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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Frontiers of stellar evolution

The present conference discusses theoretical and observational views of star formation, spectroscopic constraints on the evolution of massive stars, very low mass stars and brown dwarfs, asteroseismology, globular clusters as tests of stellar evolution, observational tests of stellar evolution, and mass loss from cool evolved giant stars. Also discussed are white dwarfs and hot subdwarfs, neutron stars and black holes, supernovae from single stars, close binaries with evolved components, accretion disks in interacting binaries, supernovae in binary systems, stellar evolution and galactic chemical evolution, and interacting binaries containing compact components.

Lambert, David L.↗
NASA NTRS1994

The pre-cataclysmic binary EUVE 2013+400

New optical spectroscopy shows a 0.706 d orbital period for Extreme Ultraviolet Explorer (EUVE) 2013+400 and confirms its membership in a class of close binary systems emerging from common-envelope evolution. This binary, like the prototype Feige 24, consists of an extreme ultraviolet (EUV) emitting hot white dwarf and a late-type dwarf. Bergeron et al.'s (1994) optical spectroscopy and ultraviolet spectrophotometry indicate that the white dwarf is hot (T(sub eff) approximately equals 50 000 K) and therefore very young (t(sub age) less than or equal 5 x 10(exp 6) yr), and extreme ultraviolet photometry places EUVE 2013+400 along a neutral hydrogen column density in the interstellar medium of n(sub H) approximately equal to 10(exp 19)/sq cm. The white dwarf is a DAO type and we obtained two independent estimates of the helium abundance from EUV photometric measurements (log(y) approximately equal to -3.2) and from the He II lambda-4686 line profile (log(y) approximately equal to -2.8). The data possibly indicate a level of heterogeneity expected in the context of on-going chemical separation in the photospheric layers. The Balmer lines show narrow emission that varies with binary phase with the equivalent widths of the emission trailing the radial velocities by 1/4 cycle: this phasing shows that most of the emission arises on the EUV-illuminated face of the red dwarf. A spectrophotometric decomposition shows that the secondary's spectral type is near M3 and that it contributes about 15%-25% of the total light near 6500 A; the resulting H-alpha emission is twice as strong as in Feige 24, with an equivalent width of 37-61 A with respect to the red dwarf continuum. EUVE 2013+400 is an important addition to the class of close binary stars discovered in EUV all-sky surveys.

Thorstensen, John R.↗
NASA NTRS1994

A general catalogue of close binary systems

A comprehensive catalog of close binary stars to be used for the study of the fundamental properties of stars and for the exploration and elucidation of evolutionary processes in those systems, is presented. Spectroscopic binaries, variable stars, suspected variable stars, and interacting binaries are included in the scope of the catalog.

Webbink, Ronald F.↗
NASA NTRS2010

SIM Lite Detection of Habitable Planets in P-Type Binary-Planetary Systems

Close binary stars like spectroscopic binaries create a completely different environment than single stars for the evolution of a protoplanetary disk. Dynamical interactions between one star and protoplanets in such systems provide more challenges for theorists to model giant planet migration and formation of multiple planets. For habitable planets the majority of host stars are in binary star systems. So far only a small amount of Jupiter-size planets have been discovered in binary stars, whose minimum separations are 20 AU and the median value is about 1000 AU (because of difficulties in radial velocity measurements). The SIM Lite mission, a space-based astrometric observatory, has a unique capability to detect habitable planets in binary star systems. This work analyzed responses of the optical system to the field stop for companion stars and demonstrated that SIM Lite can observe exoplanets in visual binaries with small angular separations. In particular we investigated the issues for the search for terrestrial planets in P-type binary-planetary systems, where the planets move around both stars in a relatively distant orbit.

Pan, Xiaopei↗
DOE OSTI2023

The Evolution of Population III and Extremely Metal-poor Binary Stars

Numerical simulations have now shown that Population III (Pop III) stars can form in binaries and small clusters and that these stars can be in close proximity to each other. If so, they could be subject to binary interactions such as mass exchange that could profoundly alter their evolution, ionizing UV and Lyman–Werner photon emission and explosion yields, with important consequences for early cosmological reionization and chemical enrichment. Here we investigate the evolution of Pop III and extremely metal-poor binary stars with the MESA code. We find that interactions ranging from stable mass transfer to common envelope evolution can occur in these binaries for a wide range of mass ratios and initial separations. Mass transfer can nearly double UV photon yields in some of these binaries with respect to their individual stars by extending the life of the companion star, which in turn can enhance early cosmological reionization but also suppress the formation of later generations of primordial stars. Binary interactions can also have large effects on the nucleosynthetic yields of the stars by promoting or removing them into or out of mass ranges for specific SN types. We provide fits to total photon yields for the binaries in our study for use in cosmological simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1983

Synchronization of magnetic stars in binary systems

Asynchronous rotation of magnetic stars in close binary systems drives substantial field-aligned electrical currents between the magnetic star and its companion. The resulting magnetohydrodynamic torque is able to account for the heretofore unexplained synchronous rotation of the strongly magnetic degenerate dwarf component in systems like AM Her, VV Pup, AN UMa, and EF Eri as well as the magnetic A type component in systems like HD 98088 and 41 Tauri. The electric fields produced by even a small asynchronism are large and may accelerate some electrons to high energies, producing radio emission. The total energy dissipation rate in systems with degenerate dwarf spin periods as short as 1 minute may reach 10 to the 33rd ergs/s. Total luminosities of this order may be a characteristic feature of such systems.

Lamb, F. K.↗
NASA NTRS2022

Ultraviolet Spectropolarimetry Conservative and Nonconservative Mass Transfer in OB Interacting Binaries

The current consensus is that at least half of the OB stars are formed in binary or multiple star systems. The evolution of OB stars is greatly influenced by whether the stars begin as close binaries, and the evolution of the binary systems depend on whether the mass transfer is conservative or nonconservative. FUV/NUV spectropolarimetry is poised to answer the latter question. This paper discusses how the Polstar spectropolarimetry mission can characterize the degree of nonconservative mass transfer that occurs at various stages of binary evolution, from the initial mass reversal to the late Algol phase, and quantify its amount. The proposed instrument combines spectroscopic and polarimetric capabilities, where the spectroscopy can resolve Doppler shifts in UV resonance lines with 10 km/s precision, and polarimetry can resolve linear polarization with 10 −3 precision or better. The spectroscopy will identify absorption by mass streams and other plasmas seen in projection against the stellar disk as a function of orbital phase, as well as scattering from extended splash structures, including jets. The polarimetry tracks the light coming from material not seen against the stellar disk, allowing the geometry of the scattering to be tracked, resolving ambiguities left by the spectroscopy and light-curve information. For example, nonconservative mass streams ejected in the polar direction will produce polarization of the opposite sign from conservative transfer accreting in the orbital plane. Time domain coverage over a range of phases of the binary orbit are well supported by the Polstar observing strategy. Special attention will be given to the epochs of enhanced systemic mass loss that have been identified from IUE observations (pre-mass reversal and tangential gas stream impact). We show how the history of systemic mass and angular momentum loss/gain episodes can be inferred via ensemble evolution through the r–q diagram. Combining the above elements will significantly improve our understanding of the mass transfer process and the amount of mass that can escape from the system, an important channel for changing the final mass and ultimate supernova of a large number of massive stars found in binaries at close enough separation to undergo interaction.

Geraldine J. Peters↗
NASA NTRS1992

Tidal heating and mass loss in neutron star binaries - Implications for gamma-ray burst models

A neutron star in a close binary orbit around another neutron star (or stellar-mass black hole) spirals inward owing to gravitational radiation. We discuss the effects of tidal dissipation during this process. Tidal energy dissipated in the neutron star's core escapes mainly as neutrinos, but heating of the crust, and outward diffusion of photons, blows off the outer layers of the star. This photon-driven mass loss precedes the final coalescence. The presence of this eject material impedes the escape of gamma-rays created via neutrino interactions. If an e(+) - e(-) fireball, created in the late stages of coalescence, were loaded with (or surrounded by) material with the mean column density of the ejecta, it could not be an efficient source of gamma-rays. Models for cosmologically distant gamma-rays burst that involve neutron stars must therefore be anisotropic, so that the fireball expands preferentially in directions where the column density of previously blown-off material is far below the spherically averaged value which we have calculated. Some possible 'scenarios' along these lines are briefly discussed.

Meszaros, P.↗
DOE OSTI2025

Gas and dust dynamics in γ Cephei-type disks

Context. Giant planets are observed orbiting the primary stars of close binary systems. Such planets may have formed in compact circumprimary disks, which once surrounded these stars, under conditions much different than those encountered around single stars. Aims. In order to quantify the effects of the strong gravitational perturbations exerted on circumprimary disk material, the three-dimensional (3D) dynamics of gas and dust in orbit around the primary star of a compact and eccentric binary system was modeled by applying the stellar and orbital parameters of γ Cephei, a well-known system that can be representative of a class of close binaries. Methods. Circumprimary gas was approximated as an Eulerian viscous and compressible fluid and modeled by means of 3D hydrodynamical simulations, assuming locally isothermal conditions in the medium around the primary star. Dust grains were modeled as Lagrangean particles, subjected to gravity and aerodynamic drag forces. Models that include a giant planet were also considered. Results. Models indicate that spiral density waves excited around pericenter passage propagate toward the inner boundary of the disk, through at least a few pressure scale-heights from the mid-plane, inducing radial and vertical mixing in the gas. However, perturbations imparted to gas, both in terms of eccentricity and precession, are far weaker than previously estimated by two-dimensional (2D) simulations. Models predict small eccentricities, ≲0.03, and slow retrograde precession. The addition of a giant planet does not change the low eccentricity state of the disk. The parameters applied to the disk would lead to the formation of a massive planet, many times the mass of Jupiter, in agreement with some observations. Micron to mm-size dust grains are well coupled to the gas, resulting in similar dynamics and statistically similar distributions of orbital elements. The planet only affects the dust distributions locally. In agreement with outcomes of recent 2D models, the lifetime of an isolated circumprimary disk would be brief, ~10 5 years, because of its compact nature, requiring a long-term external supply of mass to allow for the in situ formation of a giant planet.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1982

The Mg II resonance line emission at 2800 A in stars with different rotational velocities and different metal abundances

In many investigations, a study of the Mg II 2800 A emission was conducted in order to derive more information about the correlation of chromospheric emission with the properties of the convection zone. It has been suggested by Ayres and Linsky (1980) that there is a positive correlation between rotation and chromospheric emission at least for binary stars. The present investigation is concerned with such a correlation between rotation and chromospheric emission. Since large differences in rotational velocities are observed for F stars for which also strong chromospheric emission is observable, this particular study deals mainly with F stars. On the basis of observations of the Mg II emission in F and G stars, it is found that the emission is abnormally strong in close binary F stars. This may be explained by the generation of a large differential rotation due to tidal effects which may give very efficient dynamo generation of a surface magnetic field.

Boehm-Vitense, E.↗
NASA NTRS1980

Models for galactic X-ray sources

Attention is given to those compact galactic X-ray sources whose X-ray luminosities are considerably in excess of the solar luminosity. It is pointed out that the key breakthrough in the development of an understanding of compact galactic X-ray sources was the discovery of X-ray pulsars with the UHURU satellite. There is now overwhelming evidence that these objects are neutron stars in close binary stellar systems. The X-ray pulsations are thought to be thermal emission from the magnetic polar caps of a neutron star that is accreting matter from a companion star and whose magnetic field is misaligned with its rotation axis. Among the compact galactic X-ray sources that are not X-ray pulsars, some still show direct evidence of binary membership, such as X-ray eclipses. There is evidence that the galactic-bulge sources are, in fact, close binary stellar systems. It is concluded, that the great majority of bright galactic X-ray sources, with only a tiny handful of exceptions (such as the Crab and Vela pulsars), are likely to be binaries.

Joss, P. C.↗
NASA NTRS1985

Magnetic Effects in the Heating and Modification of Flows in the Outer Stellar Atmospheres with Application to Early Type Star Case

Possible magnetic effects in the heating and modification of flows in early type star atmospheres are discussed by referring to the physically related phenomena dealt with for late type stars, young stars, and close binary systems. It is pointed out as the result of that the magnetic field may play important roles also in early type star atmospheres in converting the energy of the radiatively driven outflow into heat, or in modifying the outflow by nozzling or by initial modification of temperature and/or momentum by which the effect of the radiation pressure may be made the most of in accelerating the outflow.

Uchida, Y.↗
NASA NTRS1993

VLBI astrometric identification of the radio emitting region in Algol and determination of the orientation of the close binary

A minute displacement of the radio source in Algol was measured by VLBI during two consecutive orbital revolutions of the close binary. The magnitude of the displacement unambiguously indicates that the less massive star of the close binary, a K subgiant, is the star responsible for the nonthermal radio emission of the system. This is consistent with the idea that the radio emission in Algol is related to the strong magnetic activity of the subgiant. The orientation and sense of the displacement on the sky that are directly deduced from our astrometric VLBI observations imply: (1) that the orbital plane of the close binary is at P.A. = +52 deg +/- 5 deg; and (2) that the sense of circulation of the close binary is clockwise, as seen on the sky. Thus, the long-period and close binary orbital motions are almost orthogonal and counterrevolving and this is relevant for evolution and dynamical studies.

Lestrade, Jean-Francois↗
NASA NTRS1986

Effects of high-energy neutrino production and interactions on stars in close X-ray binaries

Limits are discussed that may be placed on binary systems in which a compact partner is a strong source of high-energy particles that produce photons, neutrinos, and other secondary particles in the companion star. The highest energy neutrinos are absorbed deep in the companion and the associated energy deposition may be large enough to affect its structure or lead to its ultimate disruption. This neutrino heating is evaluated, starting with a detailed numerical calculation of the hadronic cascade induced in the atmosphere of the companion star. For some theoretical models, the resulting energy deposition from neutrino absorption may be so great as to disrupt the companion star over a time scale of 10,000-100,000 yr. Even if the energy deposition is smaller, it may still be high enough to alter the system substantially.

Gaisser, T. K.↗
NASA NTRS1985

Evidence for Non-radiative Activity in Stars with T Sub Eff 10000 K

Major advances in the acquisition of evidence for and the understanding of nonradiative heating and other activity in stars cooler than T sub eff = 10,000 K has occurred in the last few years primarily as a result of the IUE and Einstein spececraft. This evidence is critically reviewed and trends that are now becoming apparent are noted. The existence for nonradiatively heated outer atmospheric layers (chromospheres, transition regions, and coronae) in dwarf stars cooler than spectral type A7, in F ang G giants, pre-main sequence stars, and close binary systems in unambiguous, and chromospheres exist in the K and M giants and supergiants. The existence of nonradiative heating in the outer layers of the A stars remains undetermined despite repeated searches at all wavelengths. Some important trends in these data are the decrease in plasma emission measure with age on the main sequence and decreasing rotational velocity. Variability and atmospheric inhomogeneity is commonly seen, and there is considerable evidence that magnetic fields define the geometry and control the energy balance in the outer atmospheric layers.

Linsky, J. L.↗
NASA NTRS1992

IRAS observations of novae. III - The related objects

Results are presented on an analysis of IRAS observations of a selected sample of 116 objects that show properties similar to those of classical novae detected and modeled by Harrison and Gehrz (1988, 1991). These objects include dwarf novae, novalike variables, symbiotic stars, and planetary nebulae with close binary central-star systems. A high detection rate of 80 percent was found for this sample, as compared with about 50 percent detection rate found in the earlier examined sample. A reexamination of data showed that, at low galactic latitudes, source confusion can account for many of the detections of novae. The seemingly high detection rates of other objects and the many high-latitude novae are difficult to explain.

Harrison, Tom↗
NASA NTRS1986

Electron-cyclotron maser emission from the planets and the stars

Auroral kilometric radiation (AKR), Jupiter's decametric radio emission, microwave spike bursts from the Sun, and related bursts from flare stars and close binaries are discussed. Although all of these are produced by the same instability, the plasma conditions in the source regions differ; for the planets the ratio of the plasma frequency to the electron-cyclotron frequency is less than 1, whereas for the Sun and stars it is greater than or = 1. It is shown that as the ratio increases the frequency of the emissions moves to higher harmonics of the electron-cyclotron frequency and the mode changes from electromagnetic to electrostatic. Implications for AKR, microwave spike bursts, and related bursts from the stars are discussed.

Winglee, R. M.↗
DOE OSTI2021

High tide: a systematic search for ellipsoidal variables in ASAS-SN

ABSTRACT The majority of non-merging stellar mass black holes are discovered by observing high energy emission from accretion processes. Here, we pursue the large, but still mostly unstudied population of non-interacting black holes and neutron stars by searching for the tidally induced ellipsoidal variability of their stellar companions. We start from a sample of about 200 000 rotational variables, semiregular variables, and eclipsing binary stars from the All-Sky Automated Survey for Supernovae. We use a χ2 ratio test followed by visual inspection to identify 369 candidates for ellipsoidal variability. We also discuss how to combine the amplitude of the variability with mass and radius estimates for observed stars to calculate a minimum companion mass, identifying the most promising candidates for high mass companions.

79 ASTRONOMY AND ASTROPHYSICS↗