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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Optical photometric variability of 2S 0114+65

In this paper we present Johnson V photometry of the Be/x-ray binary star system 2S 0114+65. Although this star exhibits periodic variations in x-rays, optical studies have failed to reveal fluctuations greater than 5 millimag. The data presented in this paper provide the first evidence for periodic optical variability in 2S 0114+65. On each of four nights in October 1993, we find low amplitude variations with a period of 2.77 +/- 0.48 h and with a semiamplitude of 4 millimag. This period is in good agreement with results of a comprehensive study of the x-ray data. We explore the possibility that this period represents the pulsational period of the B-star primary and the possibility that it is the rotational period of the neutron star. If the latter is the correct interpretation, we calculate a spin-up time scale of 5 x 10(exp 5) yr.

Taylor, M.↗
NASA NTRS2006

Full-Duplex Digital Communication on a Single Laser Beam

A proposed free-space optical communication system would operate in a full-duplex mode, using a single constant-power laser beam for transmission and reception of binary signals at both ends of the free-space optical path. The system was conceived for two-way data communication between a ground station and a spacecraft in a low orbit around the Earth. It has been estimated that in this application, a data rate of 10 kb/s could be achieved at a ground-station-to-spacecraft distance of 320 km, using a laser power of only 100 mW. The basic system concept is also applicable to terrestrial free-space optical communications. The system (see figure) would include a diode laser at one end of the link (originally, the ground station) and a liquid-crystal- based retroreflecting modulator at the other end of the link (originally, the spacecraft). At the laser end, the beam to be transmitted would be made to pass through a quarter-wave plate, which would convert its linear polarization to right circular polarization. For transmission of data from the laser end to the retroreflector end, the laser beam would be modulated with subcarrier phase-shift keying (SC-PSK). The transmitted beam would then pass through an aperture- sharing element (ASE) - basically, a mirror with a hole in it, used to separate the paths of the transmitted and received light beams. The transmitted beam would continue outward through a telescope (which, in the original application, would be equipped with a spacecraft-tracking system) that would launch the transmitted beam along the free-space optical path to the retroreflector end.

Hazzard, D. A.↗
NASA NTRS1992

Modified Synthetic-Discriminant-Function Optical Filter

Experiments demonstrated feasibility of synthetic-discriminant-function filter encoded in binary spatial light modulator. Filter is part of optoelectronic apparatus indicating degree of correlation between input image and any number of training images of same object at various positions and orientations. Used in optical correlator to recognize rotated images, or in tracking system to recognize moving vehicle or other substantially rigid object from any direction.

Reid, Max B.↗
NASA NTRS1994

10 micron imaging of UZ Tauri: Evidence for circumstellar disk clearing due to a close companion star

We present 10 micrometer images of the multiple T Tauri star system UZ Tau taken with the Berkeley mid-infrared array camera at the United Kingdom Infrared Telescope (UKIRT) and evidence that UZ Tau E and W are a common proper pair. The mid-infrared emission is resolved for the first time into the two components UZ Tau E and UZ Tau W. The mid-infrared excess deduced for UZ Tau W appears to be much lower than that observed for UZ Tau E. This excess emission is consistent with an optically thin circumstellar disk in the case of UZ Tau W, whereas UZ Tau E's excess is consistent with an optically thick disk. We suggest that the close binary star pair in UZ Tau W is responsible for the observed difference between UZ Tau E and W's mid-infrared excess. In the proposed model, the binary star interacts with the local circumstellar disk environment and clears out much of the material inside its orbital radius (approximately 50 AU). As a result, the hot dust, observed at mid-infrared wavelengths, in UZ Tau W is suppressed compared to its 'wider' companion UZ Tau E. This scenario can also plausibly account for differences observed in UZ Tau E's and UZ Tau W's optical line strengths and profiles.

Chez, A. M.↗
NASA NTRS1976

A review of 3U 1700-37 = HD 153919

X-ray, spectroscopic, and photometric data for the source are reviewed briefly. Some points of controversy and difficulty are discussed. The X-ray source 3U 1700-37 is moderately strong (approximately 100 Uhuru counts) and shows a long eclipse, with a period of 3.412 days. The X-rays are attenuated near 0.5 phase, and show a very wide gradual decrease on either side of the total eclipse. The low-energy cutoff is the strongest of all the X-ray binaries. These characteristics are all qualitatively compatible with the optical star's, which represent an extreme in several ways: (1) the primary is an extreme star with large mass outflow through a spherically symmetric stellar wind; (2) it is the hottest of all X-ray binary primaries (with possible exception of Cen X-3); and (3) the mass ratio is very high and the relative separation of the stars is low.

Hutchins, J. B.↗
NASA NTRS1976

X-ray observation of 3U 1700-37

X-ray observations with Copernicus reveal three categories of flux variability in 3U 1700-37. High amplitude hourly variations are energy independent in the 3-11 keV range while a change in the low energy absorbing column causes variations in flux level on an orbital time scale. This absorption is most severe prior to eclipse ingress, suggesting that the distribution of absorbing material around the X-ray source is asymmetrical with respect to the line of centers of the binary system. The absorbing material may be identical with a high density region inferred from optical observations of HD 153919. In the third category, the maximum source intensity per binary cycle is variable by at least a factor of two between observations. Measurement of the eclipse duration on three occasions indicate that it is significantly less than when observed by Uhuru.

Mason, K. O.↗
NASA NTRS1983

Stimulated emission and the flat Balmer decrements of cataclysmic variable stars

Balmer emission lines from cataclysmic variables often have nearly equal intensities rather than the rapid decrement predicted by simple nebular theory. Traditionally, this has been interpreted in terms of local thermodynamic equilibrium emission from a dense gas with small volume located just above the accretion disk. It is shown that the intense radiation field within a close binary system can affect excited state populations and optical emission in ways which allow a relatively low density gas to closely mimic the high density situation. In at least one case, the old nova V603 Aql, the emitting gas has a low density and nearly fills the orbital plane of the system. If this is characteristic of other systems, then the determination of orbital parameters and masses of cataclysmic variables from emission line radial velocities, as well as the prediction of soft X-ray emission from accreting binaries, will be affected.

Elitzur, M.↗
NASA NTRS1987

1E 1048.5 + 5421 - A new 114 minute AM Herculis binary

The discovery of a new AM Herculis binary system, found as a serendipitous Einstein X-ray source, is described. Like the previously discovered mass-transfer binaries involving synchronously rotating magnetic white-dwarf primaries, the system exhibits strong circular polarization, X-ray and optical continuum variations, and optical emission lines, all of which seem to be modulated with these binary periods of 114.5 + or - 0.2 minutes. Although all data are not concurrent, the new system appears to possess the highest ratio of F(x)/F(opt) yet found for an AM Her system. The surprising accumulation of AM Her variables with periods near 114 minute is commented on.

Morris, Simon L.↗
NASA NTRS1992

The orbit of Phi Cygni measured with long-baseline optical interferometry - Component masses and absolute magnitudes

The orbit of the double-lined spectroscopic binary Phi Cygni, the distance to the system, and the masses and absolute magnitudes of its components are presented via measurements with the Mar III Optical Interferometer. On the basis of a reexamination of the spectroscopic data of Rach & Herbig (1961), the values and uncertainties are adopted for the period and the projected semimajor axes from the present fit to the spectroscopic data and the values of the remaining elements from the present fit to the Mark III data. The elements of the true orbit are derived, and the masses and absolute magnitudes of the components, and the distance to the system are calculated.

Armstrong, J. T.↗
NASA NTRS1992

The orbit of Alpha Equulei measured with long-baseline optical interferometry - Component masses, spectral types, and evolutionary state

The apparent orbit of the double-lined spectroscopic binary Alpha Equulei was measured using observations, from June 13, 1989 to September 15, 1990, with the Mark III Optical Interferometer. The results, combined with the spectroscopic results of Rosvick and Scarfe (1991), were used to obtain estimates of the masses of the components, their absolute magnitudes, and the distance to the system. In addition, the magnitude differences between the components were determined at four wavelengths; these were combined with the colors reported by Stickland (1976) to derive colors for the two Alpha Equulei components and to estimate their spectral types.

Armstrong, J. T.↗
NASA NTRS1986

Orbital variability in the wind of the massive X-ray binary HD 153919/4U1700-37

High resolution IUE spectra of HD 153919, the optical counterpart to 401700-37, were examined for evidence of the Hatchett-McCray effect. Although the resonance lines of C IV, N V, and Si IV are too heavily saturated to be very useful, the subordinate line of N IV at 1718 A clearly shows orbital variability in the correct sense to be explained as the removal of parent ions by the X-ray flux from the neutron star.

Howarth, Ian D.↗
NASA NTRS1981

4U 1626-67 - A prograde spinning X-ray pulsar in a 2500 s binary system

The binary period of 4U 1626-67 was found from an analysis of its optical pulsations. A single lower frequency sideband of the 2.4% amplitude 7.68-s optical pulsations from this X-ray pulsar was detected on at least three different nights in Fourier transforms of high-speed photometry obtained with the CTIO 4 m telescope. The 0.42% sidelobe pulsations have a frequency which is 0.4011(2) mHz lower than the frequency of the direct pulsations near 130.26 mHz. The weaker sidelobe pulsations are interpreted as arising from X-ray to optical reprocessing on the companion star and are shifted to the lower frequency by the rotation frequency of the binary orbit because the X-ray pulsar spins in the same sense as the orbital motion (direct or prograde).

Middleditch, J.↗
NASA NTRS1982

Observations and analysis of the R Aquarii jet

Ultraviolet, optical and radio observations of the symbiotic star R Aquarii are discussed in the light of the discovery of a bright radio and optical jet from this star. The star is probably a binary with a period of 44 years. The VLA maps of the jet reveal a protruding structure extending approximately 10 arc sec from the central radio source with a position angle virtually identical to that of the optical jet observed at Lick. The observations of R Aqr are interpreted as indicating the existence of an accretion disk around an unseen companion. The hot subdwarf has effective temperature approximately 65,000 K. It is suggested that the Mira primary and the hot secondary are in orbit around each other with a high eccentricity. At periastron the hot subdwarf accretes at super critical rates and a jet forms. It is difficult to understand how an accretion disk would have eclipsed the Mira in 1928-1935 and 1974-1980. The suppression of maximum light in these two periods is interpreted as due to a distortion of the Mira envelope at periastron by the tidal interaction with the secondary. The jet may help to explain the excitation of the R Aqr nebula. It is possible that R Aqr flared up as a nova approximately 1000 years ago forming the nebula.

Kafatos, M.↗
NASA NTRS1972

Identification of the X-ray pulsar in Hercules: A new optical pulsar

A series of photographic, photoelectric, and spectroscopic observations beginning June 1, 1972 has led to the optical identification of Her X-1 (2U 1705 + 34), a pulsed X-ray source in an eclipsing binary system, with the thirteenth magnitude blue variable star HZ Herculis. The detection of optical pulses at the frequency of the X-ray pulsar on three nights makes the identification conclusive and establishes HZ Her as the second known optical pulsar. The strength of the optical pulses may be correlated with the orbital phase but is not obviously related to the high or low intensity states of the X-ray source.

Davidsen, A.↗
NASA NTRS1982

Model fitting of the Algol binaries

Energy distribution of the component stars of the Algol type semidetached binaries were studied by combining IUE low dispersion spectra with optical scans made with the same resolution. In most cases the flux distributions are matched by Kuruz model atmospheres with normal solar composition. Deviations from normal atmospheres which indicate a higher level of activity and interaction in the binaries are examined. Eclipse observations in U Cep and V356 Sgr reveal emission lines of the W serpentis type.

Dobias, J. J.↗
NASA NTRS1985

HD 8358 - A new active chromosphere binary

The results of an extensive study of the eighth-magnitude G star HD 8358 employing optical photometry and spectroscopy, as well as UV observations with the IUE satellite, are presented. The star is found to be an active chromosphere binary with orbital and photometric period of 0.516 days. It exhibits photometric variability of 0.1-0.2 mg in V, due to starspots. At times the light curve is stable for several months, indicating that the spots persist essentially unchanged for more than 200 rotations. At other times, the spot configuration changes in a month or less. HD 8358 is an unusual member of the 'short-period' group of active chromosphere binaries due to its high space velocity and its very broad and highly variable H-alpha emission.

Bopp, B. W.↗
NASA NTRS1972

Photon counting and Laguerre detection.

In this correspondence maximum-likelihood binary detection theory is applied to an incoherent optical system model employing photodetectors governed by Laguerre counting statistics. It is shown that a maximum-likelihood Laguerre detector corresponds to a count comparison over each signaling interval. Laguerre error probabilities are presented and compared with those for Poisson counting.

Gagliardi, R. M.↗
NASA NTRS1980

The X-ray light curve of 4U 2129+47

The light curve of 4U 2129+47 is presented showing that it almost certainly has a period of approximately 0.22 days. This is the same period as the optical candidate proposed by Thorstensen et al. (1979). Binary X-ray source models, consisting of an M dwarf plus either a neutron star or a white dwarf, are briefly discussed.

Ulmer, M. P.↗