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NASA NTRS1988

Active late-type stars

The basic mechanisms and characteristics of stellar activity in evolved stars are discussed, summarizing and analyzing the results of ground-based and space observations obtained in different regions of the electromagnetic spectrum. The types of active stars, the parameters controlling activity, and the underlying astrophysics are reviewed; the specific applications of optical and IR photometry, optical and UV spectroscopy, X-ray photometry and spectroscopy, and radio observations are considered; and particular attention is given to results on RS CVn systems and M dwarfs. Extensive diagrams, graphs, and tables of numerical data are included.

Linsky, Jeffrey L.↗

NASA NTRS1988

The classical nova outburst

The astrophysics of outbursts in classical and recurrent novae is explored, summarizing and analyzing the results of ground-based and space observations obtained in different regions of the electromagnetic spectrum. The stages of fast and slow outbursts are reviewed; the thermonuclear processes involved are described; and some observations of recent novae are listed and briefly characterized. Particular attention is then given to the specific contributions of optical, UV, IR, radio, and X-ray studies of nova outbursts.

Starrfield, Sumner↗

NASA NTRS1988

Supernovae and supernova remnants

The basic features and astrophysics of supernovae of types Ia, Ib, and II and of SNRs are discussed, summarizing the results of recent ground-based and space observations obtained at different wavelengths. Typical data are presented in graphs and sample images, and consideration is given to their implications for shock heating by the initial explosion, radioactive energy input, circumstellar interaction, and pulsar energy input. SNRs described include Tycho's remnant, Kepler's remnant, the Cyg loop, Pup A, the Crab Nebula, the Vela and Crab pulsars, and 0540-69.3 in the LMC. The need for high-spatial-resolution IR and X-ray spectra of these objects is indicated.

Chevalier, Roger A.↗

NASA NTRS1988

Active galactic nuclei

The astrophysical processes in AGN are examined, reviewing the results of ground-based and space observations obtained in different regions of the electromagnetic spectrum. Topics addressed include blazars and blazar variability, the apparently nonthermal broadband continuum emission of blazars, simple synchrotron self-Compton models, inhomogeneous models, and the need for multiwavelength spectra of blazars. Consideration is given to nonblazar emission-line AGN, the radio/IR power law, dust emission in the IR, the NIR excess, host-galaxy starlight, 'blue bumps', the X-ray power law, the big blue bump, broadband X-ray emission, and emission lines. The great potential value of multiwavelength variability studies of AGN is stressed.

Urry, C. Megan↗

NASA NTRS1988

Instrumentation for gamma-ray astronomy

The current status of gamma-ray-telescope technology for ground, airborne, and space observations is surveyed and illustrated with drawings, diagrams, and graphs and tables of typical data. For the low- and medium-energy ranges, consideration is given to detectors and detector cooling systems, background-rejection methods, radiation damage, large-area detectors, gamma-ray imaging, data analysis, and the Compton-interaction region. Also discussed are the gamma-ray interaction process at high energies; multilevel automated spark-chamber gamma-ray telescopes; the Soviet Gamma-1 telescope; the EGRET instrument for the NASA Gamma-Ray Observatory; and Cerenkov, air-shower, and particle-detector instruments for the TeV and PeV ranges. Significant improvements in resolution and sensitivity are predicted for the near future.

Bertsch, David L.↗

NASA NTRS1989

Coordinating the activities of a planner and an execution agent

A research program was defined that will explore the link between planning and execution systems. A simple scenario was defined in which a very capable off-line planning system interacts with the user and a smaller, less capable, on-line real-time system executing plans and reacting to faults. However, the on-line execution system may have a more flexible representation of the plans it is executing. This imbalance in the capabilities of the two agents involved should clarify some of the research objectives and give an experimental framework for the work. The task is to investigate the knowledge representations and communication protocols needed to link a user stating some requirements for a task to be carried out through a planning system to the (remote) execution agent that can carry out the user's wishes. The notion that a single representation can encapsulate the expression of the user's requirements, the capabilities for action, the communication to the execution agent, the successful or faulty response from the execution agent and the means of keeping the user informed, is examined. Methods of creating plan patches to update the plans separately held by each of the parties involved to keep them in step as they each react to changing circumstances in real-time is investigated. This involves the specification of plan patch attachment points that can be understood by the recipient. Transaction based methods are also investigated for coordinating the activities of the planner with those of the execution agent and user. The trial application area for the research is in the command and control of an advanced Earth Observation Space Platform.

Tate, Austin↗

NASA NTRS1989

Three-dimensional structure of human serum albumin

The three-dimensional structure of human serum albumin has been solved at 6.0 A resolution by the method of multiple isomorphous replacement. Crystals were grown from solutions of polyethylene glycol in the infrequently observed space group P42(1)2 and diffracted X-rays to lattice d-spacings of less than 2.9 A. The electron density maps are of high quality and revealed the structure as a predominantly alpha-helical globin protein in which the course of the polypeptide can be traced. The binding loci of several organic compounds have been determined.

Carter, Daniel C.↗

NASA NTRS1990

Interplanetary magnetic field enhancements - Evidence for solar wind dust trail interactions

Magnetic disturbances related to the passage of the asteroid 2201 Oljato are described. It is pointed out that the process leading to these disturbances must be associated with material in the orbit of Oljato and not the Oljato asteroid itself. Using data from latest space observations, the statistical association of these disturbances with the orbit of 2201 Oljato is updated, and the possible mechanisms for causing the disturbances are discussed. The phenomenon is considered to be associated with comet-like processes in the solar wind.

Russell, C. T.↗

NASA NTRS1990

The theoretical, discrete, and actual response of the Barnes objective analysis scheme for one- and two-dimensional fields

The response of the Barnes objective analysis scheme is studied as a function of wavenumber or wavelength. The first- and second-pass theoretical response functions for continuous two-dimensional fields are derived using Fourier transforms. The results are compared with Barnes' (1973) responses for one-dimensional waves. The continuous theoretical response for one- and two-dimensional waves is compared with the response for discrete applications using uniformly spaced observations for the case where interpolation points and observation points are coincident and for the case where interpolation points are midway between observation points. The actual response of an idealized discrete application of the Barnes scheme is examined, confirming the results of the analysis of the discrete theoretical response.

Pauley, Patricia M.↗

NASA NTRS1991

Volcanic effects on climate

Volcanic eruptions which inject large amounts of sulfur-rich gas into the stratosphere produce dust veils which last years and cool the earth's surface. At the same time, these dust veils absorb enough solar radiation to warm the stratosphere. Since these temperature changes at the earth's surface and in the stratosphere are both in the opposite direction of hypothesized effects from greenhouse gases, they act to delay and mask the detection of greenhouse effects on the climate system. Tantalizing recent research results have suggested regional effects of volcanic eruptions, including effects on El Nino/Southern Oscillation (ENSO). In addition, a large portion of the global climate change of the past 100 years may be due to the effects of volcanoes, but a definite answer is not yet clear. While effects of several years were demonstrated with both data studies and numerical models, long-term effects, while found in climate model calculations, await confirmation with more realistic models. Extremely large explosive prehistoric eruptions may have produced severe weather and climate effects, sometimes called a 'volcanic winter'. Complete understanding of the above effects of volcanoes is hampered by inadequacies of data sets on volcanic dust veils and on climate change. Space observations can play an increasingly important role in an observing program in the future. The effects of volcanoes are not adequately separated from ENSO events, and climate modeling of the effects of volcanoes is in its infancy. Specific suggestions are made for future work to improve the knowledge of this important component of the climate system.

Robock, Alan↗

NASA NTRS1987

An unsupervised feature extraction method for high dimensional image data compaction

A new on-line unsupervised feature extraction method for high-dimensional remotely sensed image data compaction is presented. This method can be utilized to solve the problem of data redundancy in scene representation by satellite-borne high resolution multispectral sensors. The algorithm first partitions the observation space into an exhaustive set of disjoint objects. Then, pixels that belong to an object are characterized by an object feature. Finally, the set of object features is used for data transmission and classification. The example results show that the performance with the compacted features provides a slight improvement in classification accuracy instead of any degradation. Also, the information extraction method does not need to be preceded by a data decompaction.

Ghassemian, Hassan↗

NASA NTRS1991

Statistical analysis of power-size-redshift distributions of extragalactic jets

This paper investigates whether a hot, sparse, yet cosmologically significant intergalactic medium is consistent with data collected from extragalactic radio sources. This is done by use of Monte Carlo simulations which employ previously run pseudohydrodynamical simulations to cover an observational parameter space. These observational parameters include the scale height, central density, and temperature of a (isothermal) galactic halo, and the power of the central engine which drives the jet. The Monte Carlo simulations generate distribution of sizes in bins of (received) power and redshift, which have been compared with observational data using Kolmogorov-Smirnov tests. Results of this analysis are consistent with the existence of an IGM with temperature and density mentioned above. In addition, this analysis suggests that the active lifetime of powerful extragalactic radio sources decreases with increasing power.

Rosen, Alexander↗

NASA NTRS1991

Rotational modulation in IUE spectra of cool dwarf chromospheres. I - Data analysis and period search techniques

Time-sequenced IUE spectra of a number of a bright F-K dwarfs have been used to investigate rotational modulation in several important chromospheric and transition emission lines. Stellingwerf's phase dispersion minimization (PDM) technique forms the basis of this time-series analysis of these sparsely sampled, irregularly spaced observational sequences, which consist of no more than 13 spectra in any one season. In such highly sample-limited time series, the resultant PDM spectrum is greatly complicated by overlapping alias orders which invariably produce strong interference effects, but the deliberately irregular sampling has proven of value in the development of techniques to identify the intrinsic stellar flux modulation period. Two stars are selected to illustrate these new techniques in detail.

Hallam, K. L.↗

NASA NTRS1991

Microwave simulations of a tropical rainfall system with a three-dimensional cloud model

A three-dinensional cloud model-microwave radiative transfer model combination is used to study the relations among the precipitation and other microphysical characteristics of a tropical oceanic squall line and the upwelling radiance at pertinent microwave frequencies. Complex brightness temperature-rain rate relations are evident at the full horizontal resolution (1.5 km) of the models, with spatial averaging producing smoother, shifter relations in most cases. Nonprecipitating cloud water is shown to be important in understanding the resulting distribution of brightness temperature. At the mature stage, convective portions of the cloud system are shown to produce different brightness temperature relations than the stratiform portion, primarily related to the distribution of cloud water. The evolution of the convective system from a small convective complex through its mature stage and the beginning of its dissipation also is shown to result in a variation of brightness temperature-rain relations, related to the distribution of cloud water and the evolution of ice in the precipitating system. The results of the study point to the need to take into account the evolution of nonprecipitating cloud water and precipitation-sized ice in the retrieval of rain from passive microwave space observations. This effect is evident for both the life cycle of individual convective elements and the life cycle of the convective system as a whole.

Adler, Robert A.↗

NASA NTRS1991

Seasat-A - A retrospective

This paper traces the highlights of the Seasat-A project from its earliest conceptual phases through the orbital operations phase. The primary objective of the project was to demonstrate the feasibility of remotely sensing fundamental oceanographic phenomena on a global, accurate, reliable and timely basis from an earth-orbiting platform. The project successfully achieved its primary objective, in spite of a premature spacecraft failure, and thus provided a firm basis for the development of sensors for future ocean-observing space missions.

Giberson, W. E.↗

NASA NTRS1990

A model of the 8-25 micron point source infrared sky

A model is developed that permits the representation of the Galactic disk and bulge, the molecular ring, extragalactic sky, and other Galactic structures in terms of the IR point-source sky. Full characterization is achieved for up to 87 types of Galactic sources in terms of scale heights and absolute magnitudes, and the model is guided by a parallel Monte Carlo simulation of the Galaxy at 12 microns. The model predicts differential and cumulative IR source counts for all bandpasses in the IRAS ranges and can therefore be employed to predict the character of the point-source sky related to IR space observations.

Wainscoat, Richard J.↗

NASA NTRS1990

Effects of plasma mass flow on Alfven wave phase mixing in coronal loops

Ground-based and space observations suggest that flow phenomena are intrinsic to the solar corona loops. The present analysis addresses flow effects on Alfven wave behavior in coronal loops. The effect of flow on the shear Alfven wave continuum and the associated damping process resulting from phase-mixing is investigated. Flow Doppler-shifts the Alfven wave continuum, thus displacing the range of frequencies for optimum heating. The present study explores Alfven resonance effects on surface waves propagating along coronal loops that are under the influence of flow. Coupling to the Alfven resonance leads to damping of the surface waves. The damping rate in the presence of sub-Alfvenic flows is computed. Flow increases the damping rate of certain modes, thus enhancing the heating effectiveness of those modes. Therefore, these calculations suggest that flow is potentially an important ingredient for an accurate evaluation of heating the solar corona by dissipation of Alfven waves via phase-mixing.

Peredo, M.↗

NASA NTRS1991

A comprehensive mission to planet Earth: Woods Hole Space Science and Applications Advisory Committee Planning Workshop

The NASA program Mission to Planet Earth (MTPE) is described in this set of visuals presented in Massachusetts on July 29, 1991. The problem presented in this document is that the earth system is changing and that human activity accelerates the rate of change resulting in increased greenhouse gases, decreasing levels of stratospheric ozone, acid rain, deforestation, decreasing biodiversity, and overpopulation. Various national and international organizations are coordinating global change research. The complementary space observations for this activity are sun-synchronous polar orbits, low-inclination, low altitude orbits, geostationary orbits, and ground measurements. The Geostationary Earth Observatory is the major proposed mission of MTPE. Other proposed missions are EOS Synthetic Aperture Radar, ARISTOTELES Magnetic Field Experiment, and the Global Topography Mission. Use of the NASA DC-8 aircraft is outlined as carrying out the Airborne Science and Applications Program. Approved Earth Probes Program include the Total Ozone Mapping Spectrometer (TOMS). Other packages for earth observation are described.

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