bluuebunny/crossref_metadata_2025_split huggingface dataset:
Astronomical Publications
Authors: de la Cotardière Philippe 
Published: July 2016

The glory of the heavens is available to everyone, and anyone, whatever their level of scientific knowledge, is able to appreciate their beauty, poetry and mystery. They are a window to the inaccessible and the unknown and have always attracted attention and aroused Man’s curiosity. This natural fascination for the universe is a precious card in the popularization of astronomy. Three centuries ago, Fontenelle knew how to exploit it in his Entretiens sur la pluralité des mondes, which made him famous. Many others followed him in the 18th and 19th centuries, of which Camille Flammarion may be mentioned especially. Printings of his famous Astronomie Populaire grossed 130000 copies between 1879 and 1924.Science nowadays does not arouse the same enthusiasm as it did in Flammarion’s day. Since the development of astrophysics, astronomy has become ever more complex, making the task of those who wish to explain new developments more difficult.
Main Sequence Abundances: Observational Aspects
Authors: Jugaku Jun 
Published: July 2016

AbstractAlthough once it was thought that main-sequence stars are remarkably homogeneous with respect to their chemical composition, the upper main-sequence stars (30000 > Te > 7000) show a variaety of chemically peculiar stars besides the so-called normal stars. Those include the Am, Ap, λ Bootis, He-deficient, and He-rich stars. This review summarizes the current data, which are necessary to construct and test the theoretical models of these stars. In the second half of the review we concentrate on Li. In the lower main-sequecnce stars abundances of Li have been determined in hundreds of stars. Some of the remarkable results are: (1) A uniform upper abundance value irrespective of stellar effective temperature, (2) abundance gap in the F stars of the Hyades, and (3) increasing depletion with smaller stellar mass for the Hyades.
Nonlinear Oscillation of the Magnetosphere around Neutron Stars
Authors: Hanami Hitoshi 
Published: July 2016

SummaryWe investigate the unsteady motion of mass reservoir formed by the accretion onto the magnetosphere around rotating neutron stars. The unsteady motion of the reservoir induces secondary accretion to neutron star by R-T instability. The nonperiodic or quasiperiodic phenomena of X-ray bursters seems to be related to this property of mass reservoir on the magnetosphere. We classify the typical dynamical state of the reservoir into three types with the parameters which are accretion rate acc and angular velocity of neutron star Ωs. They are nonsequential oscillation, sequential periodic (quasi-periodic) oscillation, and chaotic oscillation states.
Mass Ejection During Helium Shell Flashes from a Massive White Dwarf
Authors: Saio Hideyuki , Kato Mariko , Hachisu Izumi 
Published: July 2016

AbstractWe have simulated the helium shell flashes on an 1.3 M⊙ white dwarf and estimated the amount of mass loss. Our results may suggest a serious difficulty for the theories of the formation of Type I supernovae and of the accretion-induced formation of neutron stars because a significant amount of envelope mass is ejected during a helium shell flash.
SN 1987a: Calculations Versus Observations
Authors: Wilson James R. 
Published: July 2016

In this report the result of old calculations (Mayle 1985; Woosley, Wilson, Mayle 1986; Mayle, Wilson, Schramm 1987) of collapse driven explosions and new calculations of the kelvin-Helmholtz proto-neutron star cooling will be compared with the neutrino observations of supernova 1987a. The calculations are performed by a modern version of the computer model of Bowers and Wilson 1982. (See Mayle 1985 for more recent improvements).First we give the results of the old calculations. In the collapse, bounce and cooling of the central iron core of a massive star, about 0.1% of the binding energy of the eventual neutron star is emitted in a short deleptonization burst as the bounce shock passes through the photosphere; 5% is emitted in the total deleptonization process; and 95% is released as thermal emission in all neutrino species. In a survey of a wide range of stellar masses, stars in the range 20 to 30 Mθ are found to have the most energetic antineutrino spectra . In calculations where black holes were formed (Woosley, Wilson, Mayle 1986 and Wilson 1971) very little neutrino emission was found associated with black hole formation. The neutrinos associated with BH formation also have low energies. The time history of the neutrino pulse is sensitive to the explosion mechanism. If the mechanism is a prompt exiting through the star of the bounce shock wave, the pulse has a high peak as the shock wave passes near the photosphere. It falls rapidly for the next first few tenths of a second and then declines slowly over several seconds to effectively zero. If no prompt explosion occurs then the shock becomes an accretion shock and matter continues to fall onto the proto-neutron star keeping up the luminosity. After the late time mechanism ejects the envelope the luminosity drops several fold to the luminosity associated with the bare proto-neutron star. During the accretion phase the energy rises to about 15 mev.
Hard X-Rays and Gamma-Rays from SN 1987A
Authors: Itoh M. , Kumagai S. , Shigeyama T. , Nomoto K. , Nishimura J. 
Published: July 2016

Gamma-rays originating from radioactive decays of 56Ni and 56Co and hard X-rays due to Compton degradation of γ-rays have been predicted to emerge when the supernova becomes sufficiently thin. The X-ray detections by Ginga (Dotani et al. 1988) and Kvant (Sunyaev et al. 1988) and more recent report of γ-ray detections by SMM (Matz et al. 1988) were much earlier than the theoretical predictions. (See Itoh et al. 1987 and references therein.)These observations would give important constraints on the distribution of the heavy elements and 56Co in the ejecta. We adopted the hydrodynamical model 11E1Y6 (Nomoto et al. 1988) and carried out Monte Carlo simulation for photon transfer. A step-like distribution of 56Co was assumed where the mass fraction of 56Co in the layers at Mr ≤ 4.6 M⊙, 4.6 − 6 M⊙, 6 − 8 M⊙, and 8 − 10 M⊙ are XCo = 0.0128, 0.0035, 0.0021, and 0.0011, respectively. Other heavy elements were distributed with mass fractions in proportion to 56Co.
Formation of a planetary nebula by continuous mass loss
Authors: Harpaz A. , Kovetz A. 
Published: July 2016

The evolution of a 1.2Mʘ star along the asymptotic branch with continuous mass loss is presented, showing that this mass loss leads to the formation of a PN with a typical central star in its center.A former investigation (Harpaz and Kovetz, 1980) has shown that mechanisms for PN creation based on sudden violent processes are not likely to work in the envelope of a red giant star. On the other hand, significant mass loss from red giants was observed as a general phenomenon.We have followed the evolution of a 1.2Mʘ star along the asymptotic branch, including in the evolutionary calculations a mass loss according to Reimers’ empirical formula. It was found that towards the end of this stage, the mass loss rate was about 2.7xl0-6Mʘ/y, which is consistent with the formation of a typical PN within 30,000 years. When the mass content of the hydrogen rich envelope dropped to 1.5x10-3Mʘ, the star began to contract rapidly, forming a typical central star of 0.6Mʘ
What “masses” for Cepheids?
Authors: Davis Cecil G. 
Published: July 2016

AbstractTo understand the evolution of giant stars, it is important to pin down the masses for Cepheids. The 7– to 10–day “bump” Cepheids imply lower than evolutionary mass (60%). Recent theoretical work, though, indicates that for Cepheids with periods of 15 to 16 days, the best understanding of the light curves results from using evolutionary masses.
Non conservative evolutionary scenario for 100 Algols
Authors: Mardirossian F. , Giuricin G. 
Published: July 2016

AbstractWe have examined the observational data of 100 Algols in order to check the validity of several simple models of non-conservative mass transfer. Strong evidence of mass and angular momentum loss has been found at least in about 20% of our Algols. Case B mass exchange is favoured for low-mass Algols, while case A predominates, though not so widely as expected, in Algols of higher total mass.
Ultraviolet and optical observations of the mass-losing contact binary SV Centauri
Authors: Drechsel H. , Radecke H.D. , Rahe J. , Rupprecht G. , Wargau W. , Wolf B. 
Published: July 2016

SV Cen is a well known early-type contact binary. The less massive component is a slightly evolved B1 star. The secondary is of spectral type B4 III. The period of the system is P = 1.6585 days. SV Cen shows with Ṗ/P = -2 10-5 yr-1 one of the largest known period decreases. We carried out ground-based photoelectric and spectroscopic (coudé) observations at ESO, and high dispersion UV observations at VILSPA, with the aima) to derive new orbital parameters of SV Cenb) to determine further epochs of minima (i.e. to study the period variations)c) to look for possible mass loss indicators in the ultraviolet range.
Evolutionary computations for intermediate mass close binary systems
Authors: van der Linden Th. J. 
Published: July 2016

AbstractNumerical simulations of the evolution of close binaries with primary mass between 3 and 15 Mʘ and mass ratios of ~ 1.5 were carried out. These results show that after mass transfer the system consists of a bright main-sequence.star together with a faint He-star in a rather wide orbit (p> 60d) Evolution of this kind predicts isotope anomalies for the CNO-elements with respect to their solar values.
Detection of Solar Five-Minute Oscillations of Low Degree
Authors: Scherrer Philip H. , Wilcox John M. , Christensen-Dalsgaard J. , Gough D.O. 
Published: July 2016

AbstractSolar five-minute oscillations of degree l = 3, 4, and 5 have been observed at Stanford, in the Doppler shift of the Fe 5124 line. The frequencies and amplitudes are in broad agreement with previous observations of modes with l ≤ 3, though we note that there are some systematic discrepancies between the results of different observers.
Statistical Considerations in the Analysis of Solar Oscillation Data by the Superposed Epoch Method
Authors: Forbush S. E. , Pomerantz M. A. , Duggal S. P. , Tsao C. H. 
Published: July 2016

AbstractAlthough the method of superposed epochs (Chree analysis) has been utilized for seven decades, a procedure to determine the statistical significance of the results has not been available heretofore. Consequently, various subjective methods have been utilized in the interpretation of Chree analysis results in several fields. The major problem in the statistical treatment of Chree analysis results arises from the fact that in most studies of natural phenomena, data are neither random nor sequentially independent. In this paper, a statistical procedure which takes this factor into account is developed.
Chromospheric Emission and Rotation of Main Sequence Stars
Authors: Catalano S. , Marilli E. 
Published: July 2016

Here we present a quatitative approach to the problem of the chromospheric emission and rotation in main sequence stars based on a consistent analysis of recent published data of stars from F8 to K5. This analysis has been performed using the following physical parameters:a) total power emission in the Call K line, Lk;b) stellar rotation period, Prot, from chromospheric emission variability;c) stellar ages from lithium abundance.
Stellar Activity and Calcium Emission Variability
Authors: Baliunas Sallie L. 
Published: July 2016

ABSTRACT.Time series analysis of fluctuations of Ca II H and K chromospheric emission has provided us with much information concerning stellar activity. On all timescales, events which parallel solar behavior can be observed: activity cycles, on timescales of years; rotation of stars and evolution of active areas on timescales of days to weeks; flare-like phenomena on timescales as short as minutes.We expect that the analogues of solar activity exist on other stars . By studying stellar counterparts to solar activity, we can hope to investigate the physical parameters which are thought to influence chromospheric and coronal activity. The stellar surfaces are usually spatially unresolvable; it is thus difficult to measure directly either small-scale surface inhomogeneities or the associated magnetic fields expected from spatially restricted areas.On the Sun, however, areas with strong surface magnetic fields show intense chromospheric Ca II H and K emission (Babcock and Babcock 1955; Skumanich et al 1975). Although indirect, the Ca II H and K features are good indicators of stellar magnetic activity. A major advantage of the Ca II features is their accessibility to ground-based observatories. Long-term synoptic programs are in progress to monitor stellar chromospheric activity, and this paper will highlight ongoing work at Mt. Wilson. Monitoring variations of Ca II H and K chromospheric emission over different timescales can reveal different physical phenomena: (1) Long-term (years) variations corresponding to stellar activity cycles; (2) intermediate term (days-months) variations indicating rotation or evolution of stellar active areas; (3) short-term (minutes-hours) variations resulting from impulsive and flare-like phenomena.
RS CVN Stars: Chromospheric Phenomena
Authors: Bopp Bernard W. 
Published: July 2016

ABSTRACTThe observational information regarding chromospheric emission features in surface-active RS CVn stars is reviewed. Three optical features are considered in detail: Call H and K, Balmer H-alpha and Hel λ 10830. While the qualitative behavior of these lines is in accord with solar-analogy/rotation-activity ideas, the quantitative variation and scaling is very poorly understood. In many cases, the spectroscopic observations with sufficient S/N and resolution to decide these questions have simply not yet been made. The FK Com stars, in particular, present us with extreme examples of rotation that may well press our understanding of surface activity to its limits.
Eruptive Phenomena as a Source of the Observed Variations of Intrinsic Polarization in Long Period and T Tau Variables
Authors: Sole M. , Strazzulla G. 
Published: July 2016

ABSTRACTThe correlation between the rapid rise of intrinsic polarization, increasing U-B and enhanced equivalent width of Balmer, H and K emission lines is interpreted as a consequence of the activation of colour centres in circumstellar silicate dust by X/UV photons from flares. The temperature dependence of bleaching is discussed and the number of centres producing polarization changes is estimated.
Magnetic Instabilities in Stellar Atmospheres
Authors: Priest E.R. 
Published: July 2016

ABSTRACT.The extensive theory for magnetohydrodynamic instability of a flux tube is briefly reviewed, together with its application to tokamaks and solar flares. In a star a single coronal loop whose footprints are anchored in the dense photosphere may become unstable to the kink instability when it is twisted too much. Magnetic arcades may also be subject to an eruptive instability when they are sheared too much. After the eruption the magnetic field closes back down by reconnection and continues to heat the plasma long after the impulsive phase. Global instability of a large part of the coronal magnetic field is also possible when the stored energy is too great.
The Stability of Some Asteroids
Authors: Vicente R.O. 
Published: July 2016

AbstractThe utilization of two different stability criteria, namely, Hill's modified stability criterium and the method of surface of section, has been employed for asteroid orbits. The idea is to compute different criteria of stability for the same asteroids in order to compare the results and see the practical interest of the computations for researches about evolutionary trends of individual asteroids, groups and families of asteroids.
On the Stability of Resonant Asteroid Orbits
Authors: Hadjidemetriou J.D. , Ichtiaroglou S. 
Published: July 2016

AbstractThe stability of the asteroid orbits has been studied by the method of surface of section. Families of simple symmetric periodic orbits of the asteroid and their stability have been computed and this served as a guide for the selection of the energy levels for the surface of section. In this way all possible cases for the structure of phase space have been obtained. It was found that the region in phase space around the resonant orbits at the resonances 1/3, 3/5, 5/7,.... is unstable, but small stability regions of doubly symmetric periodic orbits near the above resonances are also present. At the resonances 1/2, 2/3, 3/4, .... it was found that there exist two separate regions in phase space at about the same resonance 1/2, 2/3, 3/4,...., respectively, one being stable and the other unstable. At certain energy levels only the stable region appears. The above results are consistent with the observed distribution of the asteroids.
Collisional Origin of Asteroid Families: Effects of the Target's Gravity
Authors: Zappalà Vincenzo , Farinella Paolo , Paolicchi Paolo 
Published: July 2016

AbstractThe outcomes of asteroidal catastrophic collisions are strongly affected by the target asteroid's gravity, since only the fragments escaping with initial velocities higher than the target's escape velocity are not reaccumulated into “rubble pile” remnants. This idea can be compared with the observational evidence on the properties of family asteroids in several ways : (1) the shape and spin period of the “reaccumulated” family asteroids will roughly fit the relationships valid for self-gravitating fluid bodies; (2) the relative velocities of the few escaping fragments arising from a breakup event marginally overcoming self-gravity will often have an anisotropic distribution, affecting the final distribution of orbital elements; (3) the amount of mass which in a given family escaped to “infinity” will be correlated with the target's size, since only for objects larger than ~ 100 km self-gravity plays an important role. These predictions are discussed and compared with the available data.
Boundaries for the Equipotential Curves in the Elliptic Restricted Three-Body Problem
Authors: Delva Magda 
Published: July 2016

AbstractIn the elliptic restricted three body problem an invariant relation between the velocity square of the third body and its potential is studied for long time intervals as well as for different values of the eccentricity. This relation, corresponding to the Jacobian integral in the circular problem, contains an integral expression which can be estimated if one assumes that the potential of the third body remains finite. Then upper and lower boundaries for the equipotential curves can be derived. For large eccentricities or long time intervals the upper boundary increases, while the lower decreases, which can be interpreted as shrinking respectively growing zero velocity curves around the primaries.
The eclipse of CI Cygni in 1980 on the objective prism spectra
Authors: Mikołajewska J. , Mikołajewski M. 
Published: July 2016

The observations of CI Cyg were carried out with the Toruń 60/90 cm Schmidt telescope with the objective prism giving a dispersion of 250 A/mm at H-gamma. Intensity traces of 20 selected spectra , made on the Kodak IIa-O plates, were made. The results were corrected for all instrumental effects and the interstellar extinction. The relative emission lines intensities have been obtained from the tracings after normalization to H-beta = 100.The spectra were typical for the quiet symbiotic star. So, all changes in the spectrum were caused by geometrical effects (eclipse).
Helium and Hydrogen of the Local Interstellar Medium Observed in the Vicinity of the Sun
Authors: Bertaux Jean-Loup 
Published: July 2016

AbstractThe Sun is moving in respect to the nearby stars with a velocity of 20 km.s-1 in the direction of the Apex, α = 271° and δ = 30° (celestial coordinates). As the lights of a car illuminate the water droplets when driving in the fog, the Sun illuminates the Hydrogen and helium atoms of the interstellar medium which it travels through. As a result, the sun and the whole solar system are imbedded in a glow of the resonance lines of hydrogen (H Lyman α ; 121.6 nm) and helium (58.4 nm), which have been studied by several space instruments in the last 14 years.From the intensity distribution of the glow in the solar system, one can derive the density of H and He in the L1SM and the direction of the relative motion between the sun and the LISM in the very vicinity of the sun. The velocity module Vw and the LISM temperature T are more adequately found from a measurement of the Lyman α line shape, which is an image of the velocity distribution of H atoms.A summary of results will be presented, together with a discussion of the methods of interpretation and their difficulties. The vector is found to be 20 ± 1 km.s-1 in the direction α = 254 ± 3°, δ = - 17 ± 3°, quite different from the Apex direction. This means that the LISM is moving also in respect to the local frame of reference giving rise to the socalled Interstellar Wind. This wind blows in the galactic plane at 16 km.s-1, in the direction , significantly different from the direction found by interstellar absorption lines on stars within ≃ 100 pc, pointing to a local significance of this flow. The temperature of the LISM is T = 8,000 ± 1,000 K, the density n (H) ≃ 0.04 to 0.06 cm-3, and the helium density n (He) ≃ 0.015 to 0.020. The high helium/hydrogen ratio, in respect to the cosmological ratio, would imply that a substantial part of the hydrogen is ionized. Temperature, density and degree of ionization of the LISM are suggesting that the sun is now in an intermediate phase of the interstellar medium, at the Interface between a hot and tenuous gas, and a dense and cold cloud of gas.
Absorption Line Studies and the Distribution of Neutral Gas in the Local Interstellar Medium
Authors: Bruhweiler Frederick C. 
Published: July 2016

AbstractPrevious published absorption line studies performed at ultraviolet and visual wavelengths are combined with new ultraviolet data in order to map out the distribution of HI within 150 pc of the Sun. Newly presented data for distances less than 50 pc further support the local cloud model as presented by Bruhweiler (1982). The Sun is embedded, near the edge of a diffuse cloud with total column density of 2 x 1019cm-2. Most observed directions within 50 pc away from the cloud body reveal trace amounts of gas (N)HI) ~ 1018 cm-2) presumably arising in the outer skin of the local cloud. At greater distances (50 ≲ d ≲ 150 pc) most directions show significant absorption with N(HI)>1019 cm-2. Two directions, one toward the northern galactic pole (NGP), the other toward β CMa exhibit unusually low HI column densities out to distances of 150-200 pc. However, substantial amounts of gas, N(HI) > 1019 cm-2, are seen toward the NGP at greater distances. The implications of these results on astronomy at wavelengths shortward of 912Å are discussed.