bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiation driven winds from CV accretion disks
Authors: Proga Daniel , Drew Janet E. , Stone James M. 
Published: July 2016

AbstractWe present some initial results of our numerical, 2D hydrodynamical models of line driven flows from the accretion disk in cataclysmic variables. We assume the disk radiation pressure pushes out the isothermal material from a flat, geometrically thin, Keplerian disk.We calculate the disk radiation field using the surface brightness of a standard “α disk” (Shakura & Sunyaev 1973). We do not include a bright boundary layer in the calculations. We approximate the total radiative line acceleration, adopting the formalism due to Castor, Abbott, & Klein (1975). We use our generalized 2D version of their force multiplier. The multiplier is still described by two parameters representing the number of lines and the ratio of optically thin to optically thick lines. The main modification of the original CAK force multiplier is in the depth parameter, which is now a function of the gradients of two velocity components instead of the single velocity gradient as in the ID case.We investigate how the disk structure and mass loss rate depend on the disk and central star luminosity, and boundary conditions such as the disk density.We find that transonic flows from disks do not relax toward steady states. However, their time averaged properties become constant after some time. Our models show that most of mass loss originates from close to the central star – a few stellar radii. Models without a central star radiation field produce flows more vertical than models in which one is present. However, other global, time averaged properties of flows such as the total wind mass, the wind mass loss rate, and velocity are similar. The ratio between the wind mass loss and disk accretion rate increases rapidly with the accrection rate.
Uncovering Flickering in Time-Resolved Spectroscopy for the Nova-like Variable UX Ursa Majoris
Authors: White James C. 
Published: July 2016

AbstractThe flickering phenomenon in cataclysmic variables (CVs) is manifest photometrically as variations in system brightness with amplitudes up to about 1 mag and on timescales from seconds to tens of minutes. Although a pronounced characteristic of CVs, flickering has been studied, in general, only tangentially and in the context of overall CV photometric properties. It is usually uncovered in CV photometry, yet my Doppler tomographic analysis of data collected on the KPNO 2.1-meter telescope in 1982 by Schlegel, Honeycutt, and Kaitchuck (1983) for the nova-like variable UX Ursa Majoris suggests that flickering also exists in this system’s spectroscopy.Using the integrated continuum flux from the UX UMa observations and Bruch’s (1992) methodology for classifying high- and low-flicker data, I constructed two data subsets corresponding to high- and low-flicker states. I generated Doppler tomograms of these high- and low-flicker states and interpret differences between the tomograms as spectroscopic signatures of flickering in the system.In UX UMa’s Hβ Doppler tomograms, a small, faint, incomplete ring of emission is visible for both flickering states. Dominating ring emission is strong emission in the (+Vx,+Vy) quadrant. The usual location for Swave emission, in the (−Vx,+Vy) quadrant, is here the region of faintest emission. Differenced Doppler tomograms, produced by subtracting from the tomograms the symmetric ring-emission component, show clear differences between the high- and low-flicker states. Further, these early results suggest Doppler tomography may be a useful technique for studying the secondary stars in CVs imaged in this manner. Enhanced chromospheric activity of the red dwarf companion is clearly visible in the high-flickering state tomogram at (0, Krd) and may, therefore, afford investigators the opportunity to estimate the chromospheric flux and radial velocity of the secondary star.
Millimeter VLBI Observations of the Gamma-Ray Blazar NRAO 530
Authors: Bower Geoffrey C. 
Published: July 2016

AbstractWe present here 3 epochs of 3 and 7 millimeter wavelength VLBI observations and 2 epochs of lower frequency VLBA imaging of the gamma-ray blazar NRAO 530. These observations document the evolution of the parsec scale jet in this source during the brightest flare in 3 decades. New jet components were created during the flare and are probably related to an increase in gamma-ray activity. The components travel at superluminal velocities, further confirming the connection between superluminal sources and gamma-ray blazars. The rapid evolution of the source makes tracking of components difficult. It appears that either components significantly decelerate or that there is rapid cooling and acceleration of elections. We may be identifying structure due to standing shocks. The jet is bent on all scales between 100 μarcsec to 10 arcsec. The results indicate the ability of 3 mm wavelength imaging to probe the nuclei of blazars rapidly and reliably.
EVN+MERLIN Observations of 3C 66B and a Two-Fluid Model for VLBI Jets
Authors: Fraix-Burnet D. , Despringre V. , Baudry A. 
Published: July 2016

AbstractWe present observations of the FRI radiogalaxy 3C 66B made during a joint EVN + MERLIN VLBI session in May 1995. The jet is mapped from the 5 mas scale up to about 3 arcmin. The newly mapped VLBI jet shows essentially two elongated blobs in the direction of the brightest kpc jet (NE). We also present the first results obtained for a two-fluid model for VLBI jets.
The Radio Jet of Quasar 0153+744
Authors: Hummel C.A. 
Published: July 2016

AbstractWe highlight a few aspects of the radio jet of quasar 0153+744. Some challenge the relativistic beaming model to explain a stationary jet of short length and ending in a bright secondary component, extreme bending of the jet, and the lack of any emission on the counter jet side. We discuss a model of a precessing mildly relativistic jet for 0153+744.
A Multi-Frequency VLBI Polarization Study of the CSS Quasar 3C 309.1
Authors: Aaron Scott E. , Wardle John F.C. , Roberts David H. 
Published: July 2016

AbstractWe discuss the rotation measure properties of the CSS quasar 3C 309.1, determined from high dynamic range, large field of view VLBA images at several frequencies between 1.4 and 15 GHz. We consider the general properties of the ambient medium by considering the structure of the Faraday screen across various parts of the radio source.
Statistical Effects of Doppler Beaming and Malmquist Bias on Flux-Limited Samples of Compact Radio Sources
Authors: Lister Matthew L. , Marscher Alan P. 
Published: July 2016

AbstractWe examine the effects of Doppler beaming on flux-limited samples of compact extragalactic radio sources using Monte Carlo simulations. We incorporate a luminosity function and z-distribution for the parent population, and investigate models in which the unbeamed synchrotron luminosity L of a relativistic jet is related to its bulk Lorentz factor Γ. The predicted flux density, redshift, monochromatic luminosity, and apparent velocity distributions of our simulated flux-limited samples are compared to the Caltech-Jodrell Bank (CJF) sample of flat-spectrum, radio core-dominated active galactic nuclei (AGNs).We find that a relation between L and Γ is not needed to reproduce the characteristics of the CJF sample. Introducing a positive correlation between these quantities results in an underabundance of objects with high viewing angles, while a negative correlation gives generally poor fits to the data.
The Effects of Light Travel Time on the Appearance of Relativistic Jets
Authors: Mioduszewski A. J. , Hughes P. A. , Duncan G. C. 
Published: July 2016

AbstractWe present simulated maps showing the appearance in total intensity of flows computed using a relativistic hydrodynamic code (Duncan k. Hughes 1994: ApJ, 436, L119). The radiation transfer calculations allow for full treatment of relativistic effects, such as Doppler boosting and time delay. Depending on viewing angle, and the speed of emitting features, the appearance of a jet can be strongly influenced by either effect; in both cases the map differs dramatically from the morphology exhibited by the hydrodynamic quantities.
The Parsec-Scale Radio Polarization of Three GHz-Peaked–Spectrum Radio Sources
Authors: Stanghellini C. , Dallacasa D. , O’Dea C.P. , Baum S.A. , Fanti C. , Fanti R. 
Published: July 2016

AbstractPreliminary results on the parsec-scale polarization properties at 15 GHz of 3 GHz-peaked-spectrum radio sources are presented.
The Alignment Effect in Compact Steep Spectrum Radio Sources
Authors: de Vries W. H. , O’Dea C. P. , Baum S. A. , Barthel P. D. 
Published: July 2016

AbstractUsing Hubble Space Telescope WFPC2 images of 3CR compact steep spectrum (CSS) radio sources and literature radio maps makes detailed comparison between optical and radio structures possible. All CSS sources for which the optical and radio orientation can reliably be measured, display good alignment between the optical and radio emission. This alignment is observed down to the lowest redshift in the sample, at z ~ 0.1. Optical emission from CSS galaxies is found to be dominated by this aligned component, especially at higher redshifts. Both the alignment and the relative brightness of this component indicate that CSS sources have large amounts of matter co-spatial with the radio structure. In order to assess the nature of the aligned light, we calculated line emission contamination in the passband using ground based spectra. From this we can conclude that at least in some sources (notably 3C 213.1, 3C346, and 3C 380) line emission is not important. The detailed optical–radio correspondence makes optical synchrotron the most likely mechanism for these three sources.
VLBI Astrometry of the Ultra-Compact Nucleus of M81
Authors: Ebbers A. , Bartel N. , Bietenholz M. F. , Rupen M. P. , Beasley A. J. 
Published: July 2016

AbstractM81 has been shown to have a compact flat-spectrum core with a possible steep-spectrum jet. We report on position determinations of the brightness peak of the nucleus relative to the position of the early supernova 1993J with uncertainties as low as 0.08 mas. At early epochs, the supernova was largely pointlike at any frequency and therefore an ideal phase reference. We describe how VLBI astrometry at several frequencies could be used to support a model with a core and a one-sided jet for the nucleus of M81.
The Nuclear Region of a Megamaser in a Southern AGN, NGC 5793: Parsec-Scale Structure and OH Absorption
Authors: Hagiwara Y. , Kawabe R. , Nakai N. , Diamond P.J. 
Published: July 2016

AbstractWe have carried out VLBA observations of the OH absorption lines toward the nucleus of the active galaxy, NGC 5793, which is known to have a megamaser in its center. We have also successfully made its continuum image at the L band. It reveals the typical “core-jet” structure on parsec scales. Uniform values of optical depth at each point against the background radio continuum source shows that the column densities of the OH absorbing cloud uniformly distributes around the radio compact nucleus.
Results from Space-VLBI Pre-Launch Surveys: H2O Masers
Authors: Migenes V. , Horiuchi S. , Inoue M. , Edwards P. , Fomalont E. B. , Slysh V. I. , Val’tts I. E. 
Published: July 2016

AbstractWe report on the first results of our ground-survey of H2O masers to establish a list of suitable candidates for space-VLBI observations. Due to the large VSOP/HALCA baselines and its limited sensitivity only very strong and compact sources will be detected. The best candidates from this survey will be part of The VSOP Survey which intends to observe a large number of continuum and maser sources. This systematic and uniform survey, of a large number of sources, will be invaluable in determining the properties of the sub-milliarcsecond emission from maser sources.
Proper Motions of Water Masers in Circumstellar Shells
Authors: Marvel K. B. , Diamond P. J. , Kemball A. J. 
Published: July 2016

AbstractWe present measurements of proper motions for circumstellar water maser observations obtained with the VLBA. Results of the observations and modeling indicate that the water masers exist in a kinematically complex region of the circumstellar envelope. A change in position of the maser spots as a function of velocity is discussed.
Serendipitous VLBI Observations of Intraday Variability in the BL Lac Objects 1334–127, 2131–021, and 2155–152
Authors: Kochanev P. Yu. , Gabuzda D. C. 
Published: July 2016

AbstractGlobal λ = 6 cm VLBI polarization observations of intraday variability in the three BLLacertae objects 1334–127, 2131–021, and 2155–152 are analyzed. Integrated VLA measurements during the VLBI observations show that although there were no substantial total intensity variations, the polarizations for these three sources varied significantly during the VLBI experiment. The VLBI data were divided into 2-3 hour segments in order to search for corresponding rapid variability in the VLBI polarization structure. Our analysis shows that the VLA polarization variability in 2155–152 and 2131–021 is present in the VLBI data (i.e., it occurred on mas scales), but this is not the case for 1334–127.
Do Jets Exist in All Compact Extragalactic Objects?
Authors: Kovalev Yu. A. , Kovalev Y. Y. 
Published: July 2016

AbstractNew results of instantaneous spectra study confirms an old hypothesis that extragalactic radio sources have a double structure. Instantaneous 1–22 GHz spectra and their long-term variability for VLBI-compact extragalactic objects monitored during 1979–1997 at the RATAN–600 are used. Analysis of these spectra gives that a VLBI-compact continuous jet have to be by a general structure and spectra component of such objects. The observed multi component VLBI-structures are bound to be, as a rule, the brightest regions of such continuos jet. A second component is a relatively extended, optically thin cloud (a lobe or an envelope, connected with the jet), weaker to higher frequencies. Thus, the HF-component of such spectra, measured by VLBI and by a single dish antenna, have to be practically the same. Such jets can exist in about 200 compact objects of our sample and seem to exist in majority or even all extragalactic compact objects.
Mapping Small Scale Structure in Galactic H ɪ with the VLBA
Authors: Faison M. D. , Goss W. M. , Diamond P. J. 
Published: July 2016

AbstractWe present the first VLBA maps of Galactic H ɪ opacity towards the QSO 3C 138. The maps show significant opacity structure down to angular scales of 20 mas, which implies density structures in the cold neutral medium on physical scales of 10 AU or less
PKS 1830–211: VLBA λ7mm Polarization Observations
Authors: Garrett M. A. , Leppänen K. , Porcas R. W. , Patnaik A. R. , Nair S. , Teräsranta Harri 
Published: July 2016

AbstractWe present λ7mm multi-epoch and polarization VLBA maps of the gravitational lens PKS 1830–211. The maps suggest that the radio structure of both images evolves rapidly. The offset between the polarized intensity and the total intensity may be used to constrain the magnification matrix.
Measuring the Properties of the Gravitational Lens PKS 1830–211
Authors: Lovell J. E. J. , McCulloch P. M. , Ellingsen S. P. , Phillips C. J. , Reynolds J. E. , Jauncey D. L. , Sinclair M. W. , Wilson W. E. , Tzioumis A. K. , King E. A. , Gough R. G. , Preston R. A. , Jones D. L. , Backus P. R. 
Published: July 2016

AbstractPKS 1830–211 is the strongest known radio gravitational lens by almost an order of magnitude and has the potential to provide a measurement of H0, provided the lensing system can be parameterized. Attempts to identify optical counterparts, to measure redshifts, have so far proved unsuccessful and this has lead to radio and millimetre spectral line observations. We present our discovery of an absorption system at z = 0.19. A brief description is also made of our ATCA observations to measure the lensing time delay for this source.
Imaging the Absorbing Cloud at z = 0.88582 toward 1830–211
Authors: Carilli C. L. , Menten Karl M. , Reid Mark J. , Rupen M. , Claussen M. 
Published: July 2016

AbstractWe summarize results of a detailed imaging program of the molecular absorbing cloud at z = 0.88582 toward the “Einstein ring” radio source PKS 1830–211.
Apparent Relativistic Motion in Cygnus X-3
Authors: Spencer R. E. 
Published: July 2016

AbstractWeak and strong flaring has been observed at cm-wavelengths on Cygnus X-3. The weak flares seem to have different statistical properties to those of the strong flares. Previous observations have shown the ejection of radio emitting blobs at around 0.3c following major flares. However recent VLBA observations show apparent superluminal expansion and contraction during weak flaring.
Radio Properties of the X-Ray Binary GX 339–4
Authors: Sood R. K. , Campbell-Wilson D. , Durouchoux Ph. , Corbel S. , Fender R. , Spencer R. , Nowak M. A. , Tzioumis A. K. 
Published: July 2016

AbstractGX 339–4 has been monitored over a period of two and a half years with MOST and ATCA to investigate the flux variations and spatial structure of its radio emission. The data are summarized and discussed.
Phase–Referencing Observations of Galactic Circumstellar Masers
Authors: van Langevelde Huib Jan , Sjouwerman Loránt O. , Diamond Philip J. , Schilizzi Richard T. , Baudry Alain 
Published: July 2016

AbstractTwo projects are discussed in which a phase referencing technique is used to determine stellar parallaxes and/or proper motions by means of the circumstellar masers. The observations are special in the sense that both continuum and line sources need to be detected. To obtain stellar motions assumptions on the location of the maser with respect to the star need to be made.
The Radio Reference Frame
Authors: Gaume R. A. , Fey A. L. 
Published: July 2016

AbstractThe Radio Reference Frame, defined by the radio positions of a large number of extragalactic sources, marks a milestone in the production of a global, self-consistent, quasi–inertial celestial reference frame accurate at the milliarcsecond level. A brief review of the current status and future direction of the project is presented.
Progress in VLBI Stellar Astrometry for the NASA/Stanford Relativity Mission (Gravity Probe B)
Authors: Ratner M. I. , Lebach D. E. , Shapiro I. I. , Bartel N. , Bietenholz M. F. , Ransom R. R. , Lestrade J.-F. 
Published: July 2016

AbstractThe NASA/Stanford Relativity Mission (Gravity Probe B) is to test the unverified “frame-dragging” prediction of general relativity through measurements of the precessions of orbiting gyroscopes. For mission accuracy goals to be met, the proper motion of a “guide star,” whose position will be used as an inertial reference, must be determined in an extragalactic reference frame with a standard error less than 0.5 mas/yr. We discuss our VLBI observations of the current guide-star candidates (radio stars HR 1099, HR 5110, and HR 8703) and our techniques for obtaining differential astrometric positions with the needed accuracy.
VLBA Observations of Radio Reference Frame Sources. II. Astrometric Suitability Based on Observed Structure
Authors: Fey A. L. , Charlot P. 
Published: July 2016

AbstractWe use source models derived from VLBA observations of 169 extragalactic sources to quantify the expected effects of intrinsic source structure on astrometric bandwidth synthesis VLBI observations. We define a source “structure index” based on the median structure corrections and suggest that this index can be used as an estimate of the astrometric quality of the sources. A correlation between the compactness of the sources and their formal position uncertainties was found indicating that the more extended sources have larger formal position uncertainties.
The Future of Artificial Satellite Theories: Hybrid Ephemeris Compression Model
Authors: Hoots Felix R. , France Richard G. 
Published: July 2016

AbstractSince the time of Newton, astrodynamics has focused on the analytical solution of orbital problems. This was driven by the desire to obtain a theoretical understanding of the motion and the practical desire to be able to produce a computational result. Only with the advent of the computer did numerical integration become a practical consideration for solving dynamical problems. Although computer technology is not yet to the point of being able to provide numerical integration support for all satellite orbits, we are in a transition period which is being driven by the unprecedented increase in computational power. This transition will affect the future of analytical, semi-analytical and numerical artificial satellite theories in a dramatic way. In fact, the role for semi-analytical theories may disappear. During the time of transition, a central site may have the capacity to maintain the orbits using numerical integration, but the user may not have such a capacity or may need results in a more timely manner. One way to provide for this transition need is through the use of some type of satellite ephemeris compression. Through the combined use of a power series and a Fourier series, good quality ephemeris compression has been achieved for 7 day periods. The ephemeris compression requires less than 40 terms and is valid for all eccentricities and inclinations.
Rosetta Radio Science Investigations: Gravity Investigations at Comet P/Wirtanen
Authors: Pätzold M. , Neubauer F.M. , Wennmacher A. , Aksnes K. , Anderson J.D. , Asmar S.W. , Tinto M. , Tsurutani B.T. , Yeomans D.K. , Barriot J.-P. , Bird M.K. , Boehnhardt H. , Gill E. , Montenbruck O. , Grün E. , Häusler B. , Ip W.H. , Thomas N. , Marouf E. A. , Rickman H. , Wallis M.K. , Wickramasinghe N.C. 
Published: July 2016

AbstractThe Rosetta Radio Science Investigations (RSI) experiment was selected by the European Space Agency to be included in the International Rosetta Mission to comet P/Wirtanen (launch in 2003, arrival and operational phase at the comet 2011–2013). The RSI science objectives address fundamental aspects of cometary physics such as the mass and bulk density of the nucleus, the gravity field, non-gravitational forces, the size and shape, the internal structure, the composition and roughness of the nucleus surface, the abundance of large dust grains and the plasma content in the coma and the combined dust and gas mass flux on the orbiter. RSI will make use of the radio subsystem of the Rosetta spacecraft.
The Capture of Halley-Type and Jupiter-Family Comets From the Near-Parabolic Flux
Authors: Emel’yanenko V.V. , Bailey M. E. 
Published: July 2016

AbstractWe have considered the transfer of comets from the near-parabolic flux to short-period orbits under the perturbations of Jupiter, Saturn, Uranus, and Neptune for 5 Gyr. We have developed a combined analytical and numerical scheme which includes all essential features of the dynamical evolution. Secular resonances are amongst the most important factors causing large changes in perihelion distances. We have studied the evolution of about 105 randomly oriented near-parabolic orbits with initial inclinations i uniformly distributed in cos i and perihelia q distributed in all the planetary region. The main contribution to Halleytype comets comes from q < 2 AU where the probability of the capture is 0.02. The number of Halley-type objects arising from the observed near-parabolic cometary flux of all inclinations and absolute magnitudes brighter than H10 = 7, is hundreds of times larger than the number of known Halley-type comets. In contrast with Halley-type comets, the majority of observable Jupiter-family comets originate from orbits with q > 10 AU. The flux of comets in high-eccentricity orbits may be the dominant source of the observed Jupiter family.