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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Ground-based observations at 34 microns.

Filtering techniques for a new photometric band from 28 to 40 microns are described together with the results of ground-based observations of planets, stars, and galactic nebulae conducted with 28- and 61-in. telescopes in this wavelength interval. The data indicate that high angular resolution and good sensitivity can be obtained at 34 microns from the ground. Some stars have very cold (less than 100 K) circumstellar dust shells or clouds. The Kleinmann-Low nebula in M42 is extremely bright at 34 microns, whereas the Ney-Allen nebula associated with the Trapezium stars is much weaker.

Low, F. J.↗
NASA NTRS1987

Star formation in Carina OB1: Observations of a giant molecular cloud associated with the eta Carinae Nebula

A giant molecular cloud associated with the eta Carinae nebula was fully mapped in CO with the Columbia Millimeter-Wave Telescope at Cerro Tololo. The cloud comples has a mass of roughly 700,000 solar mass and extends about 140 pc along the Galactic plane, with the giant Carina HII region situated at one end of the complex. Clear evidence of interaction between the HII region and the molecular cloud is found in the relative motions of the ionized gas, the molecular gas, and the dust; simple energy and momentum considerations suggest that the HII region is responsible for the observed motion of a cloud fragment. The molecular cloud complex appears to be the parent material of the entire Car OB1 Association which, in addition to the young clusters in the Carine nebula, includes the generally older cluster NGC 3325, NGC 3293, and IC 2581. The overall star formation efficiency in the cloud complex is estimated to be approximately 0.02.

Grabelsky, D. A.↗
NASA NTRS1990

Tidal events and galactic activity

Researchers report some results from recent and ongoing work which relate to the connection between nuclear activity and tidal interactions. They suggest that tidal events are in general a necessary but not sufficient condition for nuclear activation. They also suggest that nuclear activity generally develops at a 'late stage' of a tidal encounter, following star-formation and dust evaporation, and when the most obvious morphological disturbances may have disappeared. The quantitative results from quasi-stellar object imaging, radio source evolution, HI observations, and an Infrared Astronomy Satellite (IRAS) source survey are given in tabular form.

Hutchings, J. B.↗
NASA NTRS1994

Far-infrared emission from the bulges of early-type spirals: KAO observations of NGC 4736 (M94) and NGC 3627 (M66)

We present new high spatial resolution Kuiper Airborne Observatory (KAO) 50 and 100 micrometers measurements of the ringed Sab galaxy NGC 4736 and the Sb galaxy NGC 3627. We detect strong far-infrared emission (approximately 10(exp 9) solar luminosity) from the bulge areas of these galaxies, regions where there is little observed star formation. This far-infrared radiation is extended over the bulge with spatial distributions similar to that of the old stellar population. The ratio of far-infrared to H-alpha luminosity for these central sources is significantly larger than for the star-forming regions in these galaxies. This ratio is higher than can be accounted for by dust heating due to a population of young stars with a mass distribution similar to the Salpeter initial mass function assuming current estimates of extinction, unless the upper mass limit is unusually low (approximately B1 stars). On the other hand, the bolometric luminosity of the observed bulge stars is sufficient to account for the far-infrared radiation. Thus, older stars are likely to be important in heating dust in these bulges. The dust in the centers of these galaxies is quite warm, approximately 40 K (lambda(exp -1) emissivity), however, the interstellar radiation fields derived from the optical luminosities are consistent with these temperatures without invoking hidden central star formation or a dusty active galactic nucleus.

Smith, Beverly J.↗
NASA NTRS1994

Organic Material in the ISM

Spectra of objects which lie along several lines of sight through the diffuse interstellar medium (ISM) all contain an absorption feature near 3.4 micrometers which has been attributed to saturated aliphatic hydrocarbons on interstellar grains. The similarity of the absorption bands near 3.4 micrometers along different lines of sight reveal that the carrier of this band lies in the diffuse dust. Several materials have been proposed as "fits" to the 3.4 micrometers feature over the years. A comparison of these identifications is presented. A remarkable similarity between the spectrum of the diffuse dust and an organic extract from the Murchison meteorite suggests that some of the interstellar organic material may be preserved in primitive solar system bodies. The optical depth/extinction tau /A(sub v) ratio for the 3.4 micrometers band is higher toward the Galactic center than toward sources which sample the interstellar medium in the local neighborhood. A similar trend has been observed previously for silicates, indicating that the two materials may be simultaneously enhanced in the Galactic center.

Pendleton, Yvonne↗
NASA NTRS2016

Overview of LBTI: A Multipurpose Facility for High Spatial Resolution Observations

The Large Binocular Telescope Interferometer (LBTI) is a high spatial resolution instrument developed for coherent imaging and nulling interferometry using the 14.4 m baseline of the 2x8.4 m LBT. The unique telescope design, comprising of the dual apertures on a common elevation-azimuth mount, enables a broad use of observing modes. The full system is comprised of dual adaptive optics systems, a near-infrared phasing camera, a 1-5 micrometer camera (called LMIRCam), and an 8-13 micrometer camera (called NOMIC). The key program for LBTI is the Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS), a survey using nulling interferometry to constrain the typical brightness from exozodiacal dust around nearby stars. Additional observations focus on the detection and characterization of giant planets in the thermal infrared, high spatial resolution imaging of complex scenes such as Jupiter's moon, Io, planets forming in transition disks, and the structure of active Galactic Nuclei (AGN). Several instrumental upgrades are currently underway to improve and expand the capabilities of LBTI. These include: Improving the performance and limiting magnitude of the parallel adaptive optics systems; quadrupling the field of view of LMIRcam (increasing to 20"x20"); adding an integral field spectrometry mode; and implementing a new algorithm for path length correction that accounts for dispersion due to atmospheric water vapor. We present the current architecture and performance of LBTI, as well as an overview of the upgrades.

The Large Binocular Telescope Interferometer (LBTI↗
NASA NTRS1974

Monte Carlo calculations of the surface brightness profiles of spherical dark nebulae

Theoretical surface brightness profiles of spherical dark nebulae of both uniform density and a density proportional to 1/r squared are being discussed. The albedo and asymmetry factor of the dust grains and the optical radius measured from the cloud center were the variable parameters in this study, which further assumed an isotropically incident radiation field. The occurrence of dark cores in the surface brightness profiles is examined, and their frequent existence in galactic dark nebulae is interpreted as resulting from a strongly forward scattering phase function and a high optical depth of the associated objects. The shape and depth of the profiles of the dark cores is closely related to the internal density distribution of the clouds, and it is suggested that detailed observations of the surface brightness profiles of dark nebulae will reveal important information on the type of their internal density distribution and, thus, their evolutionary status.

Witt, A. N.↗
NASA NTRS1977

A survey of interstellar molecular hydrogen. I

Data from the Copernicus satellite's ultraviolet telescope were used to survey column densities of atomic and molecular hydrogen from a large sample of early-type stars; these data have bearing on an eventual understanding of diffuse and dense interstellar clouds. Column densities are derived by fitting damping profiles to the observed spectra, most of which exhibit strong damping lines in the lower rotational levels surveyed. Plots of dust column density, fractional abundance of molecular hydrogen, and the logarithm of fractional abundance versus total gas column density are given for many of the stars; stars with abnormally large or small hydrogen column densities, as well as some distant stars at high galactic latitudes, are considered. Equilibrium and nonequilibrium theories accounting for the abundance of interstellar hydrogen are compared, and support is found in the data for an account which balances hydrogen formation on interstellar grains with destruction through photodissociation. Overall averages for atomic and molecular hydrogen levels in the galactic plane are also calculated.

Savage, B. D.↗
NASA NTRS1978

Infrared observations of the galactic center. II - Forbidden Ne II emission

The forbidden Ne II line flux has been measured with a 5-arcsec diaphragm at eight positions in the galactic-center (Sgr A-West) region. The line fluxes - and hence the density of ionized gas - are not correlated with the presence of discrete compact sources of 10-micron continuum radiation. The discrete sources probably contain sources of energy that heat nearby dust instead of being regions of enhanced dust density.

Willner, S. P.↗
NASA NTRS1998

Near-infrared spectroscopy of the proto-planetary nebula CRL 618 and the origin of the hydrocarbon dust component in the interstellar medium

A new 2.8-3.8 micrometers spectrum of the carbon-rich protoplanetary nebula CRL 618 confirms the previous detection of a circumstellar 3.4 micrometers absorption feature in this object (Lequeux & Jourdain de Muizon). The high resolution and high signal-to-noise ratio of our spectrum allow us to derive the detailed profile of this absorption feature, which is very similar to that observed in the spectrum of the Galactic center and also resembles the strong 3.4 micrometers emission feature in some post-asymptotic giant branch stars. A weak 3.3 micrometers unidentified infrared band, marginally detected in the CRL 618 spectrum of Lequeux & Jourdain de Muizon, is present in our spectrum. The existence of the 3.4 micrometers feature implies the presence of relatively short-chained, aliphatic hydrocarbon materials (-CH2-/-CH3 approximately = 2-2.5) in the circumstellar environment around CRL 618. It also implies that the carriers of the interstellar 3.4 micrometers feature are produced at least in part in circumstellar material, and it calls into question whether any are produced by the processing of interstellar ices in dense interstellar clouds, as has been previously proposed. Other features in the spectrum are recombination lines of hydrogen, rotational and vibration-rotation lines of molecular hydrogen, and a broad absorption probably due to a blend of HCN and C2H2 bands.

Spectroscopy, Near-Infrared↗
NASA NTRS2016

Parsec-Scale Accretion and Winds Irradiated by a Quasar

We present numerical simulations of properties of a parsec-scale torus exposed to illumination by the central black hole in an active galactic nucleus (AGN). Our physical model allows to investigate the balance between the formation of winds and accretion simultaneously. Radiation-driven winds are allowed by taking into account radiation pressure due to UV and IR radiation along with X-ray heating and dust sublimation. Accretion is allowed through angular momentum transport and the solution of the equations of radiative, viscous radiation hydrodynamics. Our methods adopt flux-limited diffusion radiation hydrodynamics for the dusty, infrared pressure driven part of the flow, along with X-ray heating and cooling. Angular momentum transport in the accreting part of the flow is modeled using effective viscosity. Our results demonstrate that radiation pressure on dust can play an important role in shaping AGN obscuration. For example, when the luminosity illuminating the torus exceeds L greater than 0.01 L(sub Edd), where L(sub Edd) is the Eddington luminosity, we find no episodes of sustained disk accretion because radiation pressure does not allow a disk to form. Despite the absence of the disk accretion, the flow of gas to smaller radii still proceeds at a rate 10(exp -4)-10(exp -1)M dot yr(exp -1) through the capturing of the gas from the hot evaporative flow, thus providing a mechanism to deliver gas from a radiation-pressure dominated torus to the inner accretion disk. As L L(sub edd) increases, larger radiation input leads to larger torus aspect ratios and increased obscuration of the central black hole. We also find the important role of the X-ray heated gas in shaping the obscuring torus.

accretion disks - galaxies: active - galaxies: Sey↗
NASA NTRS1993

The narrow-line region of high-luminosity active galactic nuclei

The HST's Faint Object Spectrograph and Kitt Peak ground instruments have been used to gather high S/N spectroscopic observations of seven radio-loud quasars; the resolutions obtained allow a separation of emission line broad and narrow components to be made. Attention is given to the relative weakness of the narrow UV lines, in contradiction to the predictions of dust-free photoionization models; there is not a single definite detection of a narrow UV line in any of the seven quasars. Two explanations of the observed reddening are discussed.

Wills, Beverley J.↗
DOE OSTI2023

The IRX–β relation in kpc-sized star-forming regions in nearby galaxies

The effect of dust attenuation on a galaxy’s light depends on a number of physical properties, such as geometry and dust composition, both of which can vary across the faces of galaxies. To investigate this variation, we continue analysis on star-forming regions in 29 galaxies studied previously. We analyse these regions using Swift /UV Optical Telescope and Wide-field Infrared Survey Explorer images, as well as Sloan Digital Sky Survey/Mapping Nearby Galaxies at Apache Point Observatory emission line maps to constrain the relationship between the infrared excess (IRX) and the ultraviolet spectral index, β, for each star-forming region. This relationship can be used to constrain which dust attenuation law is appropriate for the region. We find that the value of D n (4000) for a region is correlated with both IRX and β, and that the gas-phase metallicity is strongly correlated with the IRX. This correlation between metallicity and IRX suggests that regardless of aperture, metal-rich regions have steeper attenuation curves. We also find that integrated galactic light follows nearly the same IRX–β relationship as that found for kpc-sized star-forming regions. Here, this similarity may suggest that the attenuation law followed by the galaxy is essentially the same as that followed by the regions, although the relatively large size of our star-forming regions complicates this interpretation because optical opacity and attenuation curves have been observed to vary within individual galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1976

High-resolution far-infrared observations of the galactic center

A map at 53 microns with 17-arcsec resolution and three-color observations at 53, 100, and 175 microns with 30-arcsec beams of Sgr A are presented. Sagittarius A is resolved into two main sources, one associated with the cluster of strong 10-micron sources and another about 45 arcsec to the southwest coincident with a weak 10-micron source. The dust temperature peaks near the strong 10-micron sources, but the 100-micron and 175-micron fluxes and the far-infrared optical depth are greatest near the southwest source. The amount of dust required to explain the far-infrared emission is comparable to that observed in absorption in the near-infrared.

Harvey, P. M.↗
DOE OSTI2023

BEYONDPLANCK XIV. Polarized foreground emission between 30 and 70 GHz

We constrain polarized foreground emission between 30 and 70 GHz with the Planck Low Frequency Instrument (LFI) and WMAP data within the global Bayesian BeyondPlanck framework. We combine for the first time full-resolution Planck LFI time-ordered data with low-resolution WMAP sky maps at 33, 40 and 61 GHz. Spectral parameters are fit with a likelihood defined at the native resolution of each frequency channel. This analysis represents the first implementation of true multi-resolution component separation applied to CMB observations for both amplitude and spectral energy distribution (SED) parameters. For synchrotron emission, we approximate the SED as a power-law in frequency and find that the low signal-to-noise ratio of the current data strongly limits the number of free parameters that may be robustly constrained. We partition the sky into four large disjoint regions (High Latitude; Galactic Spur; Galactic Plane; and Galactic Center), each associated with its own power-law index. We find that the High Latitude region is prior-dominated, while the Galactic Center region is contaminated by residual instrumental systematics. The two remaining regions appear to be signal-dominated, and for these we derive spectral indices of $β$ S Spur = -3.17 ± 0.06 and $β$ S Plane = -3.03 ± 0.07, in good agreement with previous results. For thermal dust emission we assume a modified blackbody model and we fit a single power-law index across the full sky. We find $β$ d = 1.64 ± 0.03, which is slightly steeper than reported from Planck HFI data, but still statistically consistent at the 2σ confidence level.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1977

Galactic distribution of X-ray burst sources

Data on X-ray bursts recorded by the OSO-8 and SAS-3 satellites and criteria (rise time, duration, recurrence) for X-ray bursts are examined in a study of possible correlation between the galactic longitude distribution of X-ray burst sources and globular clusters. Correlations are weak, with only two X-ray bursts sources (NGC6624 and the rapid burster) coinciding with globular clusters, another seven possibly coinciding, most not correlated. Ad hoc explanations (globular clusters obscured by dust clouds, bursts associated with remnants of disrupted globular clusters evolved into supermassive black holes) are considered briefly.

Lewin, W. H. G.↗
NASA NTRS1994

Extinction, ejecta masses, and radial velocities of novae

Interstellar reddening is determined for a number of recent novae based upon emission-line ratios which are generally observable using CCDs. Large values of extinction are found for most systems, possibly indicative of an intrinsic component of reddening in postoutburst novae. The unusual characteristics of the (O I) lines in novae, which are strong and optically thick, require a large population of very dense globules which are the likely sites of dust formation. These pyroclasts must be ejected from the white dwarf. The total mass of the neutral gas in the globules in some of the objects is substantially larger than the masses normally derived for the ionized ejecta of novae. The distribution of radial velocities of Galactic novae in the Tololo sample, although uncertain, shows an asymmetry in having predominantly negative values. Either high internal absorption in the expanding ejecta skews the emission lines to bluer wavelengths, or most of the novae are moving out from the center of the Galaxy.

Williams, Robert E.↗
NASA NTRS1995

The neutral atomic phases of the interstellar medium

We calculate the thermal equilibrium gas temperature of the diffuse interstellar medium. Our method incorporates a new photoelectric heating rate from small grains and polycyclic aromatic hydrocarbons (PAHs) that accounts for a size distribution of particles extending from 100 to 3 A radius. We also include a detailed treatment of the ionization rates and heating due to the soft X-ray background and due to cosmic rays. Phase diagrams (thermal pressure P versus hydrogen density n) are presented for gas that is illuminated by local interstellar far-ultraviolet (FUV) and X-ray radiation fields. A stable two-phase medium is produced with thermal pressure in the range P/k approximately = to 10(exp 3-4) K/cc. We demonstrate that photoelectric heating from PAHs dominates in the warm neutral phase (WNM) and cold neutral phase (CNM). If the C II (158 micrometers cooling per hydrogen nucleus in the solar neighborhood represents an average value for the Galaxy, we predict L(sub CII) approximately = to 7 x 10(exp 7) solar luminosities from the CNM in the Galaxy, comparable to that observed by the Cosmic Background Explorer (COBE). We discuss the dependence of the results on absorbing column density, gas phase abundances, dust abundances and metallicity, FUV field, and the X-ray radiation field. These results will be useful in modeling the multiphase structure of high-velocity clouds in the halo, the interstellar matter (ISM) at other galactocentric radii, and the ISM in external galaxies and galactic nuclei.

Wolfire, M. G.↗