bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radial Velocity Variations of the Rapidly Oscillating Ap Star 33 Lib
Authors: Hatzes A. P. , Kanaan A. , Mkrtichian D. 
Published: July 2016

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

AbstractHigh accuracy measurements of variations in the radial velocity of the K1 giant star Arcturus have been obtained. The observations span 5 years and have a point-to-point repeatability of 5 ms−1 and night-to-night stability of better than 20 ms−1. Velocity oscillations of Arcturus were discovered during the course of this work in 1986. Subsequent, extensive additional data, indicate that Arcturus is exhibiting global nonradial acoustic oscillations with characteristics similar to those occurring in the Sun.All observations were done using a radial velocity spectrometer, designed to search for extrasolar planets, at a dedicated facility of the University of Arizona on Kitt Peak. A dedicated facility was crucial to this work — because of the changing nature of the oscillations, many observing runs, over several years, were required to understand the star’s behavior. Continuous data sets as long as 30 days were acquired. Preliminary pulsation models were performed in collaboration of Art Cox at Los Alamos National Lab.The velocity power spectra are complicated and variable. There is substantial evidence that the variations are solar-like p-mode oscillations. At least 10 frequencies have been identified, over the range 8.3 to 1.7 days. A spectrum of evenly spaced modes is apparent, yielding a value for Δν0 ≈ 1.2 μ Hz. The average power spectrum peaks near 3 days. There is a broad envelope of power with a distribution reminiscent of that seen in the Sun. Both the mode spacing and the period of peak power are consistent with scaling from the Sun (Kjeldsen & Bedding 1995). The oscillations appear to undergo abrupt discontinuities and have phase coherence times of a few weeks. We interpret the driving to be due to stochastic excitation by convection.Recent observations of the G5 IV star η Boo by Brown et al. (1997) have failed to confirm the detection of p-mode oscillations reported by Kjeldsen et al. (1995) Thus, Arcturus may be one of the first stars known to exhibit solar-like oscillations. If other K-giant variables can be shown to exhibit similar oscillations, Arcturus may represent the prototype for a new class of variable stars. We know some other K-giants are variable on short time scales (Hatzes and Cochran 1994b; Edmonds & Gilliland 1996), but many are not (Horner 1996).
Radial Velocity Variations from Starspots
Authors: Hatzes Artie P. 
Published: July 2016

AbstractIn this contribution the radial velocity (RV) variations expected for starspots on solar-type stars are examined. The spot-induced RV amplitude is found to vary linearly with spot filling factor and is less than 1 m−1 for spot sizes comparable to large sunspots and as high as 20 m s−1 for spot filling factors of 1%. Also, for a given spot size the RV amplitude increases linearly with υ sin i. All of these findings confirm the results of Saar & Donahue (1997). It is also shown that two spectral lines with different temperature sensitivity can have different RV amplitudes which may provide a diagnostic for confirming planet detections. The RV variations due to starspots correlate well with the displacement of the line core and centroid and this can be used to correct RV measurements for the effects of cool starspots.
Stellar Surface Convection, Line Asymmetries, and Wavelength Shifts
Authors: Dravins Dainis 
Published: July 2016

AbstractWavelength positions of photospheric absorption lines may be affected by surface convection (stellar granulation). Asymmetries and wavelength shifts originate from correlated velocity and brightness patterns: rising (blueshifted) elements are hot (bright), and convective blueshifts result from a larger contribution of such blueshifted photons than of redshifted ones from the sinking and cooler (darker) gas. For the Sun, the effect is around 300 m s−1, expected to increase in F-type stars, and in giants. Magnetic fields affect convection and induce lineshift variations over stellar activity cycles. A sufficient measuring precision reveals also the temporal variability of line wavelengths (due to the evolution of granules on the stellar surface). A major future development to come from adaptive optics and optical interferometry will be the study of wavelength variations across spatially resolved stars, together with their spatially resolved time variability. Thus, precise radial velocities should soon open up new vistas in stellar atmospheric physics.
Upward Revision of the Individual Masses in Alpha Cen: Implications for the Evolutionary State of the System
Authors: Neuforge C. , Pourbaix D. , Noels A. , Scuflaire R. 
Published: July 2016

AbstractA new calibration of the α Cen system is presented. It shows that a theoretical model consistent with the observations and with the higher masses determined by Pourbaix (1999) can be obtained. Our model of α Cen A has a convective core. This could serve as a discriminant in a future asteroseismological calibration of the system.
On the Influence of the Atmospheric Dust on the Zodiacal Light Polarization
Authors: Divari N. B. , Krylova S. N. 
Published: July 2016

Three-color observations of the nightglow brightness and polarization were made at the Majaky Observatory in October 1969 to determine the brightness of zodiacal light at the ecliptic pole. On the assumption that the degree of polarization of zodiacal light is 0.20 at the ecliptic pole, the corresponding brightnesses are found to be 68, 70, and 96 G2 stars of the 10th magnitude per square deg. at 0.37, 0.53, and 0.58μ.The large diurnal variations in observed intensity and direction of polarization are attributed to the effects of dust in the Earth’s atmosphere.
The Cometary and Asteroidal Origins of Meteors
Authors: Kresák Lubor 
Published: July 2016

A quantitative examination of the gravitational and nongravitational changes of orbits shows that for larger interplanetary bodies the perturbations by Jupiter strongly predominate over all other effects, which include perturbations by other planets, splitting of comet nuclei and jet effects of cometary ejections. In an approximation to the restricted three-body problem, Sun-Jupiter-comet/asteroid, the value of the Jacobian integral represents a parameter of conspicuous stability which can be applied to delineate the evolutionary paths of the potential parent bodies of the meteoroids in the system of conventional orbital elements. Earth-crossing orbits can be reached along three main paths by the comets, and along two by the asteroids.The structure of meteor streams, however, indicates that the mutual compensation of the changes in individual elements entering the Jacobian integral, which is characteristic for the comets, does not work among the meteoroids. It appears that additional forces of a different kind must exert appreciable influence on the motion of interplanetary particles of meteoroid size. Nevertheless, the distribution of the Jacobian constant in various samples of meteor orbits, from those of faint Super-Schmidt meteors up to those of meteorite-dropping fireballs, furnishes some information on the type of their parent bodies and on the relative contribution of individual sources.
Cometary vs Asteroidal Origin of Chondritic Meteorites (Abstract)
Authors: Wetherill George W. 
Published: July 2016

Monte Carlo calculations indicate excellent agreement between observed and predicted orbits of Prairie network fireballs, if it is assumed that fireballs are derived from remnants of short period comets of Jupiter’s family. No such satisfactory agreement has been found for any other proposed source. The distribution of radiants and time of fall observed for chondrites will also be reproduced by this source, provided that consideration is given to the fact that the Earth’s atmosphere will permit low velocity bodies to survive but will destroy high velocity bodies. Again, no other proposed source has been found to be adequate.It now appears likely that the mean lifetime of chondrites is limited to ˜107 yr by the high probability of complete fragmentation following impact by smaller bodies. This improves the agreement between the observed cosmic ray exposure ages and those predicted for a cometary source. This also requires some modification of the earlier discussions of alternative sources, but does not result in them becoming more satisfactory.
Bar Properties as a Function of Hubble Type
Authors: Elmegreen Debra Meloy 
Published: July 2016

AbstractPrevious optical surface photometry of barred spiral galaxies revealed that there are two distinct types of bars: large bars tend to have a nearly constant surface brightness (”flat“ bar), while smaller bars tend to have a decreasing surface brightness with a scale length similar to the disk (”exponential“ bar). Statistically, flat bars tend to occur in early Hubble types and exponential bars in later types. Studies of resonances in spirals indicate that flat bars end inside corotation, while exponential bars end between the inner Lindblad and 4:1 resonances. Near-infrared (JHK) surface photometry of bars is presented in order to compare the stellar distributions and bar potentials in flat and exponential barred galaxies. The presence of isophotal twists in some galaxies provides additional information on resonances. The grand design and fiocculent optical structures in the two types of barred galaxies will be compared and contrasted with their near-infrared light distributions.
The Far-Infrared Radiation in M83
Authors: Jones L. V. , Keel W. C. 
Published: July 2016

The fact that a galaxy is barred may have an effect on the source of the far-infrared (FIR) radiation observed. Yet, to date, no one has addressed the effects that that might have on interpreting the global FIR signal. We hope to add to the existing data on FIR radiation in galactic bulges by comparing a barred galaxy, M83, to an unbarred galaxy, M74.We use optical, Ha and UV images that are blurred to the same resolution as the IRAS HIRES images. Looking at the blurred UV images, bright "globs" were chosen and apertures were fit to them. The “globs” were then located on the optical, Hα and FIR images and fluxes were determined for each aperture used.
Molecular Gas in the Central Regions of Barred Galaxies
Authors: Kenney Jeffrey 
Published: July 2016

AbstractThe morphology and kinematics of molecular gas in the central regions of barred galaxies are described. The largest gas concentrations are often located near ILRs, although there is a range of morphologies. The gas motions associated with star-forming rings are predominantly circular, while motions just beyond the rings are often non-circular and in some cases show clear radial inflow. In barred galaxies with circumnuclear starbursts in early phases of evolution, the CO is centrally peaked, perhaps inside IILRs. The most intense star formation occurs where the gas motions are circular, and where the rotation curve rises steeply and is nearly solid body.
HI Absorption as a Tracer of Nuclear Rings in Galaxies
Authors: Koribalski Bärbel 
Published: July 2016

AbstractH ɪ absorption measurements against strong continuum background sources are an excellent tool to study the cold ISM in the line of sight to the object (e.g. pulsars, galaxies, quasars). Here we present a brief overview of such studies against the nuclear region of starburst galaxies. The high angular resolution provided by synthesis telescopes allows us to resolve the central region of nearby galaxies and thus investigate the gas kinematics close to the nucleus. The detection of fast-rotating nuclear rings is related to the bars in these galaxies which in turn might have been triggered by tidal galaxy-galaxy interactions.
Non-Axisymmetrical Components in the Gravitational Potential of Isolated Spiral Galaxies and the Presence of Nuclear Activity
Authors: Márquez I. 
Published: July 2016

AbstractFrom a detailed photometric analysis together with some kinematical information for a sample of isolated spirals, we conclude that most of them host rings or bars, features generally explained as originating from a non-axisymmetrical component of the gravitational potential. In a previous study, we have determined that all the isolated spirals hosting an active nucleus show these kinds of non-axisymmetrical components, the presence of which could be connected with the nuclear activity in the form that they can be very effective in transporting gas into the central parts. Therefore, as non-active spirals show a similar behavior, a detailed analysis of the possible differences between the central regions of active and non-active isolated spirals is motivated.
Modelling the Structure of the Ringed Spiral NGC 4736
Authors: van Driel Wim , Mulder Pieter , Combes Françoise 
Published: July 2016

AbstractWe studied the ringed RSab(r)-type spiral NGC 4736, which has a probably slightly oval disk and a very small bar. We mapped the galaxy in the HI and Hα spectral lines and we obtained long-slit optical spectra. These data were modeled using a 2-D gas dynamical code. The 2-D potential used is axisymmetric in the inner and outer regions and oval (b/a=0.8) at intermediate radii only. The oval component rotates at a pattern speed of 40 km s–1 kpc–1, close to the observed value. Inner and outer rings, like those observed, form at the inner and outer Lindblad resonances, though they co-exist only during a limited time interval in the simulations. The morphology and kinematics of the inner ring and spiral structure as observed in neutral and ionized hydrogen can be well understood in terms of gas dynamical simulations, given the form of the (stellar) potential. What remains to be explained is the origin of the nonaxisymmetric features in the mass distribution defining the potential.
Counterrotation and Barred Galaxies
Authors: Galletta G. 
Published: July 2016

AbstractIn this review we discuss the phenomenon of counterrotation, observed in ~40 apparently normal galaxies where gas or stars are rotating in a direction opposite to the main stellar body. It appears in all morphological types, from ellipticals to spirals or irregulars.The problem of the origin and the evolution of counterrotation is discussed, in the wider frame of the galaxies accreting matter from their environment (e.g., minor-axis dust-lane ellipticals or polar-ring S0s). Various sources of matter appear to be candidates for the production of the counterrotation.Due to the tendency of the bar potential to populate particular families of orbits, some cases of counterrotation found in barred galaxies are interpreted as intrinsic to barred galaxies.
A Tidal Trigger of Starburst or Seyfert Activity
Authors: Chatterjee Tapan K. 
Published: July 2016

Some of the classical seyferts are observed to be prototypical ovals, e.g. NGC 1068 and 4151 (e.g., Bosma 1981; Kormendy 1982; Scoville et al. 1988). Such a non-axisymmetric potential corresponding to an oval disk can produce inward flow of gas and induce mild activity. To test the efficiency of this process, we study a collision between a face-on spiral with a high gaseous content and an equally massive compact elliptical, under marginally bound conditions, as such encounters are most frequent.We model the spiral galaxy by an exponential model disk (of radius R) with a (static) thickness and scale length α = 4/R and a spherical polytropic bulge (n=0,3,4, equally weighted combination) containing 1/3 of the mass (cf. Chatterjee 1990); about 20% of the mass of the disk contains gas particles. The elliptical is modeled identically as the bulge. The gravitational potential is softened with softening constants of ∊ = r∘/5, r∘/3, and 0.8r∘, for the bulge of the spiral as well as the elliptical, stellar and gaseous components of the disk, respectively. Here r∘ is the radius containing 75% of the total mass of the galaxy in question, while the mutual gravitational interaction is softened with a softening constant of r∘/4.
Stellar Orbits in Barred Galaxies with Nuclear Rings
Authors: Heller Clayton H. , Shlosman Isaac 
Published: July 2016

AbstractWe investigate the dynamical response of stellar orbits in a rotating barred galaxy potential to the perturbation by a nuclear gaseous ring. The change in 3D periodic orbit families is examined as the gas accumulates near the inner Lindblad resonance. It is found that the x2/x3 loop extends to higher Jacobi energy and a vertical instability strip forms in each family. These strips are connected by a symmetric/anti-symmetric pair of 2:2:1 3D orbital families. A significant distortion of the x1 orbits is observed in the vicinity of the ring, which leads to the intersection between orbits over a large range of the Jacobi integral. We also find that a moderately elliptical ring oblique to the stellar bar produces significant phase shifts in the x1 orbital response.
Modelling the Galactic Bar using Red Clump Stars
Authors: Stanek K. Z. , Mateo M. , Udalski A. , Szymański M. , Kałuzny J. , Kubiak M. , Krzemiński W. 
Published: July 2016

AbstractThe color-magnitude diagrams of ~ 1 × 106 stars obtained for 19 fields towards the Galactic bulge with the OGLE project reveal a well-defined population of bulge red clump stars. We found that the distributions of the extinction-adjusted apparent magnitudes of red clump stars in fields lying at ι = ±5° in galactic longitude differ by ∼ 0.4 mag. A plausible explanation of this observed difference in the luminosity distribution is that the Galactic bulge is a triaxial structure, or a bar, which is inclined to the line of sight by no more than 45°. The part of the bar at the positive galactic longitude is closer to us. Work is now under way to model the Galactic bar by fitting the observed luminosity functions in the red clump region for various fields. Preliminary results indicate that the angle of the inclination of the bar to the line of sight can be as small as ∼ 20°. Gravitational microlensing can provide us with additional constraints on the structure of the Galactic bar.
Pole Coordinates by the IMPS Stations
Authors: Yumi S. , Yokoyama K. , Ishii H. 
Published: July 2016

AbstractPole coordinates derived from the latitude data of the IPMS stations during 1962.0 – 1974.3 are compared with thos’e by the 5 ILS stations. A systematic change in the difference is mainly attributed to a supposed change in a local effect at Ukiah and an annual variation in those at Kitab and Carlo-forte, noting that the results from a more numerous set of stations would give a more precise solution.
Hybrid Systems for Use in the Dynamics of Artificial Satellites
Authors: Kozai Y. 
Published: July 2016

AbstractFor observed positions ofi artificial satellites and their orbital elements, many kinds of reference coordinate systems have been available. Some are more convenient for reductions of observations, while others are more convenient for analyzing the orbital elements for geodesy. In this review paper, perturbations produced owing to the adoption of diffrent kinds of reference systems are discussed.
General Principles for the Realization of Reference Systems for Earth Dynamics
Authors: Veis G. 
Published: July 2016

A reference system is useful to express conveniently the location of a point and to study kinematic and dynamic phenomena. Although the definition of a reference system is theoretically very simple, its realization becomes very fifficult since it must be achieved by measurements reduced and expressed in this system.A referenoe system can be materialized by direct measurements of the coordinates or, more frequently, indirectly by measuring differential quantities and calculating the coordinates “de proche en proche.” The accuracy of the system definition cannot be better than the accuracy of the measurements themselves.For Earth dynamics we need a reference system related to the Earth, but since observations of other bodies such as galaxies, stars, planets, and satellites also may be required, the reference systems in which the positions of these bodies are expressed must also be related to the selected terrestrial system.To optimize the selection of a reference system one must consider both the phase of the operations for the establishment of the system and the phase of the utilization of the system, because the establishment of a reference system is not the final goal.
The Role of VLBI in the Establishment of Coordinate Systems
Authors: Zhongolovitch I. 
Published: July 2016

Considering the future development and general solution of the problem under consideration and also the high precision attainable by astronomical observations, the following procedure may be the most rational approach:1. On the main tectonic plates of the Earth’s crust, powerful movable radio telescopes should be mounted at the same points where standard optical instruments are installed. There should be two stations separated by a distance of about 6 to 8000 kilometers on each plate. Thus, we obtain a fundamental polyhedron embracing the whole Earth with about 10 to 12 apexes, and with its sides represented by VLBI.
Practical Realization of a Reference System for Earth Dynamics by Satellite Methods
Authors: Anderle R. J. , Tanenbaum M. C. 
Published: July 2016

AbstractObservations of artificial earth satellites provide a means of establishing an.origin, orientation, scale and control points for a coordinate system. Neither existing data nor future data are likely to provide significant information on the .001 angle between the axis of angular momentum and axis of rotation. Existing data have provided data to about .01 accuracy on the pole position and to possibly a meter on the origin of the system and for control points. The longitude origin is essentially arbitrary. While these accuracies permit acquisition of useful data on tides and polar motion through dynamio analyses, they are inadequate for determination of crustal motion or significant improvement in polar motion. The limitations arise from gravity, drag and radiation forces on the satellites as well as from instrument errors. Improvements in laser equipment and the launch of the dense LAGEOS satellite in an orbit high enough to suppress significant gravity and drag errors will permit determination of crustal motion and more accurate, higher frequency, polar motion. However, the reference frame for the results is likely to be an average reference frame defined by the observing stations, resulting in significant corrections to be determined for effects of changes in station configuration and data losses.