bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations of Highly-Ionized Interstellar Iron
Authors: Hobbs L.M. 
Published: July 2016

AbstractThe spectra of 24 stars, including 5 at distances d < 200 pc, have been observed in the regions of the coronal [Fe X] λ6375 and [Fe XIV] λ5303 lines at detection limits near an equivalent width of 1 mÅ in the best cases. In general agreement with predictions based on a multi-phase model of the interstellar medium, no absorption which can be attributed to Fe X or Fe XIV ions in hot interstellar gas emitting the soft x-ray background is seen in any of these spectra, except for two. Toward λ Cephei an absorption line near λ6375 is measured with an equivalent width of 8.1 ± 2 mÅ, a width corresponding to 20 ± 5 km s-1 or a temperature T ≤ (0.5 ± 0.25) x 106 °K, and, if it is caused by Fe X ions, a radial velocity of -355 km s-1. On that hypothesis, the hot interstellar gas constitutes at least 63% of the column density of gas along this light path.
A Neutral Gas Jet in a Low Velocity Shock Front at the Boundary of the Draco Nebula
Authors: Kalberla P.W.M. , Herbstmeier U. , Mebold U. 
Published: July 2016

Abstract21-cm line observations with the Westerbork Synthesis Radio Telescope of a dust and molecular filament at the boundary of the Draco Nebula (l≈ 91°, b≈ 38°) reveal a jet-like neutral hydrogen feature funneling through an outlet in the low velocity shock front at the interface between the Draco Nebula and the surrounding gas. The jet-like feature is apparently connected with a high velocity filament at VLSR = -180 km s-1. We suggest that the soft x-ray emission observed in the area is thermal bremsstrahlung produced by the deceleration of high velocity gas in galactic gas.
Non Equilibrium Ionization in the Local Hot Bubble
Authors: Arnaud M. , Rothenflug R. , Rocchia R. 
Published: July 2016

AbstractSoft X-ray surveys proved the existence of a local hot bubble surrounding the solar system (Mc Cammon et al 1983). Recently two experiments measured the spectrum of this hot interstellar medium with solid state detectors during rocket flights between 300 and 1000 eV (Rocchia et al 1984). The good resolution of the experiment permitted to measure CV, CVI and OVII line emissivities with good accuracy. We use these data to put some constraints on a model where the emission comes from a supernova remnant expanding in a finite pressure medium (Cox and Anderson 1982). We show the importance of non equilibrium ionization phenomena.
Introduction
Authors: Philip A.G. Davis 
Published: July 2016

The last meeting on the determination of radial velocities was held at the University of Toronto, June 20 - 2A 1966, eighteen years ago. Five of the participants of this meeting were present at that meeting; Abt, Batten, Bertiau, Fehrenbach and Griffin. The lead article was “Photoelectric Measurements of Radial Velocities” by Griffin, followed by “Radial Velocities From Image Tube Spectra” by Rubin, Ford and Christy. These were the major new methods of determining radial velocities.This meeting was planned to discuss the major advances made in the accuracy with which radial velocities can now be measured, and the applications of these methods to astronomical problems. I made a formal proposal at the Commission 30 meetings in Patras, Greece, to hold such a meeting in 1984 and the members of the commission ratified the idea. Subsequently, proposals were made to the Executive Committee of the IAU for sponsorship and to the National Science Foundation for financial support. Union College provided the first financial support and agreed to act as host for the meeting. The result of these activities is the presence of all of you in Schenectady for this meeting. I trust that it will be a productive meeting and I wish you all success with your deliberations.
Digital Stellar Speedometry
Authors: Latham David W. 
Published: July 2016

AbstractMany areas of research have been opened up by the advent of instruments that can mass-produce radial velocities for large numbers of faint stars with precisions better than ± 1 km s−1. This paper summarizes the instruments and techniques in use at Center for Astrophysics (CfA), and the performance that they achieve for the digital speedometry of stars.
Cross-Correlation Spectrocsopy Using Coravel
Authors: Mayor M. 
Published: July 2016

AbstractSeveral studies are reviewed to illustrate the possibilities of cross-correlation spectroscopy to derive rotational velocities, macroturbulence, metallicities, magnetic fields and information on oscillation modes.The validity of radial-velocities of SB2 systems derived from the cross-correlation device has sometimes been criticized. The total absence of any basis to this criticism can easily be demonstrated. Indeed, this method is well suited to the study of SB2 with low radial velocity amplitudes, as for example, visual binaries.Finally, as a result of different radial-velocity surveys carried out with CORAVEL, the eccentricity-period relations are discussed, showing the concurrent influence of the tidal circularization, circularization by mass-exchange and the dependence of the initial eccentricity distribution with the orbital period.
Radial Velocities of Late-Type Population II Stars
Authors: Ardeberg A. , Lindgren H. 
Published: July 2016

AbstractEarly radial-velocity work on high-velocity stars has been summarized. Present samples of such stars have been reviewed. Selection methods and sample bias have been discussed. Spectroscopic as well as photometric methods have been examined. In order to find a reasonably bias-free sample of late-type stars of Population II, photometric survey techniques have to be applied. Our survey for cool Population II stars is presented. With uvby photometry we have covered a total of about 5000 stars in an attempt to derive an unbiased sample of late-type stars suitable for a study of galactic distribution and kinematical properties as a function of evolutionary phase. Especially for the metal-poor stars of our sample we have made highaccuracy CORAVEL scanner measurements of radial velocities. So far, around 1700 stars have been observed for radial velocities, most of them more than once. The CORAVEL measurements have been very successful also for stars with extremely low abundance of heavy’ elements. Many previously unknown high-velocity stars have been found. Some of them have very high radial velocities. A comparison between our radial-velocity data and our preliminary metallicity indices confirms the early evolutionary phase reached in our survey. Our results also seem to confirm the limited ranges occupied by Intermediate Population II in metallicity and in radial velocity.
Les Mesures de Vitesses Radiales au Prisme Objectif Dans Le Programme Hipparcos
Authors: Fehrenbach Ch. 
Published: July 2016

L’Organisation Européenne de Recherches Spatiales (E.5.A.) doit lancer en 1986 un satellite, Hipparcos, pour exécuter un programme astrométrique.La description complète du projet et des programmes est donnée dans le Compte Rendu du Colloque de Strasbourg (22-23 février 1982), publication E.S.A. SP-177. Le programme général comprend la mesure de la position de 200 000 étoiles dont environ 100 000 sont prioritaires. 1000 d’entre elles sont plus proches que 50 parsecs.La durée du vol doit permettre d’obtenir des mouvements propres. La précision attendue est de 0,002" par an. Un satellite ultérieur permettra d’améliorer cette précision. Il est important de compléter ces mouvements propres par des déterminations de Vitesses Radiales (VR).Il est utile d’étudier rapidement la précision de ces VR et la possibilité de les mesurer.
Radial Velocity Measurements with Objective Prisms for the Hipparcos Program
Authors: Fehrenbach Ch. 
Published: July 2016

In 1986, the European Space Agency (ESA) will launch an astrometrie satellite, Hipparcos (see ESA SP-177) with the objective of measuring positions for 200,000 stars. Proper motions will be determined with an accuracy of 0.002 "/yr. It is also very important to have radial velocities for the program stars.We will show here that an accuracy of 4 to 5 km/s for the radial velocity is good enough for a number of studies. For stellar studies, we need highly accurate radial velocities, and correlation methods (Griffin, Mayor et al.) allow that but are restricted to cool stars. Radial velocities are also needed for studies of stellar dynamics. In the case of star clusters (open and globular) we need a high accuracy, however the study of motions of stars in our galaxy do not require such a high accuracy. Only by increasing the sample can we improve our knowledge. In Table I we give data for the velocity ellipsoid. Kinematical data are from Allen and we have added absolute magnitudes and distances for stars having mv = 7.5. From an examination of this table we see that an accuracy of 4-5 km/s is good enough to study B star motions. The last column gives the dispersion in proper motion, and some of the values are astonishing, but it is well known that the proper motions for the nearby stars show a very high dispersion.
Radial Velocity Variations in Cool Supergiants
Authors: Harris Hugh C. 
Published: July 2016

AbstractA survey of F, G, and W supergiants has been carried out with the DAO radial velocity spectrometer, an efficient instrument for detecting low-amplitude velocity variations in cool stars. Observations of 78 stars over five seasons show generally good agreement with OORAVEL results for spectroscopie binaries. The majority of supergiants show low-amplitude variability, with amplitudes typically 1 to 2 km s−1. The width of the cross-correlation profile has been measured for 58 supergiants. It reveals 14 stars with unusually broad lines, indicative of rotation velocities of 15 to 35 km s−1. Several have short-period binary companions and may be in synchronous rotation. The other broad-lined stars are apparently single or with long orbital periods; they may be making their first transition from the main sequence to become red supergiants.
Coravel Radial-Velocity Curves for Cepheids in the Large Magellanic Cloud
Authors: Imbert M. , Andersen J. , Ardeberg A. , Bardin C. , Benz W. , Lindgren H. , Martin N. , Maurice E. , Mayor M. , Nordström B. , Prevot L. 
Published: July 2016

Radii and luminosities for Cepheid variables provide fundamental information on stellar evolution. Such data, obtained by the Baade-Wesselink method, are available and have been used for a number of galactic Cepheids. It is of particular interest to obtain corresponding data for Cepheids in the Magellanic Clouds. Firstly, this allows a comparative study of stellar evolution between the Galaxy and the Magellanic Clouds. Secondly, it provides data for an independent determination of the distance to the Magellanic Clouds.Radial-velocity observations have been made for a total of around 20 Cepheid variables in both the LMC and the SMC. All measurements were made with the photoelectric scanner CORAVEL attached to the Cassegrain focus of the Danish 1.54-m telescope at European Southern Observatory, La Silla, Chile. Observations were made from January 1981 through October 1983. The accuracy of individual radial-velocity observations is of the order of 1 km s−1. The B magnitudes of the six Cepheids presented range from 13.0 to 15.5.
The Bologna/ESO Search for Double Degenerates
Authors: Bragaglia Angela , Greggio Laura , Renzini Alvio , D’Odorico Sandro 
Published: July 2016

In 1984 a program has been set up for a systematic search of double degenerates (DD) among spectroscopically confirmed white dwarfs. For each WD at least two CCD spectra are obtained, which are then cross-correlated in order to get a radial velocity difference, if any. For this purpose we have used the ESO Faint Object Spectrograph and Camera (EFOSC) attached at the ESO 3.6m telescope. Exposure times are typically in the range 5–15 min, and the typical error in the radial velocity difference (Δυx) is ∼ 20 km s−1.Until now we had two observing runs, respectively in September 1985 and January 1988, for a total of 5 usable nights. For 20 WDs we have obtained more than one spectrum. Among them we have singled out two DD candidates. The first object (WD0957–666) has shown Δυr values up to ∼ 220 km s−1 and three other spectra were kindly taken for us in April 1988 by Stefano Cristiani. These also showed Δυr,’s up to ∼ 140 km s−1. Another object (WD0954–710) exhibits a Δυr ≃ 70 km s−1. The two DD candidates will be observed again in the next observing run in order to confirm their binarity and in case determine the periods.
A Variational Approach to Understanding White Dwarf Evolution
Authors: Wood M. A. , Winget D. E. 
Published: July 2016

The observed falloff in the white dwarf luminosity function at log (L/L⊙) ≈ −4.5 (Liebert, Dahn, and Monet 1988) is most easily explained as a result of the finite age of the Galactic disk. Using a simple perturbation approach as our method and a white dwarf evolution code as our tool, we have mapped the sensitivity of the ages of the model sequences in this low-luminosity regime to the uncertainties in the input physics and model parameters. We present here a preliminary overview of what we’ve learned.We have updated the White Dwarf Evolution Code of Lamb and Van Horn (1975) to include both carbon and oxygen in the core. We interpolate to the mixture composition using our pure-C and pure-O tables and the additive-volume technique (Fontaine, Graboske, and Van Horn 1977). The envelope subroutines calculate stratified H/He/C envelopes of essentially arbitrary layer masses within the range 0 to ∼ 10−2M*, and treat the composition transition zones as discontinuities. Because the equation of state tables referenced by the envelope routines do not include crystallization, a given sequence ends when the crystallization front reaches the core/envelope boundary.
The Coalescence of White Dwarfs And Type I Supernovae
Authors: Mochkovitch Robert , Livio Mario 
Published: July 2016

AbstractIn the context of the white dwarf coalescence model for type la supernovae, we compute post-coalescence configurations involving a thick disk, rotating around a central white dwarf (the original primary), having the same total mass, angular momentum and energy as the initial system. We show that carbon ignition in rather low density material (105 – 10° g.cm−3) can be triggered during the merging process itself or later, by dissipation due to turbulence in the disk. The evolution of the object following carbon ignition is very uncertain.
Evolutionary Trends in Wide Binary Systems
Authors: van de Kamp Peter 
Published: July 2016

Zdenek Kopal has kindly invited me, and I have accepted, to “instruct the theoreticians on known facts”. He also asked me to express my opinion on the relative evolutionary stages of components.I am essentially an observing astronomer, occupied with stars in our immediate neighborhood, say within 10 or at most some 25 parsec, i.e., the lower main sequence and the white dwarf degenerate branch.I hope that I may perhaps contribute by surveying and reporting some relevant data. I shall touch on a number of topics, limited because of selection and lack of knowledge. My contributions to binary stars lie in the realm of parallaxes, mass-ratios and masses, – and for the past half century, perturbations, interpreted as unseen companions, stellar and otherwise. I shall briefly report on some results, and I shall be wondering and hoping that some trace of stellar evolution may possibly be present in these results. After having witnessed for more than half a century my own astronomical evolution, the time has come for me to become more aware of theoretical, evolutionary and cosmological aspects of the cosmic material, I have been playing with so long.
Evolution of Close Binary Stars: Observational Aspects
Authors: Plavec Mirek J. 
Published: July 2016

AbstractDetached close binary systems define the main sequence band satisfactorily, but very little is known about the masses of giants and supergiants. High-dispersion IUE observations promise an improvement, since blue companions are now frequently found to late-type supergiants. The Interesting cases of μ Sagittarii and in particular of ε Aurlgae are discussed in more detail. The barium star abundance anomaly appears now to be due to mass transfer in interacting systems. The symbiotic stars are another type of binary systems containing late-type giants; several possible models for the hotter star and for the type of Interaction are discussed. The W Serpentis stars appear to be Algols in the rapid phase of mass transfer, but a possible link relating them to the symbiotics is also indicated. Evidence of hot clrcumstellar plasmas has now been found in several ordinary Algols; there may exist a smooth transition between very quiescent Algols and the W Serpentis stars. β Lyrae Is discussed in the light of new spectrophotometry results.
Evolutionary Possibilities and Impossibilities for Solar Type Contact Binaries in NGC 188
Authors: Van ’T Veer Frans 
Published: July 2016

AbstractWe give a great number of arguments for the hypothesis that several epochs of star formation have taken place at different times in the old galactic cluster NGC 188.From the last burst of star formation in this cluster, not more than a few times 108 years ago, 4 contact binaries are still now visible as W UMa stars. With the aid of a simplified probability calculation we argue that these 4 contact binaries are physically related and that the alignment of the orbital axes is not accidental.
Did SU UMa Undergo a Classical Nova Outburst?
Authors: Bode M.F. , Evans A. , Bruch A. 
Published: July 2016

AbstractRecent observations of an apparent soft X-ray halo around the dwarf nova SU UHa have led to speculation that this may well be evidence of the object having undergone a classical nova-like outburst within historical times (Cordova and Mason 1980). By combining the relationship between quiescent X-ray luminosity and speed class for classical novae and the observed X-ray luminosity of SU UMa we derive a distance dependent apparent magnitude at outburst for the object. Distance estimates for SU UMa and absolute magnitude ranges for classical novae then determine the apparent magnitude of an outburst more exactly. From the angular size of the halo and the absolute magnitude - ejection velocity relationship for classical novae we derive the approximate date of any outburst. Comparison with historical records does not reveal any promising candidates. An alternative interpretation of the halo in terms of scattering of soft X-rays from dwarf nova outbursts by interstellar grains is suggested.
Azimuthal variations in Saturn’s A ring
Authors: Lumme Kari , Irvine Willian M. 
Published: July 2016

ABSTRACTThe observations defining the azimuthal brightness variations in ring A are reviewed. This phenomenon is entirely separate from the “spokes” which are present in ring B. An explanation in terms of scattering by “density wakes” produced by large ring particles seems most reasonable.
Saturn rings: divisions, gaps and ringlets from ground-based telescopes
Authors: Dollfus Audouin 
Published: July 2016

ABSTRACTThe high magnification visual telescopic observation of Saturn’s rings exhibits divisions, gaps and bright sub-rings. B. Lyot gave a first description of these features. Later, with still more resolving telescopes, we improved the analysis of the ring features. Some gaps and concentric bright or dark sub-rings are phase angle dependent; the steep luminance peaks of their light curves around zero phase angle are volume-density dependent (opposition effect); the overall result produces changes in the shapes and intensities of these features at small phase angles, which are analysed.
The rings of Uranus
Authors: Elliot James L. 
Published: July 2016

ABSTRACTThe Uranian ring system consists of nine, narrow rings that have an average geometric albedo of 0.02. Since their discovery in 1977, the rings have been regularly observed with the technique of stellar occultations, which provides a spatial resolution of about 0.1 km in the positions of ring segments and about 4 km resolution in their structural details. The occultation data are well fitted by a kinematic model that describes the rings as ellipses, which are inclined to the equatorial plane of Uranus and precess due to harmonic terms in the Uranian potential field. The main characteristics of the Uranian ring system that need a confirmed theoretical explanation are: narrow rings, sharp edges, uniform orbital precession, origin of the eccentricities and inclinations, the structure of the e ring, the structure of the η ring and the origin of the ring system.
The Jovian ring
Authors: Burns Joseph A. 
Published: July 2016

ABSTRACTLying in Jupiter's equatorial plane is a diaphanous ring having little substructure within its three components (main band, faint disk, and halo). Micron-sized grains account for much of the visible ring, but particles of centimeter sizes and larger must also be present to absorb charged particles. Since dynamical evolution times and survival life times are quite short (≲102-3yr) for small grains, the Jovian ring is being continually replenished; probably most of the visible ring is generated by micrometeoroids colliding into unseen parent bodies that reside in the main band.
Asymmetrical Ejection of Matter in a Thermonuclear Model of a Supernova Explosion
Authors: Chechetkin V.M. , Denisov A.A. , Koldoba A.V. , Poveschenko Yu.A. , Popov Yu.P. 
Published: July 2016

With the recent Supernova 1987a in the LMC, new and interesting possibilities have arisen for the solution of a problem relating to the explosion mechanism of supernovae. The presupernova was probably a B3Ia, the blue supergiant, and not a red giant as it was earlier thought likely. Calculations of the evolution, which have been made recently, show that the loss of hydrodynamical stability may be connected with carbon burning in the stellar core during the blue giant stage. This loss of stability of the CO core is the main factor in our explanation of the recent event of SN 1987a.Before we consider the thermonuclear model of a supernova based on a thermal flash in the degenerate CO core, let us dwell on the present situation in the theory of supernovae. The main problem in supernova theory is the simultaneity of births of a compact remnant and an expelled envelope. The compact remnant later becomes a neutron star. The expelled envelope determines the curve of brightness. Now, it is clear that a supernova explosion may result in either the total disruption of a star or in the simultaneous production of a compact remnant and an expelled envelope.
The Reionization of Unshocked Ejecta in SN1006
Authors: Hamilton A.J.S. , Fesen R.A. 
Published: July 2016

AbstractThe fortuitous positioning of the Schweizer and Middleditch OB subdwarf behind SN1006 has permitted the detection and subsequent confirmation by IUE of broad (±5000 km/s) Fe II absorption features which probably arise from unshocked iron ejecta in the center of SN1006. The mass of detected Fe II, ∽0.012 M⊙, is however only 1/25 of the ∽0.3 M⊙ of Fe within ±5000 km/s predicted by carbon deflagration models. IR and optical observations exclude any appreciable iron in grains or Fe I, but high ion stages, Fe III and up, oould be present. Promising mechanisms for ionizing the unshocked iron in SN1006 include the radioactive decay of 44Ti, and photoionization by UV and X-ray emission from the reverse shock. Although the photoionization model works, insofar as it permits as much as 0.2 M⊙ of unshocked iron in the center of SN1006, agreement with the IUE data requires that the ejecta density profile be flatter, less centrally concentrated, than the W7 deflagration model of Nomoto, Thielemann, and Yokoi.
A Model for the Interaction between Stars and Gas in the Interstellar Medium
Authors: Chiang Wei-Hwan , Bregman Joel N. 
Published: July 2016

AbstractA global model for the ISM is described in which separate fluids of stars and gas interact through star formation, mass loss, stellar heating, and gaseous cooling processes. In all simulations, a steady state develops in which rarefied ionized regions separate ridges of neutral gas.