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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Time-resolved spectroscopy and photometry of the eclipsing AM Herculis binary EXO 033319 - 2554.2

Time-resolved optical observations of the eclipsing AM Herculis binary EXO 033319 - 2554.2 are presented. High-speed photometry of an eclipse is presented and used to derive a new ephemeris for the system and to estimate the size of the region responsible for the cyclotron emission. Optical spectra that span the orbital cycle are presented, the cyclotron emission in these spectra is discussed, and the flux and radial velocity variations of H-beta, H-gamma, and He II 4686 A are examined. Models of the flux and radial velocity variations of the emission lines indicate that about half the line emission comes from low-velocity material that is about 1.4 x 10 to the 10th cm from the white dwarf. The rest comes from high-velocity material that is about 10 to the 10th cm from the white dwarf and is moving toward it at about 600 km/s.

Allen, Richard G.↗
NASA NTRS1989

Finite element simulations of thermosolutal convection in vertical solidification of binary alloys

Dendritic vertical solidification of a binary alloy is modeled using the finite element method to assess the effect of thermosolutal convection in macrosegregation. The mathematical model assumes steady-state solidification with a planar, undeformable surface defined by the dendrite tips and the eutectic isotherm. The dendritic region is assumed to advance at a constant solidification velocity v. The stability of the modeled system has been investigated and nonlinear calculations performed that show finger-like convection when the system is unstable. Results for lead-tin alloys show that when the system is unstable, convection is only significant in the uppermost part of the mush and is entirely driven by convection in the bulk fluid.

Heinrich, J. C.↗
NASA NTRS1988

Simultaneous Exosat and VLA observations of the W UMa binaries, VW Cep and XY Leo - A flare on VW Cep

Two UMa-type contact binaries, XY Leo and VW Cep, have been observed simultaneously with Exosat, the VLA, and, in the case of XY Leo, optically. The temporal coverage of each star was sufficient to monitor them throughout two orbital revolutions (P about 0.25 days), however, no orbital modulation of either the X-ray or 6-cm data was seen for either star. A large flare from VW Cep was detected, the first such simultaneous flare ever seen on a star other than the sun. Its behavior before, during, and after the flare is remarkably similar to that found in solar flares. For both stars, it is demonstrated that the 6-cm emission cannot be the result of bremsstrahlung radiation of the X-ray emitting plasma.

Vilhu, Osmi↗
NASA NTRS1989

A survey of the radio continuum emission of RS Canum Venaticorum and related active binary systems

Observations of 77 RS CVn and related active binary systems were made with VLA at a continuum frequency of 4.86 GHz. The results are combined with other VLA observations to produce a total number of observed sources of 122. A search for correlations of radio properties with various systemic and stellar parameters is performed. Significant correlations are found between the normalized radio luminosity L(6)/L(bol) and the normalized soft X-ray luminosity L(x)/L(bol). It is suggested that the close correlation between low-level 6-cm emission and the hot component of the soft X-ray emission observed by the Einstein solid state spectrometer is caused by both emissions being produced by the same thermal electrons.

Drake, Stephen A.↗
NASA NTRS1989

Optical observations of the unusual interacting binary V644 Monocerotis (HD 51480)

New optical spectroscopic and UBV photometric observations of the bright Be/shell star V644 Mon (HD 51480) are presented. The object, which has been described as an interacting binary system, exhibits strong, variable Balmer emission as well as numerous metallic emission features in the blue. No signs of absorption features due to any late-type companion are seen at wavelengths below 6500 A.

Bopp, Bernard W.↗
NASA NTRS1990

Photometric and spectroscopic modeling of starspots on the RS Canum Venaticorum binary HD 26337

Results are presented on photometric and spectroscopic observations made in 1987-1988 on the rapidly rotating G5 subgiant in the single-lined RS CVn binary HD 26337. Results show the existence of a cool polar spot on HD 26337, which is rather long lived, persisting at least the nine years of the photometry observations. The polar spot contributes only insignificantly to the light curve amplitude, but is crucial for the overall brightness of the system. Evidence is also found for extremely rapid light curve shape variations on a time scale of only one or two rotation cycles. These changes could be modeled by rapidly decreasing a spot area.

Strassmeier, Klaus G.↗
NASA NTRS1989

Distortion range of filter synthetic discriminant function binary phase-only filters

This paper considers the performance of filter synthetic-discriminant-function binary-phase-only filters (fSDF-BPOFs) with images in the distortion range that were not members of the training set. This evaluation was performed to understand better the distortion range that can be effectively covered by fSDF-BPOFs. The peak correlation and peak clutter responses were measured over various distortion ranges for in-plane and out-of-plane rotations. The peak correlation initially decreased rapidly as the distortion range increased but decreased gradually as the distortion range became larger for the images used in this study. The distortion ranges that can be effectively covered by fSDF-BPOFs appear to be modest: 0-30 deg for in-plane rotation and 0-10 deg for out-of-plane rotation. The results indicate that a temporal multiplexing scheme will be required to cover a large distortion range when BPOFs are used.

Jared, David A.↗
NASA NTRS1990

Symmetrical jet action in the R Aquarii binary system

Collimated mass flow in opposite directions is detected in the R Aqr binary-system jet by means of high-resolution long-slit spectroscopy of several optical emission lines. Also presented are images of the jet structure in the forbidden line of O III, which clearly show bipolar symmetry extending to distances of about 2750 AU on either side of the central Mira variable. The Mira light was greatly reduced by utilization of a vignetting disk on the window of the imaging CCD. This result confirms the recent report of morphological evidence for an R Aqr jet from the detection of bipolar radio continuum emission at 6 cm, and provides the necessary kinematical evidence to show that jet action is actually taking place.

Hollis, J. M.↗
NASA NTRS1990

Long-wave morphological instabilities in the directional solidification of a dilute binary mixture

Long-wave instabilities in a directionally-solidified binary mixture may occur in several limits. Sivashinsky (1983) identified a small-segregation-coefficient limit and obtained a weakly nonlinear evolution equation governing subcritical two-dimensional bifurcation. Brattkus and Davis (1988) identified a near-absolute-stability limit and obtained a strongly nonlinear evolution equation governing supercritical two-dimensional bifurcation. The present investigation identifies a third strongly nonlinear evolution equation, arising in the small-segregation-coefficient, large-surface-energy limit. This equation links both of the former and describes the change from the sub- to super-critical bifurcations. This study sets the previous long-wave analyses into a logical framework.

Riley, D. S.↗
NASA NTRS1990

Orbital variability in the wind of the massive X-ray binary HD 153919/4U 1700-37

A set of forty high-dispersion IUE spectra of HD 153919, the Of-type primary in the 4U 1700-37 X-ray binary system, have been examined for evidence of orbital profile variability associated with the Hatchett-McCray effect. Although the effect is negligible in the resonance lines of C IV, Si IV, and N V, some subordinate lines show clear orbital changes. The variability in the absorption profile of N IV 1718, in particular, is shown to be in agreement with model calculations. The interstellar spectrum is studied, showing that highly ionized species can be maintained by the primary's radiation field alone.

Hammerschlag-Hensberge, G.↗
NASA NTRS1990

HD 43246 and HD 127208 - Two unusual F-G + B binary systems

New optical spectroscopic observations along with ultraviolet IUE observations have been obtained for the two interacting F or G III + B V binaries: HD 43246 and HD 127208. Photometric observations indicate random changes superimposed on regular ellipsoidal light variations, the latter probably the result of tidal distortion of the giant primaries. Mass transfer and loss is apparent in inverted mass ratios derived from orbital analysis, strong wind features present in the spectra, and the presence of circumsystem shells. Regular and irregular changes in the spectral features are discussed in this context.

Dempsey, Robert C.↗
NASA NTRS1990

Discovery of a cyclotron absorption line in the spectrum of the binary X-ray pulsar 4U 1538 - 52 observed by Ginga

A cyclotron absorption line near 20 keV has been found in the spectrum of the massive eclipsing binary X-ray pulsar 4U 1538 - 52 in observations with the Ginga observatory. The line is detected throughout the 529 s pulse cycle with a variable equivalent width that has its maximum value during the smaller peak of the two-peak pulse profile. It is found that the profile of the pulse and the phase-dependence of the cyclotron line can be explained qualitatively by a pulsar model based on recent theoretical results on the properties of pencil beams emitted by accretion-heated slabs of magnetized plasma at the magnetic poles of a neutron star. The indicated field at the surface of the neutron star is 1.7 (1 + z) x 10 to the 12th G, where z is the gravitational redshift.

Clark, George W.↗
NASA NTRS1989

Associative memory - An optimum binary neuron representation

Convergence mechanism of vectors in the Hopfield's neural network is studied in terms of both weights (i.e., inner products) and Hamming distance. It is shown that Hamming distance should not always be used in determining the convergence of vectors. Instead, weights (which in turn depend on the neuron representation) are found to play a more dominant role in the convergence mechanism. Consequently, a new binary neuron representation for associative memory is proposed. With the new neuron representation, the associative memory responds unambiguously to the partial input in retrieving the stored information.

Awwal, A. A.↗
NASA NTRS1989

On the separations of common proper motion binaries containing white dwarfs

It is expected, on the basis of proper motion and estimated colors, that over 500 known common proper motion binaries (CPMBs) contain at least one white dwarf (WD) component, usually paired with a late type main sequence (MS) star. This paper examines 210 probable MS + MS and 26 probable WD + MS pairs from the LDS catalog to determine whether significant orbital expansion occurred as a consequence of the post-MS mass loss expected to accompany the formation of WDs in the CPMBs. It was found that, in the WD + MS pairs, the physical separation is nearly twice that in the MS + MS pairs.

Oswalt, T. D.↗
NASA NTRS1990

Apparent orbit of the spectroscopic binary Beta Arietis with the time Mark III Stellar Interferometer

The spectroscopic binary Beta Ari has been directly resolved with the Mark III Stellar Interferometer. Observations in 1988 were analyzed to determine the visual orbit of the system with the following results: eccentricity = 0.903 +/- 0.012, semimajor axis = 0.0361 +/- 0.0003 arcsec, inclination = 44.7 +/- 1.3 deg, longitude of periastron = 209.1 deg +/- 1.2 deg, position angle of ascending node = 79.1 deg +/- 0.8 deg. The measured magnitude difference between two components, Delta m = 2.63 +/- 0.22 at 800 nm, yields individual visual magnitudes of m(v1) = 2.70 +/- 0.02 and m(v2) = 5.80 +/- 0.20. Combined with data from spectroscopic observations, masses M1 = (2.34 +/- 0.10) solar masses, M2 = (1.34 +/- 0.07) solar masses, and geometrical parallax pi = 0.053 arcsec +/- 0.002 arcsec are derived. These results demonstrate that both components of Beta Ari agree well with the empirical mass-luminosity relation.

Pan, X. P.↗
NASA NTRS1990

Is the Coma cluster binary dominated?

It is investigated whether the model of an expanding cluster dominated by a massive binary galaxy, first suggested by Valtonen and Byrd (1979), is consistent with optical data on the surface density and velocity dispersion of the Coma cluster. The evolution of this model is simulated for a wide variety of initial conditions. It is found that galaxy counts in the model can be made to agree with observation, but that the observed velocity dispersion profile cannot be reproduced. A number of other arguments suggest that the central galaxies in Coma cannot be as massive as required by the model. This model is not a viable representation of the Coma cluster.

The, Lih Sin↗
NASA NTRS1990

The long-period binary AL Velorum - The atmospheric eclipse of a bright K0 giant

The properties of the AL Vel binary system, a Zeta Aur system containing a B dwarf and a bright K0 giant, are reviewed with reference to IUE observations of its atmospheric eclipse and eclipse of the accretion disk around the B-dwarf component. It is found that the conditions in the chromosphere are rather similar to those in the Zeta Aur supergiants, once allowance is made for the different sizes and scale heights involved. The conditions for Mg II suppression in the wind through ionization by the B star is discussed, and it is found that radiative excitation and subsequent ionization will suffice for the conditions encountered in the AL Vel system.

Eaton, Joel A.↗
NASA NTRS1991

Orthogonal Patterns In A Binary Neural Network

Report presents some recent developments in theory of binary neural networks. Subject matter relevant to associate (content-addressable) memories and to recognition of patterns - both of considerable importance in advancement of robotics and artificial intelligence. When probed by any pattern, network converges to one of stored patterns.

Baram, Yoram↗