bluuebunny/crossref_metadata_2025 huggingface dataset:
Toward a Trigonometric Parallax of Sgr A*
Authors: Reid M. J. , Readhead A. C. S. , Vermeulen R. C. , Treuhaft R. N.
Published: July 2016

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

From three VLBA observations at 5 GHz, spanning 13 months, we have measured the trigonometric parallax of Sco X-1 of 0.23 ± 0.28 mas; hence its distance is > 1300 pc. This supports the hypothesis that the the x-ray luminosity is near the Eddington Limit.

All three VLBA observations show a radio core of flux density 0.5 mJy and size < 4 mas. However, the third VLBA observation revealed two additional radio components, separated by 12 mas (≈ 20 au) on opposite sides of the radio core. The evolution of these new components is unknown until additional observations can be made. The relative luminosity and separation of the two radio components are inconsistent with the Doppler beaming of two identical ejecta from the radio core.
Deceleration in the Expansion of SN 1993J
Authors: Marcaide J. M. , Alberdi A. , Ros E. , Diamond P. , Shapiro I. I. , Guirado J. C. , Jones D.L. , Mantovani F. , Pérez-Torres M. A. , Preston R. A. , Schilizzi R. T. , Sramek R. A. , Trigilio C. , Van Dyk S.D. , Weiler K. W. , Whitney A. R.
Published: July 2016

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

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

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

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

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

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

We describe a space VLBI experiment involving an earth-orbiting satellite (SURFSAT) and simulated satellites, a space VLBI ground tracking station, an array of ground radio telescopes, and a space VLBI correlator. The purpose of this experiment was to provide as complete as possible an end-to-end simulation of space VLBI in preparation for the first space VLBI mission, VSOP, and in particular to test the most critical aspect of space VLBI, viz. the ability to generate a stable and accurate frequency standard (clock) for the orbiting VLBI element.
Lunar Motion: Theory and Observations
Authors: Chapront Jean , Chapront-Touzé Michelle
Published: July 2016

Results of several fits of the lunar theory ELP 2000–82B and of Moons’ theory of libration are presented. The theories are fitted both to JPL numerical integrations and to LLR observations.
Hyperion as a Dust Source in the Saturnian System
Authors: Banaszkiewicz Marek , Krivov Alexander V.
Published: July 2016

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

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

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

The study of lunar rotation has attracted considerable interest with the advent of the epoch of exploration of the Solar system by space technology. A series of works on an investigation of the lunar gravitational field carried out with the help of artificial lunar satellites have greatly advanced our possibility for that study. The problem concerning the landing on the lunar surface of spacecraft, and the creation of durable lunar bases, impose heavy demands on the accuracy of theoretical description of orbital and rotational motion of the Moon.

The development of the observational technology with the help of radio-and laser ranging (LLR) provides at the present time measurements of the distance to a given point on the Moon with an accuracy of about 2 cm, probably improved in the future to about 5mm (Banerdt, 1995). By using differential VLBI measurement with extragalactic radio sources angularly near the Moon, it should be possible to obtain routine estimates of angular position of the beacon to 0.1 mas from each observation (Baudry, 1995). Therefore, combining VLBI and LLR techniques will provide a means of achieving new objectives, and that calls for the development of the theories adequate to an accuracy for observations.
A New Nutation Series for a Rigid Earth Model
Authors: Hartmann Torsten , Soffel Michael
Published: July 2016

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

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

In this paper a new method of construction of the perturbation motion theory of celestial bodies, based on the averaging principle in view of frequency resonances, is stated. The first approximation of the asymptotic theory is the exact solution of the dynamics averaging equations, in which are included “secular” and “long-periodic” terms. The high-degree approximations are the exact solution of a known Krylov-Bogoliubov generalized equation. It is shown that these iterations are expressed in the analytical form by multiple Fourier series.
Integration of Orbital Motions with Chebyshev Polynomials
Authors: Barrio Roberto , Elipe Antonio
Published: July 2016

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

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

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

The accurate positions of extragalactic radio sources are in use to link the radio and fundamental reference frames and contribute to determining relative orientation of HIPPARCOS and the radio reference frames as well as HIPPARCOS and FK5. Catalogues of intermediate stars chosen in the vicinity of extragalactic radio sources are an important part of the link and can be used for extension and densification of the HIPPARCOS frame. The description of main catalogues of intermediate stars is given. Results of investigation and comparison beetween CAMC, RRS2, PIRS and CRIS are presented.
Observations of Saturn’s Inner Satellites During the August 1995 Ring-Plane Crossing
Authors: Poulet F. , Sicardy B. , Beuzit J.L. , Prado P.
Published: July 2016

We present observations of Saturnian inner satellites, Janus, Epimetheus, Pandora and the new objects 1995S5 and 1995S6. Data were obtained with the COME-ON+ adaptive optics system mounted on the 3.6-m telescope of the European Southern Observatory, during the 10 August 1995 Earth crossing. During this time, the usually bright rings become faint, an ideal time to study the small inner satellites. Two unresolved objects have been detected. They have been identified with the objects 1995S5 and 1995S6, which have been detected on frames obtained with the Hubble Space Telescope, more than one day later. Astrometric reductions relative to the brighter satellites and the Cassini division yield planetocentric positions with accuracies of 015 and 026, respectively. These measurements, combined with the HST data, and the NIR photometric parameters point to the possible transient character of these objects, and provide a more accurate solution for the 1995S5 orbital parameters.
First Results of the PHESAT95 Campaign of Observation of the Phenomena of the Satellites of Saturn
Authors: Arlot J.-E. , Thuillot W. , Colas F. , Vu D.T. , Berthier J. , Descamps P. , Ruatti CH.
Published: July 2016

From 1992 to 1999, the satellites of Saturn are involved in several phenomena: eclipses or occultations by the planet, transits in front of Saturn, or transits of their umbra. These phenomena occur thanks to the geometrical circumstances in 1995 when the Earth and the Sun went through the plane of the Saturnian ring and consequently through the orbital planes of the main satellites. These circumstances are also favorable to the observation of mutual phenomena occurring when the satellites eclipse or occult each other. These mutual phenomena and the eclipses by Saturn are rare as they occur only every 15 years. But, they are very useful to get highly accurate astrometric observations and they allowed us to estimate some physical parameters. We have organized the PHESAT95 campaign to observe these phenomena and a special effort was made to observe as many events as possible. At the present time, the observations are still being collected from different teams and different countries; this paper shows the first results which have been obtained in several sites, and the first comparison with the theory of the motions.
EUV and Microwave Observation of a Filament
Authors: Chiuderi-Drago F. , Bocchialini K. , Lamartinie S. , Vial J.-C. , Bastian T. , Alissandrakis C.E. , Harrison R. , Delaboudinière J.-P. , Lemaire P.
Published: July 2016

Simultaneous XUV and microwave (μ – ѡ) observations of a solar filament, performed by several instruments onboard SOHO and by the Very Large Array (VLA), are analyzed. The filament appears as a dark structure, very similar in shape to the optical Hα filament, in all images taken in the transition region (TR) lines observed by CDS, in the Ne VIII lines observed by SUMER at λ = 770Å and 780Å and at all radio wavelengths with 1.7 cm ≤ λ ≤ 6 cm. Contrary to that, in six TR lines observed by SUMER at λ > 1300Å no trace of the filament, either in absorption or in emission, is visible. Finally, at λ = 21 cm, as well as in all images taken in coronal lines by CDS and EIT, a dark feature is present at the filament position, although with less defined contours than in the first-mentioned TR images. The constraints imposed by all these observations are discussed and interpreted.
3-D Twisted Flux-Tube in a Linear Force-Free Equilibrium
Authors: Aulanier G. , Démoulin P.
Published: July 2016

It is now commonly accepted that prominence plasma is supported in magnetic dips, in particular in twisted flux tubes. But present two-dimensional models are unable to explain the observed presence and structure of prominence feet. This requires three-dimensional models. We modelled the field using linear force-free field equations. Combining a small number of harmonics, and using observational constraints, we have found the area in the parameter space where prominences are likely to be present. Then, adding 3-D harmonics, we show that feet appear periodically underneath the prominence body. For great helicity, the parameter space is mostly fulfilled by configurations which have feet alternating between both sides of the prominence axis, as observed. The lateral feet are formed by dips in the vicinity of small magnetic polarities, that are located in a low field corridor where the prominence stands. The modelled configurations show in a natural fashion many observational aspects of prominences, such as the vector magnetic field measurements in prominences and the chirality patterns.
Nonstationary Electric Drifts in the Solar Atmosphere
Authors: Veselovsky I.S.
Published: July 2016

Induced electric fields and nonstationary drift motions are considered. Nonstationary electric drifts may be important in erupting prominences, rising and shrinking coronal loops, and other phenomena in the solar atmosphere. Theoretical limitations are indicated for the concept of dominant plasma motions along magnetic field lines.
A Model of Plasma Sheets in Equilibrium
Authors: Koutchmy S. , Molodensky M. , Vibert D.
Published: July 2016

We consider large coronal streamers as confined thin plasma sheets overlying the filament and/or the magnetic polarity inversion lines. Confirmation is found in recent synoptic LASCO/SOHO data and simulations. We discuss the 3D axi-symmetric consistent MHD solution which provides the necessary properties of confinement and equilibrium by including gravity forces in the Grad-Shafranov equation.
Infrared Doppler Oscillations in a Solar Filament
Authors: Molowny-Horas R. , Oliver R. , Ballester J.L. , Baudin F.
Published: July 2016

We present the results of a high spatial resolution investigation of Doppler oscillations in a solar filament, using the He I 10830Å infrared line. Fourier power spectra of Doppler shifts reveal the presence of periodic signals. Two features, showing oscillations at 2.7 min and 12.5 min, have been studied. The use of the so-called wavelet analysis enables us to estimate the size of both features at 2.7 arc sec and 4.75 arc sec, respectively. Their approximate lifetimes are 10 min and 20 min.
Prominence Oscillations and the Influence of the Distant Photosphere
Authors: Schutgens N.A.J. , Kuperus M. , van den Oord G.H.J.
Published: July 2016

We model vertical prominence dynamics, describing the evolution of the magnetic field in a self-consistent way. Since the photosphere imposes a boundary condition on the field (flux conservation), the Alfvén crossing time τ0/2 between prominence and photosphere has to be taken into account. Using an electrodynamical description of the prominence we are able to compare two basic prominence models: Normal Polarity (NP) and Inverse Polarity (IP).

The results indicate that for IP prominences, the stability properties are sensitive to ωτ0 (ω: oscillation frequency of prominence). For ωτ0 ≳ 1 instability results. Forced oscillations of five minutes are efficiently excited in IP prominences that meet certain criteria only. NP prominences on the other hand, are insensitive to the Alfvén crossing time. Forced oscillations of five minutes are difficult to excite in NP prominences.
Linear Waves in Force-Free Fibrils
Authors: Zhugzhda Y.D.
Published: July 2016

The advanced thin flux tube approximation for force-free thin magnetic flux tubes is used to derive a dispersion relation for linear waves. All wave modes appear to be coupled in a twisted flux tube. In the case of a weakly twisted flux tube, it has been found that torsional Alfvén waves have dispersion and produce pressure and temperature fluctuations. The effect of tube rotation is pointed out. These properties of linear waves have an impact on prominence oscillations.
2-D Radiative Transfer Simulations with Angle-Dependent Partial Frequency Redistribution
Authors: Gorshkov A.B. , Heinzel P.
Published: July 2016

We demonstrate how the angle-dependent redistribution function can be incorporated into the 2-D transfer modelling of solar prominences. Some preliminary numerical simulations have been performed and we present their results by comparing the emergent hydrogen Lα line profiles computed with the angle-averaged and angle-dependent redistributions.
Evolution of Complex Filaments
Authors: Dumitrache Cristiana
Published: July 2016

This study focusses on the less studied aspects of filaments evolution: the coupling of two or more filaments to form a complex filament and also the split of one such filament into many components. This phenomenon was first observed by d’Azambuja – we apply statistical mathematical methods to obtain evolutionary sequences and detect the complex filaments.
Evidence of Prominences on Cool Late-type Stars
Authors: Byrne P.B. , Eibe M.T. , van den Oord G.H.J.
Published: July 2016

We review the observed characteristics of co-rotating clouds of neutral hydrogen recently detected in rapidly rotating, chromospherically active late-type stars and commonly termed “stellar prominences”. Their observed properties are placed in an overall interpretive framework and compared to standard solar prominences.
Magnetic Field Reconnection in the Hα Eruptive Prominence on September 18, 1995
Authors: Karlický Marian , Kotrč Pavel , Šimberová Stanislava , Knížek Miloslav , Varady Michal
Published: July 2016

A violent evolution of the September 18, 1995 eruptive prominence is studied. The fast changes of the prominence structure started immediately after a weak radio burst on 3 GHz indicating the presence of non-thermal processes. A comparison with Yohkoh soft X-ray pictures was made. A detailed analysis of observations indicates magnetic field line reconnection, mainly in the space below the rising Hα prominence. The reconnection processes are manifested by structural changes of the Hα prominence and X-ray loops and also by the character of Doppler velocities in the Hα spectrum formed close to the reconnection space.
MHD Simulation of Dark Filament Eruption in the Quadrupole Source Model
Authors: Uchida Y. , Hirose S. , Cable S. , Uemura S. , Fujisaki K. , Torii M. , Morita S.
Published: July 2016

A magnetohydrodynamic simulation in a 2.5D approximation is performed for the quadrupole source model for arcade flares treated years ago by Uchida (1980), and recently supported by the observations from Yohkoh. It is shown that this model can explain several key characteristic features of arcade flares found by Yohkoh, and can avoid some of the paradoxes existing in the “classical model”.
Filaments and the Solar Dynamo
Authors: Seehafer N.
Published: July 2016

Filaments are a global phenomenon and their formation, structure and dynamics are determined by magnetic fields. So they are an important signature of the solar magnetism. The central mechanism in traditional mean-field dynamo theory is the alpha effect and it is a major result of this theory that the presence of kinetic or magnetic helicities is at least favourable for the effect. Recent studies of the magnetohydrodynamic equations by means of numerical bifurcation-analysis techniques have confirmed the decisive role of helicity for a dynamo effect. The alpha effect corresponds to the simultaneous generation of magnetic helicities in the mean field and in the fluctuations, the generation rates being equal in magnitude and opposite in sign. In the case of statistically stationary and homogeneous fluctuations, in particular, the alpha effect can increase the energy in the mean magnetic field only under the condition that also magnetic helicity is accumulated there. Generally, the two helicities generated by the alpha effect, that in the mean field and that in the fluctuations, have either to be dissipated in the generation region or to be transported out of this region. The latter may lead to the appearance of helicity in the atmosphere, in particular in filaments, and thus provide valuable information on dynamo processes inaccessible to in situ measurements.
The Skew of Polar Crown X-ray Arcades
Authors: McAllister A.H. , Hundhausen A.J. , Mackay D. , Priest E.
Published: July 2016

The one-to-one relationship between the chirality of filament channels and the skew (relative orientation) of the overlying coronal arcades can be coupled with the predictions for the axial component of polar crown filaments based on past magnetic field observations to predict the skew of polar crown arcades in the recent cycle 22. We have surveyed the actual skew as seen in the Yohkoh SXT images over the declining phase of cycle 22 and found a result opposite to that expected. The SXT arcades have been compared with numerical models to show that while some of this result can be explained by flux distribution around switchbacks, other mechanisms such as differential rotation are also needed.
Are All Prominences Either Sinistral or Dextral?
Authors: Zirker J.B. , Leroy J.-L. , Gaizauskas V.
Published: July 2016

A reanalysis of the prominence magnetic field measurements obtained by Leroy et al. (1983) indicates that only a small fraction of these prominences did not obey the chirality rules they discovered and that Martin et al. (1994) confirmed.
LASCO/EIT Observations of Coronal Mass Ejections from Large-Scale Filament Channels
Authors: Plunket S.P. , Dere K.P. , Howard R.A. , Michels D.J. , Brueckner G.E. , Thompson B.J. , Delaboudinière J.-P.
Published: July 2016

Solar activity in the latter half of 1996 was dominated by the presence of an extended filament channel in the southern hemisphere, forming a switchback configuration where it merged with the polar crown. Several large coronal mass ejections (CMEs) were observed to originate on or near this magnetic neutral line by the LASCO and EIT instruments on SOHO. As this channel gradually disappeared, a new, extended channel formed to the west of the old one, and this new channel also produced a number of large CMEs. We report here on observations of two events (December 23, 1996 and February 7,1997), and discuss the global nature of these events.
Astrometric versus Spectroscopic Radial Velocities
Authors: Dravins Dainis , Gullberg Dag , Lindegren Lennart , Madsen Søren
Published: July 2016

The apparent radial velocity of a star, as deduced from wavelength shifts, comprises not merely its true velocity, but also components arising from dynamics in the star’s atmosphere, gravitational redshift, and other effects. For the Sun, such phenomena can be segregated since the relative Sun-Earth motion is known from planetary system dynamics. This is now becoming possible also for other stars, whose true radial motions are determined through space astrometry. A study of the differences between accurate astrometric velocities (from Hipparcos), and precise spectroscopic values (from ELODIE) is in progress. Data for cool stars in the Hyades indicate a tendency of relative blueshifts among earlier main-sequence F-type stars, and in giants. This is theoretically expected: an increased convective blueshift due to the more vigorous convection in F-stars, and a decreased gravitational redshift in giants.
Steps Towards Absolute Accuracy In Radial Velocities
Authors: Gullberg Dag
Published: July 2016

We are developing methods to reach high absolute accuracy in spectroscopic radial velocities for stars of different spectral types. The basic idea is to remove the effects from convection and surface gravity that cause large systematic errors, in order to improve the absolute accuracy of radial velocities by one order of magnitude. This paper briefly describes observations and methodology in computing the radial velocities.
Characterizing the Nearby Solar-Type Stars
Authors: Soderblom D. R. , King J. R.
Published: July 2016

We present a brief discussion of solar-type stars, what is known about them, why they are ideal targets for precise radial-velocity observations, and some open questions.
The ESO Precise RV Survey for Extra-solar Planets: Results from the First Five Years
Authors: Kürster M. , Hatzes A. P. , Cochran W. D. , Dennerl K. , Döbereiner S. , Endl M.
Published: July 2016

Results are presented from the first five years of the high precision RV survey carried out with the 1.4m CAT+CES spectrograph at ESO La Silla. This RV survey of 37 solar-type stars was begun in Nov. 1992. Using an iodine gas absorption cell for self-calibration we currently achieve a long-term precision of 20 m/s in a 30-min exposure of a 5.5 mag star. This value is the typical ‘working’ precision in survey work, i.e. an average over all observing conditions.

We present the RV data for our most variable star, ι Hor (G0V), with a possible periodicity of 600 d that could imply a companion of minimum mass m sin i = 2.0 MJup. However, these data are severely complicated by stellar activity to which a large part of the variability must be attributed. Our RV data for ϕ2 Pav (F8V) contain a possible period of 43 d which would imply a planet with m sin i = 0.69 MJup. It must be stressed that for both stars the significance of the periods is still insufficient to conclude that planets are indeed orbiting them. We also show our data for a Hipparcos astrometric brown dwarf candidate, GJ 570A, that do not confirm expectations for a correspondingly high RV signal. Longer monitoring of the star is required in order to confirm a possible low amplitude variation.
The Planet Orbiting ρ Coronae Borealis
Authors: Noyes R. W. , Contos A. R. , Korzennik S. G. , Nisenson P. , Brown T. M. , Horner S. D.
Published: July 2016

Continuing precise radial velocity observations of ρ Coronae Borealis have allowed the determination of updated parameters of the 40-day orbit of its Jupiter-mass companion. This confirms the previously reported period and amplitude, and shows a small but marginally significant non-zero eccentricity. It also provides improved predictions for the times of possible transit of the companion in front of the star. The new data provide upper limits to the mass of a possible second companion to the system. The orbital parameters are discussed in the light of scenarios for the origin and migration of extra-solar giant planets.
The Puzzling K and Early-M Giants: A Summary of Precise Radial Velocity Results for 15 Stars
Authors: Larson Ana M. , Yang Stephenson L. S. , Walker Gordon A. H.
Published: July 2016

Nearly a decade ago, “yellow giants” were introduced as a new class of low-amplitude radial-velocity variable stars. In this report we discuss new results for 12 spectral type K and early-M giants based on long-term monitoring using both the hydrogen-fluoride and iodine-cell techniques. We compare these results with those of published data for 3 additional stars (ϒ Cephei, β Geminorum, and β Ophiuchi), and discuss possible implications for the underlying physical mechanism(s).
High precision radial-velocity measurements of late-type evolved stars
Authors: Cummings I.N. , Hearnshaw J.B. , Kilmartin P.M. , Gilmore A.C.
Published: July 2016

High dispersion spectra for 44 southern evolved stars of spectral type K or M have been obtained. From these observations relative radial velocities of 50 m/s precision have been obtained by the method of digital cross-correlation. This method of achieving precise relative radial velocities for late-type stars, and the problems encountered in its use, are discussed. Using this method, statistically significant radial-velocity variations have been found. Two of the observed stars have their precise radial velocities presented and the potential mechanisms of their variation examined.
Differential Fe I Line Shifts as Convective Signatures in R = 40 000 Échelle Spectra?
Authors: Gullberg Dag
Published: July 2016

The convection in stellar atmospheres causes spectral lines to be more or less blue-shifted. The differential wavelength shift between two groups of spectral lines could be used to characterize the convection. This paper describes such an effort using cross-correlations between R ≈ 40 000 échelle spectra and laboratory wavelength templates.
Radial Velocities of Visual and Interferometric Binaries
Authors: Scarfe C.D. , Barlow D.J.
Published: July 2016

We discuss the use of precise radial velocities for orbit studies of binary stars. Although they are desirable to achieve highly accurate masses for systems of large amplitude, their greatest value will be for systems of long period and low amplitude. These studies require high spectrograph stability, and in some cases resolution of the spectra may prove troublesome. Radial velocities must be combined with visual or interferometric observations for mass determination, since eclipsing binaries of long period are rare, but the number of resolved spectroscopic systems is increasing.

We review observational requirements, reduction techniques, and methods of solving for elements that satisfy simultaneously the observations in three dimensions, based on experience with radial velocities whose precision is near the lower limit for this Colloquium, obtained over the past 35 years with the Dominion Astrophysical Observatory (DAO) coudé spectrograph, and consider the gains that should be achievable over similar intervals in the future, by means of higher precision in all the relevant data. We discuss, from our own experience, the reasons why no masses have yet been determined by these methods, to an accuracy better than 2%.
α Centauri revisited: when the spectroscopic and the astrometric mass ratios become consistent
Authors: Pourbaix D.
Published: July 2016

Precise radial velocities lately published (Murdoch, Hearnshaw & Clark 1993) allow a simultaneous least-squares adjustment of all visual and spectroscopic observations. Starting with the same data as Murdoch & Hearnshaw (1993), we obtain a mass ratio that agrees better with Kamper & Wesselink’s (1978) astrometric estimate. Our results suggest upward revisions of the distance to the system as well as of the individual masses of the components.
Imaging and Modeling of Double Stars with the Navy Prototype Optical Interferometer: a Continuation of the Mark III Double Star Program
Authors: Hummel Christian A.
Published: July 2016

We present results from the new Navy Prototype Optical Interferometer (NPOI) – the orbit of the double star Mizar A and measurements of Matar – which are compared to an orbit determined with the predecessor of NPOI, the Mark III Interferometer. Uncertainties of the orbital inclination are between 0.1 and 0.3 degrees; those of the semi-major axis are less than 0.5 percent. We determine the component masses and other parameters of the double star system, including relative photometry, directly through a fit to a combination of interferometric and spectroscopic data. Algorithms were developed to handle any hierarchical stellar system.

We describe plans for the study of spectroscopic double stars with NPOI, which draw from our experience with the Mark III binary program. This program yielded orbits of 26 stars, of which 17 were published with mass determinations of 24 components using spectroscopy. The accuracy of the physical parameters were often limited by the spectroscopy. We show that in order to benefit from the high precision of the interferometric observations, new high-precision spectroscopic observations, combined with improved algorithms for the detection of the secondaries, are required.
Mass Influx Obtained from Low-Light-Level Television Observations of Faint Meteors
Authors: Naumann Robert J. , Clifton K. Stuart
Published: July 2016

Since the advent of low-light-level television (LLLTV) systems, it has been recognized that such devices offer the ability to observe meteors as faint as 10th magnitude which allows the extension of optical meteor data to masses as small as 10-4 gram. The Space Sciences Laboratory at Marshall Space Flight Center has been actively engaged in such observations using image orthicons and intensified SEC vidicons.

The results of these observations are presented along with an interpretation in terms of mass-flux. This interpretation includes the development of a relationship between peak luminosity of a meteor and mass, velocity, and zenith angle that was derived from single body meteor theory and compares favorably with results obtained from the Artificial Meteor Program. Also included in the mass-flux interpretation is an analysis of the observation response of a LLLTV system to fixed and moving point sources.
Determination of Meteor Parameters Using Laboratory Simulation Techniques
Authors: Friichtenicht J. F. , Becker D. G.
Published: July 2016

Atmospheric entry of meteoritic bodies is conveniently and accurately simulated in the laboratory by techniques to be described which employ the charging and electrostatic acceleration of macroscopic solid particles in the 0.02 to 1 μ diameter range. Velocities from below 10 to above 50 km/s are achieved for particle materials which are elemental meteoroid constituents (e.g.: Fe, Si, Mg) or mineral compounds with characteristics similar to those of meteoritic stone (e.g.: FeTiO3). The velocity, mass, and kinetic energy of each particle are measured nondestructively, after which the particle enters a target gas region. Because of the small particle size, free molecule flow is obtained at target pressures ≦ 10 torr. At typical operating pressures (0.1 to 0.5 torr), complete particle ablation occurs over distances of 25 to 50 cm; the spatial extent of the atmospheric interaction phenomena (luminous trails, ionized wakes, etc.) is correspondingly small, simplifying many experiments. Procedures have been developed for measuring the spectrum of light from luminous trails and the values of fundamental quantities defined in meteor theory: heat transfer coefficient λ, drag coefficient Γ, ionization probability β, and photographic luminous efficiency τpg. Results of these measurements are presented, with emphasis on recent, improved evaluations of τpg and β over wide velocity ranges; it is shown that the laboratory values of τpg for iron are in excellent agreement with those for 9 to 11 km/s artificial meteors produced by rocket injection of iron bodies into the atmosphere. Also discussed in some detail is the relevance of these measurements to the interpretation of meteor observations and the methods of inferring from them numerical values of τpg and β for natural meteors.
Spectral Analysis of Four Meteors
Authors: Harvey Gale A.
Published: July 2016

Four meteor spectra from the NASA LRC Faint Meteor Spectra Patrol are analyzed for chemical composition and radiative processes. The chemical compositions of the Taurid, Geminid, and Perseid meteors were found to be similar to that of a typical stony meteorite. The chemical composition of the sporadic meteor was found to be similar to that of a nickel-iron meteorite. The radiation from optical meteors (+ 1 to —10 absolute photographic magnitude) was found to be similar to that of a low-temperature gas, except that strong, anomalous ionic radiation is superposed on the neutral radiation in bright (< — 3 mag), fast meteors.
An Unusual Meteor Spectrum
Authors: Cook A. F. , Hemenway C. L. , Millman P. M. , Swider A.
Published: July 2016

An extraordinary spectrum of a meteor at a velocity of about 18.5±1.0 km s-1 (approximate uncertainty) was observed from the Springhill Meteor Observatory with an image-orthicon camera at 1970 August 10 d2h 48m 518 UT. The radiant of the meteor was at an altitude of about 49°. It was first seen shoioing a yellow-red continuous spectrum alone at a height of 137±8 km (estimated uncertainty) which we ascribe to the first positive group of nitrogen bands. At 1.608 after its initial appearance the meteor had descended to 116±6 km above sea-level when it brightened rapidly from its previous threshold brighness into a uniform continuum. After a further 0.738 at a height of 106±6 km the D-line of neutral sodium appeared and 0.148 later (height 105±5 km) all the other lines of the spectrum also appeared. The continuum remained dominant to the end 0.408 later (height 87±5 km) or 3.878 after initial appearance.

Water of hydration and entrained carbon flakes of characteristic dimension about 0.2 micron or less are proposed as constituents of the meteoroid to explain these phenomena.
Origin and Evolution of Recent Leonid Meteor Showers
Authors: McIntosh Bruce A.
Published: July 2016

The four most prominent returns of the Leonid shoiver in the past decade fall into two broad classes. The 1966 and 1969 showers were of short duration, had a high proportion of small particles, and occurred with the longest apparent delay after the perihelion passage of the parent comet Temple-Tuttle. By contrast, the 1961 and 1965 returns were of long duration, and had more large particles. The 1961 return preceded the comet.

There are three major influences on particle orbits: ejection velocity, radiation pressure, and close encounters with planets. The observations are explainable in a qualitative way on the basis of the first two. But some speculation concerning the results of planetary perturbations must be invoked.
Cosmic Dust in the Atmosphere and in the Interplanetary Space at 1 AU Today and in the Early Solar System
Authors: Fechtig H.
Published: July 2016

Reliable measurements of cosmic dust abundances have been obtained by ionization detectors during particle impact and by collectors controlled either by inflight shadowing or by penetration-hole identification. A description of the techniques used is given.

Crater-number densities observed on the lunar surface and on lunar samples represent an important source of information on cosmic dust fluxes. The related results from the Apollo 11 and 12 missions are reviewed. The overall knowledge gained from these measurements leads to the following flux model: The cumulative flux Φ vs mass m follows the extrapolation from larger meteoroid-size range (Watson’s Law) and can be described by

The Pioneer 8 dust experiment and lunar samples indicate a depletion of the flux at approximately 10-8g. However, cosmic dust particles exist in interplanetary space at least down to 0.3 μ. diameter. They are interpreted as nonmetallic particles in the solar system.

The atmosphere shows an enhancement in particles of about one order of magnitude compared to the flux in interplanetary space at 1 AU. No depletion or cutoff could be detected. These particles are interpreted as lunar debris or as disintegrated products from fireballs.

The numbers of large lunar craters (>140 m diameter) in Mare Tranquillitatis and in Oceanus Procellarum are compared with the meteoroid flux. These comparisons lead to a time-variable flux of Φ.e-Bt, with B = 2.6 and t = time in 109 yr. Thus, the meteoroidflux at the formation of the lunar maria was approximately 4 orders of magnitude higher than today.
Possible Evidence of Ablation on Cosmic Dust Particles
Authors: Hemenway Curtis L.
Published: July 2016

Öpik (1937) and Whipple (1950) have predicted that small dust particles should be able to enter the Earth’s atmosphere without reaching their melting temperature and thus retain their original shape prior to entry. They have shown that the critical size is a strong function of velocity as well as the physical parameters of the dust particle. A number of investigators have collected particles at high altitude believed to be of this type (Hemenway and Soberman, 1962; Wright and Hodge, 1964; Thomsen, 1963). This brief paper presents possible evidence of the existence of small bodies collected with our Sesame collector (Hemenway et al., 1967; Hemenway et al., 1971) which apparently were sufficiently large to experience surface ablation and melting.
Ablation in Meteors
Authors: Lebedinets V. N.
Published: July 2016

Photographic and Radar Observations of meteors reveal essential discrepancies from the simplest physical theory of meteors. The simplest theory (Whipple, 1943; Herlofson, 1948; Kascheev et al., 1967) proceeds from the following suppositions: (1) the meteoroid is a dense non-fragmenting body; (2) the sole ablation mechanism is evaporation; and (3) the whole energy transferred to a body by colliding air molecules is spent on evaporation. In addition, the simplest theory of radiowave reflection from meteor trails that does not take into account diffusive and thermodiffusive expansion of a meteor trail and change of the electron line density along the trail is used for the interpretation of the results of radar observations.