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NASA NTRS1986

Measuring interstellar dust grains from the haloes of binary X-ray sources

A method for determining the location, size distribution, and composition of interstellar dust grains from the haloes of binary X-ray sources is described. The method is based on the time dependence of the halo X-ray emission during an eclipse of the point source. The distance of the dust cloud is inferred directly from observations of the growth of the dark circle around the eclipsed point source. Grain size distribution in the interstellar dust clouds is derived from the halo brightness profile at a given photon energy. The composition of the grains is obtained by observing the spectral features in the total optical depth due to X-ray scattering near the photoionization thresholds of the elements in the grains. The haloes become dim just below the ionization threshold, and sharply increase in function brightness as the photon energy increases beyond the absorption edge of the relevant atom. The method makes it possible to observe and analyze the halo emission during eclipse even without imaging the source. It is suggested that haloes probably account for the soft X-rays observed during eclipses and dips observed in sources including 4U1915-05 and X1755-338.

Xu, Y.↗
NASA NTRS1986

Orbital elements of the binary X-ray pulsar GX 301-2

X-ray outbursts from GX 301-2 were observed with Hakucho on two occasions during April and May 1982 and with Tenma in April 1984. Pulse arrival times measured with Hakucho were combined with those previously measured with Ariel 5 and SAS 3. The joint timing analysis of these data sets yields an orbital period of 41.5 days as the only acceptable solution; this is consistent with the period derived from the X-ray flaring events of the source. The orbital elements of the binary system, established from the joint timing analysis, are presented. The orbital solution suggests that all the peaks of X-ray flares observed during the past 10 yr occur at the orbital period, but consistently appear about 1.4 days before the time of periastron passage of the X-ray star.

Sato, N.↗
NASA NTRS1985

Radio polarization characteristics of two RS CVn binaries

The results of multifrequency epoch VLA observations of polarized radio emission from the nearby active RS CVn binaries UX Arietis and HR 1099 are reported. For both systems, there is an excellent correlation between handedness of circular polarization and frequency. Helicity reversal is almost always seen between 1.4 and 5.0 GHz, possibly due to optical depth effects. There may also be an anticorrelation between total intensity and fractional circular polarization, especially at 5 GHz. This is consistent with models in which intense flares are associated with compact selfabsorbed synchrotron sources, while the quiescent emission arises from larger gyrosynchrotron-emitting plasma.

Mutel, R. L.↗
NASA NTRS1986

Polarization in X-ray binaries

A summary is presented of theoretical and observational characterization of the physical properties of accreting objects which emit X-ray, such as binary systems, through polarimetry of the observed light from the objects. X-ray polarimetry focuses on the accretion disk around secondary object. The electron scattering within the disk was predicted by Chandrasekhar (1946) to be detectable as polarization that varies with the phase of the eclipse between the third and fourth contacts. A relationship is also known to exist between the behavior of the linear polarization and the inclination of the system to the line-of-sight. Sample polarization data from several accreting stellar objects, including suspected black holes, is discussed in terms of the possible physical characteristics of the sources of the radiation.

Dolan, J. F.↗
NASA NTRS1986

On the behavior of double degenerate binaries associated with Type I supernovae

An analytical investigation is performed of the evolution of double degenerate dwarf binary systems into Type I supernovae. The discussion is limited to systems consisting of carbon-oxygen and oxygen-neon-magnesium dwarfs and those composed of two carbon-oxygen dwarfs. The companions spiral together and the secondary, with a mass more than about 0.6 solar mass, fills its Roche lobe. The radius of the secondary increases faster than the Roche lobe due to mass overflow, which becomes unstable. The instability can lead to a Type I explosion and may or may not cause the formation of a neutron star. If a neutron star forms, the secondary, reduced to below 0.6 solar mass, will spiral inward to the primary and eventually be absorbed by the neutron star. If a white dwarf remnant remains after the supernova explosion of the overflow radius, then a second supernova explosion can occur.

Cameron, A. G. W.↗
NASA NTRS1986

Universal amplitude ratios and the interfacial tension near consolute points of binary liquid mixtures

The interfacial tension of the binary liquid mixtures triethylamine/heavy water, triethylamine/water, and cyclohexane/methanol near their consolute temperatures is determined experimentally by measuring the densities of the phases and the capillary lengths. The results are presented in tables and graphs and compared with published data obtained by other methods and with theoretical predictions. The findings are shown to be in good agreement with previous experiments, confirming the discrepancy between temperature-independent universal amplitude ratios calculated from such data and those predicted by renormalization-group calculations or Monte Carlo simulations of Ising models.

Moldover, M. R.↗
NASA NTRS1986

IRAS observations of binaries with compact objects

The infrared emission data, obtained on 260 binary systems by the all-sky IRAS survey in wavelengths between 12 and 100 microns, are reported. Of all the 260 sources, which contained compact objects including white dwarfs, neutron stars, or possibly black holes, only 32 contained detectable IR radiation. The X-ray emitting Be-type stars (gamma-Cas and X Per) were found to have their energy flux proportional to frequency in the range of the log nu values of 12.7-14.7. However, the GS304-1 flux distribution is unique, in that its flux rises by several orders of magnitude as the wavelength changes from 4000 A to 60 microns. A static dust cloud was detected, with a radius of about 1 AU, which has formed around the classical nova RR Pic since its 1925 eruption. The post-eruption far-IR light curve of a classical nova provides strong evidence for IR emissions from both dust grains formed during the eruption and dust grains existing from previous eruptions.

Schaefer, B. E.↗
NASA NTRS1987

Theory of Periodic-Binary-Sequence Generators

Algorithms yield feedback shift registers with maximum regularity. Report provides extensive mathematical treatment of new and previous results related to generation of pseudo-noise binary sequences by feedback shift registers. Generator architectures amenable to efficient implementation in very-large-scale integrated (VLSI) circuits. Report includes literature references to applications of such sequences in random-number generation, radar, VLSI testing, data encryption and decryption, algebraic error-detection and error-correction encoding and decoding, and feedback-shift-register synthesis of sequential machines.

Perlman, M.↗
NASA NTRS1986

Measuring interstellar grains from the haloes of binary X-ray sources

Coherent forward scattering of X-rays by interstellar grains creates a halo around the X-ray image of a compact source. The fractional halo brightness at 2 keV is typically of order 10% moderately reddened galactic sources. The angular brightness distribution of the halo, which extends over several arcminutes, indicates the size distribution of the grains, and the spectrum of the halo indicates the composition of the grains. The halo will persist for several hours after the point source vanishes during an eclipse of a binary source; this provides a way to avoid systematic errors in measuring halo brightness due to an extended point response function of the X-ray telescope. Indeed, it is possilbe to infer the size distribution and composition of the grains without an imaging X-ray telescope by observing the time-dependence of the halo spectrum during eclipse.

Xu, Y.↗
NASA NTRS1986

The luminosities of the binary cepheids SU Cyg, SU Cas and W Sgr

Absolute magnitudes for binary classical Cepheids were derived by ratioing IUE low dispersion spectra in regions where the blue companion dominates with spectra of main sequence spectral type standards. The IUE spectra are also used to determine the magnitude difference between the Cepheid and the blue companion. Absolute magnitudes determined for SU Cyg and W Sgr agree with the absolute magnitudes of Sandage and Tammann and Caldwell within the + or - 0m2 estimated uncertainty, but not with the fainter absolute magnitudes of Schmidt. The absolute magnitude of SU Cas is in better agreement with the PLC relations if it is pulsating in the first overtone mode.

Evans, Nancy Remage↗
NASA NTRS1986

Gravitational macrosegregation in binary Pb-Sn alloy ingots

A space shuttle experiment employing the General Purpose (Rocket) Furnace (GPF) in its isothermal mode of operation is manifested on MSL-3, circa 1989. The central aim of this experiment is to investigate the effect of reduced gravity levels on the segregation behavior in a slowly, and isothermally, cooled sample of a binary Pb-15 wt% Sn alloy. This experiment should be able to simulate, in a small laboratory sample, some aspects of the segragation phenomena occurring in large industrial ingots. Ground-based experiments conducted in the single-cavity simulator of the GPF, in support of the microgravity experiment are described in detail. The results of the MSFC experiments are compared with other related experiments conducted at Case Western Reserve University (CWRS), wherein the isothermal constraints were relaxed. The isothermally processed samples indicate a small and gradual increase in fraction eutectic, and a corresponding increase in tin content, from the bottom to the top of the ingot. The radial variations are minimal near the ingot bottom, but there are large radial variations in the top half. In the CWRU experiments, more severe segregations, including segregation defects known as freckles. Follow up experiments employing the GPF without the isothermal constraints, or other suitably modified space shuttle hardware are suggested.

Laxmanan, V.↗
NASA NTRS1986

Cellular and dendritic growth in a binary melt - A marginal stability approach

A simple model for the constrained growth of an array of cells or dendrites in a binary alloy in the presence of an imposed positive temperature gradient in the liquid is proposed, with the dendritic or cell tip radius calculated using the marginal stability criterion of Langer and Muller-Krumbhaar (1977). This approach, an approach adopting the ad hoc assumption of minimum undercooling at the cell or dendrite tip, and an approach based on the stability criterion of Trivedi (1980) all predict tip radii to within 30 percent of each other, and yield a simple relationship between the tip radius and the growth conditions. Good agreement is found between predictions and data obtained in a succinonitrile-acetone system, and under the present experimental conditions, the dendritic tip stability parameter value is found to be twice that obtained previously, possibly due to a transition in morphology from a cellular structure with just a few side branches, to a more fully developed dendritic structure.

Laxmanan, V.↗
NASA NTRS1986

Effects of high-energy neutrino production and interactions on stars in close X-ray binaries

Limits are discussed that may be placed on binary systems in which a compact partner is a strong source of high-energy particles that produce photons, neutrinos, and other secondary particles in the companion star. The highest energy neutrinos are absorbed deep in the companion and the associated energy deposition may be large enough to affect its structure or lead to its ultimate disruption. This neutrino heating is evaluated, starting with a detailed numerical calculation of the hadronic cascade induced in the atmosphere of the companion star. For some theoretical models, the resulting energy deposition from neutrino absorption may be so great as to disrupt the companion star over a time scale of 10,000-100,000 yr. Even if the energy deposition is smaller, it may still be high enough to alter the system substantially.

Gaisser, T. K.↗
NASA NTRS1986

A spectroscopic study of the cataclysmic binary star SU Ursae Majoris

Spectroscopic observations of SU UMa, the prototype of a class of short-period cataclysmic binaries, are reported. The orbital period is found to be 0.076351 + or - 4.3 x 10 to the -5th days. The velocity amplitude of the emission line source is 58 + or - 4 km/s, leading to a mass function of about 0.0015 solar mass and implying a moderately low inclination. The line cores in H-alpha and H-beta lead the wings slightly in orbital phase, contrary to the predictions of simple hot spot models of the line core. The velocity widths of the Balmer series increase toward higher members of the series, suggesting that pressure broadening may contribute nonnegligibly to the emission line widths.

Thorstensen, John R.↗
NASA NTRS1986

Orbital period changes in massive X-ray binaries

Data from long-term pulse-timing observations of Cen X-3 are compiled and analyzed to determine the evolution of the orbital period, and the implications of the results for other massive X-ray binaries are discussed. Third-body effects, tidal effects, and mass-loss/transfer effects are considered as possible causes for the orbital-period decay observed in Cen X-3, and it is concluded that strong tidal coupling between the companion star and the orbital causes the period decay via orbital instability and/or mass loss. Applying these results to the Roche-lobe-overflow models of Savonije (1983), the evolutionary expansion rate of the Cen X-3 companion and the Roche-lobe shrinking rate are estimated as about 2 x 10 to the -7th/yr and about 1 x 10 to the -6th/yr, respectively, implying an X-ray lifetime of about 5000 yr. Estimates of the companion mass-change rate and period decay for Cen X-3 and four other objects are presented in a table.

Kelley, Richard L.↗
NASA NTRS1986

Traveling and standing waves in binary-fluid convection in finite geometries

The effect of finite geometry on the competition between traveling waves and standing waves in systems with a Hopf bifurcation to a state with spatial structure is considered in the linear and weakly nonlinear regimes. The spatial structure observed by Kolodner et al. (1986) in binary-fluid convection is explained in terms of the reflection of the linear traveling waves. The reflection coefficient is calculated, and is found to go to zero as the frequency of the waves becomes small. The pattern expected in a saturated nonlinear state is discussed.

Cross, M. C.↗
NASA NTRS1986

Theoretical spectra of nonmagnetized low-mass X-ray binaries

Theoretical X-ray spectra of low-mass X-ray binaries with negligible magnetic fields are presented. The geometry of the X-ray emitting region, the energetic efficiency of the accretion in the disk and in the boundary layer which leads to a relation between the disk and the boundary layer luminosities, and the irradiation of the disk by the boundary layer are studied. The model of the radiation spectrum emerging from the neutron star and the innermost part of the disk is presented. The relativistic and Doppler effects and their influence on the spectrum as a function of inclination angle are discussed. A simple method for comparing the spectrum model with observations by studying the hardness ratio is given, and the results for three X-ray sources in globular clusters observed by the Einstein satellite are presented. The range of applicability of the spectrum models is also discussed.

Czerny, Bozena↗
NASA NTRS1987

The moderately interacting Algol binary RS Cephei

In agreement with previous observers, it is found that the eclipsing binary RS Cep is an Algol-type semidetached system. From IUE spectra and Lick Observatory optical scans, the spectral types of the components are determined as B9.7e V + G8 III-IV. The effective temperature of the primary star is found to be 9670 K (with an uncertainty of about 150 K). From the photometric elements, the spectral types, and the semidetached nature of the system, a satisfactory model of the system is developed, giving masses 2.4 and 0.4 solar mass, radii 2.3 and 7.6 solar radii, and separation of the components 32 solar radii. This model leads to a distance of 910 pc; the color excess is E(B - V) = 0.03 mag. Balmer emission lines are observed in the optical scans, so that the system is a Be star. An IUE spectrum obtained during the total primary eclipse reveals a number of UV emission lines, typical for interacting Algols and W Ser stars. Power emitted in these lines is about twice as high as that in TT Hya or U Cep, therefore, RS Cep is a relatively active Algol system. A broad 'bulge' of excess relative flux is observed roughly between wavelengths 210 and 270 nm in the totality spectrum, and interpreted as broad blends of emission lines of Fe II; the same Fe II lines, formed in a circumstellar shell or disk, cause additional absorption in the out-of-eclipse spectra.

Plavec, Mirek J.↗