bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistics of Three-Body Experiments
Authors: Valtonen M. J. 
Published: July 2016

A large number of three-body interactions involving one initial binary have been studied by a numerical regularization technique. In each set of experiments some parameters have fixed values, whereas others are selected by uniform sampling of the corresponding distribution functions. Similar statistical results are obtained for different random number sequences at a lower integration accuracy.This experimental approach permits an approximate determination of the final distributions of eccentricity, velocity and lifetime. These results show a strong dependence on the total angular momentum, total energy and the mass range, whereas other parameters are usually of secondary importance.
Time Variations of Solar X-ray Bright Points
Authors: Golub L. , Krieger A. S. , Silk J. K. , Timothy A. F. , Vaiana G. S. 
Published: July 2016

SummaryAn example of the overall view of the X-ray corona (nominal filter passband 2–32 Å and 44–54 Å) showing a coronal hole, filament activity, bright points and the large scale-scale loop structures, is shown in Figure 1. This is one of the 32000 X-ray images obtained with the AS & E X-ray telescope on Skylab. A comprehensive review describing the characteristics of the various features and their implications regarding the high velocity solar streams, evolution of magnetic fields in active regions, and sources of soft X-ray emission has been given by Vaiana et al. (1975). In the present summary we will only be concerned with the bright points. Studies of solar X-ray bright points, show that these features represent a distinct class of solar activity. Bright points appear first as a diffuse cloud of soft X-ray emission typically growing to 30″ in diameter, with growth rates of ∼1 km s−1. Several hours after the point first becomes visible a bright compact core forms, growing to 10″. The lifetime distribution of bright points follows a Poisson distribution with a mean of eight hours (see references). The points are distributed uniformly over the entire solar surface, with approximately 500 on the Sun at any time. Their occurrrence appears to be independent of major active regions, except for a visibility factor near high loop structures or a possible decrease in number in active region latitudes.
X-Ray Spectroscopy of Solar Active Regions During the Third Skylab Mission
Authors: Pye J. P. , Hutcheon R. J. , Parkinson J. H. , Pounds K. A. 
Published: July 2016

SummaryThis paper describes the analysis of soft X-ray spectra of solar active regions observed on a Skylark sounding rocket flight. The experiment was launched from Woomera, South Australia, at 0535 UT on 26th November 1973. The payload consisted of 3 plane scanning Bragg crystal spectrometers, covering the wavelength range 4 to 23 Å, and collimated to 3 arc min FWHM. The instrument was the same as that used by Parkinson (1972, 1973). The launch was part of a collaborative observing program with American Science & Engineering who obtained X-ray photographs of the Sun with the S0-54 ATM X-ray telescope, simultaneously with the Leicester observations. We report preliminary results for McMath region 12624 (S10 W28). This region was observed about 60 min after the peak of an importance – N, class CO flare.
Soft X-Radiation from Single Active Regions
Authors: Brabban D. H. , Dorling E. B. , Glencross W. M. , Herring J. R. H. 
Published: July 2016

SummaryThe MSSL/Leicester University package on OSO 5 contained proportional counters having fields of view small compared with the area of the solar disk (Herring et al., 1971). Results discussed here were obtained with a detector sensitive in the band 0.3–0.9 nm. This had an entrance window collimated to examine a strip of angular width 2′ lying across the Sun.
The Interpretation of Spectra, Polarization, and Directivity of Solar Hard X-Rays
Authors: Brown John C. 
Published: July 2016

The importance of interpretation of hard X-ray burst spectra, polarisation and directivity to the flare process as a whole is emphasised. After critically reviewing observations of these and related burst characteristics, the problems of analytic and numerical inversion of the X-ray spectrum to give the flare electron spectrum are discussed and it is concluded that electron spectra cannot be accurately and unambiguously inferred from their bremsstrahlung emission. Consideration of directional, albedo, and model-dependent effects, on the other hand, shows that none of the X-ray data are at present inconsistent with a power-law electron acceleration spectrum.Characteristics of thick-target, thin-target and electron-trap models of hard X-ray sources are discussed quantitatively and their ability to fit the observations is examined. Selection of a satisfactory model is precluded by lack of both sufficient observations and of adequate theoretical description of models. Nevertheless, it is suggested that redistribution of the flaring atmosphere and the effects of collective energy losses may reconcile even behind-the-limb burst observations and interplanetary electron spectra with a thick-target description (which fits other data well). This is attractive since a thick-target X-ray source makes the minimal demand on flare energy. Even a thick-target, however, requires an embarrassingly large number and energy of fast electrons. Therefore the review is completed by discussing how these requirements might be reduced if thermal emission extended to hard X-ray energies or if multiple reacceleration of electrons occurred.
Nuclei of Heavy Elements from Solar Flares
Authors: Fan C. Y. , Gloeckler G. , Hovestadt D. 
Published: July 2016

This paper presents a comprehensive review of the up to date knowledge on nuclear species of Z>2 from solar flares. It covers the following five topics:
(I)Solar flare particles of energies >15 MeV n-1 and solar composition;(II)solar flare particles of energies >15 MeV n-1, the enrichment of heavier elements;(III)theoretical interpretation of the enrichment;(IV)the charge states of solar particles; and(V)isotopic abundances of solar flare particles.
Molecular Cloud Densities from Observations of Carbon Monosulfide
Authors: Linke Richard A. , Goldsmith Paul F. 
Published: July 2016

AbstractWe have made carefully calibrated measurements of the J=1→0 and J=2→1 transitions of CS in 32 molecular sources in order to obtain density and fractional abundance information from the excitation of this molecule. The antennas used provided beams of nearly equal size. The line intensities, which fall between 1 and 5K, have typically been determined with a (1σ) uncertainty of ∼10%. The two transitions show nearly equal intensities and linewidths which are, respectively, about one tenth and one half of the corresponding quantities for CO. Our observations are seen to be in good agreement with the results of excitation calculations involving either a velocity gradient model or a purely micro-turbulent model since in both cases optical depths are small (0.3 to 3.0). Values obtained for n(H2) and X(CS)/dv/dr from the velocity gradient model fall in the range 2×104 to 2×105 cm−3 and 3×10−11 to 3×10−10 (km s−1pc−1)−1 respectively.
The Formation of Hydrocarbons and Iron-Hydrides on Cold Interstellar Grains-Experimental Studies
Authors: Bar-Nun A. , Litman M. , Pasternak M. , Rappaport M. L. 
Published: July 2016

Cold hydrogen atoms at T ≥ 7K were shown experimentally to react with graphite grains at the same temperature to produce CH4 and smaller amounts of C2H6, C2H4 and C2H2. At T < 20K the hydrocarbon mantle could polymerize to form carbonaceous substances, similar to those found in carbonaceous chondrites. Further encounters with H-atoms would result in their recombination on the hydrocarbon mantle around the grains. At higher grain temperatures, the hydrocarbons formed could be ejected into the gas phase.Cold iron atoms at T < 5K were shown experimentally to react with molecular hydrogen in a T < 5K matrix. Mössbauer studies with 57Fe demonstrated the formation of an Fe-H2 bond. FeH2 and FeH molecules could be formed on grains by encounters of iron atoms with either H-atoms or H2 molecules.
The 12C/13C Ratio in Interstellar Dark Clouds
Authors: Mccutcheon W.H. , Dickman R. L. , Shuter W.L.H. , Roger R. S. 
Published: July 2016

Since 13C is believed to be produced by non-equilibrium CNO processing in stellar evolution (Truran 1977), measurements of the carbon ratio Rc ≡ [12C] / [13C] in the interstellar medium may provide important information on nucleo-synthesis. Commonly, the ratio (N13/N18)LTE ≡ [13CO/C18O]LTE is measured and from this RLTE ≡ [12CO/13CO]LTE is deduced and these values are often identified with Rc. However, this line of reasoning can be misleading for two reasons (Dickman et al. 1979):(1) The difficulty of determining accurate column densities, [13C16O] and [12C18O], because of the complexity of the radiative transfer problem;(2) The possible role of fractionation, whereby RCO ≡ [12CO] / [13CO] does not necessarily reflect the initial atomic abundance ratio RC (Watson et al. 1976, Langer 1977, Liszt 1978).
The Rapidly Rotating Giants of the FK Comae-type
Authors: Bopp B. W. , Rucinski S. M. 
Published: July 2016

We present new spectroscopic and photometric observations and discuss a small but important group of rapidly rotating G - K giants (FK Com=HD 117555, UZ Lib=BD−8°3999, HD 199178 possibly others) which are photometrically variable, show slightly redshifted and variable Ca II H and K emission and variable Hα emission, show rotationally broadened spectral lines (50–100 km/s), and yet show no large radial velocity variations. Possible explanations of the properties of these stars are discussed and coalescence of a W UMa binary system seems to be the most probable evolutionary state.The most extreme of the group, FK Com is discussed in detail. Its type, G2IIIa (Keenan, priv.comm.) implying MV=−1 (the IR indices are consistent with a giant) suggests a reduction of log g (relative to Sun) −1.5 to −2.5; this can be only marginally reconciled with the dimensions of about 5 Ro resulting from the photometric period 2.4 d. and Vrot sin i about 100 km/s. The photometric variability (0.05 in I, 0.07 in R) is most probably due to spots asymmetrically distributed in longitude. The brightness minima observed by Chugainov in 1966 and 1974 and the new minimum observed in 1979 (JD 2443949.025) can be phased with one period 2.3995±0.0002 d. The erratic behavior of rotationally broadened spectral lines precludes obtaining a radial velocity orbit but an upper limit of 25 km/s for any periodic variations implies that the secondary must be a very low mass object. The strong Hα emission is variable in relative intensity of its double peaks but has a constant full width in excess of 20 A. The full half width at base implies rotational velocities of the order of 570 km/s; the half separation of peaks implies 300 km/s. Existence of an excretion disc of the type suggested by Webbink is possible.
Enhancement of Thermonuclear Reaction Rate due to Strong Screening
Authors: Itoh N. , Totsuji H. , Ichimaru S. , DeWitt H.E. 
Published: July 2016

The enhancement factor for the rate of thermonuclear reactions which involve two kinds of nuclei with charges Zi and Zj in the strong-screening regime is given for general cases of surrounding nuclear plasmas by the formula, exp[1.25Γij −0.095τij(3Γij/τij)2]. Here, Γij = 2ZiZje2/(ai+aj)T; ai = [3Zi/4πΣkZknk]1/3; τij = [(27π2/4)(2μijZi2Zj2e4Th2)]1/3; μij is the reduced mass for the two reacting nuclei Zi and Zj; and nk is the number density of nuclei Zk. The calculation is based on the recent results of Monte Carlo computations for binary ion mixtures, which have shown that the screening functions hij(r) at intermediate distances [0.5 ≤ r/[(ai+aj)/2] ≤ 1.6] can be expressed to a good degree of accuracy by
Application to the calculation of carbon ignition in the carbon-oxygen core of a highly evolved star is discussed. The carbon ignition temperature is found to be single-valued as a function of the density in contrast to the work of Graboske.
General Relativistic Collapse of an Axially Symmetric Star Leading to the Formation of Neutron Stars and Black Holes
Authors: Nakamura Takashi , Maeda Kei-Ichi , Miyama Shoken , Sasaki Misao 
Published: July 2016

Using the [(2+1)+1]-dimensional representation of the Einstein equations, we have computed the general relativistic collapse of a rotating star. We adopt the cylindrical coordinate. The system is assumed to be axially and plane symmetric. The number of meshes is 28×28 in R and Z direction. The equation of state is P=1/3ρε for ρ< ρ*≡3×1014 g/cm3 and P=(ρ-ρ*)ε+1/3ρ*ε for We use the following initial conditions; ρ∝exp(-(R2+Z2)/λ), Ω∝exp(-R2/λ) where Ω and λ are angular velocity and a size parameter, respectively. We have calculated three models;
(1)Model 1 M=10M⊙, ρc=3×1013g/cm3, α=0.20, β=0.05.(2)Model 2 M=10M⊙, ρc=3×1013g/cm3, α=0.20, β=0.12.(3)Model 3 M=10M⊙, ρc=3×1013g/cm3, α=0.20, β=0.22.
where α=Eint/|Egrav| and β=Erot/|Egrav|. In all models, an apparent horizon was formed, that is, a black hole was formed. In Model 1, the final density distribution is oblate shape. In Model 2, there is a ringlike peak of the proper mass density distribution at the final stage. In Model 3, the determinant of the metric tensor goes to nearly zero at the ring in the equatorial plane, so that the proper mass density shows strong ringlike peak which is inside the apparent horizon. As the curvature invariant made from the Riemann tensor becomes very large at this ring, this may be a ring singularity of the space-time. These rotating black holes look like the Kerr black hole.
INFRARED STUDIES OF THE STELLAR CONTENT IN EXTRAGALACTIC SYSTEMS
Authors: Aaronson Marc 
Published: July 2016

Normal galaxies emit most of their radiation longward of one micron, and many problems related to our understanding of galaxy formation and evolution can be fruitfully addressed with measurements at near-infrared wavelengths. Such problems include the make-up of the red stellar population, the star formation rate, the initial mass function, metallicity effects, and mass-to-light ratio. How these various quantities depend on morphological type, on total mass (or absolute magnitude), on radial position, and on environment is also of great interest. In this review recent infrared observations of extragalactic stars, star clusters, and galaxies having important bearing on these questions are discussed. Particular emphasis is placed on new evidence for the presence of a finite intermediate age population in early-type systems. This evidence comes from observations of intermediate age stars in many Magellanic Cloud globular clusters, observations of such stars in at least one nearby dwarf spheroidal (Fornax), the difficulties of fitting theoretical isochrone models to the red V-K colors of E and SO galaxies, and the differences in the infrared color-magnitude relations for the Virgo and Coma clusters.“It is not very bright to measure a blue magnitude for a red object.”– Vera Rubin
The Unification of Radio-Loud AGN
Authors: Urry C. M. , Padovani Paolo 
Published: July 2016

In a recent review paper we summarized the current status of unification of radio-loud AGN (Urry & Padovani 1995 PASP 107, 803), connecting high-luminosity (FR II) radio galaxies with quasars, and low-luminosity (FR I) radio galaxies with BL Lac objects. Unified schemes are motivated by the knowledge that AGN appearance depends strongly on orientation (Fig. 1): optical/UV light from the centers of many AGN is obscured by circumnuclear matter, and in radio-loud AGN, bipolar relativistic jets beam light along the jet axes. Understanding these radiation anisotropics allows us to unify apparently distinct classes of AGN that differ primarily because of orientation.Our review described the classification and general properties of AGN and summarized the evidence for anisotropic emission caused by circumnuclear obscuration and relativistic beaming. We outlined the evidence, both observed isotropic properties and statistical arguments, for connecting FR IIs with quasars and FR Is with BL Lacs. The population statistics (with beaming) are in accordance with available data and suggest γ ≃ 5 for low-luminosity AGN and γ ≃ 10 for high-luminosity AGN. The distinctions between X-ray-selected and radio-selected BL Lac objects, and between BL Lacs and flat-spectrum variable quasars, still not understood, provide clues to the underlying physics of blazars. Our review discussed several possible problems and complications, and concluded with a list of the ten questions we believe are the most pressing in this field.
The Distant DRAGNs Survey
Authors: Law-Green J. D. B. 
Published: July 2016

DRAGNs (Double Radio sources Associated with Galactic Nuclei, Leahy 1991) are the class of powerful extragalactic radio sources thought to be produced by the interaction of a jet with the ambient medium. They exhibit strong cosmological evolution in comoving number density; at z ≃ 2 the “classical double” FR II DRAGNs were ≃ 1000 times as common as they are now (Dunlop & Peacock 1990).To understand this, systematic studies of complete DRAGN samples at low and high z and differing levels of flux density are required, in order to resolve the P – z ambiguity. The Distant DRAGNs Survey is a long-term project to image with the VLA and MERLIN, matched samples of DRAGNs at high redshift.
Redshift Distribution & Nature of μ-Jy Radio Sources
Authors: Hammer F. , Crampton D. , Lilly S. , LE Fèvre O. 
Published: July 2016

During the preliminary deep imaging phase of our large spectroscopic survey of faint field galaxies (CFRS), one of our fields (10 arcmin × 10 arcmin) was chosen to coincide with the Fomalont et al (1991, A.J. 102,1258, hereafter FWKK) radio source field, including 36 S≃ 16μJy radio sources of their complete sample. All sources but two have been identified to V < 25 and/or IAB ≤ 24, and/or KAB ≤ 21.The microJy population is mainly constituted of three distinct populations of galaxies with different redshift regimes: early-type galaxies at z > 0.75 with a low powered AGN in their cores, post-starburst galaxies at intermediate redshifts (z = 0.375 to z = 0.8 or slightly > 1), and emission-line galaxies at z < 0.45 containing AGNs. The fraction of μJy sources with z > 1 could be as high as 30%. Most of the μJy radio sources (> 50%) are likely associated to AGNs, conversely to what is found at mJy levels (mostly starburst galaxies, Benn et al, 1993, MNRAS, 263, 98). Only one galaxy in our sample has a classical starburst spectrum.The strong decrease of the radio spectral index from sub-mJy to μJy counts appears to be due to a combination of three factors: (1) the emergence of an elliptical population at high redshifts with moderate radio emission (2) an increasing fraction of narrow emission-line AGNs (Seyfert 2 and LINER); (3) a higher contribution of the thermal radiation to the radio emission from spirals, and the almost complete disappearance of starburst galaxies. Details of the results summarized here can be found in Hammer et al (1995, MNRAS, 276, 1085).
Interferometric imaging of stellar surfaces
Authors: Mozurkewich D. 
Published: July 2016

Until recently, all study of stellar surface structure, except for the sun, has been limited to indirect methods. This state of affairs is rapidly changing. With the introduction of interferometric techniques to optical astronomy, direct imaging of stellar surfaces is finally possible. Within a few years we will have images with sub-milliarcsecond resolution and 10 or more resolution elements across the stellar surface.In this talk, I will describe the technique of optical interferometry and explain how it can be made to work through the earth's turbulent atmosphere. I will show some actual data and describe what can be expected in the near future.
Particle transport and surface abundance inhomogeneities
Authors: Michaud G. 
Published: July 2016

The various mechanisms leading to the appearance of horizontal inhomogeneities at the surface of ApBp stars are critically reviewed. The effect of magnetic fields is essential but is it more to control locally, on the surface, the appearance of anomalies that are caused by the vertical transport of particles, or is it to create directly the horizontal inhomogeneities by horizontal transport? The time scales for horizontal and vertical transport will be discussed in this context.The processes discussed include: a) ambipolar diffusion of protons and hydrogen in the presence of magnetic fields; b) the guiding of diffusion by magnetic fields; c) the horizontal component of radiative accelerations; d) mass loss; e) light induced drift.
Contribution of Soviet-Bolivian Astronomical Observatory in the Construction of the Inertial Coordinate System
Authors: Polozhentsev D. D. , Potter H. I. , Yagudin L. I. , Zelaya J. A. , Zalles R. F. 
Published: July 2016

The work on photographic astrometry in Bolivia begun in 1983, when an expeditional astrograph was put there (D=23 cm, F=230 cm, working field of 4°x4°). The main purpose of the observations with this telescope is extending the inertial coordinate system to different classes of stars. For this purpose we have carried out and are currently carrying out the following observational astrometric programs:1. The preliminary catalog of precise positions of 200 000 southern stars to mag 11 with declination in the range from 0° to −90° was created. Each star was observed four times with displacement of the photoplate by 2° in δ and by 8 secδ in α. The exposure time is from 4 to 12 minutes. The accuracy of the preliminary catalog is ±0.247 arcsec and the final one is ±0.15 arcsec.2. We are not far from finishing the work on a catalog of 1900 bright stars (−90° < δ; 0°, m ≥ 6.05). Each star was observed not less than 2 times for different positions of a special filter which diminished the light of bright stars.3. The work on astrometry of equatorial stars to mag 12 in the range of declination from −20° to +20° was begun. From the beginning of the observations on 1 May 1987, 1150 astroplates were obtained. On the whole it is necessary to obtain 3840 photoplates. All three programs use the reference catalog SRS, compiled by Pulkovo and Washington astronomers, in the FK5 system.
Occultation of Radio Sources for the Linkage of Radio and Stellar Reference Frames
Authors: Sôma Mitsuru , Miyamoto Masanori , Aoki Shinko 
Published: July 2016

The right ascension of the radio source 3C273B, which serves as a right ascension zero point in radio astrometric work, has been determined from lunar occultations and photographic observations.We re-analyze here the lunar occultations of 3C273B using the recent precise lunar ephemeris and obtain its right ascension referred to the FK5 equinox at J2000.0. The obtained right ascension is 12h29m06s.6946±0s.007 at its mean observation epoch of 1963.62.Predictions of occultations of radio sources by the Moon and planets are also given. Observations of them are encouraged in order to improve the accuracy of the linkage between radio and stellar reference frames.