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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

X-RAY AND GAMMA-RAY EMISSIONS FROM ROTATION POWERED MILLISECOND PULSARS

The Fermi Large Area Telescope has revealed that rotation powered millisecond pulsars (MSPs) are a major contributor to the Galactic {gamma}-ray source population. Such pulsars may also be important in modeling the quiescent state of several low-mass X-ray binaries (LMXBs), where optical observations of the companion star suggest the possible existence of rotation powered MSPs. To understand the observational properties of the different evolutionary stages of MSPs, the X-ray and {gamma}-ray emissions associated with the outer gap model are investigated. For rotation powered MSPs, the size of the outer gap and the properties of the high-energy emission are controlled by either the photon-photon pair-creation process or magnetic pair-creation process near the surface. For these pulsars, we find that the outer gap model controlled by the magnetic pair-creation process is preferable in explaining the possible correlations between the {gamma}-ray luminosity or non-thermal X-ray luminosity versus the spin-down power. For the accreting MSPs in quiescent LMXBs, the thermal X-ray emission at the neutron star (NS) surface resulting from deep crustal heating can control the conditions in the outer gap. We argue that the optical modulation observed in the quiescent state of several LMXBs originates from the irradiation of the donor star by {gamma}-rays from the outer gap. In these systems, the irradiation luminosity required for the optical modulation of the source such as SAX J1808.4-3658 can be achieved for a NS of high mass. Finally, we discuss the high-energy emission associated with an intra-binary shock in black widow systems, e.g., PSR B1957+20.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

OPTICAL SPECTROSCOPY OF THE HIGH-MASS γ-RAY BINARY 1FGL J1018.6−5856: A PROBABLE NEUTRON STAR PRIMARY

We present medium-resolution optical spectroscopy with the SOAR telescope of the O star secondary of the high-mass γ-ray binary 1FGL J1018.6–5856 to help determine whether the primary is a neutron star or black hole. We find that the secondary has a low radial velocity semi-amplitude of 11–12 km s{sup −1}, with consistent values obtained for H and He absorption lines. This low value strongly favors a neutron star primary: while a black hole cannot be excluded if the system is close to face on, such inclinations are disallowed by the observed rotation of the secondary. We also find the high-energy (X-ray and γ-ray) flux maxima occur when the star is behind the compact object along our line of sight, inconsistent with a simple model of anisotropic inverse Compton scattering for the γ-ray photons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A coordinated X-ray and optical campaign of the nearest massive eclipsing binary, δ Orionis Aa. II. X-ray variability

We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the δ Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of ≈479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5–25 Å is confirmed, with a maximum amplitude of about ±15% within a single ≈125 ks observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the nine-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate the variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S xv, Si xiii, and Ne ix. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at ϕ = 0.0 when the secondary δ Ori Aa2 is at the inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind–wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A coordinated X-ray and optical campaign of the nearest massive eclipsing binary, δ Orionis Aa. IV. A multiwavelength, non-LTE spectroscopic analysis

Eclipsing systems of massive stars allow one to explore the properties of their components in great detail. We perform a multi-wavelength, non-LTE analysis of the three components of the massive multiple system δ Ori A, focusing on the fundamental stellar properties, stellar winds, and X-ray characteristics of the system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

REINSTATING THE M31 X-RAY SYSTEM RX J0042.3+4115 AS A BLACK HOLE X-RAY BINARY AND COMPELLING EVIDENCE FOR AN EXTENDED CORONA

The M31 X-ray source RX J0042.3+4115 was originally identified as a black hole (BH) binary because it displayed characteristic low-state variability at conspicuously high luminosities; unfortunately, this variability was later found to be artificial. However, analysis of 84 Chandra ACIS observations, a Hubble Space Telescope Advanced Camera for Surveys (ACS)/WFC observation, and a 60 ks XMM-Newton observation has supplied new evidence that RX J0042.3+4115 is indeed a BH binary. The brightest optical star within 3{sigma} of the position of RXJ0042.3+4115 had a F435W ({approx}B) magnitude of 25.4 {+-} 0.2; M{sub B} > -0.4, hence we find a low-mass donor likely. RX J0042.3+4115 was persistently bright over {approx}12 years. Spectral fits revealed characteristic BH binary states: a low/hard state at 2.08 {+-} 0.08 Multiplication-Sign 10{sup 38} erg s{sup -1} and a steep power-law state at 2.41 {+-} 0.05 Multiplication-Sign 10{sup 38} erg s{sup -1} (0.3-10 keV). The high-luminosity low state suggests a {approx}20 M{sub Sun} primary; this is high, but within the range of known stellar BH masses. The inner disk temperature during the steep power-law state is 2.24 {+-} 0.15 keV, high but strikingly similar to that of GRS 1915+105, the only known Galactic BH binary with a low-mass donor to be persistently bright. Therefore, RX J0042.3+4115 may be an analog for GRS 1915+105; however, other mechanisms may account for its behavior. We find compelling evidence for an extended corona during the steep power-law state, because compact corona models where the seed photons for Comptonization are tied to the inner disk temperature are rejected.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Pressure tuning the lattice and optical response of silver sulfide

Binary transition metal chalcogenides have attracted increasing attention for their unique structural and electronic properties. High pressure is a powerful tool for tuning the lattice and electronic structure of transition metal chalcogenides away from their pristine states. In this work, we systematically studied the in situ structural and optical behavior of silver sulfide (Ag{sub 2}S) under pressure by synchrotron X-ray diffraction and infrared spectroscopy measurements in a diamond anvil cell. Upon compression, Ag{sub 2}S undergoes structural symmetrization accompanied by a series of structural transitions while the crystallographic inequivalence of the two Ag sites is maintained. Electronically, pressure effectively tunes the ambient semiconducting Ag{sub 2}S into a metal at ∼22 GPa. Drude model analysis shows that the optical conductivity evolves significantly, reaching the highest value of 100 Ω{sup −1} cm{sup −1} at ∼40 GPa. Our results highlight the structural and electronic tunability of silver chalcogenides as a function of pressure and suggest the potential of Ag{sub 2}S as a platform for developing optical and opto-electronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

THE ChaMPlane BRIGHT X-RAY SOURCES-GALACTIC LONGITUDES l = 2 Degree-Sign -358 Degree-Sign

The Chandra Multi-wavelength Plane (ChaMPlane) survey aims to constrain the Galactic population of mainly accretion-powered, but also coronal, low-luminosity X-ray sources (L{sub X} {approx}< 10{sup 33} erg s{sup -1}). To investigate the X-ray source content in the plane at fluxes F{sub X} {approx}> 3 Multiplication-Sign 10{sup -14} erg s{sup -1} cm{sup -2}, we study 21 of the brightest ChaMPlane sources, viz., those with >250 net counts (0.3-8 keV). By excluding the heavily obscured central part of the plane, our optical/near-infrared follow-up puts useful constraints on their nature. We have discovered two likely accreting white dwarf binaries. CXOPS J154305.5-522709 (CBS 7) is a cataclysmic variable showing periodic X-ray flux modulations on 1.2 hr and 2.4 hr; given its hard spectrum the system is likely magnetic. We identify CXOPS J175900.8-334548 (CBS 17) with a late-type giant; if the X-rays are indeed accretion powered, it belongs to the small but growing class of symbiotic binaries lacking strong optical nebular emission lines. CXOPS J171340.5-395213 (CBS 14) is an X-ray transient that brightened {approx}>100 times. We tentatively classify it as a very late type (>M7) dwarf, of which few have been detected in X-rays. The remaining sources are (candidate) active galaxies, normal stars and active binaries, and a plausible young T Tauri star. The derived cumulative number density versus flux (log N-log S) relation for the Galactic sources appears flatter than expected for an isotropic distribution, indicating that we are seeing a non-local sample of mostly coronal sources. Our findings define source templates that we can use, in part, to classify the >10{sup 4} fainter sources in ChaMPlane.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The Araucaria project. The distance to the small Magellanic Cloud from late-type eclipsing binaries

We present a distance determination to the Small Magellanic Cloud (SMC) based on an analysis of four detached, long-period, late-type eclipsing binaries discovered by the Optical Gravitational Lensing Experiment (OGLE) survey. The components of the binaries show negligible intrinsic variability. A consistent set of stellar parameters was derived with low statistical and systematic uncertainty. The absolute dimensions of the stars are calculated with a precision of better than 3%. The surface brightness-infrared color relation was used to derive the distance to each binary. The four systems clump around a distance modulus of (m – M) = 18.99 with a dispersion of only 0.05 mag. Combining these results with the distance published by Graczyk et al. for the eclipsing binary OGLE SMC113.3 4007, we obtain a mean distance modulus to the SMC of 18.965 ± 0.025 (stat.) ± 0.048 (syst.) mag. This corresponds to a distance of 62.1 ± 1.9 kpc, where the error includes both uncertainties. Taking into account other recent published determinations of the SMC distance we calculated the distance modulus difference between the SMC and the Large Magellanic Cloud equal to 0.458 ± 0.068 mag. Finally, we advocate μ{sub SMC} = 18.95 ± 0.07 as a new 'canonical' value of the distance modulus to this galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

MULTI-WAVELENGTH OBSERVATIONS OF THE DISSOCIATIVE MERGER IN THE GALAXY CLUSTER CIZA J0107.7+5408

We present results based on X-ray, optical, and radio observations of the massive galaxy cluster CIZA J0107.7+5408. We find that this system is a post-core-passage, dissociative, binary merger, with the optical galaxy density peaks of each subcluster leading their associated X-ray emission peaks. This separation occurs because the diffuse gas experiences ram pressure forces, while the effectively collisionless galaxies (and presumably their associated dark matter (DM) halos) do not. This system contains double-peaked diffuse radio emission, possibly a double radio relic with the relics lying along the merger axis and also leading the X-ray cores. We find evidence for a temperature peak associated with the SW relic, likely created by the same merger shock that is powering the relic radio emission in this region. Thus, this system is a relatively rare, clean example of a dissociative binary merger, which can in principle be used to place constraints on the self-interaction cross-section of DM. Low-frequency radio observations reveal ultra-steep spectrum diffuse radio emission that is not correlated with the X-ray, optical, or high-frequency radio emission. We suggest that these sources are radio phoenixes, which are preexisting non-thermal particle populations that have been re-energized through adiabatic compression by the same merger shocks that power the radio relics. Finally, we place upper limits on inverse Compton emission from the SW radio relic.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Understanding and Manipulating Helical Nanofilaments in Binary Systems with Achiral Dopants

Here, in this paper, we report the relationship between helical pitch of the helical nanofilament (HNF) phase formed by bent-core molecule NOBOW and the concentration of achiral dopants 5CB and octane, using linearly polarized resonant soft X-ray scattering (RSoXS). Utilizing theory-based simulation, which fits well with the experiments, the molecular helices in the filament were probed and the superstructure of helical 5CB directed by groove of HNFs was observed. Quantitative pitch determination with RSoXS reveals that helical pitch variation is related to 5CB concentration with no temperature dependence. Doping rodlike immiscible 5CB led to a pitch shortening of up to 30%, which was attributed to a change in interfacial tension. By shedding light not only on phase behavior of binary systems but also enabling control over pitch length, our work may benefit various applications of HNF-containing binary systems, including optical rotation devices, circularly polarized light emitters, and chirality transfer agents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Dielectric function in the NIR-VUV spectral range of (In{sub x}Ga{sub 1−x}){sub 2}O{sub 3} thin films

We determined the dielectric function of the alloy system (In{sub x}Ga{sub 1−x}){sub 2}O{sub 3} by spectroscopic ellipsometry in the wide spectral range from 0.5 eV to 8.5 eV and for In contents ranging from x = 0.02 to x = 0.61. The predicted optical transitions for binary, monoclinic β-Ga{sub 2}O{sub 3}, and cubic bcc-In{sub 2}O{sub 3} are well reflected by the change of the dielectric functions' lineshape as a function of the In content. In an intermediate composition range with phase-separated material (x ≈ 0.3…0.4), the lineshape differs considerably, which we assign to the presence of the high-pressure rhombohedral InGaO{sub 3}-II phase, which we also observe in Raman experiments in this range. By model analysis of the dielectric function, we derived spectra of the refractive index and the absorption coefficient and energy parameters of electronic band-band transitions. We discuss the sub-band gap absorption tail in relation to the influence of the In 4d orbitals on the valence bands. The data presented here provide a basis for a deeper understanding of the electronic properties of this technologically important material system and may be useful for device engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The SDSS-III APOGEE radial velocity survey of M dwarfs. I. Description of the survey and science goals

We are carrying out a large ancillary program with the Sloan Digital Sky Survey, SDSS-III, using the fiber-fed multi-object near-infrared APOGEE spectrograph, to obtain high-resolution H-band spectra of more than 1200 M dwarfs. These observations will be used to measure spectroscopic rotational velocities, radial velocities, physical stellar parameters, and variability of the target stars. Here, we describe the target selection for this survey, as well as results from the first year of scientific observations based on spectra that will be publicly available in the SDSS-III DR10 data release. As part of this paper we present radial velocities and rotational velocities of over 200 M dwarfs, with a vsin i precision of ∼2 km s{sup –1} and a measurement floor at vsin i = 4 km s{sup –1}. This survey significantly increases the number of M dwarfs studied for rotational velocities and radial velocity variability (at ∼100-200 m s{sup –1}), and will inform and advance the target selection for planned radial velocity and photometric searches for low-mass exoplanets around M dwarfs, such as the Habitable Zone Planet Finder, CARMENES, and TESS. Multiple epochs of radial velocity observations enable us to identify short period binaries, and adaptive optics imaging of a subset of stars enables the detection of possible stellar companions at larger separations. The high-resolution APOGEE spectra, covering the entire H band, provide the opportunity to measure physical stellar parameters such as effective temperatures and metallicities for many of these stars. At the culmination of this survey, we will have obtained multi-epoch spectra and radial velocities for over 1400 stars spanning the spectral range M0-L0, providing the largest set of near-infrared M dwarf spectra at high resolution, and more than doubling the number of known spectroscopic vsin i values for M dwarfs. Furthermore, by modeling telluric lines to correct for small instrumental radial velocity shifts, we hope to achieve a relative velocity precision floor of 50 m s{sup –1} for bright M dwarfs. With three or more epochs, this precision is adequate to detect substellar companions, including giant planets with short orbital periods, and flag them for higher-cadence followup. We present preliminary, and promising, results of this telluric modeling technique in this paper.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE NEEDLE IN THE 100 deg{sup 2} HAYSTACK: UNCOVERING AFTERGLOWS OF FERMI GRBs WITH THE PALOMAR TRANSIENT FACTORY

The Fermi Gamma-ray Space Telescope has greatly expanded the number and energy window of observations of gamma-ray bursts (GRBs). However, the coarse localizations of tens to a hundred square degrees provided by the Fermi GRB Monitor instrument have posed a formidable obstacle to locating the bursts’ host galaxies, measuring their redshifts, and tracking their panchromatic afterglows. We have built a target-of-opportunity mode for the intermediate Palomar Transient Factory in order to perform targeted searches for Fermi afterglows. Here, we present the results of one year of this program: 8 afterglow discoveries out of 35 searches. Two of the bursts with detected afterglows (GRBs 130702A and 140606B) were at low redshift (z = 0.145 and 0.384, respectively) and had spectroscopically confirmed broad-line Type Ic supernovae. We present our broadband follow-up including spectroscopy as well as X-ray, UV, optical, millimeter, and radio observations. We study possible selection effects in the context of the total Fermi and Swift GRB samples. We identify one new outlier on the Amati relation. We find that two bursts are consistent with a mildly relativistic shock breaking out from the progenitor star rather than the ultra-relativistic internal shock mechanism that powers standard cosmological bursts. Finally, in the context of the Zwicky Transient Facility, we discuss how we will continue to expand this effort to find optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

OPTICAL IDENTIFICATION OF He WHITE DWARFS ORBITING FOUR MILLISECOND PULSARS IN THE GLOBULAR CLUSTER 47 TUCANAE

We used ultra-deep UV observations obtained with the Hubble Space Telescope to search for optical companions to binary millisecond pulsars (MSPs) in the globular cluster 47 Tucanae. We identified four new counterparts (to MSPs 47TucQ, 47TucS, 47TucT, and 47TucY) and confirmed those already known (to MSPs 47TucU and 47TucW). In the color–magnitude diagram, the detected companions are located in a region between the main sequence and the CO white dwarf (WD) cooling sequences, consistent with the cooling tracks of He WDs with masses between 0.15 M{sub ⊙} and 0.20 M{sub ⊙}. For each identified companion, mass, cooling age, temperature, and pulsar mass (as a function of the inclination angle) have been derived and discussed. For 47TucU we also found that the past accretion history likely proceeded at a sub-Eddington rate. The companion to the redback 47TucW is confirmed to be a non-degenerate star, with properties particularly similar to those observed for black widow systems. Two stars have been identified within the 2σ astrometric uncertainty from the radio positions of 47TucH and 47TucI, but the available data prevent us from firmly assessing whether they are the true companions of these two MSPs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE DENSEST GALAXY

We report the discovery of a remarkable ultra-compact dwarf galaxy around the massive Virgo elliptical galaxy NGC 4649 (M60), which we call M60-UCD1. With a dynamical mass of 2.0 × 10{sup 8} M {sub ☉} but a half-light radius of only ∼24 pc, M60-UCD1 is more massive than any ultra-compact dwarfs of comparable size, and is arguably the densest galaxy known in the local universe. It has a two-component structure well fit by a sum of Sérsic functions, with an elliptical, compact (r{sub h} = 14 pc; n ∼ 3.3) inner component and a round, exponential, extended (r{sub h} = 49 pc) outer component. Chandra data reveal a variable central X-ray source with L{sub X} ∼ 10{sup 38} erg s{sup –1} that could be an active galactic nucleus associated with a massive black hole or a low-mass X-ray binary. Analysis of optical spectroscopy shows the object to be old (∼> 10 Gyr) and of solar metallicity, with elevated [Mg/Fe] and strongly enhanced [N/Fe] that indicates light-element self-enrichment; such self-enrichment may be generically present in dense stellar systems. The velocity dispersion (σ ∼ 70 km s{sup –1}) and resulting dynamical mass-to-light ratio (M/L{sub V} = 4.9 ± 0.7) are consistent with—but slightly higher than—expectations for an old, metal-rich stellar population with a Kroupa initial mass function. The presence of a massive black hole or a mild increase in low-mass stars or stellar remnants is therefore also consistent with this M/L{sub V} . The stellar density of the galaxy is so high that no dynamical signature of dark matter is expected. However, the properties of M60-UCD1 suggest an origin in the tidal stripping of a nucleated galaxy with M{sub B} ∼ –18 to –19.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

SEARCHING FOR BINARY Y DWARFS WITH THE GEMINI MULTI-CONJUGATE ADAPTIVE OPTICS SYSTEM (GeMS)

The NASA Wide-field Infrared Survey Explorer (WISE) has discovered almost all the known members of the new class of Y-type brown dwarfs. Most of these Y dwarfs have been identified as isolated objects in the field. It is known that binaries with L- and T-type brown dwarf primaries are less prevalent than either M-dwarf or solar-type primaries, they tend to have smaller separations and are more frequently detected in near-equal mass configurations. The binary statistics for Y-type brown dwarfs, however, are sparse, and so it is unclear if the same trends that hold for L- and T-type brown dwarfs also hold for Y-type ones. In addition, the detection of binary companions to very cool Y dwarfs may well be the best means available for discovering even colder objects. We present results for binary properties of a sample of five WISE Y dwarfs with the Gemini Multi-Conjugate Adaptive Optics System. We find no evidence for binary companions in these data, which suggests these systems are not equal-luminosity (or equal-mass) binaries with separations larger than ∼0.5–1.9 AU. For equal-mass binaries at an age of 5 Gyr, we find that the binary binding energies ruled out by our observations (i.e., 10{sup 42} erg) are consistent with those observed in previous studies of hotter ultra-cool dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Binary pseudo-random array standards for calibration of 3D optical surface profilers used for metrology with aspheric x-ray optics

High-accuracy surface metrology is vitally important in manufacturing ultra-high-quality free-form mirrors designed to manipulate x-ray light with nanometer-scale wavelengths. The current and potential capabilities of x˗ray mirror manufacturing are limited by inherent imperfections of the integrated metrology tools. Metrology tools are currently calibrated with super-polished flat test-standard/reference mirrors. This is acceptable for fabrication of slightly curved x-ray optics. However, for even moderately curved aspherical x-ray mirrors the flat-reference calibration is not sufficiently accurate. For micro-stitching interferometry developed for surface measurements with curved x-ray mirrors, the tool aberration errors are known to be transferred into the optical surface topography of x-ray mirrors. Our approach to improving metrology is to thoroughly calibrate the measuring tool and apply the results of the calibration to deconvolution of the measured data. Here we explore the application of a recently developed technique for calibrating the instrument transfer function (ITF) of 3D optical surface profilers to metrology with significantly curved x-ray optics. The technique, based on test standards patterned with two-dimensional (2D) binary pseudo-random arrays (BPRAs), employs the unique properties of the BPRA patterns in the spatial frequency domain. The inherent 2D power spectral density of the pattern has a deterministic white-noise-like character that allows direct determination of the ITF with uniform sensitivity over the entire spatial frequency range and field of view of an instrument. The high efficacy of the technique has been previously demonstrated in application to metrology with flat and slightly curved optics. Here, we concentrate on development of an efficient fabrication process for production of highly randomized (HR) BPRA test standards on flat and 500-mm spherical optical substrates. We also compare and discuss the results of the ITF calibration of an interferometric microscope when using the HR BPRA standards on flat and curved substrates.

Munechika, Keiko↗
DOE OSTI2011

THE REVISED ORBIT OF THE {delta} Sco SYSTEM

In anticipation of the possible collision between a circumstellar disk and the secondary star in the highly eccentric binary system {delta} Scorpii, high angular resolution interferometric observations have been acquired, aimed at revising the binary parameters. The Navy Prototype Optical Interferometer was used to spatially resolve the binary components in 2000 and over a period between 2005 and 2010. The interferometric observations are used to obtain the angular separations and orientations of the two stellar components at all epochs for which data have been obtained, including 2005 and 2006, for which, based on previous studies, there was some uncertainty as to if the signature of binarity can be clearly detected. The results of this study represent the most complete and accurate coverage of the binary orbit of this system to date and allow for the revised timing of the upcoming periastron passage that will occur in 2011 to be obtained.

79 ASTRONOMY AND ASTROPHYSICS↗