SEARCH · Engineering Papers

Results for “FINE STRUCTURE”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27

All sources NASA NTRS DOE OSTI

NASA NTRS1984

High-resolution IUE observations of interstellar absorption lines in the Vela supernova remnant

Ultraviolet spectra of 45 stars in the vicinity of the Vela supernova remnant were recorded by the short-wavelength echelle spectrograph aboard the International Ultraviolet Explorer (IUE). Over one-third of the stars show interstellar absorption lines at large radial velocities (greater than 60 km/s). The mapping of these high-velocity components in the sky suggests the motions are chaotic, rather than from a coherent expansion of the remnant material. In accord with earlier conclusions from Copernicus data, the gas at high velocity exhibits higher than normal ionization and shows substantially less depletion of nonvolatile elements than normal interstellar material at low velocities. Relatively strong lines from neutral carbon in the two excited fine-structure states indicate that the neutral clouds within the remnant have had their pressures enhanced by the passage of the blast wave from the supernova. Also, the remnant seems to show a significant enhancement in the abundances of low-velocity Si IV, C IV, and N V over those found in the general interstellar medium.

Jenkins, E. B.↗

NASA NTRS1984

Solar noise storms - The polarization of storm Type III and related bursts

The spectral and polarization characteristics of 19 noise storms that occurred during 1976-1982 are reported. All components of the storms - Type I bursts and continuum, storm Type III bursts, and fine structures such as reverse drift pairs - are found to have the same sense of circular polarization. While the degree of polarization p of Type I bursts and continuum is generally greater than or approximately equal to 0.5, that of storm Type III bursts is almost always less than 0.5. Two set of storm Type III bursts stand out: one with less than or approximately equal to 0.2 and another with greater than or approximately equal to 0.3. Because these sets respectively have degrees of polarization so similar to those of fundamental (F) the harmonic (H) components of non-storm F - H pairs, it is deduced that storm Type III bursts are due sometimes to fundamental plasma radiation and sometimes to harmonic. However, F - H pairs are extremely rare among storm Type III bursts.

Dulk, G. A.↗

NASA NTRS1984

Far-infrared spectroscopy of neutral interstellar clouds

A summary is presented of airborne observations of the far-infrared fine structure lines of neutral atomic oxygen and singly-ionized carbon, and of the far-infrared rotational lines of CO, OH, NH3 and HD, together with a brief description of the analysis and interpretation of the spectra. The 'state of the art' in instrument performance and the prospects for improved sensitivity and resolution are also surveyed.

Watson, D. M.↗

NASA NTRS1984

IUE observations of DQ Herculis and its nebula, and the nature of the cold nova shells

The nebula ejected in the 1934 outburst of the classical nova DQ Her is remarkable for its unprecedentedly low temperature of Te 500 K as measured by Williams et al. (1978). In this paper, IUE observations are combined with Steward optical spectra. It is confirmed that the gas is quite cold. It is further shown that the gas is ionized by the radiation field of the central object. X-ray, ultraviolet, optical and infrared observations of the underlying binary are combined with the extreme-ultraviolet continuum deduced from the level of ionization of the nebula to obtain a composite energy distribution for the central object. This energy distribution bears no resemblance to that predicted by theoretical models of accretion disks. Photoionization models of the nebula using the deduced continuum, as well as theoretical accretion disk continua, are presented to show that the low electron temperature is the result of the very high metal abundances which characterize nova shells. Infrared fine-structure lines are efficient coolants, and low temperatures are achieved for a wide variety of radiation fields. The implications of these results for nebulae surrounding other old novae are discussed.

Ferland, G. J.↗

NASA NTRS1984

Detection of shocked atomic gas in the Kleinmann-Low nebula

The 63 micrometer (3)P(1)-(3)P(2) fine structure line emission of neutral atomic oxygen at the center of the Orion nebula with a resolution of 30'' is presented. There are three main emission peaks. One is associated with the region of strongest thermal radio continuum radiation close to the Trapezium cluster, and probably arises at the interface between the H II region and the dense Orion molecular cloud. The other two line emission peaks, associated with the Kleinmann-Low nebula, are similar in both distribution and velocity to those of the 2 micrometer S(1) line of molecular hydrogen and of the high velocity wings of rotational CO emission. The OI emission from the KL nebula can be produced in the shocked gas associated with the mass outflows in this region and is an important coolant of the shocked gas.

Werner, M. W.↗

NASA NTRS1984

Research Relative to High Spatial Resolution Passive Microwave Sounding Systems

Methods to obtain high resolution passive microwave weather observations, and understanding of their probable impact on numerical weather prediction accuracy were investigated. The development of synthetic aperture concepts for geosynchronous passive microwave sounders were studied. The effects of clouds, precipitation, surface phenomena, and atmospheric thermal fine structure on a scale of several kilometers were examined. High resolution passive microwave sounders (e.g., AMSU) with an increased number of channels will produce initialization data for numerical weather prediction (NWP) models with both increased spatial resolution and coverage. The development of statistical models for error growth in high resolution primitive equation NWP models which permit the consequences of various observing system alternatives, including sensors and assimilation times and procedures is discussed. A high resolution three dimensional primitive equation NWP model to determine parameters in an error growth model similar to that formulated by Lorenz, but with more degrees of freedom is utilized.

Staelin, D. H.↗

NASA NTRS1984

Measurement of high temperature strain by the laser-speckle strain gauge

By using the laser-speckle strain gauge, the strain of metal at the temperature lower than 250 C is measured. The principle of the gauge is to measure the expansion or contraction of the fine structures of surface by detecting the resultant speckle displacement in an optoelectronic way, whereby the effect of rigid-body motion is automatically cancelled out with the aid of a differential detection system. A transportable apparatus was built and a comparison experiment performed with a resistance strain gauge at room temperature. It has a strain sensitivity of .00002, a gauge length smaller than 1 mm, and no upper limit in a range of strain measurement. In the measurement of high-temperature strain it is free from the need for a dummy gauge and insensitive to an electric drift effect. As examples of strain measurement at high-temperature, thermal expansion and contraction of a top of a soldering iron are measured. The interval of the measurement can be made at shortest 1.6 sec. and the change in the strain is clearly followed until the ultimate stationary temperature is reached.

Yamaguchi, I.↗

NASA NTRS1985

Effect of Scattering on Instabilities in Line-driven Stellar Winds

Line driven O-B stellar winds are unstable to perturbations of short spatial wavelength and the growth rates for such instabilities are very rapid. The nature of the nonlinear development of this instability is unknown, but might possibly be one of blobs of gas driven through ambient gas or a quasiregular train of outward moving shocks. In either case the resulting dissipation of mechanical energy might explain the observed anomalous heating n O-B stars as evidenced by their X-ray emission and high ionization state. It also might explain the observed fine structure of the absorption lines and their time variability. The driving due to the absorption of the stellar continuum flux was considered and the effects of the diffuse, scattered radiation field were neglected. It was shown that under certain special conditions the effect of scattering could reduce the instability growth rate to zero. A stability analysis that includes scattering, but that uses the more physically realistic assumption of complete redistribution instead of coherent scattering, and that includes the effects of transverse velocity gradients, which become important as the flow moves away from the stellar surface is presented. It is found that the instability is eliminated right at the base of the wind, but that as the flow moves outward the instability rate rapidly becomes equal to a substantial fraction of the calculated value, the fraction asymptotically reaching 80% at large radii. Since this still implies many e folds in a characteristic outflow time, the primary conclusion that these winds are highly unstable is unchanged.

Owocki, S. P.↗

NASA NTRS1984

Far-infrared Spectroscopy of Interstellar Gas

Research results of far-infrared spectroscopy with the Kuiper Airborne Observatory are discussed. Both high and intermediate resolution have been successfully employed in the detection of many new molecular and atomic lines including rotational transition of hydrides such as OH, H2O, NH3 and HCl; high J rotational transitions of CO; and the ground state fine structure transitions of atomic carbon, oxygen, singly ionized carbon and doubly ionized oxygen and nitrogen. These transitions have been used to study the physics and chemistry of clouds throughout the galaxy, in the galactic center region and in neighboring galaxies. This discussion is limited to spectroscopic studies of interstellar gas.

Phillips, T. G.↗

NASA NTRS1984

Far-infrared Spectroscopy of Galaxies: the 158 Micron C(+) Line

The C II 158 micron fine structure line in six gas rich galaxies was investigated. These data are combined with other measurements of the C II line (in various galactic sources) and are compared to studies of the CO J = approaches O rotational line at 2.6 mm, the H I 21 cm line, and the far infrared continuum emission in the same objects.

Crawford, M. K.↗

NASA NTRS1985

Far-infrared line observations of planetary nebulae. 1: The O 3 spectrum

Observations of the far-infrared fine structure lines of O III have been obtained for six planetary nebulae. The infrared measurements are combined with optical O III line fluxes to probe physical conditions in the gas. From the observed line intensity ratios, a simultaneous solution was obtained for electron temperature and density, as well as means of evaluating the importance of inhomogeneities. Densities determined from the far-infrared O III lines agree well density diagnostics from other ions, indicating a fairly homogeneous density in the emitting gas. Temperatures are determined separately from the O III 4363/5007 A and 5007 A/52 micron intensity ratios and compared. Systematically higher values are derived from the former ratio, which is expected from a nebula which is not isothermal. Allowance for the presence of temperature variations within these nebulae raises their derived oxygen abundances, determinations to be reconciled with the solar value.

Dinerstein, H. L.↗

NASA NTRS1984

Observations of Mesospheric Turbulence by Rocket Probe and VHF Radar, Part 2.4A

Data from the Jicamarca VHF radar and from a Languir probe fine-structure on a Nike Orion rocket launched from Punto Lobos, Peru, have been compared. A single mesospheric scattering layer was observed by the radar. The Langmuir probe detected irregularities in the electron-density profile in a narrow region between 85.2 and 86.6 km. It appears from a comparison between these two data sets that turbulence in the neutral atmosphere is the mechanism generating the refractive index irregularities.

Royrvik, O.↗

NASA NTRS1984

The far-infrared laser magnetic resonance spectrum of the SiH radical and determination of ground state parameters

The far-infrared laser magnetic resonance spectrum of the SiH radical in the v = O level of its X2Pi state has been recorded. The signals are rather weak. The molecules were generated in the reaction between fluorine atoms and SiH4. Rotational transitions have been detected in both 2Pi1/2 and 2Pi3/2 spin components but no fine structure transitions between the spin components were observed. Proton hyperfine splittings were resolved on some lines. The measurements have been analyzed, subjected to a least-squares fit using an effective Hamiltonian, and the appropriate molecular parameters determined. The weakness of the spectrum and the failure of attempts to power saturate favorable lines are both consistent with a small value for the electric dipole moment for SiH.

Brown, J. M.↗

NASA NTRS1984

Topological reaction rate measurements related to scuffing

A ball-on-plate (both consisting of hardened M-50 steel) sliding elastohydrodynamic contact was run with trimethylolpropane triheptanoate (TMPTH) with and without tricresyl phosphate (TCP). The contact area of the plate was optically profiled with a phase-locked interference microscope (PLIM) both before and after exposure to alcoholic hydrochloric acid. As scuffing was approached, the profile within the contact region changed more rapidly after the acid treatment; after scuffing, it assumed a constant high value. A metallurgical phase found in the scuff mark was apparently responsible for the high reactivity. The microscopic profile changes (sensitivity, + or - 3 nm (+ or - A) in depth) involved primarily the small asperities (radius, 3 microns); the larger ones were unaffected. Soaking the steel in TCP smoothed the fine structure of the surface profile but increased its reactivity toward alcoholic hydrochloric acid before sliding was started. Thus it would appear that PLIM examination could be used for screening potentially scuff-resistant materials.

Lauer, J. L.↗

NASA NTRS1984

Circumstellar material around rapidly rotating B stars. II - On the nature of ultraviolet shell lines in the spectra of Be and shell stars

Using high-resolution (FWHM approximately 0.05 A) ultraviolet spectral data obtained with Copernicus, the nature of shell lines in Be and shell stars. Scans were obtained for various excited fine-structure lines of Fe III, Si II, and O I. It is found that Be stars, in general, do not display shell lines in the ultraviolet, contrary to the findings of previous work at lower resolution. The only Be stars that display strong UV shell lines are the 'classical' shell stars, i.e., stars that also display shell lines in the optical region. Furthermore, it is found that the shell lines, when present, have essentially zero velocity shift with respect to the star. The resonance shell lines seen in the shell stars are generally asymmetric on the short-wavelength side, indicating that the lines are formed in a low-velocity outflowing region. The results presented here argue strongly in favor of a flattened disk structure for the shell line forming region, and against some recent scenarios involving spherical symmetry.

Oegerle, W. R.↗

NASA NTRS1984

Detailed studies of the dynamics and energetics of coronal bullets

Coronal bullets are small ejecta of cool, dense plasma observed to accelerate through the solar atmosphere from 20 to 450 km/s. The NRL Dynamic Flux Tube Model has been used to simulate the evolving physical properties of these dynamic events. The present calculations utilize an adaptive-gridding technique to resolve the fine structure within and around the bullets. In this work, an identification was made of a component of shocked plasma which piles up ahead of the bullet and eventually dominates both the dynamics and heating of the original bullet mass. The observational consequences of this shocked component are discussed in terms of the available HRTS EUV data, and suggestions are made for optimizing future observations of this phenomenon. An investigation has also been conducted of the structure of the bullet material visible in EUV spectral lines and the observable characteristics of the EUV-emitting plasma. Finally, the most likely mechanisms for accelerating the bullets, as well as favorable sites of origin are evaluated.

Karpen, J. T.↗

NASA NTRS1984

On Bowen enhancement of the N III spectrum under solar and nebular conditions

Expected enhancement of the N III emission-line spectrum by the Bowen He II to O III to N III resonant photoexcitation process is computed using a six-configuration model. Preliminary comparisons with available solar and nebular observations indicate that the process may play only a small role, although photoexcitation quenching of the N III and O III far-infrared fine-structure lines is noted as a possibly important mechanism. Some features are discussed in connection with the nebular emission at 1750 A, which is suggested as an indicator of excitation class for planetary nebulae.

Kastner, S. O.↗

NASA NTRS1985

A model for the CI (609 micron) emission of Orion

A numerical model energy balance and chemical equilibrium in the photodissociation regions at the edge of molecular clouds is presented. The model is used to calculate the emergent intensities of the following fine-structure lines: OI (at 63, 145 microns); CI (at 609, 370 microns); C II (at 158 microns); and the low-lying rotational transitions of CO. It is shown that column densities in the range 2 x 10 to the 17th to 2 x 10 to the 18th per sq cm can be obtained for the C(+)/C/CO transition region at the edges of molecular clouds. The difference in the column densities is attributed to changes in the charge exchange reactions of C(+) with SiO and S, and to the process of carbon self-healing. It is found that the calculations are in good agreement with the observed conditions in the photodissociation regions behind Orion (1) C Ori, and near the surface of OMC 1.

Tielens, A. G. G. M.↗