bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulations of Advective Flows Around Black Holes
Authors: Chakrabarti Sandip K. , Ryu D. , Molteni D. , Sponholz H. , Lanzafame G. , Eggum G. 
Published: July 2016

Observational results of compact objects are best understood using advective accretion flows (Chakrabarti, 1996, 1997). We present here the results of numerical simulations of all possible types of such flows.Two parameter (specific energy ε and specific angular momentum λ) space of solutions of inviscid advective flow is classified into ‘SA’ (shocks in accretion), ‘NSA’ (no shock in accretion), ‘I’ (inner sonic point only), ‘O’ (outer sonic point only) etc. (Fig. 1 of Chakrabarti, 1997 and references therein). Fig. 1a shows examples of solutions (Molteni, Ryu & Chakrabarti, 1996; Eggum, in preparation) from ‘SA’, ‘I’ and ‘O’ regions where we superpose analytical (solid) and numerical simulations (short dashed curve is with SPH code and medium dashed curve is with TVD code; very long dashed curve is with explicit/implicit code). The agreement is excellent. In presence of cooling effects, shocks from ‘SA’ oscillate (Fig. 1b) when the cooling timescale roughly agrees with postshock infall time scale (Molteni, Sponholz & Chakrabarti, 1996). The solid, long dashed and short dashed curves are drawn for T1/2 (bremsstrahlung), T0.4 and T0.75 cooling laws respectively. In the absence of steady shock solutions, shocks for parameters from ‘NSA’ oscillate (Fig. 2) even in the absence of viscosity (Ryu et al. 1997). The oscillation frequency and amplitude roughly agree with those of quasi-periodic oscillation of black hole candidates. When the flow starts from a cool Keplerian disk, it simply becomes sub-Keplerian before it enters through the horizon. Fig. 3a shows this behaviour where the ratio of λ/λKeplerian is plotted. When the flow deviates from a hot Keplerian disk, it may develop a standing shock as well (Fig. 3b) (Molteni et al. 1996).
Magnetic Flux Transport in Protostellar Accretion Disks
Authors: Contopoulos John , Königl Arieh 
Published: July 2016

AbstractCentrifugally driven winds from the surfaces of magnetized accretion disks are a leading candidate for the origin of bipolar outflows and have also been recognized as an attractive mechanism for removing the angular momentum of the accreted matter. The origin of the open magnetic field lines that thread the disk in this scenario is, however, still uncertain. One possibility is that the field lines are transported through the disk, but previous studies have shown that this process is inefficient in disks with turbulent viscosity and diffusivity. Here we examine whether the efficiency can be increased if angular momentum is transported from the disk surfaces by large-scale magnetic fields instead of radially by viscous stresses. In this picture, the removal of angular momentum is associated with the establishment of a global poloidal electric current driven by the radial EMF in the disc, and it does not necessarily need to involve super-Alfvénic outflows. We address this problem in the context of protostellar systems and present representative solutions of the time evolution of a resistive disk that is initially threaded by a uniform vertical field anchored at a large distance from its surfaces. We assume that the angular momentum transport in the disk is controlled by the large-scale magnetic field and take into account the influence of the field on the disk structure.
Time-Resolved Optical Spectroscopy of V795 Herculis
Authors: Dickinson Rachel J. , Prinja Raman K. , Rosen Simon R. , King Andrew R. , Hellier Coel , Horne Keith 
Published: July 2016

AbstractHigh resolution optical spectroscopy of V795 Herculis shows complex time- and phase-dependent behaviour of the disk emission. Separate low- and high-velocity fluctuations phased on the 2.6 hr orbital period are observed in the wings of the Balmer lines, prompting a gas stream overflow model.
SPH Simulations of Protoplanetary Perturbers in Gas Disks
Authors: Maddison Sarah , Barge Pierre 
Published: July 2016

AbstractWe use Smoothed Particle Hydrodynamics (SPH) to numerically investigate gap clearing around a protoplanetary body in a selfgravitating gaseous disk. It has been suggested that proto-Jupiter regulated it’s own growth by clearing a gap around itself and thus halting accretion.
The Effect of the Nova Explosion on the Evolution of Cataclysmic Variables
Authors: Naylor T. , Somers M.W. 
Published: July 2016

Classical nova outbursts are thermonuclear explosions on the surfaces of the white dwarfs in cataclysmic variables. The explosion heats the surface layers of the white dwarf, which are expected to cool on a timescale of a hundred years. The hot white dwarf should have two obvious effects on the system.(1)It will heat the surface of the accretion disc and secondary star, increasing the overall luminosity of the system.(2)By irradiating the surface of the secondary star it may bloat it and drive more mass transfer, thus again increasing the overall luminosity.
Thirty Years of VLBI: Early Days, Successes, and Future
Authors: Moran J.M. 
Published: July 2016

AbstractThe early days of VLBI are discussed, with emphasis on the fifteen experiments performed in the U.S. and Canada in 1967. Some key technical ideas are described that influenced the development of the technique, including digital fringe rotation, bandwidth synthesis, spectral phase referencing, phase closure and self-calibration, and water vapor radiometry.
Model of a Precessing Jet in 3C 279
Authors: Abraham Z. , Carrara E.A. , Zensus J.A. 
Published: July 2016

AbstractThe parsec scale radio jet of 3C 279 presents a number of superluminal features that move along straight trajectories with constant velocities. The position angles P.A. of these trajectories, projected in the plane of the sky, and the velocities βobs of the individual components are different. We interpret the differences in the these velocities as differences in the angle between the jet and the line of sight and apply the model of a precessing beam to the data. All the geometrical parameters of the precessing jet and the Lorentz factor γ of the relativistic particles are determined. The model predicts the behavior of the Doppler factor δ as a function of time and we verify that its maximum value occurred at the epochs in which strong optical and X-ray flares were observed.
VLBI of Southern EGRET Identifications
Authors: Murphy D.W. , Tingay S.J. , Preston R.A. , Meier D.L. , Jones D.L. , Edwards P.G. , Costa M.E. , Lovell J.E.J. , McCulloch P.M. , Jauncey D.L. , Reynolds J.E. , Tzioumis A.K. , King E.A. , Nicolson G.D. , Quick J.F.H. , Wan T.-S. , Shen Z.-Q. 
Published: July 2016

AbstractWe have undertaken VLBI observations of 8 Southern Hemisphere EGRET radio sources. Using our data as well as data obtained from the literature we have examined the difference in radio properties between gamma-ray loud and gamma-ray quiet radio sources. In particular, we find no evidence that gamma-ray loud radio sources lie preferentially in sources with straight radio jets as has been suggested.
Magnetic Fields in AGN
Authors: Wardle J. F. C. 
Published: July 2016

AbstractWe review VLBI polarization results. In particular, we discuss the a) “shock in jet paradigm”, b) the orientation of the magnetic field in jets as a function of optical identification, c) rotation measure and Faraday dispersion measurements as a probe of the narrow line region, and d) future directions of polarization observations. Results we emphasize are i) there is still a strong correlation between optical L/C ratio or EW and magnetic field orientation in the jets of blazars, even for high redshift weak-lined objects, ii) observed rotation measures are much smaller than expected from the properties of the NLR, except for some CSS sources. Also iii) a faint boundary layer or sheath (with a parallel magnetic field) has been observed around the jet of the weak-lined blazar 1055+018, and iv) circular polarization has been detected for the first time in the jets of 3C 84 and 3C 279.
A VSOP Survey Program Pre-launch Continuum Survey
Authors: Edwards P. G. , Fomalont E. B. 
Published: July 2016

AbstractThe VSOP Survey Program will observe a complete survey of flat-spectrum sources at 5 GHz. In order to determine which of the sample sources are strong and small enough to be detected with VSOP, a pre-launch survey of 377 continuum sources north of δ > −43° was conducted at 5 GHz with the VLBA over 24 hours in June 1996. About 250 of the sources had correlated flux densities ≥ 0.4 Jy between MK–SC and have been included in the VSOP survey sample.
Comparison of Total Flux and VLBI Properties of a Sample of 15 AGN at 22 GHz
Authors: Wiik K. , Valtaoja E. 
Published: July 2016

AbstractA sample of 15 bright AGN has been observed at 22 GHz with two epoch global VLBI observations. The sample consists of all sources in the complete 2 Jy catalogue of Valtaoja et al. (1992) previously unobserved at 22 GHz VLBI. We have begun to investigate how much structural information can be derived just from total flux density (TFD) monitoring and how to use total flux density observations to complement space VLBI observations. As an example we present Doppler boosting factors derived in four different methods.
Structure and Variability of Sources from Geodetic VLBI-Data
Authors: Pyatunina T. B. 
Published: July 2016

Abstract8 GHz maps of 39 radiosources have been obtained with ≈ 0.5 mas resolution from geodetic VLBI-data. Structure variability has been investigated on ≈ monthly interval during the bursts of radio emission of two sources 0059+581 and 0202+149 in period from June 1994 to February 1996. Bright jet components in the sources show no steady outward motion, but may be some oscillations near stationary positions.
A Multi-Frequency VLBI Total Intensity and Polarization Study of the BL Lacertae Object 0716+714
Authors: Kovalev Y. Y. , Gabuzda D. C. , Krichbaum T. P. , Alef W. , Witzel A. 
Published: July 2016

AbstractNew polarization-sensitive global VLBI and VLBA images of the BL Lacertae object 0716+714 at 6 cm (1991.4) and 3.6 cm/1.3 cm (1994.2) are presented. The source shows a compact, one-sided core–jet structure in structural position angle ~ 13°. The 3.6 cm total intensity image shows the jet beginning to curve toward the arcsecond-scale structure, which lies in position angle ~ −45°. Comparison with previously published data suggests that the apparent velocity of a 6 cm jet component is > 1.09 ± 0.15c, if the red shift of 0716+714 is z > 0.3. Linear polarization from the VLBI core was detected at all three frequencies; in addition, polarization from the innermost jet component was detected at 1.3 cm. This compact jet polarization appears to be quite high, ~ 50%, and to be aligned with the jet direction, which can be understood if it is a transverse shock. The VLBI core polarization at our earlier epoch was perpendicular to the VLBI jet direction, but had rotated to align with the jet direction by the later epoch, about a year later. This rotation may indicate the imminent birth of a new VLBI component (shock).
The Ultimate Fate of CSOs
Authors: De Young D. S. 
Published: July 2016

AbstractRecently Readhead et al. (1996b) have presented empirical evidence that CSOs evolve into larger double sources many kpc in extent. The implications of this are explored analytically and numerically. It is found that pure luminosity evolution on the small scales of CSOs is unlikely in the presence of any ambient density gradients. However, the transition from CSO to MSO may involve a nearly constant lobe advance speed as suggested by Readhead et al.. This seemingly unphysical result can be seen to result from the interaction of the propagating jet with its surrounding medium.
Short-Term Variability of Sagittarius A* at Millimeter Wavelengths
Authors: Tsutsumi T. , Kawabata T. , Miyazaki A. , Tsuboi M. 
Published: July 2016

AbstractWe present preliminary results from the observations of the Galactic Center compact source, Sgr A* at 3 and 2 millimeter wavelengths using the Nobeyama Millimeter Array to monitor flux density variations on timescales shorter than a month. Such high spatial resolution observations at millimeter wavelengths are important to shed more light on the origin of the variability and the nature of this compact source. Our observations indicate the flux density varies at least by ~30% in one to two weeks at 3 mm.
Water Maser Emission and the Parsec–Scale Jet in NGC 3079
Authors: Trotter A. S. , Moran J. M. , Greenhill L. J. 
Published: July 2016

AbstractWe have imaged the H2O maser and 22, 8, & 5 GHz continuum in the nucleus of NGC 3079, using the NRAO VLBA. The maser features are distributed over ~ 2 pc along an axis aligned with the plane of the kpc–scale edge–on molecular disk. The masers are not angularly coincident with any detected continuum emission. The two brightest continuum features, which trace a parsec–scale jet, have similar spectra that peak at frequencies ν > 5 GHz. We also detected faint maser emission along the jet axis.
Multi-Epoch VLBA Observations of the SiO Maser Emission Towards R Aquarii (R Aqr)
Authors: Boboltz D. A. , Diamond P. J. , Kemball A. J. 
Published: July 2016

AbstractWe have observed ν = 1, J = 1 – 0, 43-GHz SiO maser emission towards the symbiotic Mira variable R Aqr at four different epochs in the stellar pulsation cycle using the VLBA.
An Update on Radio Supernovae
Authors: Van Dyk Schuyler D. , Sramek Richard A. , Weiler Kurt W. , Montes Marcos J. , Panagia Nino 
Published: July 2016

AbstractThe radio emission from supernovae (SNe) is nonthermal synchrotron radiation of high brightness temperature, with a “turn-on” delay at longer wavelengths, power-law decline after maximum with index β, and spectral index α asymptotically decreasing with time to a final, optically thin value. Radio supernovae (RSNe) are best described by the Chevalier (1982) “mini-shell” model, with modifications by Weiler et al. (1990). RSNe observations provide a valuable probe of the SN circumstellar environment and constraints on progenitor masses. We present a progress report on a number of recent RSNe, as well as on new behavior from RSNe 1979C and 1980K, and on RSNe as potential distance indicators. In particular, we present updated radio light curves for SN 1993J in M81.
Galilean Satellites and the Galileo Space Mission
Authors: Lieske J.H. 
Published: July 2016

AbstractThe Galileo spacecraft arrived at Jupiter in December 1995 to start its two-year mission of exploring the Jovian system. The spacecraft will complete eleven orbits around Jupiter and have ten more close encounters with the outer three Galilean satellites, after the initial close approach to Io on December 7, 1995. Since the Io encounter occurred closer to Io than originally designed, the spacecraft energy change was greater than nominally planned and resulted in an initial spacecraft orbital period about 7 days less than that designed in the nominal tour. A 100-km change in the Io-encounter distance results in an 8-day change in initial period of the spacecraft. Hence the first Ganymede encounter was moved forward one week, and the aim points for the first two Ganymede encounters were altered, but all other encounters would occur on their nominal dates and at the nominal altitudes. This was accomplished without expending spacecraft fuel and resulted in the first Ganymede flyby occurring on June 27, 1996 rather than the nominally scheduled July 4.Earth- and spacecraft-based data were employed in developing ephemerides in support of the Galileo space mission. An analysis of CCD astrometric observations from 1992–1994, of photographic observations from 1967–1993, of mutual event astrometric data from 1973–1991, of Jovian eclipse timing data from 1652–1983, of Doppler data from 1987–1991, and of optical navigation data from the Voyager spacecraft encounter in 1979, produced the satellite ephemerides for the Galileo space mission.
Space Debris – The Short Term Orbital Evolution in the Earth Gravity Field
Authors: Wnuk Edwin 
Published: July 2016

AbstractTwo aspects of the orbital evolution of space debris – the long-term evolution and the short-term one – are of interest for an exploration of the near- Earth space. The paper presents some results concerning the estimation of the accuracy of predicted positions of Earth-orbiting objects for the short-term: a few revolutions or a time-span interval of a few days. Calculations of predicted positions take into account the influence of an arbitrary number of spherical coefficients of the Earth gravity potential. Differences in predicted positions due to differences in the best contemporary geopotential models (JGM-2, JGM-3 and GRIM4-S4) are estimated with the use of an analytical theory of motion and a numerical integration.
Using Close Encounters of Minor Planets for the Improvement of their Masses
Authors: García A. López , Medvedev Yu. D. , Fernández J. A. Moraño 
Published: July 2016

AbstractThe orbits of 6807 numbered minor planets on the time interval 1975–2010 have been integrated. The possibility of determining masses for asteroids with close encounters with each other has been investigated, including several kinds of situations. The importance of the observational time arc, as well as the distribution of observations, for determining the masses are shown. The mass of asteroid (24) Themis from its perturbations on asteroid (2296) Kugultinov, and the mass of (10) Hygiea from its perturbations on (1259) Ógyalla have been determined.
Precession and Nutations of Mars calculated with Kinoshita’s Model
Authors: Bouquillon S. , Souchay J. 
Published: July 2016

AbstractThis paper presents the theoretical study of precession and nutation of Mars in a rigourous way. For this work we choose a natural reference system, based on the concept of non-rotating origin, and the appropriate canonical variables. Then, we solve the equations of the problem by taking into account the effects of the Sun, the Earth, Jupiter, and satellites of Mars, Phobos and Deimos.
Analytical Effects of Gravitational Waves on the Motion of an Artificial Satellite
Authors: Youssef M.H. , Ahmed M.K. 
Published: July 2016

AbstractThe motion of an artificial satellite in the Earth’s gravitational field is discussed in the post-Newtonian framework including the effect of weak gravitation waves using the perturbation technique of the canonical Lie-transformations. Two successive canonical transformations are used to derive analytical expressions for the short-period, long-period and secular perturbations of orbital elements. The solution is expressed in terms of the Delaunay variables.
Monitoring Earth Orientation Using Various Techniques: Current Results and Future Prospects
Authors: Gambis D. 
Published: July 2016

AbstractUntil 1972, astrometry based on a network of optical instruments was the only technique able to monitor the Earth orientation (polar motion, Universal Time and nutation). Since various techniques have shown their capability to give all or a part of these parameters: Doppler observations of navigation satellites, laser ranging to the Moon and to dedicated artificial satellites, Very Long Baseline Interferometry (VLBI) and more recently GPS and DORIS. The different Earth Orientation Parameters (EOP) series obtained by the individual techniques are inhomogeneous in time span, quality, time resolution – which supports the concept of combined solutions taking advantage of the various contributions.The main task of IERS is the maintenance of both a conventional terrestrial reference system based on observing stations and a conventional celestial reference system based on extragalactic radio sources and also the matrix product allowing the transformation between these two systems which takes into account precession-nutation, polar motion and Earth rotation.The objective of this paper is to present the evolution, the state of the art and future prospectives concerning the multi-technique EOP combined solution made at IERS/CB.
Solar-Radius Variations Over a Solar Cycle Observed with the Tokyo Photoelectric Meridian Circle
Authors: Yoshizawa M. 
Published: July 2016

AbstractAs the Sun shows the well-known magnetic activity of eleven-year period, many other interesting observational features of the Sun have been examined in connection with the solar cycle. The diameter of the Sun is one of these interesting observable quantities. The apparent radius of the Sun has been observed regularly since 1985 with the Tokyo Photoelectric Meridian Circle (Tokyo PMC) at Mitaka. Here, we show the average value of the solar radii observed by us. We also show that the annual-mean values of the observed radii take the smallest value near the solar-cycle maximum, in 1989 and 1990, and the largest ones around the solar-cycle minimum, in 1986 and 1994. The average peak-to-peak shift of the annual-mean solar radius for the solar cycle is ΔR⊙/R⊙ ~ 1.2 × 10−4, which is close to the relative change of the frequency of the 5-minute p-mode solar oscillation within one solar cycle.
The History of Solar Prominence Research: Historical Introduction to IAU Colloquium No. 167 “New Perspectives on Solar Prominences”
Authors: Tandberg-Hanssen Einar 
Published: July 2016

AbstractWe trace the history of observational solar prominence research from the early period when total solar eclipses provided the only means of observation, via the introduction of photography and spectroscopy in the 1860’s, to the present epoch when application of the Zeeman and the Hanle effects makes possible determination of the all-important magnetic fields in prominences.Dividing prominence models into two classes, those that treat the support of the prominence against gravity and those concerned with the physical conditions in the prominence plasma itself, we describe the progress made in both classes of models since the 1950’s, when the first models were proposed. Finally, we comment on the necessity of combining aspects of the two classes of prominence models into a comprehensive picture that can account for the global nature of prominence support and stability, and where the adjacent coronal structures play an important role.
Concerning Magnetic Field Measurements in Prominences Using Zeeman and Hanle Methods
Authors: Bashkirtsev V.S. , Mashnich G.P. 
Published: July 2016

AbstractA critical review is made of the results of magnetic field measurements in prominences obtained by the Zeeman and Hanle methods. By considering the example of three prominences, some discrepancies between the methods are shown. The authors consider that the magnetic field measurements by the Hanle method inadequately represent the actual magnetic field pattern. To overcome these discrepancies a comparative analysis of magnetic field measurements in prominences by both methods is required.
Vector Magnetic Fields at the Base of Filaments and the Filament Environment
Authors: Wang Jingxiu , Li Wei 
Published: July 2016

AbstractBased on an analysis of three active filaments in AR 6891, we find that vector magnetic fields at the base of filaments and the filament environment is characterized by the following: (1) The transverse field is parallel along the magnetic neutral line for most of the filaments. The average transverse field beneath the filaments is more than 400 G. (2) The horizontal gradient of the line-of-sight field crossing the neutral line is, more or less, constant along the major fraction of a filament, but very steep at the two ends. The average gradient is 0.06 G/km. (3) For each of the filaments there is a squeezing magnetic structure which represents an intrusion of a satellite bipole into the main flux system. The neutral line for a squeezing magnetic structure has a large curvature, a strong sheared transverse field of more than 1 KG, and a steep field gradient of approximate 0.3 G/km. (4) The transverse field and field gradient are clearly enhanced before the filament eruption.