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At least 1,621 records · Page 90
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Proton acceleration in neutron star magnetospheres

To explain the emission of TeV and PeV gamma rays from accreting X-ray binary sources, protons must be accelerated to several times the gamma-ray energy. It is shown here that at certain times, the plasma in the accretion column of the neutron star may form a deep enough pool that the top portion becomes unstable to convective motions in spite of the strong magnetic field. The resulting turbulence produces fluctuations in the strength of the magnetic field that travel up the accretion column, taking energy out to the region of the energetic protons. The protons resonantly absorb this energy and are accelerated to high energies. Including the synchrotron radiation losses of the protons, it is shown that they can be accelerated to energies that are high enough to explain the gamma-ray observations.

Smith, I. A.↗
NASA NTRS1993

The progenitor of supernova 1993J - A stripped supergiant in a binary system?

Supernova 1993J in the spiral galaxy M81 is the brightest supernova since SN1987A and, like the latter, appears to be another 'peculiar' type II supernova. The available photometry of the supernova region before the explosion requires the presence of at least two supergiants (one of early spectral type and the other of late type), but the actual progenitor has yet to be identified. We show that the explosion of a late-type supergiant can explain the initial sharp peak in the supernova light curve, provided that the star had lost almost all of its hydrogen-rich envelope before the explosion. In our model, the secondary brightening of the supernova, about 10 days later, is then a consequence of the radioactive decay of Ni-56 (and subsequently Co-56) produced in the explosion. The progenitor could have lost its hydrogen-rich envelope either in a strong stellar wind or, as seems more likely, through mass transfer to a companion star. In the latter case, the companion should reappear after the supernova photosphere has receded, the system having become a binary composed of a neutron star with a massive stellar companion.

Podsiaklowski, PH.↗
NASA NTRS2003

A Chandra X-Ray Study of NGC 1068 IL the Luminous X-Ray Source Population

We present an analysis of the compact X-ray source population in the Seyfert 2 galaxy NGC 1068, imaged with a approx. 50 ks Chandra observation. We find a total of 84 compact sources on the S3 chip, of which 66 are located within the 25.0 B-mag/arcsec isophote of the galactic disk of NGC 1068. Spectra have been obtained for the 21 sources with at least 50 counts and modeled with both multicolor disk blackbody and power-law models. The power-law model provides the better description of the spectrum for 18 of these sources. For fainter sources, the spectral index has been estimated from the hardness ratio. Five sources have 0.4 - 8 keV intrinsic luminosities greater than 10(exp 39)ergs/ s, assuming that their emission is isotropic and that they are associated with NGC 1068. We refer to these sources as intermediate-luminosity X-ray objects (ISOs). If these five sources are X-ray binaries accreting with luminosities that are both sub-Eddington and isotropic, then the implied source masses are approx greater than 7 solar mass, and so they are inferred to be black holes. Most of the spectrally modeled sources have spectral shapes similar to Galactic black hole candidates. However, the brightest compact source in NGC 1068 has a spectrum that is much harder than that found in Galactic black hole candidates and other ISOs. The brightest source also shows large amplitude variability on both short-term and long-term timescales, with the count rate possibly decreasing by a factor of 2 in approx. 2 ks during our Chundra observation, and the source flux decreasing by a factor of 5 between our observation and the grating observations taken just over 9 months later. The ratio of the number of sources with luminosities greater than 2.1 x 10(exp 38) ergs/s in the 0.4 - 8 keV band to the rate of massive (greater than 5 solar mass) star formation is the same, to within a factor of 2, for NGC 1068, the Antennae, NGC 5194 (the main galaxy in M51), and the Circinus galaxy. This suggests that the rate of production of X-ray binaries per massive star is approximately the same for galaxies with currently active star formation, including "starbursts."

Smith, David A.↗
NASA NTRS1973

Spectroscopic observations of the optical candidate for Cygnus X-1.

The spectroscopic binary BD+34 3815 (= HDE 226868) with a period of 5.6 days, which is the brightest object in the position box for the X-ray source Cyg X-1, is studied to determine whether it meets all the requirements for being a black hole. Evidence is presented that the mass of the secondary is larger than the upper limits for white dwarfs or neutron stars, but there is no conclusive evidence that the optical binary is an X-ray source, and that the secondary is a collapsed object.

Brucato, R.↗
NASA NTRS1972

A note on mass loss during collisions between galaxies and the formation of giant systems.

Stars will be liberated from the outer portions of galaxies which interact tidally. Using models based on the density distribution observed in the E1 galaxy NGC 3379, the mass loss is computed for hyperbolic collisions on an approximate but conservative basis. Binary collisions are then summed to show that large numbers of stars will be evaporated from elliptical members of dense clusters of galaxies. An estimate of one trillion solar masses is obtained for the amount of material dispersed in the Coma cluster, and in rich very dense systems (Morgan's Type I) the large amount of tidally dispersed debris may constitute the centrally located galaxies designated cD systems which often dominate these clusters.

Gallagher, J. S., III↗
DOE OSTI2021

Double Image Polarimeter—Ultra Fast: Simultaneous Three-color (BVR) Polarimeter with Electron-multiplying Charge-coupled Devices

We describe a new instrument capable of high-precision (10{sup −5}) polarimetric observations simultaneously in three passbands (BVR). The instrument utilizes electron-multiplying charge-coupled device (EM CCD) cameras for high efficiency and fast image readout. The key features of the Double Image Polarimeter—Ultra Fast (DIPol-UF) are: (i) the optical design with high throughput and inherent stability; (ii) great versatility, which makes the instrument optimally suitable for observations of bright and faint targets; and (iii) a control system, which allows the use of the polarimeter remotely. Examples are given of the first results obtained from high signal-to-noise observations of bright nearby stars and of fainter sources such as X-ray binaries in their quiescent states.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2017

X-Ray Emissions from Accreting White Dwarfs: A Review

Interacting binaries in which a white dwarf accretes material from a companion-cataclysmic variables (CVs) in which the mass donor is a Roche-lobe filling star on or near the main sequence, and symbiotic stars in which the mass donor is a late type giant-are relatively commonplace. They display a wide range of behaviors in the optical, X-rays, and other wavelengths, which still often baffle observers and theorists alike. Here I review the existing body of research on X-ray emissions from these objects for the benefits of both experts and newcomers to the field. I provide introductions to the past and current X-ray observatories, the types of known X-ray emissions from these objects, and the data analysis techniques relevant to this field. I then summarize of our knowledge regarding the X-ray emissions from magnetic CVs, non-magnetic CVs and symbiotic stars, and novae in eruption. I also discuss space density and the X-ray luminosity functions of these binaries and their contribution to the integrated X-ray emission from the Galaxy. I then discuss open questions and future prospects.

cataclysmic variables – stars: dwarf novae –↗
NASA NTRS1985

Velocity fields in binary protostellar clouds - An alternative to retrograde rotation

Observations of the emission from optically thin molecular species in several dense interstellar clouds have been interpreted as indicating rotating of cloud envelopes in one direction and of cloud cores in the opposite direction (retrograde rotation). This has been taken as evidence for the presence of magnetic fields sufficiently strong to have caused the retrograde rotation. However, it is shown that the velocity fields that are produced when a nonmagnetic interstellar cloud collapses to form a binary protostellar system yield spatial velocity maps that appear to be at least qualitatively consistent with the (C-13)O observations. An embedded star has been detected recently in one of these clouds (Barnard 5). If the binary protostar model is correct, then another protostar, as yet undetected, should also be present in Barnard 5.

Boss, A. P.↗
DOE OSTI2021

The Solar Neighborhood. XLVII. Comparing M-dwarf Models with Hubble Space Telescope Dynamical Masses and Spectroscopy

We use HST/STIS optical spectroscopy of 10 M dwarfs in five closely separated binary systems to test models of M-dwarf structure and evolution. Individual dynamical masses ranging from 0.083 to 0.405 M {sub ⊙} for all stars are known from previous work. We first derive temperature, radius, luminosity, surface gravity, and metallicity by fitting the BT-Settl atmospheric models. We verify that our methodology agrees with empirical results from long-baseline optical interferometry for stars of similar spectral types. We then test whether or not evolutionary models can predict those quantities given the stars’ known dynamical masses and the conditions of coevality and equal metallicity within each binary system. We apply this test to five different evolutionary model sets: the Dartmouth models, the MESA/MIST models, the models of Baraffe et al., the PARSEC models, and the YaPSI models. We find marginal agreement between evolutionary model predictions and observations, with few cases where the models respect the condition of coevality in a self-consistent manner. We discuss the pros and cons of each family of models and compare their predictive power.

47 OTHER INSTRUMENTATION↗
NASA NTRS2019

The Random Transiter – EPIC 249706694/HD 139139

We have identified a star, EPIC 249706694 (HD 139139), that was observed during K2 Campaign 15 with the Kepler extended mission that appears to exhibit 28 transit-like events over the course of the 87-day observation. The unusual aspect of these dips, all but two of which have depths of 200 ± 80 ppm, is that they exhibit no periodicity, and their arrival times could just as well have been produced by a random number generator. We show that no more than four of the events can be part of a periodic sequence. We have done a number of data quality tests to ascertain that these dips are of astrophysical origin, and while we cannot be absolutely certain that this is so, they have all the hallmarks of astrophysical variability on one of two possible host stars (a likely bound pair) in the photometric aperture. We explore a number of ideas for the origin of these dips, including actual planet transits due to multiple or dust emitting planets, anomalously large TTVs, S- and P-type transits in binary systems, a collection of dust-emitting asteroids, ‘dipper-star’ activity, and short-lived starspots. All transit scenarios that we have been able to conjure up appear to fail, while the intrinsic stellar variability hypothesis would be novel and untested.

S. Rappaport↗
NASA NTRS1978

Location of the Norma transient with the HEAO 1 scanning modulation collimator

A precise position has been obtained for an X-ray transient source in Norma. The location uncertainty includes a variable star previously suggested to be the optical counterpart. This transient is associated with the steady X-ray source MX 1608-52 and probably with an X-ray burst source. A binary system containing a low-mass primary and a neutron-star or black-hole secondary of a few solar masses is consistent with the observations.

Fabbiano, G.↗
NASA NTRS1989

The binary companion of the classical Cepheid AW Per

An analysis of IUE spectra of the companion of AW Per shows it to be an extreme BpSi/HeW star with a spectral type of B7 V to B8 V. The flux of the composite spectrum from 1200 A through V is found to be well matched by F7 Ib and B8 V standard stars with Delta M(V) = 3.1 mag. The results suggest that the mass of the Cepheid must be greater than 4.7 solar masses. The flux distribution of the star and the mass limits from the orbit are consistent with a companion that is itself a binary.

Evans, Nancy Remage↗
NASA NTRS1990

Acceleration by pulsar winds in binary systems

In the absence of accretion torques, a pulsar in a binary system will spin down due to electromagnetic dipole radiation, and the spin-down power will drive a wind of relativistic electron-position pairs. Winds from pulsars with short periods will prevent any subsequent accretion but may be confined by the companion star atmosphere, wind, or magnetosphere to form a standing shock. This paper investigates the possibility of particle acceleration at such a pulsar wind shock and the production of VHE and UHE gamma-rays from interactions of accelerated protons in the companion star's wind or atmosphere. It is found that, in close binaries containing active pulsars, protons will be shock accelerated to a maximum energy dependent on the pulsar spin-down luminosity. If a significant fraction of the spin-down power goes into particle acceleration, these systems should be sources of VHE and possibly UHE gamma-rays. The application of the pulsar wind model to binary sources such as Cygnus X-3 is discussed, as well as the possibility of observing VHE gamma-rays from known binary radio pulsar systems.

Harding, Alice K.↗
NASA NTRS1982

The hot components of hydrogen deficient binaries

Low resolution IUE observations of the hot components of three very similar but peculiar objects: LSS 4300, Upsilon Sgr, and KS Per were compared. The possible evolutionary scenarios from observations and the extremely low hydrogen contents of the visible stars are discussed. It is suggested that the hot secondaries in hydrogen deficient binaries should also be hydrogen deficient.

Drilling, J. S.↗
NASA NTRS1976

Pulsating X-ray sources - Slowly rotating neutron stars

The origin of the slowly pulsating X-ray sources is considered. It is shown that tidal forces in a presupernova binary system will lead to synchronization of the stellar rotation with the orbital period. Consideration of the structure of the presupernova star then indicates that X-ray periods of the correct order of magnitude will be produced in these systems.

Lea, S. M.↗
NASA NTRS1987

New developments in studies of compact X-ray binaries

Several recent developments, both observational and theoretical, on the study of X-ray binaries and the compact objects they contain are discussed. The recent discovery of the first binary periods for the globular cluster X-ray sources has stimulated a new model for their origin. As a variant of the 'standard' tidal capture origin model, this predicts an enhanced number of neutron stars in globular clusters. Long term timing studies of X-ray binaries may be consistent with many of these systems, primarily X-ray burst sources, being in fact hierarchical triple systems. Finally, the radio studies of Cyg X-3 and other X-ray binaries suggest that nonthermal processes are as important, energetically, as accretion processes in these systems.

Grindlay, Jonathan E.↗
NASA NTRS1987

Chromospherically active stars. III - HD 26337 = EI Eri: An RS CVn candidate for the Doppler-imaging technique

Spectroscopic observations of the chromospherically active G5 IV single-lined binary HD 26337 = EI Eri are presented. An orbital period of 1.94722 days is found for the star. It has moderately strong Ca II H and K emission and strong ultraviolet emission features, while H-alpha is a weak absorption feature that is variable in strength. The inclination of the system is 46 + or - 12 deg, and the unseen secondary is probably a late K or early M dwarf. The v sin i of the primary is 50 + or - 3 km/s, resulting in a minimum radius of 1.9 + or - 0.1 solar radius. The star is within the required limits for Doppler imaging. The primary is close to filling its Roche lobe, resulting in a strong constraint that the mass ratio is 2.6 or greater, with a primary mass of at least 1.4 solar mass. The distance to the system is estimated at 75 pc.

Fekel, Francis C.↗
DOE OSTI2020

Kepler-1661 b: A Neptune-sized Kepler Transiting Circumbinary Planet around a Grazing Eclipsing Binary

We report the discovery of a Neptune-sized (R{sub p}=3.87±0.06R{sub ⊕}) transiting circumbinary planet, Kepler-1661 b, found in the Kepler photometry. The planet has a period of ∼175 days and its orbit precesses with a period of only 35 yr. The precession causes the alignment of the orbital planes to vary, and the planet is in a transiting configuration only ∼7% of the time as seen from Earth. As with several other Kepler circumbinary planets, Kepler-1661 b orbits close to the stability radius, and is near the (hot) edge of the habitable zone. The planet orbits a single-lined, grazing eclipsing binary, containing a 0.84 M{sub ⊙} and 0.26 M{sub ⊙} pair of stars in a mildly eccentric (e = 0.11), 28.2 day orbit. The system is fairly young, with an estimated age of ∼1–3 Gyr, and exhibits significant starspot modulations. The grazing eclipse configuration means the system is very sensitive to changes in the binary inclination, which manifests itself as a change in the eclipse depth. The starspots contaminate the eclipse photometry, but not in the usual way of inducing spurious eclipse timing variations. Rather, the starspots alter the normalization of the light curve, and hence the eclipse depths. This can lead to spurious eclipse depth variations, which are then incorrectly ascribed to binary orbital precession.

79 ASTRONOMY AND ASTROPHYSICS↗