bluuebunny/crossref_metadata_2025_split huggingface dataset:
Filament Channels: Contrasting Their Structure in Hα and He I 1083 nm
Authors: Harvey Karen L. , Gaizauskas Victor 
Published: July 2016

AbstractFrom a direct comparison, we find that filament channels are more easily detected in He I λ1083 than in Hλ, particularly for polar crown filaments. He I 1083 nm filament channels appear to coincide with the outer boundaries of Yohkoh/SXT X-ray cavities.
Force-Free Models of a Filament Channel in which a Filament Forms
Authors: Mackay D.H. , Gaizauskas V. , Priest E.R. 
Published: July 2016

AbstractOver the years few examples of the formation of filament channels or filaments have been observed. One such example was recently seen by Gaizauskas et al. (1997). This paper constructs force-free models of the main stages of formation.
Helical Structure in an Eruptive Prominence Related to a CME (SUMER, CDS, LASCO)
Authors: Kucera T.A. , Poland A.I. , Wiik J.E. , Schmieder B. , Simnett G. 
Published: July 2016

AbstractSOHO (SUMER/CDS) observed an eruptive prominence on May 1,1996, associated with a CME observed by LASCO. We investigate the physical conditions of this prominence in order to quantify velocity, temperature, and density. SUMER spectra in Si IV and O IV lines are used to obtain Doppler-shift images of the prominence. The prominence shows large-scale red and blueshifted regions, revealing a large helical structure with a global twist. In addition, fine structure analysis shows multiple components in the line profile, suggesting integration of many threads along the line-of-sight with a large dispersion of velocities (±50 km s−1).
Horizontal Expansion of Eruptive Prominences
Authors: Rompolt Bogdan 
Published: July 2016

It is well known that quiescent prominences (QPs) as well as active region prominences (ARPs) occasionally undergo eruptions. The process of eruption of these prominences is caused by eruption of a huge magnetic system (HMS) associated with the prominence channel and the prominence itself (Rompolt 1984). Material of these prominences is frozen-into only a part of such a magnetic system – before as well as during the eruption. When an HMS erupts it simply lifts with it the frozen-in prominence material.Usually during the eruption a large part of the prominence material is lifted high into the corona and/or into interplanetary space. Nevertheless, on some occasions during the eruption a significant part of the original prominence material flows down to the chromosphere (Rompolt 1990).
Radio and X-ray Investigations of Erupting Prominences
Authors: Gopalswamy N. , Hanaoka Y. , Lemen J.R. 
Published: July 2016

AbstractProminence eruption is one of the most important solar phenomenon because of the possibility of using it as proxy of geoeffective solar disturbances. In a series of investigations using Nobeyama radio observations in conjunction with Yohkoh data we have found that there is more to a prominence eruption than the simple picture portrayed by Hα observations. The extent of coronal volume associated with the eruption is much larger than the prominence. We illustrate this with several examples and discuss the implication of the results for understanding the interplanetary manifestation of coronal mass ejections.
Digital “Cartes Synoptiques de la Chromosphere Solaire et Catalogues des Filaments et des Centres d’Activite”
Authors: Coffey Helen E. , Hanchett Christine D. 
Published: July 2016

AbstractAlmost 70 years ago Lucien d’Azambuja published the first “Cartes Synoptiques de la Chromosphere Solaire et Catalogue des Filaments de la Couche Superieure” (d’Azambuja 1928), a compendium of reduced solar observations covering the time period March 1919–January 1920. The compiled database gives both visual and quantitative measures of solar activity beginning with Carrington rotation 876. Since then, data through 1989 have been published in succeeding Cartes Synoptiques issues. The World Data Center A (WDC-A) for Solar-Terrestrial Physics has digitized several long term solar publications, including the numerical text portion of the Cartes Synoptiques. We present an overview of this extraordinary historical solar database. WDC-A is using current technology to meet user requirements for data management, analysis and distribution, has compiled over 100 Megabytes of historical solar data and made it available over the Internet as part of a continuing data rescue effort. The data can be accessed via the World Wide Web at http://www.ngdc.noaa.gov/stp.
Application of the Telluric-Line Technique to Study Late-Type Stars for Radial-Velocity Variations
Authors: Greimel Robert , Yang Stephenson L.S. 
Published: July 2016

AbstractAlthough the use of telluric lines as wavelength fiducials to measure radial velocities does not achieve as high a precision as other fiducial-imposition techniques, this very convenient technique can be used concurrently with other observing programs to increase the temporal sampling of target stars. We have been carrying out a program to monitor the line-profile variations of early-type non-radial pulsators at the Hα and He I 667.8-nm region. With the rather modest reciprocal dispersion of 1nm/mm and the use of a 4096-element CCD, the telluric lines in the 630-nm region are also available in the observed spectra. We decided to use these telluric lines as wavelength fiducials to monitor bright, latetype stars for radial-velocity variations. As an experiment, we have also decided to reduce the spectra using available simple IRAF tasks to see how high a velocity precision can be achieved with only minor tweaking. The precision certainly would not rival other precise techniques, but the convenience in both the observing and reduction procedure may enable more target stars to be monitored by more observers. Moreover, interesting results can still be obtained with a mere 100 m/s precision. The result for a few late-type stars which also have prior HF velocities will be presented.
Limitations of Precise Radial Velocity Measurements in Pulsating Stellar Atmospheres
Authors: Vinkó J. , Kaszás G. , Kiss L. L. 
Published: July 2016

AbstractWe study the velocities of specific stellar absorption lines of Cepheid-type variable stars determining line bisector velocities from newly obtained high-resolution echelle spectra. We compare these velocities with recent CORAVEL measurements of Cepheids to reveal systematic differences of 2 – 3 kms−1.
Radial-velocity Variations of Late-type Variables
Authors: Yang Stephenson L.S. , Walker Gordon A.H. , Larson Ana M. 
Published: July 2016

AbstractLow-amplitude, radial-velocity variations of bright late-type stars were monitored at the 1.2-m telescope of the Dominion Astrophysical Observatory (DAO) with the hydrogen fluoride (HF) absorption-cell technique. Many of the stars appear to be semi-regular red variables (SRb and SRc) and irregular red variables (Lb). The radial-velocity amplitudes range from a few tens of meters per second to a few kilometers per second while the timescales of the variations appear to range from a few tens of days to a few hundreds of days. These irregular-looking velocities are analysed for multiperiodicities. There are also variations in the chromospheric Ca II 8662 index for a few of the variables.
Future Directions for Radial-Velocity Research
Authors: Latham David W. 
Published: July 2016

AbstractI review the status of ground-based radial-velocity searches for extrasolar planets and speculate about the new results that can be expected in this field over the coming years. Then I review the plans for astrometric space missions and speculate about the impact that these missions will have on ground-based radial-velocity work, citing the specific examples of extra-solar planet research, the mass-luminosity relation for M dwarfs and metal-poor stars, and Galactic structure and evolution.
Radial Pressure in the Solar Nebula as Affecting the Motions of Planetesimals
Authors: Whipple Fred L. 
Published: July 2016

In the classical rotating Laplacian-type nebula, pressure gradients can develop radially to the protosun because of central radiation, particle ejection, and magnetic-field expansion or because of radial temperature or total gas density gradients. Except for the last two effects, the acting central acceleration for the gas is reduced from the gravitational value; the pressure gradient in the gas caused by temperature or density gradients may either add to or subtract from the gravitational acceleration, depending on the sense of the pressure gradient. Planetesimals in the nebula may thus experience tangential accelerations (+ or —) with respect to the gas because of the differential radial accelerations acting on the particles and the gas. As a consequence, the planetesimals may spiral outward or inward with respect to the protosun. The present paper deals with growing planetesimals and a range of drag laws depending on the Reynolds number and on the ratio of particle size to mean free path.Particles spiral in the direction of positive pressure gradient, thus being concentrated toward toroidal concentrations of gas. The effect increases with decreasing rates of particle growth, i.e., with increasing time scales of planet formation by accretion. In the outer regions, where evidence suggests that comets were formed and Uranus and Neptune were so accumulated, the effect of the pressure gradient is to clear the forming comets from those regions. The large mass of Neptune may have developed because of this effect, perhaps Neptune’s solar distance was reduced from Bode’s “law,” and perhaps no comet belt exists beyond Neptune. In the asteroid belt, on a slow time scale, the effect may have spiraled planetesimals toward Mars and Jupiter, thus contributing to the lack of planet formation in this region.
Infrared Emission from Barred Spiral Galaxies
Authors: Hawarden Tim G. , Huang J. H. , Gu Q. S. 
Published: July 2016

AbstractAmongst relatively undisturbed spiral galaxies of type ≤ Sc barred morphology is unquestionably associated with powerful mid- and Far-IR emission. On the other hand, even amongst early type galaxies, those with LFIR/LB < 1/3 exhibit no association of high relative FIR luminosity with barred morphology, but some association of IR colors resembling those of star formation regions (SFRs). Amongst systems with LFIR/LB < 0.1 this ratio may be anti-correlated with barredness. It appears that enhanced IR emission from those galaxies whose star formation rate is currently elevated by the the bar translates them into the group with higher FIR-to-optical luminosity ratios. Depletion of extended nearnuclear gas and dust, once the bar has swept up the currently-available supplies, may reduce the fraction of the background stellar radiation field which can be converted to FIR radiation in the inner, most luminous parts of the galaxy. Thus, after the starburst has subsided, such galaxies may be less FIR-luminous than unbarred systems. Several uncertainties remain: it is still not clear whether barred morphology is a necessary condition for the generation of a starburst in an otherwise undisturbed galaxy, while evidence as to the effect of differing bar strengths is conflicting.
A Nuclear Ring in the Sa(r!) Galaxy NGC 7742
Authors: Wakamatsu K. , Hamabe M. , Nishida M. T. , Tomita A. 
Published: July 2016

NGC 7742 is well known for its prominent blue nuclear ring around an EO-like core, and so appears as a Hoag-type galaxy, an elliptical galaxy with an outer ring (Schweizer et al. 1987). The galaxy is classified as Sa(r!) in the Revised Shapley-Ames Catalog (Sandage and Tammann 1987) with an exclamation mark to emphasize the prominence of the ring. Its photographs are published in Laustsen et al. (1987), Wray (1988), and Sandage & Bedke (1994).The ring has a diameter of 19″ = 1.6 kpc at a distance of 17.1 Mpc (Buta & Crocker 1993), and so should be a nuclear ring of the galaxy. Nuclear rings and pseudorings are often detected in strongly barred (SB) galaxies, and interpreted to be linked to the inner Lindblad resonance (Buta & Crocker 1993). These nuclear features are, however, also found in some weakly-barred (SAB) and non-barred (SA) galaxies. NGC 7742 is a galaxy of the highest circular symmetry in its core, ring, and main body, and so the best object for a detailed study of formation mechanisms of nuclear rings in non-barred galaxies.
O/H Abundances in the Ringed Galaxy NGC 4736: Mixing Processes in the Interstellar Medium
Authors: Martin P. , Belley J. 
Published: July 2016

AbstractImaging spectrophotometry in the main nebular lines has been performed on 65 H ɪɪ regions in the ringed galaxy NGC 4736. O/H abundances were derived using the line ratios [O ɪɪɪ]/Hβ and [N ɪɪ]/[O ɪɪɪ] calibrated by Edmunds & Pagel (1984). We show that the O/H scatter in the resonance ring of star forming regions is small, no greater than normally expected in the well-mixed ISM of disks of gas-rich galaxies. The global O/H gradient (−0.046 dex/kpc) in the disk of NGC 4736 is shallower than gradients of normal spirals but comparable to gradients observed in weakly barred spirals. This last result could indicate that radial mixing is or was present in NGC 4736. The oval distortion in the central regions can be responsible for this homogenization but it is also possible that a strong bar was present in the past.
H II Region Statistics in Barred and Non-Barred Galaxies
Authors: Rozas M. , Beckman J. E. , Knapen J. H. 
Published: July 2016

AbstractWe present new high quality Ha continuum-subtracted images of the grand design galaxies NGC 157, NGC 3631, NGC 6764, and NGC 6951, two of them barred and two non-barred, and describe the statistical properties of the HII regions. We have determined the positions, angular sizes and fluxes of individual HII regions, and construct luminosity functions and diameter and density distributions. We find no significant differences between arm and interarm HII region properties, or between the barred and non-barred galaxies. This paper summarizes work described in more detail by Rozas et al. (1995a,b)
A Search for Symmetries in the Star Formation Patterns of Spiral Disks: Barred Galaxies
Authors: Rozas M. , Beckman J. E. , Knapen J. H. 
Published: July 2016

AbstractThe Hα brightness distribution of a face-on galaxy is a classical representation of the massive star formation rate per unit surface area. Here, we present a test for the degree of symmetry in this distribution, aimed at deciding whether this parameter shows a significant difference between barred and non-barred galaxies. The test consists in deriving the cross-correlation function of the Hα brightness as a function of curvilinear distance along pairs of opposed arms. In order to use the test, we first apply a geometrical unfolding technique. Here we explain this technique, and present the initial results of applying the test to NGC 157 and NGC 6764.
Study of the Gas Kinematics in the Center of the Barred Spiral Galaxy NGC 4258.
Authors: Dodonov S. N. 
Published: July 2016

AbstractIntegral Field Spectrograph observations of southeast (SE) gas outflow in the center (11×13 arcsec) of NGC 4258 with spatial sampling 0.6 and 1.2 arcsec were made with the 6-m Telescope. Reconstructed spatial and kinematic structure of the SE outflow from 20-30 pc to 200-220 pc are presented.
The Extent of The HI Halo in Five Isolated SB Galaxies
Authors: Kristen H. , Jörsäter S. 
Published: July 2016

AbstractWe investigate the extent of the HI halo in five isolated SB galaxies featuring strong bars. VLA1 observations of these objects are used to determine the diameter ratio between the HI and the optical distribution. The mean diameter ratios D1.82/D(0) and DHI/D(0), for the sample presented here, are 1.1±0.1 and 1.2±0.1 respectively (1σ r.m.s.). For samples of various types, Bosma (1981) and Broeils (1992) find D1.82/D(0) = 2.2±1.1 and DHI/D(0) = 1.8±0.4 respectively. Our result thus could indicate compactness of the HI halo in galaxies with strong bars.
Photometry and Kinematics of the Ringed Barred Galaxy NGC 3081
Authors: Purcell Guy B. , Buta R. 
Published: July 2016

AbstractWe present a preliminary analysis of B- and I-band CCD images and Rutgers imaging Fabry–Perot Hα interferometry of the galaxy NGC 3081. We find that the outer R1 and inner ring are both intrinsically oval. We derive a bar pattern speed from the velocity field.
Bar Destruction Mechanism by External Interactions
Authors: Nishida M. T. , Wakamatsu K. 
Published: July 2016

AbstractTo investigate bar destruction by a vertical head-on galaxy encounter, the dynamical evolution after the instantaneous momentum change of the impulsive approximation of a vertical head-on galaxy encounter, and the instability of finite amplitude one-armed perturbations to barred structure, are investigated by 2-dimensional N-body simulations.Preliminary results show that off-center vertical head-on collisions induce bar destruction but collisions in which the colliding galaxy passes through the very center of the target galaxy do not induce bar destruction.
Multiple Gas Rings in SA Galaxies
Authors: Palouš J. , Jungwiert B. 
Published: July 2016

Rings are frequently observed in barred galaxies (e.g. Buta & Crocker 1993). Their origin is attributed to gas accumulation near resonances, which is due to a combination of the gravitational torques of a bar component acting on inelastically colliding clouds: outer rings are presumably associated with the Outer Lindblad Resonance (OLR), inner rings with the 4/1 resonance, and nuclear rings with the Inner Lindblad Resonance (ILR).However, multiple rings are also observed in normal non-barred, or not obviously barred galaxies (e.g. NGC 7217, Verdes-Montenegro et al. 1995) so that we may ask what is the mechanism of their formation. We argue in this contribution that even a very weak bar or a triaxial distortion in the galaxy center, which would hardly be identified from observations, leads to long-lasting ring-like distributions of gaseous clouds. The formation time-scales of rings associated with different resonances are similar in our model so that all types of rings can coexist in galaxies with a high degree of axial symmetry in their central parts, such as SA galaxies.
Secondary Bars and Triaxial Bulges within Primary Bars
Authors: Friedli Daniel 
Published: July 2016

AbstractNumerous galaxies clearly show two misaligned nested stellar bars or one bar plus one structure with twisted isophotes. Some galaxies seem even to have three distinct triaxial structures. Recent optical and near-infrared multi-band observations show that the angle between the primary and secondary bars does not take any peculiar value. The best way to reconcile such observations with theory certainly consists in postulating that the secondary bar rotates faster than the primary one. Numerical simulations have demonstrated the viability of such systems, and both direct and counterrotating models with bars within bars can be computed. Bar-within-bar systems could play a significant role in fueling AGN’s and/or circumnuclear starbursts, since AGN’s and/or blue or Hα nuclear rings are frequently hosted by such galaxies.
A Survey of Orbits in 2D N-body Bars
Authors: Sundin M. 
Published: July 2016

AbstractA barred galaxy is mainly built of billions of stars moving on different orbits. Understanding of the orbital structure is essential for the interpretation of observations. The orbital structure can be investigated using analytical models and N-body simulations. This paper presents a method to classify orbits found in N-body simulations, i.e. orbits in a time-dependent potential. I present some results about mass loss and mass gain of bars and the influence of a bulge.
Observational Evidence for a Bar in the Milky Way
Authors: Kuijken Konrad 
Published: July 2016

AbstractEvidence from a variety of sources points towards the existence of a bar in the central few kpc of the Galaxy. The measurements roughly agree on the direction of the bar major axis, but other parameters (axis ratio, size, pattern speed) are still poorly determined. Current dynamical models are limited by the quality of hydro simulations, the degeneracy of stellar orbit models, stellar-kinematic data and the significant lopsidedness of the central kpc. Microlensing promises new constraints on the mass distribution in the bulge/bar region.
Gravimetric and Astrogeodetic Reference Systems in Space and Time
Authors: Moritz H. 
Published: July 2016

AbstractThis paper is concerned with conceptual aspects of terrestrial reference systems to be used in connection with gravimetric and astrogeodetic methods. Two principal kinds of reference systems are discussed: natural coordinates, based on the gravity field (geoid and plumb lines), and geodetic coordinates, which numerically approximate the natural coordinates but are based on a reference ellipsoid instead of the geoid and are, therefore, directly related to spatial rectangular coordinates.The discussion includes temporal variations due to Earth tides, and problems posed by the definition of the origin because of polar motion and by the change of station position due to plate motion, etc., as well as questions raised by the definition of reference ellipsoids, including effects of the atmosphere. A final section deals briefly with references for gravity observations.
Coordinates Used in Range or Range-Rate Systems and Their Extension to a Dynamic Earth
Authors: Newton R. R. 
Published: July 2016

AbstractThis paper describes briefly the coordinates that have been used with satellite systems that measure range or range-rate, and it shows that the methods previously used to define them lead naturally to the coordinate system needed for a dynamic Earth. This is one in which the Earth has no linear momentum and no angular momentum, and it is the only system that allows the motion of the Earth to be separated into a translation, a rotation, and an internal motion, and that preserves the usual forms of the equations of motion. The observations needed to define this system are outlined.
Geodetic and Astrometric Results of Very Long-Baseline Interferometric Measurements of Natural Radio Sources
Authors: Moran J. M. 
Published: July 2016

AbstractThe technique of very long-baseline interferometry, initially developed in 1967 to study the angular structure of compact radio sources on the order of a thousandth of a second of arc, has been used to measure to great accuracy geometric quantities of geodetic and geophysical importance. The baseline vector between various radio telescopes has been measured to an accuracy of about 1 m (the accuracy of the measurement of the length of the baseline vector is better than 50 cm). Variations in UT1 have been measured to an accuracy of 1 msec, polar motion to 500 cm, and the coordinates of radio sources to about 0.1 ardsec. Improvement of about 1 order of magnitude is expected in the next 5 years. The major work has been done by three groups: the Massachusetts Institute of Technology/National Aeronautics and Space Administration group; the Jet Propulsion Laboratory group; and the National Radio Astronomy Observatory/California Institute of Technology group. The results available in June 1974, the factors limiting their accuracy, and the prospects for the future are discussed in this paper.
Prospects for Rapid Realization of a Quasi-Earth-Fixed Coordinate System
Authors: Bender P. L. 
Published: July 2016

AbstractIt appears that a combination of VLBI, lunar ranging, and satellite ranging can provide a quasi-Eiarth-fixed coordinate system with high accuracy and good coverage more rapidly than any one technique alone. In considering this possibility, the conceptual separation of the job into two parts seems useful. There are: 1) establishment of a global network of at least three fundamental reference points on major plates, and 2) the determination of a larger number of regional reference points of geodynamic interest. The example of lunar ranging plus satellite ranging is used to illustrate one way in which an accurate realization of an initial terrestrial system could be achieved quickly.