bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Velocity Absorption Components Toward the LMC
Authors: Vladilo G. , Molaro P. , Monai S. , Centurion M. 
Published: July 2016

AbstractHigh-resolution (λ/δλ ⋍ 6 x 104) spectra of R136 (the central object of 30 Dor) and of 2 LMC supergiants obtained at ESO with the 1.4-m telescope have been analysed in order to study the high-velocity absorption components at VLSR ⋍ +60 km s-1 and ⋍ +130 km s-1 first seen in satellite ultraviolet spectra in the general direction of the LMC. Our data have been integrated with previous literature results of SN1987a and of other 4 LMC supergiants obtained from spectra of similar spectral resolution.At least 6 (possibly 9) interstellar components are found in the range +40 km s-1 ≤ VISR ≤ + 150 km s-1, suggesting that the IUE features at ⋍ +60 km s-1 and ⋍ +130 km s-1 are in fact splitted in several components when observed at higher resolution. Two components originally discovered toward SN1987a (VLSR ⋍ +42 km s-1 and +107 km s-1), are detected for the first time in the Call interstellar spectrum of R136. A component at VLSR ⋍ +49 km s-1 shows significant variations both in Call and in Nal along the different lines of sight. A relatively broad component at VLSR ⋍ +58 km s-1 is present in Call toward R136, but is generally undetected in Nal in the other lines of sight. Also the components in the range +100 km s-1 ≤ VLSR ≤ +150 km s-1 are detected in Call, but not in Nal. Two weak absorptions, detected at +125 km s-1 and +141 km s-1 toward R136, may be associated with the ⋍ +130 km s-1 component characteristic of the ultraviolet spectra.The almost perfect velocity coincidence of the +107 km s-1, +42 km s-1, +49 km s-1 and +57 km s-1 components along different lines of sight suggests a common origin of the absorbing gas and a location close to our Galaxy. In spite of the low detection limit in our spectra (Wλ ⋍ 5 mÅ), the lack of detection of Nal is compatible with the presence of foreground gas clouds with hydrogen column density N(HI) ≤ 2 x 1019 cm-2, or even greater. The fact that we can detect more easily Call absorptions than the corresponding Nal absorptions indicates a very low value of Call depletion.
Observations of the Galactic Halo
Authors: de Boer Klaas S. 
Published: July 2016

Summary.After reviewing the history of the early research on gas in the Milky way halo, observational methods to investigate the halo are described. The meaning of the concepts Halo and HVC is discussed and selectional bias in databases is pointed out. The essentials of the interpretation of observed velocities are given. The scanty information on distances of HVCs is reviewed and an outlook is given on the possibilities to firmly settle the distance of at least a few HVCs.
The Violent Interstellar Medium in Messier 31
Authors: Brinks Elias , Braun Robert , Unger Stephen W. 
Published: July 2016

ABSTRACT:TAURUS observations in the line of Hα and VLA HI mapping of the HII complex No. 722 in M31, reveal what seems to be a spherical cavity 330 pc in diameter blown out by a stellar association of over 20 × 106 year old. Evidence of induced star formation which was initiated less than 5 × 106 years ago is present in the form of bright HII emission and numerous O, B and Wolf-Rayet stars which are found within the shell surrounding the cavity. The energy necessary to create the HI shell is estimated to be about 5 × 1051 erg.
Contributions of Supernovae to the Chemical and Dynamical Evolution of the ISM
Authors: Trimble Virginia 
Published: July 2016

ABSTRACT:Supernovae of Types Ia, Ib, and II contribute, on average, 1051 ergs of turbulent energy to the interstellar medium for each 2 Mo of new heavy elements. This permits a dynamical extension of the homogeneous one-zone model (with constant IMF and instantaneous recycling) that is familiar from studies of galactic chemical evolution. Chemically possible scenarios predict current kinetic energy inputs ranging from 1039 to 1040 erg yr−1 per solar mass of interstellar gas. Dynamical studies might narrow this.
Large-Scale Coronal Magnetic Structure and Its Variations during an 11-year Solar Cycle
Authors: Ivanov E. V. 
Published: July 2016

AbstractMaps of coronal magnetic fields at different heights calculated under potential approximation, have been used to reconstruct the corona shape in different phases of solar cycles 21 and 22. The shape of the solar corona depends on the maximum heliolatitudes and the structure of the heliospheric current sheet (HCS) that, in turn, are determined by space-time variations of the 3 main components of the global magnetic field of the Sun: 1) the axial dipole component; 2) the inclined dipole component; and 3) the quadrupole component. Variations of theHCSmaximum heliolatitudes and the width of the corona at 2.5R⊙during a solar cycle are compared with variations of the global magnetic field indices in the photosphere and at the source surface. The role of the solar cycle reference points and the global magnetic field indices in the corona shape variations over a solar cycle are discussed.
White-Light Coronal Structures: Streamers and CMEs
Authors: Hildner E. 
Published: July 2016

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.
Observed Large-Scale East-West Asymmetries in the Solar Corona
Authors: Noëns J. C. , Pech B. , Xanthakis J. , Mavromichalaki H. , Tritakis V. , Petropoulos V. , Paliatsos A. 
Published: July 2016

AbstractSome new results are presented and discussed about the problem of the asymmetries in the observed corona between the east and west limbs. “Local effects” are analysed. Relations within one eleven-year solar activity cycle are shown.
Large-Scale Coronal Magnetic Field and Density Structures
Authors: Gibson S. , Bagenal F. 
Published: July 2016

AbstractWe have modelled the large-scale magnetic field and density structures in the corona using the magnetostatic model of Bogdan and Low (1986) and white light images from both NASA’s Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the High Altitude Observatory Mark III (MkIII) K-coronameter (Bagenal and Gibson, 1991; Gibson and Bagenal, 1992.)We have used the magnetostatic model to calculate the magnetic field, density, pressure, and temperature distribution in the corona. Moreover, we have studied how, if at all, photospheric magnetic field observations could be used to improve predictions of coronal fields.We are at present examining the implications of our predictions of magnetic field and density structures have for coronal heating and solar wind acceleration. We are also analysing the robustness of these predictions, studying both observational and model related errors.
Coronal Mass Ejections and the Critical Velocity Ionization Phenomenon
Authors: Golbraikh E. , Filippov M. , Steinitz R. 
Published: July 2016

AbstractWe propose a new viewpoint concerning the mechanism for coronal mass ejection (CME) formation in the solar corona. According to developed approach the origin of CME is connected with high-speed movement in the transition zone or lower. The high-speed flows of neutral gas are able to produce explosive events (EEs) and jets in the chromosphere by the critical ionization velocity (CIV) mechanism. They can be sources of eruptive prominences. In this case CIV phenomenon results in ion and electron heating up to tens of eV. In turn high-energy electrons can cause weak flares. The eruptive prominences generate CMEs with velocities ≥ 100 km s−1. Thus, the following chain of phenomena appears to form the observed CME: high-speed movements of neutral gas – its ionization due to CIV phenomenon – eruptive prominences (weak flares) – CMEs.
Filling of Magnetic Loops by an Electric Current
Authors: Gopasyuk S. I. 
Published: July 2016

AbstractResults of investigations of the magnetic fields and electric currents in the active region are presented. The calculations based on the observational data showed that the electric currents are more concentrated in lower magnetic loops. The cause of this is the magnetic loop stretching. For a stretching magnetic loop the self-inductance increases and the current decreases.
Flaring Coronal Structures
Authors: Watanabe T. 
Published: July 2016

AbstractThe highlights of the Japanese solar mission,Yohkoh, are presented, with emphasis on flaring structures in the solar corona. Definitive evidences of the magnetic reconnection in the solar corona are observationally confirmed for the first time. New insights in the location of hard X-ray sources are obtained. Completely blueshifted line emissions from highly ionized plasmas are seen at the very initial phase of solar flares. It is revealed that the solar corona is very dynamic in various time scales in X-ray intensities. Ample evidences of numerous flare-like activity like microflares and X-ray jets conclude that they are also the manifestation of the magnetic reconnection.
The Superthermal Electrons in Flare Loops
Authors: Karlický M. 
Published: July 2016

AbstractIn this paper the collisional, return current, mirroring and wave-particle interaction effects on the propagation of superthermal electrons in flare loops are reviewed. Moreover, the electron bombardment of dense layers of the solar atmosphere and corresponding atmospheric response are presented. The accompanied X-ray, radio and Hαemissions during the evaporation process are discussed.
Can Soft X-Rays Be Used as a Proxy for Total Energy Injected by a Flare into the Interplanetary Medium?
Authors: Smith Z. K. , Dryer M. , Armstrong M. 
Published: July 2016

AbstractSolar flares are a source of impulsive energy releases on the Sun that can inject energy into the interplanetary medium. Some of these energy injections drive interplanetary shocks that can, in turn cause disturbances in Earth’s environment. In an attempt to quantify these energy releases using readily available observational data, we explore the possibility of using, as a proxy, the solar flare signatures observed in soft X-ray data. Our motivation has been prompted by the real-time operational requirements of NOAA and U. S. Air Force to provide estimates of arrival times and strengths of shocks that impact Earth’s magnetosphere. The luxury of extensive,ex post factostudies of flare total energy outputs is not possible in an operational context. This study is restricted to flares associated with shocks seen in the corona as metric type II radio bursts. Using GOES data, the energy released in the 1-8Å X-ray wavelength band is computed and then compared to the estimates made from a numerical model based on two-dimensional, time-dependent MHD modeling of flare-initiated interplanetary shocks. We find that the proxy energy estimates computed from the GOES data provideno advantageover the estimates made using the MHD-based numerical model.
Fine Structure of Prominences and Filaments
Authors: Mein P. 
Published: July 2016

AbstractThe fine structures of prominences and filaments are involved in many phenomena such as formation and magnetostatic support, instabilities and eruptions. After a short introduction (Section 1), we concentrate on quiescent prominences, and we review some recent results about resolved structures (Section 2), statistical properties of “threads” (Section 3), and detailed analysis of average line profiles (Section 4). We mention magnetic field measurements (Section 5) and thermal problems (Section 6). New magnetostatic models (Section 7) are very promising. We discuss briefly the problem of the scale of fine structures, and we suggest some directions for further works (Section 8).
On the Motion of Eruptive Prominences
Authors: Molodensky M. M. , Vial J.-C. 
Published: July 2016

AbstractThe increase of current in filaments can be evidenced by the variation of its twist. We show two examples of such a current increase, the last stage of which is the filament eruption and the flare. We suggest a theory of the equilibrium and the eruptive motion including the interaction of the filament current with the magnetic fields of the active region and the mirror current. We take into account the curvature of filament.
Line Formation and Intensity Enhancement of the He II 304Å Line in the Solar Atmosphere
Authors: Jordan S. D. 
Published: July 2016

AbstractObservations of He II 304Å line profiles from the Goddard solar EUV sounding rocket flight of May 9, 1991 are analyzed to determine lower limits on the small scale non-thermal velocities in the regions observed. In the quiet Sun, a lower limit of 30 km/s is obtained over much of the spectrograph slit. It is argued that a sufficient fraction of the He II ions will survive in their upward motions, before collisional excitation to produce a 304Å photon, to enhance the computed line intensity up to the observed values, in contrast to earlier theoretical results that yield total line intensities generally smaller than observed values.
The Excitation Equilibrium in the Solar Corona and Non-Maxwellian Electron Distributions
Authors: Dzifčáková E. 
Published: July 2016

AbstractWe demonstrate the influence of an electron non-Maxwellian distribution function on the collisional excitation coefficient and, as an example, on the excitation equilibrium of Fe XIV in the solar corona. The results can be used for specific applications in the solar corona, especially in the active corona, where deviations from Maxwellian distribution can be significant.
Dissipation of Coronal Waves
Authors: Edwin P. M. , Laing G. B. 
Published: July 2016

AbstractThe dissipation of ducted, fast magnetoacoustic waves by ion viscosity, electron heat conduction and radiation in a cold plasma is re-considered. The results are compared with earlier ones and it is now found, contrary to previous belief, that the ducted waves are not readily dissipated in the solar corona and are therefore unlikely to play a role in the heating of the solar atmosphere.
Total Solar Eclipses, 1994 – 1999
Authors: Pasachoff J. M. 
Published: July 2016

AbstractI summarize total solar eclipses that will occur during the 1990s, as part of the coordinating task of the Working Group on Eclipses of the International Astronomical Union. These eclipses will provide several favorable opportunities to provide coronal and other solar observations not only for intrinsic data reduction but also to compare with observations obtained from a variety of spacecraft.
On the 3D Solar Corona Structure
Authors: Koutchmy S. , Molodensky M. M. , Vial J.-C. 
Published: July 2016

AbstractWe consider the 3D structure of the solar corona using eclipse observations. We use a pseudostereoscopic effect of the rigidly rotating corona to determine the true position of the main coronal structures: broad threads, rays and streamers. We find that observations collected by the “Multi-station International Coronal Experiment” are well suited for solving this problem. Formula and error estimation are given to demonstrate the feasibility of the method. An example of stereo-view deduced from a simple analysis of results coming from the 1991 eclipse is given. The observed apparent shifts allow for the first time to apprehend the true 3D structure of the corona. The structure of streamers was compared with the pecularities (pleats and cusps) of the solar heliosphere current sheet, deduced from the sourse surface. The positions of the two main streamers systems rays (near the N-E and S-limb) coincide with the pleats of the current heliosphere layer. We conclude that large helmet streamers are composed by the pleats of the heliosphere current sheet projected on the plane of the sky.
A Method to Obtain Stereo-Diagrams of the Solar Disc
Authors: Molodensky M. M. , Starkova L. , Koutchmy S. 
Published: July 2016

AbstractIn order to obtain a 3D picture of the Solar disc planoconvex spherical and elliptical lenses were made by the authors using organic glass. The comparison between the effects produced by the lenses and the results of the calculation have shown that the elliptical lenses give the best results.
Equations of State in Stellar Structure and Evolution
Authors: Van Horn H. M. 
Published: July 2016

AbstractIn this paper I summarize some of the recent advances in studies of dense matter. Research on phase separation in the binary ionic mixtures (BIMs) that constitute the matter in white dwarfs has been motivated by the need to obtain accurate estimates for the ages of the faintest white dwarfs and thus of the disk of our Galaxy. Substantial age increases appear possible, but it is not yet clear whether such large increases occur in real white dwarfs. A second advance is the prediction, based on state-of-the-art physical calculations, that ionization of H at low temperatures and increasing densities may occur via a first-order “plasma phase transition” (PPT). Astrophysical consequences of this result are still being explored in an effort to test this prediction. Related to these equation-of-state calculations are calculations of the enhancement of nuclear reaction rates at high densities. New thermonuclear rates have been computed for C+C reactions in BIMs, although there is currently some controversy about results at the highest densities. New pycnonuclear reaction rates have also been calculated for BIMs, and it has been suggested that He-burning at T = 0 may occur through a first-order phase transition. Finally, calculations of the equation of state of matter in strong magnetic fields and of radiative opacities at high densities have undergone very recent and substantial improvements, which are just beginning to be utilized in astrophysical calculations.
Onsager-molecule approach to screening potentials in strongly coupled plasmas
Authors: Rosenfeld Yaakov 
Published: July 2016

AbstractThe solution of the exact integral equation for the liquid pair-structure in the asymptotic strong coupling limit for the plasma, as mapped on the Onsager charge-smearing optimization for the energy lower bound, features “Onsager atoms” and “Onsager molecules”. The universal properties of this asymptotic limit make it a natural reference starting point for an asymptotic strong coupling expansion for the fluid structure and thermodynamics, playing the role of an “ideal liquid” state. In particular, the leading strong coupling terms for the potential energy, direct correlation functions, and screening potentials for the Coulomb and Yukawa mixtures (corresponding to classical plasmas and electron screened classical plasmas), with full thermodynamic consistency, are presented. These are in complete agreement with the Alastuey-Jancovici analysis of early simulations data by Hansen in strong coupling, and with recent highly accurate simulations data of Ogata, Iyetomi, and Ichimaru. Data analysis errors lead Ogata, Iyetomi, and Ichimaru to incorrect results for the short range screening potentials in strong coupling. Their calculations for the short range screening potentials, bridge functions, and enhancement factors for nuclear reaction rates in strongly coupled plasmas, should be revised.
High Pressure Experiments for Astrophysics
Authors: Loubeyre P. 
Published: July 2016

AbstractIn the past decade, measurements of the properties of H2and He systems at very high pressures have made great progress, now reaching density at the limit of the plasma phase transition of hydrogen. The potentialities and limits of static and dynamic methods will be reviewed. Then, a survey of the major experimental results is presented. It is the intention of this article to show how these measurements can bring information to model low-mass astrophysical objects. Three levels of usefulness are distinguished on selected examples: data for codes of planetary interiors, constraints for theoretical descriptions of dense matter, observations of unsuspected properties at very high density.
Giant Planet, Brown Dwarf, and Low-Mass Star Interiors
Authors: Hubbard W.B. 
Published: July 2016

AbstractAstrophysical objects of low mass, ranging from giant planets to extreme dwarf main-sequence stars, have a number of physical characteristics in common due to properties of their equations of state. Their luminosities are low (much less than the solar luminosity L⊙) and their evolutionary timescales are typically measured in Gyr. So far there are few observational examples of these objects, although they are undoubtedly numerous in the galaxy. The lower mass limit is set by the object’s ability to retain hydrogen during accumulation (about the mass of Saturn), while the upper mass limit is set by the lifting of electron degeneracy by high internal temperature. Objects confined within this broad range, which extends up to about 0.1 M⊙, are governed by the thermodynamics of liquid metallic hydrogen. In this paper, we discuss the implications of this feature of their interior structure for their radii, interior temperatures, thermonuclear energy generation rates, and luminosities. We conclude with a brief assessment of the confrontation between observations and theory in galactic clusters and in the solar system.
On the Equation of State in Jovian Seismology
Authors: Provost J. , Mosser B. , Chabrier G. 
Published: July 2016

AbstractWe have investigated the effect on the seismological properties of the giant planet Jupiter of different descriptions of the equation of state (EOS) of the fluid hydrogen helium envelop. Recent Jovian models by Chabrier et al. 1992 use the equation of state of Saumon et al. (1992) which predicts the PPT (plasma phase transition). We show that different hypothesis at the level of the PPT induce large differences in the internal structure of the corresponding models, specially the sound speed. This gives rise to substantial differences of the oscillation frequencies up to 100 μHz, for modes of degrees l up to 20. These results show the great capability of Jovian seismology to test the physics involved in the interior of the giant planets.
A Simple Method for the Solution of the Stellar Structure Equations Including Rotation and Tidal Forces
Authors: Kippenhahn R. , Thomas H.-C. 
Published: July 2016

AbstractIn the following a method is presented for computing the internal structure of nonspherical stars assuming that the force per gram causing the deviation from spherical symmetry is conservative. The method has the advantage that in a normal (spherical) stellar structure code only slight changes have to be made in order to obtain nonspherical stellar models. The method can be applied as well to rotating stars as to stars distorted by tidal effects. Although it is similar to that of Faulkner et al. (1968) in the case of purely rotating stars, it is not necessary to use the division into two zones, where either slow rotation or negligible contribution to the gravitional potential is assumed.
Some Results of the Spectroscopic Study of Four Close Binary Systems of Early Spectral Types
Authors: Galkina T. S. 
Published: July 2016

It is necessary to have quantitative estimates of the intensity of lines (both absorption and emission) to obtain the physical parameters of the atmosphere of components.Some years ago at the Crimean observatory we began the spectroscopic investigation of close binary systems of the early spectral type with components WR, Of, O, B to try and obtain more quantitative information from the study of the spectra of the components.