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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 235 records · Page 13
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NASA NTRS2003

Wave and Particle Interactions in the High and Low-Altitude Auroral Region During Rising Solar Activity

The project has resulted in four separate investigations, which are each in various stages of publication in the refereed scientific journals. The first investigation was of the generation of electrostatic electron cyclotron waves observed by the Polar spacecraft throughout the auroral regions, dayside cusp, and polar magnetosphere. We have since discovered that these waves are also present within the magnetopause and magnetosheath, which is one of the topics of a second study, entitled: 'Polar observations of plasma waves in and near the dayside magnetopause/magnetosheath.' A third study of plasma waves focussed on kilometric continuum (KC) emission. This work is reported in a paper entitled 'Near-source and Remote Observations of Kilometric Continuum Radiation From Multi-spacecraft Observations'.The final investigation of this program concerns the possible transverse heating of auroral ions by impulsive wave structures. We summarize that substantial transverse ion heating has already occurred at lower altitudes. Abstracts of the above four studies are included in the Appendix to this final report.

Gurnett, Donald A.↗
NASA NTRS2004

Advances in Inner Magnetosphere Passive and Active Wave Research

This review identifies a number of the principal research advancements that have occurred over the last five years in the study of electromagnetic (EM) waves in the Earth's inner magnetosphere. The observations used in this study are from the plasma wave instruments and radio sounders on Cluster, IMAGE, Geotail, Wind, Polar, Interball, and others. The data from passive plasma wave instruments have led to a number of advances such as: determining the origin and importance of whistler mode waves in the plasmasphere, discovery of the source of kilometric continuum radiation, mapping AKR source regions with "pinpoint" accuracy, and correlating the AKR source location with dipole tilt angle. Active magnetospheric wave experiments have shown that long range ducted and direct echoes can be used to obtain the density distribution of electrons in the polar cap and along plasmaspheric field lines, providing key information on plasmaspheric filling rates and polar cap outflows.

Green, James L.↗
NASA NTRS2003

Linear Polarization Measurements of Chromospheric Emission Lines

We have used the Zurich Imaging Stokes Polarimeter (ZIMPOL I) with the McMath-Pierce 1.5 m main telescope on Kitt Peak to obtain linear polarization measurements of the off-limb chromosphere with a sensitivity better than 1 x 10(exp -5). We found that the off-disk observations require a combination of good seeing (to show the emission lines) and a clean heliostat (to avoid contamination by scattered light from the Sun's disk). When these conditions were met, we obtained the following principal results: 1. Sometimes self-reversed emission lines of neutral and singly ionized metals showed linear polarization caused by the transverse Zeeman effect or by instrumental cross talk from the longitudinal Zeeman effect in chromospheric magnetic fields. Otherwise, these lines tended to depolarize the scattered continuum radiation by amounts that ranged up to 0.2%. 2. Lines previously known to show scattering polarization just inside the limb (such as the Na I lambda5889 D2 and the He I lambda5876 D3 lines) showed even more polarization above the Sun's limb, with values approaching 0.7%. 3. The O I triplet at lambda7772, lambda7774, and lambda7775 showed a range of polarizations. The lambda7775 line, whose maximum intrinsic polarizability, P(sub max), is less than 1%, revealed mainly Zeeman contributions from chromospheric magnetic fields. However, the more sensitive lambda7772 (P(sub max) = 19%) and lambda7774 (P(sub max) = 29%) lines had relatively strong scattering polarizations of approximately 0.3% in addition to their Zeeman polarizations. At times of good seeing, the polarization spectra resolve into fine structures that seem to be chromospheric spicules.

Sheeley, N. R., Jr.↗
NASA NTRS2005

The FUV Flux Irradiating the Surfaces of Protostellar Disks

This grant was intended for, and has been used for, the support of the specialized CalFUSE data reduction required for these non-standard observations. The goal of the program was to search for FUV continuum radiation from T-Tauri stars, which would have affected the chemistry in the proto-planetary disk. Because of the low flux expected, the standard background subtraction method would not be appropriate. Rather on-chip background determination was expected to be required.

Andersson, B.-G.↗
NASA NTRS2007

THz Sources for Space

Terahertz is the primary frequency for line and continuum radiation from cool (5-100K) gas (atoms and molecules) and dust. This viewgraph presentation reviews the reasons for the interest in Terahertz Space Applications; the Terahertz Space Missions: in the past, present and planned for the future, Terahertz source requirements and examples of some JPL instruments; and a case study for a flight deliverable: THz Local Oscillators for ESA s Herschel Space Telescope

space applications↗
NASA NTRS2016

Probing Acceleration and Turbulence at Relativistic Shocks in Blazar Jets

Diffusive shock acceleration (DSA) at relativistic shocks is widely thought to be an important acceleration mechanism in various astrophysical jet sources, including radio-loud active galactic nuclei such as blazars. Such acceleration can produce the non-thermal particles that emit the broad-band continuum radiation that is detected from extragalactic jets. An important recent development for blazar science is the ability of Fermi-Large Area Telescope spectroscopy to pin down the shape of the distribution of the underlying non-thermal particle population. This paper highlights how multiwavelength spectra spanning optical to X-ray to gamma-ray bands can be used to probe diffusive acceleration in relativistic, oblique, magnetohydrodynamic (MHD) shocks in blazar jets. Diagnostics on the MHD turbulence near such shocks are obtained using thermal and non-thermal particle distributions resulting from detailed Monte Carlo simulations of DSA. These probes are afforded by the characteristic property that the synchrotron vF(sub v), peak energy does not appear in the gamma-ray band above 100 MeV. We investigate self-consistently the radiative synchrotron and inverse Compton signatures of the simulated particle distributions. Important constraints on the diffusive mean free paths of electrons, and the level of electromagnetic field turbulence are identified for three different case study blazars, Mrk 501, BL Lacertae and AO 0235+164. The X-ray excess of AO 0235+164 in a flare state can be modelled as the signature of bulk Compton scattering of external radiation fields, thereby tightly constraining the energy-dependence of the diffusion coefficient for electrons. The concomitant interpretations that turbulence levels decline with remoteness from jet shocks, and the probable significant role for non-gyroresonant diffusion, are posited.

Baring, Matthew G.↗
NASA NTRS2013

Vertical Settling and Radial Segregation of Large Dust Grains in the Circumstellar Disk of the Butterfly Star

Circumstellar disks are considered as the environment for the formation of planets. The growth of dust grains in these disks is the first step in the core accretion-gas capture planet formation scenario. Indicators as well as evidence of disk evolution can be traced in spatially resolved images and the spectral energy distribution (SED) of these objects. Aims. We aim at developing a model for the dust phase of the edge-on orientated circumstellar disk of the Butterfly Star which allows one to fit observed multi-wavelength images as well as the SED simultaneously. Our model is based on spatially resolved high angular resolution observations at 1.3 mm, 894 μm, 2.07 μm, 1.87 μm, 1.60 μm and 1.13 μm as well as an extensively covered SED ranging from 12 μm to 2.7 mm, including a detailed spectrum obtained with the Spitzer Space Telescope in the range from 12 μm to 38 μm. A parameter study based on a grid search method, involving the detailed analysis of every parameter, was performed to constrain the disk parameters and find the best-fit model for the independent observations. The individual observations were modeled simultaneously, using our continuum radiative transfer code MC3D. We derived a model that is capable of reproducing all of the observations of the disk at the same time. We find quantitative evidence for grain growth up to ~100 μm sized particles, vertical settling of larger dust grains toward the disk midplane, and radial segregation of the latter toward the central star. Our results are consistent with current theoretical models for the evolution of circumstellar disks and the early stages of planet formation.

Radiative transfer↗
NASA NTRS2020

CO, Water, and Tentative Methanol in η Carinae Approaching Periastron

The complex circumstellar environment around the massive binary and luminous blue variable η Carinae is known to harbor numerous light molecules, emitting most strongly in rotational states with upper level energies to ∼300 K. In circumstellar gas, the complex organic molecule methanol (CH3OH) has been found almost exclusively around young stellar objects, and thus regarded as a signpost of recent star formation. Here we report the first potential detection of methanol around a highly evolved high-mass star, while using the Atacama Large Millimeter Array to investigate molecular cloud conditions traced by CO (2–1) in an orbit phase preceding the 2020 periastron. The methanol emission originates from hot (T(gas) ≃ 700 K) material, ∼2″ (0.02 pc) across, centered on the dust-obscured binary, and is accompanied by prominent absorption of continuum radiation in a cooler (T(gas) ≃ 110 K) layer of gas. We also report a first detection of water in Herschel observations at 557 and 988 GHz. The methanol abundance is several to 50 times higher than observed toward several lower-mass stars, while water abundances are similar to those observed in cool, dense molecular clouds. The very high methanol: water abundance ratio in the core of η Car may suggest methanol formation processes similar to Fischer–Tropschtype catalytic reactions on dust grains. These observations prove that complex molecule formation can occur in a chemically evolved massive stellar environment, given sufficient gas densities and shielding conditions as may occur in material around massive interacting companions and merger remnants.

Patrick W Morris↗
NASA NTRS2013

A Census of X-ray Gas in NGC 1068: Results From 450 ks of CHANDRA High Energy Transmisson Grating Observations

We present models for the X-ray spectrum of the Seyfert 2 galaxy NGC 1068. These are fitted to data obtained using the High Energy Transmission Grating on Chandra. The data show line and radiative recombination continuum emission from a broad range of ions and elements. The models explore the importance of excitation processes for these lines including photoionization followed by recombination, radiative excitation by absorption of continuum radiation, and inner shell fluorescence. The models show that the relative importance of these processes depends on the conditions in the emitting gas and that no single emitting component can fit the entire spectrum. In particular, the relative importance of radiative excitation and photoionization/recombination differs according to the element and ion stage emitting the line. This in turn implies a diversity of values for the ionization parameter of the various components of gas responsible for the emission, ranging from log(E ) = 1 to 3. Using this, we obtain an estimate for the total amount of gas responsible for the observed emission. The mass flux through the region included in the HETG extraction region is approximately 0.3M/yr, assuming ordered flow at the speed characterizing the line widths. This can be compared with what is known about this object from other techniques.

galaxies: Seyfert↗
NASA NTRS1993

Ionized absorbers, ionized emitters, and the X-ray spectrum of active galactic nuclei

Broad absorption features are common in the X-ray spectrum of low-luminosity AGNs. The features have been modeled by leaky neutral absorbers or by highly ionized gas that completely occult the continuum source. Such models are incomplete since they do not take into account all the physical processes in the gas. In particular, no previous model included the X-ray emission by the ionized absorbing gas and the reflection of the continuum source radiation. The present work discusses the emission, absorption, and reflection properties of photoionized gases with emphasis on conditions thought to prevail in AGNs. It shows that such gas is likely to produce intense X-ray line and continuum radiation and to reflect a sizable fraction of the nonstellar continuum at all energies. If such gas is indeed responsible for the observed X-ray absorption, then absorption edges are much weaker than commonly assumed, and some residual X-ray continuum is likely to be observed even if the line of sight is completely blocked. Moreover, X-ray emission features may show up in sources not showing X-ray absorption. This has immense consequences for medium-resolution X-ray missions, such as BBXRT and Astro-D, and for the planned high-resolution experiments on board XMM and AXAF.

Netzer, Hagai↗
NASA NTRS1989

The nature of the annihilation radiation and gamma-ray continuum from the Galactic center region

Analysis of the observations of the time-dependent, electron-positron annihilation line radiation and gamma-ray continuum emission from the region of the Galactic center shows that ther are two components to the emission: (1) a variable, compact source of 511 keV annihilation line and higher energy continuum emission active from about 1977 through 1979 at or near the Galactic center; and (2) a steady, diffuse interstellar source of 511 keV annihilation line and orthopositronium continuum emission, having a galactic longitudinal distribution consistent with that of the more than 70 MeV gamma rays or the molecular (CO) gas. It is found that the continuum spectrum of the compact source shows no evidence for orthopositronium annihilation. It is suggested that all of the three-photon orthopositronium continuum observed so far originates from the diffuse interstellar component. The continuum spectrum of the compact source is very similar to that of the black-hole candidate Cygnus X-1, supporting our earlier arguments that this object, at or near the Galactic center, is a black hole of stellar mass.

Lingenfelter, Richard E.↗
NASA NTRS1982

Calculation of radiative transition probabilities and lifetimes

Procedures for calculating bound-bound and bound-continuum (free) radiative transition probabilities and radiative lifetimes are summarized. Calculations include rotational dependence and R-dependent electronic transition moments (no Franck-Condon or R-centroid approximation). Detailed comparisons of theoretical results with experimental measurements are made for bound-bound transitions in the A-X systems of LiH and Na2. New bound-free results are presented for LiH. New bound-free results and comparisons with very recent fluorescence experiments are presented for Na2.

Zemke, W. T.↗
NASA NTRS1987

The largest white light flare ever observed: 25 April 1984, 0001 UT

The X13/3B flare of 25 April 1984, 0001 UT, was accompanied by intense white light emission that reached a peak power output approx 2x10 to the 29 erg/sec in the optical/near UV continuum; the total energy radiated in the continuum alone reached 10 to the 32 power ergs. This was the most powerful white light flare yet recorded, exceeding the peak output of the largest previously known event by more than one order of magnitude. The flare was a two-ribbon type with intense embedded kernels as observed in both Balmer-alpha line and Balmer continuum, and each of these flare ribbons covered separate umbrae shortly after the maximum of the event. The onset and peak of the white light emission coincided with the onset and peak of the associated E greater than 100 KeV hard X-ray burst, while the 1-8 angstrom soft X-ray emission reached its maximum 4 minutes after the peak in white light.

Neidig, D. F.↗
NASA NTRS1992

Warm neutral halos around molecular clouds. IV - H I and continuum: Aperture synthesis observations towards the molecular cloud B5

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.

Andersson, B.-G.↗
NASA NTRS1980

On the detection of other planetary systems - Detection of intrinsic thermal radiation

There is currently no unambiguous observational evidence for the existence of other planetary systems. One possible way to detect and study such systems is infrared observations of continuum blackbody radiation from planets revolving around other stars. It is shown that the effective temperature of large planets revolving around mid- to late-spectral-type main-sequences stars is set by energy sources internal to the planet rather than by equilibrium with the radiation field of the central star, making them easier to detect than had been previously thought. Consideration is given to the two major observational constraints on detecting planetary companions to nearby stars, namely, angular resolution and sensitivity. A comparison is made between the performance of an ambient (T 200 K), single-aperture telescope and a cooled interferometer. In each case the required aperture (baseline) is large (in the 10-m class), but consistent with Shuttle launch capability.

Black, D. C.↗
NASA NTRS1980

Application of finite-element-techniques to the interaction of conduction and radiation in an absorbing, scattering and emitting medium

In this paper, the authors demonstrate that a Galerkin finite element method of analysis, utilizing isoparametric elements, offers a viable means of solving continuum thermal radiation problems with conduction in a participating medium. The participating medium was considered to be a gray radiation medium exhibiting isotropic absorption, emission, and scattering characteristics and optical properties that are independent of temperature. The medium was considered to be bounded by infinite parallel opaque, gray surfaces with diffuse emission and reflection characteristics. In solving this problem, a finite element formulation was developed to describe a system in radiative equilibrium. Then the results of this first analysis were linked with a second finite element model which incorporated conduction into the analysis. The results of this study were found to be in good agreement with existing published data. The model offers the following advantageous features: geometric generality, a computational algorithm which is 'convenient' and 'computable', and a functional basis for extension of the radiation model to higher order approximation.

Wu, S. T.↗