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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Infrared Astronomy

Several observational programs in infrared astronomy are described and significant findings are briefly discussed. The near infrared work concentrates largely on the use of the 5 m Hale telescope in spectroscopic and photometric studies of extragalactic sources. Observations of the P alpha line profile in a low redshift quasar, X-ray bursters, reflection nebula, and cataclysmic variables are included. Millimeter continuum observations of dust emission from quasars and galactic molecular clouds are also discussed. Finally, improvements to instrumentation are reported.

Neugebauer, G.↗
NASA NTRS2015

Wide-Field InfraRed Survey Telescope (WFIRST) Mission and Synergies with LISA and LIGO-Virgo

The Wide-Field InfraRed Survey Telescope (WFIRST) is a NASA space mission in study for launch in 2024. It has a 2.4 m telescope, wide-field IR instrument operating in the 0.7 - 2.0 micron range and an exoplanet imaging coronagraph instrument operating in the 400 - 1000 nm range. The observatory will perform galaxy surveys over thousands of square degrees to J=27 AB for dark energy weak lensing and baryon acoustic oscillation measurements and will monitor a few square degrees for dark energy SN Ia studies. It will perform microlensing observations of the galactic bulge for an exoplanet census and direct imaging observations of nearby exoplanets with a pathfinder coronagraph. The mission will have a robust and wellfunded guest observer program for 25% of the observing time. WFIRST will be a powerful tool for time domain astronomy and for coordinated observations with gravitational wave experiments. Gravitational wave events produced by mergers of nearby binary neutron stars (LIGO-Virgo) or extragalactic supermassive black hole binaries (LISA) will produce electromagnetic radiation that WFIRST can observe.

Wide-Field InfraRed Survey Telescope (WFIRST) Miss↗
NASA NTRS1973

The number-intensity distribution of X-ray sources observed by Uhuru.

The Uhuru catalog of X-ray sources is used to analyze the number versus apparent-intensity relation of X-ray objects, by constructing (log N, log S)-plots similar to those used in radio astronomy. The source number distribution is corrected for nonuniform sky coverage of the spacecraft. Two distinct distributions for objects at low (less than 20 deg) and high (more than 20 deg) galactic latitude are discussed. The distribution for low galactic latitude objects (which are mainly galactic) gives further information on their location within the Galaxy and their intrinsic luminosity. The distribution for high-latitude objects is consistent with an extragalactic origin of these sources. Evidence from the longitudinal distribution of these objects is used to further demonstrate their extragalactic nature.

Matilsky, T.↗
NASA NTRS1973

Diffuse X and gamma radiation.

The most reliable measurements in the energy range from 0.1 MeV to 100 MeV are presented in graphs. Studies in the region from 1 keV to 100 keV are discussed, giving attention to nonthermal mechanisms, thermal emission from a uniform intergalactic medium, the contribution of discrete extragalactic sources to the isotropic X-ray background, discrete diffuse X-ray sources in galaxy clusters, the contribution of galaxy clusters to the isotropic X-ray background, and fluctuations in the X-ray background. Diffuse X rays below 1 keV are also considered together with diffuse galactic X and gamma rays above 1 keV and the significance of diffuse X and gamma radiation for astronomy.

Silk, J.↗
DOE OSTI2020

Inpainting Galactic Foreground Intensity and Polarization Maps Using Convolutional Neural Networks

The Deep Convolutional Neural Networks (DCNNs) have been a popular tool for image generation and restoration. In this work, we applied DCNNs to the problem of inpainting non-Gaussian astrophysical signal, in the context of Galactic diffuse emissions at the millimetric and submillimetric regimes, specifically Synchrotron and Thermal Dust emissions. Both signals are affected by contamination at small angular scales due to extragalactic radio sources (the former) and dusty star-forming galaxies (the latter). Furthermore, we compare the performance of the standard diffusive inpainting with that of two novel methodologies relying on DCNNs, namely Generative Adversarial Networks and Deep-Prior. We show that the methods based on the DCNNs are able to reproduce the statistical properties of the ground-truth signal more consistently with a higher confidence level.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

The Energetic Gamma-Ray Experiment Telescope (EGRET) Science Symposium

The principle purpose of this symposium is to provide the EGRET (Energetic Gamma-Ray Experiment Telescope) scientists with an opportunity to study and improve their understanding of high energy gamma ray astronomy. The Symposium began with the galactic diffusion radiation both because of its importance in studying galactic cosmic rays, galactic structure, and dynamic balance, and because an understanding of its characteristics is important in the study of galactic sources. The galactic objects to be reviewed included pulsars, bursts, solar flares, and other galactic sources of several types. The symposium papers then proceeded outward from the Milky Way to normal galaxies, active galaxies, and the extragalactic diffuse radiation.

Fichtel, Carl E.↗
DOE OSTI2021

Optimal observing strategies for velocity-suppressed dark matter annihilation

Numerous particle models for the cosmological dark matter feature a pair-annihilation rate that scales with powers of the relative velocity between the annihilating particles. As a result, the annihilation rate in the central regions of a dark matter halo can be significantly lower than at the halo’s periphery for particular ambient gravitational potentials. While this might be offset by an increasing dark matter pair number density in the inner halo, it raises the question; what angular region for dark matter models with velocity-suppressed annihilation rates optimizes the signal to noise ratio? We consider simplified background models for galactic and extragalactic targets and demonstrate that the optimal observing strategy varies greatly case by case. Generally, a bright central source warrants an annular region of interest, while a flatter background warrants as large as possible an angular region, possibly including the central regions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Harnessing the Population Statistics of Subhalos to Search for Annihilating Dark Matter

The Milky Way's dark matter halo is expected to host numerous low-mass subhalos with no detectable associated stellar component. Such subhalos are invisible unless their dark matter annihilates to visible states such as photons. One of the established methods for identifying candidate subhalos is to search for individual unassociated gamma-ray sources with properties consistent with the dark matter expectation. However, robustly ruling out an astrophysical origin for any such candidate is challenging. In this work, we present a complementary approach that harnesses information about the entire population of subhalos—such as their spatial and mass distribution in the Galaxy—to search for a signal of annihilating dark matter. Using simulated data, we show that the collective emission from subhalos can imprint itself in a unique way on the statistics of observed photons, even when individual subhalos may be too dim to be resolved on their own. Additionally, we demonstrate that, for the models we consider, the signal can be identified even in the face of unresolved astrophysical point-source emission of extragalactic and Galactic origin. Furthermore, this establishes a new search technique for subhalos that is complementary to established methods, and that could have important ramifications for gamma-ray dark matter searches using observatories such as the Fermi Large Area Telescope and the Cerenkov Telescope Array.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Interstellar medium model

A model of the ionized part of the interstellar medium was developed, based on the low frequency observations by the Radio Astronomy Explorer Satellite with a background of nonthermal radiation. This nonthermal background radiation is caused by synchrotron emission from cosmic ray electrons, and at low frequencies this emission is heavily absorbed by free-free absorption from the residual thermal electrons in the interstellar medium. By an appropriate model, parameters relevant to both the thermal and nonthermal components of the interstellar medium are shown. The observations were taken with the 100 deg dipole antenna and separated into galactic and extragalactic components. This model was developed using only the separated galactic component.

Novaco, J. C.↗
NASA NTRS1981

Infrared astronomy; Proceedings of the Symposium, Kona, HI, June 23-27, 1980

The role of infrared studies in numerous aspects of astronomy is examined. Topics include the composition of planetary atmospheres; spectrophotometric remote sensing of planets and satellites; thermal studies of planetary surfaces; infrared sources in dense molecular clouds; globules, dark clouds, and low mass pre-main sequence stars; protostellar objects; molecular hydrogen emission; and the Orion molecular cloud. Also considered are dust spectrophotometry; polarimetry of infrared sources; emission line observations of H II regions; observation and interpretation of emissions from the galactic plane; the galactic center; stellar content of extragalactic systems; star formation in galactic nuclei; and active extragalactic nuclei.

Wynn-Williams, C. G.↗
NASA NTRS1982

Gamma-ray astronomy

Cosmic gamma rays, the physical processes responsible for their production and the astrophysical sites from which they were seen are reported. The bulk of the observed gamma ray emission is in the photon energy range from about 0.1 MeV to 1 GeV, where observations are carried out above the atmosphere. There are also, however, gamma ray observations at higher energies obtained by detecting the Cerenkov light produced by the high energy photons in the atmosphere. Gamma ray emission was observed from sources as close as the Sun and the Moon and as distant as the quasar 3C273, as well as from various other galactic and extragalactic sites. The radiation processes also range from the well understood, e.g. energetic particle interactions with matter, to the still incompletely researched, such as radiation transfer in optically thick electron positron plasmas in intense neutron star magnetic fields.

Ramaty, R.↗
NASA NTRS1988

A very low frequency radio astronomy observatory on the Moon

Because of terrestrial ionospheric absorption, very little is known of the radio sky beyond 10 m wavelength. An extremely simple, low cost very low frequency radio telescope is proposed, consisting of a large array of short wires laid on the lunar surface, each wire equipped with an amplifier and a digitizer, and connected to a common computer. The telescope could do simultaneous multifrequency observations of much of the visible sky with high resolution in the 10 to 100 m wavelength range, and with lower resolution in the 100 to 1000 m range. It would explore structure and spectra of galactic and extragalactic point sources, objects, and clouds, and would produce detailed quasi-three-dimensional mapping of interstellar matter within several thousand parsecs of the Sun.

Douglas, James N.↗
NASA NTRS1992

Low Frequency Interstellar Scattering and Pulsar Observations

Radio astronomy at frequencies from 2 to 30 MHz challenges time tested methods for extracting usable information from observations. One fundamental reason for this is that propagation effects due to the magnetoionic ionosphere, interplanetary medium, and interstellar matter (ISM) increase strongly with wavelength. The problems associated with interstellar scattering off of small scale irregularities in the electron density are addressed. What is known about interstellar scattering is summarized on the basis of high frequency observations, including scintillation and temporal broadening of pulsars and angular broadening of various galactic and extragalactic radio sources. Then those high frequency phenomena are addressed that are important or detectable at low frequencies. The radio sky becomes much simpler at low frequencies, most pulsars will not be seen as time varying sources, intensity variations will be quenched or will occur on time scales much longer than a human lifetime, and many sources will be angularly broadened and/or absorbed into the noise. Angular broadening measurements will help delineate the galactic distribution and power spectrum of small scale electron density irregularities.

Cordes, James M.↗
NASA NTRS1972

Advances in solar and cosmic X-ray astronomy - A survey of experimental techniques and observational results.

The current status of X-ray astronomy is surveyed by reviewing observational results and theoretical conclusions gained within the past two years in areas dealing with the quiet-sun, slowly-varying, and burst components of solar X-radiation and with the features of cosmic X-ray sources. Thermal and nonthermal processes responsible for a wide variety of X-ray emission mechanisms in nature are explained, and characteristics of X radiation from specific solar structures are described. Attention is given to the effects of interstellar and intergalactic matter on cosmic X-rays; the properties of galactic and extragalactic X-ray sources; and the specifications of such instruments as gas-filled ionization detectors, proportional counters, Geiger counters, scintillation detectors, photoelectric detectors, polarimeters, collimators, spectrometers, and imaging systems.

Hoover, R. B.↗
NASA NTRS1982

The implications of precise timekeeping of Doppler gravitational wave observations

Gravitational radiation from galactic and extragalactic astrophysical sources will induce spatial strains in the solar system, strains which can be measured directly by the Doppler radio link to distant spacecraft. Current noise sources in Pioneer and Voyager Doppler data are delineated and a comparison is made with expected signal levels from gravitational wave sources. The main conclusion is that it is possible to detect gravitational radiation with current DSN hydrogen maser systems stable in fractional frequency + or - 2 x 10 to the minus 14th power over 1000 sec. In the future, however, a serious Doppler observational program in gravitational wave astronomy will require frequency systems stable to at least 10 to the minus 16th power, but at the same time the current single frequency S-band uplink transmission will have to be replaced by a dual frequency capability.

Anderson, J. D.↗
NASA NTRS2010

Science Results From The ARCADE Open-Aperture Cryogenic Balloon Payload

The Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) is a balloon-borne instrument to measure the frequency spectrum of the cosmic microwave background and diffuse Galactic foregrounds at centimeter wavelengths. ARCADE greatly reduces measurement uncertainties compared to previous balloon-borne or ground-based instrument using a double-nulled design that features fully cryogenic optics with no windows between the atmosphere and the 2.7 K instrument. A four-hour flight in 2006 achieved sensitivity comparable to the COBE/FIRAS satellite measurement while providing new insights for emission ranging from spinning dust in the interstellar medium to an unexpectedly bright extragalactic radio background. I will discuss scientific results from the ARCADE program and implications of the ARCADE cold optics for millimeter and sub-mm astronomy.

Kogut, Alan J.↗
NASA NTRS1975

Scientific instrumentation of the Radio-Astronomy-Explorer-2 satellite

The instrumentation of the RAE-2 spacecraft is described. The instruments include a pair of long travelling-wave antennas, a 37-m dipole, two radiometers making one frequency scan every 144 sec, and two rapid-sampling total-power burst receivers which cover the range from 0.025 to 13.1 MHz in 32 discrete steps. Effects of terrestrial noise on RAE-1 and RAE-2 observations are discussed, and it is noted that RAE-2 is uniquely capable of observing repeated lunar occultations of strong radio sources at very low frequencies. Some observational programs are briefly noted, including observations of the galactic background distribution, measurements of lunar occultations of solar radio bursts, and searches for more radio sources among the planets, galactic objects, and extragalactic sources.

Alexander, J. K.↗
NASA NTRS1973

The luminosity function of galactic X-ray sources - A cutoff and a 'standard candle'

Analysis of the 2- to 10-kev luminosity distribution of 36 X-ray sources in the Local Group having known or estimated distances, showing that there exists a luminosity cutoff of approximately 10 to the 37.7th ergs/sec in agreement with the theoretical (Eddington) limit for the luminosity of an approximately 1 solar mass star. Furthermore, among the complete sample of high-luminosity sources, there appears to be a statistically significant group of X-ray 'standard candles' at (within less than 0.8 mag) the critical luminosity. This finding (which is in agreement with the self-consistent mass flow accretion models) presents the possibility that X-ray sources may be used as extragalactic distance indicators in the next generation of X-ray astronomy experiments.

Margon, B.↗