bluuebunny/crossref_metadata_2025_split huggingface dataset:
An a priori model for the reduction of nutation observations: KSV1994.3 nutation series
Authors: Herring T.A. 
Published: March 2016

AbstractWe discuss the formulation of a new nutation series to be used in the reduction of modern space geodetic data. The motivation for developing such a series is to develop a nutation series that has smaller short period errors than the IAU 1980 nutation series and to provide a series that can be used with techniques such as the Global Positioning System (GPS) that have sensitivity to nutations but can directly separate the effects of nutations from errors in the dynamical force models that effect the satellite orbits. A modern nutation series should allow the errors in the force models for GPS to be better understood. The series is constructed by convolving the Kinoshita and Souchay rigid Earth nutation series with an Earth response function whose parameters are partly based on geophysical models of the Earth and partly estimated from a long series (1979-1993) of very long baseline interferometry (VLBI) estimates of nutation angles. Secular rates of change of the nutation angles to represent corrections to the precession constant and a secular change of the obliquity of the ecliptic are included in the theory. Time dependent amplitudes of the Free Core Nutation (FCN) that is most likely excited by variations in atmospheric pressure are included when the geophysical parameters are estimated. The complex components of the prograde annual nutation are estimated simultaneously with the geophysical parameters because of the large contribution to the nutation from the S1 atmospheric tide. The weighted root mean square (WRMS) scatter of the nutation angle estimates about this new model are 0.32 mas and the largest correction to the series when the amplitudes of the ten largest nutations are estimated is 0.17 ± 0.03 mas for the in phase component of the prograde 18.6 year nutation.
Recent Results of the Nutation Theory for a Rigid Earth
Authors: Souchay J. , Kinoshita H. 
Published: March 2016

AbstractAlthough the main questions remaining in the frame of the study of the nutation-precession phenomena concern principally the effects due to physical interactions, recent works have shown that even in the simplified case of a rigid Earth model of nutation, important changes have to be taken into account. Here we present the various steps having led to a more complete and more accurate rigid Earth nutation theory, since the pionnier work of Woolard (1953), insisting on the most recent improvements.
Internal dynamics and magnetism of the Sun
Authors: Paternò L. 
Published: March 2016

The present internal dynamics and magnetism of the Sun have been determined by the initial conditions in the pre-main sequence age, by the angular momentum loss and its redistribution in the interior, and the interaction of motion with magnetic field.The history of the Sun rotation is traced back by observing the present rotation of stars with the same mass as the Sun at earlier evolutionary stages. The present angular momentum of the Sun, as deduced from its internal rotational behavior derived from helioseismological data, appears to be a small percentage of the original one contained in similar mass stars (T Tauri and α Persei). It is not easy to reconcile the sharp decrease in the surface angular velocity, which follows the α Persei phase, with the subsequent soft decrease, taking place after Pleiades phase, unless some very effective mechanism transfers angular momentum from inner to outer regions, where is lost in the solar wind. Such a mechanism is probably magnetic in origin, since purely hydrodynamic instabilities fail to transfer angular momentum at a rate sufficient to determine the presently observed flat radial gradient of the internal angular velocity.
Dust Around Young Stars: How Related to Solar System Dust?
Authors: Hanner Martha S. 
Published: March 2016

Study of the dust in circumstellar disks around young stars is currently an extremely active area in astronomy. There is little doubt that accretion disks are a natural part of protostellar evolution. Much recent observational and theoretical work is giving us a clearer picture of the physical conditions in dust disks and their evolutionary progression. IRAS observations revealed that many main-sequence stars, such as p Pictoris, have circumstellar disks. But whether these disks are related to planetary formation is not yet understood.A portion of the dust in disks around young stars ultimately may be incorporated into planetary systems. Thus, study of the dust in our own solar system complements the remote sensing of protostellar regions and aids in reconstructing the evolutionary history of the dust. Since comets formed in the cold outer regions of the solar nebula, they may contain intact interstellar grains. As the comets lose material during passage through the warm inner solar system, some of these grains will be released into interplanetary space. Technical advances now allow analysis of individual micrometer or smaller grains in interplanetary dust particles and primitive meteorite samples. Isotopic anomalies and patterns of crystal growth in these particles are yielding tantalizing clues about the interstellar material incorporated into these solar system samples.
Synthetic Template Spectra
Authors: Kurucz Robert L. 
Published: March 2016

I will compute representative spectra for all spectral types for which my model calculations (Kurucz 1992; 1993a; 1994a) are valid. High-resolution zero-rotation fluxes and intensities will be distributed on CD-ROMS together with programs (Kurucz 1993B) for broadening the spectra to arbitrary rotation velocities, macroturbulent velocities, and instrumental profiles, and for transmitting the spectrum through an atmosphere.Since the line data are still not well determined, I actually have to make two calculations, one with only the lines with good wavelengths to preserve wavelength detail, and one with all lines, including predicted, to preserve the energy distribution for photometric calibration. In the first case the spectrum is usable as a radial velocity, abundance, or classification template. Even though the line list is incomplete, its signal-to-noise can be higher than that of observed spectra for cross-correlating.The models are plane parallel, LTE, in hydrostatic equilibrium, and have no triatomic opacities. Therefore, M stars and supergiants cannot be computed realisticly. The abundances available now are scaled-solar and alpha-enhanced scaled-solar. Individual abundances can be changed for the spectrum calculation. My new model atmosphere program, ATLAS 12 (Kurucz 1993c), which does not yet work, will allow arbitrary abundances.I have made test calculations for Arcturus, the sun, Vega, Sirius, and a17000K B. star. Figure 1 shows the effect of resolution on the appearance of the spectrum. Figure 2 shows the effect of rotation. The spectrum for Arcturus is displayed in Kurucz (1994b) with the molecular bands labelled.
Planetary Nebula Luminosity Functions and Prospects for the Future
Authors: Ciardullo Robin 
Published: March 2016

AbstractUntil now, [O III] λ5007 surveys of extragalactic planetary nebulae (PN) have been aimed at determining distances and identifying test particles for future (cinematica] studies. However, PN observations are useful in another area of astrophysics - the investigation of stellar populations. Because the production rate of [O III] bright PN in a galaxy can vary by an order of magnitude, this number is potentially a powerful discriminant between age and metallicity in an evolved stellar population. A strong inverse correlation exists between galaxy absolute magnitude and bolometric luminosity-specific PN density (α2.5), with the small metal-poor ellipticals having values of α2.5 in exact accordance with the predictions of stellar evolution theory. This correlation, along with the direct dependence of α2.5 on galactocentric radius, and the scatter in α2.5 seen in “young” galaxies, argues strongly that elliptical galaxies are old systems which follow a metallicity sequence. It also suggests that the combination of absorption line spectroscopy, UV photometry, and PN measurements can be a powerful probe of elliptical galaxy stellar populations.
Cepheid Variables: Period and Mass Determination
Authors: Moskalik Pawel 
Published: March 2016

Determination of masses has been a long standing problem in the Cepheid research. Since the early days of Cepheid modeling different methods of mass calibration have lead to conflicting results, implying serious discrepancies between the evolution and pulsation theories (see Cox 1980 for a review). In recent years this situtation has been mostly remedied, and the Baade-Wesselink masses, pulsation masses and evolutionary masses are now in good agreement with each other (e.g., Gieren 1989). However, both the bump masses inferred from the position of the secondary bump on the light curve and the beat masses obtained from the period ratios of the double mode Cepheids turned out to be very resilient to a reconciliation.There are 13 Cepheids in the Galaxy in which two vibrational modes are simultaneously excited (e.g., Szabados 1988). The period ratios measured in these variables can be used in conjunction with the linear pulsation theory to infer the masses of these stars. The method was first applied by Petersen (1973) who obtained masses ranging from 1Mʘ to 3Mʘ for Cepheids with fundamental mode periods between 2.1 d and 6.3 d. Such ‘beat” masses are 2—4 times smaller than the evolutionary or Baade-Wesselink masses for these objects.
Theoretical Simulations of Fundamental Processes of the H2 Formation Reaction on Dust Surfaces
Authors: Takahashi Junko 
Published: March 2016

AbstractClassical molecular dynamics (MD) computer simulations were performed to investigate the whole fundamental processes of the H2 formation reaction on the amorphous water ice as a model surface of icy mantles of dust grains. The product energy distribution and formation pumping mechanism of H2 for med on dust grains were also examined.
Environs and Formation of Massive Stars
Authors: Lizano Susana , Garay Guido 
Published: March 2016

Massive stars in our Galaxy are born predominantly within the dense cores of giant molecular clouds. They affect their environment very soon after a stellar core has formed through their large rate of ionizing photons and their strong stellar winds. Massive stars are formed in clusters with stellar densities n* ~ 104 stars/pc3 and sizes 0.2 — 0.4 pc, and seem to preferentially form near the central region of the cores. Disks have been found in several sources (see Cesaroni, this volume). Associated with massive stars also are bipolar molecular outflows, which have masses, mass loss rates, and energies that are factors of ~ 100 larger than those of low mass stars (see review of Churchwell 1999).An understanding of the physical processes that dominate during the early stages of formation of massive stars and their influence back on the molecular gas from which they formed requires a detailed knowledge of the physical conditions of the environment prior to and after the formation of the star. Here we present an abstract of an extensive review on this subject by Garay & Lizano (1999). For compactness, most of the references have been omitted.
The Spacewatch Outer Solar System Survey
Authors: Larsen Jeffrey A. 
Published: March 2016

AbstractWe present our results from a wide area search for the brightest and rarest members of the Transneptunian and Centaur/Scattered-Disk asteroid populations. Our data encompasses 1483.8 square degrees of sky taken with the Spacewatch 0.9 meter telescope on Kitt Peak between September of 1995 and September of 1999. We found five new Transneptunian asteroids, three new Centaurs, and two new Scattered Disk Objects. These objects are among the larger members of the population and their relative brightness will make them ideal candidates for physical observations.
Composition of Comets and Interstellar Dust
Authors: Ehrenfreund Pascale 
Published: March 2016

AbstractRecent observational results from ground and space-based observatories in combination with laboratory simulations allow us to monitor the evolution, survival, transport and transformation of cosmic dust from molecular clouds and the diffuse interstellar medium, until their incorporation into Solar System material. The composition of comets encodes information on their origin and can be used as a tracer for processes which were predominant in the protosolar nebula. A comparison of the composition and abundances of interstellar molecules and cometary volatiles reveals a general correspondence, but discrepancies are also apparent. Detailed studies indicate that cometary ices are a mixture of original interstellar material with material that has been moderately to heavily processed in the pre-solar nebula. The inventory and distribution of ice and organic molecules in interstellar clouds and in comets and their common link are briefly described.
Mixing in the Solar Tachocline
Authors: Brun Allan Sacha 
Published: March 2016

AbstractWe conduct numerical simulations of updated solar models including a physical treatment of the tachocline (Spiegel & Zahn 1992), the rotational transition layer localized at the base of the solar convection zone. We first describe what is the current understanding of this thin shear layer. We then show that we improve substantially the agreement between the models and the observed Sun by taking into account the macroscopic mixing occuring within this region.
How Oxygen Affects the CMDs and Predicted Ages of Extreme Population II Stars
Authors: VandenBerg Don A. , Bell R.A. 
Published: March 2016

AbstractStellar evolutionary models for [Fe/H] = −2.27 have been constructed to examine how predicted C-M diagrams, age versus turnoff-luminosity relations, the luminosities of the red-giant “bump” and tip, and the Teff/color of a zero-age horizontal branch model of fixed mass are affected by varying the assumed abundance of oxygen (with and without enhancements in the other α-elements).
Dust in Evolving Galaxies
Authors: Andreani Paola 
Published: March 2016

AbstractI will first review the observational evidence relating dust emission and the energy production in the far-IR/submm range. This latter contains crucial information on the global baryons transformation and the related stellar activity in the Universe. Present knowledge on this topic relies mainly on the far-IR local surveys of IRAS and ISO missions and on submm/mm surveys performed with SCUBA and MAMBO arrays. Further constraints are provided by the measurements of the Cosmic far-IR Background (CFIRB). Our scanty knowledge of galaxy formation and evolution is mainly caused by the difficulties of unveiling stellar activity at redshifts larger than 1 and at present we may only have detected massive objects in a transient hyper-luminous phase. We still lack an unbiased census of the much more numerous population of lower luminosity dusty objects. It will soon be possible to disclose the entire history of evolving dusty objects, and therefore of the stellar activity, selecting unbiased samples out of far-IR imaging and photometry in deep far-IR surveys.
Radio Halos in Merging Clusters
Authors: Giovannini Gabriele , Feretti Luigina 
Published: March 2016

AbstractThe number of known diffuse radio sources in clusters of galaxies (halos and relics) has grown in recent years, making it possible to derive statistical considerations on the physical conditions of these sources and on the properties of related clusters. We will discuss the percentage of clusters with a diffuse source and will show evidence that diffuse sources are associated with X-ray luminous clusters which have undergone recent merger processes.
Photometric Calibrations after HIPPARCOS or: The Fine Structure of the HR-Diagram Revealed
Authors: Grenon Michel 
Published: March 2016

AbstractThe Hipparcos parallaxes allow us to revisit photometric calibrations in terms of Mv and to evaluate the effects of the overall metallicity across the HR-diagram. For evolved stars the spread in mass remains the major and irreducible source of errors in the photometric Mv. If the relative locations of open cluster main-sequences are fully explained by the ∆Mv versus ∆[M/H] relation, the residual scatter in the lower main sequence appears due to additional parameters such as rotation or gravitational settling of the heavy elements. These cannot readily be studied by a purely photometric approach.
Some Aspects of Galactic Cosmic Ray Acceleration
Authors: Butt Yousaf Mahmood 
Published: March 2016

AbstractI give a synopsis of two aspects of the Galactic Cosmic Ray (GCR) acceleration problem: the importance of the medium energy gamma-ray window, and several specific astrophysical sources which merit further investigation. NOTE: figures may be found in the on-line version only: astro-ph/0309758.
Ejection of Bi-Helical Fields from the Sun
Authors: Brandenburg Axel , Blackman Eric G. 
Published: March 2016

AbstractIt is argued that much of the observed magnetic helicity losses at the solar surface may represent a reduction of an otherwise more dominant nonlinearity of solar and stellar dynamos. This nonlinearity is proportional to the internal twist (as opposed to writhe) of helical and sigmoidal surface structures.
Helicity and the SOLIS Vector-Spectromagnetograph
Authors: Keller Christoph U. , Harvey John W. , Henney Carl J. , Jones Harrison P. 
Published: March 2016

AbstractThe SOLIS Vector-Spectromagnetograph (VSM) is a compact, highly efficient vector-polarimeter that measures the magnetic field vector over the full solar disk within 12 minutes. Helicity-related quantities will be derived from the observed vector field.
HST Observations of Young Stellar Clusters in Nearby Galaxies
Authors: Larsen Søren S. 
Published: March 2016

AbstractThe HST data archive contains images of several nearby spirals, suitable for detailed studies of the properties of individual star clusters and their surroundings. By combining structural information derived from HST images with ground-based photometry, it is possible to study cluster properties as a function of age and mass. While both the core and effective radii of young clusters correlate with mass, the slopes of these relations are shallower than for a constant-density relation, implying that the mean density increases with cluster mass. This must be accounted for in theories for cluster formation.
Stellar Populations, Butcher-Oemler Effect, Star Formation in Clusters
Authors: Poggianti Bianca M. 
Published: March 2016

AbstractIn this brief overview of the stellar populations of galaxies in clusters I highlight some of the most recent results, including the downsizing of the k+a population and the star formation-local density relation. I conclude discussing some open questions regarding the interpretation of the observational results, and speculating on the current meaning of the words “primordial” and “environmental”.
Can Bars be Destroyed by Central Mass Concentrations?
Authors: Athanassoula E. , Dehnen W. , Lambert J. C. 
Published: March 2016

AbstractWe use N-body simulations to follow the evolution of bars in the presence of a central mass concentration (CMC). We find that the bar amplitude decreases in response to the CMC, but the bar is not totally destroyed unless the CMC mass is several percent of that of the disc. More centrally concentrated CMCs are more efficient. The bar evolution does not stop after the CMC has fully grown, but continues well after that time.
“Super” Star Clusters
Authors: Grijs Richard de 
Published: March 2016

AbstractThe production of “super star clusters” (SSCs; luminous, compact star clusters) seems to be a hallmark of intense star formation, particularly in interacting and star-burst galaxies. Their sizes, luminosities, and mass estimates are entirely consistent with what is expected for young Milky Way-type globular clusters (GCs). SSCs are important because of what they can tell us about GC formation and evolution (e.g., initial characteristics and early survival rates). They are also of prime importance as probes of the formation and (chemical) evolution of their host galaxies, and of the initial mass function in the extreme environments required for cluster formation. Recent evidence lends support to the scenario that Milky Way-type GCs (although more metal rich), which were once thought to be the oldest building blocks of galaxies, are still forming today.
Material Processing of Interstellar Dust in Comets
Authors: Kimura Hiroshi , Mann Ingrid 
Published: March 2016

AbstractTo better understand the processing of pristine materials in comets, we compare the composition of cometary and interstellar dust. We suggest that the deficit of N in comet dust bears evidence for the processing of the organic refractory mantle of pre-solar interstellar dust, unless it arises from the protosolar disk chemistry. The amorphous silicate core, in contrast, seems to be protected against processing due to the presence of the organic refractory mantle.
From Interstellar Matter To Comets: A Laboratory View
Authors: Ehrenfreund Pascale , Botta Oliver 
Published: March 2016

AbstractComets, formed in the cold outer parts of the solar system, provide a record of pristine material from the parent interstellar cloud. The investigation of outgassing curves from bright comets has provided a relationship to the abundances of interstellar ices and gas phase molecules. However, being porous and stratified in various layers of different densities and temperatures, the out-gassing characteristics of comets can not always be directly reconciled with the interstellar composition. This is due to the structure of the nuclear ice component, which contains different coexisting ice phases, clathrates, and trapped gases. Ices, silicates and carbonaceous compounds – studied through astronomical observations and by laboratory simulations – serve as reference material to obtain information on cometary bulk material. A major fraction of cosmic carbon in the interstellar medium, comets and meteorites seems to be incorporated into complex aromatic networks, which are difficult to observe and to identify spectroscopically. However, recent measurements of the macromolecular structure and soluble organic species in carbonaceous meteorites provide a powerful tool to investigate the link of small bodies in the solar system.
Rapid Interstellar Scintillation of Quasar PKS 1257-326
Authors: Bignall Hayley E. , Jauncey David L. , Lovell James E. J. , Tzioumis Anastasios K. , Macquart Jean-Pierre , Kedziora-Chudczer Lucyna 
Published: March 2016

AbstractPKS 1257—326 is one of three quasars known to show unusually large and rapid, intra-hour intensity variations, as a result of scintillation in the turbulent Galactic interstellar medium. We have measured time delays in the variability pattern arrival times at the VLA and the ATCA, as well as an annual cycle in the time-scale of variability for this source. Results of the two-station time delay observations are presented here. Implications for the scintillation of this source are discussed in the light of these results, together with results from two years of monitoring with the ATCA.
The Jets in Micro-Quasars and Quasars: A Comparison
Authors: Spencer Ralph 
Published: March 2016

AbstractThe discovery of relativistic jets in radio emitting X-ray binaries in our own galaxy has led to the term ‘microquasar’ being coined for these objects. In this paper the properties of microquasars are compared with those of quasars and radio galaxies, with the aim of trying to see how the similarities and differences can inform us about the physical conditions and evolution of jets. GRS1915+105 and SS433 are also discussed in more detail.