bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Non-Linear Theory of Spiral Structure
Authors: Contopoulos G. 
Published: July 2016

AbstractThe main steps of the non-linear theory of spiral structure are described. Near each of the main resonances the basic periodic orbits are calculated, and the sets of non-periodic orbits that follow them are found. A different integral of motion is applicable for each set, besides the Jacobi integral. Then the initial distribution function, f, is expressed as a function of the two integrals and the corresponding angles. The final distribution function is found by averaging over the angles:Then by integratingover all velocities we find the response density σresp. In order that σrespshould be equal to the imposed density, σimpwe must adjust the parameters of the imposed spiral field. The form of σrespaway from resonances can be derived explicitely for tight ana open spirals or bars; however near the resonances σrespcan be only calculated numerically. If the imposed field has almost constant amplitude, then the amplitude of the response is very large near the Inner Lindblad Resonance. In the case of a tight spiral the azimuth of the response density maximum with respect to the imposed density maximum tends to zero outside the ILR, while it tends to -90° inside the ILR. One possible self-consistent solution has zero amplitude inside the ILR both in the case of tight spirals and of bars. Finally an important quadrupole term was found near the ILR.
Solar Cosmions
Authors: Spergel David N. 
Published: July 2016

AbstractTwo of the outstanding problems in astrophysics are the solar neutrino problem and the missing mass problem. The “solar cosmion”, a weakly interacting massive particle, could solve both problems. Several particle physics models have been suggested for the solar cosmion.The solar cosmion may have other interesting astrophysical effects. It will alter the predicted helioseismology spectrum, effect horizontal branch evolution and may alter the mass-radius relationship in low mass stars. These considerations constrain solar cosmion properties.Several laboratories have begun an active experimental search for the solar cosmion. The UCSB-UCB-Saclay silicon experiment in the Oroville mine has already placed stringent limits on solar cosmions that couple to matter through spin-independent interactions. A planned Saclay experiment may either detect or rule out the existence of “solar cosmions”.The Sun is an powerful laboratory for exploring particle physics beyond the standard model. Even if “solar cosmions” do not exist, the Sun can help “illuminate” the search for other weakly interacting particles posited as solutions to the missing mass problem.
The Long Term Behaviour of Classical Old Novae
Authors: Bianchini A. 
Published: July 2016

AbstractQuiescent novae are more stable against mass transfer rate than dwarf novae. They may however show cyclical variations of their quiescent magnitudes on time scales of years, probably caused by solar–type cycles of activity of the secondary. The probability density function of the periods of the cycles observed in CVs is similar to that for single stars. Sometimes, periodic or quasi periodic light variations on time scales of tens to hundreds of days are also observed. Although the magnitudes of prenovae and postnovae are essentially the same, the definition of the magnitude of a quiescent nova is still uncertain. At present, the hibernation theory for old novae seems to be supported only by the observations of two very old novae.
Spin Period Variations of the White Dwarf in FO Aqr/H2215-086
Authors: Augusteijn Thomas 
Published: July 2016

AbstractAn investigation of the rotation period variation of the white dwarf in FO Aqr/H2215-086 is presented. A cubic ephemeris is derived for the arrival times of maxima of the pulse light curve which is associated with the white dwarf rotation. Potential problems, resulting from variations of the pulse arrival time as function of orbital phase, and from the change with wavelength of the pulse light curve shape, are investigated. A possible explanation is given for the second effect, being caused by a variable contribution of a modulation at the beat period (of the pulse and orbital periods) as a function of orbital phase.
A Possible Nova from the IRAS Point Source Catalogue
Authors: Garcia-Lario P. , Manchado A. , Sahu K.C. , Pottasch S.R. 
Published: July 2016

AbstractDuring a spectroscopic survey of IRAS sources with infrared colours similar to those in planetary nebulae, IRAS 06518-1041 revealed itself as a possible nova-like object. The spectrum of IRAS 06518 – 1041, which is shown in Figure 1, presents strong and broad hydrogen Balmer lines together with broad permitted lines of He and C. This spectrum also shows a much weaker narrow nebular component, with forbidden lines of [OIII] and narrow Hα. The mean velocity associated to the observed line widths is about 800 km s−1. The observed emission lines correspond well to typical post-novae objects in the quiescent phase (Warner, 1989). Another argument which supports the idea of this object being a nova-like star is that there are some indications of the binarity of the source if we attend to the asymmetries observed both in the Hβ and Hα profiles. The high resolution spectrum at Hα shows the presence of a sharp double-peaked central emission from a low expanding envelope at a velocity of 35±5 km s−1, together with a much broader emission with velocities of several hundred kilometers. The displacement between both components is about 130 km s−1. This broad component could be due to the presence of an accretion disk around the system with hydrogen-rich material falling onto the compact companion. This is supported by the fact that the broad emission looks like the combination of different velocity components giving rise to a complex and asymmetric line profile. From this high resolution spectrum we derive a VLSR = 57 km s−1, which points to a distance of 5.5 kpc if we adopt the model rotation curve of the Galaxy given by Pottasch (1984) and a distance of 9 kpc from the Sun to the galactic center. The large infrared excess detected by the IRAS satellite is probably the result of the formation of dust grains in the outer parts of the common envelope at a temperature of about 160 K, as can be derived from the infrared data. This infrared excess is also present in other nova-like objects and is specially important in old and slow novae (Callus et al, 1987) where the continuous ejection of mass produces dust shells which are strong emitters in the infrared.
Spectroscopic Observations of the Southern Old Novae CP Pup and V841 Oph
Authors: Bianchini A. , Friedjung M. , Sabbadin F. 
Published: July 2016

AbstractNew spectroscopic observations of the old nova CP Pup suggest most probable orbital period of 0.061375 days. First systematic monitoring of the very old nova V841 Oph reveals orbital motion with a most probable period of about 0.6 days. A slightly eccentric solution at P = 0.3755 days is less probable.
Measurements of Outburst Characteristics, Temperatures, Densities and Abundances in the Ejecta of Nova Muscae 1983
Authors: Hassall B.J.M. , Snijders M.A.J. , Harris A. W. , Cassatella A. , Dennefeld M. , Friedjung M. , Bode M. , Whittet D. , Whitelock P. , Menzies J. , Evans T. Lloyd , Bath G.T. 
Published: July 2016

We present results for IUE, optical and IR observations of Nova Muscae 1983, from early outburst to January 1986 obtained by the European IUE Target of Opportunity Team. A detailed description of the data will appear elsewhere (Hassall et al., 1989), but here we summarise the most important results.The outburst lightcurve initially indicated a fast speed class for this nova, but was later characterised by a rather slow optical decline with two or more secondary outbursts with sudden doubling of the bolometric flux. In Figure 1, we show the contributions of X-ray, UV, optical and IR to the total luminosity for 1200 days following outburst, assuming a distance of 4.3kpc and an interstellar extinction E(B-V)=0.5. In the absence of dust formation, first the UV and later the X-ray flux (Ögelman et al, 1984) dominate the radiative energy late into the nebular phase. There was a plateau stage lasting about 500 days, with a bolometric luminosity of ~ 1038ergs s−1 near the Eddington limit. The secondary outbursts were thus super-Eddington. We estimate a total outburst energy (including kinetic and gravitational potential energy of the ejecta) of ~ 5·l046 ergs, corresponding to a mass of ~ 4·10−6Mº of hydrogen burnt in the thermonuclear runaway.
Optical Observations of Recent Novae
Authors: Wolf B. 
Published: July 2016

AbstractThe observations of two rather different classical novae, V 1500 Cyg (= Nova Cyg 1975) and NQ Vul (= Nova Vul 1976), are presented and compared. Nova Cyg 1975 is outstanding with respect to absolute magnitude (M = -10), range of brightening (Δm = 19), and speed of evolution (t3= 3.6 days). Its prenova object had to be fainter than about magnitude 9. The corresponding values for Nova Vul 1976 are rather conservative (M≈-7.5, Δm ≈ 12, t3=40 days, absolute magnitude of the prenova ≈4.5). The light curve of Nova Cyg 1975 is very smooth. Some superimposed photometric variations of a small and slightly variable amplitude of a period of 3.4 hours are most naturally ascribed to a binary nature of Nova Cyg 1975. Nova Vul 1976 has a completely different lighteurve with extremely strong rapid irregular variations of considerably amplitude. There is a remarkable second maximum about 14 days after discovery.
3. The Constitution of Cometary Nuclei
Authors: Whipple F. L. 
Published: July 2016

For many comets the accelerations radially from the Sun have been determined by deviations from gravitational orbits. The radial force per unit area can be calculated on the basis of certain assumptions concerning the nature of the vaporizing material, the physical circumstances, and the geometry of the cometary nucleus. The observed accelerations combined with the calculated forces yield numerical values for (1-A)/R where A is the albedo, and R the radius of the nucleus. At extreme solar distances photometry provides the well-known quantity area-times-albedo or RA1/2. Solutions are then possible for R and A for the nuclei of the comets. The derived quantity, (1-A)A1/2, provides a limiting check on the basic assumptions and, therefore, on the basic physical properties of the nuclei. For ten short-period comets with q < 1.5 AU, the observations are satisfied by H2O ice. About half show “spotty” surfaces.For comets of a single apparition H2O ice is generally not volatile enough to produce the observed radial accelerations. The resulting problems are discussed including the possibility that in some cases displacements of the photometric from the gravitational nucleus may produce spurious non-gravitational accelerations.The physical characteristics of comets vary with their orbits and with their age. New comets on their first near solar passage from the Oort cloud are extremely active. The activity falls statistically with increasing age. This sequence must represent a corresponding sequence or layering of structure from the surface of a new comet inwards and is described qualitatively in this paper.The excessive activity of new comets is ascribed to cumulative cosmic-ray damage that activates the outer few hundred gm cm-2 from the surface. The total energy input in 4.6 x 109 yr reaches 50,000 cal gm-1 near the surface so that both crystalline structures and molecules are severely damaged if not completely destroyed. Annealing at T - 10 K must be very small. Hence significant exothermic energy in the form of defects, vacancies and radicals is added to produce the extraordinary activity observed in new comets.Other aspects and problems of cometary activity are discussed.
GRADES: A New Instrument for Spectroscopy of the Local Hot Gas
Authors: Hurwitz M. , McKee C. , Edelstein J. , Vallerga J. , Jelinsky P. , Freyberg M. , Breitschwerdt D. 
Published: July 2016

AbstractCompeting models for the origin of the local component of the diffuse X-ray background span more than an order of magnitude in temperature. We propose to test these models with a new instrument, the GRating Array Diffuse EUV Spectrometer (GRADES), which is sensitive to diffuse emission in the 90 – 260 Å bandpass, and offers a peak spectral resolution of about λ/127.
On the Zero-Level of the Soft X-ray Background
Authors: Freyberg M.J. 
Published: July 2016

AbstractThe soft X-ray background (SXRB, 0.1 – 2.0 keV) is generally believed to be comprised of a local component, the Local (Hot) Bubble (LHB), which is only marginally absorbed, and of distant emission (galactic halo, extragalactic background). It is vital to know the foreground emission (spectrum, intensity) if one wants to disentangle and determine the 3-dimensional structure of the X-ray emitting regions. During the ROSAT PSPC All-Sky Survey non-cosmic enhancements of the measured X-ray count rate have been observed. These lasted typically for up to 8 hours (i.e. a couple of orbits). Using PSPC data it has been shown that these so-called “long-term enhancements” (LXE) are related to geomagnetic storms and variations of the solar wind. Moreover, during an observation of the comet Hyakutake indications for a correlation of the X-ray background with the X-ray brightness of the comet have been found. This can be interpreted in terms of an X-ray emitting region around the Earth. Although the variable component of these enhancements could be subtracted from the sky maps an uncertainty remained concerning an undetected and relatively constant contribution which might be present in soft X-ray observations. As a consequence this could explain or contribute to the high PSPC count rate observed from the dark side of the Moon.
Modeling the Local Bubble
Authors: Cox Donald P. 
Published: July 2016

AbstractModeling the Local Bubble is one of those activities fraught with danger. It is very easy to be too naive, to fail to consider the dependence of the model on assumptions about the nearby ambient state, or the likelihood of such a structure. It is similarly easy to become so caught up in the details of the vicinity that it is unclear where to begin a necessarily idealized modeling effort. And finally, it is important to remember that the data we have may in some cases be lying to us, and that we have not yet learned to read their facial expressions quite carefully enough.That said, I’ve tried in this paper to be helpful to those who may wish to take the risks. I surveyed the very most basic stories that the data seem to tell, and pointed out the standard coincidences that may be telling us a lot about what is happening, but may turn out once again to have been just coincidences. I’ve described 5 distinct conceptions that in one flavor or another pretty well survey the collection of mental images that have so far been carried by those who’ve attempted models. One may be right, or something entirely different may be more appropriate. It’s at least vital to realize that a conception comes first, followed by a simplified model of details. I’ve also included a long list of questions directed at observers. Some have partial answers, some one wouldn’t know today quite how to approach. But it is a list that students of the soft x-ray background, interstellar absorption lines, possible instrumentation, and the heliosphere may wish to review from time to time, just to see whether they can figure out how to be more helpful. There is another list for modelers, things the models must address, however-so-flimsily if necessary, because there are strong observational constraints (and stronger ones coming) on what can and cannot be present in the local ISM. To that I’ve added a few remarks concerning x-ray emission coming from beyond the Local Bubble, and another few on how x-ray emission from within the solar system might be contaminating what we see. That last bit is new, exciting, and possibly wrong, but it is an example of the ongoing wariness I believe one has to take toward the facts in the case. By the way, Dieter, it really was a great meeting.
The Evaporation of Nearby Clouds and the Soft X-ray Background
Authors: Slavin Jonathan D. 
Published: July 2016

AbstractIn recent years the nature of the low density clouds within the Local Bubble has been increasingly well characterized. These clouds, including the one which surrounds the solar system, are embedded in the hot gas and therefore should be evaporating via thermal conduction. If several evaporation fronts exist within the Local Bubble, the emissivity and spectrum of the hot gas is significantly different from a single temperature, equilibrium ionization plasma. We explore models in which the the temperature, density and ionization in the hot gas are influenced by cloud evaporation and compare the results with the observed Soft X-ray Background.
The Local Magnetic Field in the Milky Way
Authors: Uyaniker B. , Fürst E. , Reich W. , Reich P. , Wielebinski R. 
Published: July 2016

AbstractA radio continuum survey at medium Galactic latitudes with the 100−m telescope of the Max-Planck-Institut für Radioastronomie is being carried out at a center frequency of 1.4 GHz in total power and linear polarization. We present polarization and depolarization structures detected at medium latititudes with no corresponding observable structure in total power emission. Existence of such kind of polarization structures imply that the emission, due to the Faraday modulation of the Galactic synchrotron foreground, occurs in thin sheetlike regions. This phenomenon is a sign for fluctuating local magnetic field.
Dust in Hot Environments: Giant Dusty Galactic Halos
Authors: Ferrara Andrea 
Published: July 2016

AbstractI review some of the evidences for dust in the Local Bubble and in galactic halos and show that a general mechanism based on radiation pressure is capable of evacuating dust grains from regions dominated by massive star energy input and thus originate huge dusty halos. A Monte Carlo/particle model has been developed to study the dust dynamics above HII chimneys and the results, among other findings, show that dust can travel several kpc away from the plane of the parent galaxy. The cosmological implications of extragalactic dust are briefly outlined.
26Al in the Local Interstellar Medium
Authors: Knödlseder J. , Bennett K. , Bloemen H. , Diehl R. , Hermsen W. , Oberlack U. , Ryan J. , Schönfelder V. , von Ballmoos P. 
Published: July 2016

AbstractWe estimate the 1.8 MeV luminosity of the Sco-Cen association due to radioactive decay of 26A1 to (4 – 15) 10−5ph cm−2 s−1. We propose a low surface brightness, limb brightened bubble for the 1.8 MeV intensity distribution. The detectibility of this distribution with existing γ-ray telescopes is discussed.
Gravitational Fragmentation in Expanding Shells
Authors: Theis Ch. , Ehlerová S. , Palouš J. , Hensler G. 
Published: July 2016

AbstractWe investigate the gravitational fragmentation in expanding shells by applying an instability ’thermometer’ similar to the Toomre parameter for instabilities in self-gravitating disks. For Sedov–like evolving systems the onset of instability is mainly depending on the density of the ambient medium and the sound speed of the shell matter, whereas the energy injection rate is less important. Shells evolve towards gravitational instability, if the density gradient of the ambient medium is shallower than an isothermal profile, otherwise they become more stable. For density gradients flatter than ∝ r−1, the fragmentation becomes non-linear on the same time scale as the gravitational instability needs to start. In a homogeneous ambient medium the typical size of gravitationally unstable shells is 1 kpc for a gas density of n = 1 cm−3 and decreases to 10 pc for n = 104 cm−3.
Evidence for Azimuthal Asymmetry in Be Star Winds
Authors: Peters Geraldine J. 
Published: July 2016

AbstractExtensive IUE observations from 1987-96 have provided compelling evidence for azimuthal asymmetry in the winds of Be stars. Two identified types of wind/FUV flux behavior are briefly discussed. Interpretations based upon both nonradial pulsations and rotation of one or more active regions appear plausible.
Optical Interferometry of Non-spherical Winds
Authors: Vakili Farrokh , Mourard Denis , Stee Philippe , Bonneau Daniel 
Published: July 2016

AbstractOptical Long Baseline Interferometry (OLBI) combined with spectral resolution is capable to sounding the stratification of luminous star winds. In this paper we review some few, yet unique results obtained on P Cyg and Be stars from OLBI observations. We also examine the prospects for studying hot stars winds offered by optical synthesis arrays presently under construction.
The Wind Momentum – Luminosity Relationship of Blue Supergiants
Authors: Kudritzki Rolf-Peter 
Published: July 2016

AbstractThe prediction of the Wind Momentum - Luminosity Relationship (WLR) based on the theory of radiation driven winds is verified by quantitative spectroscopy of winds of A-, B- and O-supergiants. The relationship depends on spectral type. New stellar wind calculations are presented reproducing the observed spectral type dependence. The impact of spectral variability on the WLR is investigated by an analysis of some hundred spectra of the luminous A0Ia-supergiant HD92207 obtained within the Heidelberg Spectral Variability Survey and found to be small.Finally, the WLR is discussed as a tool for the determination of extragalactic distances. Recent results obtained for the Galaxy, M31 and M33 are presented. The potential of the method is discussed with the conclusion that it may allow independent distance moduli to be obtained with an accuracy of ten percent out to the Virgo and Fornax clusters of galaxies.
Building Galaxy Models with Schwarzschild Method and Spectral Dynamics
Authors: Zhao Hongsheng 
Published: July 2016

AbstractTremendous progress has been made recently in modelling the morphology and kinematics of centers of galaxies. Increasingly realistic models are built for central bar, bulge, nucleus and black hole of galaxies, including our own. The newly revived Schwarzschild method has played a central role in these theoretical modellings. Here I will highlight some recent work at Leiden on extending the Schwarzschild method in a few directions. After a brief discussion of (i) an analytical approach to include stochastic orbits (Zhao 1996), and (ii) the “pendulum effect” of loop and boxlet orbits (Zhao, Carollo, de Zeeuw 1999), I will concentrate on the very promising (iii) spectral dynamics method, with which not only can one obtain semi-analytically the actions of individual orbits as previously known, but also many other physical quantities, such as the density in configuration space and the line-of-sight velocity distribution of a superposition of orbits (Copin, Zhao & de Zeeuw 1999). The latter method also represents a drastic reduction of storage space for the orbit library and an increase in accuracy over the grid-based Schwarzschild method.