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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 235 records · Page 13

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NASA NTRS1973

On the primordial condensation and accretion environment and the remanent magnetization of meteorites

In the context of various models for the early evolution of a solar nebula, the possible roles assigned to ambient magnetic fields and the paleointensities required to establish the stable natural remanent magnetization observed in meteorites, are discussed. It is suggested that the record of paleofields present during condensation, growth, and accumulation of grains is likely to have been preserved as chemical or thermochemical remanence in unaltered meteoritic material. Fine particle theories appear adequate for treating meteoritic remanence, if models based on corresponding types of permanent magnet materials, e.g., powder ferrites for chondrites and diffusion hardened alloys for iron meteorites, are adopted.

Brecher, A.↗

NASA NTRS1974

What is special about Cygnus X-1?

The X-ray evidence from several experiments is reviewed, with special emphasis on those characteristics which appear to distinguish Cygnus X-1 from other compact X-ray emitting objects. Data are examined within the context of a model in which millisecond bursts are superposed upon shot-noise fluctuations arising from events of durations on the order of a second. Possible spectral-temporal correlations are investigated which provide additional evidence that Cygnus X-1 is very likely a black hole.

Boldt, E. A.↗

NASA NTRS1975

What is special about Cygnus X-1 - Black holes in theory and observation: X-ray observations

Of the eight X-ray sources now known which may be associated with binary stellar systems, Cygnus X-1 is the most likely candidate for being a black hole. The X-ray evidence from several experiments is reviewed, with special emphasis on those characteristics which appear to distinguish Cygnus X-1 from other compact X-ray emitting objects. Data are examined within the context of a model in which millisecond bursts (Rothschild et al., 1974) are superposed on shot-noise fluctuations (Terrell, 1972) arising from 'events' of durations on the order of a second. Possible spectral-temporal correlations are investigated which indicate new measurements that need to be made in future experiments.

Boldt, E.↗

NASA NTRS1976

Coronal propagation: Variations with solar longitude and latitude

Observational results on the East-West effect are summarized and discussed in the context of existing models of coronal propagation. The variation of the number of events with solar longitude is shown to be surprisingly similar for particles covering a large interval of rigidities. Also, over large longitudinal distances, time delays to the event onset and maximum intensity are independent of energy and velocity. This has important implications and will require probably a transport process which is determined by fundamental properties of solar magnetic fields, e.g. reconnection processes between open and closed field configurations. The relative role of open and closed field configurations is extensively discussed. Some evidence is presented that the acceleration of protons to higher (approximately 10 MeV) energies is related with a shock wave traveling in the solar atmosphere. The importance of measurements performed from spacecraft out-of-the-ecliptic plane is stressed.

Wibberenz, G.↗

NASA NTRS1976

Solar-wind interaction with planetary ionospheres

Planetary encounters by numerous spacecraft have furnished information concerning the solar wind interaction with the planets Mercury, Venus, Mars, and Jupiter. While direct measurements have indicated a wide range of atmospheric densities and intrinsic magnetic field strengths, the data seem to indicate that the flow pattern around nonmagnetized or weakly magnetized planets with atmospheres optically thick at ionizing wavelengths is basically the same as that around a strongly magnetized planet's magnetosphere, such as the earth's. The planetary ionosphere apparently presents a hard obstacle to the flow, with bow shock formation required in the supersonic, super-Alfvenic flow to slow and direct most of the solar wind plasma around the planetary ionosphere. Various aspects of the interaction are examined in the context of theoretical models in an attempt to explain observed details of the interaction regions of Venus and Mars.

Cloutier, P. A.↗

NASA NTRS1977

X-ray signatures: New time scales and spectral features

The millisecond bursts from Cyg X-1 are investigated and the overall chaotic variability for the bulk of the Cyg X-1 emission is compared to that of Sco X-1, showing that the essential character is remarkably similar (i.e. shot noise) although the fundamental time scales involved differ widely, from a fraction of a second (for Cyg X-1) to a fraction of a day (for Sco X-1). Recent OSO-8 observations of spectra features attributable to iron are reviewed. In particular, line emission is discussed within the context of a model for thermal radiation by a hot evolved gas in systems as different as supernova remnants and clusters of galaxies. Newly observed spectral structure in the emission from the X-ray pulsar Her X-1 is reported.

Boldt, E. A.↗

NASA NTRS1979

A survey of ultraviolet circumstellar absorption lines in the spectra of early Be and shell stars

Copernicus UV data are used to examine the rich shell absorption spectra between 1120 and 1140 A in 17 Be and shell stars. Previous observations of the program stars are reviewed, the general appearance of the shell spectra between 1120 and 1140 A is described, and the shell spectra are compared with the spectra of four bright B-type supergiants in the same wavelength region. The line strengths are analyzed to determine quantitative shell strengths and shell column densities; the shell line velocities are discussed in the context of different models. It is shown that UV shell lines can exist in stars with no visible-wavelength shell features, that Fe III shell lines dominate the spectra between 1120 and 1140 A in Be and shell stars with circumstellar absorption features, and that the spectra of Be and shell stars in this region strongly resemble those of supergiants of similar effective temperature.

Snow, T. P., Jr.↗

NASA NTRS1979

The ratio of deuterium to hydrogen in interstellar space. IV - The lines of sight to Delta, Epsilon, and Iota Orionis

Deuterium absorption features in spectra of Delta, Epsilon, and Iota Ori obtained with Copernicus are analyzed. The Iota Ori line-of-sight analysis, which is quite detailed because of the high-velocity H I components superposed on the deuterium features, gives a D/H ratio (which is uncertain because of a complex profile) of 0.000014. A D/H ratio of the order of 7 millionths is determined for Delta and Epsilon Ori. For the complex line profiles involved, one may regard this as a formal lower limit. Several attempts were made to increase the ratio N(D I)/N(H I) in the context of reasonable models for the line of sight, but with no success; the derived values are therefore regarded as actual values, not lower limits. Since the derived value is an average on the line of sight, the possibility cannot be ruled out that the true ratios N(D I)/N(H I) in individual nearby components differ from the mean values. The mean value for these two directions is lower by a factor of 4 than the best value for the Zeta Pup line of sight (the highest yet derived for path lengths greater than 50 pc).

Laurent, C.↗

NASA NTRS1980

IUE observations of circumstellar emission from the late type variable R Aquarii /M7 + pec/

IUE observations of R Aquarii (M7 + pec) have been obtained in low dispersion in order to study its circumstellar emission. Strong permitted, semiforbidden, and forbidden emission lines are identified that are superposed on a bright ultraviolet continuum. From the analysis it is deduced that the strong emission-line spectrum that involves semiforbidden C III, C IV, semiforbidden Si III, forbidden O II, and forbidden O III probably arises from a dense compact nebula the size of which is comparable to the binary system of which R Aqr is the primary star. Low-excitation emission lines of Fe II, Mg II, O I, and Si II suggest the presence of a warm chromosphere (T less than about 10,000 K) in the primary M7 late type giant. The secondary is identified as a white dwarf, comparable to or somewhat brighter than the sun, since such a star can produce enough ionizing photons to excite the continuum and emission-line spectrum and yet be sufficiently faint to escape detection by direct observation. The UV continuum observed is attributed to Balmer recombination and not to blackbody emission from the hot companion. The general spectral properties of R Aqr between 1200 A and 3200 A are discussed in the context of the model for the circumstellar nebula, the companion, and the mass-loss rate of the primary star.

Michalitsianos, A. G.↗

NASA NTRS1981

X-ray detection of the symbiotic star AG Draconis

The detection of the yellow symbiotic star AG Draconis is reported. The star was detected by an imaging proportional counter at a count rate of 0.27 counts/s. The object is an intense source of very soft X-rays, and the X-ray luminosity is estimated to be equal to approximately 10 to the 32nd ergs/s, with a temperature of less than 2,000,000 K. If an interstellar column density of 3 x 10 to the 20th/sq cm is assumed, the emission measure is deduced to be greater than 3 x 10 to the 55th/ cu cm from the X-ray data, and less than 3 x 10 to the 59th/cu cm from the optical data. The observation is discussed in the context of various models of the symbiotic stars.

Anderson, C. M.↗

NASA NTRS1982

An IUE survey of the Hyades star cluster

To date 11 of the brightest X-Ray stars (F-K dwarfs) in the Hyades have been observed with the IUE satellite with the short wavelength spectrograph. The IUE results and the X-Ray observations from the Hyades survey with the Einstein Observatory were combined. The differential emission measure function was estimated for each of the 7 stars which showed evidence of emission lines. Constraints on stellar atmospheric parameters (chromospheric pressure, coronal temperature and filling factor were derived. The implications of these results in the context of loop models for the corona and transition region (TR) of these stars are discussed.

Zolcinski, M. C.↗

NASA NTRS1982

IUE observations of the peculiar star RX Puppis

The first set of high-dispersion UV observations of RX Pup are presented. Anomalous line profile structure observed in a number of high-excitation emission lines is discussed in context with a model that includes streams and complex mass motions in the system. Anomalies in high-excitation lines suggest dynamic activity in circumstellar material that probably has the form of rings and/or gas streamers between the cool giant and the hot companion. The continuum in low dispersion is fairly flat around 1200-2000 and rises toward longer wavelengths, and cannot be due to a star earlier than A0 II. Alternatively, it may be from an accretion disk. Photoionizing radiation may be due to the presence of an unseen, hot subdwarf with most probable effective temperature 75,000-90,000 K. Alternatively, it may be due to an accretion disk around a secondary with boundary layer temperature about 100,000 K.

Kafatos, M.↗

NASA NTRS1982

1 millimeter continuum observations of quasars

Broadband 1-mm continuum observations of 37 active extragalactic objects are discussed in the context of several models of the radio and IR continuum emission of compact extragalactic objects. The observed correlation of the 1-mm flux density of 'blazars', or BL Lac objects and optically violent, variable quasars, with both radio and IR emission, is a natural consequence of the attribution of the radio-to-optical blazar continuum to synchrotron radiation from a relativistic jet viewed nearly along its axis. It is shown that a Comptonization model in which the IR continuum of quasars is produced by the upscattering of radio photons into the IR by a thermal plasma will be in accord with the 1-mm and IR data, if these photons have frequencies in the 10 to the 12th to 10 to the 13th Hz range.

Ennis, D. J.↗

NASA NTRS1984

The nature of AFGL 2591 and its associated molecular outflow: Infrared and millimeter-wave observations

The results of infrared photometry from 2 to 160 microns of AFGL and CO(12) observations of its associated molecular cloud and high velocity molecular outflow are presented and discussed. The observed solar luminosity is 6.7 x 10(4) at a distance of 2 kpc. The spectrum of AFGL 2591 is interpreted in the context of a model in which a single embedded object is the dominant source of the infrared luminosity. This object is determined to be surrounded by a compact, optically thick dust shell with a temperature in excess of several hundred degrees kelvin. The extinction to this source is estimated to be between 26 and 50 visual magnitudes. The absolute position of the infrared sources at 10 microns was determined to an accuracy of + or in. This indicates for the first time that the IR source and H2O source are not coincident. The CO(12) observations show the high-velocity molecular flow near AFGL 2591 to be extended, bipolar and roughly centered on the infrared emission. The observations suggest that the red-shifted flow component extends beyond the boundary of the ambient cloud within which AFGL 2591 is embedded. The CO(12) observations also show that AFGL 2591 is embedded in a molecular cloud with an LSR velocity of -5 km/s.

Lada, C. J.↗

NASA NTRS1984

Observations of the reappearance of polar coronal holes and the reversal of the polar magnetic field

Observational data relating to the evolution of the polar magnetic field around sunspot maximum is examined. Particular emphasis is given to coronal hole observations performed during the last two solar maxima. Long-term averages of the latitudinal dependence of the photospheric magnetic field and the evolutionary pattern of the polar crown filaments are used to trace the poleward motion of the reversal of the large-scale field and are compared to the redevelopment of polar holes. Within the context of phenomenological models of the solar cycle, it is concluded that: (1) the process of polarity reversal and redevelopment of polar holes is discontinuous, with surges of flux of old-cycle polarity interrupting the poleward migration of new-cycle flux; (2) contrary to the Babcock (1961) hypothesis, the polar crown disappears months after the magnetic pole reversal; and (3) the observations support suggestions of a poleward meridional flow around solar maximum that cannot be accounted for by Leighton-type (1964) diffusion.

Webb, D. F.↗

NASA NTRS1985

The intensity recovery of Forbush-type decreases as a function of heliocentric distance and its relationship to the 11-year variation

Recent data indicating that the solar modulation effects are propagated outward in the heliospheric cavity suggest that the 11-year cosmic ray modulation can best be described by a dynamic time dependent model. In this context an understanding of the recovery characteristics of large transient Forbush type decreases is important. This includes the typical recovery time at a fixed energy at 1 AU as well as at large heliocentric radial distances, the energy dependence of the recovery time at 1 Au, and the dependence of the time for the intensity to decrease to the minimum in the transient decreases as a function of distance. These transient decreases are characterized by their asymmetrical decrease and recovery times, generally 1 to 2 days and 3 to 10 days respectively at approx. 1 AU. Near earth these are referred to as Forbush decreases, associated witha shock or blast wave passage. At R equal to or greater than + or - 10 AU, these transient decreases may represent the combined effects of several shock waves that have merged together.

Lockwood, J. A.↗

NASA NTRS1984

The nature of AFGL 2591 and its associated molecular outflow Infrared and millimeter-wave observations

The results of infrared photometry from 2 to 160 microns of AFGL and CO(12) observations of its associated molecular cloud and high velocity molecular outflow are presented and discussed. The observed solar luminosity is 6.7 x 10(4) at a distance of 2 kpc. The spectrum of AFGL 2591 is interpreted in the context of a model in which a single embedded object is the dominant source of the infrared luminosity. This object is determined to be surrounded by a compact, optically thick dust shell with a temperature in excess of several hundred degrees kelvin. The extinction to this source is estimated to be between 26 and 50 visual magnitudes. The absolute position of the infrared sources at 10 microns was determined to an accuracy of + or - 1 in. This indicates for the first time that the IR source and H2O source are not coincident. The CO(12) observations show the high-velocity molecular flow near AFGL 2591 to be extended, bipolar and roughly centered on the infrared emission. The observations suggest that the red-shifted flow component extends beyond the boundary of the ambient cloud within which AFGL 2591 is embedded. The CO(12) observations also show that AFGL 2591 is embedded in a molecular cloud with an LSR velocity of -5 km/s.

Lada, C. J.↗

NASA NTRS1986

Interpretation of temporal features in an unusual X-ray and microwave bursts

Observations are briefly discussed of an event in which microwave and hard X-ray emissions were not correlated in the accepted way. Two impulsive peaks of roughly equal intensity were observed at three different microwave frequencies. The hard X-ray peaks accompanying these, however, differ in intensity by almost two orders of magnitude. Various possible interpretations of this burst are discussed, in the context of familiar models of these emissions. The most likely explanation is that the electron spectrum in the first burst has a break at about 350 keV. General implications for interpretation of X-rays and microwaves are discussed.

Mackinnon, A. L.↗