bluuebunny/crossref_metadata_2025_split huggingface dataset:
Co-ordinated Optical and Radio Observations of Symbiotic Stars
Authors: Ivison R. J. , Bode M. F. , Meaburn J. , Davis R. J. , Nelson R. F. , Spencer R. E. 
Published: July 2016

AbstractWe present preliminary results from absolutely flux-calibrated optical spectroscopy, together with 5 GHz radio flux measures of 17 symbiotic stars. The data were obtained quasi-simultaneously using the Manchester Echelle Spectrograph on the Isaac Newton Telescope, La Palma between 1988 September 20 and 24, and the Broad Band Interferometer at Jodrell Bank during 1988 October. This represents the largest sample of these stars observed in this way to date. Distances are calculated using visual extinctions and are compared with other quoted values. In general, the agreement is surprisingly good. Plots of individual line luminosities vs. radio luminosity indicate that the D-type (dusty) symbiotics (both also proto-planetary nebulae) have far higher radio luminosities than S-types (stellar) for comparable recombination and forbidden line luminosities. This may however be due to underestimation of optical line luminosities for the D-types as the circumstellar extinction contribution is uncertain. The single D’-type (cool dust, yellow secondary) lies at the low luminosity end of the S-type region. ‘Very slow novae’ in our sample lie in both groups.
Flare Star Observations in the Praesepe Region
Authors: Jankovics I. 
Published: July 2016

In a program of systematic search for flare stars in clusters and associations we have carried out a photographic survey in the region of Praesepe. The previously obtained interesting results in the Pleiades cluster and the Orion association stimulated us to continue the work of Haro (1968) and Rosino (1966) in Praesepe. The importance of observations in this cluster is obvious if we consider the following circumstances:
1. Praesepe and Pleiades have nearly the same distance from the Sun, 160 and 125 pc, respectively.2. There exists a difference in age between the 2 clusters of at least one order of magnitude.3. The use of Schmidt telescopes allows observations in large cluster regions.A great number of observational data are desirable for comparison of flare activity in the regions of Pleiades and Praesepe.
The Unusual Object KR Aurigae
Authors: Popova M.D. , Vitrichenko E.A. 
Published: July 2016

AbstractThe photometric and spectrographic data of the peculiar variable KR Aur have been analyzed. The Hβ line contour shows an accretion with velocity of 3200 km/s. The assumption is made that KR Aur may be a black hole.
Nova V1500 Cyg - Photometry and Period Variations Study
Authors: Semeniuk I. , Kruszewski A. , Schwarzenberg-Czerny A. , Chlebowski T. 
Published: July 2016

This study aims to present our photometric observations of Nova Cygni V1500 1975, and to discuss the period changes of brightness variation on the basis of all available data.The Nova was observed from 2 September 1975 to 26 October 1976 using the single channel UBV photometer attached to the 60-cm reflector of the Ostrowik station of Warsaw University Observatory. The brightness of the Nova decreased considerably during that time and it was necessary to use a sequence of four comparison stars. The variable was usually monitored in the V filter and occasionally measured with B and U filters. The V band is not well suited for observing novae in the nebular stage, since the dominant light contribution comes from O III emission lines.
Secular Mass Loss from Cataclysmic Variables
Authors: Smak Józef 
Published: July 2016

The mass loss from cataclysmic binaries seems an important and worth studying phenomenon for a number of reasons. It is probably enough to mention only two of them:(a) Whenever we can directly observe the ejected material, determine its amount and the rate of mass loss, as well as its chemical composition (this being the case of the expanding envelopes of novae), we are getting a good insight into the basic physical mechanisms responsible for the observed phenomena.(b) The mass loss (together with the mass transfer) and the loss of the orbital angular momentum are related directly to the dynamical evolution of a binary system and - indirectly - to the evolution of its components.
Period Changes of W Ursae Majoris Stars
Authors: Kreiner J.M. 
Published: July 2016

About 6000 times of minima for 120 W Ursae Majoris stars were collected by Mrs. Z. Frasińska and the writer in the Cracow Astronomical Observatory. From this material 15 O - C diagrams (fig. 1) with large number of minima were taken into consideration. Each of them covered more than 30,000 epochs. The analysis of O - C curves leads to the following conclusions:
1. The periods of all well-observed W UMa stars are variable.2. There are no “pure” parabolae in well-observed O - C curves.3. The periods change in a rather short time and then remain constant for 5,000 - 25,000 E (fig. 2).4. The number of increases and decreases of periods is approximately the same. The mean absolute change of period of 15 investigated stars amounts to 0.d00000365 = 0.P0000105. (The mean increase of period = 0.d00000386 = 0.P0000109, the mean decrease of period = 0.d00000349 = 0.P0000102).5. The mean absolute change of period for 15 investigated stars was plotted versus parameter q (mass ratio = m2/m1) (fig. 3). Systems with almost equal masses of stars have a tendency to show violent changes of period.
Infrared Observations of Late Type Stars
Authors: Merrill K.M. 
Published: July 2016

AbstractSubstantative mass-loss resulting in appreciable circumstellar dust envelopes is common in late-type stars. The evolutionary history and physical state of a cool star determine the chemistry within the outer stellar atmosphere mirrored by the molecular and particulate material present in the envelope. The observational consequences of this debri determined by moderate spectral resolution (λ/Δλ ~ 50-100) infrared spectrophotometry are reviewed. Significant information is provided by observations of the emergent energy flux of both the cool stellar photosphere and of the circumstellar dust envelope. While most of the infrared features observed in late-type stars can be plausibly identified, an as yet unknown emission mechanism marked by strong infrared band structure is known to be operative in a variety of infrared sources. The observed range in shell optical depth in both M and C stars suggests that mass-loss occurs to some degree throughout late stellar evolutionary phases and that occasional periods of high mass-loss are not uncommon.
Ultra-High Resolution Ca II Observations of the LISM
Authors: Welsh Barry Y. , Lallement Rosine , Crawford Ian 
Published: July 2016

AbstractWe report on the status of a long-term program of mapping the velocity structure of the local ISM using ultra-high resolution observations of Call K-line absorption towards nearby B and A-type stars. Absorption components common to the local interstellar cloud (LIC) have been detected in many (but not all) lines-of-sight. Our preliminary results indicate that the local ISM has a complex velocity pattern of inhomogeneous absorption, indicative of a shocked filamentary nature.
Small Scale Structure in Nearby Molecular Gas
Authors: Falgarone Edith 
Published: July 2016

AbstractRecent observations at high angular resolution of molecular clouds of low column density have revealed the presence of a conspicuous net of small scale filamentary structures, visible in the 12CO rotational lines only. In addition, the existence of unresolved structure at scales as small as ~ 200 AU in space and/or velocity space is inferred from the spectral properties of the 12CO and 13CO emission. The resolved structures are part of the hierarchy of structures observed in molecular gas in the Solar Neighborhood and appear as non self-gravitating elements confined by an ambient pressure P0/kB ~ 3 × 104cm−3 K. We show why these structures might have their origin in the intermittent structures of turbulence in which viscous dissipation is concentrated in space and time.
Intensity Variations of the Soft X-ray Background: the Boundary Structure of the Local Hot Bubble at Low Galactic Latitudes
Authors: Park S. , Finley J.P. , Snowden S.L. 
Published: July 2016

Abstract42 ROSAT PSPC pointed observations in the Galactic plane (l ~ 4° – 26°) are mosaicked in order to study the spatial structure of the X-ray emitting gas in the Local Hot Bubble (LHB). Degree scale X-ray intensity variations are detected at the ±10% level in the ¼ keV band, which imply a likely influence from a clumpy boundary shell of the LHB in the observed ¼ keV band X-ray background. The possible origins of such a clumpy boundary structure of the LHB are discussed.
A Limit on Galactic Extinction Not Correlated with Far IR Emission
Authors: Finkbeiner Douglas P. , Schlegel David J. , Davis Marc 
Published: July 2016

AbstractWe have reprocessed the IRAS and DIRBE full-sky 100 μm maps, using Hi as a zero-point, to produce a map of Galactic extinction. This map is crosscorrelated with APM galaxy counts over the full APM region, including dusty regions of the sky not used to compute the APM correlation function in Maddox et al.(1990a). The angular correlation function, w(θ), of galaxy counts is computed with and without the extinction correction, and is used to suggest that our map accounts for ~ 90% of the dust-induced correlation in the APM region on scales from 2 – 10°. This is the first time that a limit has been placed on the correlation function of the extinction not represented in a given map.
Simulations of Halo Supernova Remnants
Authors: Shelton R.L. 
Published: July 2016

AbstractHigh latitude observations find C3+, N4+, and O5+, while shadowing by intervening hydrogen clouds indicates the presence of soft X-ray emitting gas in the halo of our galaxy. This paper reports on detailed hydrocode simulations of one of the possible source types: isolated supernova remnants evolving in the tenuous ambient medium of the halo. Their O5+ column densities are similar to those observed from the halo. The N4+, C3+, and X-ray properties are also simulated and discussed. The calculations may also be of interest for the Local Bubble, external galaxies, and non-thermal pressure estimations.
The Galactic X-ray Halo
Authors: Pietz J. , Kerp J. , Kalberla P.M.W. , Burton W.B. , Hartmann Dap , Mebold U. 
Published: July 2016

AbstractWe analyzed the soft X-ray background (SXRB) source intensity distribution of the ¾ keV and ¼ keV photons by correlating the public ROSAT PSPC All-Sky Survey data with the new Leiden/Dwingeloo HI Survey. We found that the ¾ keV and ¼ keV distant background source intensity distribution can be modelled by an isothermal (T = 1.5.106 K) disk-like (scale length A1 = 15 kpc) X-ray halo in addition to the radiation of the extragalactic X-ray background.
Magnetic Reconnection and Extraplanar Diffuse Ionized Gas
Authors: Birk Guido T. , Lesch Harald , Neukirch Thomas 
Published: July 2016

AbstractMany observations indicate the occurrence of ionized gas in the distant halos of galaxies (among them our own). Since photoionization by stars (mainly O stars, young or evolved low mass stars depending on the kind of galaxy) does not seem to be exclusively responsible for the ionization of the hydrogen filaments that should otherwise cool and recombine quickly, the question arises which energy source may result in the quasistationary ionization. We propose that localized magnetic field dissipation in current filaments may contribute to the ionization of the extraplanar halo gas. The dissipated magnetic energy is converted into heat, which then is transferred to the neutrals, resulting in re-ionization on a time scale shorter than the recombination time scale. Quasistatic solutions are characterized by plasma temperatures and densities that agree nicely with the observed values for the diffuse ionized gas component of the Galactic interstellar medium.
Turbulent Heating in the Galactic Diffuse Ionized Gas
Authors: Minter Anthony , Balser Dana S. 
Published: July 2016

AbstractThe observed properties of the diffuse ionized gas (DIG) in our Galaxy are not easily reconcilable with simple photoionization models. This suggests that there are different or additional physical processes at work in the DIG. We have developed a model of the DIG whereby it is ionized by a relatively soft ionizing spectrum (Teff ≤ 32,000 K) and is also heated by an additional thermal mechanism: the dissipation of turbulence. This model predicts the same electron temperature, [N II] λ 6583/Hα ratio, [S II] λ 6716/Hα ratio and He I λ 5876/Hα ratio as observed in the DIG. Without the turbulent thermal heating term, this model will not reproduce the observed properties of the DIG. The dissipation of turbulence may also be important in other phases of the ISM.
Superbubbles in Dwarf Galaxies: Blown Out or Blown Away?
Authors: Low Mordecai-Mark Mac , Ferrara Andrea 
Published: July 2016

AbstractWe numerically model the impact of superbubbles produced by starbursts on the gas in dwarf galaxies, using realistic gravitational potentials including the contributions from dark matter haloes, and galaxy radii based on empirical laws. We find that the metal-rich gas is very efficiently ejected in many cases, contradicting previous results; the ambient gas is far more difficult to eject. X-ray emitting plumes can last more than 108 yr after the end of the active starburst.
Rotationally Modulated Winds of BA-Type Supergiants
Authors: Kaufer Andreas 
Published: July 2016

AbstractExtended spectroscopic monitoring programs with high resolution and coverage in wavelength and time have revealed a new picture of the winds and the circumstellar environments of late B- and early A-type supergiants. Dramatic line-profile variations (LPV) of the wind-sensitive Hα line with characteristic cyclical V/R variations indicate the presence of deviations of the envelopes from spherical symmetry. Time-series analysis of these LPVs suggest that the wind variations are caused by rotating surface structures which modulate the lower wind region. Occasionally observed high-velocity absorptions (HVA) indicate the presence of rotating extended and dense streakline or loop structures in the envelopes. The potential use of these circumstellar features to determine the true stellar rotation periods is discussed.
Using Spectropolarimetry to Determine Envelope Geometry and Test Variability Models for Hot Star Circumstellar Envelopes
Authors: Bjorkman Karen S. 
Published: July 2016

AbstractA survey and monitoring of the spectropolarimetric characteristics of hot stars over the entire visible wavelength range has been carried out over the past 8 years using the HPOL instrument at the Pine Bluff Observatory. Data from these projects is being used to derive physical characteristics of circumstellar envelopes. Quantitative modeling of the polarization, in combination with optical interferometry, has shown that the circumstellar disks of classical Be stars are geometrically thin, consistent with either the wind-compressed disk model or with hydrostatically supported Keplerian disks. Furthermore, spectropolarimetric variability, which is significant in a large fraction of the hot stars observed, provides information about changes occuring in the circumstellar envelope. For example, polarimetric changes provide a critical test of the one-armed density wave models proposed to explain observed V/R variations.
Disk Winds of B[e] Supergiants
Authors: Zickgraf Franz-Josef 
Published: July 2016

AbstractThe class of B[e] supegiants is characterized by a two-component stellar wind consisting of a normal hot star wind in the polar zone and a slow and dense disk-like wind in the equatorial region. The properties of the disk wind are discussed using satellite UV spectra of stars seen edge-on, i.e. through the equatorial disk. These observations show that the disk winds are extremely slow, v∞ ≃ 50 ‒ 90 km s−1, i.e. a factor of ~ 10 slower than expected from the spectral types. Optical emission lines provide a further means to study the disk wind. This is discussed for line profiles of forbidden lines formed in the disk.
Modeling Oblique Rotators: Magnetospheres and Winds
Authors: Shore Steven N. 
Published: July 2016

AbstractThe upper main sequence chemically peculiar (CP) stars display evidence of trapped circumstellar gas and nonspherical outflows. These stars are also known to possess strong magnetic fields that are often highly inclined to the rotational axis. Their phenomenology can be understood by using the oblique rotator model, which has successfully accounted for the observed behavior of the cooler CP stars. This paper reviews some features of the oblique rotator model, in which the magnetic field is assumed to provide a rigid framework for the structuring of the stellar and circumstellar gas. Corotation of circumstellar plasma is enforced out to the Alfven radius in the magnetic equatorial plane, while for the hotter stars, a radiatively driven wind emerges from the magnetic polar caps. Some observable consequences of the model are discussed, especially the Hα and ultraviolet resonance line absorption and emission periodic variability that has been observed in the He-peculiar stars and nonthermal radio emission. Magnetospheres may also be present in O stars, e.g. θ1 Ori C, and in the Herbig Ae/Be stars.
Wind Variations of Wolf-Rayet Stars
Authors: Moffat Anthony F.J. 
Published: July 2016

AbstractWhat distinguishes WR stars from most of their progenitor phases is their dense winds, that often completely hide their small hydrostatic cores. Thus, to learn about these cores, which are especially important in an evolutionary context, we are generally limited to studying the winds only. One way to do this is to examine their ubiquitous variability. Variability studies of (single) WR stars using various techniques have revealed two main classes of wind variation: (1) large-scale and periodic, probably related to rotating disturbances (e.g. NRP or magnetic structures) close to the core surface, and (2) small (multi-) scale and stochastic, probably intrinsic to the winds themselves. The former is only seen rarely in WR stars, contrary to other hot stars. The latter appears to be universal in WR and probably (though less obvious) in all hot-star winds.
Non-radially Pulsating Hot Stars: Non-radial Pulsations and Be Phenomenon
Authors: Osaki Yoji 
Published: July 2016

AbstractWe discuss a possible role of non-radial oscillations as a cause of mass-loss in hot stars. In particular, we propose a working model for the episodic mass-loss in Be stars. In this model, equatorial mass loss is thought to be driven by wave-breaking phenomenon of large-amplitude non-radial waves and a circumstellar disk could thus be formed around the equatorial plane of a rapidly rotating star. A kind of relaxation-oscillation cycle could be established between the Be phase and non-Be phase, in which an interplay between non-radial oscillations in stellar atmosphere and the circumstellar disk is essential. We also discuss a viscous decretion-disk model for the circumstellar envelope around Be stars.
Linear Strange Modes in Massive Stars
Authors: Glatzel Wolfgang 
Published: July 2016

AbstractThe occurrence and properties of strange modes and associated instabilities in massive stars are reviewed. If applicable, strange modes may be classified by the maximum of the opacity they are associated with. Whether they are still present in the limit of vanishing or infinite thermal timescales – which corresponds to the NAR and adiabatic approximations respectively – is another criterion for classification. A model for the instability mechanism of strange mode instabilities is discussed.
Conference Summary: The Demise of Spherical and Stationary Winds
Authors: Appenzeller Immo 
Published: July 2016

AbstractThe observational evidence and the theoretical work presented at this colloquium demonstrate that significant non-spherical effects and time variations are very common phenomena in the winds from hot stars. Hence, the assumptions of spherical symmetry and stationarity, while highly successful for the theory of stellar structure, appear to be inadequate for describing and understanding the winds of hot stars. This conclusion has significant consequences for the appearance and evolution of hot stars.
Bianchi Cosmologies as Dynamical Systems
Authors: Maciejewski Andrzej J. , Szydłowski Marek 
Published: July 2016

AbstractWe discuss specific properties of dynamical systems originating from cosmology and relativity. In particular, we present results of our study of the Bianchi class A cosmological models. We introduce new variables in which the Hamiltonian constraint for all the class A models is solved algebraically. We present results of dimension reduction of the investigated models.
Star Cluster Simulations: The State of The Art
Authors: Aarseth Sverre J. 
Published: July 2016

AbstractThis paper concentrates on four key tools for performing star cluster simulations developed during the last decade which are sufficient to handle all the relevant dynamical aspects. First we discuss briefly the Hermite integration scheme which is simple to use and highly efficient for advancing the single particles. The main numerical challenge is in dealing with weakly and strongly perturbed hard binaries. A new treatment of the classical Kustaanheimo-Stiefel two-body regularization has proved to be more accurate for studying binaries than previous algorithms based on divided differences or Hermite integration. This formulation employs a Taylor series expansion combined with the Stumpff functions, still with one force evaluation per step, which gives exact solutions for unperturbed motion and is at least comparable to the polynomial methods for large perturbations. Strong interactions between hard binaries and single stars or other binaries are studied by chain regularization which ensures a non-biased outcome for chaotic motions. A new semi-analytical stability criterion for hierarchical systems has been adopted and the long-term effects on the inner binary are now treated by averaging techniques for cases of interest. These modifications describe consistent changes of the orbital variables due to large Kozai cycles and tidal dissipation. The range of astrophysical processes which can now be considered by N-body simulations include tidal capture, circularization, mass transfer by Roche-lobe overflow as well as physical collisions, where the masses and radii of individual stars are modelled by synthetic stellar evolution.
Distribution of Kolmogorov-Sinaï Entropy in Self-Consistent Models of Barred Galaxies
Authors: Wozniak H. , Pfenniger D. 
Published: July 2016

AbstractThe properties of chaos in 2D self-consistent models of barred galaxies are investigated using Kolmogorov-Sinai entropy hKS. These models are constructed with Schwarzschild’s method which combines orbits as elementary building blocks.Most models are dominated by chaos near the 2/3 of the length of the bar and close to corotation. These locations correspond to regions where star-forming HII regions are observed because gas clouds could shock, shrink and fragment such that star formation could be ignited.The model the most similar to N-body models shows a peak of hKS between the corners of the rectangular-like x1 orbits and the maximum extension points of the Lagrangian orbits. This emphasizes the role of Lagrangian orbits in the morphology of bars. Most models essentially contain ‘semi-chaotic’ orbits confined inside the corotation.