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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

The 5 Hour Pulse Period and Broadband Spectrum of the Symbiotic X-Ray Binary 3A 1954+319

We present an analysis of the highly variable accreting X-ray pulsar 3A 1954+319 using 2005-2009 monitoring data obtained with INTEGRAL and Swift. This considerably extends the pulse period history and covers flaring episodes in 2005 and 2008. In 2006 the source was identified as one of only a few known symbiotic X-ray binaries, Le" systems composed of a neutron star accreting from the inhomogeneous medium around an M-giant star. The extremely long pulse period of approximately 5.3 h is directly visible in the 2008 INTEGRAL-ISGRI outburst light curve. The pulse profile is double peaked and not significantly energy dependent. During the outburst a strong spin-up of -1.8 x 10(exp -4) h h(exp -1) occurred. Between 2005 and 2008 a long term spin-down trend of 2.1 x 10(exp -5) h h(exp -1) was observed for the first time for this source. The 3-80 keV pulse peak spectrum of 3A 1954+319 during the 2008 flare could be well described by a thermal Comptonization model. We interpret the results within the framework of a recently developed quasi-spherical accretion model for symbiotic X-ray binaries.

Marcu, Diana M.↗
NASA NTRS1980

Mass transfer between binary stars

The transfer of mass from one component of a binary system to another by mass ejection is analyzed through a stellar wind mechanism, using a model which integrates the equations of motion, including the energy equation, with an initial static atmosphere and various temperature fluctuations imposed at the base of the star's corona. The model is applied to several situations and the energy flow is calculated along the line of centers between the two binary components, in the rotating frame of the system, thereby incorporating the centrifugal force. It is shown that relatively small disturbances in the lower chromosphere or photosphere can produce mass loss through a stellar wind mechanism, due to the amplification of the disturbance propagating into the thinner atmosphere. Since there are many possible sources of the disturbance, the model can be used to explain many mass ejection phenomena.

Modisette, J. L.↗
NASA NTRS2014

Symbiotic Stars in X-rays

Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. Here we describe the detection with the X-ray Telescope (XRT) on the Swift satellite of 9 white dwarf symbiotics that were not previously known to be X-ray sources and one that was previously detected as a supersoft X-ray source. The 9 new X-ray detections were the result of a survey of 41 symbiotic stars, and they increase the number of symbiotic stars known to be X-ray sources by approximately 30%. Swift/XRT detected all of the new X-ray sources at energies greater than 2 keV. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component, which we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component, which likely arises in a region where low-velocity shocks produce X-ray emission, i.e. a colliding-wind region. The third group consists of those sources with both hard and soft X-ray spectral components. We also find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk typically are not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, simultaneous Swift UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk. To place these new observations in the context of previous work on X-ray emission from symbiotic stars, we modified and extended the alpha/beta/gamma classification scheme for symbiotic-star X-ray spectra that was introduced by Muerset et al. based upon observations with the ROSAT satellite, to include a new sigma classification for sources with hard X-ray emission from the innermost accretion region. Since we have identified the elusive accretion component in the emission from a sample of symbiotic stars, our results have implications for the understanding of wind-fed mass transfer in wide binaries, and the accretion rate in one class of candidate progenitors of type Ia supernovae.

stars↗
NASA NTRS1980

Pulsation of late B-type stars

Radial velocity observations of three of the brightest stars in the Pleiades, Alcyone, Maia and Taygeta, made during the course of one night, 25 October 1976, are discussed. All three stars were discovered to be pulsating with periods of a few hours. Analysis of all published radial velocities for each star, covering more than 70 years and approximately 100,000 cycles, has established the value of the periods to eight decimal places, and demonstrated constancy of the periods. However, amplitudes of the radial velocity variations change over long time intervals, and changes in spectral line intensities are observed in phase with the pulsation. All three stars may also be members of binary systems.

Beardsley, W. R.↗
NASA NTRS1980

The 1979 X-ray outburst of Cen X-4

X-ray observations of the first major outburst (since its initial discovery in 1969) of the "classical" transient X-ray source Cen X-4 were obtained with the Ariel 5 All-Sky Monitor. The flare light curve exhibits a double-peaked maximum at a level of approximately 4 times the Crab nebula, and its duration and characteristic decay time scale are the shortest yet observed from the class of "soft" X-ray transients. A total X-ray output of approximately 3 x 10 to the 43rd power ergs, a factor of approximately 20 less than that of the 1969 outburst is estimated. In addition, evidence is found for a regular modulation of the flux during the decline phase at a period of 8.2 plus or minus 0.2 hours. The existing data are consistent with a source model involving episodic mass exchange from a late-type dwarf onto a neutron star comparison in a relatively close binary system.

Kaluzienski, L. J.↗
NASA NTRS1980

X-ray bursters and the X-ray sources of the galactic bulge

Type 1 X-ray bursts, optical, infrared, and radio properties of the galactic bulge sources, are discussed. It was proven that these burst sources are neutron stars in low mass, close binary stellar systems. Several burst sources are found in globular clusters with high central densities. Optical type 1 X-ray bursts were observed from three sources. Type 2 X-ray bursts, observed from the Rapid Burster, are due to an accretion instability which converts gravitational potential energy into heat and radiation, which makes them of a fundamentally different nature from Type 1 bursts.

Lewin, W. H. G.↗
NASA NTRS1980

The 1979 X-ray outburst of Centaurus X-4

X-ray observations of the first major outburst of the classical transient X-ray source Centaurus X-4 since its discovery in 1969 are presented. The observations were obtained in May, 1979, with the all-sky monitor on board Ariel 5. The flare light curve is shown to exhibit many of the characteristics of other transients, including a double-peaked maximum, as well as significant, apparently random, variations and a lower peak flux and shorter duration than the 1969 event. Application of a standard epoch-folding technique to data corrected for linear decay trends indicates a possible source modulation at 0.3415 days (8.2 hours). Comparison of the results with previous other data on Cen X-4 and the characteristics of the soft X-ray transients allows a total X-ray output of approximately 3 x 10 to the 43rd ergs to be estimated, and reveals the duration and decay time of the 1979 Cen X-4 outburst to be the shortest yet observed from soft X-ray transients. The observations are explained in terms of episodic mass exchange from a late-type dwarf onto a neutron star companion in a relatively close binary system.

Kaluzienski, L. J.↗
NASA NTRS1981

IUE observations of eight dwarf novae - A study of the outburst cycle from 0.12 to 3.5 microns

The dwarf novae are a class of close binary systems with a G-M star transferring mass to a white dwarf. The transferred material accumulates in a disk and accretes onto the white dwarf. Dwarf novae are characterized by outbursts on time scales of weeks to months possibly triggered by instabilities in the disk. To test the steady state models and the behavior of the disk at various stages of the outburst cycle, IUE observations were conducted for eight dwarf novae. Selected UV continuum points were joined to nonsimultaneous optical and IR spectrophotometry and broad-band photography to yield flux distributions over a large wavelength range. These flux distributions are discussed in terms of available accretion disk models.

Szkody, P.↗
NASA NTRS1980

Models for Type I supernovae

Two somewhat disjoint scenarios for Type I supernovae are presented. One scenario is based on mass accretion by a white dwarf in a binary system, while the other involves a star of 8 to 10 solar masses which may or may not be a solitary star. In spite of the apparent dissimilarities of the two models, it may be that each occurs to some extent in nature, for they both share the possibility of producing substantial quantities of Ni-56 and explosions in stars devoid of hydrogen envelopes. It is concluded that these are two properties that must be shared by any viable Type I model.

Woosley, S. E.↗
NASA NTRS1985

Coronal Temperatures

The solid state spectrometer (SSS) on the Einstein Observatory (HEAO 2) was sensitive in the energy range 0.5 to 4.5 keV to fluxes as low as 4x10 to the 12th power ergs/cu cm/s. Good spectra were obtained for 19 stars, including Algol, 7 RS CVn systems, 2 dMe stars, 2 W UMa binaries, 1 GV single star, and 3 0B supergiants, 2 BV stars and 1 07 binary. This is a very incomplete survey of stellar coronae, but it does include coverage of several late and early types and usually more than 1 sample of the class. The results for these stars suggest two generalizations despite the small numbers: (1) there is a broad variety of X-ray spectra of stellar coronae; and (2) there probably are X-ray spectral types (X-ray coronae of stars of similar other properties have similar temperatures). Evidence indicating that some emission distributions are bimodal is discussed. Finally, some remarks are made concerning the spectra of the early type stars and constraints on the presence of very high temperatures.

Swank, J. H.↗
NASA NTRS1986

The Pinhole/Occulter as a tool for X-ray astronomy

The two X-ray transform telescopes on the Pinhole/Occulter Facility (P/OF) will provide sub-arcsecond angular resolution, high sensitivity imaging in hard X-rays for the first time, as well as improved capabilities for timing studies and spectroscopy. Although the design was driven by solar observing requirements, the result is an instrument of major importance for astronomical as well as solar observations. Fundamental astrophysical measurements could be made on supernova remnants, clusters of galaxies, active galaxy cores, accreting binary systems, and active coronae of nearby stars. Ways in which astronomical observations will benefit solar research are discussed.

Wood, K. S.↗
NASA NTRS1991

Enhanced winds and tidal streams in massive X-ray binaries

The tidal effects created by the presence of a compact companion are expected to induce a stream of enhanced wind from the early-type primary star in massive X-ray binary systems. In this paper, two-dimensional gasdynamical simulations of such streams are presented. It is found that the wind enhancement is a sensitive function of the binary separation, and develops into a tidal stream as the primary approaches its critical surface. For typical system parameters, the Coriolis force deflects the stream sufficiently that it does not impact directly on the compact companion but passes behind it. The density in the stream can reach values of 20-30 times the ambient wind density, leading to strong attenuation of the X-ray flux that passes through the tidal stream, providing a possible explanation of the enhanced absorption events seen at later phases in the X-ray observations of massive X-ray binary systems such as Vela X-1. In contrast to the time-variable accretion wake, the tidal stream is relatively stationary, producing absorption features that should remain fixed from orbit to orbit. For systems with a strong tidal stream, the large asymmetry in the accreting wind results in the accretion of angular momentum of constant sign, as opposed to systems without streams, where the sign of the accreted angular momentum can change.

Blondin, John M.↗
NASA NTRS2014

Constraints on the Progenitor System of the Type Ia Supernova 2014J from Pre-Explosion Hubble Space Telescope Imaging

We constrain the properties of the progenitor system of the highly reddened Type Ia supernova (SN Ia) 2014J in Messier 82 (M82; d (is) approx. 3.5 Mpc). We determine the supernova (SN) location using Keck-II K-band adaptive optics images, and we find no evidence for flux from a progenitor system in pre-explosion near-ultraviolet through near-infrared Hubble Space Telescope (HST) images. Our upper limits exclude systems having a bright red giant companion, including symbiotic novae with luminosities comparable to that of RS Ophiuchi. While the flux constraints are also inconsistent with predictions for comparatively cool He-donor systems (T (is) approximately 35,000 K), we cannot preclude a system similar to V445 Puppis. The progenitor constraints are robust across a wide range of RV and AV values, but significantly greater values than those inferred from the SN light curve and spectrum would yield proportionally brighter luminosity limits. The comparatively faint flux expected from a binary progenitor system consisting of white dwarf stars would not have been detected in the pre-explosion HST imaging. Infrared HST exposures yield more stringent constraints on the luminosities of very cool (T (is) less than 3000 K) companion stars than was possible in the case of SN Ia 2011fe.

RS Ophiuchi↗
NASA NTRS1980

HEAO 1 observations of active coronae in main-sequence and subgiant stars

The HEAO 1 data has been searched for evidence of X-ray emission from 105 bright late-type stars of luminosity classes IV and V, selected on the basis of indirect optical evidence of the presence of a hot corona. Six of the target stars were detected at the 3-standard deviation level and 15 were coincident with 2-standard deviation X-ray sources. On a statistical basis no more than 5 of these 21 sources are spurious, and the probability that the identification with the class of active chromosphere stars is spurious is less than 0.00001. The sources lie near a line of X-ray/bolometric luminosity ratio = 0.0001, similar to a solar plage, and it is concluded that the most active coronae of late-type stars which are not members of close binary systems are being observed. The RS CVn systems discovered to date seem to form a distinct class of coronal X-ray sources, but the lowest X-ray luminosity members of the group, of which Capella may be the prototype, appear to overlap the domain of these single stars with active coronae. The data do not fit the coronal model of Gorenstein and Tucker (1976), but they are consistent with the coronal loop model of Rosner et al. (1978) as extended by Walter et al. (1980).

Walter, F. M.↗
NASA NTRS1997

The RS CVn Binary HD 155555: A Comparative Study of the Atmospheres for the Two Component Stars

We present GHRS/HST observations of the RS CVn binary system HD 155555. Several key UV emission lines (Fe XXI, Si IV, O V, C IV) have been analyzed to provide information about the heating rate throughout the atmosphere from the chromosphere to the corona. We show that both the G and K components reveal features of a chromosphere, transition region and corona. The emission measure distribution as a function of temperature for both components is derived and compared with the RS Cvn system, HR 1099, and the Sun. The transition region and coronal lines of both stars show nonthermal broadenings of approx. 20-30 km/s. Possible physical implications for coronal heating mechanisms are discussed.

Airapetian, V. S.↗
NASA NTRS1984

Hot subdwarfs in detached binary systems and thick-disk cataclysmic variables from the Palomar-Green survey

A total of 19 stars from the Palomar Green (PG) survey which were found to show composite spectra, generally with a hot subdwarf primary and a cool main-sequence secondary star, are discussed. The primary components have Teff values between 27,000 and 38,000 K (Mv = +5 to +7) and log g = about 6.5, while the secondaries generally show spectral types G8 to K4.5; however, these ranges are undoubtedly limited by selection effects, and extremely helium-rich subdwarfs were excluded as well. Aproximately half of all the PG subdwarfs could be in undetected binaries. Only two thick-disk cataclysmic variables with predominantly absorption-line spectra were found in the PG survey, which provides strong evidence that this kind of cataclysmic variable is luminous and confined to the Galactic plane (Population I). On the other hand, a few of the detached binaries show evidence for spectroscopic variations. Those which are close enough for a significant reflection effect on the secondary star may be progenitors to cataclysmic variable systems.

Ferguson, D. H.↗
NASA NTRS2005

Proceedings of Protostars and Planets V

Oral presentation sessions in this conference include: Clouds and cores; Star formation and protostars; Binaries and multiples; Newborn massive stars; jets and outflows; Clusters and associations; T Tauri stars and disks; Brown dwarfs; Planet formation and evolution; Extrasolar planets; Dust and protoplanetary disks; Early solar system and Astrobiology. Poster presentations included: Clouds and Cores. Collapse and Protostars, Binaries and Multiples, Clusters, Associations, and the IMF, Jets and Outflows, T Tauri Stars and Other Young Stars, Disks and Disk Accretion, Brown Dwarfs, Herbig Ae/Be Stars and Massive Stars, Solar System Objects, Planet Formation, Extrasolar Planets and Planet Detection, Properties of Protoplanetary Disks, Migration and Planetary Orbits and Meteoritics and Astrobiology

Source record↗
NASA NTRS1980

Binary X-ray pulsars

Progress made over the last decade in the understanding of the binary X-ray pulsars is reviewed. The characteristics of the pulse profiles of the known binary X-ray pulsars are discussed, and observed variations in pulse period corresponding to the spin-up of the neutron star are considered. Determinations of the orbits and binary system parameters of the binary X-ray pulsars from measurements of pulse arrival times are then examined. Attention is also given to current problems in binary X-ray pulsars, including the apsidal motion test, which allows the determination of the mass distribution within a star, the X-ray source 4U 1626-67, which is believed to be a highly compact binary X-ray source, and the observation of very faint X-ray pulsars with the Einstein Observatory.

Rappaport, S.↗