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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 469 records · Page 26
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NASA NTRS1988

L151-81A/B - A unique white dwarf binary with DB and DA components

Spectroscopic observations of the wide binary L151-81A/B reveal that both components are white dwarfs with spectral types DB3 and DA4, the first such binary identified in a comprehensive survey of Luyten and Giclas common proper motion pairs. Assuming log g = 8, measurements of the helium line profiles in the DB primary yield Teff = 16,000 + or - 2,000, while the hydrogen profiles for the DA companion yield Teff =12,000 + or - 2,000. The existence of a helium-rich/hydrogen-rich degenerate pair offers several interesting tests of theoretical white dwarf formation channels and surface abundance evolution.

Oswalt, Terry D.↗
NASA NTRS1988

The long-period semi-detached giant binary system 5 Ceti

The binary system 5 Ceti consists of a K3 III star at or near its Roche lobe and a small hot companion best studied in the satellite ultraviolet. The hot radiation source at the secondary star is immersed in the chromosphere of the K giant, and the slight enhancements of a few UV absorption lines at secondary minimum are used to estimate chromospheric column densities. The variability and flatness of the spectrum is evidence for considering the object a main-sequence star accreting mass by way of Roche-lobe overflow at the rate of 5 X 10 to the minus 7 solar masses/yr. Thus 5 Ceti may represent the elusive rapid stage of mass transfer in which matter is lost from the shrinking Roche lobe of the more massive star. The Fe II UV spectrum in interacting binaries is also discussed.

Eaton, Joel A.↗
NASA NTRS1989

Iron K lines from low-mass X-ray binaries

Models are presented for the 6-7 keV iron line emission from low-mass X-ray binaries. A simplified model for an accretion disk corona is used to examine the dependence of the observable line properties, line width and mean energy, on the radial distance of the emission region from the X-ray source, and on the fraction of the X-rays from the source which reach the disk surface. The effects of blending of multiple line components and of Comptonization of the line profile are included in numerical calculations of the emitted profile shape. The results of these calculations, when compared with the line properties observed from several low-mass X-ray binaries, suggest that the broadening is dominated either by rotation or by Compton scattering through a greater optical depth than is expected from an accretion disk corona.

Kallman, T.↗
NASA NTRS1989

VLSI binary updown counter

A pipeline binary updown counter is comprised of simple stages that may be readily replicated. Each stage is defined by the Boolean logic equation: A(sub n)(t) = A(sub n)(t - 1) exclusive OR (U AND P(sub n)) inclusive OR (D AND Q(sub n)), where A(sub n)(t) denotes the value of the nth bit at time t. The input to the counter has three values represented by two binary signals U and D such that if both are zero, the input is zero, if U = 0 and D = 1, the input is -1 and if U = 1 and D = 0, the input is +1. P(sub n) represents a product of A(sub k)'s for 1 is less than or equal to k is less than or equal to -1, while Q(sub n) represents the product of bar A's for 1 is less than or equal to K is less than or equal to n - 1, where bar A(sub k) is the complement of A(sub k) and P(sub n) and Q(sub n) are expressed as the following two equations: P(sub n) = A(sub n - 1) A(sub n - 2)...A(sub 1) and Q(sub n) = bar A(sub n - 1) bar A(sub n - 2)...bar A(sub 1), which can be written in recursive form as P(sub n) = P(sub n - 1) AND bar A(sub n - 1) and Q(sub n) = Q(sub n - 1) AND bar A(sub n - 1) with the initial values P(sub 1) = 1 and Q(sub 1) = 1.

Truong, Trieu-Kie↗
NASA NTRS1989

Emission lines from X ray binaries

Emission lines are probes of the conditions in the accretion flows associated with binary X-ray sources. The hard X-ray iron K line, soft X-ray lines, and UV lines, and what they indicate about the conditions in binary X-ray sources are discussed. These lines are interpreted using an X-ray illuminated accretion disk model. The structure and dynamics of the heated disk, its spectral signatures, and the major unsolved theoretical issues surrounding them are investigated.

Kallman, T. R.↗
NASA NTRS1989

Timing analysis of binary X ray pulsars observed by HEAO 1

Timing analysis of the pointed observations of 5 selected binary X ray pulsars, in two categories of disk-fed and wind-fed sources, by HEAO 1 A-2 is reported. The power spectral analysis was performed on the data in the frequency range from approx. 1 MHz to 6.25 Hz. The coherent signal of the pulsation, the continuum of the power spectrum, varies in time and differs among sources. Quasi-Periodic Oscillation (QPO) is probably related to a fast spinning but weakly magnetized neutron star in the low mass X ray binaries. QPO was searched for in this frequency range to see if scaling laws exist among these two systems which may have possessed different order of magnitude of magnetic field strengths and the inner disk radii. One possible QPO is found centering at 0.062 Hz in 4U0115+63 during a flare.

Soong, Y.↗
NASA NTRS1989

Ionization effects in the radiative driving of stellar winds in massive X ray binary systems

Massive X ray binaries consist of an early type primary lossing mass via a strong stellar wind driven by the stars radiation field, and an accreting neutron star companion. The X rays from the neutron star affect the wind dynamics by changing the temperature and ionization structure. The effect of the accretion powered X rays on the radiative line force that drives the stellar wind is calculated. The consequences of these calculations for the wind dynamics in massive X ray binaries is discussed.

Stevens, Ian R.↗
NASA NTRS1989

Evolution of wide binary millisecond pulsars in globular clusters

The evolution of a binary radio pulsar in a wide orbit about a low-mass degenerate dwarf companion in a globular cluster environment is investigated. An extensive series of numerical scattering experiments is used to study encounters between such a pulsar and passing cluster field stars. A wide range of initial orbital periods from 3 to 1000 days is considered with a corresponding range of masses for the degenerate dwarf companions. The calculative results are summarized in the form of scattering cross sections. In particular, cross sections are presented for three final 'channels' in which the end product of the encounter is an isolated neutron star. Cross sections for inducing various orbital eccentricities into initially circular orbits are also derived. The implications of the results for the formation of the single millisecond pulsars in M28 and M15 and for the nearly circular obit of the M4 binary radio pulsar are discussed.

Rappaport, S.↗
NASA NTRS1989

Soft X-ray emission lines from low-mass X-ray binaries. I - Collision-dominated models

The soft X-ray line emission from five low-mass X-ray binaries observed by the Einstein Observatory (HEAO 2) Objective Grating Spectrometer is examined. Observed spectra are fitted to model spectra consisting of emission from an optically thin plasma. Fits are performed using a variety of different assumptions for elemental abundances, heating and ionization mechanisms, and the distribution of gas temperature and ionization parameter. The results are discussed in the context of current models for the accretion flow in low-mass X-ray binaries.

Kallman, T. R.↗
NASA NTRS1990

Buoyancy-driven instability in a vertical cylinder: Binary fluids with Soret effect. I - General theory and stationary stability results

The buoyancy-driven instability of a monocomponent or binary fluid completely contained in a vertical circular cylinder is investigated, including the influence of the Soret effect for the binary mixture. The Boussinesq approximation is used, and the resulting linear stability problem is solved using a Galerkin technique. The analysis considers fluid mixtures ranging from gases to liquid metals. The flow structure is found to depend strongly on both the cylinder aspect ratio and the magnitude of the Soret effect. The predicted stability limits are shown to agree closely with experimental observations.

Hardin, G. R.↗
NASA NTRS1990

Chromospheric Ca II H and K and H-alpha emission in single and binary stars of spectral types F6-M2

New observations of the Ca II H and K and H-epsilon region and/or the Balmer H-alpha line are presented for 100 mostly very active stars but also for weak or inactive stars with suspected activity. Correlations between chromospheric activity at Ca II H and K and H-alpha and effective surface temperature and rotation are identified, and several new stars with chromospheric Ca II H and K emission are discovered. No single activity-rotation relation can be derived for all luminosity classes, and there is clear evidence that evolved stars are generally more active than main-sequence stars of the same rotation period. Binary within the evolved stars appears to play no role, while main-sequence binary stars show generally higher levels of activity than their single counterparts. Chromospheric emission in the Ca II H and K lines depends on surface temperature in that flux declines with cooler temperature.

Strassmeier, Klaus G.↗
NASA NTRS1989

Binary X-ray sources

The present state of understanding of binary X-ray sources is surveyed. The observed properties of the luminous quasi-periodic oscillation sources are discussed, and a recently developed, unified model of low-mass X-ray binary behavior is described. The most up-to-date models of X-ray spectral states, horizontal branch oscillations, and normal branch oscillations are examined.

Lamb, F. K.↗
NASA NTRS1990

Comparisons of SiO maser and long-period variable positions in the R Aquarii and Omicron Ceti binary systems

It has been determined that the absolute position of the centroid of SiO maser-emitting spots toward both R Aqr and Omicron Cet are coincident with the position of the long-period variables (LPVs) in these binary systems to within the errors of measurement. The SiO positions were determined with the Hat Creek interferometer, while the LPV positions were determined with the 8-in transit circle of the US Naval Observatory. These results contradict an earlier report of a circumbinary SiO maser far removed from the LPV in the R Aqr binary system; statistical reasons for the discrepancy are suggested. High-resolution spectra of both sources are presented and possible models are discussed.

Hollis, J. M.↗
NASA NTRS1990

A homogeneous sample of binary galaxies: Basic observational properties

A survey of optical characteristics for 585 binary systems, satisfying a condition of apparent isolation on the sky, is presented. Influences of various selection effects distorting the average parameters of the sample are noted. The pair components display mutual similarity over all the global properties: luminosity, diameter, morphological type, mass-to-luminosity ratio, angular momentum etc., which is not due only to selection effects. The observed correlations must be caused by common origin of pair members. Some features (nuclear activity, color index) could acquire similarity during synchronous evolution of double galaxies. Despite the observed isolation, the sample of double systems is seriously contaminated by accidental pairs, and also by members of groups and clusters. After removing false pairs estimates of orbital mass-to-luminosity ratio range from 0 to 30 f(solar), with the mean value (7.8 plus or minus 0.7) f(solar). Binary galaxies possess nearly circular orbits with a typical eccentrity e = 0.25, probably resulting from evolutionary selection driven by component mergers under dynamical friction. The double-galaxy population with space abundance 0.12 plus or minus 0.02 and characteristic merger timescale 0.2 H(exp -1) may significantly influence the rate of dynamical evolution of galaxies.

Karachentsev, I. D.↗
NASA NTRS1990

Abundance anomalies of carbon and nitrogen in the IUE spectra of Algol-type interacting binaries

There are two primary ways in which the products of nucleosynthesis in stellar interiors may appear at the surface of a star. These are mixing and/or loss of the original unburned stellar envelope. In interacting binaries, overflow can contribute dramatically to envelope loss. The simplest abundance anomalies to be expected from nuclear burning of hydrogen, helium, or carbon would be under or over abundances H, He, C, O, Ne, and Mg. In addition, it is expected that carbon is initially severely depleted, while nitrogen is enhanced during hydrogen burning via the CNO cycle in stars above two solar masses. Other, more subtle anomalies are also expected, and elements heavier than magnesium can be created during very late evolution by nuclear burning in massive stars. Consequently, it is expected that abundance anomalies of various kinds should occur in interacting binaries where one or both stars have lost significant amounts of mass.

Mccluskey, Carolina P. S.↗
NASA NTRS1990

Changes in the orbital periods of close binary stars

A number of close binary stars show erratic changes in their orbital periods on time scales of order 5-10 yr. Recently it has been proposed that the period changes are the result of changes in the quadrupole moment of one star, caused in turn by an alteration of the internal structure of that star. Magnetic pressure, which either distorts the shape of the star or changes its tidally induced quadrupole moment, is suggested as the driving force behind the alteration. Here, the amount of energy required to distort one component of a binary and match the observed period changes is estimated. The rate at which energy is produced or lost is governed by the thermal time scale of the star, and the estimates indicate that the observed period changes would take at least 1000 yr for the tidal quadrupole mechanism, and of order 60 yr to match a period change in V471 Tau which took only 4 yr.

Marsh, T. R.↗
NASA NTRS1990

MS 1603.6 + 2600, an unusual X-ray selected binary system at high Galactic latitude

The discovery of an eclipsing binary system at Galactic latitude 47 deg, found as a serendipitous X-ray source in the Einstein Extended Medium Sensitivity Survey, is described. The object has X-ray flux 1.1 x 10 to the -12th ergs/sq cm s (0.3-3.5 keV) and mean magnitude R = 19.4. An orbital period of 111 minutes is found. The problem discussed is whether the system has a white dwarf or neutron star primary, in the end preferring the neutron star primary model. If the system has either optical or X-ray luminosities typical of low mass X-ray binaries (LMXB), it must be at a very large distance (30-80 kpc). Blueshifted He I absorption is seen, indicating cool outflowing material, similar to that seen in the LMXB AC 211 in the globular cluster M15.

Morris, Simon L.↗