bluuebunny/crossref_metadata_2025 huggingface dataset:
Three Dimensional MHD Simulations of Parker Instability in Differentially Rotating Disk
Authors: Matsuzaki T. , Matsumoto R. , Tajima T. , Shibata K.
Published: July 2016

Nonlinear growth of the Parker instability (PI) and the Balbus & Hawley instability (BHI) in accretion disks have been studied by local three-dimensional magnetohydrodynamic (MHD) simulations. In high-β disks (β = Pgas/Pmag > 1), the PI has only minor effects on the saturation level of BHI. In low β disks (β ≤ 1), the disk stays in a low-β state because magnetic flux cannot escape fast enough to convert the disk into a high-β state. We found that even in low-β disk the BHI generates fluctuating magnetic fields. The effective magnetic viscosity αB(= –⟨BrBΦ/4πP0⟩) is O(0.1) when β ~ 1.
3-D Hydro dynamic Simulation of Accretion Disk Formation in LMC-X4
Authors: Owen Michael P. , Blondin John M.
Published: July 2016

We present preliminary results of a time-dependent, three-dimensional hydrodynamic simulation of LMC-X4, an HMXB known to be undergoing RLOF. The simulation is initialized with the collapsed companion embedded in the undisturbed primary wind. The primary is in contact with the Roche surface, although no tidal stream or accretion disk is initialed; they are allowed to form independently.

Several features of general interest to disk-fed HMXBs are apparent in the simulation. First, the primary immediately develops a compressed-wind disk in the orbital plane. This may be a natural result in most disk-fed HMXBs. Fora circularized system in an orbit close enough for RLOF to take place, we may expect the primary to be in corotation. The surface velocity may then be a significant fraction of the breakup velocity, leading to a compressed-wind disk.
High-Speed Optical Spectroscopy of a Cataclysmic Variable Wind: BZ Cam (0623+71)
Authors: Ringwald F. A. , Naylor T.
Published: July 2016

The nova-like variable BZ Cam (also called 0623+71) is an unusual cataclysmic variable star in that it resides in a nebula, discovered by Ellis, Grayson, & Bond (1984) and designated EGB 4. It is more unusual in that its optical spectrum reveals a wind from its accretion disk. This was discovered serendipitously during a radial velocity study to find orbital period by Thorstensen, Thomas, & Patterson (1993; see also Patterson et al. 1996), who found intermittent P Cygni profiles in the He I λ 5876 Å and Hα emission lines.

The 4.2-m William Herschel Telescope and its ISIS spectrograph were used to obtain time-resolved spectra of these lines with 0.4 Å/pixel dispersion and 30-second time resolution. These new spectra have about 5 times the spectral resolution and 24 times the time resolution of those of Thorstensen et al. (1993). These observations were obtained on the nights of 1995 February 6 – 8 UT. The blue arm of ISIS was centered on the He I λ 5876 Å; the red arm covered Hα. Typical signal-to-noise ratio was 18 per resolution element.
Parameters of Dwarf Nova SS Cygni
Authors: Voloshina Irina , Khruzina Tatjana
Published: July 2016

The analysis of dwarf nova SS Cyg light curves at quiescence is performed and some important are determined.
Super-Eddington Accretion in the Formation of Low-Mass X-ray Binaries and Millisecond Pulsars
Authors: Webbink R. F. , Kalogera V.
Published: July 2016

Considerations of donor star stability, age, and mass transfer rate show that low-mass X-ray binaries and binary millisecond pulsars with orbital periods longer than a few days must have survived an initial phase of super-Eddington mass transfer. We review the physical arguments leading to this conclusion, and examine its implications for the apparent discrepancy between the death rate for low-mass X-ray binaries and the birth rate of binary millisecond pulsars.
Two New T Tauri stars and a Candidate FU Orionis Star associated with Bok Globules
Authors: Yun J. L. , Moreira M.
Published: July 2016

We present photometric and spectroscopic evidence of two new T Tauri stars formed in the conditions of isolated small Bok globules. The spectral energy distributions of these objects display excess infrared emission, they are associated with optical reflection nebulae, and their optical spectra reveal Balmer emission lines and the Li I λ6707 Å absorption line. Additionnally, we report the discovery of what is likely to be a new FU Orionis star seen towards Bok globule CB34. The star is about 4 magnitudes brighter than it appears on the Palomar plates and is associated with the aggregate of young stellar objects forming in Bok globule CB34.
The Blazar Paradigm: Synchro-Compton Emission from Relativistic Jets
Authors: Marscher Alan P.
Published: July 2016

I review the current paradigm for nonthermal emission from jets in blazars. The evidence for relativistically flowing jets seems to be more compelling than the case for incoherent synchrotron and self-Compton emission in these objects. I discuss some of the important aspects of current observations of rapid variability at radio frequencies, and stress that one must be careful when calculating the Doppler factor that saves us from the inverse Compton “catastrophe.” I discuss the possibilities for the nature of the VLBI components and present evidence that, at high frequencies, the core is a standing shock wave (Mach disk), while the superluminal components are propagating shocks. I expect that high-frequency and space VLBI will resolve many of the major outstanding issues.
Structure and Properties of AGN Cores from VLBI and Total Flux Density Variations
Authors: Valtaoja Esko
Published: July 2016

By combining VLBI and total flux density data it is possible to get an indirect “look” at the innermost, unresolved core regions of AGN and to estimate physical parameters such as the intrinsic brightness temperatures, Lorentz factors and viewing angles, unobtainable by either VLBI or multi-frequency flux monitoring alone.
Relativistic Numerical Simulations of Superluminal Sources
Authors: Gómez J.L. , Martí J. Mª. , Marscher A.P. , Ibáñez J. Mª. , Alberdi A.
Published: July 2016

We study the generation and evolution of superluminal components in relativistic jets through relativistic hydrodynamical and emission simulations of a square-wave perturbation in the jet velocity.
The Magnetic Switch as the Origin of the FR I/FR II Break
Authors: Meier D.L. , Godon P. , Edgington S. , Payne D.G. , Lind K.R.
Published: July 2016

We propose that the Fanaroff & Riley division between class I and class II radio sources has its origins in the coronae of magnetized accretion disks around black holes. The “magnetic switch”, an effect that critically controls the speed of jets produced by such disks, can explain both qualitative and quantitative differences in the properties of the two classes. These include why morphology and jet speed are functions of radio power and why the division between the two classes is a strong function of galaxy optical luminosity.
Symmetric Parsec-Scale Radio Jets in NGC 4261
Authors: Jones Dayton L. , Wehrle Ann E.
Published: July 2016

VLBA observations of NGC 4261 (3C 270) reveal highly symmetric radio structures at both 1.6 and 8.4 GHz. There is little evidence for free-free absorption in the inner few pc, despite the fact that HST imaging shows this galaxy to contain a nearly edge-on disk of gas and dust in its nucleus. However, at our highest resolution we find a narrow gap in emission just east of the radio core which we interpret as evidence for a small (sub-parsec) nearly edge-on accretion disk which is obscuring the base of the counterjet. The position angle of the pc-scale radio axis agrees with the position angle of the VLA-scale jets, which differs from the apparent rotation axis of the nuclear disk seen by HST.
S5 0836+710 A Kelvin-Helmholtz Unstable Jet on Parsec Scales?
Authors: Otterbein K. , Krichbaum T.P. , Kraus A. , Witzel A. , Hummel C.A. , Zensus J.A.
Published: July 2016

The highly redshifted quasar S5 0836+710 (z = 2.172) displays an outstanding one sided jet with complex morphology. The continuous jet shows several remarkable lateral displacements (kinks) of its ridgeline on various length scales. Despite the strength of these distortions the jet is not destroyed by them and remains well collimated. We investigated the possibility to explain the displacements by Kelvin-Helmholtz instabilities.
Superluminal Motion in the Parsec-Scale Jet of 3C 380
Authors: Polatidis A.G. , Wilkinson P.N.
Published: July 2016

Multi-epoch VLBI observations of the quasar 3C 380 reveal a bent parsec-scale radio jet with complex substructure and superluminal motion out to ~100 pc from the core.
The Slow Jet in the Nucleus of 3C 84
Authors: Dhawan V. , Kellermann K.I. , Romney J.D.
Published: July 2016

We report on proper motions in the core, jet, and counter-jet of 3C 84, monitored by the VLBA at 2cm and 7mm.
First VLBA Images of the Nuclei in 3CR Lobe-dominated Quasars
Authors: Hough D.H. , Vermeulen R.C. , Readhead A.C.S.
Published: July 2016

We report the first VLBA images of the nuclei in eight objects from the 3CR complete sample of 25 lobe-dominated quasars (LDQs): 3C 207, 3C 208, 3C 212, 3C 245, 3C 249.1, 3C 263, 3C 270.1, and 3C 275.1. These images reveal core-jet structures of considerable extent and complexity. In combination with earlier VLBI work on the 3CR LDQ sample, the partial distribution of apparent parsec-scale jet speeds for ten objects is relatively flat up to ~ 5h−1c, or perhaps even ~ 10h−1c. While this is not inconsistent with simple beaming models and quasar-FR II radio galaxy unification, it is crucial to obtain the complete speed distribution for truly definitive tests. Work is in progress on multi-frequency, dual-polarization, and phasereferencing VLBA observations on selected objects in the sample.
VLBA Studies of Molecular Gas toward Centaurus A
Authors: van Langevelde Huib Jan , Beasley Anthony
Published: July 2016

We observed the four OH 18 cm transitions against the Cen A VLBI source. With high spatial resolution we detect the same molecular absorption as previously seen with ATCA. Both the excitation and VLBI absorption suggest a cloud size of ≲ 1 pc.
Probing the Accretion Region of NGC 1275 with VLBI
Authors: Walker R.C. , Kellermann K.I. , Dhawan V. , Romney J. D. , Benson J. M. , Vermeulen R. C. , Alef W.
Published: July 2016

Multi-frequency VLBA observations were used to study the magnitude and radial dependence of free-free absorption of the radio emission from the counterjet in 3C 84.
VLBA Imaging of a Large Sample of Blazars
Authors: Attridge J. M. , Roberts D. H. , Wardle J. F.C.
Published: July 2016

As part of our continuing study of parsec-scale magnetic fields in active galactic nuclei we have obtained deep polarization-sensitive images of the blazar 1055+018 with the VLBA at 5 GHz. These dramatic images reveal a magnetized layer of material on the outer surfaces of the jet, distinct from the bulk of the jet. This morphology suggests interaction of the jet with the surrounding medium, the resulting shear stretching the magnetic field lines in the direction of the flow. Further multi-frequency polarization-sensitive observations of 1055+018 offer the opportunity to study radio jet-ambient medium interactions in detail.
VLBA Monitoring of Three Gamma-Ray Bright Blazars: AO 0235+164, 1633+382 (4C 38.41), & 2230+114 (CTA 102)
Authors: Xu W. , Wehrle A. E. , Marscher A. P.
Published: July 2016

We have been monitoring gamma-ray blazars with the NRAO VLBA at 22 and 43 GHz since late 1993. We present results on three sources: AO 0235+164, 1633+382 (4C 38.41), and 2230+114 (CTA 102).
Variability of the Radio Nucleus of the Galaxy M81
Authors: Bietenholz M. F. , Bartel N. , Rupen M. P.
Published: July 2016

We report on VLA and VLBI observations of the nucleus of the nearby spiral galaxy M81. The VLA observations show the flux density of the nucleus to be variable by 50%. The VLBI observations indicate that the structure of the nucleus of M81 is somewhat variable on timescales of weeks.
VLBI Observations of Central Region in NGC 3079
Authors: Satoh Satoko , Inoue M. , Nakai N. , Shibata K. M. , Kameno S. , Migenes V. , Diamond P. J.
Published: July 2016

We present multi-frequency observations towards the nucleus of NGC 3079 using both Japan VLBI Network (J-Net) and the VLBA including phased VLA and Effelsberg. We detected two continuum components at 1.4 and 8.4 GHz, and determined the spectral indices for each component. Further, we found several H ɪ absorption features towards the continuum components whose velocity gradient is opposite to the galaxy rotation. Assuming rotation, the central mass is estimated to be 3 × 106M⊙. The water maser distribution extends in North-South direction along the galactic disk, while no clear indication of a Keplerian rotating disk was found.
Proper Motions and the Distance to a Water Vapor Maser in the Galaxy M33
Authors: Argon A. L. , Greenhill L. J. , Moran J. M. , Reid M. J. , Menten K. M.
Published: July 2016

The relative proper motions of water vapor maser features in the H ɪɪ region IC 133 have been used to determine a distance to the galaxy M33 that is independent of the usual calibrations associated with extragalactic distance estimates, e.g., extinction and metallicity.
Imaging the Surface of a Star: VLBA Monitoring of the SiO Masers around U Herculis
Authors: Diamond P. J. , Kemball A. J.
Published: July 2016

We report on 4 epochs of VLBA polarization observations of the 43 GHz, v=1, J=1–0 SiO masers in the circumstellar envelope around the Mira variable U Herculis.
Four Southern Intraday Variable Radio Sources
Authors: Kedziora-Chudczer L. L. , Jauncey D. L. , Wieringa M. H. , Reynolds J. E. , Tzioumis A. K.
Published: July 2016

This is a progress report on the ATCA IDV survey of compact, flat or inverted spectrum radio sources. We found that four sources: PKS 0405–385, PKS 1034–293, PKS 1144–397, and PKS 1519–273 out of the sample of 125 show high flux density variability on the daily timescale. The characteristics of observed IDV are discussed and we reflect on its possible origin.
Polarization Properties of Intraday Variable Blazars
Authors: Kraus A. , Krichbaum T. P. , Witzel A.
Published: July 2016

Intraday variability (IDV) is a common phenomenon within blazars, and is seen in about 30 % of all sources in this class. Here we report on IDV observations carried out with the 100m telescope of the MPIfR, especially focusing on variations of the linear polarization.
Variable Radio Sources in the GB6 Catalog
Authors: Gregory P. C. , Scott W. K. , Poller B.
Published: July 2016

We report the results of a study of the long term and short term radio variability at 4.85 GHz of sources in the GB6 catalog.
Towards an Understanding of the Galactic Distribution of Electron-Density Fluctuations
Authors: Salgado J. F. , Salter C. J. , Ghosh T. , Junor W. , Manoharan P. K.
Published: July 2016

VLBA observations of 32 compact sources within 30° ≤ ᶩ ≤ 75°, | b | < 3° are being used to test whether the galactic electron-density fluctuations contain a spiral component.
Constraints on the Evolution of Powerful Radio Sources from GPS and CSS Sources
Authors: O’dea C. P.
Published: July 2016

I present the results of a study of the global properties of combined complete samples of GPS and CSS sources. I discuss the constraints the results place on models for the evolution of these sources.
The Evolution of Compact Steep-Spectrum Sources
Authors: Jeyakumar S. , Saikia D. J.
Published: July 2016

We used our high-resolution radio images made with VLA of a large number of compact steep-spectrum (CSS) sources selected from well-defined samples of radio sources and the radio data of these samples to explore the evolution of CSSs with time. We suggest that the majority of CSSs are likely to be young sources advancing outwards through an asymmetric inhomogeneous environment to form the larger ones. We examine the symmetry parameters of both CSSs and larger sources and compare these with both analytical and numerical estimates of propagation of jets through an asymmetric environment. We also examine the consistency of CSSs with the unified scheme for radio galaxies and quasars.
Survey of Milliarcsec Structure in Eight Seyfert Galaxies: Results on NGC 1068 and NGC 4151
Authors: Roy A. L. , Ulvestad J. S. , Colbert E. J. M. , Wilson A. S. , Norris R. P.
Published: July 2016

We are surveying eight nearby Seyfert galaxies (four Sy1s and four Sy2s) that have compact radio cores, using the VLBA. We are interested in parsec-scale morphology and low-frequency absorption effects, and so are observing four frequencies (1.6, 4.8, 8.4 and 15 GHz) to get spectral-index diagnostics. In this paper, we present results on two galaxies, NGC 1068 and NGC 4151. NGC 4151 shows a curved radio jet on the sub-parsec scale, with the smallest scale structure misaligned by 55° from the jet on scales of parsecs to hundreds of parsecs. NGC 1068 contains several components in the inner tens of parsecs, with those components showing a variety of absorption and resolution effects.
Scintillation and the Vela Pulsar’s Magnetosphere
Authors: Gwinn C. R. , Britton M. C. , Reynolds J. E. , Jauncey D. L. , King E. A. , McCulloch P. M. , Lovell J. E. J. , Flanagan C. S. , Smits D. P. , Preston R. A. , Jones D. L.
Published: July 2016

Radio-wave scattering in the Vela supernova remnant acts as an imperfect lens to resolve the pulsar’s radio emission region. We use this lens to measure the pulsar’s emission region. We suggest that refraction of radiation within the pulsar’s magnetosphere is responsible for the observed size.
GRS 1915+105: Flares, QPOs and Other Events at 15 GHz
Authors: Pooley G. G. , Fender R. P.
Published: July 2016

Monitoring with the Ryle Telescope at 15 GHz of the Galactic X-ray transient source GRS 1915+105 has revealed a remarkable range of rapid and extended flares which appear to be related to the X-ray emission as recorded by the RXTE all-sky monitor. Quasiperiodic oscillations in the range 20–40 min have been found and are probably related to oscillations in the soft X-ray flux.
New Radio Observations of Circinus X-1: A Summary
Authors: Fender R. P.
Published: July 2016

New radio observations from the Australia Telescope Compact Array of the radio jet X-ray binary Circinus X-1 are summarized. Radio flux density monitoring around nearly an entire orbit is presented, confirming continued radio flaring around phase 0.1 (near periastron passage) as well as a lesser enhancement half an orbit later.
Two-Frequency VLA Monitoring of LSI+61°303 during a Full Radio Period
Authors: Paredes J. M. , Peracaula M. , Ribó M. , Martí J. , Tavani M. , Kniffen D. A. , Mattox J. R.
Published: July 2016

We report observations of the radio periodic Be X-ray binary LSI+61°303, obtained with the VLA at 3.6 and 2.0 cm during a full 26.5 d cycle. These observations were carried out in coordination with CGRO monitoring of its possible γ-ray counterpart 2CG 135+1.
First EVN Maps of 6-GHz OH Lines in Star Forming Regions
Authors: Desmurs J.-F. , Baudry A.
Published: July 2016

We have used 3 antennas of the EVN to observe in 6 star-forming regions simultaneously, and for the first time, the 2 main lines of the J=5/2 state of OH with right and left circularly polarized feeds. Maser features and Zeeman pairs are identified by searching for emission over adjacent channels, and adjacent positions (within one synthesized beam) in both polarizations after we had mapped and used one selected simple channel as a reference. The magnetic field strength is thus estimated from the Zeeman pairs identified in our OH maps. We briefly present results obtained for W3(OH), ON1, and W51.
VLBA Imaging of 12.2 GHz Methanol Masers
Authors: Ellingsen S. P. , McCulloch P.M. , Diamond P. J. , Norris R. P.
Published: July 2016

We have used the VLBA to image the 12.2 GHz (20-3−1 E) masing transition of methanol toward the massive star formation region G345.01+1.79. The maser spots are distributed in a curved structure with a near monotonic velocity distribution along the curve. The cluster of maser emission covers an area of approximately 200 milli-arcseconds in right ascension and 70 milli-arcseconds in declination.

Comparison of the positions of the 12.2 GHz methanol maser spots in G345.01+1.79 as determined from the 1995 VLBA observations with 1988 Parkes-Tidbinbilla Interferometer observations shows that the relative positions of the maser spots detected in both epochs has changed by less than 5 milli-arcseconds during that interval. Assuming a distance of 2.3 kpc to G345.01+1.79 implies an upper limit on the relative tangential velocities of the maser spots of 7 km s−1.
0″.4 BIMA Array Mapping of the 107 GHz Methanol Maser in W3(OH)
Authors: Slysh V. I. , Val’tts I. E. , Kalenskii S. V. , Larionov G. M. , Mundy L. G.
Published: July 2016

Using A-configuration of the BIMA-array with 0″.4 angular resolution maps were obtained of the 107 GHz methanol line in W3(OH). The 107 GHz masers have their counterparts in another methanol transition at 6.7 GHz. The strongest maser spots are unresolved with the BIMA-array and are less than , which corresponds to the lower limit of the brightness temperature 5×105 K. A model of Class II methanol masers emitted in the extended atmosphere of icy planets orbiting around the O-star which excites H ɪɪ region is proposed.
Link of the Hipparcos Stellar Reference Frame to the Distant Quasars
Authors: Lestrade J.-F. , Preston R.A. , Jones D.L. , Phillips R.B. , Rogers A.E.E. , Titus M.A. , Reynolds J.E. , Jauncey D.J. , Gabuzda D.C. , Rioja M.J. , Guirado J.C. , McCulloch P.M.
Published: July 2016

The link of the Hipparcos and VLBI extragalactic reference frames has been achieved with a precision of 0.0005″ in global orientation at the epoch of the catalogue (1991.25) and of 0.0003″/yr in rate of rotation by VLBI observations of 12 radio-emitting stars.
High Precision Astrometry with Closure Constraints
Authors: Ros E. , Marcaide J. M. , Guirado J. C. , Ratner M. I. , Shapiro I. I. , Krichbaum T. P. , Witzel A. , Preston R. A.
Published: July 2016

We determine the relative separations of the sources in the triangle 1803+784/1928+738/2007+777 with submilliarcsecond accuracy from global 8.4 GHz VLBI observations. We remove the ionospheric contribution to the phase-delay observable using ionospheric total electron content estimates obtained from Global Positioning System (GPS) data. The triangular geometry provides a consistency check through sky closure.
Giga-bit VLBI Data Recorder, New Concept of Formatter Independent
Authors: Nakajima J. , Koyama Y. , Sekido M. , Kiuchi H. , Hama S. , Kondo T. , Takahashi Y. , Kawaguchi N. , Chikada Y. , Miyoshi M.
Published: July 2016

A high performance VLBI recorder project using advanced digital technology started in 1995. TOSHIBA GBR 1000 and VLBI interface define 32 parallel, 32 MHz clock standard digital interface and support transparent recording/play-back to extremely high-speed digital bit stream. This is the formatter independent scientific recording bind the UTC to observed data. This highly reliable, low-bit-error-rate (10−16) recording system is also expected to be used in other scientific field. For the first example to examine the recorder performance in VLBI, we had been prepared 1024 Mbps sampler (256/512/1024 MSps, 2 bit, 4/2/1 ch). And here, an experimental giga-bit correlator specification for these VLBI acquisition system is introduced.
Gigabits XF Type Correlator
Authors: Hashimoto T. , Ozeki K. , Natori K.
Published: July 2016

The National Astronomical Observatory of Japan (NAO), has an Optical Linked VLBI Experiment Project named OLIVE that directly connects a correlation site wit h some other VLBI observation stations in network by optical fiber, and correlates in real time. 2 Gbps (1 Gsps 2-bit or 2 Gsps 1-bit) or 8 Gbps (4 Gsps 2-bit) VLBI correlator is necessary in OLIVE. We are developing Gigabits correlators (XF type) using special-purpose correlation chips developed by NAO. We have already completed the Ultra Wideband Correlator named UWBC (2 Gsps 2-bit 256 lags) of 15 baselines for the Nobeyama Millimater Array (NMA). The Nobeyama Radio Observatory (NRO) offered the common use of a new wide-band observation system to astronomers since March 1997. We consider that the 2-Gbps VLBI correlator, which is needed in the OLIVE project, is possible to manufacture. It is also possible to manufacture a 8 Gbps-VLBI correlator using the UWBC chip.
Operating a Telescope Larger than the Earth: How to Schedule the HALCA Space VLBI Mission
Authors: Meier D. L.
Published: July 2016

We outline the HALCA Space VLBI mission scheduling process, with special emphasis placed on software that decides when to observe the proposed sources and how to ensure that the highest quality science is obtained. This information will be useful to the many principal investigators whose very high resolution VLBI observations are being supported by the mission.
Comet and Asteroid Ephemerides for Spacecraft Encounters
Authors: Yeomans Donald K.
Published: July 2016

To a significant degree, the success of spacecraft missions to comets and asteroids depends upon the accuracy of the target body ephemerides. In turn, accurate ephemerides depend upon the quality of the astrometric data set used in determining the object’s orbit and the accuracy with which the target body’s motion can be modelled. Using error analyses studies of the target bodies for the NEAR, Muses-C, Clementine 2, Stardust, and Rosetta missions, conclusions are drawn as to how to minimize target body position uncertainties at the times of encounter. In general, these uncertainties will be minimized when the object has a good number of optical observations spread over several orbital periods. If a target body lacks a lengthy data interval, its ephemeris uncertainties can be dramatically reduced with the use of radar Doppler and delay data taken when the body is relatively close to the Earth. The combination of radar and optical angle data taken at close Earth distances just before a spacecraft encounter can result in surprisingly small target body ephemeris uncertainties.
Radar Contributions to Asteroid Astrometry and Dynamics
Authors: Ostro Steven J.
Published: July 2016

Almost every radar observation of asteroids has measured some characteristics of the distribution of echo power in time delay (range) and Doppler frequency (radial velocity). Such measurements, which are orthogonal to optical plane-of-sky angular astrometry, are also done in the well-known, “absolute” reference frame of the planetary ephemerides, often with fractional precision that is much finer than can be achieved with other kinds of groundbased observations; they therefore can dramatically refine orbits and ephemerides. This statement is most true for near-Earth asteroids (NEAs), which constitute the most prolifically observed radar targets and are likely to be observed in increasing abundance as instrumental capabilities improve and CCD-based, NEA search programs expand. Moreover, studies of closely approaching NEAs benefit tremendously from the inverse fourthpower dependence of echo strength on target distance. For these reasons, I devote the bulk of this paper to NEAs
The Galactic Disk Tidal Force: Simulating the Observed Oort Cloud Comets
Authors: Dybczyński P. A. , Prȩtka H.
Published: July 2016

In previous papers (Prȩtka and Dybczyński, 1994; Dybczyński and Prȩtka, 1996) we presented detailed analysis of selected examples of the long-term evolution of the orbit of Oort cloud comets under the influence of the galactic disk tidal force, as well as some statistical characteristics of the simulated observable comet population. This paper presents further improvements in our Monte Carlo simulation programme which allow us to represent in a better way the real processes of production of observable comets due to galactic perturbations.

In our second paper (Dybczyński and Prȩtka, 1996), following some other authors (see for example Matese and Whitman, 1989), we treated a comet as observable when its osculating perihelion distance decreased below some adopted observability limit (5 AU in our case). Limiting the investigation to the evolution of osculating elements allowed us to use very fast and efficient averaged Hamiltonian equations of motion in our simulation. However, further detailed analysis of the problem showed that the adopted observability definition was insufficient: what makes a comet observable is not its osculating perihelion distance but its true distance from the Sun, smaller than some adopted threshold value. It may happen that when the osculating perihelion distance is at its smallest, the comet is around its aphelion distance.
Galactic Perturbations Influence on Observability of Interstellar Comets
Authors: Prȩtka H.
Published: July 2016

Some cases of the cometary evolution from the interstellar space to the observability region due to the galactic disk perturbations are shown. Simulated parameters of potentially observable interstellar comets are presented.
Evolution of the Rotational Motion of a Planet with a Liquid core
Authors: Sidorenko V. V.
Published: July 2016

Secular changes in the rotational motion of a planet due to dissipation of energy in its core are investigated. It is assumed that the effect of a liquid core is equivalent to the action on a “frozen” planet of a special type of nonconservative torque. The Bogoliuboff-Mitropolsky method is used to explain the secular effects. The following qualitative features of the evolution of the motion are established: the fast rotation of a planet gradually becomes slower and the inclination of its equator to the orbital plane gradually increases.
Agreements and Disagreements between Theories of Rigid Earth Nutation
Authors: Souchay J.
Published: July 2016

The necessity to elaborate a theory of nutation and precession matching the accuracy of very modern techniques as Very Long Baseline Interferometry and Lunar Laser Ranging led recently to various works. We discuss here the good agreement between those related to the nutation when considering the Earth as a solid body. In comparison we show the uncertainty concerning the modelisation of the transfer function leading to theoretical determination of the nutation coefficients when including dominant geophysical characteristics.
On the Problem of post-Newtonian Rotational Motion
Authors: Klioner Sergei A.
Published: July 2016

The problems of modeling of the rotational motion of the Earth are considered in the framework of general relativity. Both, rigid and deformable bodies are discussed. Rigorous definitions of the tensor of inertia, Tisserand-like axes and the angular velocity of rotation of an extended deformable body moving and rotating in external gravitational fields are proposed in the first post-Newtonian approximation. The implications of these post-Newtonian definitions on modeling of Earth rotation are analyzed.
First Year of Observations with SOHO/EIT of the “Quiet” Sun Corona
Authors: Portier-Fozzani F. , Maucherat A.J. , EIT Team
Published: July 2016

Since January 1996 (EIT first light) the Extreme Ultraviolet Telescope aboard SOHO has produced about 20,000 wide-field images of the corona and transition regions. Four different emission lines (He II, Fe IX/X, Fe XII, Fe XV) were selected to detail morphologies of magnetic structures in the corona. They show the different structures present in the corona with information about their topologies (Neupert et al. 1998). They provide the global temperature distribution in the quiet corona in the range 0.5 to 3 × 106 K.

The evolution of the corona during the first year of the SOHO mission revealed its nonuniform aspect and the nonregularity of the appearance of new active regions. Changes observed in active regions and coronal holes (e.g., August–September 1996) showed the complex role of magnetic fields including magnetic interactions and possible reconnections needed to explain some loop morphology evolution.
NLTE Model of a Quiescent Filament
Authors: Kononovich E.V. , Gorshkov A.B. , Smirnova O.B. , Kotrč P.
Published: July 2016

The Sacramento Peak Observatory VTT Echelle Spectrograph was used to obtain high resolution spectrograms of the filament at W06° S27° observed on April 9, 1991 in hydrogen Hα, Hβ, and CaII H and λ 8498 lines. The line profiles were measured and digitized. A numerical code based on the MALI approach with partial frequency redistribution (PRD) in resonance lines was applied to obtain theoretical profiles of hydrogen and CaII lines. As a result of fitting the observed and calculated profiles, the physical parameters of the filament plasma were obtained. They include temperature, gas pressure, electron density and turbulent velocity.
Prominence Emission Lines Observed With SUMER and Two Ground-based Telescopes
Authors: de Boer C.R. , Stellmacher G. , Wiehr E.
Published: July 2016

Two sets of H, He, and Ca+ emission lines were observed in a quiescent prominence simultaneously with the VTT and the Gregory telescope on Tenerife. At the same time, SUMER took two scans of low-ionized EUV emission lines.

The emission ratios of Ca+–to–Balmer lines from ground vary little in the prominence, indicating a largely constant gas-pressure. In contrast, the ratio of He–to–Balmer from the ground shows the (known) increase toward the prominence borders, indicating higher temperature there. Similarly, the two-dimensional distributions of the ratios S IV/N II and C III/He I show pronounced bright prominence rims.

The reduced He 537Å and He 584Å line widths are 2.6 and 3.6 times larger, respectively, than those of He D3 and He 3888Å. Explaining this by the optical thickness yields τ0 = 104 and τ0 = 2 · 105 for the two EUV lines. The total He 584 emission amounts to 13 watt/m2 ster in the main prominence body where the D3 line yields 4 watt/m2 ster; existing models, however, predict a factor 0.18.

The widths of simultaneously observed optical lines with different atomic weights yield thermal and non-thermal broadening parameters of Tkin ≈ 8000 K and 2.5 < ξ < 6.5 km/s. The EUV lines, however, show line widths which correspond to much higher temperatures and non-thermal velocities. Assuming for each ion the corresponding ionization temperature, the line widths require non-thermal velocities of 15–40 km/s which is similar to values for the quiet corona.
Modelling of Non-Uniform Prominence Slabs
Authors: Heinzel P. , Anzer U.
Published: July 2016

We present new slab models for quiescent prominences in which both the condition of magnetohydrostatic equilibrium as well as NLTE are fulfilled. Using the Kippenhahn-Schlüter model, a unique relation between the components of the magnetic field on one hand and the gas pressure and width on the other is established for a given uniform temperature. We construct a grid of such NLTE models and compare them with the set of isothermal-isobaric models of Gouttebroze et al. (1993).
Spectroscopic Study of a Quiescent Prominence
Authors: Park Y.D. , Yun H.S. , Ichimoto K. , Sim K.J. , Moon Y-J.
Published: July 2016

We have analyzed a set of spectra of Hα and CaII H & K lines taken from a quiescent prominence with the G1 CCD camera attached to a 25 cm coronagraph at the Norikura Coronal Station, the National Astronomical Observatory of Japan. From these lines we have determined temperature, turbulent velocity and electron density at various locations on the prominence. The final analysis shows that the averaged temperature of the prominence is about 8600K with mean turbulent velocity of 7.5 km/s and with a mean electron density of < ne > = 2.4×1010cm−3.
Stability of an Idealised Equilibrium Model of Prominences in Rapidly-Rotating Stars
Authors: Ferreira Miguel
Published: July 2016

We study the stability of an idealised model of stellar prominences. We find that surface fields of a few hundred gauss are required to hold them in a stable equilibrium.
Analysis of Hα Observations of High Altitude Coronal Condensations
Authors: Allen U.A. , Bagenal F. , Hundhausen A.J.
Published: July 2016

Preliminary analysis of Hα images of high-altitude coronal condensation known as “coronal spiders” is presented. The kinematics of material seen draining from the coronal spiders are also studied. An estimate of the mass of the object for a range of electron temperatures and electron densities is obtained.
Hα Observations of the Dual Eruptive Prominences of June 29, 1994
Authors: Lenža L.
Published: July 2016

Our results in the field of observing prominences at our observatory show dual eruptive prominences on June 29, 1994 obtained by a coronograph at our observatory at Valašské Meziříčí. We tracked the evolution of these eruptive prominences in time and morphology.
On the Eruption of Prominences and Disappearance of Quiescent Filaments
Authors: Gupta S.S. , Singh Jagdev
Published: July 2016

The analysis of an eruptive prominence and disappearing quiescent filaments indicates that the prominence height on the limb increases after the filament develops a twist as seen in the Hα on the disc. The increase in prominence height, large change in the shear angle, and the appearance of filament as a U-shaped structure before the disappearance of the filament or prominence eruption can be explained by assuming that the middle portion of the filament rises above the solar surface with its edges anchored in the chromosphere. Further, the loop-like structure of the filament splits into two parts 2–3 days prior to its disappearance and the gap between the two increases with time. The increasing gap and simultaneous disappearance of both parts of the filament suggests that heating of the top of the loop-like structure begins about 2 days before its disappearance. The cause for this portion of the filament not being visible in Hα may be that it is heated to a high temperature.
On a Possible Mechanism of Quiescent Prominence Destabilization
Authors: Nenovski P. , Dermendjiev V.N. , Madjarska M.S. , Vial J.-C.
Published: July 2016

The possibility of multiple reflections generating standing surface wave modes carrying field-aligned current (FAC) in an arch-like prominence structure is studied. The conditions for enhancement of FAC leading to observable destabilising effects are specified.
Filament Disparition Brusque and CME – September 25–26, 1996 Event
Authors: van Driel-Gesztelyi L. , Schmieder B. , Aulanier G. , Démoulin P. , Martens P.C.H. , Zarro D. , DeForest C. , Thompson B. , Cyr C.St. , Kucera T. , Burkepile J.T. , White O.R. , Hanaoka Y. , Nitta N.
Published: July 2016

During the September 1996 campaign of multi-wavelength observations with the SOHO (SUMER, CDS, EIT, MDI, LASCO) and Yohkoh (SXT) spacecraft, the HAO Mauna Loa Solar Observatory Chromospheric Helium Imaging Photometer and the Nobeyama radioheliograph, a filament disparition brusque (DB) associated with a Coronal Mass Ejection (CME) was observed. The timeline of this complex event, which lasted for tens of hours, shows that the CME had started before the DB of a filament, while the main “bubble” of the CME was probably launched hours after the DB from the so-called “zipper” region. All these suggest that a general reorganization of large-scale fields was taking place on the Sun, and both the DB and the CME were symptoms of this.
Soft X-Ray Observations of Eruptive Prominences
Authors: Watanabe T. , Yamamoto M. , Hudson H. , Irie M. , Ichimoto K. , Kurokawa H. , Yatagai H.
Published: July 2016

Evolution of magnetic structures in the region around an eruptive prominence of August 28, 1992 are examined using soft X-ray images obtained by Yohkoh. The eruption was preceded by the appearance of a large-scale soft X-ray jet which was ejected from near the root of the southern end of the prominence. Changes of magnetic geometry at the southern end of the prominence appeared to trigger the eruption. In the course of prominence eruption, helically twisted soft X-ray loops were observed around the prominence. This indicates that magnetic reconnection of a sheared arcade took place underneath the erupting prominence.
New Evidence of Chromospheric Evaporation
Authors: Kašparová J. , Kotrč P. , Heinzel P. , Nikulin I.F. , Rudawy P.
Published: July 2016

Hα spectra obtained at Sternberg Astronomical Institute in Moscow during the gradual phase of the flare on May 16, 1981 are analysed. The flare-ribbon profiles show a red asymmetry of the emission peaks, and we interpret this as an absorption in the blue wing of the profile due to expected upflows. We demonstrate a good correlation between the observed Hα profiles and those computed with the flare model Fl and upflows reaching 10 km s−1.
The Present and Future of the Prominence Observations at Valašské Meziříčí Astronomical Observatory
Authors: Lenža L. , Dokoupilová D.
Published: July 2016

This observatory is not a large institution, though we do carry out long term photographic monitoring of prominences. Our intention is to inform everybody about our observation programmes, the quality of our observations, our archive and the possibilities for its use.

We present examples of our photographic observations, an electronic archive of observation intervals and events, a prominence catalogue, and we discuss possible future co-operation.
Development of an Instrument Based on a Fibre-Bonded CCD Camera for Prominence Observations
Authors: Verma V. K. , Uddin Wahab , Gaur V.P.
Published: July 2016

We have devloped and tested an instrument based on a fibrebonded CCD camera for observations of solar prominences. To record faint prominences we have used a solid aluminized glass cone which reflects bright solar disc light outside the telescope tube. The prominence monitor is installed at the back end of a 15-cm f/15 coude refractor telescope after the H-alpha filter. This prominence monitor is capable of recording prominence images at an interval of 5 sec, but during prominence eruptions it can record images at an interval of 2 sec.
Doppler Detection of Extrasolar Planets
Authors: Marcy G. W. , Butler R. Paul , Fischer D. A.
Published: July 2016

We have measured the radial velocities of 540 G and K main sequence stars with a precision of 3−10 ms−1 using the Lick and Keck échelle spectrometers. We had detected 6 companions that have m sin i < 7 MJup. We announce here the discovery of a new planet around Gliese 876, found in our Doppler measurements from both Lick and Keck. This is the first planet found around an M dwarf, which indicates that planets occur around low-mass stars, in addition to solar-type stars. We combine our entire stellar sample with that of Mayor et al. to derive general properties of giant planets within a few AU of these stars. Less than 1% of G and K main sequence stars harbor brown dwarf companions with masses between 5 and 70 MJup. Including Gliese 876b, 8 companions exhibit m sin i < 5 MJup which constitute the best planet candidates to date. Apparently, 4% of stars have planetary companions within the range m sin i = 0.5 to 5 MJup. Planets are distinguished from brown dwarfs by the discontinuous jump in the mass function at 5 MJup. About 2/3 of the planets orbit within just 0.3 AU due in part to their favorable detectability, but also possibly due to a real “pile up” of planets near the star. Inward orbital migration after formation may explain this, but the mechanism to stop the migration remains unclear. Five of eight planets have orbital eccentricities greater than that of our Jupiter, eJup = 0.048, and tidal circularization may explain most of the circular orbits. Thus, eccentric orbits are common and may arise from gravitational interactions with other planets, stars, or the protoplanetary disk. The planet-bearing stars are systematically metal-rich, as is the Sun, compared to the solar neighborhood.
Radial Velocity Variations of the Rapidly Oscillating Ap Star 33 Lib
Authors: Hatzes A. P. , Kanaan A. , Mkrtichian D.
Published: July 2016

We present precise stellar radial velocity (RV) measurements of the rapidly oscillating Ap (roAp) star 33 Lib taken in rapid succession over a 3-hr time span. A Fourier analysis of the data clearly shows the 8.2 min. pulsation period found previously by photometric investigations and gives a peak-to-peak (2K) amplitude of about 80 ms−1. We find, like in other roAp stars we have studied, that the RV amplitude depends on the spectral region used for measuring the pulsational RV amplitude and is as high as 57 ± 4.7 ms−1 in the region 5411–5500 Å and as low as 7 ± 3 ms−1 in the 5877–5976 Å region. An analysis of individual spectral lines show considerable scatter in the RV amplitude, ranging as high as 320 ms−1 and as low as 7 m−1. There is an overall trend of increasing RV amplitude with decreasing line strength. We also found that spectral lines due to nickel have a higher mean RV amplitude than chromium lines. We believe that the line strength variations result from the vertical atmospheric structure of the pulsations and that the elemental differences are related to the inhomogeneous distribution of elements known to occur on Ap stars. Precise stellar radial velocity studies of roAp stars may be a powerful tool for studying both the spatial (surface) and vertical structure to the pulsational velocity field.
Precise Velocity Observation of K-giants: Evidence for Solar-Like Oscillations in Arcturus
Authors: Merline W. J.
Published: July 2016

High accuracy measurements of variations in the radial velocity of the K1 giant star Arcturus have been obtained. The observations span 5 years and have a point-to-point repeatability of 5 ms−1 and night-to-night stability of better than 20 ms−1. Velocity oscillations of Arcturus were discovered during the course of this work in 1986. Subsequent, extensive additional data, indicate that Arcturus is exhibiting global nonradial acoustic oscillations with characteristics similar to those occurring in the Sun.

All observations were done using a radial velocity spectrometer, designed to search for extrasolar planets, at a dedicated facility of the University of Arizona on Kitt Peak. A dedicated facility was crucial to this work — because of the changing nature of the oscillations, many observing runs, over several years, were required to understand the star’s behavior. Continuous data sets as long as 30 days were acquired. Preliminary pulsation models were performed in collaboration of Art Cox at Los Alamos National Lab.

The velocity power spectra are complicated and variable. There is substantial evidence that the variations are solar-like p-mode oscillations. At least 10 frequencies have been identified, over the range 8.3 to 1.7 days. A spectrum of evenly spaced modes is apparent, yielding a value for Δν0 ≈ 1.2 μ Hz. The average power spectrum peaks near 3 days. There is a broad envelope of power with a distribution reminiscent of that seen in the Sun. Both the mode spacing and the period of peak power are consistent with scaling from the Sun (Kjeldsen & Bedding 1995). The oscillations appear to undergo abrupt discontinuities and have phase coherence times of a few weeks. We interpret the driving to be due to stochastic excitation by convection.

Recent observations of the G5 IV star η Boo by Brown et al. (1997) have failed to confirm the detection of p-mode oscillations reported by Kjeldsen et al. (1995) Thus, Arcturus may be one of the first stars known to exhibit solar-like oscillations. If other K-giant variables can be shown to exhibit similar oscillations, Arcturus may represent the prototype for a new class of variable stars. We know some other K-giants are variable on short time scales (Hatzes and Cochran 1994b; Edmonds & Gilliland 1996), but many are not (Horner 1996).
Radial Velocity Variations from Starspots
Authors: Hatzes Artie P.
Published: July 2016

In this contribution the radial velocity (RV) variations expected for starspots on solar-type stars are examined. The spot-induced RV amplitude is found to vary linearly with spot filling factor and is less than 1 m−1 for spot sizes comparable to large sunspots and as high as 20 m s−1 for spot filling factors of 1%. Also, for a given spot size the RV amplitude increases linearly with υ sin i. All of these findings confirm the results of Saar & Donahue (1997). It is also shown that two spectral lines with different temperature sensitivity can have different RV amplitudes which may provide a diagnostic for confirming planet detections. The RV variations due to starspots correlate well with the displacement of the line core and centroid and this can be used to correct RV measurements for the effects of cool starspots.