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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 217 records · Page 12
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NASA NTRS1980

Transient mass transfer caused by local surface heating in close binaries

The surge of mass from one component of a binary system resulting from local surface heating is analyzed. The impact of such surges on the companion can produce transient phenomena such as those seen in X-ray binaries, RS CVn objects, and cataclysmic variables. The heating may be caused by nonlinear g-mode oscillations or by X-ray heating by the companion in X-ray binaries, among other possible mechanisms. As an example, model calculations have been performed for a surge, triggered by a relatively moderate local heating, in a hypothetical X-ray binary; the results show that such a surge can account for X-ray turn-ons.

Modisette, J. J.↗
NASA NTRS1980

Spectroscopic observations of the optical counterpart of Centaurus X-4

The optical spectrum of the transient X-ray burst source Centaurus X-4 was observed about 5 weeks after the source reached its maximum. The brightness of the optical counterpart had decreased to V = 18.2, and the star had become appreciably redder (B - V = 0.7) compared to its color at maximum. The spectrum of Centaurus X-4 is similar to that of cataclysmic variables showing strong emission lines of H-1 and weaker lines of He-1 and He-2. The N03 lambda 4640 line is not visible. The continuum energy distribution of Centaurus X-4 shows the presence of a main-sequence star in the system, with spectral type between K3 and K7. This is consistent with the orbital period of 8.2 hr proposed by Kaluzienski et al (1980), if the main-sequence star is close to filling its Roche lobe.

Van Paradijs, J.↗
NASA NTRS1980

X-ray spectra of galactic X-ray sources

The spectroscopic properties of the various classes of Galactic X-ray sources are discussed, with particular emphasis on binary sources containing an accreting compact object, where post-emission scattering in an accretion disk often prevents the initially produced X-radiation from being observed directly. Theoretical interpretations and X-ray observations are considered for the cataclysmic variables, binary systems with a white dwarf as the compact object and which suffer relatively less from Thomson scattering, and the similar phenomenological spectral characteristics of the bulge sources, including soft transients, bursters and steady X-ray sources with thermal spectra, thought to represent an accreting neutron star, are pointed out. The spectral characteristics of X-ray pulsars in accreting binary systems (rather than the Crab pulsar, which is losing rotational kinetic energy with time) are then presented and interpreted in terms of accretion in the polar regions, and mechanisms for the newly discovered X-ray emission from late-type RS CVn stars are considered.

Holt, S. S.↗
NASA NTRS1981

An X-ray survey of nine historical novae

The Einstein Observatory Imaging Proportional Counter has been used to search for X-ray emission from nine nearby historical novae. Six of the novae have been detected with estimated X-ray intensities between 0.1 and 4 keV of 10 to the -13th to 10 to the -11th erg/sq cm-sec, comparable to the intensities of previously detected cataclysmic variables. The X-ray intensity of one of the novae, V603 Aql, varies over times of several hundred seconds. The data suggest a correlation between the decay rate of the historical outburst and the current X-ray luminosity. Alternatively, the X-ray luminosity may be related to the inclination of the binary system.

Becker, R. H.↗
NASA NTRS1981

Infrared observations of AE Aquarii

Broadband infrared observations of the cataclysmic variable AE Aquarii are reported. The observations were obtained in the J, H, K and L filters with the InSb photometer attached to the 1-m telescope of the European Southern Observatory. The infrared energy distribution observed from 0.35 to 3.5 microns for phase 0.5 suggests a spectral type of K5 V for the secondary and a distance to the system of approximately 70 pc if an absolute magnitude of 7.3 is assumed. Monitoring of the flux at 2.2 microns reveals a variability with an amplitude of approximately 0.3 magnitude over one third of the orbital period, the nature of which is under investigation.

Tanzi, E. G.↗
NASA NTRS1981

Changes in the high state of AM Herculis - A simultaneous X-ray, optical, polarimetric, and spectroscopic study

Simultaneous UBVR photometry, circular polarimetry, and high resolution spectroscopy observations (during May, 1979), coordinated with a monitor proportional counter and a solid state spectrometer, are reported for the cataclysmic variable AM Her, when it was in its normal 'high' state, where the mean visual magnitude was 12.5 mag versus 15 mag for the infrequent 'low' state. The circular polarization was always negative and had the smallest peak to peak amplitude yet reported. The emission lines He II 4686, H-beta, N III 4634, N III 4640-4641, C III 4650-4651, and He I 4713 present at least two components identified with the broad and sharp components of Greenstein at al. (1977). The radial velocity curve of the broad component shows a 50% reduction of amplitude in comparison to their values, and a third very broad component in 4686 is identified. No correlation between the optical photometry and 1-10 keV X-ray intensity was found on flickering time scales. Results of the observations are discussed within the framework of models with accretion onto one or both magnetic poles of the white dwarf.

Crosa, L.↗
NASA NTRS1982

Binary stars: Mass transfer and chemical composition

It is noted that mass exchange (and mass loss) within a binary system should produce observable changes in the surface chemical composition of both the mass losing and mass gaining stars as a stellar interior exposed to nucleosyntheses is uncovered. Three topics relating mass exchange and/or mass loss to nucleosynthesis are sketched: the chemical composition of Algol systems; the accretion disk of a cataclysmic variable fed by mass from a dwarf secondary star; and the hypothesis that classical Ba II giants result from mass transfer from a more evolved companion now present as a white dwarf.

Lambert, D. L.↗
NASA NTRS1981

Identification of 4U 1849-31 with V1223 Sagittarii and discovery of optical pulsations

The X-ray source 4U 1849-31 is identified with the 13 mag star V1223 Sgr, on the basis of a precise HEAO 1 modulation collimator X-ray position uniquely selected by the Ariel-5 sky survey location. It is shown by optical spectroscopy and photometry that V1223 Sgr is a cataclysmic variable, displaying a photometric period of 13.2 min that is interpreted as being due to the rotation of a degenerate dwarf. The similarity of this system to H2252-035 is noted.

Steiner, J. E.↗
NASA NTRS1982

Phase resolved optical spectroscopy of the compact X-ray binary 2A1822-371

The optical, X-ray, and ultraviolet emissions of the X-ray system 2A1822-371 are modulated with a period of 5.57 hr. The 5.57 hr modulation is believed to reflect orbital motion about a mass donating companion star. The modulation at high energies is caused by the combined effects of an occultation by the companion and by a bulge on the accretion disk. The present investigation is concerned with an extension of the study of 2A1822-371, taking into account medium resolution optical spectroscopy of the system covering the 5.57 hr cycle. Broad shallow absorption lines are observed in the optical spectrum of 2A1822-371. These lines are similar to the rotationally broadened lines which are found in the spectra of disk accreting cataclysmic variables. Their presence in 2A1822-371 is, therefore, strong confirmation that it is a disk accreting star. The He II 4686 A and H-alpha emission lines have a breadth comparable to the absorption lines at all phases in the 5.57 hr cycle.

Mason, K. O.↗
NASA NTRS1982

Stellar contributions to the hard X-ray galactic ridge

The number density of serendipitous sources in galactic plane Einstein Observatory IPC fields are compared with predictions based on the intensity of the HEAO-1 A2 unresolved hrd X-ray galactic ridge emission. It is concluded that theoretically predicted X-ray source populations of luminosity 8 x 10 to the 32nd power to 3 x 10 to the 34th power ergs s have 2 KeV to 10 KeV local surface densities of less than approximately .0008 L(32) pc/2 and are unlikely to be the dominant contributors to the hard X-ray ridge. An estimate for Be/neutron star binary systems, such as X Persei, gives a 2 keV to 10 keV local surface density of approximately 26 x 10 to the -5 power L(32) pc/2. Stellar systems of low luminosity, are more likely contributors. Both RS CVn and cataclysmic variable systems contribute 43% + or - 18% of the ridge. A more sensitive measurement of the ridge's hard X-ray spectrum should reveal Fe-line emission. We speculate that dM stars are further major contributors.

Worrall, S. M.↗
NASA NTRS1983

X-ray evidence for white dwarf binaries in globular clusters

Data from an X ray survey of globular clusters by means of instrumentation on the Einstein Observatory indicate the existence of a distinct class of low-luminosity (L) sources. L was measured in the 10 to the 32nd to 10 to the 34th ergs/sec range when viewing point-like objects. The L-value is three orders of magnitude less than that of neutron star binaries, and is consistent with projections for binaries with 0.5 solar mass white dwarfs. They were located outside the cluster cores, which was taken as an indication of low mass. More than three sources at the lowest luminosity bound were observed in two clusters, suggesting a steep rise in the luminosity function, which agreed with observational data on galactic plane cataclysmic variables.

Hertz, P.↗
NASA NTRS1983

Compton heated winds and coronae above accretion disks. I Dynamics

X rays emitted in the inner part of an accretion disk system can heat the surface of the disk farther out, producing a corona and possibly driving off a strong wind. The dynamics of Compton-heated coronae and winds are analyzed using an approximate two-dimensional technique to estimate the mass loss rate as a function of distance from the source of X rays. The findings have important dynamical implications for accretion disks in quasars, active galactic nuclei, X ray binaries, and cataclysmic variables. These include: mass loss from the disk possibly comparable with or exceeding the net accretion rate onto the central compact object, which may lead to unstable accretion; sufficient angular momentum loss in some cases to truncate the disk in a semidetached binary at a smaller radius than that predicted by tidal truncation theories; and combined static plus ram pressure in the wind adequate to confine line-emitting clouds in quasars and Seyfert galaxies.

Begelman, M. C.↗
NASA NTRS1983

An infrared study of the eclipsing dwarf nova U Geminorum

One series of data comprising the present J, H, K broadband IR photometry of the cataclysmic binary system U Geminorum over the course of two orbital cycles was obtained several days before an outburst, while a second was gathered when the system had almost completely returned to quiescence from that outburst. In quiescence, the M4-M5.5 red dwarf star supplies most of the IR luminosity of the system, while the light curves at this time are tidally induced ellipsoidal variations of the red dwarf which exhibit an amplitude such that the red dwarf must fill, or nearly fill, its Roche lobe. This shows directly that Roche lobe overflow is important in cataclysmic variable stars. The range of the disk IR colors after outbursts suggest that cool and optically thick gas, together with optically thin gas, supply most of the IR light of the disk.

Berriman, G.↗
NASA NTRS1983

The optical counterparts of compact galactic X-ray sources

Ninety-six optical identifications of X-ray sources presumed to be compact objects are presented and discussed. X-ray and optical classifications of the sources are considered, and the several types of systems are discussed. These include neutron star binaries with massive and low-mass stellar components, neutron stars in supernova remnants, cataclysmic variables, and 'isolated' hot white dwarfs. The information that can be derived from optical observations of neutron-star systems with low-mass optical companions is emphasized.

Bradt, H. V. D.↗
NASA NTRS1984

Radial velocity studies of cataclysmic binaries. II - The ultrashort period dwarf nova T Leonis

Spectroscopic and photometric observations of T Leo which reveal the object to be an ultrashort period dwarf nova are presented. In particular, the analysis indicates that T Leo has an orbital period of 84.69936 (plus or minus 0.00068) minutes, which is the third shortest orbital period of any known cataclysmic variable and the shortest known for any U Gem type dwarf nova. These observations enable the placement of upper limits of 0.19 and 0.4 solar mass on the mass of the red dwarf and white dwarf, respectively. The overall energy distribution is relatively flat (f-sub-lambda approximately constant) which is consistent with a low mass accretion rate. The models of Williams and Ferguson (1982) suggest that the mass accretion rate is about 10 to the -10th solar mass/yr. A narrow peak component of H-alpha is observed, the phasing of which cannot be explained by the canonical hot spot model. Possible explanations for its origin are presented and discussed. It is predicted that future observations of T Leo may reveal the object to be a SU UMa type dwarf nova.

Shafter, A. W.↗
NASA NTRS1984

E2003 + 225 - A 3h 42m AM Herculis type binary system

The bright soft X-ray source E2003 + 225, originally discovered by the HEAO 1 low-energy detectors, has been found to be a new AM Herculis type binary. The optical counterpart shows a rich emission spectrum of He II, He I, and H as well as circular and linear polarization. Larger polarization in the near-infrared than in the ultraviolet argues for its origin as high harmonic cyclotron emission. Optical photometry, polarimetry, spectroscopy, and the X-ray light curves are all consistent with an orbital period of 222.51 m, the longest period known for AM Herculis systems, and only the second on the long side of the 2-3 hour cataclysmic variable period gap.

Takalo, L. O.↗
NASA NTRS1984

The nonaxisymmetric baroclinic instability in thin accretion disks

The instability of linear, nonaxisymmetric baroclinic waves in the radiative regions of a thin accretion disk is investigated with simplifying assumptions used in the representation of the structure of the basic state. As in stars with rotation laws deviating from rotation on cylinders, the departure from barotropy ('baroclinicity') resulting from such rotation feeds potential energy from the basic state into the kinetic energy of the baroclinic motions. The baroclinic instability is considered as a possible mechanism for driving turbulence in disks. Estimations of the Reynolds stress from baroclinic waves indicate that the degree of baroclinicity in stationary disk models is insufficient to account for the large viscosity inferred from observations of, e.g., cataclysmic variables.

Cabot, W.↗
NASA NTRS1984

The evolution of highly compact binary stellar systems in globular clusters

A highly compact binary represents a system which is composed of a collapsed object (degenerate dwarf, neutron star, or black hole) in orbit with a low-mass (equal to or less than 0.5 solar mass) secondary star. Matter may be transferred from the secondary to the collapsed star due to the decay of the orbit resulting from the emission of gravitational radiation. The present investigation has the objective to study quantitatively the evolution of highly compact binaries in globular cluster cores, subject to the interplay of gravitational radiation and collisions with field stars. The investigation is exploratory in nature. The numerical methods employed are based on the techniques developed by Rappaport et al. (1982). It is found that occasional close encounters with field stars strongly dominate the evolution of highly compact binaries in dense globular cluster cores. Attention is given to the applicability of the findings to observations of X-ray sources and cataclysmic variables.

Krolik, J. H.↗