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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The binary weight distribution of the extended (2 sup m, 2 sup m-4) code of Reed-Solomon code over GF(2 sup m) with generator polynomial (x-alpha sup 2) (x-alpha sup 3)

Consider an (n,k) linear code with symbols from GF(2 sup m). If each code symbol is represented by a binary m-tuple using a certain basis for GF(2 sup m), a binary (nm,km) linear code called a binary image of the original code is obtained. A lower bound is presented on the minimum weight enumerator for a binary image of the extended (2 sup m, 2 sup m -4) code of Reed-Solomon code over GF(2 sup m) with generator polynomical (x - alpha)(x- alpha squared)(x - alpha cubed) and its dual code, where alpha is a primitive element in GF(2 sup m).

Lin, Shu↗
NASA NTRS1986

Origin and evolution of X-ray binaries in globular clusters

The theoretical model developed by Grindlay (1984 and 1985) and Grindlay and Hertz (1985) to explain the relative numbers of low-luminosity and high-luminosity X-ray sources in Galactic globular clusters is briefly characterized, and the relevant observational evidence is summarized. In the model, high-rate mass transfer onto white dwarfs in about 1 percent of the low-luminosity binary sources produces neutron stars, which then form compact high-luminosity X-ray binaries (by tidal capture in the dense cluster cores); these in turn evolve into hierarchical triple systems. Evidence considered includes observations of the high-luminosity giant-fed X-ray binary in M 15, the results of searches for CVs in globulars, comparisons of X-ray-binary and host-globular evolution, and indications that GX 17 + 2 is a bound triple.

Grindlay, Jonathan E.↗
NASA NTRS1986

Head-on binary collisions in globular clusters

Collision probabilities between identical binaries of three different binding energies are computed for binaries in the cores of globular clusters. The more tightly bound a binary is, the smaller the chance is that it suffers a collision. It is found that a given binary in a globular cluster core probably does not suffer more than a very few collisions. If it is not broken up into single stars, it will become so tightly bound that collisions involving it are very rare. Since it is found that head-on collisions are so rare, the collisions which are probably more important in affecting the evolution of the cluster core are the long-range (large impact parameter) encounters.

Hoffer, James B.↗
NASA NTRS1987

Evolution of magnetic cataclysmic binaries

The physics of magnetic cataclysmic binary evolution is considered, and it is suggested that DQ Her stars will not evolve into AM Her stars (assuming that mu1 remains constant throughout their evolution), in contradiction to previous assertions. Four regimes that depend on mu1 values are identified, and it is suggested that the mu1 values of the known DQ Her stars are significantly less than those of the known AM Her stars (unless all known stars of both groups have M1 greater than 1 solar mass). A new way of producing ultrashort period binaries is proposed in which synchronization of the magnetic degenerate dwarfs injects angular momentum into the binary, driving the system apart and producing a synchronization-induced period gap. The secondaries in these binaries are shown to be hydrogen-rich rather than hydrogen depleted or pure helium.

Lamb, D. Q.↗
NASA NTRS1988

A catalog of chromospherically active binary stars

A catalog of 168 chromospherically active binary stars is presented, including the class of RS CVn, BY Dra binaries, and other binaries which show strong Ca II H and K emission in their spectra. The catalog contains information on the photometric, spectroscopic, orbital, and physical properties of the systems as well as the space motions and positions. Summarized in a candidate list are in additional 37 stars having similar characteristics but which are not definitely known binaries or have not had H and K emission observed. The catalog contains stars in both the northern and the southern sky.

Strassmeier, K. G.↗
NASA NTRS1988

Binary stars - Formation by fragmentation

Theories of binary star formation by capture, separate nuclei, fission and fragmentation are compared, assessing the success of theoretical attempts to explain the observed properties of main-sequence binary stars. The theory of formation by fragmentation is examined, discussing the prospects for checking the theory against observations of binary premain-sequence stars. It is concluded that formation by fragmentation is successful at explaining many of the key properties of main-sequence binary stars.

Boss, Alan P.↗
NASA NTRS1987

New developments in studies of compact X-ray binaries

Several recent developments, both observational and theoretical, on the study of X-ray binaries and the compact objects they contain are discussed. The recent discovery of the first binary periods for the globular cluster X-ray sources has stimulated a new model for their origin. As a variant of the 'standard' tidal capture origin model, this predicts an enhanced number of neutron stars in globular clusters. Long term timing studies of X-ray binaries may be consistent with many of these systems, primarily X-ray burst sources, being in fact hierarchical triple systems. Finally, the radio studies of Cyg X-3 and other X-ray binaries suggest that nonthermal processes are as important, energetically, as accretion processes in these systems.

Grindlay, Jonathan E.↗
NASA NTRS1989

Masses and the evolution of Wolf-Rayet binaries

Recent polarimetric observations have provided inclinations of double-line spectroscopic binary systems containing Wolf-Rayet stars with O star companions. Therefore, reasonably accurate masses of ten Wolf-Rayet stars in binaries are now known. These data are compared to evolutionary models of massive close binaries based on the scenario that O + O systems evolve into WR + O systems. Good agreement is found between the observations and nonconservative binary models with classical cores for the observed range of contemporary masses. The models with large convective-core overshooting fail to describe systems with Wolf-Rayet stars having observed masses larger than about 10 solar masses.

Schulte-Ladbeck, Regina E.↗
NASA NTRS1990

Trompe L'Oeil 'binary' pulsars

A freely precessing pulsar produces pulse phase residuals which can mimic those of a pulsar in a binary orbit. In particular, discrete sets of phase residuals due to precessional motion of an isolated pulsar are sampled; it is shown that this data is well fit by residuals from a binary pulsar in a sufficiently tight orbit. Analytic and numerical relationships between the projected orbital size, a(p) sin i, and the orbital eccentricity, e, of a misidentified binary pulsar; are found the observations that would distinguish between these models are discussed. Regardless of the mechanism that causes the precession, the maximum amplitude of the phase residual is pi/2: consequently, a(p)sin i is (approximately) bounded by cP(puls)/4. The newly discovered 'binary' millisecond pulsars in the globular cluster 47 Tuc is discussed, and it is shown that the periodic frequency modulation reported cannot be explained by free precession.

Nelson, Robert W.↗
NASA NTRS1989

Laboratory comparison of continuous vs. binary phase-mostly filters

Recent developments in spatial light modulators have led to devices which are capable of continuous phase modulation, even if only over a limited range. One of these devices, the deformable mirror device is used, to compare the relative merits of binary and partially-continuous phase filters in a specific problem of pattern recognition by optical correlation. Each filter was physically limited to only about a radiation of modulation. Researchers have predicted that for low input noise levels, continuous phase-only filters should have a higher absolute correlator peak output than the corresponding binary filters, as well as having a larger SNR. When continuous and binary filters were implemented on the DMD and they exhibited the same performance; an ad hoc filter optimization procedure was developed for use in the laboratory. The optimized continuous filter gave higher correlation peaks than did an independently optimized binary filter. Background behavior in the correlation plane was similar for the two filters, and thus the SNR showed the same improvement for the continuous filter. A phasor diagram analysis and computer simulation have explained part of the optimization procedure's success.

Monroe, Stanley E., Jr.↗
NASA NTRS1990

Acceleration by pulsar winds in binary systems

In the absence of accretion torques, a pulsar in a binary system will spin down due to electromagnetic dipole radiation, and the spin-down power will drive a wind of relativistic electron-position pairs. Winds from pulsars with short periods will prevent any subsequent accretion but may be confined by the companion star atmosphere, wind, or magnetosphere to form a standing shock. This paper investigates the possibility of particle acceleration at such a pulsar wind shock and the production of VHE and UHE gamma-rays from interactions of accelerated protons in the companion star's wind or atmosphere. It is found that, in close binaries containing active pulsars, protons will be shock accelerated to a maximum energy dependent on the pulsar spin-down luminosity. If a significant fraction of the spin-down power goes into particle acceleration, these systems should be sources of VHE and possibly UHE gamma-rays. The application of the pulsar wind model to binary sources such as Cygnus X-3 is discussed, as well as the possibility of observing VHE gamma-rays from known binary radio pulsar systems.

Harding, Alice K.↗
NASA NTRS1990

Acceleration by pulsar winds in binary systems

In the absence of accretion torques, a pulsar in a binary system will spin down due to electromagnetic dipole radiation and the spin-down power will drive a wind of relativistic electron-positron pairs. Winds from pulsars with short periods will prevent any subsequent accretion but may be confined by the companion star atmosphere, wind, or magnetosphere to form a standing shock. The authors investigate the possibility of particle acceleration at such a pulsar wind shock and the production of very high energy (VHE) and ultra high energy (UHE) gamma rays from interactions of accelerated protons in the companion star's wind or atmosphere. They find that in close binaries containing active pulsars, protons will be shock accelerated to a maximum energy dependent on the pulsar spin-down luminosity. If a significant fraction of the spin-down power goes into particle acceleration, these systems should be sources of VHE and possibly UHE gamma rays. The authors discuss the application of the pulsar wind model to binary sources such as Cygnus X-3, as well as the possibility of observing VHE gamma-rays from known binary radio pulsar systems.

Harding, Alice K.↗
NASA NTRS1990

Selection effects and binary galaxy velocity differences

Measurements of the velocity differences (delta v's) in pairs of galaxies from large statistical samples have often been used to estimate the average masses of binary galaxies. A basic prediction of these models is that the delta v distribution ought to decline monotonically. However, some peculiar aspects of the kinematics have been uncovered, with an anomalous preference for delta v approx. equal to 72 km s(sup-1) appearing to be present in the data. The authors examine a large sample of binary galaxies with accurate redshift measurements and confirm that the distribution of delta v's appears to be non-monotonic with peaks at 0 and approx. 72 km s (exp -1). The authors suggest that the non-zero peak results from the isolation criteria employed in defining samples of binaries and that it indicates there are two populations of binary orbits contributing to the observed delta v distribution.

Schneider, Stephen E.↗
NASA NTRS1990

Optical observations of close binaries with the Mark III Stellar Interferometer

For the first time, four spectroscopic binaries have been directly resolved with the Mark III Stellar Interferometer. Observations in 1988 and 1989 were analyzed, and visual orbits for four binaries have been determined. The semimajor axes for Beta Tri, Alpha Equ, Alpha And and Beta Ari are approximately 0.008 arcsec, 0.012 arcsec, 0.024 arcsec and 0.037 arcsec, respectively. The magnitude differences between two components are 0.5, 0.7, 1.8 and 2.6 mag, respectively. All of the orbital elements for Alpha And and Beta Ari were determined from interferometric data only, and agree well with spectroscopic observations. Predictions of relative position between the two components for these binaries are consistent with the measurements to less than 0.001 arcsec. Combined with data from spectroscopy, masses and distance for the double-lined spectroscopic binary Beta Ari are derived, and the results indicate that both components of Beta Ari agree well with the empirical mass-luminosity relation.

Pan, X. P.↗
NASA NTRS1992

Binaries in globular clusters

Recent observations have shown that globular clusters contain a substantial number of binaries most of which are believed to be primordial. We discuss different successful optical search techniques, based on radial-velocity variables, photometric variables, and the positions of stars in the color-magnitude diagram. In addition, we review searches in other wavelengths, which have turned up low-mass X-ray binaries and more recently a variety of radio pulsars. On the theoretical side, we give an overview of the different physical mechanisms through which individual binaries evolve. We discuss the various simulation techniques which recently have been employed to study the effects of a primordial binary population, and the fascinating interplay between stellar evolution and stellar dynamics which drives globular-cluster evolution.

Hut, Piet↗
NASA NTRS1993

Upper limits for gravitational radiation from supermassive coalescing binaries

We report a search for waves from supermassive coalescing binaries using a 10.5 day Pioneer 10 data set taken in 1988. Depending on the time to coalescence, the initial frequency of the wave, and the length of the observing interval, a coalescing binary waveform appears in the tracking record either as a sinusoid, a 'chirp', or as a more complicated signal. We searched our data for coalescing binary waveforms in all three regimes. We successfully detected a (fortuitous) 'chirp' signal caused by the varying spin rate of the spacecraft; this nicely served as a calibration of the data quality and as a test of our analysis procedures on real data. We did not detect any signals of astronomical origin in the millihertz band to an upper limit of about 7 x 10 exp -15 (rms amplitude). This is the first time spacecraft Doppler data have been analyzed for coalescing binary waveforms, and the upper limits reported here are the best to date for any waveform in the millihertz band.

Anderson, J. D.↗
NASA NTRS1993

Wind-driven angular momentum loss in binary systems. I - Ballistic case

We study numerically the average loss of specific angular momentum from binary systems due to mass outflow from one of the two stars for a variety of initial injection geometries and wind velocities. We present results of ballistic calculations in three dimensions for initial mass ratios q of the mass-losing star to primary star in the range q between 10 exp -5 and 10. We consider injection surfaces close to the Roche lobe equipotential surface of the mass-losing star, and also cases with the mass-losing star underfilling its Roche lobe. We obtain that the orbital period is expected to have a negative time derivative for wind-driven secular evolution of binaries with q greater than about 3 and with the mass-losing star near filling its Roche lobe. We also study the effect of the presence of an absorbing surface approximating an accretion disk on the average final value of the specific angular momentum loss. We find that the effect of an accretion disk is to increase the wind-driven angular momentum loss. Our results are relevant for evolutionary models of high-mass binaries and low-mass X-ray binaries.

Brookshaw, Leigh↗
NASA NTRS1993

Spectroscopic observations of V443 Herculis - A symbiotic binary with a low mass white dwarf

We present an analysis of new and existing photometric and spectroscopic observations of the symbiotic binary V443 Herculis. This binary system consists of a normal M5 giant and a hot compact star. These two objects have comparable luminosities: about 1500 solar for the M5 giant and about 1000 solar for the compact star. We identify three nebular regions in this binary: a small, highly ionized volume surrounding the hot component, a modestly ionized shell close to the red giant photosphere, and a less dense region of intermediate ionization encompassing both binary components. The system parameters for V443 Her suggest the hot component currently declines from a symbiotic nova eruption.

Dobrzycka, Danuta↗