bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Emission Line Studies and the Warm Ionized Component of the Local Interstellar Medium
Authors: Reynolds R.J. 
Published: July 2016

AbstractObservations of diffuse, galactic Hα, [NII]λ6583, and [SII]λ6716 emission lines provide evidence for a warm (~ 104 K), primarily ionized component of the interstellar medium distributed throughout the galactic disk. This component of the interstellar gas has an electron density ≈ 0.1-0.2 cm-3 and occupies about 10-30% of the interstellar volume. Interstellar Hα emission near the galactic poles, the dispersion measure of a nearby pulsar, and observations of interstellar gas flowing into the solar system indicate that this ionized component is an important constituent of the interstellar medium in the solar neighborhood. The intensity of the Hα background at high galactic latitudes implies that this component is maintained by an average hydrogen ionization rate in the vicinity of the Sun of (2-4) x 106 s-1 per cm2 of galactic disk. The emission measure is 1.3-2.3 cm-6 pc toward the galactic poles. The sources of this ionization have not yet been identified but may include escaping Lyman continuum radiation from planetary nebulae, hot white dwarfs, and early type stars. Investigations of the regions surrounding ζ Oph (09V), the nearest (d ≃ 140 pc) 0 star, and a Vir (Bl IV), one of the nearest (d ≃ 87 pc) early B stars, have revealed areas of enhanced Hα emission extending 6°-12° from each star. However, it appears that these stars do not contribute significantly to the more diffuse ionization within the local interstellar medium.
Observations of Absorption Lines from Highly Ionized Atoms
Authors: Jenkins Edward B. 
Published: July 2016

AbstractIn the ultraviolet spectra of hot stars, we can see absorption lines from highly ionized species in the interstellar medium. Observations of these features have been very influential in revising our perception of the medium's various physical states and how gases in space are heated and ionized. The pervasiveness of 0 VI absorption lines, coupled with complementary observations of a diffuse background in soft x-rays and EUV radiation, shows that there is an extensive network of low density gas (n ≈ fewx10-3cm-3) existing at “coronal” temperatures, 5.3 ≲ log T ≲ 6.3. Thus, while we once thought that x-rays and cosmic rays were the dominant sources of excitation and heating of the interstellar gas, we now realize that shocks created by supernova explosions or mass loss from early-type stars can propagate freely through space and eventually transfer a large amount of energy to the medium. To create the coronal temperatures, the shocks must have velocities in excess of 150 km s-1; shocks at somewhat lower velocity (v ≲ 100 km s-1) can be directly observed in the lines of Si III. Observations of other lines in the ultraviolet, such as Si IV and C IV, may highlight the widespread presence of energetic uv radiation from very hot, dwarf stars. More advanced techniques in visible and x-ray astronomical spectroscopy may open up for inspection selected lines from atoms in much higher stages of ionization.
Large-Scale Bubble Structure of the Interstellar Medium (ISM) and Properties of the Local Spiral Arm (LSA)
Authors: Bochkarev Nikolay G. 
Published: July 2016

AbstractBubbles are very common structure units in the Galaxy and galaxies. Collection of radio, optical, infrared and x-ray observations of the Cyg superbubble (CSB) region of the sky show that the CSB is not a single bubble object. Between 50 to 75 percent of its x-ray emission can be ascribed to discrete sources. The other 25 to 50% x-ray emission, probably originates from bubbles around 8 OB associations of the region. All bubbles located within the spiral structure of Galaxy, M31 and M33 have diameter ≲ 300pc.The large distance of stellar association from the galactic plane (GP) combined with picture of the gas distribution within the LSA shows that a Reyleigh-Taylor instability in the LSA can develop and give use to the formation of compact steller clusters, such as the Cyg OB2 association. Development stages of the Reyleigh-Taylor instability, some peculiarities of the dust distribution and departures of the local structure from the galactic grand design suggest the absence of a spiral Shockwave in the LSA.
Kinematics of Nearby Gas and Stars
Authors: Goulet Thomas , Shuter William L.H. 
Published: July 2016

AbstractThe kinematic properties of gas and stars in the Solar neighborhood are described in terms of the line-of-sight component of a three-dimensional first order Taylor series expansion of the local velocity field. The types of object analysed are (1) 21 cm absorbing clouds (2) intercloud medium (3) main sequence B stars closer than 200 pc (4) B stars of luminosity class ranging from I to IV (5) main sequence A stars (6) K-giant stars. The least squares fitting procedure used to derive the 10 coefficients describing each of the six velocity fields was essentially the same, so that a valid comparison could be made. Marked departures from circular motion are found in most cases, but the only systematic trend is a correlation between ∂u/∂x (u being the velocity component along the x-axis directed towards the Galactic center) and stellar spectral type, where the gas behaves like a medium ‘younger’ than the early type stars. Our analysis of the gas indicated that the standard plane-parallel model provided a good description for the intercloud medium, but was inadequate for the absorbing clouds. A velocity ellipsoid description of the residuals is presented for each type of object. The influence of the Gould belt on local kinematics is discussed.
The Discovery of a Spectroscopic Binary in M 3
Authors: Latham David W. , Hazen-Liller Martha L. , Pryor Carleton P. 
Published: July 2016

AbstractBinary stars appear to be a pervasive feature of the sidereal universe. In every stellar population or habitat that has been investigated, except globular clusters, from 10 to 40 percent of the objects observed prove to have variable radial velocities that suggest they are spectroscopie binaries. To extend the search for spectroscopie binaries in the globular cluster M3, we have obtained more than 300 new radial velocities for the 111 giants previously observed by Gunn and Griffin (1979). For one of the stars, von Zeipel 164, four observations spanning ten years show a velocity variation with an amplitude of at least 18 km s−1 and a period of perhaps a few years. We believe this is a strong candidate for the first spectroscopie binary to be found in a globular cluster.
A New Radial Velocity Survey at the NGP
Authors: Adamson A.J. , Hilditch R.W. , Hill G. , Fisher W.A. 
Published: July 2016

A classical astronomical problem has been to derive the total density of matter local to the Sun from observations of the velocity and density distributions of well-defined “tracer groups” of stars near the Galactic poles. Since the original work by Oort (1932: ρ0=0.15 M⊙/pc.3), the dynamical value of ρ0, has consistently been in excess of the amount of matter actually observed ; a substantial part of the mass would seem to exist in a form which renders it undetectable.Our earlier survey of the dynamics of NGP A and F stars yielded 0.14 M⊙/pc.3 for ρ0 , (Hill et al. 1979) but employed an analytical potential derived by Camm (1950,52) requiring a (physically implausible) increase in the velocity dispersion with z-distance, although no such departure from the isothermal state was apparent in the velocity data for the F stars to z=200 pc. Such problems could well arise from the numerous simplifying assumptions involved in solving the combined Poisson and Boltzmann equations analytically. Recent studies (eg. Bahcall 1984) have used more sophisticated multicomponent mass models and solved numerically for the potential, taking as input the observed velocity dispersions and scale parameters for the various components.
The Temperatures of White Dwarfs in Accreting Binaries
Authors: Szkody Paula , Sion Edward M. 
Published: July 2016

Through the use of accreting binary systems, it is possible to study the effects of the deposition of matter and energy on the surface of a white dwarf. The observed atmospheric properties of composition and temperature obtained from direct observation of the spectral lines and the continuum flux can be used to compare with those of single white dwarfs to understand the consequences of mass accretion on binary evolution.Cataclysmic variables provide one of the best targets for this type of study because a) the primaries are all white dwarfs b) the level and the timescale of the accretion cover a large range from the high rate, relatively steady novalike accretors to the dwarf novae systems which are modulated on short timescales in a quasi-periodic manner. Unfortunately, due to the mass transfer process, an accretion disk builds up to the point where its radiation overwhelms the white dwarf light in most cases. Thus, to study the effects on the stellar primary, systems must be found which have low mass transfer rates (generally the short orbital period systems (Patterson 1984)) and/or high inclinations (since most of the disk flux emerges perpendicular to the plane of the disk). The best identification of the white dwarf emerges from IUE spectra which show a broad Lyman α absorption profile (in contrast to the normal emission lines from a disk at quiescence). The shape of this profile provides a sensitive indicator of the temperature and gravity. In some cases, broad absorption lines are also evident in the optical Balmer lines, although the broad emission lines from the disk usually make these difficult to detect. The steeply falling flux distribution of a white dwarf throughout the optical region, combined with a flat disk distribution usually means that the white dwarf contributes a minor amount to the optical flux. However, in the ultraviolet, the rising energy distribution of the white dwarf easily dominates the falling energy distribution of a low accretion rate disk (Mateo and Szkody 1984). White dwarfs are generally acknowledged to be prominent in the dwarf novae U Gem (Panek and Holm 1984), VW Hyi (Mateo and Szkody 1984) and Z Cha (Marsh, Horne and Shipman 1987) and suggested in EK TrA and WZ Sge (Verbunt 1987). In addition, the white dwarf has been seen in some novalike systems which sporadically turn off their mass transfer, (resulting in the disappearance of most of the disk and the resulting appearance of the white dwarf). This has been the case in TT Ari (Shafter et al. 1985) and some limits have been determined for MV Lyr (Szkody and Downes 1982) and V794 Aql (Szkody, Downes and Mateo 1988). Several magnetic white dwarfs have also been seen when the mass transfer ceases in the AM Her systems (summarized in Szkody, Downes and Mateo 1988).
Evidence of Complex Field Structure in the Magnetic White Dwarf in EXO 033319–2554.2
Authors: Ferrario Lilia , Wickramasinghe D. T. 
Published: July 2016

AbstractWe present detailed theoretical models for polarisation and spectroscopic data from EXO 033319–2554.2 that suggest the presence of two cyclotron emission regions of field strengths B ∼ 5.6 × 107 G and B ∼ 2.8 × 107 G, and which are separated by about 90° on the surface of the white dwarf. The large difference in magnetic field strength and the proximity of the two regions imply a more complex field structure than that of a centred dipole field distribution if it is assumed that the regions are connected by closed field lines.
High Frequency Oscillations in SS Cygni
Authors: Arévalo M.J. , Solheim J.E. , Lázaro C. 
Published: July 2016

Because of its relative brightness (mv about 11.8 in quiescence and mv about 8.6 in outburst), SS Cygni is the Dwarf Novae most extensively studied since 1896 (Mattei et al., 1985; Bath and van Paradijs, 1983).Concerning its long-term behaviour, SS Cygni has short, long and anomalous out-bursts. Correlations between outburst characteristics and periodicities have been studied by van Paradijs (1983), Campbell (1934), and Sterne and Campbell (1934).SS Cygni, as any cataclysmic variable, also presents rapid variations. Since the discovery of this variability (Warner and Robinson, 1972) many long runs of high-speed photometry have been performed for different Dwarf Novae, both during out-bursts and in quiescence stages. Regarding to SS Cygni we can summarize these variations as:
Supernovae in Binary Systems : Production of Run-Away Stars and Pulsars
Authors: De Cuyper Jean-Pierre 
Published: July 2016

AbstractThe effects of an instantaneous asymmetric supernova explosion in an eccentric binary system are analyzed, taking into account the mass loss out of the system, the influence of the impact of the supernova shell on the companion star and the extra “kick” velocity which a collapsed star might receive in an asymmetric supernova explosion. For a random orientat-ion in space of this asymmetric kick velocity, the survival probability and the runaway velocities are derived and their properties discussed for an explosion occurring at a given position in the initial keplerian orbit and the mean and extreme values of these quantities over one orbit are derived. As an example, the outcome of a possible supernova explosion in the ten best known WR+OB binaries is studied and a comparison is made with the observed run-away OB stars, radio pulsars and binary X-ray pulsars.
Physical properties of Saturn's rings
Authors: Cuzzi Jeffrey N. 
Published: July 2016

A review is given of important features of the rings, touching only lightly on aspects covered by other speakers (Spokes, E ring). This extended abstract will only convey the high points of the talk.Most of the material in Saturn's rings is concentrated in the B ring, with a lesser amount in the A ring and only small amounts in the C ring and Cassini Division. There is a very different character to these classical ring regions; the C and Cassini particles are darker and more neutral in color; (Smith et al. 1981, 1982). The A and B regions contain nearly all of the “small” particles, from microns to millimeters. Overall, however, the particles are fairly well characterized by Voyager radio occultation results as roughly following an r-3powerlaw between about 1 cm and a few meters (Tyler et al. 1982, Marouf et al. 1982). A fairly sharp cutoff in the size distribution is seen at radii varying with location from about 1 to about 5 meters. The material of the ring particles is probably mostly water ice (see e.g., Pollack 1975) but the redness of the rings requires the presence of minor constitutents. Combinations of ground-based radar and radio emission observations (Pollack 1975, Cuzzi and Pollack 1978; Pettengill, this issue) strongly indicate that the non-icy component comprises a small fraction of the total bulk material. In fact, mass densities derived from density waves (e.g. Holberg et al. 1982) and CRAND measurements (Cooper et al. 1982) combined with Voyager particle size measurements indicate a particle density more like that of snow or frost than that of pure ice.
The adiabatic invariant: a tool for the study of the dynamics of the solar system
Authors: Henrard J. 
Published: July 2016

ABSTRACTA summary of the main results of the theory of the Adiabatic Invariant is presented. They are applied to a simple one degree of freedom Hamiltonian system which is a rood model for many resonance problems in Celestial Mechanics. As an illustration of the previous concepts, the capture into resonance of the pair of satellites Enceladus-Dione is analysed.
Macrostructure and microphysics of Saturn's E-ring
Authors: Pang Kevin D. , Voge Charles C. , Rhoads Jack W. 
Published: July 2016

Abstract.All observed optical and infrared properties of Saturn's E-ring can be explained in terms of Mie scattering by a narrow size distribution of ice spheres of 2 - 2.5 micron diameter. The spherical shape of the ring particles and their narrow size distribution imply a molten (possibly volcanic) origin on Enceladus. The E-ring consists of many layers, possibly stratified by electrostatic levitation.
X-ray Observations of SNR E0102.2-72.2 in the SMC
Authors: Hughes John P. 
Published: July 2016

AbstractThe supernova remnant (SNR) E0102.2-72.2 is the brightest in the Small Magellanic Cloud (SMC) at X-ray wavelengths. This object, which is remarkable because of its high velocity (∼4000 km s−1) oxygen-rich optical emission, appears to be similarly remarkable at X-ray wavelengths. The high resolution imager (HRI) data can be quite well described by a thick ring with a radius of ∼19" (6 pc at a distance of 63 kpc). The imaging proportional counter (IPC) X-ray spectral data can be best fit by a single emission line of energy ∼0.9 keV. It seems likely that this is the emission from a plasma of almost pure neon.
Observations of “Dents” in the Radio Shells of SNRs Expanding into Dense Clouds
Authors: Velusamy T. 
Published: July 2016

AbstractHigh resolution (∼36“×90”) radio maps of SNRs W28 and W44 observed with the OSRT at 327 MHz are presented. The distortions or dents in their shell structure are associated with the parts of the shells expanding into dense molecular clouds in their vicinity and provide direct observational evidence for interaction between them.
Aperture Synthesis Observations of the Supernova Remnant G73.9+0.9
Authors: Chastenay P. , Pineault S. 
Published: July 2016

AbstractRadio continuum observations, obtained with the DRAO Synthesis Telescope, are presented of the new supernova remnant (SNR) G73.9+0.9. Our map at 1420 MHz shows indications of spatially resolved knots of emission in the brightest part of the remnant. The 408 MHz map, although of lower resolution, shows the same general morphology. The spectral index α (Sv∝v−α) between 1420 and 408 MHz is about 0.5, a value typical for shell type SNRs. The morphology however is more suggestive of a filled centre SNR.
Small-Scale Structure in Young Supernova Remnants
Authors: Reynolds Stephen P. 
Published: July 2016

AbstractRecent VLA observations of the shell supernova remnant SN 1006 AD (Reynolds and Gilmore 1986) and the Crablike remnant 3C 58 (SN 1181 AD?; Reynolds and Aller 1987) show features at high resolution that contain information on details of particle acceleration and transport in the remnants. Thin arcs at the edge of SN 1006 require time-variable particle acceleration and/or magnetic field amplification. Filaments in 3C 58 probably result from interaction of pulsar-generated relativistic fluid with filaments of thermal gas formed early in the remnant’s life by cooling or dynamical instabilities. Their sharp edges imply efficient scattering by Alfvén waves; as much as 1% of the large-scale magnetic energy density may be in magnetic turbulence on length scales of 1011 cm.
Collective Effects of Supernova Explosions in a Starburst Nucleus
Authors: Tomisaka Kohji , Ikeuchi Satoru 
Published: July 2016

AbstractThe collective effects of supernova (SN) explosions in the nucleus of a starburst galaxy are studied. It is shown that a large wind bubble with the size of a few hundred parsecs in the nucleus of a starburst galaxy will expand for SN explosion rates of 0.1 per year or greater. The bubble gradually elongates due to density stratification. Finally, the shell breaks near the top and the hot matter flows through the cylindrical shell up to 1-2 kpc above the disk plane. We will discuss the X-ray emission in the halos of galaxies such as M82 and NGC 253 and the distribution of molecular gas in such galaxies in relation to the starburst phenomenon.
The Distribution and Birthrate of Galactic SNRs
Authors: Wu Xinji , Leahy D.A. 
Published: July 2016

AbstractIn this paper we find that the spatial distribution of SNRs shows a peak in the range R = 4–6 kpc; the total number of SNRs in the Galaxy is 749±104; and the birthrate of SNRs is one in every 18±3 years.
What can we learn from ζ Aur binary systems?
Authors: Schröder K.-P. 
Published: July 2016

Abstractζ, Aur binaries are wide eclipsing systems (P ≃ 1...10 yrs), containing a late supergiant primary (G to M type) and an early dwarf companion (A0 V... B3 V ). Some recent studies of wind phenomena (mass loss rates), chromospheric properties and wind acceleration (of the supergiant) as well as wind accretion phenomena introduced by the gravitational interaction with the companion are presented, summarizing previous work of the Hamburg ’binary wind team’(mainly D. Reimers, R. Baade, A. Che-Bohnenstengel, K. Hempe, K.-P. Schröder).
The Problem of Spectral Classification of Stars in the Sequence S-SC-C
Authors: Boeshaar Patricia C. , Keenan Philip C. 
Published: July 2016

AbstractThe sequence of stars starting with type S and extending through the SC stars into the red carbon stars are brought into the following revised system of classification:In this table X stands for the temperature type and the number to the right of the slant line is an abundance index which, as suggested by Ake (1978), is essentially a measure of C/O. Intensities of ZrO and TiO are given also.
The Occurrence of Abnormal Stars in Open Clusters
Authors: Abt Helmut A. 
Published: July 2016

AbstractMorgan, Keenan, and others have found that low dispersions (80-130 Å mm-1) are ideal for obtaining spectral types and luminosity classes, especially for early-type stars. This is because at those dispersions certain blends are unresolved and remain useful, the hydrogen line wings are seen most clearly, and differences in rotational velocities are not so important. Such dispersions are also ideal or adequate for detecting some peculiarities, such as Am and Be spectra and some extreme Ap spectra, but they are inadequate for detecting abnormalities involving weak lines (as in Ap(Hg, Mn) stars) and line profiles (such as in shell spectra).
Criteria and Applications for Spectral Classification Outside the MK Domain
Authors: McCarthy M. F. 
Published: July 2016

AbstractThe area under discussion here lies beyond the domain of the MK system and includes studies of natural groups as detected in low dispersion studies; it extends to spectral regions studied now in the far ultraviolet and in the infrared and radio regions; in this paper primary consideration is given to optical spectra from the near infrared to the near ultraviolet. We give a description of “natural groups” and a brief description of new possibilities opened for research in this area through the introduction of thin prisms and the combination of prism and grating (GRISM). Finally a summary of spectral criteria useable outside the MK domain is presented.
Radio Emission from Cataclysmic Variables
Authors: Chanmugam G. 
Published: July 2016

AbstractThe study of radio emission from cataclysmic variables (CVs) is a new and developing field. Radio emission from novae, recurrent novae, dwarf novae and each of the subclasses (AM Her and OQ Her) of magnetic CVs have now been reported and are reviewed here. These observations are shown to provide, in general, a probe of the structure of the CV on length scales typically ≳1011cm. Radiation mechanisms, both incoherent and coherent, relevant to the observed radio emission are also discussed. These suggest that the red dwarf in AM Her and DQ Her is also magnetized and provides support for theories for the evolution of CVs which require a magnetized secondary star.
Multi-Wavelength Observations of Dwarf Novae during Outburst
Authors: Echevarría J. 
Published: July 2016

AbstractMulti-wavelength observations of dwarf novae during outburst are presented here. Thirty three objects were observed, of which seventeen were at outburst. Six objects were caught during the rise, and a short flare was detected in SU UMa. It lasted 20 hours and reached a maximum increase of 3.6 in flux at 5500 A. The flare was simultaneous at all observed wavelengths.