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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Observations of the stellar Mg II resonance doublet at 2795 and 2802 A.

Spectrophotometry of the Mg II resonance doublet at 2795.5 and 2802.7 A has been performed for five stars with a balloon-borne telescope and spectrometer. Spectral resolution attained was between 0.25 and 0.5 A. A description of the payload and flight operations is given. In beta Lyr the Mg II doublet displayed P Cygni characteristics, while in gamma Lyr the doublet was observed only in absorption. The star beta Cas shows broad overlapping Mg II absorption lines with possible weak emission at the line bottom. In alpha CMi, both components of the doublet are seen in emission at the bottom of the broad absorption feature. The Mg II doublet in alpha Ori is entirely in emission, with each component showing distinct self-reversal.

Kondo, Y.↗
NASA NTRS1973

The effect of Fe I absorption on the Mg II emission at 2795 A in alpha Orionis

The Fe I absorption line at 2795.01 A is derived from the observations of Mg II resonance emission in alpha Orionis by Kondo et al (1972). A spectrum is synthesized, including Mg II emission and self-absorption and also Fe I absorption, which accounts for the observed asymmetry in the Mg II 2795.5 line and for the discrepancy between the theoretical and observed intensity ratios of the two Mg II lines. The astrophysical significance of this strong Fe I absorption is discussed.

Modisette, J. L.↗
NASA NTRS1975

An analytical and experimental stress analysis of a practical mode II fracture-test specimen

A boundary collocation method has been employed to determine the Mode II stress intensity factors for a pair of through-the-thickness edge cracks in a finite isotropic plate. An elastostatic analysis has been carried out in terms of the complete Williams stress function employing both even and odd components. The results of the numerical analysis were verified by a two-step procedure whereby the symmetric and antisymmetric portions of the solution were independently compared with existing solutions. The complete solution was verified by comparison with a photoelastic analysis. A compact shear specimen (CSS) of Hysol epoxy resin was loaded in a photoelastic experiment designed to study the isochromatic fringe patterns resulting from the Mode II crack tip stress distribution. The experiment verified that a pure Mode II stress distribution existed in the neighborhood of the crack tips and confirmed the accuracy of the boundary collocation solution for the Mode II stress intensity factors.

Chisholm, D. B.↗
NASA NTRS1976

The solar XUV spectrum of He II

OSO-7 observations of the first five Lyman lines and the Lyman continuum of He II are given for the quiet sun, a coronal hole, prominences, filaments, and the flare of August 7, 1972. These data are calibrated and given in specific intensity units together with color and brightness temperatures for the He II continuum. It is found that He II is overionized in all features except the flare and that the continuum is formed at temperatures near 14,000 K. The He II-He III ionization equilibrium appears to be dominated by photoionizations and radiative recombinations. Schematic calculations for realistic chromosphere and transition-region models can account for the observed intensities of Ly-beta through Ly-epsilon, the Lyman continuum, and its color temperature. To account for the intensity of Ly-alpha, either an implausible 100-km plateau at temperatures near 80,000 K is needed or, more likely, the diffusion-enhanced collisional excitation should be incorporated into the models.

Linsky, J. L.↗
NASA NTRS1976

Seyfert galaxies with strong Fe II emission

Measurements are reported for the spectral energy distributions of the Seyfert galaxies Zw 2130+09 and Zw 0051+12 as well as the quasar 3C 273 over the wavelength range from 3300 to 10,760 A. Absolute emission-line intensities are derived for numerous Fe II blends and the O I line at 8446 A. Several new Fe II emission features are identified, the absence of Fe III emission is noted, and interesting properties of the individual spectra are described. Constraints on the ionizing continuum and on the geometry and velocity field of the emission-line regions are discussed. The observations show that Seyfert galaxies with strong Fe II emission also have strong O I 8446-A emission and that a flat continuum in the near-UV appears to be common in such objects. Assuming photoionization, it is suggested that both the Fe II and the O I emission could result from continuum fluorescence in an outer, optically thick H I zone in an emission-line region about 1 pc in radius and consisting of many small high-velocity filaments.

Oke, J. B.↗
NASA NTRS1977

The Mg II features near 2800A and spectral classification

Relatively high-resolution (about 0.4 A) observations of the Mg II resonance lines at 2795.523 and 2802.698 A as well as their respective subordinate lines at 2797.989 and 2790.768 A are discussed for main-sequence stars, giants, and supergiants. The general behavior of the Mg II lines as a function of spectral type is described. An expression is obtained for the relationship between absolute magnitude and Mg II emission widths. The variation of the absorption widths of the Mg II features with spectral type and luminosity class is briefly summarized.

Kondo, Y.↗
NASA NTRS1977

Faint emission features in the Mg II resonance-line wings

Data obtained with a rocket-borne echelle spectrograph are presented which indicate the presence of three faint emission features deep in the cores of the Mg II h and k resonance-line wings in the solar Fraunhofer spectrum. Results of wavelength measurements are discussed, and the relative intensities of the emission features are examined. It is tentatively suggested that the first feature be identified with the Fe II line at 2797.037 A, the second feature is probably the V II line at 2803.469 A, and the third feature may originate in Fe II emission at 2804.021 A. Possible emission mechanisms are proposed, and it is concluded that the detected features may be of potential diagnostic value for the analysis of depth variations of temperature and velocity in the lower chromosphere as well as for solar and possibly stellar spectroscopy.

Allen, M. S.↗
NASA NTRS1980

Spectrophotometry of H II regions and the nucleus of NGC 1566

The paper presents spectrophotometric observations of the nucleus and nine H II regions in the spiral arms of the Sbc galaxy NGC 1566. The emission line spectra of the H II regions are characterized by a low grade of ionization, and most of the line intensities do not show radial gradients; the N II/O II forbidden line ratio appears to increase toward the nucleus, and the forbidden O III/H-beta ratio may decrease in the same direction. This is explained by the increase of the oxygen abundance and decrease of the electron temperature toward the nucleus; the spectra confirm the presence of the weak, broad emission wings at H-alpha, and the nuclear spectrum of NGC 1566 resembles that of a giant H II region rather than that of a Seyfert galaxy.

Hawley, S. A.↗
NASA NTRS1980

Effect of chronic intracerebroventricular angiotensin II infusion on vasopressin release in rats

The effects of the chronic infusion of angiotensin II into the lateral cerebral ventricle on the release of arginine vasopressin in rats are investigated. Rats were subjected to a continuous infusion of angiotensin at a rate of 1 microgram/h for five days, during which they were offered water, isotonic saline or hypertonic saline ad libitum or 40 ml water/day, and fluid intake, changes in body weight, plasma sodium ion concentrations and plasma and pituitary arginine vasopressin levels were measured. Angiotensin II is found to increase the fluid intake of rats given isotonic saline and decrease plasma sodium ion levels with no changes in plasma or pituitary arginine vasopressin in those given water or isotonic saline. However, in rats given hypertonic saline, plasma sodium concentrations remained at control levels while plasma vasopressin increased, and in water-restricted rats the effects of angiotensin II were intermediate. Results thus demonstrate that angiotensin II-stimulated arginine vasopressin release is reduced under conditions in which plasma sodium ion concentration becomes dilute, compatible with a central role of angiotensin in the regulation of salt and water balance.

Sterling, G. H.↗
NASA NTRS1982

Abundances in five nearby galactic H II regions from infrared forbidden lines

Airborne measurements of the Ar II (6.99 micron) and S II (18.7) micron lines for five compact H II regions in the solar neighborhood are presented, as well as 2-4 micron and 8-13 micron spectroscopy where available. From these data and radio data, lower limits to the elemental abundances of Ar, Ne, and S are deduced. Some of these H II regions suffer substantial nebular extinction, and some are extended. After correcting for beam size effects an extinction, it is found that four of the objects are consistent with standard abundances, within the uncertainties of correcting for unobserved ionization states. A Perseus arm object, S156, is apparently overabundant in sulfur.

Herter, T.↗
NASA NTRS1983

A coronal transient associated with a high-speed type II burst

Several characteristics of a white light transient observed by the ATM Coronagraph experiment aboard Skylab are discussed. The transient was associated with a very high speed type II radio burst. The observed plane of the sky speed of the burst was 4900 km/s, 6-7 times higher than the speed of the transient itself. Based on the relative speeds of the transient and the radio burst, it is argued that the type II disturbance must have propagated in a still undisturbed corona, at an approximately 35-deg angle to the preexisting streamer and along an essentially open field configuration. The electron density gradients derived from the radio and the white light observations are compared, and it is shown that they are in agreement within the limits of the observations. The assumption that the type II was a weak MHD shock leads to large values for the coronal magnetic field. The possibility that the type II radition originated in a strong shock, with a magnetic Mach number greater than 2, is considered.

Gergely, T. E.↗
NASA NTRS1984

Type II solar radio bursts, interplanetary shocks, and energetic particle events

Using the ISEE-3 radio astronomy experiment data 37 interplanetary (IP) type II bursts have been identified in the period September 1978 to December 1981. These events and the associated phenomena are listed. The events are preceded by intense, soft X ray events with long decay times (LDEs) and type II and/or type IV bursts at meter wavelengths. The meter wavelength type II bursts are usually intense and exhibit herringbone structure. The extension of the herringbone structure into the kilometer wavelength range results in the occurrence of a shock accelerated (SA) event. The majority of the interplanetary type II bursts are associated with energetic particle events. These results support other studies awhich indicate that energetic solar particles detected at 1 A.U. are generated by shock acceleration. From a preliminary analysis of the available data there appears to be a high correlation with white light coronal transients.

Cane, H. V.↗
NASA NTRS1984

The depletion of pre-interstellar matter and an examination of Ni II oscillator strengths

IUE absorption-line data obtained at 110-320 nm with resolution 10-30 pm toward the B-star component of the multiple system of Alpha Sco are presented in graphs and tables and used to characterize the circumstellar shell around the M1.5 Iab component. Resonant lines of Ni II are identified at strengths in excess of 4 pm and fit to a growth curve constructed using the Fe II, Si II, and Mn II lines, and the results are found to confirm the oscillator strengths determined by Kurucz and Peytremann (1975) to within 50 percent. Shell depletions 2-20 times smaller than those for dense clouds such as the surrounding Oph complex are calculated and attributed to the formation of circumstellar dust. The implications of the results for the condensation of various elements in dense and diffuse clouds are explored.

Cardelli, J. A.↗
NASA NTRS1984

A multiple type-II burst associated with a coronal transient and its MHD simulation

A large coronal transient took place on May 8, 1981. The transient was related to an M7.7/2B flare and was associated with at least two coronal type-II bursts. The velocities of the type-II bursts were in the range 1100-1800 km/s, in excess of the transient velocity of 1000 km/s. Two dimensional positions of the type-II radio sources are available from both the Clark Lake and the Culgoora Radio Observatories. Two dimensional MHD simulations of the event are carried out, taking into account the observed velocity, position, and size of the type-II bursts. The multiple shocks observed during the event and their interaction are simulated, and results of the simulation are discussed.

Gergely, T. E.↗
NASA NTRS1985

The Serendip II design

Serendip II is an automated system designed to perform a real time search for narrow band radio signals in the spectra of sources in a regularly scheduled, non-Seti, astronomical observing program. Because Serendip II is expected to run continuously without requiring dedicated observing time, it is hoped that a large portion of the sky will be surveyed at high sensitivity and low cost. Serendip II will compute the power spectrum using a 65,536 channel fast Fourier transform processor with a real time bandwidth of 128 KHz and 2 Hz per channel resolution. After searching for peaks in a 100 KHz portion of the radio telescope's IF band, Serendip II will move to the next 100 KHz portion using a programmable frequency synthesizer; when the whole IF band has been scanned, the process will start again. Unidentified peaks in the power spectra are candidates for further study and their celestial coordinates will be recorded along with the time and power, IF and RF frequency, and bandwidth of the peak.

Werthimer, D.↗
NASA NTRS1987

Rotational modulation and flares on RS CVn and BY Dra systems. II - IUE observations of BY Draconis and AU Microscopii

The modulation of the strong chromospheric and transition region lines over one cycle of the optical light curves of BY Dra and AU Mic is studied using IUE observations. The IUE observations were made from October 2-5, 1981 and include 7 short wavelength (SW) spectra and 13 long wavelength (LW) spectra. The integrated line flux data reveal that for BY Dra in the SW spectra there is modulation in the C IV, C II, O I, and He II lines and nonflare surface fluxes; and in the LW spectra, flares are detected in the Mg II and Fe II bands. It is observed that there is no modulation in AU Mic, and the optical photometry data reveal a poor correlation between optical flare strength and UV emission line enhancements. The differential emission measure curves for BY Dra and AU Mic are compared with solar curves. It is noted that both stars show the presence of hot material throughout their rotation period.

Butler, C. J.↗
NASA NTRS1987

Giant H II regions in M81

H-alpha and VLA radio continuum observations at wavelengths of 6 and 20 cm are used to study the distribution of extinction and the distribution of giant radio H II regions along the spiral arms in M81. The radial distribution of visual extinction Av in the plane of M81 shows no trend, with an upper limit 0.1 mag/kpc for the radial extinction gradient and a mean Av of 1.1 + or - 0.4 mag. Nearly all the giant radio H II regions lie along the spiral arms or the inner H I ring. The radial distribution of the set of giant radio H II regions exhibits a strong maximum at a galactocentric distance R roughly 300 arcsec. Unless molecular hydrogen in M81 is also concentrated near R roughly 300 arcsec, the data disagree with Visser's (1980) model for star formation associated with a density wave. Some suggestions are made about how to change the ballistic particle model of Leisawitz and Bash to agree with the observed radial distribution of giant radio H II regions.

Kaufman, Michele↗
NASA NTRS1987

Shuttle II

This paper presents a status report on the study of a next-generation manned launch system, called Shuttle II, being conducted at the NASA Langley Research Center. Underlying reasons for considering such a system include the need for low-cost, safe, and reliable manned access to space. System and operational characteristics for a Shuttle II vehicle are presented. The need for fully reusable launch systems with radically simpler ground and flight operations is stated to be critical in reducing launch costs. Advancing technologies have a major impact on the choice of vehicle concepts. For a near-term level of technology, a two-stage vertical-takeoff rocket vehicle has been selected for further in-depth Shuttle II studies. The role of the Shuttle II vehicle in a proposed space transportation system, which includes heavy lift and Space Shuttle complementary manned systems, is discussed.

Talay, T. A.↗