bluuebunny/crossref_metadata_2025_split huggingface dataset:
ORFEUS-I Observations of Molecular Hydrogen in the Galactic Disk
Authors: Van Dyke Dixon W. , Hurwitz Mark , Bowyer Stuart 
Published: July 2016

AbstractWe present measurements of interstellar H2 absorption lines in the continuum spectra of seven early-type stars in the Galactic disk at distances between 1 and 4 kpc. The spectra, obtained with the Berkeley EUV/FUV spectrometer on the ORFEUS telescope in 1993 September, have a resolution of 3000 and statistical signal-to-noise ratios between 20 and 80. We determine column densities for each observed rotational level and derive mean excitation temperatures and proton density limits for the H2 clouds along each line of sight. The gross properties of the H2-bearing clouds (e.g., column density, spatial density, cloud size) are consistent with those derived from Copernicus observations, though our lines of sight are much longer, with lower average reddenings and neutral gas densities. We find that the molecular fraction of the neutral hydrogen remains ~ 0.1 out to distances of 4 kpc in the Galactic disk.
Physical Association Between the Southern Coalsack and Chamaeleon-Musca Dark Clouds
Authors: Wagner Corradi J.B. , Franco Gabriel A.P. , Knude Jens 
Published: July 2016

AbstractTo investigate a possible physical association between the Southern Coalsack and the Chamaeleon-Musca (SCCM) dark clouds we have obtained uubyβ photometry for 1017 stars covering the connecting area: 308° ≥ l ≥ 294° and –20° ≤ b ≤ 5°. Analysis of the various colour excess E(b – y) vs. distance diagrams has indicated the presence of a local low absorption volume limited at 150 ± 30 pc from the Sun by an extended interstellar dust sheet-like feature, that is followed by a region where almost no additional reddening is measured for the next 350 pc. Combined with other data on the local ISM the existence of the dust sheet at an identical distance of the SCCM dark clouds have suggested that these clouds could be higher density regions associated to the diffuse lane of dust of the Local-Loop I bubbles’ interface.
The Influence of the Local Bubble on the Ionization of the Local Interstellar Cloud
Authors: Slavin Jonathan D. , Frisch Priscilla C. 
Published: July 2016

AbstractThe ionization of the the Local Interstellar Cloud (LIC) is quite unusual compared with most warm (T ~ 104 K) interstellar gas. Hydrogen and helium are both partially ionized with helium surprisingly more ionized than hydrogen. Directly observed ionization sources including nearby stellar EUV sources and the diffuse emission of the Soft X-ray Background (SXRB), do not provide enough ionization and heating to account for both the ionization state and temperature of the LIC. We propose that an evaporative boundary between the LIC and the hot gas of the Local Bubble can provide the necessary ionizing radiation. Results of detailed models of the emission from the interface are presented and shown to be adequate to explain the observations.
Modeling the Galactic ¾ keV X-ray Background
Authors: Freyberg M.J. , Schmitt J.H.M.M. 
Published: July 2016

AbstractWe have analyzed the ROSAT PSPC all-sky survey maps of the soft X-ray background (SXRB) in the ¾ keV band. One approach was to study the large-scale distribution of the X-ray emission with a multipole analysis. Here a significant dipole toward the galactic center region was found. This is interpreted in terms of variation of distant X-ray emission, e.g. galactic halo. Also a smallscale structure analysis of the ¾ keV X-ray sky has been performed and a new analytic fluctuation probability distribution has been derived. No significant excess over the expected extragalactic point source contribution has been found. Finally, X-ray colours have been used to investigate spectral variations of the SXRB.
Equilibrium Ionization and Non-Equilibrium Ionization Plasma Models
Authors: Böhringer Hans 
Published: July 2016

AbstractThis paper provides a brief review on ionization and radiation models of an optically thin, hot plasma and their application to the interpretation of observations of the Local Bubble. The basic structure and atomic physics ingredients of the models are outlined. Some general characteristic results of ionization equilibrium and non-equilibrium calculations are shown. Recent progress in plasma model codes is reviewed. The interpretation of the observations of absorption lines and emission spectra from the Local Bubble is discussed in the framework of ionization equilibrium and non-equilibrium ionization models with particular reference to the fast adiabatic cooling model of Breitschwerdt and Schmutzler.
Dust Composition in the Low Density Medium Around Spica
Authors: Zagury F. , Jones A. , Boulanger F. 
Published: July 2016

AbstractDust grains in low density gas are subjected to sputtering and shattering in fast supernovae shocks. Although there has been extensive modelling of the dust destruction, still little is known about the grains which survive. Jones et al. (1996) have modeled the effect of the destruction processes on the size distribution of grains. They predict that fast J shocks are efficient in grinding large dust grains into smaller particles. We present observations of the dust emission around the nearby star Spica. Comparison of the observations to the infrared emission of ’standard’ cirrus suggest that the abundance of very small grains is significantly enhanced.
New Measurements of the 4He Abundance in Galactic HII Regions
Authors: Cioni M.R. , Cortiglioni S. , Orsini M. , Palazzi E. , Palumbo G.G.C. , Sorochenko R.L. , Tsivilev A.P. 
Published: July 2016

AbstractPreliminary results of the 4He relative abundance determination from Radio Recombination Lines observations at different frequencies in the Orion, Rosette and W3 HII regions are presented. The Orion HII region has been mapped at both 22 GHz and 36 GHz with the same beamwidth (2 arcmin) using the Medicina and Puschino radio telescopes respectively. The RRLs parameters, together with their variation with frequency and with distance were determined by centering the map on the star θ1OriC. Three positions were observed in the Rosette HII region at 8.3 GHz leading to the first detection in this region of the transition He92α. The derived 4He relative abundance is considerably greater than the ones obtained from previous measurements. The W3 HII region was observed at 36 GHz and the 4He/H value derived was compared with previous measurements performed with higher spatial resolution.
Ultraviolet Absorption Line Studies of Halo Gas
Authors: de Boer Klaas S. 
Published: July 2016

AbstractThe status of halo studies using UV absorption lines is assessed. Sin absorption is essentially only seen from gas with z ≤ 1 kpc, and shows a modest flow toward the galactic disk. CIV shows diffuse absorption in general only from gas with z ≥ 1 kpc with predominantly negative velocities. Three exceptional cases of gas showing CIV absorption without absorption by neutral components are discussed. Outflowing gas has not been detected thusfar.
The High-Velocity Clouds: Galactic or Extragalactic?
Authors: van Woerden Hugo , Wakker Bart P. , Schwarz Ulrich J. , Peletier Reynier F. , Kalberla Peter M.W. 
Published: July 2016

AbstractWe present firm evidence that one of the major high velocity clouds (HVCs), Complex A, lies in the Milky Way Halo, at a vertical distance z = 3 - 7 kpc from the Galactic plane. For clouds MII/MIII, Danly et al. and Keenan et al. had already found z < 5 kpc. We further report that the metallicity in the largest HVC, Complex C, is at least 0.1 solar. Call/Hi ratios in 6 HVCs, ranging from 0.002 to 0.07 times solar, set lower limits to their metallicities.Blitz et al. have recently suggested that most of the HVCs are relatively unprocessed, extragalactic remnants of the gas which formed the Local Group of galaxies. However, the results mentioned above indicate that several major HVC complexes are neither primordial nor extragalactic. For the smaller HVCs, some of which have much higher velocities, a location in the Local Group remains a possibility.
The Galactic Halo in Hydrostatic Equilibrium
Authors: Kalberla P.M.W. , Pietz J. , Kerp J. 
Published: July 2016

AbstractThe large scale distribution of gas, magnetic field and cosmic rays in the Galaxy is explored. We analyze recent all-sky surveys of HI gas (Leiden/Dwingeloo survey), soft X-ray radiation (ROSAT) and high energy gamma-rays (EGRET > 100 MeV) in combination with the 408 MHz survey. Prom these observations we derive a Galactic halo model consistent with hydrostatic equilibrium conditions.The large scale equilibrium configuration consists of two separate domains with different properties and scale sizes:
1)The gaseous halo consists of collisionally ionized gas at T=106.2K as well as HI and has an exponential scale height hz ~ 4.4 kpc. The radial distribution is characterized by the galactocentric scale length A1 ~ 15 kpc. All components of the halo – gas, magnetic field and cosmic rays – contribute equally to the pressure. The magnetic field in the halo is oriented parallel to the Galactic plane.2)The disk extends up to a scale height of hz ~ 1 kpc and is associated with irregular magnetic fields. Here the pressure of the magnetic field is only ⅓ of the gas pressure. The cosmic rays are only weakly coupled to the disk.
A Ring of X-rays from the Cartwheel Galaxy
Authors: Trinchieri Ginevra , Wolter Anna , Iovino Angela 
Published: July 2016

AbstractROSAT HRI observations of the Cartwheel galaxy indicate that there is X-ray emission from the outer ring in connection with the strongest HII regions in the southern portion of the ring. No significant emission is detected from the nucleus or from the inner ring. This implies a strong connection between star formation activity and X-ray emission in this ring galaxy.
Radiative Fluxes and Forces in Non-spherical Winds
Authors: Wehrse Rainer , Kanschat Guido 
Published: July 2016

AbstractFor the modelling of the radiation fields in stellar winds and the resulting forces new efficient algorithms are presented. In the first one, the radiative transfer equation for moving 3D media is solved analytically with the assumption that the source function is known, eg. from the solution of the NLTE rate equations. For a wind with inhomogeneities an a-posteriori error controlled finite element code is described that takes scattering explicitly into account. Finally, we present possibilities for the accurate inclusion of an arbitrary number of spectral lines in a deterministic and in a stochastic way.
Short-Term Variations of LBV’s
Authors: Stahl Otmar 
Published: July 2016

LBV’s are variable on many different time scales from weeks to years or even decades. The typical LBV variations on timescales of years or longer are covered in the paper by Humphreys (this volume). Here I discuss variations of LBV’s on timescales from weeks to years.Most classes of stars are little studied on these timescales. This also holds true for LBV’s. Therefore the hot star group of the Landessternwarte Heidelberg Started a monitoring program of a few bright LBV’s (and other objects) using the 70cm-telescopes at the Landessternwarte and later the ESO 50cm-telescope at La Silla. For more details about the project see the paper by Kaufer (this volume).
The Line-Driven Instability
Authors: Feldmeier Achim 
Published: July 2016

AbstractThe line-driven instability may cause pronounced structure in winds of hot, luminous stars, e.g., fragments of dense shells, strong reverse shocks, and fast cloudlets. We discuss the linear stability theory, including the line-drag effect, phase reversal due to the diffuse radiation field, and the relevance of so-called Abbott waves. Recent hydrodynamic simulations focuss on the influence of a time-dependent source function on the flow structure, and on the X-ray emission from wind shocks and cloud collisions.
Non-radial Pulsations of BA Supergiants and Be Stars
Authors: Baade Dietrich 
Published: July 2016

If observing time and number of photons are not the limit, it will probably be very difficult to find any Be star or BA supergiant that is not variable. Moreover, there is hardly any major set of observations that is not tempting to explain at least partly in terms of nonradial (g-mode) pulsations. Since a few years ago, such conjectures are also theoretically permissible because improved opacity calculations have established the classicalк-mechanism as a viable source of pulsation driving (cf. Pamyatnykh, these proceedings).Contrary to Be stars, it can for any given BA supergiant nevertheless be arbitrarily difficult to diagnose nonradial pulsations (NRP’s) with certainty because they need to be detected against considerable background ‘noise’ of other physical processes, most of which are related to mass loss and/or rotation. To make things worse, there is some evidence that NRP’s can have some effect on the dynamics of the mass loss. On the other hand, variable and non-spherical winds is the subject of this Colloquium, and this paper is accordingly biased towards the interplay between pulsation and mass loss.
Rotation and Anisotropic Losses of Mass and Angular Momentum
Authors: Maeder André 
Published: July 2016

AbstractThe expressions of the radiative flux at the surface of a non-uniformly rotating star are revised and this leads to a small extra-term in the von Zeipel theorem. The Eddington factor needs also to be carefully defined in a rotating star, as well as the critical break-up velocity. This leads us to reconsider the so-called Ω–limit. The most massive stars reach the Ω and Г limits almost simultaneously.We also examine the latitudinal dependence of the mass loss rates Ṁ(υ) in rotating stars and find two main effects: 1) the “geff” effect which enhances the polar ejection; 2) the “opacity effect” (or “к–effect”), which favours equatorial ejection. In O–stars, the geff effect is expected to largely dominate. In B– and later type stars the opacity effect should favour equatorial ejection and the formation of equatorial rings. Possible relations with η Carinae and the inner and outer rings of SN 1987 A are mentioned. Opacity peaks produce some extrema in Ṁ(υ) and this may also lead to the formation non-equatorial symmetrical rings.Anisotropic stellar winds remove selectively the angular momentum. For example, winds passing through polar caps in O–stars remove very little angular momentum, an excess of angular momentum is retained and rapidly redistributed by horizontal turbulence. These excesses may lead some Wolf–Rayet stars, those resulting directly from O–stars, to be fast spinning objects, while we predict that the WR–stars which have passed through the red supergiant phase will have lower rotation velocities on the average. We also show how anisotropic ejection can be treated in numerical models by properly modifying the outer boundary conditions for the transport of angular momentum.
Trojans in Stable Chaotic Motion
Authors: Pilat-Lohinger E. , Dvorak R. , Burger Ch. 
Published: July 2016

AbstractThe orbits of 13 Trojan asteroids have been calculated numerically in the model of the outer solar system for a time interval of 100 million years. For these asteroids Milani et al. (1997) determined Lyapunov times less than 100 000 years and introduced the notion “asteroids in stable chaotic motion”. We studied the dynamical behavior of these Trojan asteroids (except the asteroid Thersites which escaped after 26 million years) within 11 time intervals - i.e. subintervals of the whole time - by means of: (1) a numerical frequency analysis (2) the root mean square (r.m.s.) of the orbital elements and (3) the proper elements. For each time interval we compared the root mean squares of the orbital elements (a, e and i) with the corresponding proper element. It turned out that the variations of the proper elements ep in the different time intervals are correlated with the corresponding r.m.s.(e); this is not the case for sin Ip with r.m.s.(i).
Simple Periodic Orbits in Elliptical Galaxies Modelled by Hamiltonians in 1-1-1 Resonance
Authors: Palacián J. , Yanguas P. , Ferrer S. 
Published: July 2016

AbstractWe consider elliptical galactic models, whose dynamical system consists of a three-dimensional isotropic harmonic oscillator plus a potential given by a homogeneous polynomial of degree four with an additional discrete symmetry. We identify families of simple periodic orbits by studying the reduced phase space.
A New Model of Mars Rotation from Pathfinder Data
Authors: Bouquillon Sebastian , Souchay Jean 
Published: July 2016

AbstractFollowing efforts to construct an accurate modelisation of Mars rotation starting from canonical equations in an Hamiltonian theoretical frame (Bouquillon and Souchay, 1996), we use recent results from radio tracking data of the Mars Pathfinder mission (Folkner et al., 1997) to modelize in the best way the motion of precession and nutation of the planet. A complete set of coefficients related to these two motions is presented, including the main effect due to the Sun and also those due to the two satellites Phobos and Deimos as well as to the planets. Morever, Oppolzer terms are calculated and included.
Lommel Functions in some Drag-Perturbed Problems
Authors: Sławomir Breiter  , Jackson Albert A. 
Published: July 2016

Let us consider the orbital problem in which a particle is subject to the force (per unit mass)The force consists of the Newtonian two body attraction term and a drag part which is linear in both components of velocity (radial vr and transverse vt). Depending on a physical interpretation of the parameters μ and α, as well as on the particular choice of the dimensionless constant γ, the model (1) can match various two body problems with dissipation. They include the classical Poynting-Robertson effect (Robertson, 1936) with γ = 1, Poynting’s (1903) version with γ = ½ and the two body drag cases recently studied by Mittleman and Jezewski (1982) and by Mavraganis and Michalakis (1994) under the name of Danby’s drag.
Nekhoroshev Stability in Quasi-Integrable Degenerate Hamiltonian Systems
Authors: Guzzo Massimiliano 
Published: July 2016

Many classical problems of Mechanics can be studied regarding them as perturbations of integrable systems; this is the case of the fast rotations of the rigid body in an arbitrary potential, the restricted three body problem with small values of the mass-ratio, and others. However, the application of the classical results of Hamiltonian Perturbation Theory to these systems encounters difficulties due to the presence of the so-called ‘degeneracy’. More precisely, the Hamiltonian of a quasi-integrable degenerate system looks likewhere (I, φ) є U × Tn, U ⊆ Rn, are action-angle type coordinates, while the degeneracy of the system manifests itself with the presence of the ‘degenerate’ variables (p, q) є B ⊆ R2m. The KAM theorem has been applied under quite general assumptions to degenerate Hamiltonians (Arnold, 1963), while the Nekhoroshev theorem (Nekhoroshev, 1977) provides, if h is convex, the following bounds: there exist positive ε0, a0, t0 such that if ε < ε0 then if where Te is the escape time of the solution from the domain of (1). An escape is possible because the motion of the degenerate variables can be bounded in principle only by , and so over the time they can experience large variations. Therefore, there is the problem of individuating which assumptions on the perturbation and on the initial data allow to control the motion of the degenerate variables over long times.
Zonal Harmonics of the Gravity Field in Def-Variables
Authors: Aparicio Ignacio , Floría Luis 
Published: July 2016

To take advantage of thelinear and regularformulation and treatment of Celestial Mechanics problems (Kustaanheimo & Stiefel 1965; Stiefel & Scheifele 1971; Deprit, Elipe & Ferrer 1994), Sharaf & Saad (1997) have given an analytical expansion of the Earth’s gravitationalzonal potentialin terms of Kustaanheimo-Stiefel (KS) regular elements (Stiefel & Scheifele 1971, §19), with special emphasis on its application toelliptic-type two-body orbitsand, consequently, using a generalized (elliptic) eccentric anomaly as the independent variable.Motivated by these and other considerations based on the definition and use of KS elements, and following a treatment similar to that of Stiefel & Scheifele (1971, §19), we developelement equations corresponding to a DEF-formulationof the satellite problem under the effect of the zonal potential.
Catalogue reduction techniques
Authors: de Vegt Chr. 
Published: July 2016

AbstractReduction techniques as applied to astrometric data material tend to split up traditionally into at least two different classes according to the observational technique used, namely transit circle observations and photographic observations. Although it is not realized fully in practice at present, the application of a blockadjustment technique for all kind of catalogue reductions is suggested. The term blockadjustment shall denote in this context the common adjustment of the principal unknowns which are the positions, proper motions and certain reduction parameters modelling the systematic properties of the observational process. Especially for old epoch catalogue data we frequently meet the situation that no independent detailed information on the telescope properties and other instrumental parameters, describing for example the measuring process, is available from special calibration observations or measurements; therefore the adjustment process should be highly self-calibrating, that means: all necessary information has to be extracted from the catalogue data themselves. Successful applications of this concept have been made already in the field of aerial photogrammetry.
First accuracy estimates of the stellar positions in the “Preliminary Catalogue of the NPZT Program Stars” compiled on the basis of observations with the Belgrade Meridian Circle
Authors: Sadzakov S. , Saletic D. , Dacie M. 
Published: July 2016

Summary:A brief review is presented of the works under way on the elaboration of a catalogue of the NPZT program stars with the Belgrade Meridian Circle, as well as accuracy estimates of the stellar positions in the “Preliminary catalogue of the NPZT program stars”, compiled on the request of Prof. Yasuda on the basis of about 80% of the planned observations. This catalogue was dispatched to as private communication Prof. Yasuda and Prof. Gliese for use in their respective current undertakings.
The Height Dependence of Granular Motion
Authors: Nesis Anastasios 
Published: July 2016

AbstractSpectrograms of Mg I-absorptions lines have been registrated at different positions of the damping wings. The corresponding heights within the atmosphere have been approximated by the Eddington-Barbier approximation. We calculated the coherence between the intensity fluctuations in the continuum and those of the higher layers. We found a rather flat gradient up to a height of 100 km and above this a steep decrease of coherence. From this result we can conclude that above a height of 100 km any fluctuations of intensity are not due to ordinary convective processes. However, up to a height of 400 km we found a coherence between the velocity of granulation and its intensity fluctuations.