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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

A multiwavelength study of the Carlson-Henize sample of early-type Galactic extreme emission-line stars

A UV, optical, and radio study of nine early spectral type extreme emission-line Galactic stars from the Carlson and Henize (1979) sample is presented. He 3-407 and He 3-1482 appear to be analogs of the massive evolved B(e) and luminous blue variable stars of the Magellanic Clouds. The sample appears to be confined to a narrow range in spectral type from about B0 to B6. Most of the observed stars do not show strong N emission, with the striking exception of He 3-1482, and these Galactic stars may not have mixed significant quantities of nitrogen into their envelopes, unlike many of the LMC supergiants, Most of the Galactic stars are considerably fainter than those in the Magellanic Clouds, although their spectral properties are quite similar.

Shore, Steven N.↗
NASA NTRS1994

Dynamics and X-ray emission of a galactic superwind interacting with disk and halo gas

There is a general agreement that the conspicuous extranuclear X-ray, optical-line, and radio-contiuum emission of starbursts is associated with powerful galactic superwinds blowing from their centers. However, despite the significant advances in observational studies of superwinds, there is no consensus on the nature of the emitting material and even on the emission mechanisms themselves. This is to a great extent a consequence of a poor understanding of dynamical processes in the starburst superwind regions. To address this issue, we have conducted two-dimensional hydrodynamical simulations of galactic superwinds. While previous similar studies have used a single (disk) component to represent the ISM of the starburst galaxy, we analyze the interaction of the wind with a two-component disk-halo ambient interstellar medium and argue that this two-component representation is crucial for adequate modeling of starbursts. The emphasis of this study is on the geometry and structure of the wind region and the X-ray emission arising in the wind material and the shocked gas in the disk and the halo of the galaxy. The simulation results have shown that a clear-cut bipolar wind can easily develop under a range of very different conditions. On the other hand, a complex 'filamentary' structure associated with the entrained dense disk material is found to arise within the hot bubble blown out by the wind. The flow pattern within the bubble is dominated equally by the central biconic outflow and a system of whirling motions r elated to the origin and development of the 'filaments'. The filament parameters make them a good candidate for optical-emission-line filamentary gas observed in starburst halos. We find that the history of mass and energy deposition in the starburst region of the galaxy is crucial for wind dynamics. A 'mild' early wind, which arises as a result of the cumulative effect of stellar winds from massive stars, produces a bipolar vertical cavity in the disk and halo gas without strongly affecting the gaseous disk, thus creating conditions for virtually free vertical escape of the hot gas at the later, much more violent supernova-dominated phases of the starburst. We calculate the luminosity, mass, and effective temperature of the X-ray emitting gas in the 'soft' (0.1 to 0.7 keV, 0.7 to 2.2 keV, and 0.1 to 2.2 keV) and 'hard' (1.6 to 8.3 keV) energy bands and estimate the contribution of different gaseous components to the X-ray flux in these bands. Analysis of these parameters enables us to make conclusions regarding the nature of the X-ray-emitting material. We have inferred that the bulk of the soft thermal X-ray emission from starbursts arises in the wind-shocked material of the disk and halo gas rather than in the wind material itself. This enables us to predict that the integrated soft X-ray spectra of starbursts need not show an overabundance of heavy elements which are believed to be produced copiously in the centers of starbursts. Unlike soft X-ray emission, the hard component of thermal X-ray emission is found to originate in the wind material ejected from the starburst region. However, the derived ratio of hard-to-soft X-ray luminosities is too small compared to that observed in starbursts. We conclude therefore that the observed hard X-ray emission of starbursts is probably not associated with the thermal emission of hot wind or ambient shocked gas. Typical temperatures of the bulk of the soft X-ray-emitting material in our very different models have been found to agree well with the ones estimated on the basis of the ROSAT data for the soft component of X-ray emission of nearby starbursts. We predict that temperatures of the extranuclear soft X-ray-emitting gas in starburst galaxies with heavy element abundances near solar should be close to T(sub Xs = 2 to 5 x 10(exp 6)K.

Suchkov, Anatoly A.↗
NASA NTRS1993

Jet induced star formation in centrally dominant galaxies?

Using U-I CCD color maps of two centrally dominant cluster galaxies, we find unusual color structures which may be due to star formation which has been induced by their radio sources. These objects, located in the clusters A1795 and A2597, have blue central colors to radii of 20 kpc, spatially extended emission-line structures, and powerful radio sources. They reside at the centers of cooling flows with mass-accretion rates which are estimated to be approximately greater than 300 solar mass/yr. The regions of bluest local color are superposed on or along their radio-source structures. Our observations suggest that the radio sources associated with these objects may be inducing massive star formation in their central 20 kpc. The star formation may be the result of the radio plasma interacting with the warm emission-line gas and dense, x-ray emitting filaments similar to those recently discovered in two other clusters with the ROSAT Observatory. Since radio jets are likely to be transient, this may help to explain the scatter in the correlations between color and mass-accretion rate, although other factors may also contribute. Alternatively, scattered radiation from a hidden active nucleus or recent mergers may be responsible for the color structure. The color and radio properties of these objects are qualitatively similar but smaller in luminosity and spatial extent to those found in high redshift radio galaxies. Our observations of galaxies at z approximately = 0.06-0.1 show that processes similar to 'the alignment effect' found in high redshift radio galaxies occur at more recent epochs.

Mcnamara, Brian R.↗
NASA NTRS1978

Versatile communications terminal

Widely-separated parties are linked into efficient communications network by versatile control terminal. Terminal handles voice and data communications via both telephone lines and radio-frequency channels. It includes telephone-to-radio "patch", telephone autodialer, and other advanced features to provide rapid communications for applications such as emergency medical services (EMS) operations.

Belasco, N.↗
NASA NTRS1977

Far-Infrared Photometry with an 0.4-Meter Liquid Helium Cooled Balloon-Borne Telescope

A 0.4-meter aperture, liquid helium cooled multichannel far-infrared balloon-borne telescope was constructed to survey the galactic plane. Nine new sources, above a 3-sigma confidence level of 1300 Jy, were identified. Although two-thirds of the scanned area was more than 10 degrees from the galactic plane, no sources were detected in that region; all nine fell within 10 degrees and eight of those within 4 degrees of the galactic equator. Correlations with visible, compact H lines associated with radio continuum and with sources displaying spectra steeply rising between 11 and 20 microns were noted, while stellar objects were not detected.

Jacobson, M. R.↗
NASA NTRS1978

Infrared observations of the galactic center. III - 2.2 micron spectroscopy

Observations of the B-gamma line at 2.17 microns are presented for the central few parsecs of the galactic-center region. The surface-brightness distribution of the line with 3.3- and 6.6-arcsec resolution has been sampled in 25 locations. The results show that the ionized gas is concentrated within the central parsec of the galactic-center region; the fine-scale structure seen at 10 microns does not appear to be present in the ionized gas. For the central parsec (20 arcsec) the equivalent width of the B-gamma line is, within large uncertainties, independent of the 2-micron continuum flux; for radial distances of the order of 30 arcsec the line equivalent width drops significantly. A comparison of the B-gamma line strength with radio observations shows that the 2.2-micron extinction is consistent with the 2.7 mag determined from the reddening of late-type stars. Observations of the CO band at 2.3 microns in the central 30 arcsec are also presented; they strengthen the interpretation that the 2-micron flux arises from late-type giant stars.

Neugebauer, G.↗
NASA NTRS1979

Determination of the time delay in the case of two-path propagation on the basis of the attenuation characteristics for two adjacent frequencies

Pronounced fading occurring in the line of sight radio links at frequencies below 10 GHz can be traced to the effects of multipath propagation. Modulation disturbances depend on travel time differences between the direct wave and the wave which is reflected at atmospheric layers. A method described for the determination of the time delay is based on an indirect approach which utilizes the difference in fading at various frequencies. The method was employed in measurements involving a distance of 181 km. The results obtained in the measurement are discussed.

Gilroi, H. G.↗
NASA NTRS1984

MHD Waves and Turbulence in the Sun and Interplanetary Medium

The existence, nature, and dynamics of magnetohydrodynamic waves and turbulence in the solar atmosphere and interplanetary medium are addressed. Remote sensing observations of global oscillations of the Sun and their possible interpretation in terms of waves or turbulence are considered. The region of solar wind acceleration as described by coronal imaging, resonance-line spectrometry, and radio techniques is discussed. Fluctuations and discontinuities in the interplanetary medium are considered using primary data collected by spaceborne magnetometers and plasma analyzers.

Source record↗
NASA NTRS1985

A shadowed flow in the stem of the Crab nebula?

The faint radio and emission line 'jet' outward from the northern boundary of the Crab Nebula which appears as a neat right cylinder is modelled here as the convected margin of a gas cloud that accidentially cast its shallow across the nearly ballistic flow of the stellar envelope ejected in the supernova explosion. It is shown that this model is consistent with known data on the jet, and that it accounts for the strikingly regular geometrical features in a natural way. In contrast, flow instability models do not easily result in so neat a cylinder.

Morrison, P.↗
NASA NTRS1987

Molecular gas and star formation in HI-deficient Virgo cluster galaxies

Mapping of the CO emission line in 42 Virgo cluster galaxies reveals that the molecular gas contents and distributions are roughly normal in severaly HI-deficient Virgo spirals. The survival of the molecular component mitigates the impact of the HI-stripping on star formation and subsequent galactic evolution. For spirals which are deficient in HI by a factor of 10, far-infrared, H alpha line, and nonthermal radio continuum luminosities are lower by no more than a factor of 2. The fact that the inner galactic disks are stripped of HI, while CO is normal, suggests that the lifetime of the molecular phase is approximately one billion years in the inner regions of luminous spirals.

Kenney, Jeffrey D.↗
NASA NTRS1989

Shock-associated plasma density fluctuations in the interstellar medium

Theories of diffuse shock acceleration of the cosmic rays that predict that there should be regions of intense Alfven waves both upstream and downstream of the shock front are considered. Observations of similar waves near solar system shock waves show that they produce substantial density fluctuations. Such density fluctuations might produce observable scattering of radio waves. Observations which searched for angular broadening or blurring of radio sources whose lines of sight pass close to or through supernova remnants are discussed. No definite cases of remnant-associated scattering are detected. However, the source CL 4, which is viewed through the Cygnus Loop supernova remnant, may be such an object and merits further observation.

Spangler, S. R.↗
NASA NTRS1988

VLBI angular broadening measurements in the Cygnus region

Multiple-frequency VLBI observations of eight compact radio sources with lines of sight which cross the Galactic plane in Cyg are reported. The data are presented in a table and map and analyzed, with a focus on angular broadening (AB) induced by interstellar scattering. AB is confirmed in four of the sources, whereas the structures of the other four appear to be intrinsic. The AB is found to be limited to a region within a few deg of the Galactic plane.

Fey, A. L.↗
NASA NTRS1989

VLBI angular broadening measurements in the Cygnus region

Multifrequency VLBI observations of angular broadening are reported for eight compact radio sources whose lines of sight pass through the Galactic plane in Cygnus. The characteristic lambda-squared dependence of angular size is used to distinguish between scattered and intrinsic structure. The measured angular sizes of four of the eight sources exhibit a lambda-squared dependence, a result consistent with angular broadening by intervening turbulence. Variation in the strength of scattering as a function of position indicates that scattering in the Cygnus region changes by a factor of 2-5 for angular separations of a few degrees. With the exception of one source, the observed angular broadening is confined within a few degrees of the Galactic plane.

Fey, Alan L.↗
NASA NTRS1989

Multifrequency survey of the intergalactic cloud in the M96 group

The intergalactic cloud of neutral hydrogen in the M96 group are examined for signs of emission over a wide range of frequencies, from radio waves to X rays. Past or present stellar activity in the gas might have been expected to produce detectable visual infrared, CO, OH, or radio recombination-line emission. None was detected. The limits are used to study physical conditions in the intergalactic gas. In particular, B and V band limits on starlight and IRAS limits on the presence of dust strongly constrain the presence of stars or stellar by-products. However, given the uncertainties about physical conditions in the intergalactic environment, it is difficult to rule out entirely the presence of stellar-processed materials. Results of neutral hydrogen mapping from a large-scale survey of the intergalactic cloud and surrounding region are also presented. These observations confirm that the gas is confined to a large ringlike structure. The simplest interpretation remains that the intergalactic gas in Leo is primordial.

Schneider, Stephen E.↗
NASA NTRS1990

Images in the rocket ultraviolet - Star formation and extinction in the M51 system

UV images of M51 with up to 15 arcsec resolution were obtained by a rocket-borne telescope. The bandwidth was 970 A with maximum response at 2650 A. The two most prominent features of M51 in the UV are the bright central region and a region of intense star formation about 2.5 NE of the nucleus toward the companion NGC 5195. This complex is the source of 20 percent of the total UV flux in M51. The companion is much less prominent in the UV than in optical bands. Spiral arms show much higher contrast in UV and U bands than in the R band. The nuclear region in the UV band shows clumped emission from probable star-forming regions, possibly associated with the inner Lindblad resonance. These regions are probably the UV counterparts of FIR sources discovered in an EW scan across the nucleus. UV/U colors of most bright H II regions with known extinction are consistent with O star spectra reddened by amounts estimated from radio and Balmer line measurements. However, some of the brightest H II regions have redder UV/U colors, probably indicating the presence of cooler stars which contribute in the U band. CO and IR observations indicate that the companion NGC 5195 may be a reddened starburst in spite of its faintness in the UV.

Bohlin, Ralph C.↗
NASA NTRS1990

Aeronautical mobile satellite service: Air traffic control applications

Canada's history both in aviation and in satellite communications development spans several decades. The introduction of aeronautical mobile satellite communications will serve our requirements for airspace management in areas not served by line-of-sight radio and radar facilities. The ensuing improvements in air safety and operating efficiency are eagerly awaited by the aviation community.

Sim, Dave↗
NASA NTRS2000

A search for precursors of ultracompact H II regions in a sample of luminous IRAS sources. III. Circumstellar dust properties

The James Clerk Maxwell Telescope has been used to obtain submillimeter and millimeter continuum photometry of a sample of 30 IRAS sources previously studied in molecular lines and centimeter radio continuum. All the sources have IRAS colours typical of very young stellar objects (YSOs) and are associated with dense gas.

(astronomical) pre-main-sequence stars radiosource↗
NASA NTRS2021

INTEGRAL reloaded: Spacecraft, instruments and ground system

The European Space Agency’s INTErnational Gamma-Ray Astrophysics Laboratory (ESA/INTEGRAL) was launched aboard a Proton-DM2 rocket on 17 October 2002 at 06:41 CEST, from Baikonur in Kazakhstan. Since then, INTEGRAL has been providing long, uninterrupted observations (up to about 47 h, or 170 ksec, per satellite orbit of 2.7 days) with a large field-of-view (FOV, fully coded: 100 deg), millisecond time resolution, keV energy resolution, polarization measurements, as well as additional wavelength coverage at optical wavelengths. This is realized by two main instruments in the 15 keV to 10 MeV energy range, the spectrometer SPI (spectral resolution 3 keV at 1.8 MeV) and the imager IBIS (angular resolution: 12 arcmin FWHM), complemented by X-ray (JEM-X; 3–35 keV) and optical (OMC; Johnson V-band) monitor instruments. All instruments are co-aligned to simultaneously observe the target region. A particle radiation monitor (IREM) measures charged particle fluxes near the spacecraft. The Anti-coincidence subsystems of the main instruments, built to reduce the background, are also very efficient all-sky γ-ray detectors, which provide virtually omni-directional monitoring above ~75 keV. Besides the long, scheduled observations, INTEGRAL can rapidly (within a couple of hours) re-point and conduct Target of Opportunity (ToO) observations on a large variety of sources. INTEGRAL observations and their scientific results have been building an impressive legacy: The discovery of currently more than 600 new high-energy sources; the first-ever direct detection of (56)Ni and (56)Co radio-active decay lines from a Type Ia supernova; spectroscopy of isotopes from galactic nucleo-synthesis sources; new insights on enigmatic positron annihilation in the Galactic bulge and disk; and pioneering gamma-ray polarization studies. INTEGRAL is also a successful actor in the new multi-messenger astronomy introduced by non-electromagnetic signals from gravitational waves and from neutrinos: INTEGRAL found the first prompt electromagnetic radiation in coincidence with a binary neutron star merger. Up to now more than 1750 scientific papers based on INTEGRAL data have been published in refereed journals. In this paper, we will give a comprehensive update of the satellite status after more than 18 years of operations in a harsh space environment, and an account of the successful Ground Segment.

Erik Kuulkers↗