bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Dynamic Dextral-Sinistral Model for the Structure and Evolution of Prominence Magnetic Fields
Authors: Priest E.R. 
Published: July 2016

AbstractWe propose the following coherent model for prominences.(i)They are composed of many fine threads whose mass we suggest has two kinds of origin. Some of the mass may be lifted from the upper photosphere in response to cancellation of magnetic flux in small flux tubes. If this rate of mass supply is slow then the mass needs to be supported, but if the mass supply rate is as large as the natural rate of draining then no support is necessary. However, much of the mass may not need to be supplied or supported at all, if it comprises dynamic threads of cool plasma that are in pressure balance with their hot surroundings and are continually forming from the corona and heating up again in response to a localised heating mechanism.(ii)The overall structure is of a large-scale flux tube along the polarity inversion line with an overlying arcade that links the network on either side of the filament channel. The structure of the channel and of barbs is explained by the distribution of flux sources along the channels, with majority polarity producing plagettes and minority polarity the barbs.(iii)The chirality of polar-crown prominences is suggested to be caused by a combination of subsurface flows, flux emergence and reconnection. By contrast, two generic types of low-latitude filament, namely those associated with unipolar flux tongues and with the emergence of new active regions near to remnant regions, are a natural consequence of nonuniform flux distribution and converging flux.
The fiber-fed spectrograph, a tool to detect planets
Authors: Queloz D. , Casse M. , Mayor M. 
Published: July 2016

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

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

AbstractWe discuss non-spectroscopic (astrometric) ways to determine radial velocities and their potentials in future astrometric missions. Radial-velocity accuracies are presented, based on Hipparcos parallax and proper motion data for several open clusters.
Determination of Broadening Functions using the Singular Value Decomposition (SVD) Technique
Authors: Rucinski Slavek 
Published: July 2016

AbstractThe cross-correlation function (CCF) has become the standard tool for extraction of radial-velocity and broadening information from high resolution spectra. It permits integration of information which is common to many spectral lines into one function which is easy to calculate, visualize and interpret. However, the CCF is not the best tool for many applications where it should be replaced by the proper broadening function (BF). Typical applications requiring use of BFs rather than CCFs involve finding locations of star spots, studies of projected shapes of highly distorted stars such as contact binaries (as no assumptions can be made about BF symmetry or even continuity) and [Fe/H] metallicity determinations (good baselines and avoidance of negative lobes are essential). It is stressed that the CCFs are not broadening functions. This note concentrates on the advantages of determining BFs through the process of linear inversion, preferably accomplished using the singular value decomposition (SVD). Some basic examples of numerical operations are given in the IDL programming language.
Distinction between Extra-solar Planets and Low-mass Secondaries
Authors: Mazeh Tsevi 
Published: July 2016

AbstractThis paper discusses the distinction between extra-solar planets and low-mass secondaries, in principle as well as in practice. Adopting a distinction based on the presumed different processes of formation, the paper compares the characteristic features of the giant planets in our solar system with those of the low-mass secondaries in spectroscopic binaries. The discussion reveals that there is no a priori obvious feature that can identify planets. Instead, this work considers the extremely small emerging population of discovered extra-solar planets. Based on the nine “planet-candidates” discovered as of mid-1998, it was found that their mass distribution is remarkably different from the distribution of low-mass secondaries. The transition between the two populations probably occurs at 10−30 Jupiter masses. This transition could reflect the borderline between planet and brown dwarf secondary masses.
Radial Velocity Observations of Non-radially Pulsating Stars
Authors: Hatzes A. P. , Kanaan A. , Mkrtichian D. 
Published: July 2016

AbstractThe rapidly oscillating Ap stars (roAp) are a class of nonradially pulsating stars oscillating in low-degree modes with periods of 4–15 minutes. We have started a program to study the oscillations on several roAp stars using precise radial velocity (RV) measurements. The typical mean RV amplitude for the roAp stars we have observed is 50–400 ms−1, but this amplitude depends on the spectral region used for the measurement of the RV amplitude. A detailed line-by-line analysis reveals that the pulsational amplitude depends not only on atomic species, but on the line strength as well. For a given atomic species weak spectral lines exhibit a pulsational amplitude 10–100 times higher than for strong lines. The elemental effect can be understood in the context of the inhomogeneous distribution of elements known to occur on these stars and that is believed to result from the global dipole magnetic fields that are present. For instance, if an element is concentrated near the magnetic pole then it may have a higher RV amplitude than one that is distributed about the magnetic equator. The line strength effect is interpreted as arising from vertical structure to the pulsations since weaker lines are formed, on average, deeper in the atmosphere than stronger lines. Precise RV measurements may prove to be a powerful tool for probing both the vertical and horizontal structure of the pulsations in roAp stars.
Possible Detection of p-mode Oscillations on Procyon
Authors: Barban C. , Michel E. , Martic M. , Schmitt J. , Bouchy F. , Lebrun J.C. , Connes P. , Bertaux J.L. , Baglin A. 
Published: July 2016

AbstractWe have observed Procyon with the fiber-fed échelle spectrograph ELODIE coupled with a Fabry-Perot etalon at the 193-cm of the Observatoire de Haute Provence (France) over 5 nights during 1997 December – 1998 January. Here, we present the results of a search for solar-like oscillations on this star and the performance of this instrumentation for asteroseismology. The power spectra show an excess of signal between 0.42 mHz and 1.46 mHz, which could be due to stellar oscillations.
A Program for the Analysis of Long-Period Binaries: The Case of ϒ Delphini
Authors: Irwin Alan W. , VandenBerg Don A. , Larson Ana M. 
Published: July 2016

AbstractBinary systems can be analyzed like clusters but with additional constraints from the orbit. The theories of stellar interiors and atmospheres are used to analyze the color-magnitude diagram and spectra to test the consistency of theory and observation and also to provide results on the distance, chemical composition, age, and individual masses, radii, and effective temperatures. Given the total mass resulting from the theoretical analysis, it is possible to determine the complete orbit of even long-period binaries if at least 6 components of the position, velocity and acceleration vectors have been observed.For this paper we apply such a theoretical and orbital analysis to the ϒ Delphini binary consisting of a K1 IV primary (ϒ2 Del) and an F7 V secondary (ϒ1 Del). The primary has been observed with the preciseradial-velocity (PRV) technique and shows a radial acceleration of 2.2 ± 0.7 m s−1 yr−1 as well as a significant (false alarm probability < 0.01) periodic signature (P = 1.44 yr). At least three possible causes of this periodic signature are pulsation, rotation, or a planetary companion. The mass and radius results (M2 = 1.72M⊙, M1 = 1.57M⊙, R2 = 6.43R⊙, and R1 = 2.21R⊙) of our theoretical analysis help constrain the possibilities. The pulsational hypothesis requires more investigation of whether it is possible to excite a g-mode or an r-mode period that is much longer than the fundamental period of 0.5 dy derived from the mass-radius results. The rotational hypothesis leads to an inconsistency; the published value of υ sin i is a factor of 4.5 larger than the maximum value allowed by the radius and the PRV period of 1.44 yr. More investigation is required to determine whether increased macroturbulence and decreased υ sin i (by a factor of 4.5) is consistent with observed line profiles. From the PRV period and the primary mass a possible planetary companion would have υ sin i = 0.7 Jupiter masses with an orbital semimajor axis of 1.5 AU. The orbital results for the stellar binary (closest approach > 15 AU) shows there is room in the system for such a possible planetary companion of ϒ2 Del to survive the gravitational perturbations of ϒ1 Del.
A Method of Measuring Gamma-Velocities of Contact Binary Stars
Authors: Kaszás G. , Vinkó J. , Fürész G. 
Published: July 2016

AbstractGamma-velocities of bright contact binary stars (VW Cep, SW Lac, AB And, OO Aql) have been computed using cross-correlation. The template spectra were synthesized with a newly developed computer code WGMODEL.
Spectroscopic Orbit of the Eclipsing Binary BD +52°2009
Authors: Khalesseh B. 
Published: July 2016

AbstractNew radial velocity measurements of the Algol-type eclipsing binary BD +52 °2009, based on Reticon observations, are presented. The velocity measures are based on fitting theoretical profiles, generated by a physical model of the binary, to the observed cross-correlation function (ccf). Such profiles match this function very well, much better in fact than Gaussian profiles, which are generally used. Measuring the ccf’s with Gaussian profiles yields the following results: mp sin3i = 2.55 ± 0.05m⊙, ms sin3i = 1.14 ± 0.03m⊙, (ap + as) sin i = 7.34 ± 0.05R⊙, and mp/ms = 2.23 ± 0.05. However, measuring the ccf’s with theoretical profiles yields a mass ratio of 2.33 and following results: mp sin3i = 2.84 ± 0.05m⊙, ms sin3i = 1.22 ± 0.03m⊙, (ap + as) sin i = 7.56 ± 0.05R⊙. The system has a semi-detached configuration. By combining the solution of a previously published light curve with the spectroscopic orbit, one can obtain the following physical parameters: mp = 2.99m⊙, ms3 = 1.28m⊙, < Tp >= 9600K, < Ts >= 5400K, < Rp >= 2.35R⊙, < Rs >= 2.12R⊙. The system consists of an A0 primary and a G2 secondary.
Radial-Velocity Standard Stars
Authors: Stefanik Robert P. , Latham David W. , Torres Guillermo 
Published: July 2016

AbstractWe review the history of the IAU Radial Velocity Standard Stars and give a status report on recent efforts at the Harvard-Smithsonian Center for Astrophysics to establish an absolute velocity zero point for these stars and to improve their usefulness for intercomparing the results from different instruments and observatories.
Lunar Rocks as Meteoroid Detectors
Authors: Hartung Jack B. , Hörz Friedrich , Gault Donald E. 
Published: July 2016

About 5000 microcraters on seven lunar rocks recovered during the Apollo 12 mission have been systematically studied using a stereomicroscope. Based on comparisons with laboratory cratering experiments, at least 95 percent of all millimeter-sized craters observed were formed by impacts in which the impact velocity exceeded 10 km/s. The dynamics of particle motion near the Moon and the distribution of microcraters on the rocks require an extralunar origin for these impacting particles.The microcrater population on at least one side of all rocks studied was in equilibrium for millimeter-sized craters; i.e., statistically, craters a few millimeters in diameter and smaller were being removed by the superposition of new craters at the same rate new craters were being formed. Selected surfaces of some rocks, particularly those with glass coatings, are not in equilibrium. For every particle incident upon these “production” surfaces, there remains for observation a corresponding crater; thus the population of craters on such a surface is directly related to the total population of particles impacting that surface.Crater size-distribution data from production surfaces, together with an experimentally determined relationship between the crater size and the physical parameters of the impacting particle, yield the mass distribution of the interplanetary dust at 1 AU. Based on assumptions corresponding to an impact velocity of about 20 km/s and a particle density of 3 g/cm3, the cumulative particle flux versus mass distribution relationship iswhere N is the number of particles of mass m in grams, and larger, and C depends on the time-area product, which is, for the present, unknown. For particles smaller than 10-8 g, our observations indicate a sharper decrease in the absolute value of the slope of the flux versus mass curve than is indicated by satellite-borne-experiment data. This result may be due to a genuine relative decrease in the number or kinetic energy of smaller particles, or it may be due to our inability to observe quantitatively the smallest microcraters. For particles larger than 10-6 g, the slope of the flux versus mass curve increases smoothly to an absolute value greater than one.
A Possible Mechanism for the Capture of Microparticles by the Earth and Other Planets of the Solar System
Authors: Benedetto F. Di 
Published: July 2016

By application of Lyttleton’s theory for the formation of comets, it is shown that a possible mechanism for the origin and formation of a concentration of cosmic particles around the Earth and the other planets of the solar system exists.In the vicinity of the neutral point, where the velocity of colliding particles is not greater than 6 km/s, it is found that if the solid particles after collision must remain in a solid state, there can be no possibility of accretion for Mercury, Mars, and the Moon, where the maximum value of the “closing-in parameter” p (distance of the center of the planet to the asymptotic trajectory) is less than the radius of the planet.On the other hand, the capture radii of microparticles in solid form varies from a minimum of 2.95 planetary radii for Venus and 3.47 for the Earth, to about 986 for Jupiter.
Ionized Gas in Bright Barred Spiral Galaxies: Hα Images
Authors: Garcia-Barreto J. A. , Carrillo R. , Venegas S. , Escalante-Ramirez B. 
Published: July 2016

AbstractIn this paper we present the spatial distribution of ionized hydrogen gas, Hα, in a set of 52 bright barred Shapley-Ames spiral galaxies. In summary we were able to detect Hα line emission from distinct regions in the galaxies as from compact nuclei, from circumnuclear rings, from the bar, from ends of bars, from inner rings, from spiral arms, from outer rings and from places or structures perpendicular either to the bar or to the spiral arms.
The Shape of the Luminosity Profiles of Bulges
Authors: Andredakis Y. , Peletier R. , Balcells M. 
Published: July 2016

AbstractWe extract the bulge light profiles of a sample of early type spirals, using K-band photometry and a new 2-dimensional decomposition method that does not assume a priori any surface brightness laws. We find that the shape of the light profile shows a good correlation with the morphological type of the galaxy, in the sense that the profiles tend to fall off more steeply at large radii for the later types. This trend shows that the formation of or interaction with the disk has probably affected the density distribution of the bulge. The fact that the transition in shape is continuous might also imply that most of the bulges of late type spirals were not formed by different mechanisms than the ones of early types.
The Analysis of the Barred Galaxy NGC 6701
Authors: Márquez I. 
Published: July 2016

Images: 1.5m Spanish telescope in Calar Alto, Thomson blue coated 1024×1024 CCD, 0.31″pixel−1. Exposition times of 1800, 1500 and 1200 (BV R) and 2000 seconds (Hα and continuum) were used. Seeing FWHM = 1″. Spectra for NGC 6701: 3.5m telescope, PA=25°, 115°, 145° and 175° (Hβ region), 2.2m telescope, PA=25° and 115° (Hα region). The spectrum along the companion galaxy (PA=0°) was also obtained with the 2.2m telescope.In Figure 1a the bar is clearly seen, extending almost all along an axis very close to the disk minor axis. The spiral arms emerge from the bar, with the arm to the north being the more luminous one. The main spiral structure delineates a pseudo-outer ring when the arms close together. The prominent bar structure has a diamond-like aspect (22″×l2″) mainly traced by the two more intense sides. The zones just immediately inside these linear paths are notably fainter, as expected for a region in which the presence of dust is important. The ellipse fitting to the µB=23.5 mag arcsec−2 isophote gives a = 13, b = 12 and PA = 25°. Total (corrected) magnitudes are mB = 12.96(12.65), mV=12.44(12.20) and mI=11.64(11.46).
Minibars in the Centers of Normal Galaxies
Authors: Zasov A. V. , Sil’chenko O. K. 
Published: July 2016

AbstractAnalysis of ionized gas velocity fields in the circumnuclear regions of 13 normal spiral galaxies has shown that about half of them reveal a discrepancy between the kinematical axis at R < 2″ and the photometric or kinematical axes of the outer regions. This result indicates a high frequency of occurrence of non-axisymmetric gravitational potentials in the inner few hundred parsecs of galaxies. The possible nature of these minibars is discussed.
Radio Continuum Maps of Southern Barred Spiral Galaxies
Authors: Mazzolini Margaret , Long Janice , Webster Rachel 
Published: July 2016

AbstractA sample of southern spiral galaxies are being observed at 20 and 13 cm with the Australia Telescope Compact Array in order to look for examples of anomalous outflows from the nuclear region. In this paper we discuss the radio continuum maps of the three barred spiral galaxies observed to date.
Stellar Dynamics and the 3D Structure of Bars
Authors: Pfenniger D. 
Published: July 2016

AbstractRecent observational constraints restrict the strict applicability of stellar dynamics in spirals to a few rotation periods. However, stellar dynamics concepts such as periodic orbits are invaluable for understanding the various dynamical processes occurring during much more periods. A distinction of two instability types in stellar systems is pointed out, the first one being well illustrated by the bar instability, and the second one by the bar bending instability. In bars the third dimension brings essential dynamical effects which modify the views about the history of bulges and the spiral secular evolution. Bars may grow, bend, thicken, and dissolve into spheroidal bulges, and spirals may evolve along the Hubble sequence in the sense Sd→Sa. This leads to a much more dynamical picture of isolated galaxies than imagined before.
Ring and Lens Formation
Authors: Combes Françoise 
Published: July 2016

AbstractThe dynamical mechanism to form rings at Lindblad resonances in a barred galaxy is now well-known: due to its dissipative character, the gas is forced in a spiral structure, and experiences torques from the bar potential. Angular momentum is transferred until gas accumulates in the resonant rings. Some problems remain however to account for all observations, such as the very different time-scales for nuclear, inner and outer ring formation, while the three are frequently observed in the same galaxy; the shapes, orientations and thickness of the rings, etc... The adequacy of the present gas dynamical modelizations is discussed.Lenses are secondary components of barred galaxies that could originate from bar evolution. No model until now has met the observational constraints, in particular the sharp edge of the lenses, their strong velocity anisotropy, and their small thickness. We propose here that lenses are the result of partial bar destruction, a necessary step in a feedback cycle of bar formation-destruction, a cycle driven by gas accretion.
Gas and Shocks in Barred Galaxies
Authors: Teuben Peter 
Published: July 2016

AbstractA review of the dynamics of the dissipative gas component in barred galaxies is given. The formation of large scale galactic shocks is described, and its implications for star formation and global mass inflow are discussed. Different approaches for modeling the gas will be contrasted, and it will be shown they all produce the same basic morphological picture. However, they do differ in their estimates of mass inflow rates. Some possible directions for future research are indicated.
Dynamical Friction in Barred Galaxies
Authors: Debattista Victor P. , Sellwood J. A. 
Published: July 2016

Weinberg’s (1985) perturbative calculation of the dynamical friction by halos on bars predicts that bars will be slowed down very quickly. Previous numerical experiments (e.g. Hernquist & Weinberg 1992) have obtained results that are in agreement with Weinberg’s calculation.Observations, however, suggest that most bars are rotating rapidly. (In this context, a bar is slow if the major axis Lagrange point is far outside the bar, while a fast bar ends at, or near, this Lagrange point.) Neither Weinberg’s calculation nor the numerical experiments have, to the present date, been fully self-consistent, so possibly important effects such as resonance capture and the back reaction on the bar were not included.
A K-Band Search for Induced Bars in Interacting Systems
Authors: Keel William C. , Byrd Gene G. , Klarić Mario 
Published: July 2016

Both active and starburst galactic nuclei are best understood if they are fuelled by gas inflow to the nucleus (e.g. Simkin, Su & Schwarz 1980; Hutchings & Campbell 1983).There is observational evidence that the occurrence of Seyfert and QSO activity is enhanced in the presence of nearby companions (Dahari 1984; Keel et al 1985; Hummel et al. 1987). At least some samples of Seyfert host galaxies show more close companions than would be expected for a random sample of similar galaxies, though the situation for tidal disturbances themselves is more complex. The selection effects modelled by Byrd et al. (1987) suggest that virtually all the Seyfert galaxies in Dahari’s sample have a companion which is (in principle) physically sufficient to provoke gas inflow in the disk.