bluuebunny/crossref_metadata_2025_split huggingface dataset:
Limiting Brightness Temperature for Synchrotron Sources
Authors: Lähteenmäki A. , Valtaoja E. 
Published: July 2016

AbstractThe maximum brightness temperature limit for synchrotron sources derived from inverse Compton catastrophe is usually taken to be 1012 K. Readhead has argued in 1994 that the equipartition brightness temperature may be a better estimate for Tb,lim. It provides a value of 5 × 1010 K. We suggest that a reasonable estimate of the value of Tb,lim can also be achieved by comparing Doppler boosting factors from total flux density variations at 22 and 37 GHz with traditional Doppler factors from the SSC X-ray flux. We also compare our variability brightness temperatures with values calculated for individual sources observed with VLBI, obtaining other independent estimates of Tb,lim.
Low Frequency (327 MHz) VLBI Survey: First Results
Authors: Altunin V. , Beasley A. , Lűdke E. , Alekseev V. , Lipatov B. , Dagkesamansky R. , Kardashev N. , Kovalenko A. , Molotov I. , Slysh V. , Migenes V. 
Published: July 2016

AbstractIn this paper we report the first results of the 327 MHz VLBI survey which has been carried out in the last two years to select potential candidate sources for the future SVLBI missions and to search for directions of small scattering-“holes” in the interstellar scattering medium. During the three VLBI sessions conducted so far, we observed about 80 sources. Preliminary data analyzed from the first part of the survey shows that at least 17 out of 50 sources have compact components with a size smaller than 30 mas.
The Submilliarcsecond Structure of Quasars and AGN
Authors: Kellermann K. I. , Zensus J. A. , Vermeulen R. C. , Cohen M.H. 
Published: July 2016

AbstractVLBA observations of 130 quasars and AGN made at 15 GHz with submilliarcsecond resolution show a variety of structures, most of which appear linear.
A VLBA Calibrator Survey
Authors: Peck A. B. , Beasley A. J. 
Published: July 2016

AbstractThe Very Long Baseline Array (VLBA) Calibrator Survey consists of snapshot observations at 2.7 and 8.4 GHz of nearly 2000 flat-spectrum extragalactic sources selected from the Jodrell Bank–VLA Astrometric Survey (JVAS). When complete, this survey will assist in defining the extragalactic radio frame in the northern sky by providing positions for these sources which will be accurate on the milliarcsecond scale. This survey is accessible on the WWW at http://magnolia.nrao.edu/vlba_calib/index.html.
Polarization VLBI Observations of a Complete Sample of Northern BL Lacertae Objects
Authors: Pushkarev A. B. , Gabuzda D. C. 
Published: July 2016

AbstractThe polarization electric vectors in the VLBI jets of BL Lacertae objects are typically aligned with the jet structure. If the jet radio emission is optically thin synchrotron emission, this implies that the magnetic field is perpendicular to the jet, usually interpreted as a signature of shocks. The distribution of polarization position angles in the VLBI core components appears to be bimodal, with the polarization angles either aligned with or perpendicular to the jet direction. In order to study the origin of this characteristic polarization structure, we have made VLBI polarization observations of all 34 sources in the Kühr and Schmidt sample of BL Lacertae objects.
The Recent Highly-Polarized Centimeter Burst in BL Lacertae
Authors: Aller H. D. , Hughes P. A. , Aller M. F. 
Published: July 2016

AbstractObservations with the University of Michigan 26-meter paraboloid at 4.8, 8.0, and 14.5 GHz have been used to test generic shock-based models of the emitting region of BL Lacertae. Large changes in the polarization position angle since 1980 are not consistent with a jet with a simple conical flow.
Radio Emission from Low-Luminosity Active Galactic Nuclei
Authors: Van Dyk Schuyler D. , Ho Luis C. 
Published: July 2016

AbstractMany nearby galaxies show optical evidence for low-luminosity AGNs that are far less luminous than classical Seyfert nuclei and QSOs. LINERs, the most common variety of such emission-line objects, comprise ~ 1/3 of nearby galaxies, and may serve as an important “missing link“ between normal and Seyfert galaxies. To shed light on the physical origin of LINERs, which remains controversial, we are conducting a high-resolution continuum survey of a representative sample of galaxies using the VLA to search for compact radio cores. We additionally discuss the dramatic radio variability in the LINER nucleus of M81.
Proper Motions and Jets in NGC 4258: Further Evidence for a Sub-Parsec Nuclear Disk
Authors: Herrnstein J. R. 
Published: July 2016

AbstractThe evidence for a subparsec-scale disk in the nucleus of NGC 4258 is reviewed in the context of multi-epoch VLBA observations. The detection of jet continuum emission and of maser proper motions in these data bolster the case for a nuclear disk.
VLBI Observations of a Megamaser in a Seyfert Galaxy IC 2560
Authors: Nakai N. , Inoue M. , Hagiwara Y. , Miyoshi M. , Diamond P. J. 
Published: July 2016

AbstractVLBA observations of water-vapor maser emission in the active nucleus of a Seyfert 2, IC 2560, show linear velocity gradient along the north-south elongation, suggesting a compact rotating disk. The binding mass density within the disk is 7.7 × 106 M⊙ pc−3. We are also monitoring the velocity variations of the maser features with single dish telescopes. By combining the velocity drift with the linear velocity gradient, we would be able to determine the rotation speed and radius of the nuclear disk, and hence the central mass.
VLA Observations of H2O Masers in the Class 0 Protostar S106FIR
Authors: Furuya R. , Kawabe R. , Saito M. , Umemoto T. , Kitamura Y. 
Published: July 2016

AbstractWe measured relative positions of the 22 GHz H2O maser components toward the class 0 protostar S106FIR with the VLA. Two clusters of H2O masers were found. The separation between these clusters is approximately 50 AU at position angle = 73° and each cluster is spread over about 10–20 AU The size of the S106FIR maser clusters is unusually compact compared with other known H2O masers associated with outflows of forming stars. The maser emission appears to originate from MHD driven outflow very close to the star.
Intraday Variability of Flat-Spectrum Radio Sources
Authors: Wagner S. J. 
Published: July 2016

AbstractThe characteristics of rapid variability of flat-spectrum radio sources are reviewed. A large fraction of the blazar population is found to show variability on timescales shorter than one day throughout the entire electromagnetic spectrum. The spectral indices and polarization characteristics change equally fast.Structure functions of the well-monitored sources show pronounced breaks on scales of about 10 to 50 hours, with flatter slopes towards the fast end. This illustrates that Intraday Variability (IDV), i.e. the high frequency end of the power spectrum is qualitatively different and requires different mechanisms than slower variations.While intrinsic IDV provides direct clues on small-scale structure over fifteen decades in frequency, extrinsic contributions from interstellar scattering contributes at the lowest frequencies, and remains difficult to disentangle from the intrinsic effects.
VLBA and MERLIN Polarization Observations of Compact Steep-Spectrum Source
Authors: Mantovani F. , Bondi M. , Junor W. , Salter C. J. , Saikia D. J. 
Published: July 2016

AbstractA few compact steep-spectrum sources (CSSs) have been observed with the VLBA at 8.4 GHz and MERLIN at 5 GHz to study the possible dynamical interaction between jets and the ambient media suggested by previous measurements of the rotation measures.
VLBI Observations of the Gravitational Lens B1422+231
Authors: Patnaik A. R. , Porcas R. W. 
Published: July 2016

AbstractWe present results from VLBI observations of the gravitational lens B1422+231. All the four images of this system have been detected and appear unresolved at 18cm. Images A and B show elongated structures at 6cm with 1 mas resolution. With a resolution of 0.75 mas at 2cm, three images are elongated with axial ratios of about 10:1 for A and B, and 2:1 for C.
Astrometry of the Planetary-System Millisecond Pulsar B1257+12
Authors: Nunes N. V. , Bartel N. 
Published: July 2016

AbstractWe present the VLBI determined position of the millisecond pulsar PSR B1257+12 which has been shown to have a planetary system (Wolszczan & Frail 1992). The position determination for epoch June 20, 1992 is: αJ2000=13h0m3s.05005(5),δJ2000=+12°40’56″.7043(34). We indicate how the combination of such pulsar observations along with timing observations can be used to directly tie the solar-system dynamic reference frames and the extragalactic reference frame.
Toward a Trigonometric Parallax of Sgr A*
Authors: Reid M. J. , Readhead A. C. S. , Vermeulen R. C. , Treuhaft R. N. 
Published: July 2016

AbstractWe initiated a project with the VLBA to measure directly the distance to the Galactic Center, R0, via a trigonometric parallax. Here we describe the observing program and the first results–direct imaging of the effects of the Sun’s orbit about the Galactic Center.
The Evolution and Distance to SCORPIUS X-1
Authors: Fomalont E. B. , Bradshaw C. F. , Geldzahler B. J. 
Published: July 2016

AbstractFrom three VLBA observations at 5 GHz, spanning 13 months, we have measured the trigonometric parallax of Sco X-1 of 0.23 ± 0.28 mas; hence its distance is > 1300 pc. This supports the hypothesis that the the x-ray luminosity is near the Eddington Limit.All three VLBA observations show a radio core of flux density 0.5 mJy and size < 4 mas. However, the third VLBA observation revealed two additional radio components, separated by 12 mas (≈ 20 au) on opposite sides of the radio core. The evolution of these new components is unknown until additional observations can be made. The relative luminosity and separation of the two radio components are inconsistent with the Doppler beaming of two identical ejecta from the radio core.
Deceleration in the Expansion of SN 1993J
Authors: Marcaide J. M. , Alberdi A. , Ros E. , Diamond P. , Shapiro I. I. , Guirado J. C. , Jones D.L. , Mantovani F. , Pérez-Torres M. A. , Preston R. A. , Schilizzi R. T. , Sramek R. A. , Trigilio C. , Van Dyk S.D. , Weiler K. W. , Whitney A. R. 
Published: July 2016

AbstractWith new 6 cm observations we confirm the self-similar expansion of SN 1993J previously discovered at 3.6 cm and estimate the expansion deceleration parameter. The results are inconsistent with the existence of a constant pre-explosion stellar wind but otherwise confirm the standard radio supernova model. The first map at 13 cm showing shell structure is also presented.
VLBI Observations of Supernova 1993J: The First 1000 Days
Authors: Rupen M. P. , Beasley A. J. , Bartel N. , Bietenholz M. F. , Graham D. A. , Altunin V. I. , Jones D. L. , Conway J. E. , Venturi T. , Umana G. , Rius A. 
Published: July 2016

AbstractWe report on phase-referenced 5 and 8.4 GHz VLBI images of supernova SN 1993J in M81, tracking the evolution of the source from 50 to 1000 days after the explosion.
Methanol Masers—Are They in Circumstellar Disks?
Authors: Norris R. P. , Phillips C. J. , Ellingsen S. P. 
Published: July 2016

AbstractSince the discovery of the 12.2 and 6.7 GHz methanol maser lines, these masers have been studied in great detail. Even in the earliest studies, it appeared that in some fraction of the sources, the maser spots were arranged in lines. This contrasts with the well-studied OH and water masers, in which the masers tended to be clustered almost randomly around a compact H ɪɪ region. Here I describe recent work to investigate the hypothesis that these lines represent edge-on circumstellar disks.
Development of K4 Correlator for Pulsar VLBI: Japan-Russia Baseline
Authors: Sekido M. , Hama S. , Kiuchi H. , Imae M. , Hanado Y. , Takahashi Y. , Rodin A. E. , Ilyasov Y. P. 
Published: July 2016

AbstractWe are doing astrometric pulsar VLBI observation with Kashima-Kalyazin 7000 km baseline. K4 correlator is under the development for this observation program. When XF type correlator is used for pulsar processing with gating, attention should be paid to avoid fluctuation on delay result due to fractional bit effect. This influence is serious around the point that bit shift for delay tracking and pulsar period is synchronized. In this paper, the K4 correlation system is introduced and fractional bit effect on pulsar processing is explained.
Techniques for Analyzing Short Coherence Time VLBI Data
Authors: Lonsdale Colin J. , Doeleman Sheperd S. 
Published: July 2016

AbstractWe have written a suite of programs designed to deal with problems peculiar to short-wavelength VLBI. The most important difference between mm-VLBI and cm-VLBI is that one usually wishes to integrate the data for times which are long compared to the atmospheric coherence time. This causes difficulties with standard VLBI data reduction techniques, and mandates the use of the algorithms implemented in our package for accurate results.
VLBI Image Deconvolution Based on Generalized Nonlinear Information Methods
Authors: Bajkova A. T. 
Published: July 2016

AbstractA number of nonlinear image deconvolution procedures based on extremizing generalized Shannon entropy, Kullback-Leibler cross-entropy and Renyi information measures are suggested for VLBI mapping with minimal nonlinear distortions. A new approach to phaseless mapping urgent in the case of unreliable closure phases is proposed.
Simulated Space VLBI Experiment using the Tidbinbilla 11-m DSN Tracking Station and SURFSAT and Simulated Satellites
Authors: Wietfeldt R. , Smith J. , Border J. , Altunin V. , Ryne M. , Lewis C. , Benson J. , Claussen M. , Romney J. , Springett J. , Webber J. , King E. , Reynolds J. , Wilson W. , Jauncey D. , Ferris R. , Harbison P. , Jenkins B. , Costa M. , Ellingsen S. , Knight C. 
Published: July 2016

AbstractWe describe a space VLBI experiment involving an earth-orbiting satellite (SURFSAT) and simulated satellites, a space VLBI ground tracking station, an array of ground radio telescopes, and a space VLBI correlator. The purpose of this experiment was to provide as complete as possible an end-to-end simulation of space VLBI in preparation for the first space VLBI mission, VSOP, and in particular to test the most critical aspect of space VLBI, viz. the ability to generate a stable and accurate frequency standard (clock) for the orbiting VLBI element.
Hyperion as a Dust Source in the Saturnian System
Authors: Banaszkiewicz Marek , Krivov Alexander V. 
Published: July 2016

AbstractWe argue that Hyperion may act as a reasonably effective source of dust in the Saturnian system. Hypervelocity impacts of interplanetary grains and of dust particles from the outermost moon Phoebe should produce impact ejecta from Hyperion’s surface, an appreciable share of which would escape into the planetocentric orbits. Though the particles would initially be locked in a strong 4:3 mean motion resonance with Titan so that encounters with this satellite would be prohibited, the solar radiation pressure and especially plasma drag force destroy the resonant locking. Once the resonance is broken, the orbits become unstable and experience multiple close approaches to Titan. Using numerical integrations, we performed a statistical study of the grain trajectories and found that most of the grains larger than ~ 5 μm will finally collide with Titan, smaller particles down to ~ 1 μm will escape out of the system, and still smaller (submicrometer) particles will rapidly collide with Saturn. First order estimates of the dust influx to Titan are also made; they show that the upper limit of the income rate of the Hyperion particles is comparable with the direct influx of interplanetary grains.
Comparison Between Present Representations of the Motions of the Eight Major Satellites of Saturn
Authors: Duriez L. , Vienne A. 
Published: July 2016

AbstractWe compare the two current representations (TASS and that of Harper and Taylor) of the motion of Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion and Japetus. Although both theories produce almost the same (o-c) residuals with the available observations, we show that they may give positions significantly different at dates corresponding to a gap in the distribution of these observations. In the interval 2000–2020 (corresponding to the CASSINI mission) these differences can reach 5000 km for Mimas, 8000km for Hyperion, 6 000 km for Japetus. So, to test a theory of motions it is necessary to use other criteria among which the most important ones are its dynamical consistency and its internal accuracy.
A Clementine II Mission to the Asteroids
Authors: Hope A.S. , Kaufman B. , Dasenbrock R. , Bakeris D. 
Published: July 2016

AbstractClementine II is a Department of Defense (DoD) and industry interplanetary mission designed to flyby several asteroids and release science probes that will impact these asteroids. Candidate asteroids were identified and a nominal and backup mission was chosen from these candidates. The mission design is discussed and the baseline encounters are presented. A backup mission is briefly described. A mass breakdown for the baseline mission is provided as well as the proposed mission sensors. The final encounter approach B-Plane errors are determined and analyzed. A final summary of the Clementine II mission is presented.
Lunar Libration Tables and Determination of Crater Coordinates
Authors: Petrova Natasha 
Published: July 2016

The study of lunar rotation has attracted considerable interest with the advent of the epoch of exploration of the Solar system by space technology. A series of works on an investigation of the lunar gravitational field carried out with the help of artificial lunar satellites have greatly advanced our possibility for that study. The problem concerning the landing on the lunar surface of spacecraft, and the creation of durable lunar bases, impose heavy demands on the accuracy of theoretical description of orbital and rotational motion of the Moon.The development of the observational technology with the help of radio-and laser ranging (LLR) provides at the present time measurements of the distance to a given point on the Moon with an accuracy of about 2 cm, probably improved in the future to about 5mm (Banerdt, 1995). By using differential VLBI measurement with extragalactic radio sources angularly near the Moon, it should be possible to obtain routine estimates of angular position of the beacon to 0.1 mas from each observation (Baudry, 1995). Therefore, combining VLBI and LLR techniques will provide a means of achieving new objectives, and that calls for the development of the theories adequate to an accuracy for observations.
A New Nutation Series for a Rigid Earth Model
Authors: Hartmann Torsten , Soffel Michael 
Published: July 2016

AbstractA new nutation series for a rigid Earth model was derived from a new and highly accurate tidal potential series. A new second order theory for the nutational amplitudes of rotation-, figure- and angular momentum-axis based on tidal amplitudes is formulated. Amplitudes larger than 0.45μas are taken into account leading to a series with 699 terms. The new series may serve as test of other ones that were recently published in the literature.
On the Dynamics of the LAGEOS-I Spin Vector: High Precision Direct Observations and Comparisons to Theoretical Modeling
Authors: Currie D. , Kissell K. , Avizonis P. , Wellnitz D. 
Published: July 2016

AbstractLAGEOS I is a high-density geodetic satellite launched by NASA on 4 May 1976 (Johnson et al., 1976). Using a network of laser ranging stations, GSFC/NASA has maintained extremely accurate information on the orbital motions of LAGEOS I, and the later LAGEOS II and on the time-dependent evolution of their orbital parameters. The development of short-pulse laser ranging systems, and better models for atmospheric refractive effects, have dramatically improved the ability to locate the spacecraft or measure geodetic position and terrestrial crustal motion, but these systems do not measure the satellite rotational motion or gyroscopic effects, thought initially unimportant. Primarily as a result of technical strides in orbit determination, it is now recognized that the spin-motion is critical to understanding weak but important interactions with the environment.
Integration of Orbital Motions with Chebyshev Polynomials
Authors: Barrio Roberto , Elipe Antonio 
Published: July 2016

AbstractIn this communication, we use Chebyshev series for integrating orbital motions. The nice properties that Chebyshev polynomials have, such as giving good approximations of functions in the Chebyshev norm, easy handling of their algebra with algebraic manipulators, allowing very big step sizes for integration and giving the solution in the form of polynomials, make these polynomials very attractive in orbit computations.
Models of Elliptical Galaxies in 1–1–1 Resonance and their Normalization: The 3D Hénon and Heiles System
Authors: Ferrer S. , Viartola A. , Palacián J. , Yanguas P. , San Juan J.F. 
Published: July 2016

AbstractIn this Note we study perturbed isotropic harmonic oscillators in 1–1–1 resonance, which is one of the typical cases of galactic potential models. We focus on cubic and quartic axial symmetric potentials giving explicitly their normal form. The 3D normalized Hénon and Heiles case, which requires to reach fourth order, is studied showing its relative equilibria and bifurcations.
NPC, A New Combined Position Catalogue of Stars in the Northern Pole Region
Authors: Taff L.G. , Tel’nyuk-Adamchuk V.V. , Molotaj O.A. 
Published: July 2016

AbstractThe main task of this work was to construct a new catalogue of positions and proper motions of stars in the north polar cap, and using the results obtained to study the systematic features of the source catalogues as well as the reference system in the polar region. To achieve the goal, thirteen source catalogues, both meridian and photographic, covering an epoch span near one and a half century, were collected. Most of them were not involved in the process of both the PPM and the ACRS constructions. The new combined catalogue of positions and proper motions, named North Polar Catalogue (NPC), lists 4272 stars on the FK5 system, J2000.0. The catalogue was constructed using the method of infinitely overlapping circles. It represents the second use of this procedure to construct a star catalogue. External rms accuracy of positions for the epoch of 2000 is equal to 015 and 025 for the centennial proper motions, respectively. The internal rms errors of positions at the mean catalogue epoch, near 1940, are equal to 018 and 015 for right ascension and declination correspondingly, while external rms position errors for that epoch are of the order of 005. Comparisons were made between the NPC and three modern catalogues, the FK5, PPM, and ACRS. The systematic differences between the new catalogue and PPM one for the epoch of 2000 are valuable, especially in the case of errors depending on right ascension. The authors consider as an essential part of the systematic differences that, which is caused by some shortcomings of the PPM in the polar zone. For the mean epoch of the new catalogue positions the systematic differences are smaller.
Catalogues of Intermediate Stars in the Vicinity of Radio Sources
Authors: Kumkova I. , Kolomiets A. 
Published: July 2016

AbstractThe accurate positions of extragalactic radio sources are in use to link the radio and fundamental reference frames and contribute to determining relative orientation of HIPPARCOS and the radio reference frames as well as HIPPARCOS and FK5. Catalogues of intermediate stars chosen in the vicinity of extragalactic radio sources are an important part of the link and can be used for extension and densification of the HIPPARCOS frame. The description of main catalogues of intermediate stars is given. Results of investigation and comparison beetween CAMC, RRS2, PIRS and CRIS are presented.