bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Soft X-ray Halo of the LMC?
Authors: Blondiau M.J. 
Published: July 2016

AbstractROSAT X-ray observations of the LMC show several X-ray shadows in the ¾ keV and 1.5 keV bands. The ¼ keV band is dominated by emission of the galactic foreground. It is uncertain whether there is additional soft X-ray contribution from the LMC. The so-called HI-L-component is located in front of the HI-D-component and therefore the matter of the L-component accounts for most of the observed X-ray shadows. The ¼ keV ROSAT image of the LMC reveals a slightly fainter X-ray emission region at the position of the eastern part of the HI-L-component. This suggests the existence of a soft X-ray halo in the LMC. Investigations of the X-ray shadows show that also the lower energy end of the ¾ keV band originates partly from this soft X-ray plasma which is located in front of the absorption features. This additional soft X-ray emission, in the lower energy end of the ¾ keV band, is brighter than the typical diffuse galactic emission at the same galactic latitude.
Inverse Spectropolarimetric Modelling of Hot Star Wind Structure and Variability
Authors: Brown John C. , Ignace Richard , Piana M. 
Published: July 2016

Merits and limitations are discussed of using an inferential inverse, as opposed to the usual model-fitting, approach to diagnose stellar wind structure. We aspire to encourage the stellar wind community to use inversion rather than forward modelling by making it clear what inversion means, when and why it is valuable, and by giving examples of successful applications.A sub-discipline of astrophysics advances beyond the discovery era as the quality of data moves from single numbers (flux, colour, size) to well measured functions or data strings g(y) (e.g., light curves or spectra where g is flux and y is time or wavelength). As the precision δg/g and the resolution δy/y improve, we progress from data gathering and qualitative description to quantitative modelling in terms of some relevant source model function f(x), describing source “structure” in some sense. In general g(y) and f(x) do not correspond one-to-one but rather f maps to g in a “convolved” (sometimes complex and non-linear) way through the radiation processes, while f itself may be a combination of important source properties. Here we consider only the simplest situation (though our arguments can be generalised) where the relationship is of the linear integral formwhere the operator function K, represents the emission physics which we assume known. The diagnostic problem is to determine as much as possible about f(x) within the noise and resolution limits of the data g(y) and the smearing effect of K(x, y).
X-Ray Variability of the O Star ζ Puppis
Authors: Berghöfer Thomas W. 
Published: July 2016

X-ray surveys carried out with the Einstein Observatory (Chlebowski et al. 1989) and ROSAT (Berghöfer et al. 1996) have shown that all O stars are soft X-ray emitters. Since O star winds are opaque at soft X-ray energies the stars or their photospheres cannot be the origin of the observed X-ray emission, thus, this emission must be produced in their stellar winds. Obviously, the X-ray emission is connected to dynamical processes present in the winds of O stars; steady-state computations for O star winds which are able to explain many of the observational features cannot predict any X-ray emission.Lucy & White (1980) suggested the presence of hot gas in the stellar winds which is produced in shocks developing from the growth of instabilities in the winds; supersonic wind flows in O stars are known to be intrinsically unstable. Numerical simulations confirmed this scenario. However, so far these simulations are limited to one or two dimensions and are not able to explain for instance the observed X-ray luminosity of O stars.
Variable Winds in Early-B Hypergiants
Authors: Wolf Bernhard , Rivinius Thomas 
Published: July 2016

AbstractEarly-B hypergiants belong to the most luminous stars in the Universe. They are characterized by high mass-loss rates (Ṁ ≈ 10−5Mʘyr−1) and low terminal wind velocities (v∞ʘ400 kms−1) implying very dense winds. They represent a short-lived evolutionary phase and are of particular interest for evolutionary theories of massive stars with mass loss. Due to their high luminosity they play a key role in connection with the “wind momentum - luminosity relation”. Among the main interesting characteristics of early-B hypergiants are the various kinds of photometric and spectroscopic variations. In several recent campaigns our group has performed extensive high dispersion spectroscopy of galactic early-B hypergiants with our fiber-fed echelle spectrograph FLASH/HEROS at the ESO-50 cm telescope. The main outcome was that their dense winds behave hydrodynamically differently to the less luminous supergiants of comparable spectral type. Outwardly accelerated propagating discrete absorption components of the P Cyg-type lines are the typical features rather than rotationally modulated line profile variations. These discrete absorptions could be traced in different spectral lines from photospheric velocities up to 75% of the terminal velocity. The stellar absorption lines show a pulsation-like radial velocity variability pattern lasting up to two weeks as the typical time scale. The radius variations connected with this pulsation-like motions are correlated with the emission height of the P Cyg-type profiles.
Blitz Model for the Eruptions of Eta Carinae
Authors: Smith Nathan , Guzik Joyce A. , Lamers Henny J.G.L.M. , Cassinelli Joseph P. , Humphreys Roberta M. 
Published: July 2016

AbstractFollowing the “Great Eruption” of 1843, η Carinae underwent a second major eruption around 1890. We suggest a preliminary working model developed during this meeting (in one night, hence the term “Blitz”) that attempts to explain the temporal development of the 19th century eruptions of η Car, as well as the formation of the Homunculus nebula (note that we are not offering an explanation for the cause of the Great Eruption!). The essence of the model is that after the Great Eruption ends, the star’s extended outer envelope re-adjusts itself on a thermal time scale. This re-adjustment allows envelope material to crash back onto the surface of the star, inducing the second eruption in 1890.
Imaging Polarimetry of Eta Carinae with the Hubble Space Telescope
Authors: Schulte-Ladbeck Regina E. , Pasquali Anna , Clampin Mark , Nota Antonella , Hillier John , Lupie O.L. 
Published: July 2016

AbstractWe have taken advantage of the high spatial resolution attainable with the HST to map the linear polarization in the V band across the nebulosity surrounding Eta Car. There are several new results related to polarization variations on different size scales. First, we present a two-dimensional map of the amount and position angle of the polarization across the Homunculus. Second, we provide measurements of the polarization within prominent features such as the “jet”, the “paddle”, the “skirt”, and the “spot” in the south-eastern lobe. Third, we comment on polarization variations associated with the small-scale structure that can be seen in HST images (and which gives the lobes their cauliflower-like appearance). The new data provide insight into the three-dimensional distribution of dust about Eta Car.
Non-spherical Outflows in Massive Binary Systems: Circumbinary Disks?
Authors: Koenigsberger Gloria , Moreno Edmundo , Cantó Jorge 
Published: July 2016

AbstractThe trajectories of wind particles emitted from the surface of a massive star in a close binary system are analyzed. Within a radius 1000 times the separation of the two stars, a significant fraction of the particle trajectories are found to cross the orbital plane, leading to the formation of a large-scale, outflowing circumbinary disk-like structure. The shocks which arise due to the collision of particles which are within crossing streamlines are expected to produce selected regions within the wind, particularly in the orbital plane, in which a higher degree of ionization prevails than in the wind in general. X-ray emission might also be expected from these regions. Such a model is suggested to be applicable to the erupting WR/LBV binary system HD 5980 and other binary LBV systems, during phases when wind velocities are slow.
High-Resolution Spectroscopy of Stellar Winds in Recently Recognized LBV Candidates
Authors: Miroshnichenko Anatoly S. , Chentsov Eugene L. , Klochkova Valentina G. 
Published: July 2016

AbstractWe present the results of high-resolution spectroscopic observations of two high-luminosity stars, MWC 314 and AS 314, obtained at the 6-meter telescope of the Russian Academy of Sciences. Both stars are suspected to be candidate LBVs in quiescence.
ISO-SWS Spectroscopy of B[e] Stars
Authors: Voors Robert H.M. , Waters Laurens B.F.M. , Morris Patrick W. 
Published: July 2016

AbstractWe present ISO-SWS spectra of B[e] stars. We find a wide diversity of spectral characteristics of B[e] stars, suggesting different origins for the circumstellar matter. Most B[e] supergiants show hot dust with weak amorphous silicate emission. MWC 300 has a warm dust shell with strong crystalline silicate emission; its evolutionary status is unclear.
Co-Rotating Interaction Regions in 2D Hot-Star Wind Models with Line-Driven Instability
Authors: Owocki Stanley P. 
Published: July 2016

AbstractI review simulations of Co-rotating Interaction Regions (CIRs) in line-driven stellar winds. Previous CIR models have been based on a local, Sobolev treatment of the line-force, which effectively suppresses the strong, small-scale instability intrinsic to line-driving. Here I describe a new “3-ray-aligned-grid” method for computing the nonlocal, smooth-source-function line-force in 2D models that do include this line-driven instability. Preliminary results indicate that key overall features of large-scale CIRs can be quite similar in both Sobolev and non-Sobolev treatments, if the level of instability-generated wind structure is not too great. However, in certain models wherein the unstable self-excitation of wind variability penetrates back to the wind base, the stochastic, small-scale structure can become so dominant that it effectively disrupts any large-scale, CIR pattern.
Theory of Pulsational Instabilities of Hot Stars
Authors: Pamyatnykh Alexei A. 
Published: July 2016

AbstractBasic physical mechanism of the pulsational instability in OB stars is shortly reviewed. Similarities and differences in the driving effect acting in these objects and in the classical pulsating variables are emphasized. Updated theoretical instability domains in the H-R diagram, in the log g – log Teff and in the Period – log Teff diagrams are presented and compared with the observational data on β Cephei, SPB and some other types of hot variables.
The Evolution of Non-spherical and Non-stationary Winds of Massive Stars
Authors: Langer Norbert 
Published: July 2016

AbstractWe describe present theoretical ideas about the time evolution of the winds of luminous stars with emphasis to effects of non-sphericity and non-stationarity. We discuss the evolution of the winds of rotating luminous stars during their main sequence evolution, in particular when they approach their Eddington-limit or any other surface instability. We then consider the winds of post-main sequence stars up to the immediate pre-supernova stage. We connect the giant outbursts of Luminous Blue Variables with luminous rotating post-main sequence stars in thermal disequilibrium. We further discuss the spin-up effect of Heger & Langer (1998) for post-red supergiants and describe its observational consequences. We compare theoretical models with observations of the winds of B[e] supergiants and Luminous Blue Variables in general, and with SN 1987A, VY CMa and η Car and the Pistol Star in particular.
Slow and Fast Diffusion in Asteroid-Belt Resonances: A Review
Authors: Ferraz-Mello S. 
Published: July 2016

AbstractThis paper reviews recent advances in several topics of resonant asteroidal dynamics as the role of resonances in the transportation of asteroids and asteroidal debris to the inner and outer solar system; the explanation of the contrast of a depleted 2/1 resonance (Hecuba gap) and a high-populated 3/2 resonance (Hilda group); the overall stochasticity created in the asteroid belt by the short-period perturbations of Jupiter’s orbit, with emphasis in the formation of significant three-period resonances, the chaotic behaviour of the outer asteroid belt, and the depletion of the Hecuba gap.
The Use of Geocentric Variables to Search for Meteoroid Streams and Their Parents
Authors: Froeschlé CL. , Jopek T.J. , Valsecchi G.B. 
Published: July 2016

AbstractA set of geocentric variables suitable for the identification of meteoroid streams has been recently proposed and successfully applied to photographic meteor orbits. We describe these variables and the secular invariance of some of them, and discuss their use to improve the search for meteoroid stream parents.
Explicit Semianalytical Theory of Asteroid Motion
Authors: Tupikova I.V. , Vakhidov A.A. , Soffel M. 
Published: July 2016

AbstractA new semianalytical theory of asteroid motion is presented. The theory is developed on the basis of Kaula’s expansion of the disturbing function including terms up to the second order with respect to the masses of disturbing bodies. The theory is constructed in explicit form that gives the possibility to study separately the influence of different perturbations in the dynamics of minor planets. The mean-motion resonances with major planets as well as mixed three-body resonances can also be taken into account. For the non-resonant case the formulas obtained can be used for deriving the second transformation to calculate the proper elements of an asteroid orbit in closed form with respect to inclinations and eccentricities.
On The Motion of Trapped Particles in The Vicinity of Corotation Centers
Authors: Beaugé C. , Lemaître A. , Jancart S. 
Published: July 2016

AbstractIn the present paper we analyse the motion of a massless particle during the capture process in an exterior mean-motion resonance under the effects of an external dissipative force. In particular, we study the orbital evolution from its initial approach to the commensurability up to the final nesting place in the periodic orbit around the equilibrium solution.
Dimensionality of Stable and Unstable Directions in the Gravitational N—Body Problem
Authors: Miller R.H. 
Published: July 2016

AbstractThe gravitational n—body problem is chaotic. Phase trajectories that start very near each other separate rapidly. The rate looks exponential over long times. At any instant, trajectories separated in certain directions move apart rapidly (unstable directions), while those separated in other directions stay about the same (stable directions). Unstable directions lie along eigenvectors that correspond to positive eigenvalues of the matrix of force gradients. The number of positive eigenvalues of that matrix gives the dimensionality of stable regions. This number has been studied numerically in a series of 100—body integrations. It continues to change as long as the integration continues because the matrix changes extremely rapidly. On average, there are about 1.2n unstable directions out of 3n. Issues of dimensionality arise when the tools of ergodic studies are brought to bear on the problem of trajectory separation. A method of estimating the rate of trajectory separation based on matrix descriptions is presented in this note. Severe approximations are required.
Detection of Ordered and Chaotic Motion using The Dynamical Spectra
Authors: Voglis N. , Contopoulos G. , Efthymiopoulos C. 
Published: July 2016

AbstractTwo simple and efficient numerical methods to explore the phase space structure are presented, based on the properties of the “dynamical spectra”. 1) We calculate a “spectral distance”Dof the dynamical spectra for two different initial deviation vectors.D→ 0 in the case of chaotic orbits, whileD→const≠ 0 in the case of ordered orbits. This method is by orders of magnitude faster than the method of the Lyapunov Characteristic Number (LCN). 2) We define a sensitive indicator called ROTOR (ROtational TOri Recongnizer) for 2D maps. The ROTOR remains zero in time on a rotational torus, while it tends to infinity at a rate ∝N= number of iterations, in any case other than a rotational torus. We use this method to locate the last KAM torus of an island of stability, as well as the most important cantori causing stickiness near it.
Cantori, Islands and Asymptotic Curves in The Stickiness Region
Authors: Efthymioulos C. , Contopoulos G. , Voglis N. 
Published: July 2016

AbstractThe resonant structure near a noble cantorus is found. Islands of stability are located near the gaps of the cantorus. The crossing of the gaps of the cantorus by the asymptotic curves of unstable periodic orbits is shown numerically (non-schematically). We discuss how these structures influence stickiness.
Diffusion Character in Four-Dimensional Volume-Preserving Map
Authors: Sun Yi-Sui , Fu Yan-Ning 
Published: July 2016

AbstractDue to the existence of invariant tori, chaotic sea and hyperbolic structures in higher dimensional phase space of a volume-preserving map, the diffusion route of chaotic orbits will be complicated. The velocity of diffusion will be very slow if the orbits are near an invariant torus. In order to realize this complicated diffusion phenomenon, in this paper we study the diffusion characters in the different regions, i.e., chaotic, hyperbolic and invariant tori’s regions. We find that for the three different regions, the diffusion velocities are different. The diffusion velocity in the vicinity of an invariant torus is the slowest one.
Planetary Systems
Authors: Artymowicz Pawel 
Published: July 2016

AbstractThe past decade brought direct evidence of the previously surmised exoplanetary systems. A variety of planetary system types exist those around pulsars, around both young and old main-sequence stars (as evidenced by planetesimal disks of the Beta Pictoris-type), and the mature giant exoplanets found in radial velocity surveys. The surprising diversity of the exoplanetary systems is addressed by several theories of their origin.
Resonant Relaxation
Authors: Tremaine Scott 
Published: July 2016

The two main arenas of astrophysical dynamics are celestial mechanics and stellar dynamics. The former deals with the motion of few bodies in a near-Kepler potential; the latter with the motion of many bodies in a non-Kepler potential. I would like to discuss the hybrid problem of many bodies in a near-Kepler potential, which is relevant to a number of astrophysical systems, including protoplanetary disks and the centers of galaxies containing massive black holes.Consider a spherical system of radius r, containing N bodies of mass m orbiting in the gravitational field of a body of mass M ≫ N m. Assume that the orbits have moderate eccentricities and random orientations and imagine taking a time exposure of the system over several orbits. Each body is then smeared into an approximate Kepler ellipse, which precesses slowly on a timescale tprec. Each ellipse exerts a force on other bodies at comparable radius, f ~ Gm/r2. The mean force from all the ellipses is Fm ~ N f. The mean force determines the precession time through the relation L ~ rFmtprec, where L ~ (GMr)1/2 is the specific angular momentum of an orbit. Thus tprec ~ (M/Nm)tcr, where tcr ~ (r3/GM)1/2 is the crossing time.
Measuring Mass Loss Rates from Galactic Satellites
Authors: Johnston Kathryn V. , Sigurdsson Stein , Hernquist Lars 
Published: July 2016

Number count profiles of many Galactic and some extra-galactic satellite systems show evidence for associated stars beyond the cut-off in density that is identified as the point of tidal limitation (e.g. Irwin & Hatzidimitriou 1995, Grillmair et al. 1995). These “extra-tidal” stars are assumed to be debris lost from the satellite due to heating or stripping by the Galactic tidal field or (in the case of globular clusters) evaporation of stars over the tidal boundary. In this contribution we present a method for using these features to measure the mass loss rate from the satellite, and test it on the results of numerical simulations of satellite disruption. A more detailed discussion of all aspects of this work can be found in Johnston, Sigurdsson & Hemquist (1998).In the numerical simulations, the satellite’s evolution along an orbit in a three component rigid model of the Galaxy is followed using a self-consistent field (SCF) code (developed by Hernquist & Ostriker 1992) to calculate the mutual interactions of stars in the satellite. Figure 1 shows the annularly averaged number surface density from one example simulation “observed” from the viewpoint of the center of the Galaxy after several Gigayears. The closed (open) symbols show the profile recovered if only bound (all) stars are considered. Clearly there is a break in the open symbols at the radius rbreak where the analysis becomes dominated by unbound stars.
On Construction of a Long-Term Moon’s Theory
Authors: Ivanova T.V. 
Published: July 2016

An analytical long-term theory of the motion of the Moon is constructed within the framework of the general planetary theory (Brumberg, 1995). A method, different from the one of (Ivanova, 1997) designated below as (*), for the determination of the perturbations depending on the eccentricities and inclinations of lunar and planetary orbits is used which allows to obtain the solution of the problem in the purely trigonometric form up to any order with respect to the small parameters.The aim of this paper is to construct the long-term Lunar theory in the form consistent with the general planetary theory (Brumberg, 1995). For this purpose the Moon is considered as an additional planet in the field of eight major planets (Pluto being excluded). In the result the coordinates of the Moon may be represented by means of the power series in the evolutionary eccentric and oblique variables with trigonometric coefficients in mean longitudes of the Moon and the planets. The long-period perturbations are determined by solving a secular system in Laplace-type variables describing the secular motions of the lunar perigee and node and taking into account the secular planetary inequalities.
Averaging of Earth-Crossing Orbits
Authors: Gronchi G.F. , Milani A. 
Published: July 2016

The orbits of planet-crossing asteroids (and comets) can undergo close approaches and collisions with some major planet. This introduces a singularity in the N-body Hamiltonian, and the averaging of the equations of motion, traditionally used to compute secular perturbations, is undefined. We have shown (Gronchi and Milani, 1998) that it is possible to define in a rigorous way some generalised averaged equations of motion, in such a way that the generalised solutions are unique and piecewise smooth, with corners on the node crossing lines.The model is the averaged equations of motion first introduced by Kozai (1962): the perturbing planets are assumed to move in circular, coplanar orbits, and the equations of motion are averaged over the anomalies of the asteroid and of the planets. In the non-crossing case the averaging is integrable; in the planet-crossing case there is a polar singularity of order two in the equations of motion, and averaging is not possible. To define a generalized solution, we decrease the order of the polar singularity by the method of extraction of the singularities by Kantorovich. The singularity of the perturbing function is approximated by a modified inverse distance, the one between the straight lines tangent to the two orbits at the nodal points. In this approximation the averaged perturbing function has an analytical expression, allowing explicit computation with elliptic integrals and elementary functions.