimates of small-scale roughness) may be inferred from dispersion and/or polarization of the radar echo; material properties (reflectivity of dielectric constant) are derived from echo strength. Mars is a diverse target; depending on location, rms surface tilts have been found to vary over the range 0.25 to 10 deg while reflectivity covers at least 3 to 13 percent. Plains units are the most variable, having both the smoothest and roughest surfaces, cratered terrain can be considered predictable and 'average' by comparison. Recent data identify scattering by small structures (perhaps rocks on or near the surface) as playing a more important role than previously recognized. Scattering by the residual ice cap near Mars' south pole is particularly unusual. The present state of radar surface studies is summarized.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 652-685.
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    Implementation and performance of the Magellan digital correlator subsystem (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Magellan synthetic aperture radar (SAR) produces Venus surface images from data collected by the SAR carried on board the Magellan spacecraft. The core of the primary Magellan SAR processor is the digital correlator subsystem (DCS). The pipeline DSC architecture enables the Magellan primary SAR processor (PSP) to achieve real-time data processing capability. The implementation and performance of the DSC are described. Hardware (H/W) constraints that influenced the processing algorithm design are highlighted.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 2 (A93-47551 20-43); p. 1301-1304.
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    Refinement of Magellan radiometric correction using range centroid estimation (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Magellan (MGN) synthetic aperture radar (SAR) processing radiometric compensation algorithm is described, and the effective pointing error caused by the terrain is examined. It is shown how the range centroid can be computed from spacecraft ancillary data with an accurate topographic model. In cases where such data are not available, a technique is presented to estimate the range centroid from the coherent radar echoes. This technique is demonstrated using MGN SAR data.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 2 (A93-47551 20-43); p. 1167-1170.
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    The magnetic field in the heliosheath (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The interplanetary magnetic field (IMF) behaves in a reasonably well-understood manner between the Sun and the heliospheric termination shock. At the shock, the azimuthal field is amplified by a factor of four (for a strong shock) and undergoes secular amplification in the heliosheath until the flow is fully turned into the downstream direction and has reached its asymptotic state in the distant heliotail. This amplification may lead to important MHD effects that can cause the shock to be closer to the Sun than otherwise expected. Here we further examine whether there are important MHD effects in the heliosheath. We do this by calculating the kinematic compression of the magnetic field in the heliosheath using an analytic incompressible flow model of the dynamics downstream of the shock. We conclude that it is likely that MHD effects are important in the heliosheath in a narrow cone about the upstream direction.
    Keywords: ASTROPHYSICS
    Type: In: Solar Wind Seven; Proceedings of the 3rd COSPAR Colloquium, Goslar, Germany, Sept. 16-20, 1991 (A93-33554 13-92); p. 281-284.
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    A new mechanism for viscosity in cloudy accretion disks - Anomalous (turbulent) viscosity (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We analyze the dynamics of a rotating cloudy gaseous medium relative to 2D perturbations having wavelengths shorter than the disk thickness. The viscosity due to cloud-cloud collisions is confronted with the derived critical viscosity, below which a collective mode of perturbations in the disk is able to grow until going into the saturation regime where fully developed turbulence is established. It is shown that for the assumed parameters of AGN accretion disks consistent with the observational data, the viscosity due to collective modes usually dominates over that due to cloud-cloud collisions.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 280-283.
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  • 59
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    Problems for the standard black hole/accretion disk models in Cygnus X-1? (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Archival EXOSAT and HEAO1-A2 data from Cyg X-1 show the 'high energy excess' above 10 keV seen in X-ray observations of AGN. Using a likelihood ratio test, we are for the first time able to distinguish conclusively in favor of Compton reflection rather than partial covering as the origin of the high energy excess. This supports the idea of an X-ray illuminated accretion disk in Cyg X-1, but the line equivalent width is smaller by a factor of 2-3 than that expected from such a disk. While the larger optical depth required for reflection as opposed to line emission admit the possibility of seeing line without reflection, the converse is not possible. To see a reflection spectrum, including the strong iron absorption edge, implies that strong iron emission must be observed as the line and edge are causally linked.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 196-199.
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    Diagnostics of a putative black hole at the Galactic center (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A review is given of methods to constrain the mass of a putative black hole at the center of the Milky Way galaxy. These approaches are based on: (1) tidal disruption of stars by a massive black hole; (2) displacement between Sgr A* and either of the IRS 16 components; (3) electron-positron pair production by a black hole, and (4) mass outflow centered on IRS 16/Sgr A* complex.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 40-43.
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    Spectral-luminosity evolution of active galactic nuclei (AGN) (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The origin of the cosmic X-ray and gamma-ray backgrounds is explained via the mechanism of AGN spectral-luminosity evolution. The spectral evolution of precursor active galaxies into AGN, and Newton-Raphson input and output parameters are discussed.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 370-373.
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    A search for microvariability in five OVV quasars (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present results of monitoring a sample of five OVV qausars in an effort to determine if these types of AGNs exhibit microvariability similar to that detected for BL Lacertae objects. Three of the five quasars investigated clearly exhibited microvariability. The timescales for the variations for both BL Lacertae objects and OVV quasars are similar which suggests that the radiation is generated in similar spatial volumes. These variations are consistent with the results of models which explain the observed microvariability as the result of excess emission produced by flares or hot spots randomly appearing and disappearing on the accretion disks around supermassive black holes.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 247-250.
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  • 63
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    Using color-color diagrams to test models for the 'blue bump' (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Color-color diagrams are used to study the set of accretion disk plus power-law models and to determine whether they can adequately fit the optical/UV continua of a sample of 34 quasars, and the soft X-ray excesses measured for seven of the sample objects by Masnou et al. (1991). The loci of pure disk models for cos theta is greater than 0 are virtually superimposed on each other regardless of cos theta, demonstrating that a given observed spectrum cannot be described by a unique combination of S and cos theta. The distributions of model and data colors are found to overlap, showing that the disk plus power-law models do fit the distribution of data colors. For six of the seven objects, the soft X-ray excesses may be fit with an accretion disk plus power-law model without requiring the assumption of super-Eddington accretion; this shows the utility of employing Kerr disks.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 208-211.
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    X-ray FE line studies (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present the first broadband, moderate-resolution X-ray spectral observations of the Seyfert galaxies NGC 4151 and NGC 1068. The Seyfert 1 galaxy NGC 4151 is shown to have a complex X-ray spectrum with multiple components and a strong, intrinsically narrow Fe K emission line. The characteristics of the scattering medium of the Seyfert 2 galaxy NGC 1068 are determined using the very strong Fe line emission and the lack of features due to oxygen in the X-ray spectrum. The soft X-ray flux from Mrk 3 and Mrk 348 are consistent with that expected from electron scattered X-rays from an obscured Seyfert 1 nucleus. A survey of the X-ray properties of Seyfert 2 galaxies indicates that a substantial fraction may have column densities of about 10 exp 23, suggesting that NGC 1068 has an unusually thick obscuring torus.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 183-191.
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    The X-ray variability of AGN and the anomalous behavior of NGC 6814 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The power spectra of the X-ray variable AGN are typically scale invariant with no characteristic timescale. The one strong exception to this is NGC 6814, where the EXOSAT data showed evidence for a periodic component at 12200 +/- 100 seconds. The power spectra of a GINGA lightcurve from this source, found using simulation techniques to account for the uneven sampling, also cannot be well fit by a single power law. A folded light curve analysis of GINGA data shows strong evidence for this periodic component. A second GINGA observation of this source taken one year later is consistent with the phenomena being completely periodic and phase coherent for 7 periods in the range of 12,110-12,145 seconds. Including the (optimistic) limits from the folding selects a period of 12130.39 +/- 0.05 seconds. Phase coherence is not maintained between this and the EXOSAT observations, as the structure of the folded light curves is very different. Thus the periodicity is long lived and stable, but phase coherence is only maintained on timescales of about 1 year.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 83-92.
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    Radar mapping of Mercury - Full-disk images and polar anomalies (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A random-code technique has been used at Arecibo to obtain delay-Doppler radar images of the full disk of Mercury. Anomalously bright features were found at the north and south poles. The north polar feature is oblong (4 by 8 deg) and offset from the pole. The smaller south polar feature is mostly confined to the floor of the crater Chao Meng-Fu. The polar locations and radar properties of these features indicate that they may be produced by volume scattering in ice. The images also reveal a variety of more subdued reflectivity features ranging in size from hundreds to thousands of kilometers; some of these appear to have an impact origin.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 258; 5082; p. 640-643.
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    Surface chemistry and mineralogy (1992)
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    Publication Date: 2011-08-24
    Description: The accumulated knowledge on the chemistry and mineralogy of Martian surface materials is reviewed. Pertinent information obtained by direct analyses of the soil on Mars by the Viking Landers, by remote sensing of Mars from flyby and orbiting spacecraft, by telescopic observations from earth, and through detailed analyses of the SNC meteorites presumed to be Martian rocks are summarized and analyzed. A compositional model for Mars soil, giving selected average elemental concentrations of major and trace elements, is suggested. It is proposed that the fine surface materials on Mars are a multicomponent mixture of weathered and nonweathered minerals. Smectite clays, silicate mineraloids similar to palagonite, and scapolite are suggested as possible major candidate components among the weathered minerals.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 594-625.
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    On the molecular complexity of the hot cores in Orion A - Grain surface chemistry as 'The last refuge of the scoundrel' (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We have modeled the gas phase chemistry of warm molecular material around protostars that is seeded with evaporating grain mantles. We show that the release of simple molecules into the gas drives ion-molecule and neutral chemistries which can account for many of the complex O-bearing and N-bearing molecules observed in hot cores. Initial grain mantle components and secondary product molecules are identified, and the observational consequences are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 399; 1; p. L71-L74.
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    Cosmogenic nuclides in core samples of the Chico L6 chondrite - Evidence for irradiation under high shielding (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Results are presented from an analysis of core samples obtained from different depths of the Chico (New Mexico) L6 chondrite for various cosmogenic nuclides (Be-10, Al-26, and stable isotopes of He, Ne, and Ar). The relationships between the measured abundances of cosmogenic nuclides and cosmogenic Ne-22/Ne-21 ratio were compared with predictions of recent semiempirical models of Graf et al. (1990) and Reedy (1991), and it was found that both models closely reproduce the observed trends and absolute values of the data obtained. Noble gas data indicate that Chico experienced shielding similar to that of Jilin and greater than those of the Knyahinya or the Keyes chondrites. The exposure history for Chico is discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 27; 4; p. 371-381.
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    Dissemination and fractionation of projectile materials in the impact melts from Wabar Crater, Saudi Arabia (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Results are presented from the analyses of small ballistically dispersed melt samples (occurring in the form of aerodynamically shaped spheres, dumbbells, and teardrops) from the Wabar Crater (Saudi Arabia) and of melts from the Wabar and Nejed meteorites. On the basis of the data obtained and of models for crater forming processes it is concluded that the ballistically-dispersed glasses were formed from material at shallow levels in the target zone where temperatures were higher and where intimate physical contact with the disrupting impactor was achieved. Siderophile element fractionation was completed early, while the impactor was undergoing decompression and prior to mixing with the target glasses.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 27; 4; p. 361-370.
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    Long-term variability in low-mass X-ray binaries - A study using data from Vela 5B (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A complete sample of low-mass X-ray binaries in uncrowded fields obtained from Vela 5B is studied here for periodic and aperiodic time variability on time scales of more than one day. The strong 176-day periodicity in X1820 - 303 is confirmed, and evidence is found for a significant 77-day period in Cyg X-2 and for variability on time scales of less than about 200 days in Cyg X-3. Limits are set on the possible amplitude of candidate periodicities in the literature for Ser X-1 and X0614 + 091. The evidence reported here suggests that while long-term cyclic variability is common among high-mass binaries, it is a rare occurrence in low-mass systems.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 395; 2, Au; 582-591
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    Maintenance of strong rotational winds in Venus' middle atmosphere by thermal tides (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The cloud-level atmosphere of Venus takes little more than four days to complete one rotation, whereas the solid planet below has a 243-day period. Computer simulations of the circulation of the Venus middle atmosphere between 40 and 85 kilometers, as driven by solar radiation absorbed in the clouds, reproduce (1) the observed cloud-level rotation rate, (2) strong vertical shears above and below the cloud tops, and (3) midlatitude jets and strong poleward flow on the day side. Simulated circulations converge to yield nearly the same zonal winds when initialized with both stronger or weaker rotation rates. These results support the hypothesis that the observed cloud-top rotation rate is maintained by statistical balance between fluxes of momentum by thermal tides and momentum advection by mean meridional circulation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 257; 5070,; 647-650
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    Asteroid 951 Gaspra - Pre-Galileo physical model (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An effort is made to derive from Galileo's 1991 encounter of the S-type asteroid 951 Gaspra general lessons that will be applicable to prospective earth-based observations of other asteroids. Attention is accordingly given to the derivation of spin-vector and shape parameters en route to more detailed physical characterization of a given asteroid. A future encounter of Gaspra by Galileo will be required to verify the present model.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 97; 1, Ma; 124-129
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    Scintillations of the Uranian kilometric radiation - Implications for the downstream magnetopause (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Results are presented of the planetary radio astronomy observations conducted on board Voyager 2, with emphasis placed on the characteristics of the strong (3 to 6 dB) modulations of the broadband smooth Uranian radio emissions recorded from January 27-30, 1986, when the spacecraft was outbound from Uranus. The modulations were characterized by two superposed periods of about 100 sec and about 10 sec. It is suggested that the long-period modulation is due to the magnetopause surface waves, while the short-period modulations are due to the signature of ion cyclotron turbulence above the proton gyrofrequency, related to the magnetopause boundary layer.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A6, J
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    Spectroscopic investigation of cool giants and the authenticity of their reported microwave emission (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Surface velocities and metal abundances for 19 red giant stars in the spectral range G5 to M3 are derived on the basis of AAT echelle spectroscopy data. Attention is given to the question of whether the stars reported to emit radio bursts had different physical properties (rotation rate, macroturbulence, microturbulence, and metal abundance) from those without the radio bursts, which might explain why they were radio emitters. The various velocities had values consistent with those previously found for other similar stars. There was an observed increase in both macroturbulent and, less definitely, microturbulent velocities with lateness of spectral type at K3 and later. A weak correlation between surface velocities and 8.4-GHz radio surface fluxes was found. No connection between iron abundances and radio surface fluxes was detected. It is concluded that few, if any, of the cool giants are radio emitters.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 256; 3, Ju
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    A compositional classification scheme for meteoritic chondrules (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A compositionally based classification scheme for chondrules is proposed that will help in systematizing the wealth of data available and disentangling the effects of nebular and subsequent processes. The classification is not by texture or the composition of a single phase, or a mixture of these two, but rather is a comprehensive, systematic approach which uses the composition of the two main chondrule components. This scheme is applicable to over 95 percent of the chondrules and is easily applied using an electron microprobe. It stresses the original diversity of the chondrules and the complex yet facile way in which they respond to parent-body metamorphism. Results using this classification scheme suggest that arguments against an important role of chondrules in determining the compositional trends of the chondrites have been premature.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 357; 6375,
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    Infrared morphology of mass outflow from GL 2591 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Results are presented of a spectrophotometric study of a young stellar object, GL 2591, at wavelengths covering 2.10 to 2.27 microns, employing the KPNO long-slit cryogenic spectrometer. H2 emission was discovered in this source. A map of the v = 1-0 S(1) emission line shows a bipolar structure extending over 0.9 d (d/2 kpc) pc in an east-west direction roughly centered around GL 2591 IRS, with four bright knotty peaks. Br-gamma emission was detected in this source. A map of the Br-gamma emission line delineates a monopolar jetlike structure emanating over 0.2 d (d/2 kpc)pc from NIRS 1 to the southwest. The map of 2-micron continuum emission shows a multilooplike structure extending predominantly to the west. The dust distribution derived from this continuum map reveals a monopolar shell structure composed of several clumps. The spatial distribution of the H2, Br-gamma and 2-micron continuum emission is consistently explained by an outflow and dust disk model around GL 2591, if this emission is interpreted as shocked gas, ionized, gas, and swept-up dust, respectively, associated with the outflow from GL 2591.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 391; 2, Ju
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    Three-dimensional structured shocks in AM Herculis-type systems. II - Cyclotron emission from ridge-shaped emission regions (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The properties of cyclotron emission from accretion shocks in AM Herculis binaries are studied which result from nonuniform accretion onto linearly extended regions on the surface of the magnetic white dwarf. The resulting ridge-shaped postshock structures yield cyclotron spectra with prominent harmonic features over a wide range of viewing aspects, even for high total accretion rates, in contrast to what has been found previously for axisymmetric accretion shocks.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 256; 2, Ma; 329-338
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    Formaldehyde reactions in dark clouds (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The low-pressure reactions of formaldehyde (H2CO) with D(+), D2(+), D3(+), and He(+) are studied by the ion-cyclotron resonance technique. These reactions are potential loss processes for formaldehyde in cores of dark interstellar clouds. The deuterated reactants represent direct analogs for protons. Rate coefficients and branching ratios of product channels have been measured. Charge transfer is observed to be the dominant reaction of H2CO with D(+), D2(+), and He(+) ions. Only the D3(+) reaction exhibits a proton-transfer channel. All reactions proceed at rate coefficients near the collision limit. Proton-deuteron exchange reactions are found to be inefficient processes in the formaldehyde system.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 391; 1, Ma
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    SO in starburst galaxies (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The use of SO and SO2 as probes of the dense interstellar medium in the nearby starburst galaxies NGC 253 and M82 is described. Emission in the 99.3 GHz 3(2) - 2(1) rotational transition of SO was detected in NGC 253 and possibly in M82, and upper limits are reported for emission in the 219.9 GHz 6(5) - 5(4) transition of SO and two lines of SO2. The column density of SO relative to carbon sulfide, CS, is more than 0.08 in NGC 253, a value not much lower than Galactic ratios and consistent with models of dense interstellar clouds with a fractional abundance of atomic oxgyen greater than about 10 exp -7. The 218.8 GHz 3(21) - 2(20) transition of para-formaldehyde, with an excitation temperature of 68 K, was also detected in NGC 253.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 391; 1, Ma
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    Evidence for an ionized reprocessor in NGC 6814 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A detailed spectroscopic analysis of a Ginga observation of the Seyfert galaxy NGC 6814 is reported. It is shown that the X-ray data are consistent with a scenario in which the continuum radiation is reprocessed in a highly ionized medium, which can either be an accretion disk or a shell of absorbing material. Both of these can produce the strong observed iron K-alpha line, which must originate within 200 lt-sec of the continuum source. Significant iron K-beta and nickel K-alpha are predicted, based on the iron K-alpha line strength, and these lines partially conceal the iron edge in this source. The spectral variability below about 4 keV, where the apparent absorption increases as the continuum flux decreases, is probably caused by a warm absorber covering the reprocessing system.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 391; 1, Ma
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    The accretion halo in AM Herculis systems (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Previous phase-resolved spectropolarimetric observations of the AM Herculis systems V834 Centauri (E1405-451) and EF Eridani have shown broad, Zeeman-shifted absorption features during the bright phases. These features are thought to be nonphotospheric in origin, and to arise from a cool 'halo' of unshocked gas surrounding the accretion shock on the surface of the white dwarf primary. Preliminary models for the accretion halo region are presented and these models are used to perform a more detailed analysis of the relevant data for these two systems than has previously been done. To explain the observed halo Zeeman features, geometries which are consistent with the presence of linearly extended cyclotron emission regions are required. Such regions have previously been deduced from different considerations by other investigators. The estimated masses for the accretion halo are comparable to the mass of the cyclotron emission region.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 256; 1, Ma
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  • 83
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    Variability of near-infrared emission lines in NGC 4151 - Implications for nuclear star formation (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Multiaperture infrared spectra of the circumnuclear region of the Seyfert galaxy NGC 4151 taken over a 10 year period show that the N = 7-4 B-gamma hydrogen recombination line is variable. The H2 quadrupole line emission shows no sign of variability. It is shown that there is a substantial contribution to the nuclear B-gamma flux from the active nucleus, making it impossible to determine star formation rates from infrared hydrogen recombination lines in active galaxies. The lack of variability in the H2 line fluxes indicates that ionizing photons from the active nucleus is not important in exciting the molecular line emission.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 80; 1, Ma; 205-209
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  • 84
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    Coronal X rays from single, magnetic white dwarfs - A search and probable detection (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: X-ray emission from a sample of five nearby (6-20 pc), strongly magnetic (10-200 MG), relatively cool (6000-14,000 K), single white dwarfs, two of which may possess coronae was explored. One star (GR 290) at better than 99-percent confidence is detected and upper limits from Einstein Observatory IPC data for four others are given. The detected luminosities and limits are in the range 1.4-12.5 x 10 exp 27 ergs/s.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 104; 674,
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  • 85
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    Ulysses observations of escaping VLF emissions from Jupiter (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Ulysses URAP experiment has detected Jovian radio emissions in the VLF range at distances from Jupiter in excess of 1.5 AU. The URAP observations represent the first synoptic observations of Jupiter in the VLF band, from 3 to 30 kHz. In this band lie the low-frequency extent of the bKOM emission, the escaping continuum emission, and the Jovian type IIIs. Initial results indicate that the continuum varies in frequency with the solar wind ram pressure at Jupiter, whereas, the Jovian type IIIs appear to be controlled to some extent by the planetary rotation, often appearing when system III longitude 100 deg faces the spacecraft.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 19; 649-652
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  • 86
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    On the detectability of Jovian oscillations with infrared heterodyne measurements (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A method is proposed for detecting Jovian global oscillations using IR heterodyne measurements in the lower stratosphere of the planet. Measurements of the S(0) and S(1) lines over a period of a few nights permitted the detection of modes with periods of 5 to 20 min and of Doppler shifts corresponding to velocities as low as 1 m/sec (which is less than the value reported by Schmider and Mosser, 1990 from observations of the Jovian troposphere in the visible range. Possible limitations of the method are pointed out.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 96; 15-26
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  • 87
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    Analysis of Voyager 2 images of Jovian lightning (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Magalhaes and Borucki (1991) reported that Voyager-2 images of Jupiter contained bright spots due to lightning activity that was confined to two narrow altitude bands centered at 49 deg N and 13.5 deg N latitude and to a single region near 60 deg N latitude. This paper describes the Voyager 2 imaging observations in detail and associates the positions of the lightning features in the images with particular cloud features. The energetics of the lightning storms on Jupiter is examined. It is found that the ratio of the energy dissipated by Jovian lightning to the thermal flux available to drive convection motions is about 3 decades larger than the terrestrial ratio.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 96; 1-14
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  • 88
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    Fall days of the SNC meteorites - Evidence for an SNC meteoroid stream, and a common site of origin (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Four of the SNC meteorites of putative Martian origin are falls. Two of these fell on October 3: Chassigny in 1815 and Zagami in 1962. The probability of this coincidence arising from random fall days is approximately 1 in 60. If this coincidence is not the result of chance, it suggests that some of the SNC meteorites are derived from a meteoroid stream. In that Chassigny and Zagami span nearly the full range of SNC lithologies and histories, the coincidence of fall days is consistent with suggestions that all of the SNCs came from a single site (impact crater) on their parent planet.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 27; 93-95
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  • 89
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    Does an orbiting star cause periodic modulation of X-rays from NGC6814? (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An obvious candidate for the phenomenon underlying the periodicity in the X-ray emission from the Seyfert galaxy NGC6814 is the orbital motion of a star or low-mass compact object around the central black hole. It is shown here that the presence of an orbiting star could be easily verified by looking for the effects of Lense-Thirring precession of the orbital plane caused by the dragging of inertial frames around a rotating black hole. Precession-induced variations in the waveform and in the phase of the observed periodicity should have a period of between a month and a year. Such variations could account for the different waveforms present in the Ginga and Exosat data set from observations of NGC6814 and may be detectable in existing Ginga and future Rosat, OSSE/BRO, and Astro-D data.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 356; 224
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  • 90
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    Constraints on the power spectrum of the primordial density field from large-scale data - Microwave background and predictions of inflation (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: It is shown here that, by using galaxy catalog correlation data as input, measurements of microwave background radiation (MBR) anisotropies should soon be able to test two of the inflationary scenario's most basic predictions: (1) that the primordial density fluctuations produced were scale-invariant and (2) that the universe is flat. They should also be able to detect anisotropies of large-scale structure formed by gravitational evolution of density fluctuations present at the last scattering epoch. Computations of MBR anisotropies corresponding to the minimum of the large-scale variance of the MBR anisotropy are presented which favor an open universe with P(k) significantly different from the Harrison-Zeldovich spectrum predicted by most inflationary models.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 387; L1-L5
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  • 91
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    Impact-generated atmospheres over Titan, Ganymede, and Callisto (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The current distribution of atmospheres among Ganymede, Titan, and Callisto are presently accounted for by a process of competition between impact erosion and impact-furnished supply of atmosphile-laden late veneers. Titan's lower impact velocities have allowed it to accommodate an atmosphere, while Callisto and Ganymede remain barren. The model applied entails that the threshold impact velocity for atmospheric cratering by icy impactors be in the 10-14 km/sec range, consistent with the implications of the Schmidt and Housen (1987) crater-energy scaling for nonporous targets.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 95; 1-23
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  • 92
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    The structure of the BAL QSO 1700 + 518 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The paper presents 0.5-arcsec-resolution optical images of the low-redshift, bright, broad-absorption-line QSO 1700 + 518. A bright arc 2 arcsec is found to the NE of the nucleus which is redder than the surrounding host galaxy. There is also a faint radial structure to the SE, which is aligned with the core radio structure. The principal radio structure is a slightly resolved component coincident with the optical nucleus and an unresolved lobe 1 arcsec to the W which has no corresponding optical structure. The morphological and other properties of the QSO are discussed.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 104; 62-65
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  • 93
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    The COBE mission - Its design and performance two years after launch (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The COBE mission, NASA's first space mission devoted primarily to cosmology, is described and the spacecraft concepts central to enabling the mission to achieve its scientific objectives are examined. The major components of the COBE instrument and spacecraft modules are shown and their characteristics are given. Early scientific results are summarized and plans for continuing satellite operations and data analysis are addressed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 397; 2; p. 420-429.
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  • 94
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    The unusual cometary star-forming region G110-13 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present far-IR, radio continuum, and spectral line observations of an unusual, highly elongated, comet-shaped molecular cloud, located about 100 pc from the Galactic plane. The presence of three late B-type stars embedded within, or adjacent to, this low-mass cloud implies a star-forming efficiency that may be as high as 30 percent. Several mechanisms that may have been responsible for its unusual morphology and high star-forming efficiency will be described and evaluated. Although ram-pressure resulting from the rapid motion of this cloud through the interstellar medium could explain its streamlined appearance, there is evidence that G110-13 is the compression front formed by a recent cloud collision.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 397; 1; p. 174-186.
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  • 95
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    How old is the z = 3.4 radio galaxy B2 0902+34? (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The redshift 3.395 radio galaxy B2 0902+34 has been observed at K and in a 0.09 micron wide 2.21 micron filter which includes the redshifted forbidden O III 4959 and 5007 A emission lines. A value of m(K) = 19.9 +/- 0.3 is found in a 4 arcsec aperture, a magnitude fainter than Lilly's (1988) value, while the narrow-band image reveals that most of this flux is actually due to line emission. After correcting for forbidden O III 4959 and 5007A, a color is found which is consistent with the flat F(v) spectrum considered characteristic of a protogalaxy. Ages for the galaxy derived from stellar population models based on the limit R - K less than 3.8 are much younger than those for the I - K = 4.5 value reported by Lilly.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 399; 1; p. L47-L50.
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  • 96
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    Ulysses radio and plasma wave observations in the Jupiter environment (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Unified Radio and Plasma Wave (URAP) experiment has produced new observations of the Jupiter environment, owing to the unique capabilities of the instrument and the traversal of high Jovian latitudes. Broad-band continuum radio emission from Jupiter and in situ plasma waves have proved valuable in delineating the magnetospheric boundaries. Simultaneous measurements of electric and magnetic wave fields have yielded new evidence of whistler-mode radiation within the magnetosphere. Observations of auroral-like hiss provided evidence of a Jovian cusp. The source direction and polarization capabilities of URAP have demonstrated that the outer region of the Io plasma torus supported at least five separate radio sources that reoccurred during successive rotations with a measurable corotation lag. Thermal noise measurements of the Io torus densities yielded values in the densest portion that are similar to models suggested on the basis of Voyager observations of 13 years ago. The URAP measurements also suggest complex beaming and polarization characteristics of Jovian radio components. In addition, a new class of kilometer-wavelength striated Jovian bursts has been observed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 257; 5076,; 1524-153
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  • 97
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    Ulysses dust measurements near Jupiter (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Submicrometer- to micrometer-sized particles were recorded by the Ulysses dust detector within 40 days of the Jupiter flyby. Nine impacts were recorded within 50 Jupiter radii with most of them recorded after closest approach. Three of these impacts are consistent with particles on prograde orbits around Jupiter and the rest are believed to have resulted from gravitationally focused interplanetary dust. From the ratio of the impact rate before the Jupiter flyby to the impact rate after the Jupiter flyby it is concluded that interplanetary dust particles at the distance of Jupiter move on mostly retrograde orbits. On 10 March 1992, Ulysses passed through an intense dust stream. The dust detector recorded 126 impacts within 26 hours. The stream particles were moving on highly inclined and apparently hyperbolic orbits with perihelion distances of greater than 5 astronomical units. Interplanetary dust is lost rather quickly from the solar system through collisions and other mechanisms and must be almost continuously replenished to maintain observed abundances. Dust flux measurements, therefore, give evidence of the recent rates of production from sources such as comets, asteroids, and moons, as well as the possible presence of interstellar grains.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 257; 5076,; 1550-155
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  • 98
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    Evidence for unseen companions around T Tauri stars (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The observed spectral energy distributions of HK Tau, T Tau, and R Y Tau exhibit shallow (but significant) dips at mid-infrared wavelengths. This behavior can be explained by the existence of discrete gaps in their circumstellar disks since, if the temperature in the disks decreases monotonically outward, a gap would result in a range of "missing" temperatures. The gap centers for the three objects occur at radial distances of 0.5, 1.4, and 1.6 AU, respectively, while the corresponding ratios of outer to inner radii of the gaps are 6:1, 7:1, and 15:1, respectively. Larger mid-infrared dips are observed for SU Aur and GM Aur and are interpreted as correspondingly larger gaps, with almost complete clearing of the inner region of the disk in the latter case. The gaps in all cases are consistent with the tidal effects of either companion stars or planets.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 395; 2, Au
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  • 99
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    Synchrotron emission from a cosmological jet as a model of gamma-ray bursts (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The nonthermal rapidly varying spectra of gamma-ray bursts require relativistic beaming if the source is at a cosmological distance. Limits on the Lorentz factors and magnetic fields of extragalactic jet models of gamma-ray bursts are derived from the synchrotron source function, the position of the fundamental cyclotron resonance, the Thomson optical depth of radiating electrons, and the Thomson optical depth of electron-positron pairs created in photon-photon collisions of Compton upscattered radiation. The last of these constraints is the strongest, and it is satisfied by the observations if the jet's Lorentz factor is greater than 100. The limit from the position of the cyclotron fundamental requires a magnetic field strength below approximately 10 exp 10 G. Jet models producing observable cyclotron lines are allowed. The acceleration region in the burst must be separate from the emission region. The similarity of gamma-ray burst jet models to models of quasars and BL Lac objects suggest that if gamma-ray bursts are cosmological sources, they are a type of active galaxy.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 394; 2, Au; L33-L36
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  • 100
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    Detection of fundamental and harmonic type III radio emission and the associated Langmuir waves at the source region (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Type III radio emission generated in the vicinity of the Ulysses spacecraft has been detected at both the fundamental and harmonic of the local plasma frequency. The observations represent the first clear evidence of locally generated type III radio emission. This local emission shows no evidence of frequency drift, exhibits a relatively short rise time, is less intense than the observed remotely generated radio emission, and is temporally correlated with observed in situ Langmuir waves. The observations were made with the unified radio astronomy and wave (URAP) experiment on the Ulysses spacecraft between 1990 November 4 and 1991 April 30, as it traveled from 1 to 3 AU from the sun. During this time period many thousands of bursts were observed. However, only three examples of local emission and associated Langmuir waves were identified. This supports previous suggestions that type III radio emission is generated in localized regions of the interplanetary medium, rather than uniformly along the extent of the electron exciter beam.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 394; 1, Ju
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