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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 271 records · Page 15
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NASA NTRS1976

High-dispersion observations of emission lines in the postnova HR Delphini

Results are reported for analysis of high-resolution line profiles obtained with an echelle spectrograph in the postnova HR Del. The investigated emission lines include H-alpha, the forbidden N II lines at 6548 and 6583 A, and the forbidden O III line at 5007 A. Heliocentric radial velocities of the line components are given along with their normalized relative intensities. The lines are found to have considerable structure which probably arises from condensations in the expanding nebula. It is shown that all the lines contain two major velocity groups, designated as shells A and B, and that shell B is more highly ionized and probably has a higher electron temperature. A large ratio between the intensities of the 6584-A and H-alpha lines is observed in shell A, and it is concluded that this is consistent with a nitrogen excess of a factor of two or more.

Gallagher, J. S.↗
NASA NTRS1975

Line strengths of H2O and N2O in the 1900-kayser region

Laboratory measurements of the line strengths of H2O and N2O in the 1900-kayser spectral region are reported which were made with moderate resolution using a modification of a Michelson interferometer. The N2O analysis includes measurements of the line strengths of the P and R branches and the integrated strength of the Q branch of the nu-1 + nu-2(1) band as well as the integrated strengths of the Q branches of the nu-1 + nu-2(2) - nu-2 and nu-1 + nu-2(0) - nu-2(1) bands. The H2O data cover the region from 1830 to 1980 kaysers; they include line-strength measurements of 61 lines of the nu-2 band, 10 lines of the nu-2 band of H2(O-18), two lines of the nu-2 band of H2(O-17), and three lines of the 'hot' band transition 2 nu-2 - nu-2. The estimated uncertainties in the measured line strengths range from 7% to 20% for H2O, 10% to 25% for H2(O-18) and H2(O-17), and 4% to 8% for N2O.

Toth, R. A.↗
NASA NTRS1976

Association of X-ray arches with chromospheric neutral lines

Daily maps of magnetic neutral lines derived from H-alpha observations have been superimposed on solar X-ray images for the period from June 15 to 30, 1973. Nearly all X-ray-emitting structures consist of systems of arches covering chromospheric neutral lines. Areas of low emissivity, coronal holes, appear as the areas between arcades of arches. The presence of a coronal hole, therefore, is determined by the spacing between neutral lines and the scale of the arches over those neutral lines. X-ray emissivity on the solar disk extends from neutral lines in proportion to the vertical and horizontal scale of the arches over those neutral lines. Increasing scale of arches corresponds with increasing age of magnetic fields associated with the neutral line. All X-ray filament cavities coincided with neutral lines, but filaments appeared under cavities for only part of their length and for only a fraction of the disk passage.

Mcintosh, P. S.↗
NASA NTRS1977

Narrow lines from alpha-alpha reactions

Intensities and spectral shapes of the prompt gamma-ray lines of Li-7 at 0.431 MeV and Be-7 at 0.478 MeV and of the delayed 0.478-MeV line, all resulting from alpha-alpha reactions, are calculated using recent direct measurements of the cross sections for the alpha-alpha reactions. It is found that the intensities of these lines are comparable to that of the 4.44-MeV line of C-12, so that the investigated lines should be observable in large solar flares, provided their Doppler widths are not excessively large. An evaluation of the shapes of the prompt lines indicates that for an isotropic distribution of energetic alpha-particles, the two lines merge into a broad feature which essentially cannot be distinguished from the continuum. A situation in which the delayed 0.478-MeV line could be very narrow is considered.

Kozlovsky, B.↗
NASA NTRS1977

Copernicus studies of interstellar material in the Perseus II complex. III - The line of sight to Zeta Persei

Ultraviolet spectrophotometric data obtained with Copernicus are used to analyze the distribution, composition, density, temperature, and kinematics of the interstellar material along the line of sight to Zeta Persei. The far-UV extinction curve for the star is evaluated along with the kinematics of the interstellar gas, observations of atomic and molecular hydrogen, curves of growth for neutral and ionized species, atomic abundances and depletions, ionization equilibria, and observations of CO and OH lines. The results show that there are apparently three clouds along the line of sight to Zeta Persei: a main cloud at approximately +13 km/s which contains most of the material and forms all the neutral and molecular lines as well as most of the ionic lines, a second component at +22 km/s which must contribute to the strong UV lines of most ions, and a third component at roughly +2 km/s which gives rise to a strong Si III line at 1206 A. It is also found that the UV extinction curve has a somewhat steep far-UV rise, indicating the presence of a substantial number of small grains, and that about 30% of the hydrogen nuclei over the entire line of sight are in molecular form.

Snow, T. P., Jr.↗
NASA NTRS1978

A theoretical and observational analysis of He I triplet lines in class 1 Seyfert galaxy spectra

The equations of statistical equilibrium are solved for 11 levels of the helium atom that are most relevant to the production and radiative transfer of He I triplet lines. Solutions are obtained for several densities and temperatures over a run of optical depth in the 10,830-A line, and the results for emission-line strengths are plotted. Spectrophotometric scans and pertinent line strengths are presented for the class 1 Seyfert galaxies 3C 120, NGC 7469, and Mrk 618, as well as for Mrk 335, which exhibits a 'more normal' He I 5876/H-beta ratio. A comparison of the theoretically determined line intensities with the observational results verifies that the He I triplet line intensities are significantly enhanced by electron collisional excitation from 2(3)P and 2(3)S. It is suggested that the gas which gives rise to the broad He I lines in 3C 120, Mrk 618, and NGC 7469 is characterized by a number density of about 5 billion per cu cm, a temperature of approximately 15,000 K, and an optical depth of 100 to 120 in the 10,830-A line.

Feldman, F. R.↗
NASA NTRS1980

Observations of the O I 1355.6 A and C I 1355.8 A lines in solar flares

The paper presents observations of the intersystem line O I 1355.6 A and the allowed line C I 1355.8 A in solar flares. In flares, the intersystem O I line is weaker than the allowed C I line and the intensity ratio O I/C I is 0.3-0.7. On the other hand, in active regions, O I line is stronger than the C I line and O I/C I is about 1-2, while in quiet sun regions, the O I line is much stronger than the C I line and O I/C I not in excess of 20. The variation of the intensity ratio from quiet sun region to flares may be due to an electron density enhancement of a factor of about 50 in flares.

Cheng, C. C.↗
NASA NTRS1982

IUE observations of Si and C lines and comparison with non-LTE models

Classical model atmosphere techniques are applied to analyze IUE spectra, and to determine abundances, effective temperatures and gravities. Measurements of the equivalent widths and other properties of the line profiles of 24 photospheric lines of Si II, Si III, Si IV, C II, C III and C IV are presented in the range of 1175-1725 A for seven B and two O stars. Observed line profiles are compared with theoretical profiles computed using non-LTE theory and models, and using line-blanketed model atmospheres. Agreement is reasonably good, although strong lines are calculated to be systematically stronger than those observed, while the reverse occurs for weak lines, and empirical profiles have smaller wings than theoretical profiles. It is concluded that the present theory of line formation when used with solar abundances, represents fairly well observed UV photospheric lines of silicon and carbon ions in the atmospheres of main sequence stars of types B5-O9.

Kamp, L. W.↗
NASA NTRS1985

Optical emission-line properties of evolved galactic supernova remnants

New optical spectrophotometric data are presented for the supernova remnants CTB 1, OA 184, VRO 42.05.01, S147, the Monoceros Loop, G206.9 + 2.3, and G65.3 + 5.7. These data are combined with published spectral data to study some of the general properties of evolved galactic supernova remnants. It is found that (1) O I and O II forbidden line strengths, when used in conjunction with the usual H-alpha S II forbidden line ratio test, provide an excellent additional diagnostic for discriminating remnants from H II regions; (2) the line ratios H-alpha forbidden line N II, H-alpha forbidden line S II, and forbidden line S II 6717/6731 A generally do not vary substantially among the filaments of an individual remnant; and (3) the observed correlation of forbidden line N II/H-alpha with S II forbidden line 6717/6731 A in remnants is the result of observational selection rather than of evolutionary effects. A galactic nitrogen abundance gradient of d log (N/H)/dR = -0.088 dex/kpc, which is in agreement with that derived from H II regions. However, no abundance gradients for oxygen or sulfur are indicated from the remnant data.

Fesen, R. A.↗
NASA NTRS1986

Observations of far-infrared line profiles in the Orion-KL region

Measurements of several far-infrared emission line profiles in the Orion-KL region are reported. The emission from the CO, OH, and forbidden O I emission lines toward the BN-KL and H2 peak 1 positions probably comes from dense, hot molecular gas in the Orion-KL shock. The CO and forbidden O I lines have similar profiles, suggesting that the high-velocity forbidden O I emission also arises in magnetohydrodynamic 'cloud' shocks. The velocity centroids of the lines are somewhat blueshifted. The far-infrared data thus support the interpretation that the blue asymmetry of the H2 2 micron lines is not mainly due to differential dust extinction, but rather to the kinematics and geometry of the shocked gas in the Orion-KL outflow. The forbidden O I and CO lines, however, have significantly less extreme blueshifted emission than the H2 lines. Both the forbidden O I 63 micron and forbidden C II 158 micron lines have features strongly supporting a common origin near the surface of the Orion molecular cloud.

Crawford, M. K.↗
NASA NTRS1986

Swept frequency technique for dispersion measurement of microstrip lines

Microstrip lines used in microwave integrated circuits are dispersive. Because a microstrip line is an open structure, the dispersion can not be derived with pure TEM, TE, or TM mode analysis. Dispersion analysis has commonly been done using a spectral domain approach, and dispersion measurement has been made with high Q microstrip ring resonators. Since the dispersion of a microstrip line is fully characterized by the frequency dependent phase velocity of the line, dispersion measurement of microstrip lines requires the measurement of the line wavelength as a function of frequency. In this paper, a swept frequency technique for dispersion measurement is described. The measurement was made using an automatic network analyzer with the microstrip line terminated in a short circuit. Experimental data for two microstrip lines on 10 and 30 mil Cuflon substrates were recorded over a frequency range of 2 to 20 GHz. Agreement with theoretical results computed by the spectral domain approach is good. Possible sources of error for the discrepancy are discussed.

Lee, R. Q.↗
NASA NTRS1987

Emission line region kinematics in selected Seyfert galaxies

The kinematic state of the emission line regions of active galactic nuclei (AGN) is a fundamental problem which addresses the very nature of these objects. The currently popular model of the energy source of the latter is accretion onto the supermassive black hole which is believed to reside in the nuclear regions of galaxies. If this picture is correct then the emission line gas may be expected to be infalling, and may eventually provide the fuel to power them. It is very difficult to determine the kinematic state of the emission line gas because of the technical problems associated with their small apparent sizes, as seen from the earth. One can only observe the net emission from a large ensemble of clouds, so the emission lines are by necessity composite. Several very long exposures of NGC 1068, one of the very nearest Seyfert galaxies, were obtained. Because of its proximity, it is expected to have the best resolved emission line regions as seen from earth. The La emission line of neutral hydrogen will radiate preferentially in the direction of the central object because of the effects of emission line gas opacity on the transfer of radiation out of the clouds. By obtaining high dispersion observations of Doppler broadening of the line through the small entrance aperture of the IUE one can determine whether this material is in a state of outflow (expected if explosions power the central engine), inflow (expected for accretion onto a massive black hole), or rotation (expected for gas with significant angular momentum near the central regions of a galaxy).

Ferland, G. J.↗
NASA NTRS1987

Time optimal paths and acceleration lines of robotic manipulators

The concept of acceleration lines and their correlation with time-optimal paths of robotic manipulators is presented. The acceleration lines represent the directions of maximum tip acceleration from a point in the manipulator work-space, starting at a zero velocity. These lines can suggest the number and shapes of time-optimal paths for a class of manipulators. It is shown that nonsingular time-optimal paths are tangent to one of the acceleration lines near the end-points. A procedure for obtaining near-optimal paths, utilizing the acceleration lines, is developed. These paths are obtained by connecting the end-points with B splines tangent to the acceleration lines. The near-minimum paths are shown to yield better traveling times than the straight-line path between the same end-points. The near-minimum paths can be used as initial conditions in existing optimization methods to speed-up convergence and computation time. This method can be used for online robot path planning and for interactive designs of robotic-cell layouts. Examples of time-optimal paths of a two-link manipulator, obtained by other optimization procedures and their acceleration lines, are shown.

Shiller, Zvi↗
NASA NTRS1987

Spectral line shapes. Volume 4 - Proceedings of the Eighth International Conference, College of William and Mary, Williamsburg, VA, June 9-13, 1986

The present conference discusses topics in line broadening and shift phenomena in low-to-moderately dense plasmas, resonances in the continuum, hot and dense laser-produced plasmas, collisional broadening and intermolecular potentials, molecular broadening and collision-induced spectroscopy, collisional redistribution and laser-assisted collision processes, coherent and nonlinear spectroscopy, astrophysical line-shapes, and short-wavelength lasers. Attention is given to the widths and shifts of Be ion lines, the Stark broadening of Xe II and Fe I lines, perturbed and unperturbed series in the line-shapes of autoionizing Rydberg series, the line-broadening of hydrogenic ions in dense plasmas, Doppler-free line-shapes, the Franck-Condon principle, the dynamics of laser-assisted reactive collisions, the gas-kinetic effects of light, collision-induced processes in nonlinear optics, and line-shaping phenomena in cool stars.

Exton, Reginald J.↗
NASA NTRS1988

Solar magnetic field studies using the 12 micron emission lines. I - Quiet sun time series and sunspot slices

The use of the extremely Zeeman-sensitive IR emission line Mg I, at 12.32 microns, to study solar magnetic fields. Time series observations of the line in the quiet sun were obtained in order to determine the response time of the line to the five-minute oscillations. Based upon the velocity amplitude and average period measured in the line, it is concluded that it is formed in the temperature minimum region. The magnetic structure of sunspots is investigated by stepping a small field of view in linear 'slices' through the spots. The region of penumbral line formation does not show the Evershed outflow common in photospheric lines. The line intensity is a factor of two greater in sunspot penumbrae than in the photosphere, and at the limb the penumbral emission begins to depart from optical thinness, the line source function increasing with height. For a spot near disk center, the radial decrease in absolute magnetic field strength is steeper than the generally accepted dependence.

Deming, Drake↗
NASA NTRS1990

Spectropolarimetric test of the relativistic disk model for the broad emission lines of active galactic nuclei

Previously, it was claimed that the broad emission lines of the radio galaxy Arp 102B can be fitted by the line profile from a simple relativistic Keplerian thin disk. It was argued that the lines originating from the relativistic accretion disk could be polarized due to electron scattering, which is likely to be the dominant opacity in the line-emitting region of Arp 102B. In the present work, the expected polarization properties of these broad emission lines are calculated. The percentage of polarization depends strongly on the inclination angle. For some angles, the red peak of the polarized, double-peaked line profile can be higher than the blue peak. This is in contrast to the total line profile, in which the blue peak is always higher than the red one. Spectropolarimetric observations could, therefore, provide an independent test of the relativistic disk model for the broad emission lines of Arp 102B and other active galactic nuclei.

Chen, Kaiyou↗
NASA NTRS1990

Line-drawing algorithms for parallel machines

The fact that conventional line-drawing algorithms, when applied directly on parallel machines, can lead to very inefficient codes is addressed. It is suggested that instead of modifying an existing algorithm for a parallel machine, a more efficient implementation can be produced by going back to the invariants in the definition. Popular line-drawing algorithms are compared with two alternatives; distance to a line (a point is on the line if sufficiently close to it) and intersection with a line (a point on the line if an intersection point). For massively parallel single-instruction-multiple-data (SIMD) machines (with thousands of processors and up), the alternatives provide viable line-drawing algorithms. Because of the pixel-per-processor mapping, their performance is independent of the line length and orientation.

Pang, Alex T.↗
NASA NTRS1991

Gamma-ray lines from type I supernovae

Analytic calculations are made of the time-dependent fluxes, shapes, median energies, and effective widths of the gamma-ray lines expected from the decay of nucleosynthetic Ni-56, Co-56, Fe-56, and Co-57 in current models of type I SNe. The attenuation and distortion of the line shapes due to Compton scattering and photoelectric absorption in the SN ejecta, line broadening from the expansion, and further distortion by the lookback effect from the differential light-travel time across the SN and by special relativistic effects are all taken into account. It is shown that several gamma-ray lines from such SNe should be measurable by detectors on the Gamma Ray Observatory and by the high-resolution spectrometer on the proposed Nuclear Astrophysics Explorer. The most intense and most detectable lines are the 0.847 and 1.238 MeV lines from Co-56 decay. Five other Co-56 decay lines, as well as the 0.158 MeV line from Ni-56 decay, should also be measurable. The models which can be tested by such observations are pointed out.

Chan, Kai Wing↗