bluuebunny/crossref_metadata_2025 huggingface dataset:
Galactic Winds and Magnetic Fields from Spiral Galaxies
Authors: Völk H.J. , Breitschwerdt D. , McKenzie J.F.
Published: July 2016

Concentrating on our own Galaxy we discuss the dynamics of the outer halo, its magnetic structure and the occurrence of a supersonic mass loss in the form of a Galactic wind. The cosmic rays, as the nonthermal high energy component, de facto not influenced by gravity, play an essential role in the wind dynamics.
Multi-Frequency Radio Observations of Spiral Galaxies and Their Interpretation
Authors: Krause M.
Published: July 2016

After a brief historical summary of radio observations of spiral galaxies I review the methods of analyzing radio polarization data in view of the magnetic field. Special attention is drawn to the Faraday rotation and depolarization effects and to the identification of the large-scale magnetic field structure. The present observational results and open questions are discussed in terms of the predictions of the dynamo theory and prospects on future work are given.
Polarized Radio Emission from M51
Authors: Horellou C. , Beck R. , Klein U.
Published: July 2016

The polarized radio continuum emission of M51 is found to be strongest outside the optical spiral arms. The rotation measure varies double-sinusoidally with azimuthal angle which for the first time clearly shows a dominating bisymmetric spiral (BSS) structure of the large-scale magnetic field in M51. The pitch angle of the magnetic spiral is similar to that of the optical spiral arms. The lowest (axisymmetric) dynamo mode is possibly suppressed by interaction with the companion galaxy.
Radio Polarization Studies of Some Southern Galaxies
Authors: Harnett J.I. , Haynes R.F. , Wielebinski R. , Klein U.
Published: July 2016

We have begun a long-range project to study southern galaxies using the radio telescopes at Parkes and Molonglo, the Siding Spring optical facilities and soon, the Australia Telescope. Here we present the results of polarization mapping at two wavelengths of the galaxies NGC 55, 253,4945, M 83 and the Circinus Galaxy.
Modeling the 60μm/20cm Infrared-to-Radio Ratio Within Spiral Galaxies
Authors: Bicay M. D. , Helou G.
Published: July 2016

The remarkably tight global correlation between integrated far-infrared and radio continuum emission from spiral galaxies has recently stimulated interest in determining whether the relation holds spatially within galaxies (Wainscoat et al. 1987; Beck and Golla 1988; Bicay et al. 1989, hereafter Paper I). We report here on a detailed comparison of the distribution of 60μm infrared and 20cm radio continuum emission within 25 galaxies, mostly disk spirals. Local maxima in the thermal infrared and predominantly nonthermal radio maps are found to be spatially coincident on scales <0.3h−1 kpc in nearby galaxies. Superimposed on this broad correlation, we observe in the disks of most sample galaxies a slow decrease in the 60μm-to-20cm ratio Q60 with increasing radius. Values of Q60 within the central regions are often enhanced by a factor of 3 or more compared to the outer disks, whereas the corresponding enhancement in radio surface brightness is greater by at least an order of magnitude. The radial gradient in Q60 is most easily identified in nearby, face-on galaxies (e.g. NGC 5236, NGC 6946) due to the limited IRAS angular resolution. However, the gradient is also observed along the major axis of highly inclined systems (e.g. NGC 55).
The Role of Magnetic Fields in Star Forming Regions
Authors: Mestel L
Published: July 2016

The flux from the galactic magnetic field alters radically the appropriate description of the equilibrium, collapse and fragmentation of the self-gravitating gas clouds that are the locale of star formation.
Magnetic Fields in Molecular Cloud Cores
Authors: Zhou Z.P. , Zheng X.W.
Published: July 2016

Strong circular polarization of OH masers at 1665 and 1667 MHz lines has been observed towards the molecular cloud cores associated with HII regions. Magnetic field strengths of a few mG are derived from the Zeeman splitting of OH lines. For instance, a magnetic field of about 4 mG in the masing region of W3(OH) has been estimated by OH-line Zeeman splitting (Davies, 1974). VLBI observations show that the OH maser spots project onto or very close to the surface of associated compact HII regions (Reid et al., 1986). The observational evidence demonstrates that the scales of OH maser components surrounding a compact HII region (R ~ 1016 cm) are about 1014 cm in diameter with an amplification pathlength of ~1015 cm. Hence the magnetic fields determined by the Zeeman splitting of OH maser lines appear partly very close to the associated HII region. Elitzur (1979) has theoretically obtained similar results as above.
Near Infrared Polarimetry of Dark Clouds and Star Forming Regions - Two Micron Polarization Survey of T Tauri Stars
Authors: Tamura M. , Sato S.
Published: July 2016

Infrared polarimetry is one of the most useful methods to delineate the magnetic field structure in dark clouds and star-forming regions, where the intracloud extinction is so large that optical polarimetry is inaccessible. We have been conducting a near-infrared polarization survey of background field stars and embedded sources toward nearby dark clouds and star-forming regions (Tamura 1988). Particularly, the magnetic field structure in the denser regions of the clouds are well revealed in Heiles Cloud 2 in Taurus, ρ Oph core, and NGC1333 region in Perseus (Tamura et al. 1987; Sato et al. 1988; Tamura et al. 1988). This survey also suggests an interesting geometrical relationship between magnetic field and star-formation: the IR polarization of young stellar sources associated with mass outflow phenomena is perpendicular to the magnetic fields. This relationship suggests a presence of circumstellar matter (probably dust disk) with its plane perpendicular to the ambient magnetic field. Combining with another geometrical relationship that the elongation of the denser regions of the cloud is perpendicular to the magnetic field, the geometry suggests that the cloud contraction and subsequent star-formation have been strongly affected by the magnetic fields. Thus, it is important to study the universality of such geometrical relationship between IR polarization of young stellar sources and magnetic fields. In this paper, we report the results on a 2 micron polarization survey of 39 T Tauri stars, 8 young stellar objects and 11 background field stars in Taurus dark cloud complex.
Detection of Synchrotron Emission from a Unique Herbig Haro Object in Orion
Authors: Yusef-Zadeh F. , Cornwell T. , Reipurth B. , Roth M.
Published: July 2016

We have obtained radio continuum observations of an HH object, known as the “streamer” in Orion using the VLA in a number of configurations at λ2, 6 and 20cm. This object is located several arc-minutes to the north of HH34 in L1641 cloud and exhibits a remarkably long and narrow structure with dimensions of 5′ × 10′ in optical photographs unlike the morphology of any other HH object. Based on radio continuum observations, we have detected a significant linearly polarized emission at λ6cm from the core of the streamer indicating highly uniform magnetic field geometry. This unusual result suggests that the source responsible for producing the nebulosity is a nonthermal-emitting radio source. Because of the presence of a number of newly born low-mass stars in L1641 and because of the detection of a highly reddened 2μm source coincident with the synchrotron source, it is likely that the source at the core of the streamer is a low-mass star responsible for the non-thermal emission and the HH nebulosity. Presence of synchrotron emission associated with a newly born star supports further view that the magnetic field plays a strong role in the early phase of star formation.
Magnetically Driven Jets
Authors: Lovelace R. V. E. , Contopoulos J.
Published: July 2016

A simple but general theory for the formation and propagation of non-relativistic jets is derived from the basic equations of ideal magnetohydrodynamics.
The Magnetic Field in the Inner 70 Parsecs of the Milky Way
Authors: Morris Mark
Published: July 2016

Existing radiofrequency data on the center of the Galaxy are used to defend the hypothesis that the magnetic field within a radius of at least 70 pc of the nucleus has a poloidal geometry, is relatively uniform in strength, and is very strong relative to extended fields measured elsewhere in the Galaxy, having a flux density greater than or about a milligauss. The implications of this strong, pervasive field are: 1) that a strong ring current is present at radii beyond 70 pc, and 2) that the dynamics of molecular clouds in the Galactic center are significantly affected by, though probably not dominated by, the magnetic field. At radii within 5 pc, far-IR polarization data suggest a substantial deviation of the magnetic field from a poloidal geometry, at least within the gas and dust layer. There, the coupling of the field to the rapidly orbiting gas near the nucleus is presumably responsible for this local distortion of the larger-scale field geometry.
Magnetic Filaments in the Negative-Latitude Extension of the Radio Arc Near the Galactic Center
Authors: Yusef-Zadeh F. , Morris Mark , Lasenby A.N. , Seiradakis J.H. , Wielebinski R.
Published: July 2016

Continuum observations of the southern extension of the radio Arc located near 1~0.2° have been carried out at λ20 and 6cm using the VLA in its hybrid B/C and C/D array configurations. A number of long and narrow filaments have been identified on the negative latitude side of the plane. Some of the filaments appear to extend continuously into the radio continuum Arc and suggesting strongly that they are associated physically with the Arc. Other filaments appear isolated and thus have characteristics similar to those of the radio “threads” which have been seen near the Galactic center. These new threads and filaments are highly polarized at λ6cm and show rotation measures which vary between 300 and 3000 rad m−2. The details present in the high-resolution images of this region strengthen the hypotheses that the large field strength is dynamically important and that the large-scale geometry of the magnetic field is poloidal near the Galactic center.
MHD Models of Galactic Center Lobes, Shells, and Filaments
Authors: Shibata Kazunari , Matsumoto Ryoji
Published: July 2016

Magnetohydrodynamic (MHD) mechanisms producing radio lobes, shells, and filaments in the Galactic center as well as in the gas disk of the Galaxy are studied by using two-dimensional MHD code: (a) the explosion in a magnetized disk, (b) the interaction of a rotating disk with vertical fields, and (c) the nonlinear Parker instability in toroidal magnetic fields in a disk. In all cases, dense shells or filaments are created along magnetic field lines in a transient state, in contrast to the quasi-equilibrium filaments perpendicular to magnetic fields.
Dynamo Driven Mean Magnetic Field in Accretion Disks of Compact Astrophysical Objects and its Manifestations
Authors: Chagelishvili G.D. , Chanishvili R.G. , Lominadze J.G. , Sokhadze Z.A.
Published: July 2016

The simplest case of the nonlinear turbulent dynamo mechanism is proposed. It is shown that under certain conditions the generated mean magnetic field can become stronger than the small-scale one. Some manifestations (the model of Cyg X-1 bimodal behaviour, asymmetric accretion onto the magnetized rotating compact star) of this mean field are discussed.
Stability of Luminous Discharges in Strong Fields
Authors: Benford Gregory
Published: July 2016

I show that a common thermal instability of conventional plasma discharges does not occur if plasma turbulence impedes current flow. Normally, thermal discharges drain current into a single hotter filament, because classical Coulomb resistance falls as a filament heats. Anomalous resistance reverses this, stabilizing the circuit. Only small levels of turbulence are needed.
The Combined Effects of Magnetic Fields and Rotation on the Acceleration of Jets: A Quasi-One-Dimensional MHD Model
Authors: Koupelis Theodoros
Published: July 2016

Using a quasi–one-dimensional MHD model for narrow jets (which we develop by projecting the system of the ideal MHD equations onto the jet axis) we examine the relative importance of the combined effects of rotation and magnetic fields upon the acceleration of matter in jets. We also examine the relative importance of the gas pressure and the gravitational field of the source on the flow and the position of the three critical points (Alfvén, slow and fast magnetosonic). The model, being semi-analytic, allows us to easily extract the relevant physical parameters, explore extreme ranges of these parameters, find the parameter range over which outflows are possible, and identify the physical consequences of different assumptions.
Contour Simulations of Astrophysical Jets
Authors: Zaninetti L.
Published: July 2016

We apply the theory of the Kelvin-Helmholtz instabilities to trace the jet's pattern. A certain level of noise is introduced.
Filaments Evolution in Extended Radio Sources
Authors: Bodo G. , Ferrari A. , Massaglia S. , Trussoni E.
Published: July 2016

It has been recently shown (Bodo et al 1989) that filamentary structures observed in some extended radio sources (e.g. Cygnus A and M 87) can be related with thermal instabilities arising in the gas with a synchrotron radiating relativistic component. In particular is has been shown that, with the typical parameters of radio sources, two kind of unstable modes can develop on time scale comparable with the synchrotron cooling time: condensation stationary modes and travelling slow MHD waves. Both these kind of perturbations should lead to the formation of structures basically parallel to the magnetic field direction, as observed, however their general evolution, in particular if they will lead to the formation of dark or bright structures, cannot be extrapolated from the linear perturbative analysis.
The Polarization Structure of Centaurus A
Authors: Burns Jack O. , Clarke David A.
Published: July 2016

New VLA observations have revealed sharp gradients in both the depolarization and rotation measure in the lobes of Cen A. We attribute these jumps to a foreground screen in the southern lobe, and to the passage of the jet through a shock in a Malin shell in the northern lobe.
Magnetic Fields of Radio Galaxies in Abell Clusters 115 and 568
Authors: Gregorini L. , Bondi M. , Feretti L. , Giovannini G. , O'dea C.P.
Published: July 2016

Abell 115 is an intermediate–redshift cluster (z=0.1971) well studied at different wavelengths (see Giovannini et al., 1987 and references therein).
Cosmic Magnetic Fields and Superconducting Strings
Authors: Thompson Christopher
Published: July 2016

A cosmic magnetic field may play a significant role in the formation of galaxies and large scale structure. In particular, a fossil field of present strength ~ 10−9 Gauss is an essential ingredient in the superconducting string model of galaxy formation (Ostriker, Thompson and Witten 1986 (OTW); Thompson 1988a). We discuss the mechanism by which a current is induced on a superconducting string, including recent work on the reconnection of magnetic field lines near the string (Kulsrud and Thompson 1989). A substantial amount of baryonic plasma is trapped on the magnetic field lines which close around the string. The current on a loop almost certainly does not undergo exponential dynamo amplification; an oscillating superconducting loop emits a relativistic MHD wind (Thompson 1988a). Decaying superconducting loops fill most of the intergalactic medium with a relativistic, magnetized fluid. In this model, the gas between galaxies is highly clumped and strongly magnetized, the field strength approaching 1 μG. The maximum energy of cosmic ray protons accelerated at string-driven shocks is ~ 1020 eV (Madau and Thompson 1989).
On the Origin of Cosmic Magnetic Fields
Authors: Tajima T. , Shibata K.
Published: July 2016

In the past investigations of cosmological magnetic fields, Harrison (1970) assumed primordial turbulence with nonzero vorticity. More recently this idea lost favor with most cosmologists, primarily because vortices decay during the cosmic expansion (Rees, 1987). In contrast to these works we resort to no assumption as for the primordial condition but for the thermal equilibrium in the following. A plasma with temperature T in the early universe sustains fluctuations of electromagnetic fields and density even if it is in a thermal equilibrium. The level of fluctuations in the plasma for a given wavelength of electromagnetic fields, for example, can be rigorously computed by the fluctuation-dissipation theorem (Geary et al. 1986; Kubo 1957; Sitenko 1967). In particular, without assuming any turbulence we show that very low (or ~ zero) frequency magnetic fluctuations can also be excited and the level of these is computedr where summation on k is over all the available wavenumbers V the volume of the Universe, and ωp the plasma frequency (4πe2n/m)1/2. The level of fluctuation is given approximately by the equipartition value of T/2 for kωωp/c and much less than that for k>ωp/c. These fields at the early radiation epoch t=10°sec (we call the radiation epoch in which the radiation effects dominate that of gravity in the universe as the plasma epoch: tε10−2 − 1013 sec) can act as seed fields and can evolve during the plasma epoch. The result is shown in Fig. 1. We show that magnetic fields with the size of λ≤108cm can be amplified by the dynamo effect and that the field strength corresponding to this size is greater than 10–19 Gauss.
Extraction of Black Hole Rotational Energy by a Magnetic Field
Authors: Koide Shinji
Published: July 2016

We have developed a numerical method for general relativistic magnetohydrodynamic simulations in Kerr space-time. The method is applied to the basic astrophysical problem of the Kerr black hole activity in the large-scale strong magnetic field. The numerical result shows that the magnetic field extracts the rotational energy of the black hole with negative energy-at-infinity and the torsional Alfven wave is induced from the ergosphere.
Time Lags of Horizontal Branch Oscillations in Z Source GX 5–1
Authors: Qu Jin-Lu , Ding Guo-Qiang , Ji Jian-Feng , Zhang Ming-Xuan
Published: July 2016

We investigated the time lags and the evolution of the cross spectrua of Z source GX 5-1, observed by Rossi X-ray Timing Explorer (RXTE), when it is in the horizontal branch oscillations. We showed that the time lags of 3 horizontal branch oscillations are related to the position on the hardness intensity diagram. 3 QPOs were shown to be of the hard time lags. But on the cross spectra, one is in a “dip”, one in a “bump”, another has not that chracteristic. The time lags of two of the QPOs decrease with QPO's frequency, and one has a trend increasing with its freuqency. In the normal branch, we found that there is no significant time lags in the present observational data.
Probing the X-ray Variability of X-ray Binaries
Authors: Yu Wenfei
Published: July 2016

Kilohertz quasi-periodic oscillations (kHz QPOs) has been regarded as representing the Keplerian frequency at the inner disk edge in the neutron star X-ray binaries. The so-called “parallel tracks” on the plot of the kHz QPO frequency vs. X-ray flux in neutron star X-ray binaries, on the other hand, show the correlation between the kHz QPO frequency and the X-ray flux on time scales from hours to days. This is suspected as caused by the variations of the mass accretion rate through the accretion disk surrounding the neutron star. We show here that by comparing the correlation between the kHz QPO frequency and the X-ray count rate on a certain QPO time scale observed approximately simultaneous in the Fourier power spectra of the X-ray light curve, we have found evidences that the X-ray flux of millihertz QPOs in neutron star X-ray binaries is generated inside the inner disk edge if adopting that the kilohertz QPO frequency is an orbital frequency at the inner disk edge.
Giant-Amplitude X-ray Flares as Probes of the Black Hole Region of Nearby Galaxies
Authors: Komossa Stefanie , Yuan Weimin , Xu Da Wei
Published: July 2016

In the last few years, several giant-amplitude, non-recurrent X-ray flares have been observed from optically non-active galaxies. The observations were interpreted in terms of the long-predicted tidal disruption flares of stars captured by supermassive black holes. In this contribution, we review the observations and interpretation of the X-ray flares and add some new thoughts. Future X-ray observations of the flare events are expected to open up a new window to detect and investigate SMBHs and their immediate environment in galaxies. Here, we concentrate on the possibility to detect new X-ray flares in deep fields with the planned European X-ray mission XEUS.
X-ray Spectroscopy of the Cluster of Galaxies PKS 0745-191 with XMM-Newton
Authors: Chen Y. , Ikebe Y. , Böhringer H.
Published: July 2016

We present the X-ray spectroscopy of cluster PKS 0745-191 with XMM-Newton in this paper.
Fe Kα Lines of Seyfert I Galaxies: Thin-Torus Model
Authors: Ma Zhen Guo
Published: July 2016

In order to elucidate the physics of the Fe Kα line emissions from Seyfert (-like) AGNs, we propose a thin-torus model in Kerr metric and fit it to three galaxies (i.e., NGC 3516, 3C 273, and NGC 5548). It is found that only spinning-BH galaxies radiate observable line flux from a region within tens of gravitational radii of a central BH. Besides, the observer's inclination angle is around 30°.
Neutrino Masses and Mixing
Authors: Totsuka Yoji
Published: July 2016

Recent results on neutrino masses and mixing are presented. There is convincing evidence for nonzero but tiny masses of at least two flavor neutrinos, based on two types of neutrino oscillations, solar and atmospheric neutrinos. The large mixing angle between first and second flavors and also the one between the second and third flavors were found, quite contrary to small mixing angles among quark flavors, and pose a new mystery.
Differential Rotation and the v sin i Parameter
Authors: Zorec J. , de Souza A. Domiciano , Frémat Y.
Published: July 2016

We study the effects of a differential rotation upon the determination of the v sin i parameter. The effects are studied for several values of the ratio t = kinetic energy/gravitational potential energy, which include energy ratios higher than permitted for critical rigid rotation and using an internal conservative rotation law that allows for a latitudinal differential rotation in the stellar surface. Two effects are outstanding: when differential rotation is dependent on the stellar latitude the v sin i parameter does not necessarily correspond to the equatorial rotation velocity; the line width is a double valued function of v sin i and it is dependent on t and the aspect angle i.
NLTE Model Atmospheres with Rotation
Authors: Korčáková Daniela , Kubát Jiří
Published: July 2016

We present a modification of our code for calculation of NLTE model atmospheres in planar and spherical geometry to the case of rotating atmospheres. This modification enables self-consistent inclusion of the effect of rotation on the atmospheric structure.
A Search for Rotationally Modulated Hα Variability in OB Supergiants
Authors: Morel T. , Marchenko S. V. , Pati A. K. , Kuppuswamy K. , Carini M. T. , Wood E. , Zimmerman R.
Published: July 2016

We present preliminary results of a long-term spectroscopic monitoring of a magnitude-limited (V < 7.5) sample of OB-supergiants (07.5-B9) aimed at establishing the incidence of co-rotating, large-scale wind structures. In the optical, this can be achieved by detecting rotationally modulated variability in Hα. Dramatic line-profile variations operating on a daily (and in some cases on a hourly) timescale are observed. Firm conclusions regarding the origin of the variability must, however, await a detailed period analysis. There is no clear evidence for a causal link between photospheric and wind activities.
Correlation between v sin i and the Peculiar Velocities of Be Stars
Authors: Zorec J. , Chauville J. , Levenhagen R. , Leister N. V. , Ballereau D.
Published: July 2016

Rough indications that v sin i is correlated with peculiar velocities exist only in the range of early-type Be Stars. Further corrections of space velocities of Be Stars for systematic movements of stellar groups to which they belong, as well as identifications of coeval stars have to be performed in order to decide whether the high rotation of some of them could be the consequence of gravitational encounters.
Rotational Velocities of “Field” Be Stars
Authors: Zorec J. , Levenhagen R. , Chauville J. , Royer F. , Leister N. V. , Frémat Y. , Ballereau D.
Published: July 2016

Distributions of true rotational velocities as a function of spectral type for different luminosity class groups of B and Be Stars are compared. While the distributions for B stars differ clearly from one luminosity class to another, those of Be Stars differ less, which indicates that due to rotational effects many Be Stars are considered more evolved than they actually are. Be Stars ‘select’ a narrow range of true rotational velocities to display the Be phenomenon and those of latter spectral types rotate only marginally faster than the early ones.
Ionization Structure in Equatorial Winds of B[e] Supergiants
Authors: Kraus Michaela , Lamers Henny J.G.L.M.
Published: July 2016

The non-spherically symmetric winds of B[e] supergiants are investigated. An empirical density distribution is chosen that accounts for the density concentrations and ratios derived from observations, and our model winds are assumed to contain only H and He. We calculate the Strömgren radii and the more accurate ionization fractions for H and He and find that in equatorial direction the winds of B[e] supergiants can become neutral very near the stellar surface. A neutral disk therefore exists around these stars in which molecules and dust can form which are shielded from the photodissociating stellar radiation field.
Post Main-Sequence Changes in Rotational Velocities
Authors: Abt Helmut A.
Published: July 2016

From recent measurements of the rotational velocities of 1100 B stars and 1700 A stars, we determined the maximum periods of binaries with fully circularized orbits. Combined with published data, we derived the relation of period (days) = 0.001 age0.42 (yr). We were able to reproduce the rotational velocities of giants from v sin i of dwarfs only if rigid body rotation applies to both. However for evolutionary expansions greater than 5 the angular momentum is conserved in shells, which is reasonable physically.
Modelling Stellar Rotation for Optical Long Baseline Interferometry
Authors: Domiciano de Souza A. , Zorec J. , Jankov S. , Vakili F. , Abe L.
Published: July 2016

Optical long baseline interferometry is a technique sensitive to sky projected brightness distributions, constituting a powerful tool for the study of detailed stellar surface structures. Moreover, by combining high spectral and angular resolution we obtain a technique called differential interferometry that is also sensitive to mechanisms that induce chromatic signatures, such as stellar spots and large scale mass motions (e.g. rapid rotation, non-radial pulsations, shear currents produced by hydrodynamical instabilities). We present here a study of the signatures of stellar rotation on differential interferometry observables showing that they are very sensitive to differential rotation and stellar inclination.
Effects of Rotation in Low-Metallicity Stars
Authors: Heap Sara R. , Lanz Thierry
Published: July 2016

We have carried out a spectral analysis of 17 O-type stars in the Small Magellanic Cloud (SMC). We find several lines of evidence that rotation plays an important role in massive stars in this low-metallicity galaxy (Z=0.2 Z⊙): (1) strong enrichment of nitrogen in half the program stars due to rotational mixing of processed material in the core up to the surface; (2) reduction of the effective gravity by the centrifugal force; (3) apparent anomalies in cluster isochrones that imply some stars are rotating at critical velocities.
Li Enrichment, Mass Loss, and CN Abundances in High Rotating K Giants
Authors: Drake N. A. , de la Reza R. , da Silva L. , Lambert D. L.
Published: July 2016

High rotating low-mass K giants can be considered as interesting new “laboratories” for studies of the mixing process and mass loss. By means of high spectral resolution observations of some rapidly rotating K giants we found a series of connections between rotation, stellar activity, high Li abundance and mass loss. These giants show low 14N and high 13C enrichment. Nearly half of them are Li rich. This frequency is much higher than the ~ 2% corresponding to common, low rotating K giants. They are also the most suitable objects to test new models of rotation-induced mixing or planet engulfing scenarios.
HD 3980: a New “Li-spotted” roAp Star
Authors: Polosukhina N. S. , Drake N. A. , Hack M. , de la Reza R. , Shakhovskoy D.
Published: July 2016

We report on preliminary results of new high-resolution spectroscopic observations of the roAp star HD 3980 in the Li I 6708 Å line region. Strong variations of position and intensity of this line with the rotation phase enable us to consider this star as a new member of the intriguing group of “Li-spotted” CP stars.
Fossil Magnetospheres Confront Newborn Dynamos in the Rapid Braking Zone
Authors: Ayres Thomas R.
Published: July 2016

Fast spinning Hertzsprung gap giants display super-rotational broadening of UV “hot” lines like Fe XXI λ1354 and C IV λ1548, with FWHM's up to twice that expected from the photospheric v sin i. This possibly is the result of extended fossil magnetospheres enveloping the gap giants, a new type of stellar corona. The magnetospheric phase is short-lived, however, as the rapidly evolving giants develop a competing dynamo-generated surface field in the so-called Rapid Braking Zone.
Surface Differential Rotation of Evolved Fast Rotators
Authors: Petit P. , Donati J.-F. , Wade G. A. , Landstreet J. D. , Sigut T.A.A. , Shorlin S.L.S. , Bagnulo S. , Lüftinger T. , Strasser S. , Oliveira J. M. , Aurière M. , Lignières F. , Mouillet D. , Paletou F.
Published: July 2016

Zeeman-Doppler Imaging enables one to estimate the short term temporal evolution of surface brightness and magnetic structures, under the effect of differential rotation. We present here spectropolarimetric observations secured between 1998 and 2002 for two evolved active stars: the K1 subgiant of the RS CVn system HR 1099 and the single FK Com giant HD 199178. Differential rotation is detected both from brightness and magnetic images, indicating that the rotational shear, roughly solar in magnitude for the single star, is significantly weaker in the binary system. This result suggests that tidal forces, rather than stellar evolution, could be responsible for the lower rotational shear and thus the longer spot lifetime reported for binary systems.
Solar Differential Rotation Revealed by Helioseismology and Simulations of Deep Shells of Turbulent Convection
Authors: Toomre Juri , Brun Allan Sacha
Published: July 2016

The sun is supposedly a very simple star, halfway along its long and possibly boring life on the main sequence. Yet it has some distinguishing features. Since we live close to it, our existence is probably blessed by this star having only modest cycles of magnetic activity and weak winds. By being so close, we can observe many aspects of the diverse range of motions and magnetic fields linked to turbulent convection in its convection zone. And this turns out to be anything but simple as we consider the dynamical coupling of convection, rotation and magnetism within this modest star. The lessons that have emerged from recent helioseismic probing of the solar interior and from 3–D numerical simulations of turbulent convection have bearing on differential rotation and magnetic dynamo action also occurring within more complex stars. We consider recent findings from both helioseismology and theoretical modelling on the operation of the deep shell of vigorous convection within our nearest star.
Pre-Main Sequence Evolution of Rotating Stars in Relation with Observations of Young Clusters
Authors: Sofia Sabatino , Barnes Sydney A.
Published: July 2016

Assuming that pre-main sequence stars rotating at the deuterium-burning birthline as solid bodies with rates within the range observed in T-Tauri stars is an adequate initial condition to explain the rotational properties of stars in clusters of all ages, provided that appropriate evolutionary schemes are used. It is, in fact, on the evolution that most recent advances have been made, and a new paradigm has arisen. Specifically, stellar periods (as a function of mass) begin their evolution on one of two branches, and the fast rotators migrate to the slow branch through a short-lived gap. These branches represent different physical properties of the internal stellar dynamics, and are related to the type of dynamo mechanism which operates within the stars. This paradigm appears to have the potential to address several fundamental issues in stellar astronomy.
Constraints on Mixing Processes from Abundance Anomalies
Authors: Michaud G. , Richer J. , Richard O.
Published: July 2016

Abundance anomalies in the Sun, main sequence F, A and B stars, turnoff Pop II stars, the horizontal branch and white dwarfs are caused at least partly by particle transport processes. Detailed evolutionary models have been calculated for most of those objects taking into account the gravitational settling, thermal diffusion and radiative accelerations of 28 isotopes (24 atomic species). These will be used together with the observed abundances to put constraints on the mixing that rotationnally induced turbulence may lead to. The link between abundance anomalies and rotation on the HB is explained by the variation with log g of the ratio of the Eddington-Sweet and atomic diffusion velocities.
Morphology of Planetary Nebulae—Possible Effects of Rotation on Stellar Ejecta
Authors: Kwok Sun
Published: July 2016

Planetary nebulae are formed as the result of the interaction between a slow stellar wind from the asymptotic giant branch progenitor and a later-developed fast outflow from the central star. Many of the morphological and kinematic properties of planetary nebulae have been successfully explained by this interacting stellar winds model. The observed diverse morphologies of planetary nebulae can also be understood if the slow wind is not spherically symmetric. However, new observational features such as collimated outflows and multi-polar lobes suggest that the fast wind may be non-isotropic and time variable. The possible roles of magnetic fields and rotation may play in the formation of these features are discussed.
What Ejected Nebulae around Evolved Massive Stars Tell us of the Rotation of their Central Star
Authors: Nota Antonella
Published: July 2016

Most LBVs and Ofpe/WN9 stars in the Milky Way and in the Magellanic Clouds are surrounded by associated circumstellar nebulae which have been ejected in some previous phase of their evolution. These nebulae are the fossil record of the interactions of previous winds and of the violent ejections in which the stars most likely have shed their outer layers. The study of the morphology, kinematics and chemical composition of the ejected material has allowed us to gain deep insight in the ejection and shaping mechanism, and in the properties of the central star at the moment of the ejection. In this review I will address how ejected nebulae are providing independent supporting evidence that rotation plays a major role in the evolution of massive stars.
Formation and Dissipation of Viscous Disks around Be Stars
Authors: Okazaki A. T.
Published: July 2016

Based on the viscous decretion disk model for Be Stars, we study the effect of the torque from the star on the Be star disk, using a 3-D smoothed particle hydrodynamics code and turning on and off the mass ejection from the star. We find that, after the mass ejection is shut off, the innermost part of the disk begins to accrete and the accreting part gradually propagates outward. We also find that the Be disk in misaligned binaries precesses in a retrograde sense when no mass is supplied from the star. If the mass supply is resumed for such a disk, an inner disk is formed with its rotation axis misaligned with that of the outer disk. By the interaction between the inner and outer disks, the outer disk rapidly changes its direction to that of the inner disk.
An H I Census of Loose Groups of Galaxies
Authors: Pisano D. J. , Barnes David G. , Gibson Brad K. , Staveley-Smith Lister , Freeman Ken C.
Published: July 2016

We present results from our Parkes Multibeam H I survey of 3 loose groups of galaxies that are analogous to the Local Group. This is a survey of groups containing only spiral galaxies with mean separations of a few hundred kpc, and total areas of approximately 1 Mpc2; groups similar to our own Local Group. We present a census of the H I-rich objects in these groups down to a 1σ MHI sensitivity ~7×105M⊙, as well as the detailed properties of these detections from follow-up Compact Array observations. We found 7 new H I-rich members in the 3 groups, all of which have stellar counterparts and are, therefore, typical dwarf galaxies. The ratio of low-mass to high-mass gas-rich galaxies in these groups is less than in the Local Group meaning that the “missing satellite” problem is not unique. No high-velocity cloud analogs were found in any of the groups. If HVCs in these groups are the same as in the Local Group, this implies that HVCs must be located within ~300-400 kpc of the Milky Way.
The Nature of High HI Mass-to-Light Ratio Galaxies
Authors: Warren Bradley E. , Jerjen Helmut , Koribalski Bärbel S.
Published: July 2016

We present here preliminary results of our multi-wavelength investigation into high HI mass-to-light ratio dwarf galaxies identified in the HIPASS Bright Galaxy Catalog.
The Systematics of Intracluster Starlight
Authors: Ciardullo R. , Mihos J. C. , Feldmeier J. J. , Durrell P. R. , Sigurdsson S.
Published: July 2016

Surveys for intracluster planetary nebulae and red giants have been performed in a variety of cluster environments, from the well-mixed regions of the Virgo and Fornax Clusters, to the low-density areas of the M81 Group. When coupled with the results of Abell Cluster surface photometry and intracluster supernova detections, these surveys provide clues to the systematics of the intracluster light phenomenon. We analyze the results of the intracluster surveys performed to date and show how the fraction of intracluster stars depends on parameters such as cluster richness and rate of galaxy interaction. We also compare our results to numerical predictions and discuss avenues for future research.
Chemical and Thermal History of the Intracluster Medium
Authors: Böhringer Hans
Published: July 2016

Clusters of galaxies can be seen as giant astrophysical laboratories enclosing matter in a large enough volume, so that the matter composition can be taken as representing the composition of our Universe. X-ray observations allow a very precise investigation of the physical properties of the intracluster plasma allowing us to probe the cluster structure, determine its total mass, and measure the baryon fraction in clusters and in the Universe as a whole. We can determine the abundance of heavy elements from O to Ni which originate from supernova explosions and draw from this important conclusions on the history of star formation in the cluster galaxy population. From the entropy structure of the intracluster medium we obtain constraints on the energy release during early star bursts. with the observational capabilities of the X-ray observatories XMM-Newton and Chandra this field of research is rapidly evolving. In particular, first detailed observations of the intracluster medium of the Virgo cluster around M87 have provided new insights. The present contribution gives an account of the current implications of the intracluster medium observations, but more importantly illustrates the prospects of this research for the coming years.
The Dust Impact on the Intergalactic Medium
Authors: Montier L. , Giard M.
Published: July 2016

Recent observations at low and high redshift seem to confirm the presence of dust at very low abundances in the InterGalactic Medium (IGM) and especially in the IntraCluster Medium (ICM). We have studied the impact of this dust on the IGM, in terms of heating and cooling. on one hand, with an analytical model of dust emission, we have proved that the dust can be considered as the dominant cooling agent of the ICM at large scale, when the temperature is greater than T = 107 K. on the other hand, with a strong UV Background and a low temperature (Te ≤ 105 K), dust grains become an efficient heating agent of the IGM. These two opposite effects may have played an important role regarding structure formation of the Universe at large and small scales.
Subclustering in Cooling and Non-cooling Flow Clusters
Authors: Flin P. , Krywult J.
Published: July 2016

For 20 hot luminous Beppo-SAX galaxy clusters the occurrence of substrucures has been investigated in 2-D optical data, mainly through the application of the wavelet analysis. Our results are compared with others, coming from 3-D optical data, as well as X-rays. In this sample of galaxy clusters a higher percentage of substructure is observed among non-cooling flow clusters than cooling flow clusters.
High Velocity Gas in the Halos of Spiral Galaxies
Authors: Fraternali Filippo , Oosterloo Tom , Boomsma Rense , Swaters Rob , Sancisi Renzo
Published: July 2016

Recent, high sensitivity, HI observations of nearby spiral galaxies show that their thin ‘cold’ disks are surrounded by thick layers (halos) of neutral gas with anomalous kinematics. We present results for three galaxies viewed at different inclination angles: NGC 891 (edge-on), NGC 2403 (i=60°), and NGC 6946 (almost face-on). These studies show the presence of halo gas up to distances of 10-15 kpc from the plane. Such gas has a mean rotation 25-50 km s−1 lower than that of the gas in the plane, and some complexes are detected at very high velocities, up to 200-300 km s−1. The nature and origin of this halo gas are poorly understood. It can either be the result of a galactic fountain or of accretion from the intergalactic medium. It is probably analogous to some of the High Velocity Clouds (HVCs) of the Milky Way.
Holes and High Velocity H I in NGC 6946
Authors: Boomsma Rense , van der Hulst Thijs , Oosterloo Tom , Fraternali Filippo , Sancisi Renzo
Published: July 2016

We are studying the properties of the holes and the high velocity gas in NGC 6946. Here we present some puzzling results.
XMM-Newton Observations of Nearby Edge-On Starburst Galaxies
Authors: Ehle Matthias , Dahlem Michael , Jiménez Bailón Elena , Santos-Lleó Maria , Read Andrew M.
Published: July 2016

We report on the results of XMM-Newton observations of nearby starburst galaxies that form part of a multi-wavelength study of all phases of extraplanar gas in external galaxies, which is conducted in order to assess the importance of halos as repositories of a metal-enriched medium and their significance in terms of galactic chemical evolution and possible metal enrichment of the intergalactic medium (IGM). XMM-Newton observations of the starburst galaxy NGC 1511 revealed e.g. the presence of a previously unknown extended hot gaseous phase of its interstellar medium (ISM), which partly extends out of the disk plane. We also present preliminary results based on XMM-Newton observations of NGC 1808, NGC 4666 and NGC 3628.
Young Star Clusters: Clues to Galaxy Formation and Evolution
Authors: Anders Peter , Alvensleben Uta Fritze-V. , de Grijs Richard
Published: July 2016

Young clusters are observed to form in a variety of interacting galaxies and violent starbursts, a substantial number resembling the progenitors of the well-studied globular clusters in mass and size. By studying young clusters in merger remnants and peculiar galaxies, we can therefore learn about the violent star formation history of these galaxies. We present a new set of evolutionary synthesis models of our GALEV code specifically developed to include the gaseous emission of presently forming star clusters, and a new tool that allows to determine individual cluster metallicities, ages, extinction values and masses from a comparison of a large grid of model Spectral Energy Distributions (SEDs) with multi-color observations. First results for the newly-born clusters in NGC 1569 are presented.
From Star Formation to Compact Remnants: X-ray Studies of Spiral Galaxies
Authors: Soria Roberto , Wu Kinwah
Published: July 2016

High-resolution multiwavelength studies of nearby galaxies are essential to understand the full cycle of star formation, and the balance between gas recycling and creation of compact objects. In particular, we study this cycle in the environment of ultra-luminous X-ray sources.
Modelling the ISM and Star Formation in Galaxy Formation Simulations
Authors: Williams P R , Nelson A H
Published: July 2016

Using a set of 60 Tree-SPH simulations of the formation of an individual galaxy, including star formation physics, we quantitatively assess the numerical accuracy and convergence of these methods. For simulations using 24000 particles in total, the gross structures of the resultant galaxies are reliably resolved.
Cautionary Remarks on Using SPH to Model the ISM in Galaxies
Authors: Williams P R , Churches D K , Nelson A H
Published: July 2016

In many SPH simulations of galaxy formation a lower limit is imposed on the kernel radius h equal to the gravitational softening length ∈. It has been found that such a constraint can in some circumstances compromise the spatial resolution to which hydrodynamical quantities are evaluated to the extent that the evolution of the gross features of a numerical galaxies are affected. Such effects can be avoided by allowing h to evolve freely to maintain a roughly constant number of neighbours in SPH summations. Here we focus on how imposing a constraint on h may affect the velocity field.
Multiwavelength Observations of Galactic Winds: Near and Far
Authors: Veilleux Sylvain
Published: July 2016

This paper provides a critical discussion of the observational evidence for winds in our own Galaxy, in nearby star-forming and active galaxies, and in the high-redshift universe. The implications of galactic winds on the formation and evolution of galaxies and the intergalactic medium are briefly discussed. A number of observational challenges are mentioned to inspire future research directions.
Starbursts and Extra-planar Hα from SINGG
Authors: Meurer Gerhardt R.
Published: July 2016

The NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG) is the largest star formation survey of an H I selected sample. Since the selection is made without regard to optical morphology, it is not biased toward or against “interesting” types of galaxies; thus SINGG is an ideal sample for studying galaxy demographics. Of a sample of 90 extra-galactic sources observed in photometric conditions, all are detected in Hα. This indicates that dormant galaxies, those containing an appreciable ISM but no star formation, are at best rare. We have made first pass morphological surveys for starbursts, as judged by Hα surface brightness, and outflows as judged by extra-planar Hα. We find that about 15% of the sources contain starbursts, with little dependence on the neutral hydrogen mass MHI. Nearly one half of a sample ~ 35 edge-on galaxies show evidence for extra-planar Hα having a scale size of 0.5 Kpc or larger, while nearly one quarter have extra-planar Hα features 1.0 Kpc in size or larger. There is a hint that high MHI systems preferentially have displaced outflows (chimneys, or fountains) while central outflows (galactic winds) preferentially occur in low MHI systems. However, a larger sample (e.g. the full SINGG survey) is needed to confirm this trend.