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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Signatures of cloud, temperature, and gravity from spectra of the closest brown dwarfs

We present medium-resolution optical (λ/Δλ ∼ 4000) and near-infrared (λ/Δλ ∼ 8000) spectral data for components of the newly discovered WISE J104915.57-531906.1AB (Luhman 16AB) brown dwarf binary. The optical spectra reveal strong 6708 Å Li I absorption in both Luhman 16A (8.0 ± 0.4 Å) and Luhman 16B (3.8 ± 0.4 Å) confirming their substellar mass. Interestingly, this is the first detection of Li I absorption in a T dwarf. In the near-infrared data, we find strong K I absorption at 1.168, 1.177, 1.243, and 1.254 μm in both components. Neither the optical nor the near-infrared alkali lines show low surface gravity signatures. Along with the Li I absorption detection, we can broadly constrain the system age to 0.1-3 Gyr or the mass to 20-65 M{sub Jup} for each component. Compared to the strength of K I line absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker while Luhman 16B is stronger. Analyzing the spectral region around each doublet in distance scaled flux units and comparing the two sources, we confirm the J-band flux reversal and find that Luhman 16B has a brighter continuum in the 1.17 μm and 1.25 μm regions than Luhman 16A. Converting flux units to a brightness temperature we interpret this to mean that the secondary is ∼50 K warmer than the primary in regions dominated by condensate grain scattering. One plausible explanation for this difference is that Luhman 16B has thinner clouds or patchy holes in its atmosphere allowing us to see to deeper, hotter regions. We also detect comparably strong FeH in the 0.9896 μm Wing-Ford band for both components. Traditionally, a signpost of changing atmosphere conditions from late-type L to early T, the persistence and similarity of FeH at 0.9896 μm in both Luhman 16A and Luhman 16B is an indication of homogenous atmosphere conditions. We calculate bolometric luminosities from observed data supplemented with best fit models for longer wavelengths and find the components are consistent within 1σ with resultant T{sub effs} of 1310 ± 30 K and 1280 ± 75 K for Luhman 16AB respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1992

Optical computing and neural networks; Proceedings of the Meeting, National Chiao Tung Univ., Hsinchu, Taiwan, Dec. 16, 17, 1992

The present conference discusses optical neural networks, photorefractive nonlinear optics, optical pattern recognition, digital and analog processors, and holography and its applications. Attention is given to bifurcating optical information processing, neural structures in digital halftoning, an exemplar-based optical neural net classifier for color pattern recognition, volume storage in photorefractive disks, and microlaser-based compact optical neuroprocessors. Also treated are the optical implementation of a feature-enhanced optical interpattern-associative neural network model and its optical implementation, an optical pattern binary dual-rail logic gate module, a theoretical analysis for holographic associative memories, joint transform correlators, image addition and subtraction via the Talbot effect, and optical wavelet-matched filters. (No individual items are abstracted in this volume)

Hsu, Ken-Yuh↗
NASA NTRS1987

Optimizing a continuously variable filter in a hybrid optical correlator

In contrast to binary filters, continuously variable optical filters offer an ability to conpensate for certain imperfections in the optics of a hybrid correlator. Arbitrary static phase errors are introduced into a model of a phase-only filtering hybrid correlator, and a method of discovering a correction for them simulated. By a recursive technique a first approximation to the impulse's matched filter is adjusted (allowed to relax) so as to produce successively more localized distribution of the output in the correlation plane. The method is motivated by the development of continuously-variable phase-only spatial light modulators, but it is applicable to amplitude modulators and -with appropriate modification -- to binary modulators as well. The technique is robust against the form of the system's departure from ideal behavior.

Juday, Richard D.↗
NASA NTRS1985

Variable, optically thick plasma in the interacting binaries R Arae and HD 207739

Attention is given to observational evidence for the presence of variable and optically thick extrastellar gas in two binary stars, R Arae and HD 207739, which appear to be in the evolutionary phase immediately preceding or following the short lived supercritical mass transfer phase. In both binaries, spectral lines and energy distributions are variable outside eclipse.

Kondo, Y.↗
NASA NTRS1993

Optical and X-ray observations of the low-mass X-ray binary EXO 0748-676

Optical and X-ray observations of EXO-676 in late March 1989 are presented. Our optical observations provide some support for the previously observed correlation between the mean optical brightness and light curve morphology. Unexpectedly, the mean X-ray and optical flux levels during this period do not reflect similar system states. The optical counterpart is found to be in an intermediate to low state, while X-ray data imply a bright (high) state. The changed relationship between optical and X-ray fluxes is evidence showing that EXO 0748-676 has possibly evolved. We fail to find correlated variability in simultaneous X-ray and optical observations. The lack of covariability is attributed to the limited simultaneous coverage of the source and/or significant geometric modulation in the optical light curve.

Thomas, Brian↗
DOE OSTI2011

THE X-RAY QUIESCENCE OF SWIFT J195509.6+261406 (GRB 070610): AN OPTICAL BURSTING X-RAY BINARY?

We report on an {approx}63 ks Chandra observation of the X-ray transient Swift J195509.6+261406 discovered as the afterglow of what was first believed to be a long-duration gamma-ray burst (GRB 070610). The outburst of this source was characterized by unique optical flares on timescales of second or less, morphologically similar to the short X-ray bursts usually observed from magnetars. Our Chandra observation was performed {approx}2 years after the discovery of the optical and X-ray flaring activity of this source, catching it in its quiescent state. We derive stringent upper limits on the quiescent emission of Swift J195509.6+261406, which argues against the possibility of this object being a typical magnetar. Our limits show that the most viable interpretation on the nature of this peculiar bursting source is a binary system hosting a black hole or a neutron star with a low-mass companion star (<0.12 M{sub sun}) and with an orbital period smaller than a few hours.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Compositional trends of γ-induced optical changes observed in chalcogenide glasses of binary As-S system

Compositional trends of γ-induced optical changes in chalcogenide glasses are studied with the binary As-S system. Effects of γ-irradiation and annealing are compared using the changes measured in the fundamental optical absorption edge region. It is shown that annealing near the glass transition temperature leads to bleaching of As-S glasses, while γ-irradiation leads to darkening; both depend on the glass composition and thermal history of the specimens. These results are explained in terms of competitive destruction–polymerization transformations and physical aging occurring in As-S chalcogenide glasses under the influence of γ-irradiation.

Chalcogenide glasses↗
NASA NTRS1980

Performance of a near-optimum receiver for optical antipodal signals

The well known photon-counting, heterodyning and homodyning optical receivers (operating over a free-space channel) do not achieve the performance of the optimum quantum receiver, which attains significantly lower error-probabilities than the above receiver structures. A demonstration and analysis are given of a binary antipodal optical receiver that exponentially approaches the performance of the optimum quantum receiver. A general mathematical model is developed, and subsequently used to evaluate the effects of external interference and internal error-sources on receiver performance.

Vilnrotter, V. A.↗
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.↗
DOE OSTI2018

Optical Studies of 15 Hard X-Ray Selected Cataclysmic Binaries

We conducted time-resolved optical spectroscopy and/or time-series photometry of 15 cataclysmic binaries that were discovered in hard X-ray surveys by the Swift Burst Alert Telescope and the International Gamma-Ray Astrophysics Laboratory, with the goal of measuring their orbital periods and searching for spin periods. Four of the objects in this study are new optical identifications: Swift J0535.2+2830, Swift J2006.4+3645, IGR J21095+4322, and Swift J2116.5+5336. Coherent pulsations are detected from three objects for the first time, Swift J0535.2+2830 (1523 s), 2PBC J1911.4+1412 (747 s), and 1SWXRT J230642.7+550817 (464 s), indicating that they are intermediate polars (IPs). We find two new eclipsing systems in time-series photometry: 2PBC J0658.0−1746, a polar with a period of 2.38 hr, and Swift J2116.5+5336, a disk system that has an eclipse period of 6.56 hr. Exact or approximate spectroscopic orbital periods are found for six additional targets. Of note is the long 4.637-day orbit for Swift J0623.9−0939, which is revealed by the radial velocities of the photospheric absorption lines of the secondary star. We also discover a 12.76 hr orbital period for RX J2015.6+3711, which confirms that the previously detected 2.00 hr X-ray period from this star is the spin period of an IP, as inferred by Coti Zelati et al. These results support the conclusion that hard X-ray selection favors magnetic CVs, with IPs outnumbering polars.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

A luminous X-ray binary in M82

Optical CCD imaging at the position of a bright X-ray point source just off the visible disk of the nearby irregular galaxy M82 constrain it to be an X-ray binary with a 0.2-4 keV X-ray luminosity of not less than 9 x 10 exp 38 ergs/sec. Assuming that the X-ray emission is due to a single object, then by asumming an Eddington limit appropriate for pure electron scattering, this luminosity requires a minimum primary mass of not less than 15 solar masses; thus, this X-ray source is a black hole candidate. If the brightest optical object detected inside the X-ray error circle at B about 22.2 is the secondary to the X-ray emitter, it is most likely an early type star making this system the most luminous massive X-ray binary system known.

Stocke, John T.↗
DOE OSTI2010

HD 259440: THE PROPOSED OPTICAL COUNTERPART OF THE {gamma}-RAY BINARY HESS J0632+057

HD 259440 is a B0pe star that was proposed as the optical counterpart to the {gamma}-ray source HESS J0632+057. Here, we present optical spectra of HD 259440 acquired to investigate the stellar parameters, the properties of the Be star disk, and evidence of binarity in this system. Emission from the H{alpha} line shows evidence of a spiral density wave in the nearly edge-on disk. We find a best-fit stellar effective temperature of 27,500-30,000 K and a log surface gravity of 3.75-4.0, although our fits are somewhat ambiguous due to scattered light from the circumstellar disk. We derive a mass of 13.2-19.0 M{sub sun} and a radius of 6.0-9.6 R{sub sun}. By fitting the spectral energy distribution, we find a distance between 1.1 and 1.7 kpc. We do not detect any significant radial velocity shifts in our data, ruling out orbital periods shorter than one month. If HD 259440 is a binary, it is likely a long-period (>100 d) system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

X-RAY AND OPTICAL OBSERVATIONS OF THE UNIQUE BINARY SYSTEM HD 49798/RX J0648.0-4418

We report the results of XMM-Newton observations of HD 49798/RX J0648.0-4418, the only known X-ray binary consisting of a hot sub-dwarf and a white dwarf. The white dwarf rotates very rapidly (P = 13.2 s) and has a dynamically measured mass of 1.28 {+-} 0.05 M{sub sun}. Its X-ray emission consists of a strongly pulsed, soft component, well fit by a blackbody with kT{sub BB} {approx} 40 eV, accounting for most of the luminosity, and a fainter hard power-law component (photon index {approx}1.6). A luminosity of {approx}10{sup 32} erg s{sup -1} is produced by accretion onto the white dwarf of the helium-rich matter from the wind of the companion, which is one of the few hot sub-dwarfs showing evidence of mass loss. A search for optical pulsations at the South African Astronomical Observatory 1.9 m telescope gave negative results. X-rays were also detected during the white dwarf eclipse. This emission, with luminosity 2 x 10{sup 30} erg s{sup -1}, can be attributed to HD 49798 and represents the first detection of a hot sub-dwarf star in the X-ray band. HD 49798/RX J0648.0-4418 is a post-common-envelope binary which most likely originated from a pair of stars with masses {approx}8-10 M{sub sun}. After the current He-burning phase, HD 49798 will expand and reach the Roche lobe, causing a higher accretion rate onto the white dwarf which can reach the Chandrasekhar limit. Considering the fast spin of the white dwarf, this could lead to the formation of a millisecond pulsar. Alternatively, this system could be a Type Ia supernova progenitor with the appealing characteristic of a short time delay, being the descendent of relatively massive stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

AR Sco: A Precessing White Dwarf Synchronar?

The emission of the white dwarf–M dwarf binary AR Sco is driven by the rapid synchronization of its white dwarf, rather than by accretion. Synchronization requires a magnetic field ∼100 Gauss at the M dwarf and ∼10{sup 8} Gauss at the white dwarf, larger than the fields of most intermediate polars but within the range of fields of known magnetic white dwarfs. The spindown power is dissipated in the atmosphere of the M dwarf, within the near zone of the rotating white dwarf’s field, by magnetic reconnection, accelerating particles that produce the observed synchrotron radiation. The displacement of the optical maximum from conjunction may be explained either by dissipation in a bow wave as the white dwarf’s magnetic field sweeps past the M dwarf or by a misaligned white dwarf rotation axis and oblique magnetic moment. In the latter case the rotation axis precesses with a period of decades, predicting a drift in the orbital phase of the optical maximum. Binaries whose emission is powered by synchronization may be termed synchronars, in analogy to magnetars.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1978

Studies in optical parallel processing

Threshold and A/D devices for converting a gray scale image into a binary one were investigated for all-optical and opto-electronic approaches to parallel processing. Integrated optical logic circuits (IOC) and optical parallel logic devices (OPA) were studied as an approach to processing optical binary signals. In the IOC logic scheme, a single row of an optical image is coupled into the IOC substrate at a time through an array of optical fibers. Parallel processing is carried out out, on each image element of these rows, in the IOC substrate and the resulting output exits via a second array of optical fibers. The OPAL system for parallel processing which uses a Fabry-Perot interferometer for image thresholding and analog-to-digital conversion, achieves a higher degree of parallel processing than is possible with IOC.

Lee, S. H.↗
DOE OSTI2012

DETECTION OF VHE {gamma}-RAYS FROM HESS J0632+057 DURING THE 2011 FEBRUARY X-RAY OUTBURST WITH THE MAGIC TELESCOPES

The very high energy (VHE) {gamma}-ray source HESS J0632+057 has recently been confirmed to be a {gamma}-ray binary. The optical counterpart is the Be star MWC 148, and a compact object of unknown nature orbits it every {approx}321 days with a high eccentricity of {approx}0.8. We monitored HESS J0632+057 with the stereoscopic MAGIC telescopes from 2010 October to 2011 March and detected significant VHE {gamma}-ray emission during 2011 February, when the system exhibited an X-ray outburst. We find no {gamma}-ray signal in the other observation periods when the system did not show increased X-ray flux. Thus, HESS J0632+057 exhibits {gamma}-ray variability on timescales of the order of one to two months possibly linked to the X-ray outburst that takes place about 100 days after the periastron passage. Furthermore, our measurements provide for the first time the {gamma}-ray spectrum down to about 140 GeV and indicate no turnover of the spectrum at low energies. We compare the properties of HESS J0632+057 with the similar {gamma}-ray binary LS I +61 Degree-Sign 303 and discuss the possible origin of the multi-wavelength emission of the source.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Influence of intermolecular interactions on the infrared complex indices of refraction for binary liquid mixtures

This paper investigates the accuracy of deriving the composite optical constants of binary mixtures from only the complex indices of refraction of the neat materials. These optical constants enable the reflectance spectra of the binary mixtures to be modeled for multiple scenarios (e.g., different substrates, thicknesses, volume ratios), which is important for contact and standoff chemical detection. Using volume fractions, each mixture's complex index of refraction was approximated via three different mixing rules. To explore the impact of intermolecular interactions, these predictions are tested by experimental measurements for two representative sets of binary mixtures: (1) tributyl phosphate combined with n-dodecane, a non-polar medium, to represent mixtures which primarily interact via dispersion forces and (2) tributyl phosphate and 1-butanol to represent mixtures with polar functional groups that can also interact via dipole–dipole interactions, including hydrogen bonding. The residuals and the root-mean-square error between the experimental and calculated index values are computed and demonstrate that for miscible liquids in which the average geometry of the cross-interactions can be considered isotropic (e.g., dispersion), the refractive indices of the mixtures can be modeled using composite n and k values derived from volume fractions of the neat liquids. Conversely, in spectral regions where the geometry of the cross-interactions is more restricted and anisotropic (e.g., hydrogen bonding), the calculated n and k values vary from the measured values. The impact of these interactions on the reflectance spectra are then compared by modeling a thin film of the binary mixtures on an aluminum substrate using both the measured and the mathematically computed indices of refraction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Tunable Plasmonic Coupling in Self-Assembled Binary Nanocrystal Super lattices Studied by Correlated Optical Microspectrophotometry and Electron Microscopy

We study the plasmonic properties of self-assembled binary nanocrystal superlattices (BNSLs) using correlated optical microspectrophotometry and electron microscopy performed on individual BNSL domains. The strength of near-field couplings between adjacent plasmonic nanocrystals (NCs) can be systematically engineered by varying the NC size, composition, and the lattice symmetry of BNSLs, leading to broadband spectral tunability of the collective plasmonic response of BNSLs across the entire visible spectrum. Self-assembled multicomponent NC superlattices represent a versatile platform for the rational design of macroscopic three-dimensional plasmonic metamaterials with emergent optical characteristics.

Ye, XC↗