bluuebunny/crossref_metadata_2025 huggingface dataset:
Galactic Winds: The Role of Cosmic Rays
Authors: Zank Gary P.
Published: July 2016

The symbiotic nature of the relationship between galactic winds and cosmic rays (CR's) is attracting increasing interest since, on the one hand, galactic wind termination shocks have been invoked to explain the origin of the highest energy CR's (Jokipii and Morfill, 1985) while, on the other hand, it is thought that CR's may be the principal agent responsible for driving winds (Ipavich, 1975). A simple, spherically-symmetric galactic wind model which includes the dynamical effect of spatially diffusing CR's with an outward pressure gradient is presented. A hydrodynamic form of the cosmic ray transport equation is used, and the spatial diffusion coefficient κ is modelled as κ ∞ ρα (ρ the gas density) for some parameter α. The choice of α < 0 yields flow solutions which are subsonic at the source and supersonic at infinity. Such a choice of α corresponds to assuming that the level of Alfvén wave turbulence decreases with increasing distance from the galaxy. Near the galaxy κ is small and the cosmic rays are strongly coupled to the thermal gas, thus supplying additional momentum in the subsonic wind regime. Further from the galaxy, as κ increases, the cosmic rays decouple from the thermal gas and no longer contribute to the dynamics of the flow. Hence far from the galaxy, the Euler equations should be a suitable model. Furthermore, unlike classical wind models, a multiplicity of saddle points, and therefore flow solutions, exists. Finally, we show that α < 0 is most likely to lead to stable, steady-state flows.
The Role of Cosmic Rays and Alfvén Waves in the Structure of the Galactic Halo
Authors: Dougherty M. K. , Mckenzie J. F.
Published: July 2016

The effect that cosmic rays and the Alfvén waves generated by them have on the structure of the plasma distribution perpendicular to the galactic disc in a hydrostatic model is examined. It is shown that the plasma distribution exhibits two length scales, essentially because the cosmic rays and Alfvén waves lift the gas up and stretch it out beyond the galactic plane. The predicted gas density far from the galactic plane indicates that models involving hydrostatic equilibrium should be replaced by those allowing for a galactic wind.
Constraints on the Magnetic Fields in Galaxies Implied by the Infrared-to-Radio Correlation
Authors: Helou George , Bicay M. D.
Published: July 2016

We propose a physical model for understanding the tight correlation between far-infrared and non-thermal radio luminosities in star-forming galaxies. This approach suggests that the only constraint implied by the correlation is a universal relation whereby magnetic field strength scales with gas density to a power 1/3≤β≤<2/3.
The Magnetic Field in Highly Dense Molecular Clouds
Authors: El-Nawawy M.S.
Published: July 2016

General forms of the B-ρ relation are investigated in both the isothermal and the non-isothermal regions. The magnetic flux dissipation either by ambipolar diffusion or by Ohmic dissipation has been restudied. The rates of heating due to the magnetic dissipation processes have been calculated in comparison with the rate of compressional heating.
Molecular Cloud Cores and Protostars: Offsprings of Gravity and Cosmic Magnetism
Authors: Mouschovias Telemachos Ch.
Published: July 2016

The formation of cloud cores (or fragments) and their evolution into protostars are the inevitable outcome of the struggle between gravity and magnetic fields, with ambipolar diffusion as the agent employed to weaken gravity's fierce opponent. The very specific and crucial role of magnetic fields in star formation deduced from detailed quantitative calculations is summarized. Criteria for collapse against magnetic and thermal-pressure forces are given. Magnetic braking time scales for both aligned and perpendicular rotators, and ambipolar diffusion time scales in both quasistatically and dynamically contracting cores are presented, and their implications are discussed. The possible role of magnetic fields in the determination of the initial (stellar) mass function (IMF) is beginning to emerge. New calculations on the axisymmetric collapse of clouds due to ambipolar diffusion reveal that the relation Bc ∞ ρc1/2 between the magnetic field strength and the gas density in typical cloud cores holds even in the presence of ambipolar diffusion up to densities ~ 109 cm−3. Small masses, high densities, and strong fields observed in H2O masers are consistent with theoretical calculations.
Observability of the Magnetic Field in Molecular Clouds
Authors: Bel N. , Leroy B.
Published: July 2016

We have done detailed calculations of the Zeeman effect in the dozen diatomic molecules identified in interstellar clouds.
Observations and Models of Magnetic Molecular Clouds
Authors: Myers P.C. , Goodman A.A.
Published: July 2016

In the last few years our knowledge of the strengths and directions of magnetic fields in molecular clouds has increased significantly. This paper briefly reviews observations of magnetic field strength and direction, compares such observations with equipartition models, and discusses the implications of these comparisons for the typical internal structure of the field in a molecular cloud.
VLA Mapping of Magnetic Fields in W 3 and S 106
Authors: Crutcher R. M.
Published: July 2016

The importance of magnetic fields to the evolution of dense interstellar clouds and to the star formation process is now widely appreciated. Troland (this volume) has reviewed work to measure strengths of interstellar magnetic fields by observation of the Zeeman effect in radio frequency spectral lines. The next step is to map magnetic fields with radio synthesis arrays in order to obtain high spatial resolution. This abstract is a preliminary report of VIA results for two clouds - the W 3 region of massive star formation (to be published by Troland, Crutcher, Goss, and Heiles) and S 106, a biconical H II region with a confining molecular disk (to be published by Loushin, Crutcher, and Troland).
Alignment of Circumstellar H-H Flows by the Interstellar Magnetic Field
Authors: Appenzeller I.
Published: July 2016

The highly collimated H-H flows and “jets” from young stellar objects have in some cases be reported to occur parallel to the direction of the interstellar magnetic field. In order to examine the reality and universality of the apparent connection between the H-H flows and the interstellar field, we compared the position angles of all H-H flows for which (1) the flow direction is well known from monochromatic images, and where (2) the local field direction can be derived unambiguously from interstellar polarization data. The result is given in Figure 1. A more detailed description of these results will be published elsewhere (Appenzeller 1989, Proc. 4th IAP Astrophysics Meeting, P. Delache et al. eds., Paris 1989).
Radiogaps: Stability of Electron/Positron-Jets in Large-Scale Magnetic Fields
Authors: Achatz U. , Lesch H. , Schlickeiser R.
Published: July 2016

Radio gaps, i.e. regions of strongly reduced radio (and also optical) intensity between the galactic nucleus (AGN) and the radio jets in active radio galaxies, are a rather prominent feature of many of these sources. With the aim to explain this phenomenon we consider the evolution of the relativistic electron spectrum in such a source with the relevant plasma kinetic equations. We consider a possible acceleration process for relativistic electrons and positrons near the accreting central object which is based on the continuous interplay of stochastic Fermi acceleration processes and radiation losses of energetic particles. The resulting distribution function heats the background medium efficiently through the oblique Langmuir synchrotron instability once the threshold plasma energy density for the modulation instability is exceeded resulting in the outflow of material. By the concerted action of synchrotron losses and adiabatic focussing in the ordered, spatially decaying magnetic field Bo the isotropic relativistic electron distribution function rapidly develops into two oppositely directed beam distributions, explaining the formation of compact, superluminal radio jets near the AGN and the radio gap phenomenon. The stability of the electron/positron beam in the magnetized background plasma is studied by treating it as a cold beam. The linear growth rates for parallel propagating longitudinal and transversal waves are calculated. Whereas the former give rise to heating of the background plasma, the low-frequency transversal (Alfvén-) waves scatter the beam to an isotropic distribution function which then reveals itself again by synchrotron radiation. The mean free path for this isotropization process is calculated and compared with the length of the radio gaps. A discussion of the results is given in Achatz et al. (1989).
The Phenomena of High Energy Astrophysics
Authors: Blandford R. D.
Published: July 2016

A brief summary of some highlights in the study of high energy astrophysical sources over the past decade is presented. It is argued that the great progress that has been made derives largely from the application of new technology to observation throughout all of the electromagnetic and other spectra and that, on this basis, the next decade should be even more exciting. However, it is imperative to observe cosmic sources throughout these spectra in order to obtain a full understanding of their properties. In addition, it is necessary to learn the universal laws that govern the macroscopic and the microscopic behavior of cosmic plasma over a great range of physical conditions by combining observations of different classes of source. These two injunctions are illustrated by discussions of cosmology, hot gas, supernova remnants and explosions, neutron stars, black holes and ultrarelativistic outflows. New interpreations of the acceleration of Galactic cosmic rays, the cooling of hot gas in rich clusters and the nature of ultrarelativistic outflows are outlined. The new frontiers of VHE γ-ray astronomy, low frequency radio astronomy, neutrino astronomy, UHE cosmic ray physics and gravitational wave astronomy are especially promising.
The Gamma-Ray Astronomy Database: 1990-2002
Authors: Hurley K.
Published: July 2016

I review five missions (SIGMA/GRANAT, the Compton Gamma-Ray Observatory, BeppoSAX, the Interplanetary Network, and the High Energy Transient Explorer) which have contributed to a golden age of discovery in gamma-ray astronomy. The data from many of these missions and experiments have been archived and are available to the public to analyze.
Studying the Nearby Universe with Chandra
Authors: Wang Q. Daniel
Published: July 2016

I highlight results from Chandra observations of nearby galaxies, including the Milky Way. These observations have offered insights into old mysteries and indications of new high energy astrophysical phenomena and processes that are yet to be understood.
X-ray Properties of Spiral Galaxies
Authors: Soria Roberto
Published: July 2016

X-ray studies of nearby spiral galaxies with star formation allow us to investigate temperature and spatial distribution of the hot diffuse plasma, and to carry out individual and statistical studies of different classes of discrete sources (low- and high-mass X-ray binaries, Supernova remnants, supersoft and ultra-luminous sources). In particular, we briefly review the different models proposed to explain the ultra-luminous sources. We can then use the X-ray properties of a galaxy to probe its star formation history. We choose the starburst spiral M83 to illustrate some of these issues.
Non-axisymmetric Instabilities in Shocked Accretion Flows
Authors: Gu Wei-Min , Foglizzo Thierry
Published: July 2016

We investigate the stability of shocked inviscid isothermal accretion flows onto a black hole. Of the two possible shock positions, the outer one is known to be stable to axisymmetric perturbations, while the inner one is unstable. Our recent work, however, shows that the outer shock is generally linearly unstable to non-axisymmetric perturbations. Eigenmodes and growth rates are obtained by numerical integration of the linearized equations. These results offer new perspectives to interpret the variability of X-ray binaries.
X-Ray Emission from Young Supernovae
Authors: Immler Stefan
Published: July 2016

Observations of young SNe in the (∼ 0.1−100 keV) X-ray band allow to establish physical key parameters, such as the circumstellar matter (CSM) density, the mass-loss rate of the progenitor and the temperature of the outgoing and reverse shock as a function of time. Over the last ∼ 25 years, a small number of young SNe has been detected with orbiting X-ray observatories shortly after the outburst (days to months). Some highlights of recent observations with Chandra and XMM-Newton are presented and implications as to our understanding of the physical processes giving rise to the X-ray emission are briefly discussed.
Magnetorotational Mechanism: Supernova Explosions and Ejections
Authors: Ardeljan N. V. , Bisnovatyi-Kogan G. S. , Moiseenko S. G.
Published: July 2016

We made simulations of the collapse of the rotating protostellar cloud. Differential rotation leads to the amplification of the toroidal component of the magnetic field and subsequent ejection of the matter due to the magnetorotational mechanism.

Our results show that at different initial configurations of the magnetic field formation of qualitatively different types of explosion takes place. Magnetic field of the dipole type produces a jet-like explosion. Quadrupole-like magnetic field produces supernova explosion whith ejection presumably near equatorial plane. Quantitative estimations of the ejected mass and energy are given.

We have done simulation of the collapse of the white dwarf and formation of a differentially rotating neutron star. After the collapse stage the rotating neutron star was formed. The rotation of the neutron star is strongly differential. The presence of the magnetic field (even the weak one) could produce magnetorotational supernova explosion.

For the simulations we have used 2D numerical scheme, based on the specially developed numerical method (conservative, implicit, triangular grid, Lagrangian, grid reconstruction).
Neutron Stars in Supernova Remnants and Beyond
Authors: Gvaramadze Vasilii V.
Published: July 2016

We discuss a concept of off-centred cavity supernova explosion as applied to neutron star/supernova remnant associations and show how this concept could be used to preclude the anti-humane decapitating the Duck (G 5.4−1.2 + G 5.27−0.9) and dismembering the Swan (Cygnus Loop), as well as to search for a stellar remnant associated with the supernova remnant RCW 86.
Pulsars: A Roundup of Recent Results
Authors: Manchester R. N.
Published: July 2016

The past few years have been a very exciting time in the field of pulsar astronomy. A major factor in this has been the advent of the large X-ray observatories but innovations in radio astronomy have also made a significant contribution. In this article I review some of the more interesting results, especially those relating to searches and pulsar – supernova remnant associations.
A Re-investigation to the Death Line of Radio Pulsars
Authors: Qiao G. J. , Xue Y. Q. , Zhang B. , Xu R. X. , Ye F. F. , Wang H. G.
Published: July 2016

A new death line for radio pulsars is presented in this paper within the framework of vacuum gap and inverse Compton scattering (ICS) induced pair production process. The 8.5s period pulsar PSR J2144-3933 is located above the death line without any additional assumptions. An “appearance line” instead of the so-called “Hubble line”, is also presented in this paper. Both of those two lines fit observations well.
Microquasars as Sources of High Energy Phenomena
Authors: Mirabel I. F.
Published: July 2016

Relativistic outflows are a common phenomenon in accreting black holes. Despite the enormous differences in scale, accreting stellar-mass black holes (X-ray binaries, collapsars) and super-massive black holes produce jets with analogous physical properties. Here I review microquasars as sources of relativistic jets, gamma-rays, cosmic rays, and high energy neutrinos.
Flashes in Be/X-ray Binary A0535+26
Authors: Dorokhova Tatyana , Dorokhov Nickolay
Published: July 2016

A luminosity of the transient optical flashes of HMXB A0535+26 amounted to 1.4 × 1038 erg s−1, the same order of magnitudes as a power of giant X-ray outbursts of the system. The flashes are very similar to ultrafast bright (on the timescale of 1 msec) flashes which have been detected in LMXBs in the MANIA experiment. Apparently the flashes arise as a result of non-thermal processes which excited in both type of binaries. The program of searches of the high energy optical transients among HMXBs is proposed.
Two Modes of Disc Accretion in X-ray Pulsars?
Authors: Torkelsson Ulf
Published: July 2016

In this paper I compare the properties of the Be/X-ray transients to those of disc accreting X-ray pulsars that show torque reversals without significant changes in the X-ray fluxes. I find that it is unlikely that the cause of the torque reversal is a radiation-induced warp in the accretion disc. The preferred explanations of the phenomenon is that either there is an intrinsic difference in the properties of the neutron stars between the two groups of objects, or that the torque reversals appear in systems in which the accretion disc is formed from a stellar wind.
Galaxies at the Detection Limits of Deep X-ray Surveys
Authors: Griffiths Richard E. , Miyaji Takamitsu , Knudson Adam
Published: July 2016

The great sensitivities of the Chandra X-ray Observatory and XMM-Newton are allowing us to explore the X-ray emission from galaxies at moderate to high redshift. By using the stacking method, we show that we can detect the ensemble emission from normal elliptical, spiral and irregular galaxies out to redshifts approaching one. The average X-ray luminosity can then be compared with the results of models of the evolution in the numbers of X-ray binaries and can possibly be used to constrain models of star formation.
Emission Line Properties of Seyfert 1 Type AGN from RASS
Authors: Xu D. W. , Komossa S. , Wei J. Y. , Zheng X. Z. , Qian Y.
Published: July 2016

We present the optical emission line properties of a sample of 155 bright X-ray selected ROSAT Seyfert 1 type AGN. The measured properties are gathered for correlation analysis. The strong correlations between Hβ redshift, flux ratios of Fe II to Hβ broad component and [O III] to Hβ narrow component are found.
A Chandra View of the Multi-scale Structures in Centaurus A
Authors: Karovska M. , Fabbiano G. , Elvis M. , Nicastro F. , Murray S. S. , Kraft R. P.
Published: July 2016

Centaurus A (NGC 5128) is a giant early-type galaxy containing the nearest radio-bright AGN. The high-angular resolution Chandra images of Cen A reveal multi-scale X-ray structures with unprecedented detail and clarity. We present results from our study of X-ray structures surrounding the Cen A nuclear region, including the discovery of giant arc-like structures, extending to about 8 kpc in the direction perpendicular to the jet. We compare the X-ray structures with observations in other wavelengths and discuss their implication for a global understanding of the morphology of Cen A.
REM: A Fast Slewing Robotized Telescope to Catch Near-InfraRed Afterglow of GRBs
Authors: Antonelli L. A. , Zerbi F. M. , Chincarini G. , Ghisellini G. , Rodonò M. , Cutispoto G. , Conconi P. , Covino S. , Molinari E. , Tosti G. , Nicastro L. , Palazzi E.
Published: July 2016

REM (Rapid Eye Mount) is a fully robotized fast slewing telescope equipped with a high throughput Near InfraRed (Z′, J, H, K′) camera (REMIR) and an optical slitless spectrograph (ROSS). A dedicated software for data reduction and software (AQuA) has been developed to extract scientific information from REM images without any human intervent. REM is installed in La Silla (Chile) and dedicated to detect and study the prompt optical/IR afterglow of Gamma Ray Bursts with the ambitious project of discovering objects at extremely high redshift. The synergy between REMIR camera and ROSS makes REM a powerful observing tool for any kind of fast transient phenomena.
The Highest Energy Cosmic Rays, A Review and Prospects
Authors: Fukushima Masaki
Published: July 2016

The existence of extremely high energy cosmic rays (EHECRs) with energy above 1020eV have been reported by several air shower experiments. The sources of these cosmic rays were considered to be extra-galactic. Relevant high energy astrophysical sources were searched in the arrival direction of these cosmic rays but no appropriate candidates were found. The origin of EHECRs stays unexplained. We review the present status of EHECR studies and introduce several new experiments aiming to unveil its mysterious origin.
Conference Summary: What is High Energy Astrophyics?
Authors: Trimble Virginia
Published: July 2016

The original intent of the conference was to focus, first, on the physical processes (accretion, collimation, and all the rest) shared by two or more of the kinds of sources generally thought of as belonging to high energy astrophysics and, second, on the full range of phenomena, at all wavelengths, exhibited by those sources. This summary therefore addresses some of these issues as well as some new results presented at the symposium and some of the still-unanswered questions that were raised.
Rotational Velocity Distributions of A-Type Main-Sequence Stars
Authors: Royer F. , Zorec J. , Frémat Y.
Published: July 2016

The different velocity distributions (v sin i, and v) are determined for single, non peculiar, A-type main-sequence stars, using homogeneous data. These distributions, together with synthetic corrections on stellar magnitudes due to the rotation, are used to quantify the global effect of rotation on a simulated A-type main-sequence in the H-R diagram. The resulting effect is lower than (0.03, 0.006) in (B – V, MV) for 95% of the stars.
The Initial Mass Function of Be Stars
Authors: Zorec J. , Levenhagen R. , Chauville J. , Frémat Y. , Ballereau D. , Hubert A. M. , Floquet M. , Leister N. V.
Published: July 2016

Allowing for systematic differences in the counting of Be Stars due to their overluminosity, changes produced by their fast rotation on spectral types and time spent in the main sequence, a difference between the IMF (Be) and IMF(B) appears, which indicates that the appearance of the Be phenomenon may relay on differences in the initial star formation conditions.
Rotational Evolution of Intermediate and Low Mass Main Sequence Stars
Authors: Stauffer John R.
Published: July 2016

Bob Kraft (1967) showed that there is a break in the mean rotational velocity of stars at about spectral type F5, with more massive stars generally being rapid rotators and less massive stars generally being slow rotators. He also showed that in the late F spectral range at least, there is an evolution with time on the main sequence, with younger F stars being more rapidly rotating. Kraft's observational database extended only to about one solar mass due to the sensitivy limitations of photographic plates. Modern observations of low mass stars in open clusters, extending down in mass to nearly the hydrogen burning mass limit in a few clusters, have since been used to show that rotational spindown is the common feature of stars less massive than the sun but that there is a wide spread in rotational velocities when stars arrive on the ZAMS. I will review what is known empirically concerning the rotational velocities of intermediate and low mass field stars, using the open cluster data to place the field star observations in context.
Measurements of Differential Rotation in Cool Stars
Authors: Reiners A. , Schmitt J.H.M.M.
Published: July 2016

We have obtained high resolution (R ≈ 220000) - high signal-to-noise (S/N > 500) spectra of 142 field dwarfs of spectral types F–K and v sin i ≤ 45 km s–1. Using the Fourier Transform Method (FTM) we precisely determined rotational velocities (Δ v sin i < 1.0 km s–1). For stars with v sin i ≥ 12.0 km s–1 this method allows the detection of deviations from solid body rotation. In the case of symmetric profiles the differential rotation parameter α = (ωequator – ωpole) / ωequator can be determined. This was possible for 32 of our sample stars; ten stars show evidence for solar-like differential rotation with α > 0.0. Thus it becomes possible to search for connections between differential rotation, rotational velocities and other stellar parameters. Signatures of differential rotation could be found on stars rotating as fast as v sin i = 42 km s–1. Particularly the Li-depleted stars turned out to show strong signatures of differential rotation. Our measurements support the idea, that Li-depletion in fast rotators (v sin i > 15 km s–1) is closely connected to differential rotation.
WIYN Open Cluster Study: Tidal Interactions in Solar-Type Binaries
Authors: Meibom S. , Mathieu R. D.
Published: July 2016

We present an ongoing study on tidal interactions in late-type close binary stars. New results on tidal circularization are combined with existing data to test and constrain theoretical predictions of tidal circularization in the pre-main-sequence (PMS) phase and throughout the main-sequence phase of stellar evolution. Current data suggest that tidal circularization during the PMS phase sets the tidal cutoff period for binary populations younger than ~ 1 Gyr. Binary populations older than ~ 1 Gyr show increasing tidal cutoff periods with age, consistent with active main-sequence tidal circularization.
Rotation and Magnetic Fields of Solar-Like Stars
Authors: Donati J.-F.
Published: July 2016

In this paper, I review most of the current knowledge about the strong correlation observed between the rotation rates and the magnetic fields of cool active stars. I concentrate in particular on the most recent observational results, derived from studies on dynamo field generation in stellar convective envelopes from magnetic imaging of very active rapidly rotating low mass stars. I also mention the latest attempts at investigating the large scale magnetospheric structure of these objects from extrapolations of the measured photospheric field maps, as well its dependence/influence on rotation. I finally discuss the new discovery of the feedback effects that dynamo magnetic fields generate on the global dynamics of stellar convective envelopes.
A Chandra Look at the Old Open Cluster M 67
Authors: van den Berg Maureen , Tagliafferi Gianpiero , Belloni Tomaso , Verbunt Frank
Published: July 2016

We present the results of a Chandra observation of the old open cluster M 67; 25 cluster members and 13 suspected members were detected, including 22 binaries. We believe that the X-rays of most systems can be explained by enhanced activity due to rapid rotation in a tidally locked orbit. This cannot be the case for the blue and yellow stragglers with orbital periods between 40 and 5000 d, like the new source S 997. We do not understand the X-rays of these long-period binaries.
Rotation and Properties of A- and B-Type Chemically Peculiar Stars
Authors: Mathys G.
Published: July 2016

Main-sequence chemically peculiar stars of spectral types A and B, which are characterised by photospheric abundance anomalies resulting from element segregation in the stellar outer layers, rotate slower than normal stars of similar temperatures. The mechanisms by which such slow rotation is achieved are not well understood yet; different processes may be involved for different types of chemical peculiarities, including stellar magnetic fields and multiplicity. Relevant existing observational data are reviewed.
The EDdington Mission
Authors: Roxburgh Ian , Favata Fabio
Published: July 2016

The Eddington mission was given full approval by the European Space Agency on the 23rd May 2002, as part of the new “Cosmic Vision” Science programme, with launch scheduled for 2007. Its twin science objectives are asteroseismology and planet finding. In its current design it consists of 4 × 60 cm folded Schmidt telescopes, each with 5° × 5° field of view and its own CCD array camera. The current observing plan is to spend 2 years primarily devoted to asteroseismology with 1–3 months on different target fields monitoring up to 50,000 stars per field, and 3 years continuously on a single target field monitoring upwards of 100,000 stars as required for planet searching. The asteroseismic goal is to be able to detect oscillations frequencies with a precision 0.1–0.3 μHz.
Coronal Activity on Rapidly-Rotating Solar-Like Stars: Chandra Observations of ER Vul
Authors: Brown Alexander , Brown Joanna M. , Osten Rachel A. , Ayres Thomas R. , Guinan Edward
Published: July 2016

We investigate the coronal structure of rapidly-rotating, solar-like stars using Chandra HETGS spectra of the short-period binary ER Vul, and by comparison with X-ray observations of the Sun and other dwarf stars. ER Vul consists of two solar-like (G0 + G5) dwarfs with rotation rates ~ 40 times that of the Sun. This binary is not interacting and these stars are the fastest rotating G dwarfs suitable for high resolution X-ray spectroscopy. X-ray (1.8-40 Å) spectra were obtained on 2001 March 29-30 along with 10.5 hours of simultaneous VLA monitoring at 3.6 and 20 cm. These spectra show hot, multi-temperature coronal emission with emission lines ranging in temperature from O VII (2 MK) to Fe XXIV (30 MK). ER Vul showed only low-level variability during the X-ray observation. Unlike the behaviour of longer period active binaries, no large, long-duration flares were detected, consistent with previous X-ray observations of this binary. No evidence for eclipses is seen in either the X-ray or radio emission. The coronal emission measure distribution and elemental abundances were derived for ER Vul.
Rotating Models of Low Mass Giants: Rotational Evolution and Surface Abundance Anomalies
Authors: Chanamé Julio , Pinsonneault Marc , Terndrup Don
Published: July 2016

We present some first results of stellar models of low mass, solar metallicity giants that include rotation and the mixing associated with it. We base our choice of initial conditions and input physics on observational constraints obtained for main sequence (MS) and horizontal branch (HB) stars, and obtain what can be regarded as a “best case scenario” for rotational mixing. These observations suggest local conservation of angular momentum in the cores and constant specific angular momentum in convective regions on the red giant branch (RGB). We show that under these circumstances and with moderate rotation rates at the turnoff it is possible to obtain enough mixing in order to reproduce the anomalous abundance ratios of the CNO species seen in giants. It is also shown that solid body rotation in the convective envelope fails to account for the observations. It is found that rotational mixing is inefficient on the lower RGB, so there is no need to invoke any inhibiting role of μ–gradients.
Problems with the Rotational Models: Observational Constraints
Authors: Balachandran Suchitra C.
Published: July 2016

Three critical tests are applied to the models that hypothesize the transport of angular momentum and material via turbulence. The models fail on all three counts.
Mixing and the s-Process in Rotating AGB Stars
Authors: Herwig Falk , Langer Norbert , Lugaro Maria
Published: July 2016

We model the nucleosynthesis during a radiative interpulse phase of a rotating 3 M⊙ Asymptotic Giant Branch (AGB) star. We find an enhanced production of the neutron source species 13C compared to non-rotating models due to shear mixing of protons and 12C at the core-envelope interface. We estimate that the resulting total production of heavy elements by slow neutron capture (s-process) is too low to account for most observations. This due to the fact that rotationally induced mixing during the interpulse phase causes a pollution of the 13C pocket layer with the neutron poison 14N. As a result we find a maximum neutron exposure of τmax = 0.04 mbarn–1 in the s-process layer of our solar metallicity model with rotation. This is about a factor of 5 … 10 less than required to reproduce the observed stellar s-process abundance patterns. We compare our results with models that include hydrodynamic overshooting mixing, and with simple parametric models including the combined effects of overshooting and mixing in the interpulse. Within the parametric model a range of mixing efficiencies during the interpulse phase correlates with a spread in the s-process-efficiency. Such a spread is observed in AGB and post-AGB stars as well as in pre-solar SiC grains.
Dynamical Shear Instability
Authors: Hirschi Raphael , Maeder André , Meynet Georges
Published: July 2016

The dynamical shear instability is an important mixing process in the advanced stages of the evolution of massive stars. We calculated different models of 15 M⊙ with an initial rotational velocity, vini = 300 km/s to investigate its efficiency. We found that the dynamical shear instability has a timescale shorter than oxygen burning timescale and that it slightly enlarges the convective zones and smoothens the omega gradients throughout the evolution. However, its effect is too localized to slow down the core of the star.
The Effects of Field-Aligned Rotation on the Magnetically Channeled Line-Driven Winds
Authors: ud-Doula Asif , Owocki Stanley
Published: July 2016

There is extensive evidence that the radiatively driven stellar winds of OB-type stars are not the steady, smooth outflows envisioned in classical models, but instead exhibit extensive structure and variability on a range of temporal and spatial scales. We examine the possible role of stellar magnetic fields in forming large-scale wind structure. It is based on numerical magnetohydrodynamic (MHD) simulations of the interaction of a line-driven flow with an assumed stellar dipole field.

Unlike previous fixed-field analyses, the MHD simulations here take full account of the dynamical competition between field and flow, and thus apply to a full range of magnetic field strength, and within both closed and open magnetic topologies. A key result is that the overall degree to which the wind is influenced by the field depends largely on a single, dimensionless, ‘wind magnetic confinement parameter’, η∗ (= B2eqR2∗/Ṁv∞), which characterizes the ratio between magnetic field energy density and kinetic energy density of the wind.

We extend these MHD simulations to include field-aligned stellar rotation. The results indicate that a combination of the magnetic confinement parameter and the rotation rate as a fraction of the ‘critical’ rotation now determine the global properties of the wind. For models with strong magnetic confinement, rotation can limit the extent of the last closed magnetic loop, and lead to episodic mass ejections that break through the close loop and are carried outward with a slow, dense, equatorial outflow. Our 2-D numerical simulations indicate that the magnetic fields provide excessive amount of angular momentum to the wind preventing the formation of a Keplerian disk.
Binary Evolution Models with Rotation
Authors: Langer N. , Yoon S.-C. , Petrovic J. , Heger A.
Published: July 2016

We discuss the first available binary evolution models which include up-to-date rotational physics for both components, as well as angular momentum accretion and spin-orbit coupling. These models allow a self-consistent computation of the mass transfer efficiency during Roche-lobe overflow phases, and a determination of the transition from quasi-conservative to non-conservative evolution. Applications to massive binary systems lead to predictions for the spin rates of compact objects in binaries, and for the occurrence of gamma-ray bursts from collapsars in binaries. Rotational effects in accreting white dwarfs are found to stabilise the shell burning and decrease the carbon abundance in progenitor models for Chandrasekhar-mass Type Ia supernovae, and to potentially avoid a detonation of the white dwarf within the sub-Chandrasekhar mass scenario.
White Dwarf Rotation: Observations and Theory
Authors: Kawaler Steven D.
Published: July 2016

White dwarfs rotate. The angular momentum in single white dwarfs must originate early in the life of the star, but also must be modified (and perhaps severely modified) during the many stages of evolution between birth as a main–sequence star and final appearance as a white dwarf. Observational constraints on the rotation of single white dwarf stars come from traditional spectroscopy and from asteroseismology, with the latter providing hints of angular velocity with depth. Results of these observational determinations, that white dwarfs rotate with periods ranging from hours to days (or longer), tells us that the processes by which angular momentum is deposited and/or drained from the cores of AGB stars are complex. Still, one can place strong limits on these processes by considering relatively simple limiting cases for angular momentum evolution in prior stages, and on subsequent angular momentum evolution in the white dwarfs. These limiting-case constraints will be reviewed in the context of the available observations.
The Rotational Velocity of Helium-rich Pre-White Dwarfs
Authors: Rauch Thomas , Köper Sebastian , Dreizler Stefan , Werner Klaus , Heber Ulrich , Reid I. Neill
Published: July 2016

Previous investigations on hydrogen-rich white dwarfs generally yield only very small rotational velocities (v sin i). We have analyzed line profiles in high-resolution optical spectra of eight hydrogen-deficient (pre-) white dwarfs and find deviations from the dominant Stark line broadening in five cases which, interpreted as an effect of stellar rotation, indicate projected rotational velocities of 40 – 70 km s–1. For the three least luminous stars upper limits of v sin i = 15 – 25 km s–1 could be derived only. The resulting velocities correlate with luminosity and mass. However, since the mass-loss rate is correlated to the luminosity of a star, the observed line profiles may be affected by a stellar wind as well. In the case of RX J2117.1+3412, this would solve discrepancies to results of pulsational modeling (v sin i ≈ 0).
Supernovae, Gamma-Ray Bursts and Stellar Rotation
Authors: Woosley S. E. , Heger A.
Published: July 2016

One of the most dramatic possible consequences of stellar rotation is its influence on stellar death, particularly of massive stars. If the angular momentum of the iron core when it collapses is such as to produce a neutron star with a period of 5 ms or less, rotation will have important consequences for the supernova explosion mechanism. Still shorter periods, corresponding to a neutron star rotating at break up, are required for the progenitors of gamma-ray bursts (GRBs). Current stellar models, while providing an excess of angular momentum to pulsars, still fall short of what is needed to make GRBs. The possibility of slowing young neutron stars in ordinary supernovae by a combination of neutrino-powered winds and the propeller mechanism is discussed. The fall back of slowly moving ejecta during the first day of the supernova may be critical. GRBs, on the other hand, probably require stellar mergers for their production and perhaps less efficient mass loss and magnetic torques than estimated thus far.
The Ghosts of Galaxies: Tidal Debris in Clusters
Authors: Gregg Michael D. , West Michael J.
Published: July 2016

Gravitational interactions in rich clusters can strip material from the outer parts of galaxies or even completely disrupt entire systems, giving rise to large scale, low surface brightness ghostly features stretching across intergalactic space. The nearby Coma and Centaurus clusters both have striking examples of galaxy ghosts, in the form of 100 kpc-long plumes of intergalactic debris. By searching HST archival images, we have found numerous other examples of galaxy ghosts in rich clusters at low redshift, evidence that galaxy destruction and recycling are ubiquitous, important in cluster formation and evolution, and continue to mold clusters at the present epoch. Many ghosts appear in X-ray bright clusters, perhaps signaling a connection with energetic subcluster mergers.

The fate of such material has important ramifications for cluster evolution. Our new HST WFPC2 V & I images of a portion of the Centaurus plume reveal that it contains an excess of discrete objects with −12 < MV < −6, consistent with being globular clusters or smaller dwarf galaxies. This tidally liberated material is being recycled directly into the intracluster population of stars, dwarf galaxies, globular clusters, and gas, which may have been built largely from a multitude of similar events over the life of the cluster.
Molecular Gas in the Edge-On Galaxy NGC 4013
Authors: Schinnerer E. , Rand R. J. , Scoville N. Z.
Published: July 2016

Our OVRO observations at 300 pc resolution of the molecular gas disk in the edge-on spiral galaxy NGC 4013 show no evidence for extraplanar material at our sensitivity limit. The observed molecular gas kinematics are in agreement with gas motion in a barred potential.
Magnetic Activity Following Re-Accretion on to Galaxies
Authors: Nishikori H. , Machida M. , Matsumoto R.
Published: July 2016

We carried out global three-dimensional magnetohydrody-namical (MHD) simulations of galactic gaseous disks re-accreting intergalactic plasma. As the initial condition, we assume that a rotating slender torus is formed at 10kpc from the galactic center. We assume a gravitational potential generated by bulge stars, disk stars and dark matters. Numerical results indicate that magnetorotational instability (MRI) growing in the torus amplifies magnetic fields and generates turbulence. The Maxwell stress enhanced by turbulent magnetic fields drives mass accretion of the disk gas. The amplification of magnetic fields in the accreting gas disk drives magnetic activities such as flares and plasma heating due to magnetic reconnection. The magnetic activity is maintained for time scales longer than the accretion time scale, typically 5Gyr.
An Introverted Starburst: Gas and SSC Formation in NGC 5253
Authors: Turner J. L. , Beck S. C.
Published: July 2016

High resolution Brackett line spectroscopy with the Keck Telescope reveals relatively narrow recombination lines toward the embedded young super star cluster nebula in NGC 5253. The gas within this nebula is almost certainly gravitationally bound by the massive and compact young star cluster.
PAH features in Infrared Luminous Galaxies: Results from Michelle
Authors: Clemens M. S. , Nikolic B. , Alexander P. , Cotter G. , Longair M. S.
Published: July 2016

We present recent results from mid-infrared observations of a sample of nearby, infrared luminous starbursts and AGN made with the new mid-infrared instrument, “Michelle”, on UKIRT. Narrow band imaging in the 7-13 micron range with sub-arcsec resolution has been used to study the spatial distribution of polycyclic aromatic hydrocarbon (PAH) features. The comparison of these sub-arcsecond resolution data with radio continuum data at similar resolution can be used to determine, 1) the sources of excitation required for PAH emission, and 2) whether PAH features are a measure of the relative contribution of star formation and AGN to the bolometric energy output of a galaxy. Unlike the far-infrared emission from dust, that in the mid-infrared can be used to discriminate between different heating sources.
The Nature of UV-selected Galaxies in the Chandra Deep Field South
Authors: De Mello D.F. , Gardner J. P. , Dahlen T. , Conselice C. J. , Grogin N. A. , Koekemoer A. M
Published: July 2016

We report the first results of the ongoing survey using HST/WFPC2 (F300W) in parallel with ACS within the Chandra Deep Field South. A sample of 34 objects were identified in the WFPC2 images and their counterparts were found in the ACS images taken by the GOODS team; 6 of them are stars. Galaxies were classified as early-, late-types, and starbursts by template fitting which was also used to determine their photometric redshifts (z< 1). Analysis of the light concentration, asymmetry and clumpiness shows that this sample is a mixed bag, containing dwarf ellipticals, early- and late-spirals, and peculiar objects which resemble mergers in progress. This result has important implications for galaxy evolution since the intermediate redshifts are the epoch when the rise in the volume-averaged star formation rate occurs.
Physical Properties of Dlas: Metallicity and Neutral Hydrogen Column Density
Authors: Hou J. L. , Shu C. G. , Chen W. P. , Chang R. X. , Fu C. Q.
Published: July 2016

We investigate some basic properties of Damped Lyman alpha systems based on the Semi-Analytical model of disk galaxy formation theory. We derive the DLA metallicity, column density, number density, gas content and cosmic star formation rate by assuming that disks form at the center of dark halos, and the modelled DLAs are selected by Monte Carlo simulation according to the distributions of halo properties. We find that DLA hosts are dominated by small galaxies and biased to extended galaxies. In terms of model results, DLAs could naturally arise in a ACDM universe from radiatively cooled gas in dark matter halos. However, model predicts a reverse correlation between metallicity and the column density when compared with observations, regardless of the proposed observational bias. We argue that this could be resulted from the model limitations, or the inadequacy of Schmidt-type star formation mode at high redshift, or/and the diversities of DLA populations.
Quasar Winds as Dust Factories at High Redshift
Authors: Elvis Martin , Marengo Massimo , Karovska Margarita
Published: July 2016

Winds from AGN and quasars will form large amounts of dust, as the cool gas in these winds passes through the (pressure, temperature) region where dust is formed in AGB stars. Conditions in the gas are benign to dust at these radii. As a result quasar winds may be a major source of dust at high redshifts, obviating a difficulty with current observations, and requiring far less dust to exist at early epochs.
The Galaxy Merger Origin of Hot Gaseous Halos of Ellipticals
Authors: Xia X. Y. , Huo Z. Y. , Xue S. J.
Published: July 2016

We report on the properties of the hot gaseous halos of 10 nearby ultraluminous IRAS galaxies from Chandra observations. There exists diffuse soft X-ray emission surrounding the central nucleus within 10 kpc of the nuclear region with a temperature of about 0.7 keV and metallicity about Z ~ 1.0Z⊙. Also, emission lines from α elements and ions for are seen in all nearby ULIRGs in our sample. Outside the central region, the Chandra observations reveal a more extended hot gaseous halo with a temperature of about 0.6 keV and low metallicity (Z ~ 0.1Z⊙) for some of the ULIRGs. We discuss the nature and the implications of our results for the origin of X-ray halos in elliptical galaxies and the constraints this places on the feedback process.
Interactions among Active Galaxies: An HI Perspective
Authors: Lim Jeremy , Kuo Cheng-Yu , Liau Wen-Shuo , Greene Jenny , T. P. Ho Paul
Published: July 2016

Galaxy-galaxy interactions is one of the leading candidates for triggering nuclear activity in galaxies. Such interactions are thought to be able to bring a fresh supply of gas to the center of a galaxy to fuel its resident supermassive black hole. Optical observations, however, do not reveal direct evidence for interactions among the majority of active galaxies. on the other hand, neutral atomic hydrogen (HI) gas has proven to be an exquisite tracer of galaxy-galaxy interactions, even when no such interactions are visible in the optical. Here, we describe our systematic HI imaging surveys of galaxies hosting active galactic nuclei (AGNs) and quasi-stellar objects (QSOs), and present a few illustrative results.