bluuebunny/crossref_metadata_2025 huggingface dataset:
New Insights on the Local ISM from EUV Observations
Authors: Bowyer Stuart
Published: July 2016

New results from EUVE are reviewed, with emphasis on the ionization state of the ISM and the question of thermal pressure balance between warm clouds and the hot intercloud medium. A description of what may be expected from the next generation of experiments, some to be launched shortly, will also be presented.
The Interstellar and Circumstellar Environment of White Dwarfs
Authors: Barstow M.A. , Dobbie P.D. , Holberg J.B.
Published: July 2016

We have studied the EUV spectra of 13 DA white dwarfs, observed by the EUVE satellite, paying attention to the possible sources of absorbing material along the lines-of-sight in both the local interstellar medium and in the photospheres of the stars themselves. The range of interstellar column densities seen are consistent with our previous understanding of the local distribution of material. Absorption from interstellar He II is found in the direction of five stars, allowing us to measure directly the He ionization fraction and estimate, indirectly, that of H. The weighted mean ionization fractions along these lines-of-sight are 0.27 ± 0.04 and 0.35 ± 0.1 respectively. Where He II is directly detected, the observed ionization fractions are not correlated with direction or with the volume/column density of material along the line-of-sight. Furthermore, the limits on the amount of He II established in all other directions completely encompass the range of observed values. Indeed, all the data can be consistent with more or less constant He and H ionization fractions throughout the local ISM. However, observation of very hot DA stars, indicating higher He II columns, might contradict this picture if the material is not photospheric or circumstellar.
The Soft X-ray Background Spectrum from DXS
Authors: Sanders W.T. , Edgar R.J. , Liedahl D.A. , Morgenthaler J.P.
Published: July 2016

The Diffuse X-ray Spectrometer (DXS) obtained spectra of the low energy X-ray (44 – 83 Å) diffuse background near the galactic plane from galactic longitudes 150° ≲ l ≲ 300° with ≲ 3 Å spectral resolution and ~ 15° angular resolution. Thus, DXS measured X-ray spectra that arise almost entirely from within the Local Bubble. The DXS spectra show emission lines and emission-line blends, indicating that the source of the X-ray emission is thermal – hot plasma in the Local Bubble. The measured spectra are not consistent with those predicted by standard coronal models, either with solar abundances or depleted abundances, over the temperature range 105 – 107 K. The measured spectra are also inconsistent with the predictions of various non-equilibrium models. A nearly acceptable fit to DXS spectra can be achieved using a hybrid model that combines the Raymond & Smith ionization balance calculation with recently calculated (by DAL) ionic emission lines.
Planned Observations of Hot Gas in the LISM
Authors: McLean R. , Green J.C. , Gunderson K.S.
Published: July 2016

We plan to observe hot gas in the local interstellar medium (LISM) at high resolution using a rocket-borne spectrograph that can simultaneously observe OVI, NV and CIV at resolutions of 1 – 2kms−1. Data from a single flight will have sufficient signal to noise ratio to detect a broad 50kms−1 component down to a column density of N ≥ 0.5 × 1013cm−2. High-velocity components as fast as 300kms−1 can be detected. New high resolution observations of hot gas absorption line profiles will probe the kinematics of the local bubble, and comparison between the carbon, nitrogen and oxygen profiles will allow discrimination between the various production models.
Interstellar C IV and Si IV in the Direction of Loop I
Authors: Freire Ferrero Rubens
Published: July 2016

Nearby late-B and early-A stars show clear IS absorptions in Mg II, C II and other lines (IUE spectra). Some of them, in the Sco Cen direction, also show absorption features at C IV and Si IV line wavelengths. We discuss the possible formation of these lines in an intermediate temperature gas region between the dense and cold H I wall and the hot ISM, a region that could be the collision interaction between the Local Bubble and the Loop I supershell. Some individual stellar spectra are presented and discussed.
A New View of the LHB and ¼ keV X-ray Halo
Authors: Snowden S.L.
Published: July 2016

The X-ray sky at ¼ keV is completely dominated by diffuse emission. It has become clear that it originates as at least three separate components: local emission within the nearest ~ 100 pc from the Sun, halo emission from beyond most of the neutral material of the Galactic disk, and the superposition of unresolved extragalactic sources. The only way to determine the temperatures and relative emission measures of the hot plasma responsible for the Galactic components is to use the X-ray intensity variations due to column density variations in the intervening Hi to separate the components. “Shadowing” studies have been pursued for individual objects using ROSAT data, from both pointed observations and the all-sky survey with considerable success.

This paper presents the results of an all-sky analysis of the ¼ keV background from the ROSAT survey. A Local Hot Bubble is found consistent with, although somewhat smaller than, previous models. It has a temperature of 106.1 K and an emission measure which varies by a factor of ~ 3.3 over large angles. The halo emission has a temperature near 106.0 K with an emission measure which varies from near zero to more than five times that of the local emission.
ISOPHOT Observations of a Cold Filament in the Local Hot Bubble
Authors: Herbstmeier Uwe , Alexandre Wennmacher
Published: July 2016

We report on FIR measurements of the dust component towards LVC 88+36–2, a dense neutral filament in the Local Hot Bubble. The measurements were performed with ISOPHOT, the photometer on-board ESA’s Infrared Space Observatory ISO. The dust temperature derived is about 18 K and stays constant across the filament. Limb brightening at 60μm is measured in agreement with cirrus clouds not located in the Local Hot Bubble. No evidence for an increased UV radiation field along the boundaries of the cloud is found.
Interaction of Interstellar Shocks with Dense Obstacles: Formation of “Bullets”
Authors: Gvaramadze V.V.
Published: July 2016

The so-called cumulative effect take place in converging conical shock waves arising behind dense obstacles overtaken by incident interstellar shock. A significant part of energy of converging flow of matter swept-up by a radiative conical shock can be transferred to a dense jet-like ejection (“bullet”) directed along the cone axis. Possible applications of this effect for star-forming regions (e.g., OMC-1) and supernova remnants (e.g., Vela SNR) are discussed.
The Line of Sight of ϵ Canis Majoris: Depletion and Extent of the Local Cloud
Authors: Gry Cécile , Dupin Olivier
Published: July 2016

With new high resolution UV spectra of ϵ CMa we show that the gas column density in this sight-line is less than 4 1017 cm−2, that the neutral gas density is less than 10−5 cm−3 after the first 3 parsecs, and that the Local Cloud seems to be almost undepleted and to extend to no more than 0.6 pc in this direction.
The Magnetic Field Near the Local Bubble
Authors: Heiles Carl
Published: July 2016

There are almost no direct observational indicators of the magnetic field inside the local bubble. Just outside the bubble, the best tracers are stellar polarization and HI Zeeman splitting. These show that the local field does not follow the large-scale Galactic field. Here we discuss whether the deformation of the large-scale field by the local HI shells is consistent with the observations. We concentrate on the Loop 1 region, and find that the field lines are well-explained by this idea; in addition, the bright radio filaments of Radio Loop 1 delineate particular field lines that are “lit up” by an excess of relativistic electrons.
Measurements of the Size and Pressure of the Local Bubble Towards Eridanus
Authors: Burrows D.N. , Guo Z.
Published: July 2016

We have measured the size and pressure of the Local Bubble in the direction of the constellation Eridanus using ROSAT PSPC observations of soft X-ray “shadows” cast by neutral clouds against the bright X-ray emission from the Orion-Eridanus superbubble. We discuss the technique and present our results for the size of the Local Bubble in the directions of our shadowing fields. Using these distances and the measured soft X-ray emission measures, we derive the Local Bubble’s thermal pressure. For four lines of sight in Eridanus, we obtain pressures of about 1.2 × 104 K cm−3, in good agreement with measurements in several other directions.
Interaction of the Local Bubble with its environment
Authors: Egger Roland
Published: July 2016

The Local Bubble (LB), a volume of roughly 100 pc radius filled with ionized gas of high temperature and low density, is not a unique object. It is obviously surrounded by several interstellar bubbles of similar properties. Some of them are as close as to undergo interaction with the LB. Our most prominent neighbour is the Loop I superbubble formed by the Sco-Cen OB association. It is shown that this huge shell is in collision with our Local Bubble. The product of this interaction is an annular cloud of dense neutral gas at the boundary between the two bubbles. Other examples for close neighbouring bubbles are the Gum nebula, the Eridanus bubble and possibly the two radio loops II and III.
ASCA SIS X-ray Observations of the Wind Blown Bubble NGC 6888
Authors: Wrigge Matthias , Chu You-Hua , Magnier Eugene A. , Kamata Yuichi
Published: July 2016

We present ASCA SIS observations of the wind-blown bubble NGC 6888. Because the ASCA SIS is sensitive to higher energy photons and has a higher spectral resolution compared to the ROSAT PSPC, we are able to detect a T ≈ 8×106 K plasma component besides the T ≈ 1.5×106 K component known from previous PSPC observations. The existence of a high-temperature component, the observed limb-brightened X-ray surface brightness profile, and the observed level of X-ray surface brightness cannot be satisfactorily explained by currently available models. Reducing heat conduction at the contact discontinuity may raise the central temperature and produce a limb-brightening; however, the expected X-ray surface brightness is still considerably higher than the observed surface brightness.
The Galactic HI Halo
Authors: Kalberla P.M.W. , Westphalen G. , Mebold U. , Hartmann D. , Burton W.B.
Published: July 2016

We find indications for diffuse HI gas at substantial z heights in our Galaxy, with a velocity dispersion of 60 km s−1 and a vertical projected column density of 1.41019 cm−2. This pervasive component of the emission spectrum could be identified in the Leiden/Dwingeloo 21 cm Survey (LDS) after increasing the accuracy further by correcting the observations for reflections from ground. Assuming hydrostatic equilibrium an exponential scale height of 4.4 kpc for the observed diffuse high-dispersion Hi component is deduced. This differs from the scale height of lkpc derived by Lockman & Gehman (1991), which corresponds to a velocity dispersion of 34kms−1, based on an analysis of the the Bell Laboratories HI Survey (BLS). A comparison of BLS and LDS data explains the differences in the derived model parameters in terms of baseline uncertainties at a level of ≈ 30 mK. We find additional indications for baseline uncertainties in the BLS data. Concerning the LDS we cannot, however, exclude that this survey may also be affected by baseline uncertainties. Receiver bandpass and stray-radiation effects need a more thorough analysis before drawing firm conclusions.
3D Hydrodynamical Simulations of a Galactic Fountain
Authors: de Avillez M.A. , Berry D.L. , Kahn F.D.
Published: July 2016

Galactic fountains are thought to be responsible for the formation of the observed intermediate and high velocity clouds in the Galactic halo. Threedimensional simulations have been carried out to determine the evolution of the disk gas as it enters the fountain, cools and returns to the Galactic disk. The descending cold gas, headed by a shock, sweeps up the ascending flow, triggering the formation of an unstable layer where Rayleigh-Taylor instabilities grow, which may provoke the formation of the observed clouds.
A Soft X-ray Halo of the LMC?
Authors: Blondiau M.J.
Published: July 2016

ROSAT 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.
The Local Bubble and Beyond: Summary
Authors: McKee Christopher F.
Published: July 2016

Lyman Spitzer, Jr, the founder of modern studies of the interstellar medium (ISM), passed away March 31, 1997. This conference occurred shortly thereafter and is dedicated to his memory. While many of his contributions underlie the work that was discussed at this meeting, one paper stands out in particular: his theoretical “discovery” of the hot gaseous halo of the Galaxy based on the need to confine the clouds of H I observed above the Galactic plane (Spitzer 1956). We now know that much of the ISM within about 100 pc of the Sun is largely filled by very low density gas, which is generally inferred to be hot, and as a result this region is termed the Local Bubble (Cox and Reynolds 1987). This conference was convened to establish the current state of our knowledge of the Local Bubble, both observational and theoretical, and its relation to the rest of the ISM. Because it is nearby, the Local Bubble is a laboratory for interstellar astrophysics, making the dedication to Spitzer’s memory particularly appropriate.
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 form

where 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).
Wind-Compressed Disks
Authors: Bjorkman Jon E.
Published: July 2016

We discuss the wind-compressed disk (WCD) model and its ability to produce disks in the outflows from rapidly rotating stars. In particular, we discuss the recently discovered non-radial force components that may inhibit the formation of the disk and present preliminary investigations of the ionization distribution and associated line profiles in the WCD model.
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

Early-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

Following 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

We 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

The 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

We 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

We 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

I 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

Basic 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

We 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

This 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.
Small Bodies in The Outer Solar System
Authors: Marsden Brian G.
Published: July 2016

This report is a continuation of three earlier reviews (Marsden 1996a, 1996b, 1998) that included a summary of our orbital knowledge of the Kuiper Belt. Presented at conferences held in the middle of 1994, 1995 and 1996, respectively, these reviews showed the steadily developing picture of a system dominated by the platinos, librating in the 2:3 mean-motion resonance with Neptune, and the cubewanos, a somewhat more distant population of nonlibrating objects with low orbital eccentricities. The existence of a 3:4 Neptune librator and a 3:5 Neptune librator was also suspected. These librators have now been confirmed, and a possible 4:7 librator and possible second 3:5 librator have also been found. The known and suspected multiple-opposition librators are listed in Table 1. Here it is important to note that the orbital semimajor axes a (in AU), eccentricities e and inclinations i (in degrees with respect to the 2000.0 ecliptic) are mean values that eliminate the large 12-year and 30-year periodicities arising from the indirect perturbations by Jupiter and Satum on sun-centered orbits. The numbers in parentheses are the semimajor axes (in AU) corresponding to the resonances. Following the absolute magnitude H, the entries “Nep.” and “Ura.” show the minimum distances (in AU) from Neptune and Uranus (the latter being of course quite small for the most eccentric 2:3 Neptune librators) within several millennia of the present time.
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

A 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

A 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

In 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

The 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

Two 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

The 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

Due 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

The 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.
Rotational Motion of Celestial Bodies in the Relativistic Framework
Authors: Klioner Sergei A. , Soffel Michael
Published: July 2016

There are several important reasons to consider relativistic effects in rotational motion of celestial bodies. General Relativity is now recommended by the International Astronomical Union and International Union of Geodesy and Geophysics as a theoretical framework for modeling of high-precision observational data. On the other hand, various geodynamical observations provide data which are widely used for testing General Relativity itself.

In Newtonian mechanics it is well known how to describe rotational motion of an extended body. In General Relativity this is a rather subtle issue. The concept of a precessing extended rigid body in general relativity encounters fundamental difficulties and cannot be introduced even in the first post-Newtonian approximation. From a practical point of view, however, the rotational motion of the Earth even at the Newtonian level is defined operationally through the time-dependence of geocentric quasi-inertial coordinates of observing sites. An analogous operational definition can be applied in general relativity. To this end, we need a set of physically adequate reference systems.
Effective Lyapunov Numbers and Correlation Dimensions in a 3-D Hamiltonian System
Authors: Tsiganis K. , Anastasiadis A. , Varvoglis H.
Published: July 2016

Transport in Hamiltonian systems, in the case of strong perturbation, can be modeled as a diffusion process, with the diffusion coefficient being constant and related to the maximal Lyapunov number (Konishi 1989). In this respect the relation found by Lecar et al. (1992) between the escape time of asteroids, TE, and the Lyapunov time, TL, can be easilly recovered (Varvoglis & Anastasiadis 1996). However, for moderate perturbations, chaotic trajectories may have a peculiar evolution, owing to stickiness effects or migration to adjacent stochastic regions. As a result, the function χ(t), which measures the exponential divergence of nearby trajectories, changes behaviour within different time intervals. Therefore, trajectories may be divided into segments, i = 1,..., n, each one being assigned an “Effective” Lyapunov Number (ELN), λi = χ(ti).
A Symplectic Integration Scheme that allows Close Encounters between Massive Bodies
Authors: Chambers J.E.
Published: July 2016

Mixed-variable symplectic integrators provide a fast, moderately accurate way to study the long-term evolution of a wide variety of N-body systems (Wisdom & Holman 1991). They are especially suited to planetary and satellite systems, in which a central body contains most of the mass. However, in their original form, they become inaccurate whenever two bodies approach one another closely. Here, I will show how to overcome this difficulty using a hybrid integrator that combines symplectic and conventional algorithms.

A symplectic integrator works by splitting the Hamiltonian, H, for an N-body system, into two or more parts H = H0 + H1 + …, where є i = Hi/H0 ≪ 1 for i = 1, 2 …. An integration step consists of several substeps, each of which advances the system due to the effect of one part of the Hamiltonian only. The error incurred over the whole step is ∼ є τn1, where τ is the timestep, n is the order of the integrator, and є is the largest of єi.
Generalized Gylden-Type Systems in Universal DS-Like TR-Variables
Authors: Floría Luis
Published: July 2016

Scheifele (1970) applied Delaunay-Similar (DS) elliptic Keplerian elements (with the true anomaly as the independent variable) to the J2 Problem in Artificial Satellite Theory, making an element of the true anomaly. Deprit (1981) views Scheifele’s TR-mapping as an extension of Hill’s transformation from a 6-dimensional phase space to an enlarged, 8-dimensional one. To adapt this approach to elliptic-type two-body problems with a time-varying Keplerian parameter μ(t), Floía (1997, §3, §4) treated a Gylden system (Deprit 1983) and derived “Delaunay-Similar” variables via a TR-like transformation. Now we extend our treatment to perturbed Gylden systems, and modify the TR-map to deal with any kind of two-body orbit. We work out our generalization and the resulting variables within a unified pattern whatever the type of motion, in terms of universal functions (Stiefel & Scheifele 1971, §11; Battin 1987, §4.5, §4.6) and auxiliary angle-like parameters.
Orbital Structure of the Two Fixed Centres Problem
Authors: Cordero A. , Martínez Alfaro J. , Vindel P.
Published: July 2016

The set of orbits of the Two Fixed Centres problem has been known for a long time (Chartier, 1902, 1907; Pars, 1965), since it is an integrable Hamiltonian system.

We consider a plane that contains the fixed masses. Denote by φ the angle denned by this plane and the one that contains also the third body. The momentum pφ is a first integral of the system and when pφ is different from zero, the manifold generated by the generalized coordinates and momenta are two copies of the three-dimensional sphere S3. If pφ = 0, that is to say when the planet crosses the line joining both suns, the motion is restricted to a planar one. All the equilibrium points appears in this case and therefore the phase spaces are more complex. We restrict our attention to this case which has two degrees of freedom.

It is again a Bott-integrable Hamiltonian system. The set of periodic orbits of this systems can be studied from a subset of them, the Non-Singular Morse-Smale type orbits (see Casasayas, 1992). It is proved in Campos (1997) that a small perturbation of a Bott-integrable Hamiltonian system transforms it into a Non-Singular Morse-Smale system. The NMS periodic orbits belong to both the NMS system and the Hamiltonian one. Moreover, The NMS p.o. can be continued to nearly Hamiltonian systems. For instance, in our case to the Restricted Three Body Problem and in the study of the motion of a material point moving inside the gravitational field generated by two stars. This approximation is also useful when the motion of an artificial satellite around a spheroidal body is considered.
Outbursts of Southern Dwarf Novae
Authors: Bateson Frank M.
Published: July 2016

The mean cycles and types of maxima for a number of dwarf novae are tabulated. It is shown that supermaxima are not confined to dwarf novae of short mean cycles. The decline rates for some stars are examined to ascertain if the orbital period, accurate to within ten percent, could be derived from visual observations. It is shown that, at least for some stars, the rate of decline differs widely at different levels of brightness, and, also, between dissimilar maxima of the same star.
Nova Scorpii 1964
Authors: Przybylski A.
Published: July 2016

Nova Scorpii 1964 was discovered several months after its maximum on a photograph of the centre of the Milky Way taken in May 1964. Its light curve shows that it was a slow nova. At the time of the discovery the nova was in the transition phase between the “4640” stage and the early nebular stage.
Evolution and Problems of Red Long Period Variables
Authors: Wood P. R.
Published: July 2016

Variability on the red giant branch (RGB) occurs at an interesting and important stage in the life of a star. This phase of evolution is characterized by a substantial amount of mass loss (as a continuous stellar wind or as an abrupt planetary nebula ejection), by flashing of the helium burning shell (at least in stars less massive than ~ 8 M) and by surface enrichment of elements heavier than hydrogen. The galactic importance of these processes is illustrated by the calculations of Cahn and Wyatt (1978) who estimate that material is presently being lost by stars on the RGB at a rate which is roughly equal to the rate at which material is being locked up in stars by star formation. A complementary calculation by Iben and Truran (1978) shows that shell flashing in red giant stars, coupled with mass loss, is a major source of enrichment of the interstellar medium over a wide range of atomic mass from C to heavy s-process elements. Hopefully, studies of the red long period variable (RLPV) stars can assist in the investigation of some of the above processes so that a comprehensive picture of the later phases of stellar evolution can be obtained.
The Spectra of Red Variables: SC Stars
Authors: Keenan Philip C.
Published: July 2016

The value of recording the spectra of red stars depends upon one’s point of view. On the one side, to those concerned with spectral classification in general, it is of the greatest aid in calibrating the criteria of classification if those criteria are observed in a variable star in which the physical variables change by a known amount. Thus the temperature differences, amounting to three or four hundred degrees, between the maximum and minimum phases of Mira variables, have helped to establish the temperature criteria that are in general use for the coolest stars.

On the other hand, I am sure that at this meeting there is more interest in the inverse problem: how to use the behavior of the spectral features to learn more about what is going on in the variable star - or, at least, at their surfaces.