bluuebunny/crossref_metadata_2025 huggingface dataset:
Millimeter VLBI Observations of the Gamma-Ray Blazar NRAO 530
Authors: Bower Geoffrey C.
Published: July 2016

We 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.
Synchrotron Spectra of Compact VLBI–Jets
Authors: Lobanov A.P. , Zensus J.A.
Published: July 2016

We discuss the feasibility and prospects of broad–band spectral imaging based on quasi–simultaneous multi–frequency VLBI observations.
Two Stationary Components in the High-Redshift Quasar 1338+381
Authors: Bouchy F. , Lestrade J.-F.
Published: July 2016

VLBI observations of the high-redshift quasar 1338+381 reveal a source with two well defined components that are stationary and possibly, a weaker component that moves in between at a very high superluminal speed.
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

We 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

We 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

We 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

We 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

We 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

Preliminary 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

Using 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

M81 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.
Shock Origin of High-Velocity Maser Emission from Circumnuclear Disks
Authors: Maoz Eyal , McKee Christopher F.
Published: July 2016

We propose that the observed high-velocity maser emission from circumnuclear disks arises in spiral shocks, which can naturally account for several peculiar findings in the spectrum and spatial distribution of the maser emission.
Water in NGC 1068
Authors: Greenhill L. J.
Published: July 2016

We report the first VLBI images of the NGC 1068 H2O maser that include the full 600 km s−1 spread of the emission. The structure of the source is suggestive of an edge-on massive disk that is probably bound by the central engine of this AGN.
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

We 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

We 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

We 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

Global 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

New 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.
A Perspective on Scintillation
Authors: Walker Mark A.
Published: July 2016

Some comments on interstellar scintillation are presented.
Mapping Small Scale Structure in Galactic H ɪ with the VLBA
Authors: Faison M. D. , Goss W. M. , Diamond P. J.
Published: July 2016

We 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

We 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

PKS 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

We 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

Weak 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

GX 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

Two 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

The 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

The 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

We 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

Since 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

The 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

We 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.
Orbital Changes in Planet-Comet Encounters
Authors: Zheng J.-Q. , Valtonen M.J. , Rickman H.
Published: July 2016

We concentrate on the traditional model of capture from the Oort Cloud. We improve the method of calculation of captured comet populations by combining large numbers of accurate orbit calculations with Monte Carlo methods. As a first step in the development of a Monte Carlo code we calculate accurate probabilities for changes of orbit in a single planet-comet encounter. These will be later used to study the orbital evolution of the Oort Cloud comets when multiple encounters take place.
ERA: Knowledge Base for Ephemeris and Dynamical Astronomy
Authors: Krasinsky G. A. , Vasilyev M.V.
Published: July 2016

A brief description of a problem-oriented language SLON for ephemeris and dynamical astronomy and a corresponding programming system ERA is given. In the frame of the system the user has easy access to an embedded universal program package to process high precision positional observations of Solar system bodies as well as of artificial Earth satellites.
Nasa’s Spice System Models the Solar System
Authors: Acton Charles H.
Published: July 2016

The Navigation Ancillary Information Facility (NAIF) at Caltech’s Jet Propulsion Laboratory, acting under the directions of NASA’s Office of Space Science, has built a data system–named SPICE–to assist scientists in planning and interpreting scientific observations. SPICE provides geometric and some other ancillary information needed to recover the full value of science instrument data, including correlation of individual instrument data sets with data from other instruments on the same or other spacecraft.

The primary SPICE data sets are called “kernels.” One of these kernel types provides ready access to ephemerides of spacecraft, planets, satellites, comets and asteroids. A second kernel type provides a set of data specifying target body size, shape and orientation. These data are currently based primarily on IAU/IAG/-COSPAR models.

The SPICE system includes FORTRAN subroutines needed to read the kernel files and to calculate many common observation geometry parameters. Users integrate these SPICE “Toolkit” subroutines into their own application programs to compute needed information.
Rotation of the Rigid Earth
Authors: Bretagnon P.
Published: July 2016

We present the results of a solution of the Earth’s rotation built with analytical solutions of the planets and of the Moon’s motion. We take into account the influence of the Moon, the Sun and all the planets on the potential of the Earth for the zonal harmonics Cj,0 for j from 2 to 5, and also for the tesseral harmonics C2,2, S2,2C3,k, S3,k for k from 1 to 3 and C4,1, S4,1. We determine three Euler angles ψ, ω, and φ by calculating the components of the torque of the external forces with respect to the geocenter in the case of the rigid Earth. The analytical solution of the precession-nutation has been compared to a numerical integration over the time span 1900–2050. The differences do not exceed 16 μas for ψ and 8 μas for ω whereas the contribution of the tesseral harmonics reaches 150 μas in the time domain.
An Analytical Theory for a Gyrostatic Earth
Authors: Molina R. , Vigueras A.
Published: July 2016

In this paper, we consider the problem of the rotation of the Earth, using a stationary triaxial gyrostat as a model. The problem is formulated by means of dimensionless canonical variables of Serret-Andoyer, referred to the mean ecliptic of date, in a similar way to Kinoshita (1977). We choose the constant components of the gyrostatic momentum in such a way that the period of the polar motion corresponds to Chandler’s period. Finally, the problem is integrated by means of Deprit’s perturbation method.
Orbits of Geostationary TV Satellites
Authors: Drożyner Andrzej
Published: July 2016

In the frame of European cooperation among some stations (Brussels, Praha, Cagliari, Torino, Penc, Borowiec, Teddington, Metsahovi, Besançon and San Fernando) the method of time comparisons by a TV link has been used for orbit determination of the Eutelsat-F2 satellite. Observational stations are equipped with commercial TV receivers and high stability time services. The technique of observations is based on the registration of arrival times of synchronous pulses broadcast by the satellite. For this type of observations a special orbital software package (TOP-COGEOS) has been developed, which allows the determination of the dynamical state of the satellite and some additional parameters connected to applied observational technique.
Gyrostats in free Rotation
Authors: Elipe Antonio
Published: July 2016

We consider the problem of the attitude dynamics of a gyrostat under no external torques and constant internal spins. We introduce coordinates to represent the orbits of constant angular momentum as a flow on a sphere. This new representation shows that the problem is a particular case in the class of dynamical systems defined by a Hamiltonian that is a polynomial of at most degree two in a base of the Lie algebra so(3).
Principal Term of Nutation from the Combination of VLBI Observations and Optical Astrometry
Authors: Bizouard C. , Capitaine N. , Ron C. , Vondrák J.
Published: July 2016

The celestial pole offsets (CPO) in provisional HIPPARCOS reference frame determined from the optical astrometry observations since 1899.7 until 1992.0 (Vondrák et al., 1996) and CPO determined from VLBI observations since 1980.0 until 1996.0 (Ma et al., 1996) are combined to get amplitudes of the long periodic nutation terms 18.6 and 9.3 years, respectively. The amplitudes are compared with previous solution based only on VLBI observations (Souchay et al., 1995).
New Reductions of the Astrographic Catalogue: High Accuracy, Early Epoch Positions for Proper Motion Studies
Authors: Urban Sean E.
Published: July 2016

The Astrographic Catalogue (AC) measures are being reduced at the U.S. Naval Observatory to provide early epoch positions for approximately 5 million stars. The data, when combined with recent observations, provide a baseline of about 100 years with which to compute proper motions. Due to the inhomogeneity of telescopes and measuring techniques used in the AC program, each of the 22 zones is being reduced independently with the Astrographic Catalog Reference Stars (ACRS). The data are analyzed and corrected for radial distortions, tilt, magnitude-dependent terms, coma, and distortions based on reseaux and measuring apparatus. To date, eleven zones have been reduced and are available on the WWW (http://aries.usno.navy.mil/ad/ac.html) or the international data centers. Mean errors of the positional data vary from zone to zone, but are generally in the 190-320 mas range per each image.

The newly reduced AC data are being combined with the USNO’s Twin Astrograph Catalog (TAC) in support of the Sloan Digital Sky Survey. This catalog should be available by the end of 1996. When the Tycho data are released, the AC positions will be used to improve the proper motions of the Tycho stars. In order to aid this work, the AC zones released by USNO have Tycho identifications, where applicable.
Astrometry of Faint Planetary Satellites with WFPC2 of Hubble space Telescope
Authors: Pascu D. , Rohde J.R. , Seidelmann P.K. , Wells E.N. , Kowal C.T. , Zellner B.H. , Storrs A. , Currie D.G. , Dowling D.M.
Published: July 2016

Only the Hubble Space Telescope (HST) can detect about 20 of the faint satellites discovered with the two Voyager spacecraft. We describe here the techniques used in obtaining astrometric positions of the inner satellites of Uranus with the Wide Field Planetary Camera 2 (WFPC2) of HST, and those planned for our scheduled observations of the inner Neptunian satellites.
CCD Observations of Planets and Asteroids in the Extragalactic Reference Frame
Authors: Stone R.C.
Published: July 2016

This paper describes the methods used with the Flagstaff 20–cm CCD transit telescope for determining the positions of planets and asteroids directly in the extragalactic reference frame. As a result, the observations are not affected by (optical – radio) zonal errors, which can be ±0.1 arcsec or greater in catalogs based on traditional fundamental observations. The telescope can observe objects as faint as V ~ 17.5 mag with an accuracy of σ ~ ±0.16 arcsec in each coordinate. As a result, a large number of asteroids and the planets Uranus, Neptune, and Pluto are being routinely observed so that their ephemerides can be improved, masses determined, and accurate predictions made for occultation events. These observations are considerably more accurate than most previous results.
Two Astrometric Projects: LIGHT (Light Interferometer Satellite for the studies of Galactic Halo Tracers) and MIRA (Mitaka/Mauna Kea/Maui Optical and Infra-Red Interferometer Array)
Authors: Yoshizawa M. , Sato K. , Nishikawa J. , Fukushima T. , Miyamoto M.
Published: July 2016

The projects LIGHT and MIRA are the space-borne and ground-based optical/Infrared-interferometer projects of the National Astronomical Observatory of Japan. The contents of each project are gradually developing, and the descriptions given below are the preliminary ones studied at the present time.

LIGHT (Light Interferometer satellite for the studies of Galactic Halo Tracers) is a scanning astrometric satellite for stellar and galactic astronomy planned to be launched between 2007 and 2010 by a M-V launcher of ISAS, Japan. Two sets of Fizeau-type 40cm-pupil interferometers with 1 m baseline are the basic structure of the satellite optics. The multi-color (U, B, V, R, I, and K) CCD arrays are planned to be used in the focal plane of the interferometer, optimized for detecting the precise locations of fringe patterns. LIGHT is expected to observe the parallaxes and proper motions of nearly a hundred million stars up to 18th visual (15thK-band) magnitude with the precision better than 0.1 milli-arcsecond (about 50 microarcsecond in V-band and 90 micro-arcsecond in K-band) in parallaxes and better than 0.1 milli-arcsecond per year in proper motions, as well as the precise photometric characteristics of the observed stars. Almost all of the giant and supergiant stars belonging to the disk and halo components of our Galaxy within 10 to 15 kpc from the sun will be observed by LIGHT to study the most fundamental structure and evolution of the Galaxy. LIGHT will become a precursor of a more sophisticated future astrometric interferometer satellite like GAIA (Lindegren and Perryman, 1996).
Observations of Filament Structure and Dynamics
Authors: Engvold Oddbjørn
Published: July 2016

Past and recent observations of spatial and temporal variations in fine structure of solar prominences/filaments are reviewed. Magnetic fields permeate the prominence plasma and play a decisive role in shaping the fine structure and its dynamics. Consequently, the shape, orientation, and possibly the strength, of the magnetic field may be inferred from the observed sub-structures. The review discusses possible physical implications of small-scale structures in the low-β prominence plasma.
The Plasma Environment of Prominences – SOHO Observations
Authors: Moses D. , Korendyke C.M. , Moulton N. , Newmark J.
Published: July 2016

We describe the observational capabilities of the SOHO EIT and LASCO instruments for prominence research. A detailed comparison of EIT He II λ304 and BBSO Hα images of a quiescent prominence reveals differences in fine scale structure which are attributed to differences in radiation emission and transport mechanisms. Absorption features present in coronal EIT images are attributed to dense prominence features located between the source of the coronal emission and the observer. These features provide the locations of prominence material in coronal image sequences. Observations of a prominence eruption in both EIT He II and LASCO C1 Fe XIV images show the heating of chromospheric material to coronal temperatures during the prominence eruption. In the last phase of the prominence eruption, a coronal mass ejection (CME) is initiated as a dark cavity forms over the prominence material and a bright loop-like structure forms over the dark cavity.
Eclipse Polarimetric Research of Prominences
Authors: Lebedev A.N. , Belenko I.A. , Bougaenko O.I. , Kim I.S. , Matsuura O.T. , Picazzio E. , Livi R.P. , Liv Silvia H.B.
Published: July 2016

A polarization analysis of E–limb prominences on November 3, 1994 is presented. Photometry and data reduction of 24 prominence pictures based on IDL software and Stokes–vector presentation and applied to Hα emission resulted in an accuracy of 1–1.5% in determination of the polarization degree and of 1.5–2.0° in the polarization direction. Distributions of polarization degree (polarization images) for prominences and the “white light” corona are presented. A polarization degree of 2–5% for prominences and 10–25% for the nearby white light corona are found. The polarization direction is found to be tangential to the solar limb. It is noted that eclipse observations can provide a powerful method for deriving the magnetic field at high altitudes in the coronal volume.
On the Bright Rims of Hα Filaments
Authors: Paletou F.
Published: July 2016

Heinzel et al. (1995) have proposed that diffusive penetration of the incident chromospheric Hα radiation could explain the bright rims of filaments. We examine this suggestion with the help of new 2D radiative models of filaments and show that our computations do not support this explanation.
Magnetic Helicity and Filaments
Authors: Berger M.A.
Published: July 2016

Some of the most dramatic images of prominences show helical structure. Helical structure, as well as other structural features such as twist, shear, and linking, can be quantified using helicity integrals. This paper reviews how the calculation of helicity may be applied to prominence models. Recent observations indicate that the sign of helicity in an active region depends on which hemisphere the region is in. The source of this asymmetry is an important problem in solar physics. The total helicity of each hemisphere obeys a Poynting-like theorem which describes how helicity is transferred across the photosphere and the equator. Estimating this helicity transfer may help us in understanding the helicity balance of the sun.
On the Relationship Between Current and Magnetic Field in Ring-Filaments
Authors: Callebaut Dirk K. , Makarov Valentine I.
Published: July 2016

There is a type of filament that forms closed contours encircling regions of one polarity of magnetic field, while the surrounding region has the opposite polarity. One distribution of ring-filaments has sizes 2R = 40,000 to 160,000 km with the maximum around 100,000 km; the other distribution (with filaments and filament channels) has bigger sizes, with a maximum around 300,000 km. At low and mid latitudes the radial component Brs (radial for the Sun) in the region outlined by filaments varies from 50 to 100 gauss, while the longitudinal component Bϕ, varies from 10 to 30 gauss. The total current inside the filament is 1010 – 1011 A, the ratio R/a ≈ 5 to 10, the magnetic flux crossing the surface is ≈ 1021 – 1022Mx; the magnetic energy is ≈ 1029 – 1031erg. Polar ring-filaments at latitudes 60° – 80° are related to the polar magnetic field reversal and the quasi-flare processes at the poles during the field reversal. Correlation between Brs and Bϕ, for the polar filament bands cannot be satisfactorily explained. A theoretical model using the conservation laws is used to study the relations between the various fields, currents, etc. of shrinking polar ring-filaments and their evolution. According to this theory ring-filaments should rise higher above the photosphere when shrinking. However, observations show that the height lowers. Presumably the discrepancy is due to the lack of dissipation in the model.
Velocity Fields of a Filament Region Observed with Ground-Based Telescopes and from SOHO
Authors: Mein P. , Schmieder B. , Malherbe J.-M. , Wiik J.E. , Engvold O. , Brekke P. , Zirker J.B. , Poland A.I. , Delaboudinière J.-P. , Staiger J.
Published: July 2016

We present preliminary results on solar filaments observed from the ground and from SOHO in September 1996. Motions in the network and close to the filament “barbs” are shown at different levels of the chromosphere and the transition region.
Lyman Lines in Prominences and Filaments: NLTE Modelling Strategies
Authors: Heinzel P.
Published: July 2016

We briefly summarize the most important aspects of NLTE formation of hydrogen Lyman lines in prominences and filaments. A modified MALI code of Heinzel (1995) is described and its applicability to the interpretation of SOHO/SUMER data is discussed.
Solar Prominence Diagnostics From the November 3, 1994 Eclipse
Authors: Foing B.H. , Wiik J.E. , Duvet L. , Henrich N. , Cravatte S. , David F. , Altieri B. , Beaufort T. , Ligot L. , Maurice E.
Published: July 2016

We report results on solar prominences from our observations of the November 3, 1994 total solar eclipse from the North Chile alteplano. From the military base at Putre, we used our transportable CCD camera and telescope, as well as support photographic digitised observations from Putre and Parinacota volcano. The variation of density and equivalent temperature were derived in coronal holes (plumes and interplumes) and in equatorial streamers. We obtained images from the inner to the outer corona, as well as low-resolution spectra of prominences and of the inner corona. We present the analysis of images and spectra of prominences in the Balmer, He I and Ca II lines, and in the Thomson scattered continuum.
Prominences on Rapidly-Rotating Solar-Type Stars
Authors: Jardine M. , Barnes J. , Unruh Y. , Cameron A. Collier
Published: July 2016

We present Hα observations of two rapidly-rotating G2 dwarfs in the Alpha Persei cluster and of AB Dor, a young K0 dwarf. All three stars have projected rotational velocities of about 90 km s−1 and axial rotation periods ranging from 11 to 15 hours. He 520 and AB Dor show very clear transient features that move through the profile. The most likely explanation for these features is that they are huge prominences in co-rotation with the star. We also use the recently developed technique of least squares deconvolution to present simultaneous dynamic profiles of the stars’ photospheric lines which show the locations of the surface spots. This technique has allowed us to extend our studies to a greater range of stars.
MHD and Plasma Interpretation of a Prominence Eruption Observed by SOHO
Authors: Martens P.C.H.
Published: July 2016

Data on the May 1, 1996 prominence eruption, jointly observed by CDS, SUMER, and EIT, aboard SOHO, Yohkoh-SXT, and Kitt Peak and Meudon observatories are analyzed to obtain information on the plasma temperature, density, and velocities, as well as the magnetic field topology and strength. It is found that the ‘standard’ model of an erupting helical flux tube probably applies, although questions arise on the MHD stability of the prominence flux tube. The prominence is observed to remain relatively cool during its eruption (≤ 5 × 105K), while the density and velocity vary considerably on scales down to the limit of resolution. It is found that the high density, high velocity plasma blobs can be contained by the relatively weak magnetic field, as is indeed observed.
Behaviour of Hα and H Ca II Emission Lines in a Prominence Before and During its Dynamic “Disparition Brusque”
Authors: Madjarska M.S. , Dermendjiev V.N. , Mouradian Z. , Kotrč P.
Published: July 2016

Hα and H Ca II emission lines in a limb quiescent prominence (QP) undergoing destabilization are studied. The temperature, line-of-sight velocity and micro-turbulence are obtained in one of the prominence legs, just before and during the prominence activation.
Eruption of a Twisted Filament and Associated Phenomena
Authors: Uddin Wahab , Verma V.K.
Published: July 2016

In this paper we present CCD observations between February 14–20, 1994 and analysis of the giant twisted filament evolved in the active region NOAA 7671. The dynamic eruption of the filament was accompanied by a major flare (3B/M4), CME, long duration type II, IV radio bursts, great microwave bursts, a long duration soft X-ray burst, SIDs, strong geomagnetic storms and a very energetic proton flare. We analysed and estimated the twist, length, volume, mass and energy associated with filament system between February 14 and 20, 1994. The present study shows that the magnetic energy required for the solar flare came from the filament system associated with the solar flare and associated phenomena.
Coronal Plasmoid Dynamics
Authors: Delannée C. , Koutchmy S. , Zhukov A. , Veselovsky I.
Published: July 2016

A possible acceleration mechanism by the magnetic force is suggested for a plasmoid, modeled as a spherical body with a magnetic dipole situated in its center of mass. The governing equations of the motion of a dipole in an inhomogeneous magnetic field are solved analytically and numerically. Both methods show the possibility for the plasmoid to be accelerated in the direction of the external field gradient.
Filament Chirality: A Link Between Fine-Scale and Global Patterns
Authors: Martin Sara F.
Published: July 2016

Solar features that exhibit chirality are: fibril patterns in filament channels, filaments, coronal arcades over filaments, superpenumbral fibrils exterior to sunspots, whole active regions observed with magnetographs, some large-scale X-ray structures, and interplanetary magnetic plasma clouds originating from coronal mass ejections. Their signatures of chirality are briefly reviewed; some details are mentioned to further show relationships which link all of the chirality patterns into a single framework. The helicity of solar magnetic fields is the evident physical phenomena which finks each of the seven features to each other and into a broader framework. The chirality system, viewed as a whole magnetic system, reveals: (1) a consistent rotational configuration of the dominant direction of the magnetic field with height of features within and over filament channels from the photosphere to the highest part of the solar corona, and (2) the prominence cavity as a unique space between magnetic fields of opposite helicity.
Chirality, Helicity, and Joy’s Law
Authors: Foukal P.
Published: July 2016

Connections between the morphology of filaments and the global topology of the sun’s magnetic field, are an important topic that seems ready for assembly into a coherent picture. We suggest that the chirality of mid-and high-latitude filaments described by Martin et al. is most easily understood if they form in evolved “Type 1” neutral lines within active region bipoles, rather than in the “Type 2” neutral lines formed at the boundaries between bipoles, where lower-latitude filaments tend to form. This interpretation removes the disagreement between filament chirality and the well-known tilt of bipolar active regions described by Joy’s law, which exists if the high-latitude filaments formed at Type 2 neutral lines. Dynamical explanation of these two observed regularities probably implies quantitative understanding of the processes that govern the sign and magnitude of the α and ѡ-effects in a solar dynamo.
A Dynamic Dextral-Sinistral Model for the Structure and Evolution of Prominence Magnetic Fields
Authors: Priest E.R.
Published: July 2016

We propose the following coherent model for prominences.

(i)

They are composed of many fine threads whose mass we suggest has two kinds of origin. Some of the mass may be lifted from the upper photosphere in response to cancellation of magnetic flux in small flux tubes. If this rate of mass supply is slow then the mass needs to be supported, but if the mass supply rate is as large as the natural rate of draining then no support is necessary. However, much of the mass may not need to be supplied or supported at all, if it comprises dynamic threads of cool plasma that are in pressure balance with their hot surroundings and are continually forming from the corona and heating up again in response to a localised heating mechanism.

(ii)

The overall structure is of a large-scale flux tube along the polarity inversion line with an overlying arcade that links the network on either side of the filament channel. The structure of the channel and of barbs is explained by the distribution of flux sources along the channels, with majority polarity producing plagettes and minority polarity the barbs.

(iii)

The chirality of polar-crown prominences is suggested to be caused by a combination of subsurface flows, flux emergence and reconnection. By contrast, two generic types of low-latitude filament, namely those associated with unipolar flux tongues and with the emergence of new active regions near to remnant regions, are a natural consequence of nonuniform flux distribution and converging flux.
The fiber-fed spectrograph, a tool to detect planets
Authors: Queloz D. , Casse M. , Mayor M.
Published: July 2016

The use of fibers to feed spectrographs is a very efficient way to increase the precision of radial velocity measurements. It has already proved to be successful with the very first detection by the ELODIE fiber-fed spectrograph of the planet orbiting the star 51 Peg. The basic key properties of fibers in the very high radial velocity precision measurements context are described in this review. The ELODIE spectrograph is used to illustrate the thorium simultaneous calibration technique. The use and the effects of a double-scrambler to increase the stability of the slit illumination are also discussed.
Precise Radial-velocity Measurements with a Cassegrain Spectrograph, II: Radial-velocity Determination and Applications
Authors: Ilyin I. V. , Duemmler R.
Published: July 2016

We present our measurements of radial velocities of two stars suspected to have a substellar companion by using observations made with a cassegrain échelle spectrograph. The stability issues and details of the data reduction are discussed in Ilyin & Duemmler (paper I, these proceedings). The results obtained here show that relatively high accuracy of radial velocity determinations is also attainable for cassegrain spectrographs.
Radial Velocities Without Spectroscopy
Authors: Madsen Søren , Lindegren Lennart , Dravins Dainis
Published: July 2016

We discuss non-spectroscopic (astrometric) ways to determine radial velocities and their potentials in future astrometric missions. Radial-velocity accuracies are presented, based on Hipparcos parallax and proper motion data for several open clusters.