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  • ASTROPHYSICS  (578)
  • 1980-1984  (578)
  • 1960-1964
  • 1981  (578)
  • 1
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    On the generation and maintenance of turbulence in the interstellar medium (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The broad spectrum of turbulent motions observed in the interstellar medium may be produced by the shearing action of differential galactic rotation. A steady state eddy distribution is maintained as energy cascades down the eddy hierarchy to smaller-scale motions. The characteristic decay time for interstellar turbulence is found to be 50-billion yr. Objections frequently raised against the presence of long-lived turbulent motions in the interstellar medium are therefore invalid, since these arguments usually presuppose that there is no source of fresh turbulent energy.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 246
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  • 2
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    First detection of line emission from the hot interstellar medium with solid state detectors (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Previously reported enhanced soft X-ray emission from the North-Galactic Polar region supports the theory of a hot interstellar component. This paper reports the first detection of line emission from the hot interstellar component in the North-Galactic-Polar region. Measurements were made with solid state Si(Li) detectors aboard a spin-stabilized rocket launched from the White Sands Missile Range on March 22, 1980. Two features are clearly present in the low energy portion of the spectrum derived from the data. They correspond to emission lines from C V (300 eV) and C VI (360 eV), and from O VII (560 eV) and O VIII (650 eV). The detection of emission lines coming from these highly stripped ions is direct evidence for the thermal origin of the emission and confirms the presence of a hot (1-million K) component in the interstellar medium.
    Keywords: ASTROPHYSICS
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  • 3
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    Effects of gamma-ray, neutrino, and particle production on the energetics and dynamics of compact extragalactic radio sources (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Consideration is given to particle production and high-energy radiation within apparently superluminal radio components of extragalactic radio sources forming within the apparent region of nuclear activity of a quasar or active galaxy. The physical conditions in compact components observed as radio emitters are derived for the quasars 3C 273 and 3C 345 and extrapolated to those of initial components of sizes on the order of 10 to the 15th cm on the basis of two-dimensional relativistic jet and relativistic three-dimensional models of component expansion. Probabilities that a given particle avoids an inelastic collision in the relativistic plasma are calculated for both cases which show that collisions which produce particles and radiation may be very important during the formation of a compact radio component. The consequences of electron-positron production, bremsstrahlung and proton-proton inelastic collisions ultimately giving rise to neutrinos and gamma rays for the development and energetics of the radio component are then examined, and upper limits to the amount of energy which can be channeled into radio components from an active region without giving rise to a high-energy X-ray source are derived.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 245
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  • 4
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    An 81 minute modulation of the X-ray flux from 2A 0311-227 (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: It is demonstrated that the X-ray flux from 2A 0311-227 is modulated at the 81 minute orbital period of its optical counterpart. An absorption dip with N sub H approximately equal to 5 x 10 to the 22nd H atoms per sq cm is observed at magnetic phase 0.42 that is interpreted as the accretion column of a magnetic white dwarf passing in front of the X-ray source. The spectrum is thermal with a temperature of 18 keV and a 300 eV equivalent-width iron line at 6.6 keV.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 244
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  • 5
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    Solar flare theory (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Solar flare models are briefly reviewed with emphasis on the physical mechanisms invoked to explain the flare. The physics of each mechanism and their interrelations are discussed in detail. Mechanisms are classified by their drivers (the source of energy on which they feed). The application of these mechanisms to coronal heating is evaluated.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 413-470
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  • 6
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    Heating and acceleration of the solar wind (1981)
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    Publication Date: 2011-08-18
    Description: The dynamics of the expanding corona are discussed emphasizing the physical processes which accelerate the plasma as it flows away from the Sun. The solar wind plays a dominant role in the energy balance of the part of the corona in which it originates. The wind acceleration processes, in large part, with the mechanisms that transport energy to the corona in the first place.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 373-384
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  • 7
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    Oscillations and pulsations (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A theory to describe the observed photospheric 5 minute oscillations, chromospheric 3 minute oscillations, and possible motions of the interior with periods ranging from 40 to 160 minutes is discussed. It is similar to the theory of nonradial stellar oscillations developed to describe the low angluar order modes (one or two wavelengths around a circumference); however, the solar oscillations have thousands of wavelengths around a circumference. The properties of waves in stars, their restoring forces, periods and wavelengths, and their propagation and motions are discussed.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 263-287
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  • 8
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    A comparison of circumstellar gas and dust in M giants and supergiants (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: This paper presents the results of a study of circumstellar gas and dust in a larger sample of stars than that of Hagen (1978). The gas-to-dust ratio varies considerably from star to star. The observations were obtained at Cerro Tololo Interamerican Observatory and Kitt Peak National Observatory. CS gas was observed with 2.5 and 5.1 A/mm echelle spectra obtained with the 4-meter telescopes. CS dust was observed through infrared photometry done with the CTIO 60 and KPNO 50 telescopes.
    Keywords: ASTROPHYSICS
    Type: Smithsonian Astrophysics Observatory 2nd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Vol. 1; p 231-238
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  • 9
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    Convective dynamos for rotating stars (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Global dynamo theory is applied to the problem of why some stars have field reversing dynamos, and others do not. It is argued that convectively driven dynamos are the most likely source of magnetic fields in stars that have convection zones.
    Keywords: ASTROPHYSICS
    Type: Smithsonian Astrophysics Observatory 2nd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Vol. 1; p 165-179
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  • 10
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    Shock waves, atmospheric structure and mass loss in Miras (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Large amplitude shock waves are observed to be present in the atmospheres of the Mira variables: spectral line doubling with Delta v 30 km/s is present in infrared spectra. Even the visible spectra contain some evidence for such shocks. These shocks are sufficiently large to clearly dominate the energy balance of the atmosphere. Mira variables also show symptoms of substantial mass loss rates: they are strong maser and infrared continuum sources and have strong circumstellar absorption features. The pulsation induced shocks which are seen to be present are obvious suspects for causing or enhancing the mass loss from these stars. The Miras thus present an ideal case for the study of dynamical effects on atmospheric structure, since both the dynamics and the results are clearly observable. The results are given of calculations of the thermalization and cooling of the shock heated material passing through shock fronts whose properties were selected to be consistent with both the isothermal models and the spectroscopic observations.
    Keywords: ASTROPHYSICS
    Type: Smithsonian Astrophysics Observatory 2nd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Vol. 1; p 147-151
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  • 11
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    Evidence for extended chromospheres surrounding red giant stars (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: There is now an increasing amount of both observational evidence and theoretical arguments that regions of partially ionized hydrogen extending several stellar radii are an important feature of red giant and supergiant stars. This evidence is discussed and the implications of the existence of extended chromospheres in terms of the nature of the outer atmospheres of, and mass loss from, cool stars are examined.
    Keywords: ASTROPHYSICS
    Type: Smithsonian Astrophysics Observatory 2nd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Vol. 1; p 137-145
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  • 12
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    Momentum and energy balance in late-type stellar winds (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Observations at ultraviolet and X-ray wavelengths indicate that the classical picture of a static stellar atmosphere containing a radiative equilibrium temperature distribution is inapplicable to the majority of late type stars. Mass loss and the presence of atmospheric regions characterized by gas temperatures in excess of the stellar effective temperature appear to be almost ubiquitous throughout the HR diagram. Evidence pertaining to the thermal and dynamical structure of the outer envelopes of cool stars is summarized. These results are compared with the predictions of several theoretical models which were proposed to account for mass loss from latetype stars. Models in which the outflow is thermally radiatively, or wave driven are considered for identification of the physical processes responsible for the observed wind properties. The observed variation of both the wind, thermal and dynamical structure as one proceeds from the supergiant branch toward the main sequence in the cool portion of the HR diagram give consideration to potential mechanisms for heating and cooling the flow from low gravity stars.
    Keywords: ASTROPHYSICS
    Type: Smithsonian Astrophysics Observatory 2nd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Vol. 1; p 83-97
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  • 13
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    A heating mechanism for the chromospheres of M dwarf stars (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The atmospheric structure of the dwarf M-stars which is especially important to the general field of stellar chromospheres and coronae was investigated. The M-dwarf stars constitute a class of objects for which the discrepancy between the predictions of the acoustic wave chromospheric/coronal heating hypothesis and the observations is most vivid. It is assumed that they represent a class of stars where alternative atmospheric heating mechanisms, presumably magnetically related, are most clearly manifested. Ascertainment of the validity of a hypothesis to account for the origin of the chromospheric and transition region line emission in M-dwarf stars is proposed.
    Keywords: ASTROPHYSICS
    Type: Smithsonian Astrophysics Observatory 2nd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Vol. 1; p 73-79
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  • 14
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    The generation of acoustic energy from stellar convection zones (1981)
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    Publication Date: 2011-08-18
    Description: The heating of stellar chromospheres and coronae by the dissipation of acoustic waves is an important heating mechanism. It is only in the lower solar chromosphere that short period acoustic wave heating seems undisputed. The arguments leading to the rejection of the so called acoustic heating theory are derived from comparisons of calculated acoustic energy fluxes with observational or theoretical requirements.
    Keywords: ASTROPHYSICS
    Type: Smithsonian Astrophysics Observatory 2nd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Vol. 1; p 67-72
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  • 15
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    On the formation of protostellar disks (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An analysis is presented of the hydrodynamic aspects of the growth of protostellar disks from the accretion of a rotating gas cloud. Streamline equations for the flow onto the disk are derived, including the special case where the disk is very thin. For the radial structure of the disk, detailed equations of conservation of mass, momentum, angular momentum, and energy are given. Exact solutions are found for the case of no internal viscosity. For the more general case where there is viscous stress, hypotheses are formulated with the objective of discovering the main qualitative characteristics of a turbulent system and to estimate the magnitude of the turbulent stress. Solutions are also found for boundary conditions, and the large and small viscosity limits. The relation of energy balance to disk thermal structure is detailed. Finally, trends in the collapse of the dust cloud are discussed in the light of the solutions given.
    Keywords: ASTROPHYSICS
    Type: Icarus; 48; Dec. 198
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  • 16
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    The 1979-1980 eclipse of Zeta Aurigae. II - The emission spectrum (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: UV observations using the IUE are employed to discuss the strength and changes of Zeta Aur between a second contact and mid-eclipse in 1979, the relative visibility of the supergiant's chromosphere as compared with the circumstellar (CS) nebular scattering of the B star photons, and the origin of the high speed CS components observed at all orbital phases. Agreement has been found for a spectoscopic radius of 200 solar radii and a 400 pc distance, and eclipse emission lines were recorded from 1238.9-2802.7 microns. An asymmetry in the Fe III lines at 46 plus or minus 15 km/sec was seen during eclipse and is taken to indicate downflowing material. The high speed wind flowing from the K supergiant is thought to expand homogeneously until encountering the B type main sequence star, where an accretion bow shock forms, and the smaller star's passage near the K star at periastron may cause local surface heating and subsequent high speed flows.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 251
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  • 17
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    Hard X-ray structure of the Crab Nebula (1981)
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    Publication Date: 2011-08-18
    Description: Two-dimensional maps of the Crab Nebula have been synthesized in 22-64 keV range through the modulation collimator experiment. The effective angular resolution is about 15-arcmin. The result indicates that the Crab morphology is strictly controlled by the pulsar.
    Keywords: ASTROPHYSICS
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  • 18
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    Cosmic ray antiprotons in the closed galaxy model (1981)
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    Publication Date: 2011-08-18
    Description: A calculation is made of the flux of secondary antiprotons expected for the leaky box model and for the closed galaxy model of Peters and Westergaard (1977). The antiproton/proton ratio observed at several GeV is a factor of 4 higher than the prediction for the leaky box model but is consistent with that predicted for the closed galaxy model. It is found that new low-energy data are not consistent with either model. Attention is given to the possibility of a primary antiproton component.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 251
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  • 19
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    The asymmetric 4.8 hour X-ray modulation of Cygnus X-3 - Model light curves and inferred orbital parameters (1981)
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    Publication Date: 2011-08-18
    Description: The 4.8 hour X-ray light curve of Cygnus X-3 is quantitatively described by several proposed models under the assumption that the binary orbit of Cyg X-3 is elliptic. The cocoon model implies an apparent size for the X-ray star's companion, which is larger than that of its critical lobe, and it is suggested that the emission of a dense stellar wind by the companion could lead to such a situation. It is shown that a helium star, with or without a hydrogen-rich envelope, seems to be the most likely Cyg X-3 companion, and that some of the observed variations in the 4.8 hour period can be accounted for by the apparent period variations due to apsidal motion.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 251
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  • 20
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    Millimeter-wave experiments for cometary space missions (1981)
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    Publication Date: 2011-08-18
    Description: Predicted brightness temperatures, computed by means of radiative transfer techniques adapted from the modeling of terrestrial ice and snow fields, are given for cometary nucleus models consisting of homogeneous layers of water ice and refractory grain mixtures presented as functions of wavelength. The computed millimeter-wave spectra are sensitive to the values of such physically significant nucleus parameters as (1) crust thickness, (2) subsurface temperature gradient, and (3) sublimating surface boundary temperature. Although antenna beam dilution is a major obstacle for ground-based molecular spectral line radio observations of comets, a millimeter-wave radiometer in the vicinity of the comet would be immune to this effect and able to make observations of several candidate parent molecules in the gas phase.
    Keywords: ASTROPHYSICS
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  • 21
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    Far-UV, visible, and near-IR reflectance spectra of frosts of H2O, CO2, NH3 and SO2 (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Measurements in the 0.1-2.5 micron range are presented for the reflectance spectra of the frosts of several volatiles pertinent to the study of comet nuclei. The frost spectra have distinctive features permitting their identification by spectroscopic reflectance remote sensing, notably in the far UV. It is found that: (1) H2O has a minimum at 0.16 microns and a maximum at 0.13 microns; (2) CO2 has minima near 0.21, 0.18 and 0.125 microns, with maxima at 0.19, 0.135 and 0.120 microns; (3) NH3 is bright at wavelengths longer than 0.21 microns, where reflectance drops to a value of only a few per cent at shorter wavelengths; (4) SO2 has a sharp drop at 0.32 microns, with a minimum at 0.18 microns and a maximum at 0.13 microns. The features in the frost spectra largely correspond to absorption line bands in the gas phase.
    Keywords: ASTROPHYSICS
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  • 22
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    Collapse and fragmentation of rotating, adiabatic clouds (1981)
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    Publication Date: 2011-08-18
    Description: A numerical hydrodynamics code has been used to calculate the collapse of rotating, adiabatic clouds. The three-dimensional nature of the calculation allows the clouds to fragment in the dynamic collapse phase. Clouds with adiabatic exponent of 7/5 and initial cos(2 phi) density variations fragment into binary systems if the initial ratio of thermal to gravitational energy is small (about 0.05). Clouds with higher thermal energy, however, damp the density variation and form near-equilibrium ellipsoids, with ratios of rotational to gravitational energy less than the critical value for dynamic growth of nonaxisymmetry in Maclaurin spheroids. Even with an adiabatic pressure law, dynamic fragmentation of a collapsing cloud is possible, implying for star formation theory that the low thermal energy fragments produced in isothermal collapse calculations may undergo a subsequent dynamic fragmentation in the nonisothermal regime.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 250
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  • 23
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    Very high resolution observations of SS433 at 10.65 GHz (1981)
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    Publication Date: 2011-08-18
    Description: Observations of SS433 made on June 12, 1979, from West Germany, Massachusetts, and West Virginia are discussed. It is noted that SS433 did not show fringes on any baseline although all the calibration sources were seen at their expected strengths. The measured total flux density of SS433 was found to be approximately 0.5 Jy, consistent with previous observations. The source was observed by on-offs at each telescope, which indicates that they were all pointed properly during the observations. The absence of fringes is not attributed to poor observing conditions or instrumental difficulties. It is concluded that if all the 10.65 GHz radiation emanates from a single component, then that component is at least 0.005 arcsec (approximately 10 to the 14th cm) in size. The measurements made on more sensitive intercontinental baselines indicate that there is no component of SS433 smaller than 0.001 arcsec emitting 10.65 GHz radiation above a level of 50 mJy.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 98; 1, Ma; May 1981
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  • 24
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    de Sitter's model and luminosity - Distance in cosmology (1981)
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    Publication Date: 2011-08-18
    Description: The behavior of luminosity-distance with redshift is analyzed within the framework of homogeneous zero-pressure relativistic cosmology. de Sitter's model is shown to have the most redshift sensitive luminosity-distance function of all cosmologies which have q sub 0 not less than -1. Quasar data which suggest a cut-off in absolute luminosity are reanalyzed and the cut-off disappears if either de Sitter's model or the assumption L(L-alpha) = 3 L(H-beta) is used.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society; vol. 195
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  • 25
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    Fine-scale characteristics of interplanetary sector boundaries (1981)
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    Publication Date: 2011-08-18
    Description: The study examines the structure of the interplanetary sector boundaries observed by Helios 1 within sector transition regions during the time interval from December 1974 to April 1975. The transition regions are found to be complex in character, consisting of intermediate average field orientations in some cases as well as a number of large-angle directional discontinuities (DDs). It is suggested that the observed DDs represent multiple traversals of the global heliospheric current sheet caused by local fluctuations in the position of the sheet. There is evidence that such fluctuations are sometimes produced by wavelike motions or surface corrugations of scale length 0.05-0.1 AU, superimposed on the large-scale structure.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research; 86; May 1
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  • 26
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    A companion quasar to 3C345 (1981)
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    Publication Date: 2011-08-18
    Description: The discovery of a new quasistellar object (QSO) which presents the strongest evidence to date for the membership of quasars in rich clusters is reported. During X-ray observations of quasar 3C345, a serendipitous X-ray source located 8 arcmin northeast of the quasar was discovered. The observed flux of the new source is 3.2 x 10 to the -13th erg/sq cm/sec in the 0.5-4.5 keV band. Three separate observations over a six-month period failed to show intensity variability in excess of the statistical uncertainty in the count rate. The spectrum shows a modest signal-to-noise ratio but four strong emission lines. It is suggested that the redshift agreement between the two QSOs indicates a common membership in a cluster of galaxies which may well be a rich cluster.
    Keywords: ASTROPHYSICS
    Type: Nature; 290; Apr. 9
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  • 27
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    A variable mixing-length ratio for convection theory (1981)
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    Publication Date: 2011-08-18
    Description: It is argued that a natural choice for the local mixing length in the mixing-length theory of convection has a value proportional to the local density scale height of the convective bubbles. The resultant variable mixing-length ratio (the ratio between the mixing length and the pressure scale height) of this theory is enhanced in the superadiabatic region and approaches a constant in deeper layers. Numerical tests comparing the new mixing length successfully eliminate most of the density inversion that typically plagues conventional results. The new approach also seems to indicate the existence of granular motion at the top of the convection zone.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 244
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  • 28
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    Dipole and quadrupole anisotropy of the 2.7 K radiation (1981)
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    Publication Date: 2011-08-18
    Description: Results of measurements of the dipole and quadrupole anisotropy of the microwave background radiation are reported. Balloon-borne measurements of the temperature difference between two horn antennas pointed 90 deg apart and 45 deg from the zenith were carried out at frequencies of 24.8, 31.4 and 46.0 GHz to determine three dipole and four quadrupole parameters. When combined with data from two previous balloon flights, a dipole anisotropy of 3.78 + or - 0.30 mK in the direction 11.6 + or - 0.2 h RA, -12 + or - 5 deg dec is obtained. The measurements reveal a spectral index of 0.04 + or - 0.28 between 19.0 and 46.0 GHz, indicating that the dipole effect arises from an intrinsic anisotropy in the temperature of the background and/or a first-order Doppler shift due to solar motions. A statistically significant quadrupole effect is also detected which is attributed to the intrinsic anisotropy of the 2.7 K background.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 243
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  • 29
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    Far-ultraviolet spectra and flux distributions of some Orion stars (1981)
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    Publication Date: 2011-08-18
    Description: Far-ultraviolet (950-1800 A) spectra with about 2 A resolution were obtained of a number of stars in Orion during a sounding-rocket flight 1975 December 6. These spectra have been reduced to absolute flux distributions with the aid of preflight calibrations. The derived fluxes are in good agreement with model-atmosphere predictions and previous observations down to about 1200 A. In the 1200-1080 A range, the present results are in good agreement with model predictions but fall above the rocket measurements of Brune, Mount and Feldman. Below 1080 A, our measurements fall below the model predictions, reaching a deviation of a factor of 2 near 1010 A and a factor of 4 near 950 A. The present results are compared with those of Brune et al. via Copernicus U2 observations in this spectral range, and possible sources of discrepancies between the various observations and model-atmosphere predictions are discussed. Other aspects of the spectra, particularly with regard to spectral classification, are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 243
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  • 30
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    The cosmic X-ray background (1981)
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    Publication Date: 2011-08-18
    Description: The cosmic X-ray experiment performed with the A2 instrument on HEAO-1 was especially developed to make systematics-free measurements of the extragalactic X-ray sky and has yielded the broadband spectral characteristics for two extreme aspects of this radiation. For the apparently isotropic radiation of cosmological origin that dominates the extragalactic X-ray flux, the spectrum over the energy band of maximum intensity is remarkably well described by a thermal model with a temperature of a half-billion degrees. At the other extreme, broadband observations of individual extragalactic X-ray sources with HEAO-1 are restricted to objects within the present epoch. These X-ray sources include a large sample of active galaxies studied in some detail over a broad bandwidth for the first time. Details of the cosmic X-ray background at these two extremes are reviewed, and some models describing X-ray emission mechanisms are discussed.
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    Algol - A further study of the optical polarization (1981)
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    Publication Date: 2011-08-18
    Description: Results of a study of the phase-locked optical polarization of the Algol triple star system are presented. Polarimetry was obtained in the B filter during 75 nights from 1979 to 1980, and results were folded on the AB orbital period for the equatorial Stokes parameters Q and U. As expected for a nearly edge-on system, the polarization variations are predominantly in one direction of the Stokes-vector plane, and are mainly second-harmonic in character. The variable polarization indicates an eigendirection for the AB system at an angle of 137 + or - 4 deg, and a projected major axis of the third star at 133 + or - 3 deg with respect to the AB system. Considerations of the lowest-order theories of polarizing mechanisms, including limb polarization and reflection, indicate that the AB and AB-C orbital planes are almost normal to each other, rather than coplanar. An angular splitting in the Q-U curve between the two quadrature phases 0.25 and 0.75 is also found which can be explained by centrifugal flattening of the secondary's Roche lobe, or reflection from an optically thick, flattened gas cloud near the L1 point.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 243
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    Interstellar C2 molecules toward Omicron Persei (1981)
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    Publication Date: 2011-08-18
    Description: Seven weak interstellar absorption lines of the (2-0) Phillips band of C2 near the wavelength 8760 are detected in the spectrum of Omicron Persei. All of the lines have equivalent widths less than 2 mA and originate from the five lowest rotational levels of C2. The resulting total column density is N(C2) = 1.5 x 10 to the 13th/sq cm, and the excitation temperature is T = 116 plus or minus 16 K.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 243
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    Infrared and optical observations of the hydrogen lines in quasars (1981)
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    Publication Date: 2011-08-18
    Description: Infrared and optical spectrophotometric observations of the hydrogen lines in a sample of 16 quasars are discussed. The addition of these observations to previously published observations of hydrogen lines in quasars brings to 12 the number of quasars for which the P-alpha/H-alpha/H-beta line ratios have been measured and to nine the number of quasars for which the L-alpha/H-alpha line ratio has been measured. It is noted that the P-alpha/H-alpha ratios in low-redshift quasars are distributed around the case B value with a tendency toward values lower than that predicted by case B. The H-alpha/H-beta values in these same quasars are for the most part greater than the case B value. The tendency in the P-alpha/H-alpha/H-beta ratios is for the P-alpha/H-alpha ratio to decrease as the H-alpha/H-beta ratio increases. The decrease of the P-alpha/H-alpha ratio with increasing H-alpha/H-beta ratio is the most significant correlation obtained from the present data that any valid model of the line-emitting regions must explain. The low values of the L-alpha/H-alpha in comparison with the case B value are confirmed for a large sample of high-redshift quasars. L-alpha is seemingly destroyed rather than H-alpha being enhanced. It is concluded that reddening external to the emission-line regions cannot satisfactorily explain all the observed hydrogen line ratios.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 243
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  • 34
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    Nonthermal hard X-ray emission from the nucleus of NGC 1275 (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Observations confirming the HEAO 1 discovery of a hard X-ray component in the X-ray spectrum of the Perseus cluster are reported. A comparison of the results with 1978 HEAO 1 observations and 1974 balloon limits shows that this component is variable on a time scale of one year. Synchrotron self-Compton models of the compact radio source centered on the nucleus of NGC 1275 predict a substantial secondary X-ray flux based on the observed radio data. While the observed X-ray flux is one-fourth the predicted value, uncertainties in the radio data are sufficient to account for the discrepancy. It is concluded that the hard X-ray flux originates in the active nucleus of the Seyfert galaxy NGC 1275 through the synchrotron self-Compton process.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 243
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    Very dusty galaxies (1981)
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    Publication Date: 2011-08-18
    Description: The existence of a significant population of dust shrouded galaxies that do not emit much optical light but instead are primarily infrared sources is considered. It is noted that if very dusty galaxies are assumed to have a luminosity function similar to that of normal galaxies, then current observations seem to show that there are not more dusty galaxies than normal objects. Until more extensive infrared observations are obtained, however, it seems at least possible, though perhaps unlikely, that there are in fact a significant number of dusty galaxies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 243
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  • 36
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    A study of the Mg II k line in Beta Persei (1981)
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    Publication Date: 2011-08-18
    Description: Spectral scans of the Mg II k line in Beta Per were obtained with Copernicus during two primary eclipses. A brief description of observation in a short frame mode is given. The observed data are compared with computed line profiles based on the eclipse geometry of spherical stars. It is shown that a nonuniform circumstellar envelope, or cloud, probably is present. In one scan, a red-shifted line of P Cygni-type profile appeared, indicating the occurrence of an unusual event in the close binary system.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal; 86; Feb. 198
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  • 37
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    The close multiple system mu Orionis - Masses and the mass-luminosity relation (1981)
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    Publication Date: 2011-08-18
    Description: The observations made of the secondary component B of the close visual binary mu Ori are described. The Reticon observations made at red wavelengths showed the secondary to be a double-lined spectroscopic binary with a period of 4.78 days and nearly identical components having minimum masses of 1.1 solar mass each. Previous estimates are corroborated by the large spectroscopic mass ratio of B to A and B. The discovery that B is a pair of late-F dwarfs solves the apparent mass-luminosity relation discrepancy noted in previous studies.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific; vol. 92
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  • 38
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    Pulsations and oscillations (1981)
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    Publication Date: 2011-08-18
    Description: The observations of the oscillations of the solar atmosphere are a powerful diagnostic tool for research into the structure of the atmosphere from inside the convection zone to the upper chromosphere. Interpretations of the global pulsations or oscillations are presented with emphasis on using these observations to study the structure of the interior of the Sun.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 65-84
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  • 39
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    Magnetic flux tubes (1981)
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    Publication Date: 2011-08-18
    Description: The magnetohydrodynamics of flux tubes are considered. The sections on equilibrium of flux tubes, and stability and waves deal with sunspots, the largest members of the general class of photospheric flux tubes.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 385-413
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    The energy balance of the solar wind (1981)
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    Publication Date: 2011-08-18
    Description: The effects of modifying some of the 'classical' assumptions underlying many of the solar wind models constructed over the past 20 years are examined in an effort to obtain both a better fit with the observations and a deeper understanding of the relevant physical processes.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 355-372
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    Mechanical heating in the transition region (1981)
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    Publication Date: 2011-08-18
    Description: Attention is focused on the energy balance in the transition region and the role that mechanical heating plays in determining the temperature density structure of this region in a stellar atmosphere. Because of its role as the interface layer through which mass and energy flow between the chromospheres and corona, direct deposition of mechanical energy is a relatively unimportant factor in the overall energy balance in the transition region, except in the uppermost layers where the temperature approaches coronal values.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 321-329
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    Chromospheric heating (1981)
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    Publication Date: 2011-08-18
    Description: General features of the solar chromospheric heating problem, which also apply to many stellar chromospheres, are reviewed. Current theories are discussed, including: heating by short period sound waves; the weak shock theory; and the time-dependent approach.
    Keywords: ASTROPHYSICS
    Type: The Sun as a Star; p 301-319
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    Penetrative convection (1981)
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    Description: The current state of understanding of the most directly observable solar convection, the granulation and supergranulation is summarized. The body of work in which the complete time dependent Navier-Stokes equations and entropy transport equation are solved for a fully compressible atmosphere is considered. Relevant anelastic and incompressible calculations in two dimensions are also discussed.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 253-262
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    Solar flare observations and their interpretations (1981)
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    Publication Date: 2011-08-18
    Description: A solar flare has a characteristic spatial extent of 10,000 to 100,000 km. It develops rapidly, with a characteristic time scale of 100 to 1000 s but its manifestations can be observed for hours after onset. A solar flare is the source of highly energetic particles with energies that extend into the GeV range; it produces copious amounts of electromagnetic radiation from gamma-rays to wavelengths of 10 km; and it produces violent magnetohydrodynamic phenomena such as shocks and fast mass ejections. The three basic phases of a flare are described and are: the precursor (preflare) phase, lasting for minutes to hours; the flash phase, lasting for 1 to 5 minutes; and the main (gradual) phase, lasting, on occasion, for hours.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 181-227
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    Solar magnetic structure and the solar activity cycle review of observational data (1981)
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    Publication Date: 2011-08-18
    Description: Data on solar magnetism that may offer clues for understanding stellar magnetism in general were reviewed. Magnetic phenomena in the photosphere and low chromosphere, where the magnetic structure can be studied in detail, are discussed. Properties of the discrete magnetic elements and their extensions through the chromosphere and transition zone up to the corona are described. The structure and evolution of active regions and other structured aggregates of magnetic elements are considered.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 163-179
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    The chromosphere and transition region (1981)
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    Publication Date: 2011-08-18
    Description: An empirical definition of the chromosphere and chromosphere-corona transition region is presented. Various general characteristics of the chromosphere are described and include: radiative equilibrium; spatial and temporal fluctuations; spectral characteristics; and thermodynamic structure.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Sun as a Star; p 85-133
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  • 47
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    X-ray spectra of the Crab pulsar and Nebula (1981)
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    Publication Date: 2011-08-18
    Description: The X-ray spectra of the Crab pulsar and Crab Nebula are analyzed. Observations were made with OSO 8 on March 17-18, 1978, with all spacecraft telemetry assigned to one detector during seven dwell mode experiments. A resolution of 1.25 ms was obtained for pulse-height-analyzed counts in 64 channels. Progressive hardening and subsequent softening of the spectrum across the pulse was found. The fraction of the pulsed flux, exhibiting a spectral variability of about 0.14 was concentrated solely in the region between the two peaks. A model is suggested in which the pulsed X-ray emission from the Crab pulsar consists of two components: one is physically related to the double-peaked gamma-ray pulse and possibly to radio and optical pulses, but has no spectral dependence on the pulse phase, while the other exhibits spectral variability with the pulse phase but is confined to the interpeak emission seen with X-ray energies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 246
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    Identification of new infrared bands in a carbon-rich Mira variable (1981)
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    Publication Date: 2011-08-18
    Description: Complete 0.75-13 micron spectrometry of a carbon-rich, Mira-class variable star is presented for the first time. It is noted that although the near-infrared is dominated by photospheric absorption bands of the CN red system, the infrared becomes progressively dominated by the bands of the polyatomic molecules HCN and C2H2. Since the band at 3.1 microns is known to be due to HCN and C2H2, it is possible to associate bands at 1.04, 1.53, 1.85, 2.5, 2.7, 3.56, 3.85, 4.8, and 7.1 microns with HCN and C2H2. The spectrum suggests that radiative transfer in the carbon Mira class cannot be discussed quantitatively without the inclusion of HCN and C2H2 opacity. On the basis of the carbon star models of Querci and Querci (1974), it is deduced that the abundance ratio of HCN to C2H2 can be used to indicate whether 3-alpha-processed or CNO-processed material is in the outer atmosphere. An 11.3 micron SiC dust-emission feature is present, although it differs significantly from the 11.7 micron SiC feature in Y CVn. A featureless emission is present from 4 to 13 microns and can be ascribed to optically thin graphite grains having a temperature of 450 K.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 246
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    Cyg X-1 - A massive neutron star (1981)
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    Publication Date: 2011-08-18
    Description: The expected X-ray emission from Cyg X-1, considered a massive neutron star (8-15 solar masses) according to some gravity theories, is studied within the framework of Rosen's bimetric gravity theory (1973, 1974). It is shown that in such massive neutron stars, the innermost stable orbit lies far outside the star surface, and therefore the X-ray spectrum consists of two components: a soft one emitted from a cold accretion disk and a hard one emitted by the matter striking the neutron star surface after spiraling down freely from the disk. The proposed model is shown to be in good agreement with the observed luminosities. The model predicts a surface gravitational redshift of 3.16 which could be tested by the future X- and gamma-ray detectors.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 97; 2, Ap; Apr. 198
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    Interplanetary gas. XXVI - On the reconnection of magnetic fields in cometary ionospheres at interplanetary sector boundary crossings (1981)
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    Publication Date: 2011-08-18
    Description: The reconnection process in the cometary ionosphere believed responsible for the disconnecting plasma tails phenomenon is studied through the basic equations of reconnection theory and current sheet instability criteria. It is proposed that reconnection occurs when the interplanetary magnetic fields incident on a comet that has gone just past a sector boundary are pressed into the fields captured from the previous sector. The fields are of opposite polarity, and the previously captured fields constitute the 'roots' of the plasma tail. An estimated duration of reconnection during a disconnection event (DE) of 0.75 days is used along with estimates of other cometary parameters to construct fusion region dimensions and resistivity with the adopted time scale.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 245
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    On stellar wind accretion in widely separated X-ray binaries, and the nature of 4U0115+63 (1981)
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    Publication Date: 2011-08-18
    Description: Widely separated, eccentric pulsating X-ray binaries are shown to be appropriate systems for studying the basic properties of stellar wind accretion. They are free from the complications encountered in closed binaries, where the optical star nearly fills its critical lobe (Avni, 1977). A framework of four observational tests was set up to study the characteristics of wind accretion, and to distinguish between different models of wind acceleration. The tests are applied to the source 4U0115+63, and the accretion process is discussed in both its quiescent states, and during its transient high luminosity outbursts. For the quiescent steady state, two wind profiles, determined from observational data, are compared (Barlow-Lohen, 1977; Castor et al., 1975). The difficulties encountered during the transient high states with respect to the possibility of stellar wind accretion are discussed.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 102; 1, Se; Sept
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    Cosmology (1981)
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    Publication Date: 2011-08-18
    Description: The current view of the universe is summarized. The equations used to described it and the means of interpreting the diffuse gamma radiation which might result from phenomena which occurred in the distant past are described. The Friedmann model is described in detail.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 187-201
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    Diffuse radiation (1981)
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    Publication Date: 2011-08-18
    Description: A diffuse celestial radiation which is isotropic at least on a course scale were measured from the soft X-ray region to about 150 MeV, at which energy the intensity falls below that of the galactic emission for most galactic latitudes. The spectral shape, the intensity, and the established degree of isotropy of this diffuse radiation already place severe constraints on the possible explanations for this radiation. Among the extragalactic theories, the more promising explanations of the isotropic diffuse emission appear to be radiation from exceptional galaxies from matter antimatter annihilation at the boundaries of superclusters of galaxies of matter and antimatter in baryon symmetric big bang models. Other possible sources for extragalactic diffuse gamma radiation are discussed and include normal galaxies, clusters of galaxies, primordial cosmic rays interacting with intergalactic matter, primordial black holes, and cosmic ray leakage from galaxies.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 203-228
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    The interstellar medium and galactic structure (1981)
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    Publication Date: 2011-08-18
    Description: High energy gamma rays are produced by the interaction of cosmic rays with the interstellar matter in the galaxy. By combining the gamma ray information with radio data, a picture of the galaxy is presented with regard to the general structure and the effects of cosmic ray pressure. The interaction processes and galactic matter distribution are discussed. Galactic cosmic ray distribution and current gamma ray results are reported.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 99-130
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    Gamma ray astronomy in perspective (1981)
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    Description: A brief overview of the development of gamma ray astronomy is presented. Gamma ray telescopes and other optical measuring instruments are highlighted. Emphasis is placed on findings that were unobtainable before gamma ray astronomy. Information on evolution of the solar system, the relationship of the solar system to the galaxy, and the composition of interstellar matter is discussed.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 1-14
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    Relativistic astrophysics - The view from Texas in Baltimore /Review/ (1981)
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    Publication Date: 2011-08-18
    Description: Recent observational and theoretical work presented at the Tenth Texas Symposium on Relativistic Astrophysics held in Baltimore, Maryland from December 15-19, 1980, is outlined. Areas covered include the theoretical foundations of relativistic astrophysics in general relativity, quantum gravitational theory and the association of grand unification with astronomical and cosmological issues, the cosmic microwave, X-ray, gamma-ray, UV, cosmic ray and gravitational wave backgrounds, the current expansion rate and average mass-energy density of the universe, and mechanisms of galaxy formation. Also discussed are the characteristics of active galaxies and clusters emitting in the gamma-ray and X-ray regions, and compact objects formed from supernova explosions, including pulsars, X-ray-emitting neutron stars, Sco X-1 and SS 433, gamma-ray sources, and X-ray and gamma-ray bursters.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Letters; 22; 1, 19; 1981
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    One millimeter continuum observations of high redshift quasars (1981)
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    Publication Date: 2011-08-18
    Description: Upper limits to the one-millimeter continuum flux densities of the high redshift quasars B2 1225 + 31, Ton 490, and PHL 957 are presented. The upper limit to the power observed from these quasars at 1 mm is, on the average, one half of the observed power in the continuum at L-alpha. These observations are used to constrain the temperature of a hypothetical dust shell which reddens the quasar line and continuum emission by an extinction optical depth sufficient to account for the anomalously low L-alpha/H-alpha emission line ratio observed in each of these quasars. For the quasars studied, dust shell temperatures between 25 K and 50 to 95 K are prohibited by the present data. A dust shell at a temperature within this span reradiating all the power absorbed from the quasar ultraviolet continuum would produce a one-millimeter flux density greater than the measured upper limit. The average radius of the model dust shell cannot be between 70 kpc and 1 Mpc.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Letters; 22; 1, 19; 1981
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    The interstellar medium and the highly ionized species observed in the spectrum of the nearby white dwarf G191-B2B (1981)
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    Publication Date: 2011-08-18
    Description: High-resolution spectra of the nearby (48 pc) white dwarf G191-B2B, obtained with the International Ultraviolet Explorer, reveal sharp resonance lines of N V, C IV, and Si IV. The origin of these features is most likely linked to the white dwarf, possibly being formed in an expanding halo around the star. Interstellar lines of C II, N I, Mg II, Si II, and Fe II are also seen in the spectrum. Analysis of these features indicates an average neutral hydrogen number density of 0.064 for this line of sight. In combination with the recent EUV and soft X-ray results, this is interpreted to mean that the interstellar medium in the most immediate solar vicinity is of the normal density n approximately equal to 0.1/cu cm of lower ionization, while just beyond it, at least in some directions, is a hot lower density plasma. These results are apparently in conflict with the model of the interstellar medium by McKee and Ostriker (1977) in its present form.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 248
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    The 1979-1980 eclipse of Zeta Aurigae. I - The circumstellar envelope (1981)
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    Publication Date: 2011-08-18
    Description: A model of the K-star wind far from the K star, and its interaction with the B star, has been derived from a study of Mg(+) and C(+++) resonance lines in the spectrum of Zeta Aurigae during 1979 and 1980. A mass loss rate from the K star of 2 x 10 to the -8th solar masses/year is suggested by the data; the rate of accretion of the K supergiant's material by the B star then being such that the matter accreted over a period of ten years is of the order of the total mass of the photosphere of the B star.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 248
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    The chemical composition, gravity, and temperature of Sirius (1981)
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    Publication Date: 2011-08-18
    Description: Observational data available for Sirius are of poorer quality than those for Vega, with both the angular diameter and absolute fluxes at different wavelengths being less accurately known. While these data yield an effective temperature of 10,000 + or - 250 K, the 13-color photometry of Johnson and Mitchell (1975) suggests that Sirius is about 450 K hotter than Vega's effective temperature of 9650 + or - 200 K. The c(1) color of the uvby system, the 33-52 and 35-52 colors of the 13-color photometry, and the H-alpha, H-beta and H-gamma line profiles all give log g values of about 4.3, which is in agreement with the value deduced from the mass and the radius, the latter being deduced from the angular diameter and the parallax.
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    Type: Astrophysical Journal; vol. 248
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    The nearby interstellar medium (1981)
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    Publication Date: 2011-08-18
    Description: The high dispersion spectrometer on board the International Ultraviolet Explorer (IUE) satellite was used to observe interstellar absorption lines in Rasalhague (Alpha Oph). This star is located 18 pc from the sun in the direction of the North Polar Spur, a prominent radio continuum feature in the Ophiuchus region of the sky. The satellite results, combined with previous interstellar line data and observations of the 'local interstellar wind' and soft X-ray emission, support earlier suggestions that the sun is immersed in a supernova remnant which may be an extension of the 'Loop I' or 'North Polar Spur' supernova remnant seen in the Scorpius-Ophiuchus region of the sky.
    Keywords: ASTROPHYSICS
    Type: Nature; 293; Oct. 1
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    Detectors for energies less than 10 MeV (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In the energy domain 100 keV to 10 MeV, both crystal scintillations and semiconductors are widely used for gamma ray detectors in spectrometer systems. These detectors' operation depend on the fact that gamma rays lose energy by ionization in these materials and electrons and holes are produced. In the case of semiconductors, these electrons and holes are collected by an electric field, and they provide an electric signal that is a direct measure of the energy lost by the gamma ray in the material. Scintillation detectors depend on a further conversion of the energy lost in electron hole pair production to the production of photons. A photomultiplier tube measures the intensity of the photon flux, and an electrical pulse proportional to the photon intensity is produced at the photomultiplier output.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 247-303
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    Gamma ray interaction processes (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Gamma ray detection in the energy region above 1 keV involves measurements of the energy exchange or energy loss between the gamma ray and the mass of the detector. In most cases of interest, it is the kinetic energy imparted to charged particles by the gamma ray which is lost in the detector and measured in order to obtain spectral knowledge between the incident gamma ray photon and the direction of the secondary particles contains important energy information. The interaction gamma ray removal processes in matter are considered. This interaction removal process is characterized by the fact that each gamma ray is removed individually from the incident beam. The number of photons removed in this manner is proportional to the thickness of matter traversed.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 229-246
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    Solar observations (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: High energy processes that take place in the Sun's atmosphere and the relationship of these phenomena to the basic problems of solar activity are discussed. Gamma ray emission exhibits characteristics of the conditions in regions where accelerated high energy particles interact. A number of gamma ray production mechanisms are considered. These include: the Compton effect, magnetobremsstrahlung, pi meson production by proton-proton interaction or by proton-antiproton annihilation, fission and neutral of charged particle radiative capture on inelastic scatter.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 67-94
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    Gamma ray observations of the solar system (1981)
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    Publication Date: 2011-08-18
    Description: Two general categories are discussed concerning the evolution of the solar system: the dualistic view, the planetesimal approach; and the monistic view, the nebular hypothesis. The major points of each view are given and the models that are developed from these views are described. Possible applications of gamma ray astronomical observations to the question of the dynamic evolution of the solar system are discussed.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 19-24
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    Analysis of observational spectra (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The first step in the analysis of gamma ray energy loss spectra is their conversion to differential energy and differential angular photon spectra. This conversion can be carried out if the detector response and the background are both known. Once these parameters are known, there are many techniques that can be used to convert pulse height spectra to photon spectra. These techniques are discussed and background problems are considered. Emphasis is placed on the analysis of energy loss spectra in the lower gamma ray energy domain. Problems of transportations from pulse height to photon space are most complex in this domain and the methods shown illustrate many of the problems which arise in the general analysis of energy loss spectra.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 337-382
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  • 67
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    Detectors for energies greater than 10 MeV (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The detector telescopes used in gamma ray astronomy in general are more similar to particle detectors than to optical devices, since the high frequency of the radiation precludes the use of reflection or diffraction techniques, but the high energy content of each photon does enable them to be detected with scintillators, track imaging chambers, and solid state detectors. Within the gamma ray range, the basic design of the instrument changes as the energy of the gamma ray exceeds 10 to 20 MeV, and therefore, moves from the region where the Compton effect predominates in the absorption of the gamma ray to that where electron pair production is most important. In the energy range from 10 to 20 MeV to several times 10,000 MeV, gamma ray telescopes are usually built so that the electron pair may be seen and the properties of the electrons measured.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 305-336
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    Galaxies (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Normal galaxies, radio galaxies, and Seyfert galaxies are considered. The large magellanic cloud and the great galaxy in Andromedia are highlighted. Quasars and BL lacertae objects are also discussed and a review of the spectral observations of all of these galaxies and celestial objects is presented.
    Keywords: ASTROPHYSICS
    Type: Gamma Ray Astrophys.; p 165-185
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  • 69
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    Rotation of dwarf star chromospheres in the ultraviolet (1981)
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    Publication Date: 2011-08-18
    Description: Periodic variations in the ultraviolet fluxes of chromospheric emission line multiplets are investigated for F, G and K stars as evidence of rotational modulation. Vacuum ultraviolet spectra were obtained with the IUE spacecraft for six stars as many as 11 times over the period April 23 to December 3, 1980. Variations in the emission fluxes of the hydrogen Lyman-alpha, Si II and Mg II lines are observed with periods up to 47 days. The periodicity, which is identified with rotational modulation, is found to persist over many rotational cycles, although the periods and time dependences of the fluxes from the different ionic species are not identical, probably due to differential rotation and global distributions. The spread of the UV periods is observed to be within 10%, with one or two peaks per cycle and a ratio of modulated to umodulated flux ranging from 1.1 to 3.0, analogous to solar behavior.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 248
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  • 70
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    Scale covariant gravitation. V - Kinetic theory. VI - Stellar structure and evolution (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A scale covariant kinetic theory for particles and photons is developed. The mathematical framework of the theory is given by the tangent bundle of a Weyl manifold. The Liouville equation is derived, and solutions to corresponding equilibrium distributions are presented and shown to yield thermodynamic results identical to the ones obtained previously. The scale covariant theory is then used to derive results of interest to stellar structure and evolution. A radiative transfer equation is derived that can be used to study stellar evolution with a variable gravitational constant. In addition, it is shown that the sun's absolute luminosity scales as L approximately equal to GM/kappa, where kappa is the stellar opacity. Finally, a formula is derived for the age of globular clusters as a function of the gravitational constant using a previously derived expression for the absolute luminosity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 248
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  • 71
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    A search for neutral hydrogen in D and cD galaxies (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Recent X-ray spectroscopic results suggest that 2-3 solar masses/yr of cooling gas may be falling into M87 and as much as 300 solar masses/yr into giant galaxies in rich clusters. The eventual fate of the gas in the radiatively accreting flow is an open question. In an attempt to set some bounds on the evolution of the gas, a sensitive search was performed for H I in a sample of eight D and cD galaxies in rich and poor clusters. Null detections in all cases set upper limits of (4-20) x 10 to the 8th solar masses of H I in the giant galaxies. Possible reasons for these nondetections and alternative evolutionary fates for the accreting gas are discussed.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal; 86; Aug. 198
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  • 72
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    Gamma ray bursts - A review of recent high-precision measurements (1981)
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    Publication Date: 2011-08-18
    Description: (Previously announced in STAR as N81-30077)
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  • 73
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    The X-ray structure of a galaxy cluster at z = 0.54 - Implications for cluster evolution and cosmology (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: High-resolution X-ray observations of the rich cluster 0016+16 at a redshift of 0.541 are presented. The emitting gas in this cluster is hot and extremely luminous, and its structure resembles that seen in the brightest nearby cluster sources. In most of its properties, 0016+16 resembles a richer version of the Coma cluster, and it offers little support to the hypothesis that clusters at z greater than 0.5 differ fundamentally from nearer objects.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 251
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  • 74
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    Statistical equilibrium in cometary C2. III - Triplet-singlet, Phillips, Ballik-Ramsay, and Mulliken bands (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A new series of vibrational bands is predicted which arises from transitions between the lowest electron states of the triplet and singlet states of homonuclear C2. The predictions are useful for C2 identifications and for disentangling congested low resolution spectra that characterize new observations. Predictions are also made for Mulliken, Phillips, and Ballik-Ramsay band sequences, and all calculations are made with the assumed molecular constants and computational methods of KSO-II.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 251
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    Orbital stability constraints on the nature of planetary systems (1981)
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    Publication Date: 2011-08-18
    Description: A fully self-consistent, N-body computer code is used to study conditions under which model planetary systems, each consisting of a star and two 'planetary' companions, become orbitally unstable as a result of gravitational interactions between the companions. A formula describing a necessary condition for orbital stability is given. It is found that giant gaseous protoplanets of the type postulated by Cameron (1978) to be precursors of the present-day solar system planets could have stable orbits for at least 10,000 years, the time required for significant core formation in a typical giant gaseous protoplanet.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 251
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    Model for the circumstellar gas around alpha Orionis (1981)
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    Publication Date: 2011-08-18
    Description: Models are presented to explain the physical conditions in the circumstellar envelope surrounding the red supergiant Alpha Orionis. The models of the CO density and neutral atomic potassium density are calculated for the outer shell to reproduce simultaneously both the radio detection of CO and optical measurements of the amount of scattering by neutral potassium around Alpha Ori. CO and potassium loss rates of 7 x 10 to the 39th/sec and 8 x 10 to the 37th/sec are obtained, which imply a potassium to carbon ratio greater than that of the sun by about a factor of 25. The low carbon abundance may be attributed to extensive CNO processing, and, together with the potassium abundance, indicates a total mass loss rate of 0.000015 solar masses/year. The mass loss, mass and abundance properties of Alpha Ori suggest it to be the progenitor of a Type II supernova such as Cas A.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 251
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  • 77
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    On the variation of G and scale invariant gravitation - A reply (1981)
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    Publication Date: 2011-08-18
    Description: In 1977 Canuto et al. proposed a formalism to deal with the possible difference between gravitational and atomic clocks (or times). The formalism was incomplete since the authors only dealt with the gravitational Lagrangian LG, leaving the specific form of the matter Lagrangian Lm for a later study. Kembhavi and Pollock (1981) have proposed a matter Lagrangian which they define as 'the only possible one' or 'the inescapable form of Lm'. Adding this Lm to Lg, they claim that the theory does not allow for a variable G. The present paper gives a mathematical proof that the proposed matter Lagrangian, far from being 'the only one' or 'the inescapable form', is actually a very special case which already contains imprinted all the conclusions Kembhavi and Pollock claim to have discovered. Their results are therefore erroneous.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society; vol. 197
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  • 78
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    The resonance line of B II in IUE spectra of chemically peculiar stars (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A description is presented of high-dispersion spectroscopic observations of eight chemically peculiar stars including Kappa Cnc and Mu Lep, and of one normal comparison star, Nu Cap, in the vicinity of 1362 A. The reported data were obtained with the International Ultraviolet Explorer during the first 15 months of its operation. The initial reduction of the data, which were originally described in a qualitative summary by Leckrone (1980), was affected by a serious error in the calibration of the instrument's intensity transfer function. This error has been corrected in the currently presented data. The results of spectrum syntheses of the 1362 A feature are also described for several of the stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 250
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  • 79
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    New observational constraints on the M87 jet (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: New observations at 1.6-3.45 microns confirm the presence of a dramatic (change in spectral index of approximately 1) break between radio-IR wavelengths and 6,000 A in the spectrum of the M87 jet. These data, in combination with data taken in other spectral regions, show that the individual knots in the M87 jet have nearly the same spectral indices and nearly the same large (change in spectral index of approximately 1) spectral break. This large spectral break and the constancy of spectral properties between the knots pose serious constraints for models of the M87 jet.
    Keywords: ASTROPHYSICS
    Type: Nature; 294; Nov. 26
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  • 80
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    The high energy X-ray spectrum of 4U 0900-40 observed from OSO 8 (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The X-ray source 4U 0900-40 (= Vela XR-1) was observed with the high-energy X-ray spectrometer on OSO 8 for one week in 1976 and three weeks in 1978. Spectra of the source are presented above 16 keV. No systematic difference exists between the X-ray eclipse centers and the eclipse centers predicted from optical ephermerides. Short period intrinsic variability in the system's X-ray intensity may be related to changes in the Compton scattering optical depth in the system and does not require sporadic mass transfer via Roche lobe overflow. The 282 s modulation in the source's X-ray flux above 21 keV consists of two essentially similar pulses per period, most easily interpreted as arising from the two different magnetic poles of a rotating neutron star. The secondary appears to be a spherically accreting, magnetic neutron star.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 250
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  • 81
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    The visual surface brightness relation and the absolute magnitudes of RR Lyrae stars. I - Theory (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A theoretical relation analogous to the Barnes-Evans relation between stellar surface brightness and V-R color is derived which is applicable to the temperatures and gravities appropriate to RR Lyrae stars. Values of the visual surface brightness and V-R colors are calculated for model stellar atmospheres with effective temperatures between 6000 and 8000 K, log surface gravities from 2.2 to 3.5, and A/H anbundance ratios from -0.5 to -3.0. The resulting relation is found to be in reasonable agreement with the empirical relation of Barnes, Evans and Moffet (1978), with, however, small sensitivities to gravity and metal abundance. The relation may be used to derive stellar angular diameters from (V,R) photometry and to derive radii, distances, and absolute magnitudes for variable stars when combined with a radial velocity curve. The accuracies of the radii and distances (within 10%) and absolute magnitudes (within 0.25 magnitudes) compare favorably with those of the Baade-Wesselink method currently in use.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 250
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  • 82
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    Matter-antimatter separation in the early universe by rotating black holes (1981)
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    Publication Date: 2011-08-18
    Description: Consideration of the effect of rotating black holes evaporating early in the universe shows that they would have produced oppositely directed neutrino and antineutrino currents, which push matter and antimatter apart. This separation mechanism is, however, too feeble to account for a present baryon-to-photon ratio of 10 to the -9th, and has no significant observational consequences.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 249
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  • 83
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    Effect of long-term intensity variations on pulsar searches and the pulsar luminosity function (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Long-term intensity data for five pulsars are used to obtain the probability density distribution of intensities for each pulsar, and it is found that they are described satisfactorily by chi-squared distributions. Based on these distributions, the number of new pulsars expected to be found on repeatedly searching the same region of the sky with the same sensitivity is given. Nearly 25 percent more new pulsars are expected to be found on the first repeat search. It is also shown that the luminosity function deduced from either a single survey or surveys with very different sensitivities is not affected by the omission of flux density variations in the calculation of selection effects. Finally, a method is proposed for deriving the luminosity function by combining the different searches of a given area on the basis of a probabilistic approach to the evaluation of selection effects.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society; vol. 197
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    Annihilation radiation from a hot e/+/-e/-/ plasma (1981)
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    Publication Date: 2011-08-18
    Description: The radiation from electron-positron annihilations in a plasma of temperature above 10 to the 8th K is investigated as a possible source of the emission line at energies between 400 and 460 keV frequently seen in gamma-ray bursts. The annihilation rate and luminosity of an optically thin electron-positron plasma and the energy distribution of the resulting annihilation radiation are calculated by the use of a Monte Carlo technique as functions of temperature. Results indicate the annihilation spectrum to be peaked at an energy of 0.511 MeV plus a temperature-dependent blueshift, and the annihilation line to be significantly temperature-broadened. The widths of the observed burst emission lines set an upper limit of 3 x 10 to the 8th K on the temperature of any pair annihilation region in burst sources, which is considerably lower than the typical kinetic temperatures of the radiating particles. It is thus inferred that either the annihilation region is nonthermal, or spatially distinct from the burst site.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 250
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    4-8 micron spectrophotometry of OH 0739-14 (1981)
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    Publication Date: 2011-08-18
    Description: Spectrophotometry of the dust-embedded late-type star OH 0739-14 shows an absorption feature at 6.0 microns characteristic of H2O ice at temperatures significantly lower than 150 K, confirming the identification of H2O ice in the circumstellar shell in this source. The differences in the infrared spectra of HO 0739-14 and embedded molecular cloud sources are attributed to the different cloud lifetimes and temperature regimes in which the molecules are formed. A lower limit to the mass loss rate of 0.0001 solar mass per year is derived, based on the column density of ice and the size and the expansion velocity of the circumstellar cloud.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 250
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    The circumstellar envelopes of F- and G-type supergiants in the Large Magellanic Cloud (1981)
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    Publication Date: 2011-08-18
    Description: The outer atmospheres of four F- and G-type supergiants in the LMC are compared with those of their Milky Way counterparts by means of 2.5 and 5.1 A/mm high dispersion Echelle spectra. Na I D line doubling indicates extensive circumstellar envelopes, mass loss rates greater than 0.00001 solar masses/year, and outflow velocities of 10-60 km/sec. The Ca II H and K lines yield new data on extragalactic star chromospheres.
    Keywords: ASTROPHYSICS
    Type: (ISSN 0185-1101)
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    Low-frequency radio observations of poor clusters of galaxies (1981)
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    Publication Date: 2011-08-18
    Description: Observations have been made at the Clark Lake Radio Observatory of 16 poor clusters of galaxies at 34.3 MHz. Four of the poor clusters were detected at flux densities greater than 20 Jy. The spectra of the four detected clusters are all rather steep. Two of the detected clusters, AWM 4 and AWM 5, are also known to be X-ray sources. The possibility that the X-ray-emitting gas is heated by Coulomb interactions with the relativistic electrons responsible for the radio emission is investigated, and it is found that the observed X-ray luminosities can be accounted for if the electron energy spectrum extends to very low energies (gamma approximately 1-10). Collective plasma effects may increase the heating efficiency and eliminate the need to extrapolate the electron energy spectrum to such low values.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal; 86; June 198
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    The abundance and excitation of the carbon chains in interstellar molecular clouds (1981)
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    Publication Date: 2011-08-18
    Description: Emission lines from the carbon chains HC3N, HC5N, HC7N and HC9N were observed at 3 mm, 7 mm, and 1.4 cm in a number of dark clouds, Orion A and IRC(plus)10216. Non-LTE models were constructed to describe excitation and column densities. Component models for the Taurus dark cloud TMC-1 suggested that relative molecular abundances do not vary substantially along the cloud ridge, whereas the H2 density does by a factor of three. Data available for other dark clouds showed that the decrease in abundance with length from one carbon chain to the next is nearly constant, being close to 2.3. The decline in carbon chain abundance with length is steeper in Orion KL than in dark clouds by a factor of approximately four. Abundance ratios derived for the carbon star IRC(plus)10216 are uncertain, due to difficulties in modeling excitation rates in this environment.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 99; 2, Ju; June 198
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  • 89
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    Interstellar extinction by small-coated or uncoated graphite grains (1981)
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    Publication Date: 2011-08-18
    Description: Calculations have been made on the theoretical extinction of spherical graphite particles from 130 to 3500 nm. It is found that graphite particles of radius near 20 nm can have small (0.5 nm) coatings and still be responsible for the 220 nm peak in the interstellar extinction curve. New calculations also show that the effect of finite particle size is relatively unimportant in determining the extinction of graphite spheres at 220 nm.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 246
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  • 90
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    Molecular hydrogen ion /H2+/ absorption in planetary nebulae (1981)
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    Publication Date: 2011-08-18
    Description: Several IUE spectra of planetary nebulae show an absorption feature shortward of 1500 A which is believed to be due to H2(+). The nebulae are excited by stars of spectral type O3-O7 or continuum, and all but one have double-shell structure.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal; 86; June 198
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    Interplanetary Alfvenic fluctuations - A stochastic model (1981)
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    Publication Date: 2011-08-18
    Description: The concept of minimum variance is investigated for nonplanar interplanetary Alfvenic fluctuations in which the field direction varies randomly. The theory of the random wandering of a vector of constant length is developed as a representation of the magnetic field, and it is found that the minimum variance tends to coincide with the mean field directions over the correlation time of the fluctuations. The Fokker-Planck limit of the theory is then developed and used to analyze the statistic distribution of field directions with and without a reflecting barrier. Results suggest that the tendency of the Alfvenic fluctuations to have a direction of minimum variance statistically aligned with the mean magnetic field may be purely a consequence of the randomness of the fluctuation and not imply that the fluctuations are necessarily plane waves. Extensive statistical studies of the observed directional variations of the interplanetary magnetic field are necessary to test this hypothesis.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research; 86; Sept. 1
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  • 92
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    Numerical three dimensional calculations of tidally induced binary protostar formation (1981)
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    Publication Date: 2011-08-18
    Description: The manner in which interstellar clouds fragment into subcondensations capable of becoming stars is still unknown. A variety of mechanisms may be responsible for cloud fragmentation. The considered investigation is concerned with a mechanism which is based on tidal forces due to a companion cloud. A 3D code is used to study the tidal effects of point sources of various masses located in the equatorial plane of an initially uniform density, uniformly rotating, isothermal gas cloud. It is found that tidal forces can be quite effective at inducing fragmentation in an initially uniform cloud, although the effects are most pronounced for low thermal energy clouds, perturbed by perhaps unreasonably large tidal forces. It is also seen that tidal forces may be much less efficient at preventing the collapse of a cloud than has previously been supposed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 246
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  • 93
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    On the enhancement of the IMF magnitude during 1978-1979 (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The magnitude of the interplanetary magnetic field (IMF) exhibits an enhancement during 1978-1979 relative to all years back to 1963. It is shown that IMF magnitude variations over the 1966-1979 period represent the combined effect of variations in both the radial flux density of the IMF and the degree of spiraling of the IMF, consistent with the theoretical model of Parker. The 1978-1979 IMF magnitude enhancement is due to an enhancement of radial flux which was in turn related to an increase of magnetic flux leaving solar active regions. It is also shown that during the corotating stream dominated years 1973-1976, the IMF was less wound up than it was during other years, and that 1973-1974 were years of enhanced radial flux.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research; 86; June 1
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  • 94
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    1548C27 - An interesting new cometary nebula (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The object 1548C27, a faint cometary nebula of classical form, discovered by an examination of early Near Infrared Photographic Sky Survey (NIPSS) data (1979) is presented. Direct imaging and polarimetric, photometric, and spectroscopic observations are reported. Early survey test photographs show that the object lies at R.A. 19h40m48s, Decl. +23 deg 17 arcmin 09 arc sec (1950) in the Vulpecula constellation in the immediate vicinity of the complex H II region and galactic cluster NGC 6820/6823. From the photographs, the nebula was estimated to be 15 m visual and of color class one. The object was observed spectroscopically in the region 5700-6800 A using an Image Dissector Scanner with a 1.8 m reflector, and the spectral scan, obtained on November 4, 1978, is presented. New information on cometary nebulae may further illuminate the evolutionary importance of the objects.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal; 86; May 1981
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  • 95
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    VLBI observations of the nucleus of the radio galaxy Cygnus A (1981)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The central component of the radio galaxy Cygnus A has been observed in several (very long baseline interferometry) experiments between 1975 and 1979, and the results have been combined to derive a model for the brightness distribution. Some 65% of the nuclear emission appears to come from a compact core. The remaining flux density comes from a more extended region (or regions) up to 4 or 5 mas away lying along a position angle near 100 deg, which is close to that of the extended lobes. Evidence that compact central components reflect the collimation and transport of energy to the outer lobes of radio galaxies is discussed, and several interpretations of the observed asymmetries are considered.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 97; 1, Ap; Apr. 198
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  • 96
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    Globular cluster winds with central accretion by a massive compact object or subcluster (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Steady-state isothermal wind flows are computed with accretion by a central mass concentration in spherically symmetric systems of gas-losing stars. Solutions are uniquely determined by two dimensionless parameters lambda and m, where lambda is approximately equal to the square of the ratio of the central escape velocity to the sound speed and m is approximately equal to the ratio of the central point mass to the cluster core mass. The models are applied to globular clusters for two types of central mass concentration - a single massive black hole and a subcluster of massive stars. A hard (greater than a keV) X-ray source due to a central black hole fed by clusterwide inflow does not provide a consistent model for globular cluster X-ray sources. However, in the case of hot (T being greater than or approximately equal to 2 x 10 to the 5th K) winds, gas trapping by a central subcluster of neutron stars or of binaries containing white dwarfs could explain recent UV and H-alpha observations. Similar applications to elliptical galaxies are discussed.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society; vol. 195
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  • 97
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    Production spectrum of gamma rays in interstellar space through neutral pion decay (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A simple representation is obtained of the observed invariant cross section for the production of neutral pions in proton-proton collisions. Using this representation, the differential and integral production spectra of gamma rays in the galaxy are calculated from interactions of cosmic ray nuclei with interstellar gas. It is shown that the uncertainties in deducing interstellar proton spectrum by demodulating the observed spectrum have only a limited effect on the gamma ray spectrum. Also determined is the gamma ray production spectrum through bremsstrahlung process for a typical interstellar electron spectrum derived from the radio spectrum in the galaxy.
    Keywords: ASTROPHYSICS
    Type: Astrophysics and Space Science; 76; 1, Ma; May 1981
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  • 98
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    Type II Cepheids - A comparison of theory with observations (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 244
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  • 99
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    On the fragmentation of rotating interstellar clouds (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Simple physical arguments are used to estimate the time scale for fragmentation of a collapsing, rotating, isothermal, interstellar cloud. This time scale is compared with a similarly estimated time scale for the collapse upon itself of a transitory ring structure. It is shown to be plausible for a cloud with a given ratio of rotational to gravitational energy (beta) that as the ratio of thermal to gravitational energy (alpha) is varied, there is an intermediate range of alpha where a ring forms and collapses on itself, prior to fragmentation. For higher or lower alpha, however, the cloud fragments prior to ring self-collapse. The analysis is compared with the results of numerical multidimensional, gravitational, hydrodynamical collapse and shown to be in good agreement with them.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 244
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  • 100
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    Radio emission in the directions of cD and related galaxies in poor clusters. III - VLA observations at 20 cm (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: VLA radio maps and optical identifications of a sample of sources in the directions of 21 Yerkes poor cluster fields are presented. The majority of the cluster radio sources are associated with the dominant D or cD galaxies (approximately 70 percent). Our analysis of dominant galaxies in rich and poor clusters indicates that these giant galaxies are much more often radio emitters (approximately 25 percent of cD's are radio active in the poor clusters), have steeper radio spectra, and have simpler radio morphologies (i.e., double or other linear structure) than other less bright ellipticals. A strong continuum of radio properties in cD galaxies is seen from rich to poor clusters. It is speculated that the location of these dominant galaxies at the cluster centers (i.e., at the bottom of a deep, isolated gravitational potential well) is the crucial factor in explaining their multifrequency activity. Galaxy cannibalism and gas infall models as fueling mechanisms for the observed radio and X-ray emission are discussed
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal; 86; Jan. 198
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