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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Compact X-ray binaries in hierarchical triples. I - Tidal angular momentum loss and GX 17 + 2

A general formalism is developed for the enhanced mass transfer rate expected in a close binary with a (distant) third companion star. Such a hierarchical triple model is applied to the X-ray burster and QPO source GX 17 + 2, consisting of an inner mass-transferring binary comprising a main-sequence secondary and an accreting neutron star, and a more distant companion. The model is shown to account for the anomalously high mass transfer rate for this burster and other systems with short orbital periods. A G star, which does not appear to be the binary companion of the neutron star but is consistent with the sub-arc second radio error box for GX 17 + 2, may be the triple companion. A predicted velocity curve for the triple companion is presented.

Bailyn, Charles D.↗
NASA NTRS2009

Polarization from Scattering in X-Ray Binaries

A paradox of X-ray binaries is that their strong X-ray flux ionizes much nearby low density gas, making it difficult to observe. Polarization can reveal gas which is fully ionized and can provide new insight into X-ray binary environments. In this talk I will present models for the scattering and polarization in X-ray binaries, adopting gas parameters which are chosen according to current ideas about these systems. These include stellar winds from a massive companion, X-ray induced disk winds, and the photospheres of a disk or binary companion.

Kallman, T.↗
NASA NTRS1991

The mid-infrared spectrum of the carbon star HD 38218 and its possible relation to polycyclic aromatic hydrocarbons

The mid-infrared spectra of carbon giant stars with hot companions are investigated in order to search for infrared emission bands from polycyclic aromatic hydrocarbons (PAH) in the envelopes of the C giants. A strong 8-micron emission band found in TU Tau = HD 38218 is attributed to the binary A star companion. It is argued that if the 8-micron feature in HD 38218 arises from PAHs, they seem to be important constituents of the C-giant shell, and they might be large compared with some interstellar PAHs. It is suggested that because no other IR spectra of C giants show clear PAH features, the greater flux of hard radiation in the binary HD 38218 seems likely to be responsible for the 8-micron feature and for its absence in many other C giants. Thus, PAHs could be present in the same amounts relative to SiC grains in the shells of similar single C giants, and the formation of carbonaceous grains could proceed through the formation of PAHs in C giant shells.

Buss, Richard H., Jr.↗
NASA NTRS1995

Astrophysics with Pulsar/Main Sequence Star Binaries

Until very recently, all known radio pulsars in binary orbits had as companions old, degenerate stars, either neutron stars or white dwarfs. In this talk we introduce a new class of binary radio pulsars having as companions young, massive stars. Concentrating on one system in particular, we show that these systems open a new phase space for studying a variety of physical phenomena, including post-Keplerian dynamics, physics of stellar winds and interiors, and binary evolution theory.

Arecibo Telescope↗
NASA NTRS1993

Ultraviolet and optical studies of binaries with luminous cool primaries and hot companions. IV - Further IUE detections

We have obtained IUE spectra for 31 middle and late-type giant and supergiant stars whose TD-1 fluxes or ground-based spectra indicate the presence of a hot component, or whose radial velocities indicate an unseen component. Stellar components earlier than type F1 were detected in 22 cases. While 20 of the hot secondaries are seen weakly in optical spectra, two are UV discoveries: HD 58134 and HD 183864. The hot companions are classified accurately by temperature class from their far-UV spectra. The interstellar extinction of each system and the relative luminosities of the components are derived from the UV and optical fluxes, using a new grid of UV intrinsic colors for hot dwarfs. We find that many giant stars apparently have companions which are too hot and hence too luminous for consistency with the primary's spectral classification.

Parsons, Sidney B.↗
NASA NTRS1994

Evolution of vaporizing pulsars

We construct evolutional scenarios for LMXB's using a simplified stellar model. We discuss the origin and evolution of short-period, low mass binary pulsars with evaporating companions. We suggest that these systems descend from low-mass X-ray binaries and that angular momentum loss mainly due to evaporative wind drives their evolution. We derive limits on the energy and angular momentum carried away by the wind based on the observed low eccentricity. In our model the companion remains near contact, and its quasiadiabatic expansion causes the binary to expand. Short-term oscillations of the orbital period may occur if the Roche-lobe overflow forms an evaporating disk.

Mccormick, P.↗
NASA NTRS2021

KMT-2021-BLG-0322: Severe Degeneracy Between Triple-lens and Higher-order Binary-lens Interpretations

We investigate the microlensing event KMT-2021-BLG-0322, for which the light curve exhibits three distinctive sets of caustic-crossing features. It is found that the overall features of the light curve are approximately described by a binary-lens (2L1S) model, but the model leaves substantial residuals. We test various interpretations with the aim of explaining the residuals. Methods. We find that the residuals can be explained either by considering a nonrectilinear lens-source motion caused by the microlens-parallax and lens-orbital effects or by adding a low-mass companion to the binary lens (3L1S model). The degeneracy between the higher-order 2L1S model and the 3L1S model is very severe, making it difficult to single out a correct solution based on the photometric data. This degeneracy was known before for two previous events (MACHO-97-BLG-41 and OGLE-2013-BLG-0723),which led to the false detections of planets in binary systems, and thus the identification of the degeneracy for KMT-2021-BLG-0322illustrates that the degeneracy can be not only common but also very severe, emphasizing the need to check both interpretations of deviations from 2L1S models. Results. From the Bayesian analysis conducted with the measured lensing observables of the event timescale, angular Einstein radius, and microlens parallax, it was estimated that the binary lens components have masses(M1,M2)=(0.62+0.25−0.26M,0.07+0.03−0.03M), for both2L1S and 3L1S solutions, and the mass of the tertiary lens component according to the 3L1S solution isM3=6.40+2.64−2.78MJ.

Gravitational lensing: micro↗
NASA NTRS2021

Speckle Observations of TESS Exoplanet Host Stars: Understanding the Binary Exoplanet Host Star Orbital Period Distribution

We present high-resolution speckle interferometric imaging observations of TESS exoplanet host stars using the NN-EXPLORE Exoplanet and Stellar Speckle Imager instrument at the 3.5 m WIYN telescope. Eight TESS objects of interest that were originally discovered by Kepler were previously observed using the Differential Speckle Survey Instrument. Speckle observations of 186 TESS stars were carried out, and 45 (24%) likely bound companions were detected. This is approximately the number of companions we would expect to observe given the established 46% binarity rate in exoplanet host stars. For the detected binaries, the distribution of stellar mass ratio is consistent with that of the standard Raghavan distribution and may show a decrease in high-q systems as the binary separation increases. The distribution of binary orbital periods, however, is not consistent with the standard Ragahavan model, and our observations support the premise that exoplanet-hosting stars with binary companions have, in general, wider orbital separations than field binaries. We find that exoplanet-hosting binary star systems show a distribution peaking near 100 au, higher than the 40–50 au peak that is observed for field binaries. This fact led to earlier suggestions that planet formation is suppressed in close binaries.

Stellar Speckle Imager↗
NASA NTRS2011

Supergiant X-Ray Binaries Observed by Suzaku

Suzaku observations are presented for the high-mass X-ray binaries IGR 116207-5129 and IGR 117391-3021. For IGR 116207-5129, we provide the first X-ray broadband (0.5-60 keV) spectrum from which we confirm a large intrinsic column density (N(sub H) = 1.6 x 10(exp 23)/sq cm), and we constrain the cutoff energy for the first time (E(sub cut) = 19 keV). A prolonged (> 30 ks) attenuation of the X-ray flux was observed which we tentatively attribute to an eclipse of the probable neutron star by its massive companion, in a binary system with an orbital period between 4 and 9 days, and inclination angles> 50 degrees. For IGRJ17391-3021, we witnessed a transition from quiescence to a low-activity phase punctuated by weak flares whose peak luminosities in the 0.5-10keV band are only a factor of 5 times that of the pre-flare emission. These micro flares are accompanied by an increase in NH which suggests the accretion of obscuring clumps of wind. We now recognize that these low-activity epochs constitute the most common emission phase for this system, and perhaps in other supergiant fast X-ray transients (SFXTs) as well. We close with an overview of our upcoming program in which Suzaku will provide the first ever observation of an SFXT (IGRJ16479-4514) during a binary orbit enabling us to probe the accretion wind at every phase.

Bodaghee, A.↗
NASA NTRS2015

A Coordinated X-Ray and Optical Campaign of the Nearest Massive Eclipsing Binary, Delta Orionis Aa. I. Overview of the X-Ray Spectrum

We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of Delta Ori A. Delta Ori A is actually a triple system that includes the nearest massive eclipsing spectroscopic binary, Delta Ori Aa, the only such object that can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, Delta Ori Aa2, has a much lower X-ray luminosity than the brighter primary (Delta Ori Aa1), Delta Ori Aa provides a unique system with which to test the spatial distribution of the X-ray emitting gas around Delta Ori Aa1 via occultation by the photosphere of, and wind cavity around, the X-ray dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for the combined observation, having an exposure time of nearly 500 ks and covering nearly the entire binary orbit. The companion papers discuss the X-ray variability seen in the Chandra spectra, present new space-based photometry and ground-based radial velocities obtained simultaneously with the X-ray data to better constrain the system parameters, and model the effects of X-rays on the optical and UV spectra. We find that the X-ray emission is dominated by embedded wind shock emission from star Aa1, with little contribution from the tertiary star Ab or the shocked gas produced by the collision of the wind of Aa1 against the surface of Aa2. We find a similar temperature distribution to previous X-ray spectrum analyses. We also show that the line half-widths are about 0.3−0.5 times the terminal velocity of the wind of star Aa1. We find a strong anti-correlation between line widths and the line excitation energy, which suggests that longer-wavelength, lower-temperature lines form farther out in the wind. Our analysis also indicates that the ratio of the intensities of the strong and weak lines of Fe XVII and Ne X are inconsistent with model predictions, which may be an effect of resonance scattering.

Chandra HETGS↗
DOE OSTI2022

A kinematic excess in the annular gap and gas-depleted cavity in the disc around HD 169142

ABSTRACT We present ALMA band 6 images of the 12CO, 13CO, and C18O J = 2-1 line emissions for the circumstellar disc around HD 169142, at ∼8 au spatial resolution. We resolve a central gas-depleted cavity, along with two independent near-symmetric ring-like structures in line emission: a well-defined inner gas ring [∼25 au] and a second relatively fainter and diffuse outer gas ring [∼65 au]. We identify a localized super-Keplerian feature or vertical flow with a magnitude of ∼75 ms−1 in the 12CO map. This feature has the shape of an arc that spans azimuthally across a position angle range of −60° to 45° and radially in between the B1[26au] and B2[59au] dust rings. Through reconstruction of the gas surface density profile, we find that the magnitude of the background perturbations by the pressure support and self-gravity terms are not significant enough to account for the kinematic excess. If of planetary origin, the relative depletion in the gas-density profile would suggest a 1 MJ planet. In contrast, the central cavity displays relatively smooth kinematics, suggesting either a low-mass companion and/or a binary orbit with a minimal vertical velocity component.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Simulations of Precessing Jets and the Formation of X-shaped Radio Galaxies

Abstract Jet precession is sometimes invoked to explain asymmetries in radio galaxy (RG) jets and “X/S/Z-shaped” RGs, caused by the presence of a binary black hole companion to the source active galactic nucleus or by accretion instabilities. We present a series of simulations of RG jet precession to examine how these sources would evolve over time, including a passive distribution of cosmic-ray electrons so we can model radio synchrotron emissions and create synthetic radio maps of the sources. We find that a single source viewed from different angles can result in differing RG morphological classifications, confusing physical implications of these classifications. Additionally, the jet trajectories can become unstable due to their own self-interactions and lead to “reorientation events” that may look like the effects of external dynamics such as shocks, winds, or cold fronts in the medium. Finally, something akin to an “Odd Radio Circle” may be observed in the case of viewing the radio remnant of such a precessing source from a line of sight near the precession axis.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2004

Hard X-ray Emission from White Dwarfs

Hot white dwarfs may exhibit photospheric emission at X-ray wavelengths, but their X- ray emission should be soft, mutch less than 0.5 keV. Hard X-ray emission, at approx. 1 keV, is not expected from white dwarfs, unless they are in binary systems and the hard X-ray emission is produced by a late-type companion's coronal activity or by accretion of a companion's material onto the surface of the white dwarf. We proposed to use the ROSAT archive to search for hard X-ray emission from white dwarfs in order to determine whether hard X-ray emission may provide a sensitive diagnostic for the existence of a binary companion.

Chu, You-Hua↗
NASA NTRS2005

X-Ray Emission from "Uranium" Stars

The project aims to secure XMM observations of two targets with extremely low abundances of the majority of heavy elements (e.g., log[Fe/H] $\sim$-4), but that show absorption lines of uranium. The presence of an r-process element such as uranium requires a binary star system in which the companion underwent a supernova explosion. A binary star system raises the distinct possibility of the existence of a compact object, most likely a neutron star, in the binary, assuming it survived the supernova blast. The presence of a compact object then suggests X-ray emission if sufficient matter accretes to the compact object. The observations were completed less than one year ago following a series of reobservations to correct for significant flaring that occurred during the original observations. The ROSAT all-sky survey was used to report on the initial assessment of X-ray emission from these objects; only upper limits were reported. These upper limits were used to justify the XMM observing time, but with the expectation that upper limits would merely be pushed lower. The data analysis hinges critically on the quality and degree of precision with which the background is handled. During the past year, I have spent some time learning the ins and outs of XMM data analysis. In the coming year, I can apply that learning to the analysis of the 'uranium' stars.

Schlegel, Eric↗
NASA NTRS2022

KMT-2021-BLG-0912Lb: A Microlensing Super Earth Around A K-Type Star

Aims . The light curve of the microlensing event KMT-2021-BLG-0912 exhibits a very short anomaly relative to a single-lens single-source form. We investigate the light curve for the purpose of identifying the origin of the anomaly. Methods . We model the light curve under various interpretations. From this, we find four solutions, in which three solutions are found under the assumption that the lens is composed of two masses (2L1S models), and the other solution is found under the assumption that the source is comprised of binary stars (1L2S model). The 1L2S model is ruled out based on the contradiction that the faint source companion is bigger than its primary, and one of the 2L1S solutions is excluded from the combination of the poorer fit, blending constraint, and lower overall probability, leaving two surviving solutions with the planet/host mass ratios of q ∼ 2.8 × 10 −5 and ∼1.1 × 10 −5 . A subtle central deviation supports the possibility of a tertiary lens component, either a binary companion to the host with a very large or small separation, or a second planet lying near the Einstein ring, but it is difficult to claim a secure detection due to the marginal improvement of the fit, lack of consistency among different data sets, and difficulty in uniquely specifying the nature of the tertiary component. Results . With the observables of the event, it is estimated that the masses of the planet and host are ∼(6.9 M ⊕ , 0.75 M ⊙ ) according to one solution and ∼(2.8 M ⊕ , 0.80 M ⊙ ) according to the other, indicating that the planet is a super Earth around a K-type star, regardless of the solution. The fact that 16 (including the one reported in this work) out of 19 microlensing planets with M ≲ 10 M ⊕ were detected during the last 6 yr nicely demonstrates the importance of high-cadence global surveys in detecting very low-mass planets.

gravitational lensing↗
NASA NTRS1986

Can comet clouds around neutron stars explain gamma-ray bursts?

The proposal of Harwit and Salpeter (1973) that gamma-ray bursts are due to impacts of comets onto neutron stars is examined further. It is assumed that most stars are formed with comet clouds similar to the Oort comet cloud which surrounds the sun, and it is suggested that there are at least four mechanisms by wich neutron stars may be formed while retaining their comet clouds: a spherically symmetric supernova explosion in an isolated star, accretion-induced collapse of a white dwarf in a cataclysmic variable with a very low mass secondary, accretion-induced collapse of a white dwarf in a wide binary with a low-mass giant companion, and coalescence of a close binary composed of two white dwarfs. Estimates are given of the cometary impact rates for such systems. It is suggested that if the wide binary scenario is correct, optical bursts may arise from the impact of comets onto the white dwarf remnant of the giant companion.

Tremaine, S.↗
NASA NTRS1993

On the tidal interaction between protostellar disks and companions

Formation of protoplanets and binary stars in a protostellar disk modifies the structure of the disk. Through tidal interactions, energy and angular momentum are transferred between the disk and protostellar or protoplanetary companion. We summarize recent progress in theoretical investigations of the disk-companion tidal interaction. We show that low-mass protoplanets excite density waves at their Lindblad resonances and that these waves are likely to be dissipated locally. When a protoplanet acquires sufficient mass, its tidal torque induces the formation of a gap in the vicinity of its orbit. Gap formation leads to the termination of protoplanetary growth by accretion. For proto-Jupiter to attain its present mass, we require that (1) the primordial solar nebula is heated by viscous dissipation; (2) the viscous evolution time scale of the nebula is comparable to the age of typical T Tauri stars with circumstellar disks; and (3) the mass distribution in the nebula is comparable to that estimated from a minimum-mass nebula model.

Lin, D. N. C.↗