Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ScO”

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.

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

At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Balloon observations of hard X-rays from some galactic X-ray sources

An X-ray telescope consisting of 400 cm phoswich detectors (NaI(T1)/CsI(Na)) was flown from Hyderabad (India) on 18 December 1984. The field of view was 5 deg x 5 deg FWHM. In a 10 hour float at 4 MB several galactic X-ray sources were tracked by the telescope using an on-board microprocessor. Fluxes and spectra in 18-120 keV X-rays for SCO X-1, GX 1+4, Gx 5-1, GX 17+2, SCT X-1, CYC X-1 an CYG X-3 will be presented.

Damle, S. V.↗
NASA NTRS1985

Quasiperiodic oscillations in bright galactic-bulge X-ray sources

Quasiperiodic oscillations with frequencies in the range 5-50 Hz have recently been discovered in X-rays from two bright galactic-bulge sources and Sco X-1. These sources are weakly magnetic neutron stars accreting from disks which the plasma is clumped. The interaction of the magnetosphere with clumps in the inner disk causes oscillations in the X-ray flux with many of the properties observed.

Lamb, F. K.↗
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

Atlas of Saturn's rings

A preliminary summary is made from a compilation of Voyager Saturn ring data. The data base includes optical thickness radial profiles at 3.6 and 13.6 cm radio wavelength measurements, 1300 and 2640 A occultations of delta Sco, albedos in the 3000-6000 A range, time and azimuthal resolved albedo profiles, particle impacts in the G ring, and number densities of magnetospheric charged particles. Sample data tracks are provided for the A, C, and D rings and the Cassini division. Finally, the trajectory of the Voyager 2 pass through the ring system is plotted.

Collins, S. A.↗
NASA NTRS1985

Interstellar Medium Absorption Profile Spectrograph (IMAPS)

The design and fabrication of an objective-grating echelle spectrograph to fly on sounding rockets and record spectra of stars from approximately 920 to 1120A with a resolving power lambda/delta lambda = 200,000 is discussed. The scientific purpose of the program is to observe, with ten times better velocity resolution than before, the plentiful absorption lines in this spectral region produced by atoms, ions and molecules in the interstellar medium. In addition, an important technical goal is to develop and flight-quality a new ultraviolet, photon-counting image sensor which has a windowless, opaque photocathode and a CCD bombarded directly by the accelerated photoelectrons. Except for some initial difficulties with the performance of CCDs, the development of the payload instrument is relatively straightforward and our overall design goals are satisfied. The first flight occurred in late 1984, but no data were obtained because of an inrush of air degraded the instrument's vacuum and caused the detector's high voltage to arc. A second flight in early 1985 was a complete success and obtained a spectrum of pi Sco. Data from this mission are currently being reduced; quick-look versions of the spectra indicate that excellent results will be obtained. Currently, the payload is being reconfigured to fly on a Spartan mission in 1988.

Jenkins, E. B.↗
NASA NTRS1985

Quasi-periodic oscillations in bright galactic-bulge X-ray sources

Quasiperiodic oscillations with frequencies in the range 5-50 Hz have recently been discovered in X-rays from two bright galactic-bulge sources and Sco X-1. These sources are weakly magnetic neutron stars accreting from disks in which the plasma is clumped. The interaction of the magnetosphere with clumps in the inner disk causes oscillations in the X-ray flux with many of the properties observed.

Lamb, F. K.↗
NASA NTRS1986

The Cepheid mass problem and Cepheid binaries

Existing mass determinations for Cepheids with different periods are examined. Wesselink masses are independent of the adopted distance scale. For short periods (less than 6 days) they follow the sequence of evolutionary masses. For periods longer than 10 days they are lower by up to a factor of 2. The lower mass branch joins up with the bump masses. The new pulsational masses agree with the Wesselink masses for periods longer than 6 days. Cepheid masses determined by means of their giant companions also agree with the Wesselink masses and the new pulsational masses. While the error bars are large, the derived dynamical masses determined for S Mus and V636 Sco also agree with the low Wesselink and giant companion masses.

Bohm-Vitense, E.↗
NASA NTRS1986

Intersstellar absorption lines between 2000 and 3000 A in nearby stars observed with BUSS

Spectra obtained between 2000 and 3000 A with the Balloon Borne Ultraviolet Spectrophotometer (BUSS) payload were examined for interstellar absorption lines. In bright stars, with spectral types between O9V and F5V, such lines were measured of Mg I, Mg II, Cr II, Mn II, Fe II and Zn II, with Cr II and Zn II data of especially high quality. Column densities were derived and interstellar abundances were determined for the above species. It was found that metal depletion increases with increasing E(B-V); Fe was most affected and Zn showed a small depletion for E(B-V) greater than 0.3 towards Sco-Oph. The metal column densities, derived for Alpha-And, Kappa-Dra, Alpha-Com, Alpha-Aql, and 29 Cyg were used to infer N(H I). It was shown that the ratio of Mg I to Na I is instrumental in determining the ionization structure along each line of sight. The spectra of Aql stars confirms the presence of large gas densities near Alpha-Oph. Moreover, data indicated that the Rho-Oph N(H I) value needs to be altered to 35 x 10 to the 20th/sq cm, based on observed ion ratios and analysis of the Copernicus L-alpha profile.

De Boer, K. S.↗
NASA NTRS1986

Discovery of rapid quasi-periodic oscillations in Scorpius X-1

The X-ray flux from Sco X-1 can vary quasi-periodically. Fourier analysis of 5-20 keV X-ray data taken while the source was quiescent shows a power density peak at 6 Hz, with a 2 Hz FWHM, and which corresponds to 5 percent of the flux (rms amplitude). No 6 Hz peak was observed when the source was more active, but rather a broad distribution of excess power up to 25 Hz was seen. The mode of variability switched from one to the other within 500 s, settling into the 6 Hz mode about 1 hr into quiescence. A different mode of quasi-periodic oscillation with power in a broad band between 14 and 24 Hz, corresponding to a 6 percent rms amplitude, occurred for short periods during the active phase whenever the flux reached the quiescent level.

Middleditch, J.↗
NASA NTRS1986

Potential medical applications of TAE

In cooperation with scientists in the University of Washington Medical School, a microcomputer-based image processing system for quantitative microscopy, called DMD1 (Digital Microdensitometer 1) was constructed. In order to make DMD1 transportable to different hosts and image processors, we have been investigating the possibility of rewriting the lower level portions of DMD1 software using Transportable Applications Executive (TAE) libraries and subsystems. If successful, we hope to produce a newer version of DMD1, called DMD2, running on an IBM PC/AT under the SCO XENIX System 5 operating system, using any of seven target image processors available in our laboratory. Following this implementation, copies of the system will be transferred to other laboratories with biomedical imaging applications. By integrating those applications into DMD2, we hope to eventually expand our system into a low-cost general purpose biomedical imaging workstation. This workstation will be useful not only as a self-contained instrument for clinical or research applications, but also as part of a large scale Digital Imaging Network and Picture Archiving and Communication System, (DIN/PACS). Widespread application of these TAE-based image processing and analysis systems should facilitate software exchange and scientific cooperation not only within the medical community, but between the medical and remote sensing communities as well.

Fahy, J. Ben↗
NASA NTRS1986

Voyager 2 photopolarimeter experiment - Evidence for tenuous outer ring material at Saturn

Voyager 2 photopolarimeter data are employed to characterize two regions of optically thin material outside the Saturn F ring. The study consists of a statistical analysis of optical depth value fluctuations caused by occultations of starlight from Delta Sco as viewed through the material. One the optically thin regions surrounds the orbital semimajor axis of the outer F ring shepherd satellite Pandora and the other thin region lies 144,090 km farther outward. The first region, with an optical depth of 0.008-0.016, is about 200 km in radius and the second, with an optical depth of 0.005-0.013, is about 1000 km in radial width. The data had a resolution of 0.5 km.

Graps, A. L.↗
NASA NTRS1986

The interstellar carbon abundance. II - Rho Ophiuchi and Beta Scorpii

A procedure designed to obtain increased sensitivity from high-dispersion IUE spectra by using a flat-field spectrum to remove nonrandom noise due to the response pattern of the SEC vidicon detector is described. Application of this procedure to spectra of Rho Oph and Beta(1) Sco near the spin-forbidden interstellar 2325 line of C II yields 2 sigma upper limits on absorption of W (lambda) not greater than about 4 mA. The resulting depletion of carbon from the interstellar gas toward Rho Oph exceeds a factor of 1.4.

Welty, D. E.↗
NASA NTRS1986

Quasi-periodic oscillations as a probe of galactic-bulge X-ray sources

Quasi-periodic oscillations (QPOs) with frequencies in the range 5-50 Hz have recently been discovered in X-rays from two bright galactic-bulge sources and from Sco X-1. A shot-noise model that provides a mathematical framework for analyzing the constraints imposed on physical models by the observed power density spectra is described. A variety of physical models are then examined briefly. One of the most promising, the beat-frequency-modulated accretion model, is adopted as a working hypothesis to consider the clues it may provide concerning the galactic-bulge sources. Finally, some key observations are noted.

Lamb, F. K.↗
NASA NTRS1987

VLA observations of rapid 6 cm flux variations in alpha Ori

The red supergiant star alpha Ori was monitored with the Very Large Array (VLA). Thirteen observations at 6 cm show stochastic variations, at the 30 to 40 percent level, with no long term trend. All data was clipped and tapered in AIPS to minimize differences between VLA arrays. The calibration source varied by less than 10 percent over the same interval. The VLA observations of alpha Ori were continued, as well as alpha Her and alpha Sco, at both 2 and 6 cm, to confirm this result and search for long term trends. The stochastic 6 cm flux behavior, with 30 to 40 percent changes on all timescales from the shortest interval of 10 days to the longest, seems at odds with the 400 day periodic variations in U-band photometry and Mg II UV fluxes reported by Dupree, et al. The observed 6 cm flux was 25 percent below the 6 cm flux reported earlier this decade. Several models for the outer atmosphere of alpha Ori place the 6 cm optical depth unity location at several stellar radii above the optical photosphere. The rapid, stochastic variations reported are difficult to reconcile with almost any global process, such as pulsation, Alfven waves or periastron passage.

Bookbinder, J. A.↗
NASA NTRS1987

Identification of lines in the satellite ultraviolet - The spectrum of Tau Scorpii

The method of wavelength coincidence statistics (WCS) is applied to the ultraviolet spectra of Tau Sco obtained by the IUE. No identifications of elements heavier than Zn were made. With the exception of Zn IV, all identifications had been previously made in an exhaustive study of Copernicus spectra by Rogerson and Ewell (1985). A comparison of the identifications made in the two studies is in very good agreement for those spectra rich in lines, where the WCS parameters indicate the strong presence of the species. Useful information is added by WCS in cases where species are only weakly, or arguably, present. It is shown that WCS is an important tool in the exploration of any complicated stellar spectrum, and even in the case of a spectrum that has been well studied by traditional methods, it adds important information.

Cowley, Charles R.↗
NASA NTRS1989

Variability of X-ray emission from OB stars

The variability in soft X-ray emission of 12 OB stars is studied. Two different methods of analysis, one more suitable for detecting short-term variations, the other aimed at detecting long time-scale variations, are applied to all stars in the sample. The long-term variability analysis shows that Cyg-OB2 8A Zeta Pup and Delta Ori exhibit significant count rate variations between different data sections. Similar variations are marginally detected in 15 Mon; the count rate variations for the other eight stars are consistent with statistical fluctuations. The light curve of Cyg-OB2 8A suggests the existence of two different emission levels. The short-term variability analysis detects marginal variability in Tau Sco with an effective amplitude of about 30 percent and a time scale of about 50 s. The upper limits to the effective short-term variability amplitude for all other sample stars are in the 10-30 percent range.

Collura, A.↗
NASA NTRS1989

IRAS observations of dust heating and energy balance in the Rho Ophiuchi dark cloud

The equilibrium process dust emission in the Rho Ophiuchi dark cloud is studied. The luminosity of the cloud is found to closely match the luminosity of the clouds's known embedded and external radiation sources. There is no evidence for a large population of undetected low-luminosity sources within the cloud and unknown external heating is also only a minor source of energy. Most of the cloud's luminosity is emitted in the mid-to-far-IR. Dust temperature maps indicate that the dust is not hot enough to heat the gas to observed temperatures. A simple cloud model with a radiation field composed of flux HD 147889, S1, and Sco OB2 associations predicts the observed IRAS 60 to 100 micron in-band flux ratios for a mean cloud density n(H2) = 1400. Flattened 12 and 25 micron observations show much extended emission in these bands, suggesting stochastic heating of very small grains or large molecules.

Greene, Thomas P.↗
NASA NTRS1989

Velocities and rotational excitation of interstellar H2 toward Pi Scorpii

A spectrum of Pi Sco showing numerous atomic lines and 70 absorption features from the Lyman and Werner transitions of interstellar H2 in rotational level J from zero to five is presented. Their shapes of the composite column density profiles are very nearly Gaussian with a one-dimensional rms velocity dispersion of 3 km/s. The behavior of shifts in the inferred N(H2) as a function of velocity are consistent with the overall profiles being composed of nearly symmetrical, tightly paced assemblies of about seven unresolved components. The relative overall column densities in the higher J levels of H2 are consistent with a model where these states are populated by optical pumping through the Lyman and Werner transitions, powered by UV radiation from nearby stars. The slight narrowing of the high-J profiles may be due to small clumps of H2 at radial velocities some 5-8 km/s from the core of the profile are exposed to a pumping flux about 10 times lower than that for the material near the profile's center.

Jenkins, Edward B.↗