bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractWe 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.
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

AbstractSimultaneous 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

AbstractIt 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.
A Model of Plasma Sheets in Equilibrium
Authors: Koutchmy S. , Molodensky M. , Vibert D. 
Published: July 2016

AbstractWe 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

AbstractWe 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

AbstractWe 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

AbstractThe 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

AbstractWe 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.
Evidence of Prominences on Cool Late-type Stars
Authors: Byrne P.B. , Eibe M.T. , van den Oord G.H.J. 
Published: July 2016

AbstractWe 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

AbstractA 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

AbstractA 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

AbstractFilaments 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

AbstractThe 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

AbstractA 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

AbstractSolar 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

AbstractThe 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

AbstractWe 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.
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

AbstractResults 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

AbstractContinuing 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

AbstractNearly 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

AbstractHigh 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

AbstractThe 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

AbstractWe 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

AbstractPrecise 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

AbstractWe 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.