bluuebunny/crossref_metadata_2025 huggingface dataset:
A Storage Process of the Magnetic Energy in the Space Active Regions and Stellar Atmosphere
Authors: Zhongyuan Li
Published: July 2016

A few authors (Barnes and Sturrock, 1972; Ma, 1977; Svestka, 1977) have calculated the quantitative relationship between the static force-free field connecting the magnetic field and the twisting processes. They pointed out that the potential magnetic field without the current may be twisted into the force-free field with the enhanced current produced by the plasma rotation. Li et al. (1982) and Li and Hu (1984) have stated that the processes should be unsteady, and especially that they should not be static. The magnetic Reynold number is usually much larger than 100 in stellar atmosphere (Li et al., 1982). We adopt the following MHD equations:

where the force - free factor α (t, r) depends on both, t and r. According to t h e kinematical momentum conservation, the following constraint is easily obtained:
where V = (u, v, w) is the velocity field in the cylindrical coordinates. When studying the evolution of the kinematical force - free field, the in fluence of a reasonable flow on the variations of the magnetic field should be taken into account. After some reasonable simplification we deduce the specific expression of the variation law of the toroidal magnetic energy

where J1 is the Bessel function of the first order. In the active region, magnetic energy including the term of a twisted effect f(t) is larger than that of the static force - free field.
Magnetic Field of Rotating Bodies
Authors: Dolginov A.Z.
Published: July 2016

Difficulties of the dynamo and alternative theories of the magnetic field generation are briefly discussed. The correlation between η = lg μ/μo and ζ = lg J/Jo for rotating celestial bodies is considered. μ is the magnetic and J the angular momentum of the body. Existing theories do not explain such a correlation, and it may be an evidence for some new fundamental interaction.
Pulsars as Probes of the Galactic Magnetic Field
Authors: Lyne A. G.
Published: July 2016

The high linear polarization of pulsar radiation allows a reasonably easy determination of the Faraday rotation measure. Unlike other radio sources, the impulsive nature of pulsar emission also permits a determination of the number of electrons responsible for the rotation, through the dispersion measure, DM.
The Two Component Magnetic Field of the Galaxy
Authors: Andreassian R.R. , Makarov A.N.
Published: July 2016

The present paper is devoted to a study of the magnetic field configuration of our Galaxy based on Faraday rotation measures (RM) of 185 pulsars and 802 extragalactic radio sources. RM data of pulsars located near the plane of the Galaxy are used for the study of magnetic fields in neighbouring spiral arms. For the distribution of spiral arms the well-known model of Georgelin and Georgelin (1976) is used. The calculations show (for details see Andreassian and Makarov, 1987, 1989) that in the Perseus spiral arm and the local Orion arm the magnetic fields have approximately the same directions (lo;bo) ≈ (80°;0°), while in the Sagittarius-Carina arm the magnetic field has an opposite direction.
Fluctuations in the Galactic Magnetic Field
Authors: Cordes James M. , Clegg Andrew , Simonetti John
Published: July 2016

We discuss small scale structure in the Galactic magnetic field as inferred from Faraday rotation measurements of extragalactic radio sources. The rotation measure data suggest a continuum of length scales extending from parsec scales down to at least 0.01 pc and perhaps to as small as 109 cm. Such turbulence in the magnetic field comprises a reservoir of energy that is comparable to the energy in the large scale field.
Extended Polarized Emission Structures in the Galactic Plane at 11 cm Wavelength
Authors: Junkes N. , Fürst E. , Reich W.
Published: July 2016

Data from the Effelsberg Galactic plane survey at 11 cm wavelength have been used to produce a survey of polarized intensity in the first Galactic quadrant. Besides polarized sources (Supernova remnants and extragalactic objects) extended polarized emission features are visible, which are not connected to distinct radio sources. To decide whether these features reflect characteristics of the local field or the distant spiral structure of the Galaxy we performed an integration of polarized intensities as a function of Galactic longitude. An anticorrelation with the thermal background component suggests a distance of more than 6 kpc for some components of the polarized emission. This enables us to derive an upper limit for the uniform component of the Galactic magnetic field.
Magnetic Fields in Young SNRs
Authors: Dickel John R. , Jones Eric M.
Published: July 2016

There are two very important properties of the magnetic fields in supernova remnants which we wish to emphasize: 1) The net radial orientation of the magnetic vectors throughout the shell and 2) an apparent gradual increase in the fractional polarization with evolutionary age.
Bisymmetric Spiral Magnetic Fields and Gravitational Instabilities of Galactic Disks
Authors: Sawa T. , Fujimoto M.
Published: July 2016

Linearized equations of motion are solved for the self-gravitating gaseous disk in interaction with the Lorentz force due to the bisymmetric spiral (BSS) magnetic fields. Since the pattern velocity of the BSS fields is very close to that of the spiral density wave, a nearly-resonant interaction occurs between these two waves to enhance spiral condensation of gas. The BSS fields seem to compensate the spiral density waves for their secular dispersion.
Turbulent Mixing in Circumstellar Space in the Presence of Magnetic Fields
Authors: Breitschwerdt D. , Kahn F.D.
Published: July 2016

The magnetic field structure in the swept-up HII shell and the stellar wind region around an early type star is described. It is argued that the field does not become dynamically so important as to prevent self-similar flow. A condition under which reconnexion removes magnetic energy from the bubble is derived. It follows that the process of turbulent mixing between the HII region and the bubble works efficiently enough to cause severe departures from uniform expansion, even in the presence of magnetic fields.
Modelling Faraday Rotation in Galaxies
Authors: Brett Lindy
Published: July 2016

Multi-frequency radio polarization observations of external galaxies are now available. The resolution is such that we can sample many positions over the galaxy, and different scale sizes. Faraday rotation measures, initial polarization angles, and depolarization can be used as indicators of magnetic field morphology in the source. In order to interpret the variation of polarization characteristics with frequency, a numerical model of Faraday rotation in galaxies is being developed. Preliminary results show that a wide range of situations can be investigated with the model.
The Magnetic Field in M33
Authors: Buczilowski U.R. , Beck R.
Published: July 2016

Measurements at five radio wavelengths between 2.8 and 21.1 cm (Buczilowski and Beck, 1987) with the Effelsberg 100-m telescope make M33 the best studied nearby galaxy in linear polarization so far. The polarized emission is concentrated to the northwestern quadrant of the galaxy. Almost no polarization is detectable around the 35 known supernova remnant candidates. The explosions may have disturbed the interstellar magnetic field on scale sizes smaller than our antenna beams.
The Magnetic Field in Edge-On Galaxies
Authors: Hummel E. , Dahlem M.
Published: July 2016

We observed the linearly polarized emission of the edge-on galaxies NGC891 and NGC4631 in order to determine the magnetic field structure.
Dust Grain Orientation in the Interstellar Magnetic Field
Authors: Dolginov A.Z.
Published: July 2016

It is shown that the orientation of the dust grain body relative to its angular momentum J by the Barnett relaxation effect and the orientation of J relative to the interstellar magnetic field, by action of anisotropic gaseous fluxes, which always exist in space, is more effective than the orientation of the Davis-Greenstein mechanism. The linear interstellar polarization, which arises by scattering of radiation on oriented grains, is directed along the galactic magnetic field.
Optical Polarisation Studies of Galaxies
Authors: Scarrott S.M. , Rolph C.D. , Semple D.P.
Published: July 2016

High spatial resolution maps of the optical linear polarisation of a range of galaxies of different morphological types and inclinations are presented. Spiral, barred spiral and irregular galaxies with low inclinations show spiral patterns of polarisation orientation which may be interpreted to indicate that there are large-scale magnetic fields present in the discs of these galaxies. A survey of edge-on galaxies with conspicuous equatorial dust lanes shows remarkable differences in polarisation structure between early and late types. In the Sa galaxies the polarisation in the dust lane is sizeable and parallel to the dust lanes, suggesting that the magnetic field is uniformly distributed in the plane of the galaxy. This polarisation pattern disappears in the Sc galaxies suggesting that the relatively chaotic dust features do not possess a grain aligning mechanism, e.g. a magnetic field, that is uniform or coherent over large distance scales. It is clear that most galaxies do have polarisation patterns that are related to galactic structure and inclination, and further similar polarisation studies should help to unravel the relationship between the generation of polarisation and galactic magnetism.
The Rate of Angular Momentum Loss from Cloud Cores
Authors: Nakano Takenori
Published: July 2016

The angular momentum is one of the major obstacles to the contraction of interstellar clouds. An efficient process of removing the angular momentum from the cloud is via transport along the magnetic field lines to the ambient medium. When the magnetic field is nearly uniform and the direction of the field lines is parallel to the rotation axis, the spin-down time of the cloud is given by σ/2ρVA, where σ is the column density of the cloud along the field lines, and ρ and VA are the density and the Alfvén velocity, respectively, in the ambient medium (Ebert et al. 1960; Mouschovias & Paleologou 1980). However, this is for a cloud with weak gravity. Because a cloud with strong gravity has contracted dragging the field lines, the ambient field is considerably distorted from uniformity. The spin-down time of such a cloud is shorter than given above (Gillis, Mestel & Paris 1974, 1979).
Magnetic Fields in Interstellar Masers
Authors: Moran J. M.
Published: July 2016

Zeeman splitting in the spectra of molecular masers that arise in the envelopes of newly formed stars (called interstellar masers) offers a method of estimating the magnetic field in these dense regions (106–1011 cm−3). The magnetic field strengths in regions of OH and H2O masers scale as the square root of the density when compared to the density and field of the ambient interstellar medium. The direction of the field in OH masers may help trace the large scale structure of the magnetic field in the Galactic spiral arms.
Magnetic Fields in Dark Cloud Cores and H2O Masers
Authors: Güsten Rolf , Fiebig Dirk
Published: July 2016

We present results of recent circular polarization experiments with the MPIfR 100-m telescope, revealing for the first time, the magnetic field strength towards interstellar H2O masers and the dense cores of local dark cloud complexes. Weak Zeeman splittings of a few 10 kHz only in the 22.235 GHz maser transition of the non-paramagnetic H2O molecule imply magnetic field strengths of ~ 50 mG in the dense (n ~ 1010 cm−3) masing layer. With the recently identified CCS radical it became possible to study the magnetic field associated with dense (~ 105 cm−3) dark cloud cores, the potential sites of future star formation. We report the detection of a −110μG field towards TMC-1C, a low-mass core associated with the Taurus Molecular Cloud. From complementary gas density and kinetic temperature probing measurements, we derive approximate equipartition between magnetic, gravitational and thermal energy for this clump.
The Hα Emission of the PMS Star Serpens/SVS 2
Authors: Gomez De Castro A.I.
Published: July 2016

Serpens is a region of low mass star formation where the magnetic field seems to play a fundamental role. The major axis of the Serpens outflows are aligned with the magnetic field. The most outstanding object in the region is the Serpens Reflection Nebula, SRN. This is characterized by a rather complex bipolar structure with several knots of gas and dust embedded in both nebular lobes. The western lobe is directed out of the cloud toward the observer. The SRN is illuminated by the PMS star Serpens/SVS 2. The star is surrounded by a dust disk; the polarization pattern of the disk can be interpreted as produced by dust grains aligned by the magnetic field frozen-in with the disk.
The Magnetic Field in the Perseus Molecular Cloud Complex
Authors: Goodman A.A. , Myers P.C. , Bastien P. , Crutcher R.M. , Heiles C. , Kazès I. , Troland T.H.
Published: July 2016

In Figure 1, we present a map of the polarization of background starlight in the Perseus region (Goodman, Bastien, Myers, and Menard 1989) superposed on contours of integrated 13CO emission (Bachiller and Cernicharo 1986). The polarization vectors map the plane-of-the-sky field (B⊥), assuming as usual that the observed polarization is the result of selective extinction by magnetically aligned dust grains associated with the molecular clouds between the observer and background stars (e.g. Dolginov 1989).
Topological Solutions for Collimated MHD Flows
Authors: Tsinganos K. , Trussoni E.
Published: July 2016

Different astrophysicai contexts (e.g. extragalactic jets, star forming regions) are related with collimated ouflows. An analysis of this phenomenology in principle would require a fully numerical treatment, however analytical investigations are also possible by assuming a suitable behaviour of streamlines. In this framework we investigate solutions of the hydrodynamic and MHD equations describing helicoidal collimated outflows from a central gravitating object.
Resistive Instabilities in a Two-Dimensional MHD Turbulent Flow
Authors: Politano H. , Sulem P. L. , Pouquet A.
Published: July 2016

Direct numerical simulations of decaying two-dimensional incompressible MHD flows at Reynolds numbers of several thousands are reported here, using resolutions of 10242 collocation points on a uniform grid. Spatial derivation is performed using Fourier decomposition, assuming periodic boundary conditions, and nonlinear terms are computed in configuration space. The time-stepping scheme is semi-implicit, Crank–Nicolson and third-order Runge–Kutta. The magnetic Prandtl number is equal to unity in all runs. Both deterministic and random initial conditions are used, concentrated in the large scales, with quasi–equipartition between kinetic and magnetic energy. The dynamic range in amplitude of the fields is 107, ensuring well–resolved current and vorticity sheets, over roughly 20 grid points. This leaves sufficient space for tearing instabilities to develop, embedded in a turbulent flow.
Poloidal Magnetic Fields in Galactic Central Regions
Authors: Lesch H. , Crusius-Wätzel A. , Schlickeiser R. , Wielebinski R.
Published: July 2016

We discuss the origin of the observed strong poloidal fields Bz in the central regions of galaxies which have gaseous rings. In the context of galactic disk dynamo models only weak poloidal fields but strong toroidal fields result (Bϕ > Bz). Therefore we tie the strength of the poloidal fields to the central activity and apply known and tested ideas rigorously. A battery process on galactic scales is discussed which ensures the existence of a large scale magnetic field in the inner galactic region. The frozen-in field may be amplified by compression and turbulent stretching; the resulting field is poloidal. The central activity provides a nonaxisymmetric flow field which, just as the α – ω dynamo produces mostly Bϕ > Bz, can produce Bz ≥ Bϕ. This model explains the structure and strength of the magnetic field in star-burst galaxies like M82 (Lesch et al., 1989).
Shock Conditions in Magnetized Jets
Authors: Appl S. , Camenzind M.
Published: July 2016

The jets in strong radio galaxies (SRG) terminate in hot spots (HS), which are considered as the region where the jet plasma is shocked by interaction with the intergalactic medium. Little is known about the physical parameters in the jets, in particular the velocities. The jump conditions, which are a consequence of conservation of four-momentum, magnetic flux and particle number, provide a means to connect the physical parameters in the jet with those in the HS. The synchrotron radiation which is observed from the HS has a power law spectrum. If the radiating electrons are accelerated by first order Fermi processes, the spectral index in the test particle approximation is dependent on the jump conditions only. These two ingredients, the jump conditions for relativistic MHD shocks, and first order Fermi acceleration, allow to obtain estimates of the jet velocity. It is concluded that the jets in SRG have mildly relativistic velocities of ≃ 0.3c and fast magnetosonic Mach numbers of ≃ 3. Furthermore, the fact that the jets in weaker radio galaxies show no HS is attributed to submagnetosonic velocities. If the shock heats mainly protons, then the postshock plasma heats up to temperatures of a few 1011 K. How the protons can be heated and the electrons be accelerated, is subject to the subsequent contribution (Lesch, Appl and Camenzind, these proceedings). In addition, strong magnetic fields reduce the shock strength considerably. Therefore, within the framework of magnetically collimated jets, the VLBI knots are unlikely to be shocks. Details of this work are found in Appl and Camenzind (1988).
A Theoretical MHD Model for Extragalactic Jets and its Comparison with the Observations
Authors: Pietrini P.
Published: July 2016

Two aspects of the MHD stationary equilibrium model developed by Chiuderi et al.(1989) to describe extragalactic jets are analyzed and compared with the observational constraints: the global energy flux convected by the cylindrical jet and the ranges of the equilibrium parameters allowed by the stability analysis. In particular, the results obtained from the temporal stability analysis are converted into a spatial point of view. In this context, it is easier to find essentially “stable” equilibrium configurations for shorter jets. In conclusion, the fundamental hypotheses of this model (like thermal confinement and substantial equipartition among the various forms of energy considered) are such that the model turns out to be suitable for the description of class I jets, associated with rather low-power radio sources.
Origin of Magnetic Fields in Jets and Radio Galaxies
Authors: Rose William K.
Published: July 2016

Jets are known to be emitted from the centers of active galaxies and quasars. In two recent papers (Rose, 1987, 1989) calculations of magnetic fields generated in jets because electrons drift with respect to protons have been described. Electron drift velocities can result from interaction with the cosmic background radiation or with ambient gas. We describe how magnetic fields can be generated in jets and radio galaxies.
Importance of Magnetic Effects in a Two-Flow Model for Extragalactic Radio Jets
Authors: Sol H. , Pelletier G. , Asseo E.
Published: July 2016

We propose a model for extragalactic radio jets in which two different flows of particles are taken into account, (i) a beam of relativistic electrons and positrons extracted from the funnel of accretion disc and responsible for the observed superluminal motion, (ii) a classical or mildly relativistic wind of electrons and protons coming out from all parts of the disc (Sol et al., 1989). Studying the mutual interaction of the two flows, we show that the configuration is not destroyed by the plasma-beam instability as long as the magnetic field, assumed longitudinal, is strong enough, with an electron gyrofrequency ωc = eB/mec greater than the ambient plasma frequency ωp = (4πnpe2)1/2 (Pelletier et al., 1988). When ωc < ωp, the relativistic beam loses its energy and its momentum mainly through the development of strong Langmuir turbulence in the wind, and disappears quietly after some relaxation zone where heating and entrainment of the wind occur. This emphasizes one aspect of the important role likely played by the magnetic field in the dynamics of extragalactic jets and provides one example in which the magnetic field, acting on the microscopic scale of an interaction, induces strong effects on large–scale structures. Detailed data on the closest known superluminal radio source 3C120 (Walker et al., 1987, 1988; Benson et al., 1988) allow a check on the likelihood of our model. Observational estimates of the variation along the jet of the magnetic field and of the ambient plasma density np suggest that the magnetic field reaches its critical value (corresponding to ωc = ωp) at a minimal distance of about 1.4 kpc from the central engine. This is amazingly close to the location of the 4′–radio knot, a “rather curious structure” described by Walker et al. (1987), which we interpret as the beam relaxation zone in the context of our two–flow model (Sol et al., 1989).
The Production of Rotation Measure Gradients in the Lobes of Extragalactic Radio Sources
Authors: Bicknell G.V. , Cameron R.A. , Gingold R.A.
Published: July 2016

It is proposed that the large rotation measure gradients observed in the lobes of some extragalactic radio sources are produced by non–linear Kelvin–Helmholtz surface waves. Related small scale turbulence is responsible for a “diffuse spray” of relativistic plasma and magnetic field into the surrounding medium. The mixture of magnetic field and thermal plasma causes large rotation measure variations on the scale of the Kelvin–Helmholtz waves. An order of magnitude prediction of the effect is in good agreement with the observations of Cygnus A and PKS 2104–25 N.
Properties of the Medium Causing Asymmetric Depolarization in Strong Double Radio Sources with One Jet
Authors: Crusius-Wätzel A. , Biermann P.L. , Lerche I. , Schlickeiser R.
Published: July 2016

Polarization data of strong double-lobed radio sources (Garrington et al., 1988a; Laing, 1988) in many cases show that one side is more depolarized than the other. Since a jet is seen only on the less depolarized side it can be concluded that this radio lobe is nearer to us, if the one-sidedness of the jet is interpreted by bulk relativistic motion. The effect is then due to random Faraday rotation where the RMS-rotation angle is larger than about π/2 for the longer wavelength. This suggests an intervening magnetized plasma which may be the hot gas in the halos of the (elliptical) galaxies or in the cluster. Comparing the effects of both, the intracluster medium (ICM) probably is the dominating component. Garrington (1988b) comes to the same conclusion. Considering the transport of polarized radio waves in a turbulent Faraday screen (cells of size l0) we further find that the coherence length of the magnetic field is of the order of l0 = 1–4 kpc. From EINSTEIN X-ray data (for 3C9, 4C01.11, 3C270.1, 3C275.1, 3C208) we find luminosities in the range Lx = 0.6–7 × 1045erg s−1, which can only be due to the cluster gas or an active galactic nucleus. If we assume that the total X-ray flux is produced by the ICM the electron core densities are n0 = 2–7 × 10−3 cm−3. Combining this with the values for l0 gives upper limits to the ratio of thermal to magnetic pressure (plasma-beta) of βp = 50–370 and lower limits to the core magnetic field strength of B0 = 3–9 μG. If the AGN contributes substantially to the X-ray emission the given limits would be even stronger, in the direction of equipartition of energy in the hot gas and in the magnetic field, since B0 has to be larger if n0 is smaller to account for the same dispersion in Faraday rotation. We plan to separate the diffuse and the pointlike emission by ROSAT observations. A more detailed version of this paper will be presented elsewhere (Crusius–Wätzel et al., 1989).
High Frequency Observations of a Large Faraday Rotation Galaxy in a Cluster
Authors: Inoue M. , Tabara H. , Kato T. , Aizu K.
Published: July 2016

We present 22 and 49 GHz interferometric observations of Hyd A (3C218). The source was found to have a very large Faraday rotation measure (RM) (Kato et al. 1987), and to be a dominant member of a luminous X-ray cluster with a large cooling flow (David et al. 1988). These characteristics are very similar to those of Cyg A which is suggested to produce a large RM within a dense sheath around the radio lobes as a result of somehow an interaction between dense intracluster medium (ICM) and radio jets and/or lobes (Dreher et al. 1987). Hyd A is the second example of Cyg A type source. In case of Cyg A, hot spots are the place where the interaction between jets and ICM occurs (Carilli et al. 1988). We then expect in Hyd A that similar interaction also occurs to form hot spots, and consequently that high frequency observations reveal structures of the interaction.
Intermittent Magnetic Fields Generated by Turbulence in Galaxies and Galaxy Clusters
Authors: Sokoloff D.D. , Ruzmaikin A.A. , Shukurov A.
Published: July 2016

The turbulence of intracluster gas in galaxy clusters and interstellar gas in galaxies can act as a dynamo generating chaotic magnetic fields. These fields are concentrated in ropes with the doubled radius of curvature of about the turbulent correlation length l and thickness where Rm is the magnetic Reynolds number. The field strength within the ropes is close to equipartition with turbulent kinetic energy. These results favorably agree with high—resolution observations of the galaxy cluster around Cyg A and correlation analysis of the Galactic nonthermal background. Ropy magnetic fields in interstellar gas lead to observable variations of, e.g., the Faraday depth at time scale of 1 month.
Intergalactic Magnetic Fields and the Morphology of Spiral Galaxies
Authors: Battaner E. , Florido E. , Sanchez-Saavedra M.L.
Published: July 2016

The influence of the hypothetical extragalactic magnetic field upon the peripherical morphological features of spiral galaxies is examined- When the angle between and the rotation axis is neither 0° nor 90°, warps are expected to be produced. In such a case the spatial distribution of warps should not be random. This fact seems to be confirmed by observations. From the distribution it is possible to obtain the direction of B in the 20Mpc-neighborhood of the Milky Way.
Quasar Rotation Measures and Optical Absorption Spectra—What Can We Learn About Cosmic Magnetic Fields?
Authors: Perry Judith J. , Kronberg Philipp P. , Watson Alan M.
Published: July 2016

This paper reviews early attempts to deduce important constraints on the magnetic fields of high-redshift objects through a study of the rotation measure (RM) of QSOs. We have combined detailed studies of RM and optical spectra of 48 QSOs and have statistically analysed RM data on 116 objects and conclude that the objects which give rise to QSO metal-line absorption are also responsible for the observed extragalactic component of RM. This allows us to estimate their average magneto-ionic properties.
The Present State of a Primordial Galactic Field
Authors: Kulsrud Russell. M.
Published: July 2016

If the galactic field arose from flux imbedded in the protogalacticgalactic medium, then one would expect this field to be strongly wound up by the differential galactic rotation once it had formed into a disk. This process is balanced by the buoyancy forces lifting the flux out of the disk. The resulting field turns out to be only slightly wound up. Further, its magnitude depends only on properties of the ISM provided that the primordial field exceeds 10–13 gauss.
Concluding Summary Remarks
Authors: Woltjer L.
Published: July 2016

Fifty years ago at a conference on the structure of galaxies almost everything would have been ascribed to gravity. A decade later turbulence became the new thing - partly to solve angular momentum problems. Again a decade later magnetic fields followed: synchrotron radiation was observed, angular momentum could be efficiently transported and a variety of bizarre extragalactic shapes was thought to be related to magnetic fields. In the sixties, however, the situation was reversed when it turned out that spiral structure could perhaps be understood on a gravitational picture with some simple hydrodynamics and that some of the most intriguing shapes could be reproduced in simulations of the gravitational interaction between galaxies. As a consequence magnetic fields again diminished in importance. The next decade saw a much increased role for the thermodynamics of the interstellar medium. At the end of this meeting it is clear that while gravity, hydrodynamics and thermodynamics are important, magnetic fields cannot be neglected and should be integrated into the overall picture.
Mode Transitions of Black Hole Accretion Disks
Authors: Lu Ju-Fu , Gu Wei-Min , Lin Yi-Qing
Published: July 2016

The model of a bimodal accretion disk, which consists of an Shakura-Sunyaev disk (SSD) as the outer part and an advection-dominated accretion flow (ADAF) as the inner part, has been quite successfully applied to many black hole X-ray binaries. However, the precise physical mechanism through which such a transition occurs remains a matter of debate. We review briefly SSD-ADAF transition mechanisms presented in the literature, and offer a proposal that in the case of moderately strong viscosity, the thermal instability of a radiation pressure-supported SSD can trigger the transition.
The Progenitors of Type Ia Supernovae
Authors: Han Zhanwen , Podsiadlowski Philipp
Published: July 2016

Using binary population synthesis (BPS), we studied the birthrates of SNe Ia for two progenitor models – the single degenerate model and the double degenerate model. We find that the birthrates from both models are within a factor of a few comparable to those inferred observationally. For each model, we investigate different star-formation histories (single star burst or constant star formation), different metallicities (Z = 0.02, 0.004, 0.001), different parameters for the BPS model (mass transfer efficiency during stable mass transfer, common-envelope ejection parameters) and obtain the evolution of birthrates with time.
SNR 1987A: the Birth of a Supernova Remnant
Authors: McCray Richard
Published: July 2016

In 1996, the blast wave from Supernova 1987A began to strike the inner circumstellar ring, causing the appearance of “hot spots” on the ring. This event marks the birth of the supernova remnant, SNR1987A, defined as the epoch when the light of the event is dominated by interaction of the expanding debris of the supernova with its circumstellar matter.
Pulsar Observations in China – Status and Results
Authors: Wang Na , Zhang Jin , Wu Xin-Ji
Published: July 2016

We present the status and results of pulsar observations in China. Pulsar observations at Urumqi Observatory over more than two years have resulted in updated rotation parameters for 74 pulsars. Comparison with earlier observations shows that long-term period and period-derivative fluctuations are probably dominated by unseen glitches. We also monitored the variation of pulsar scintillation dynamic spectra for a few strong pulsars. The data show major variations in the scintillation parameters. A new system at a lower frequency is planned to allow investigation of the frequency dependence of pulsar properties. A 50-m telescope for millisecond pulsar timing is also being planned at the National Astronomical Observatories, Beijing, and should be constructed within three years.
A Joint Model for Radio and γ-ray Emission from Pulsars
Authors: Qiao G. J. , Lee K. J. , Wang H. G. , Xu R. X.
Published: July 2016

Although pulsars can radiate electromagnetic wave from radio to gamma ray bands, we still have no a united model to understand the multi-band emission. In this paper the effort for a joint model is presented. The inverse Compton scattering (ICS) and a second acceleration process near the null surface are involved to account for the radio and the gama-ray emission, respectively. Various kind of pulse profiles and other observational properties can be reproduced.
Long-Term X-ray Variability of Circinus X-1 as Observed by the RXTE All Sky Monitor
Authors: Wang Junfeng , Brandt W. N.
Published: July 2016

The luminous low mass X-ray binary Cir X-1 has been observed nearly continuously for about 5 years by the X-ray All Sky Monitor on board the RXTE satellite. We carried out a timing analysis on Cir X-1 with the RXTE data. We define the period from the X-ray data, comparing the period change over time with the best current ephemeris. with folded light curves of entire data set, characteristics of the system like long-term lightcurve changes, behavior of flares and dips and super-Eddington accretion were obtained. We also checked and identified the secondary flaring reported in radio band with X-ray data.
Seyfert 2 Galaxies with Spectropolarimetric Observations
Authors: Gu Qiusheng , Huang Jiehao
Published: July 2016

We compare Seyfert 2 galaxies(Sy2s) with detected polarized broad emission lines(PBL) with Sy2s without detected PBL and find that the majority of Sy2s without PBL are those sources with less powerful AGN activity, most likely caused by low accretion rates. This implies that the detectability of polarized broad emission lines in Sy2s mainly depends on their central AGN activity in most cases. We also find that Sy2s without PBL follow the exactly same FIR-radio relation as normal and starburst galaxies.
e±-rich GRB Fireball and Infrared Flashes
Authors: Li Zhuo , Dai Z. G. , Lu T.
Published: July 2016

Gamma-ray bursts (GRBs) are believed to originate from ultra-relativistic fireballs, with initial Lorentz factor η ∼ 102 − 103. However very high energy photons may still suffer from γγ interaction. We show here that in a wide range of model parameters, the resulting pairs may dominate electrons associated with the fireball baryons. This may provide an explanation for the rarity of prompt optical detections. A rapid response to the GRB trigger at the IR band would detect such a strong flash.
Characteristic Variability Time Scales of Long Gamma-Ray Bursts
Authors: Shen Rongfeng , Song Liming
Published: July 2016

We determine the characteristic variability time scales for 410 bright long GRBs by locating the maximums of their Power Density Spectra (PDSs) defined and calculated in the time domain. The averaged characteristic variability time scale decreases with peak fluxe. This is consistent with the time dilation effect expected by cosmological origin of GRBs. The occurrence distribution of the characteristic variability time scale shows bimodality, which might be interpreted as that the long GRB sample is composed of two sub-classes with different intrinsic characteristic variability time scales.
Optical Flash and Radio Flare in Wind Environment
Authors: Wu X. F. , Dai Z. G. , Huang Y. F. , Lu T.
Published: July 2016

The interaction of a relativistic fireball with its ambient medium is described through two shocks: a reverse shock that propagates into the fireball, and a forward shock that propagates into the medium. We here study very early afterglows from the reverse and forward shocks in winds. An optical flash arises from both the relativistic reverse and forward shock while a radio flare is produced by the forward shock.
On the Present Time Approximate Values of the Characteristic Parameters of the Primordial Gravitational Waves
Authors: Melek M.
Published: July 2016

An approach is used to find out the present time approximate values of the characteristic amplitudes, the spectral densities, the intensties and the frequencies of the Primordial Gravitational Waves (PmGW), in the spatially perturbed Friedman - Robertson - Walker (FRW) adiabatically expanding Universe. The temporal variation of the magnitude of the time gradient of the characteristic amplitudes of the PmGW is calculated in spatial perturbed FRW Universe. The obtained results via this non-conventional approach may be of interest to shed some light on the possibilities of searching for the PmGW at definite frequency bands by the existing and the future networks of detectors.
The Determination and Interpretation of the Rotation Parameter v sin i
Authors: Collins George W.
Published: July 2016

In this paper we review the development of the concept of the stellar rotation parameter commonly known as v sin i. We emphasize that the interpretation of the parameter in terms of physical characteristics of the star always depends on comparison with a model that is intended to represent the physical properties of the star. To that end we will trace the development of such models along with the observational means of determining the parameter. Emphasis will be place on the traditional methods involving stellar spectroscopy, but some attention will be place on indirect methods involving direct measurement of the rotation period and recent interferometric determination of stellar oblatness. In addition we will comment on recent techniques involving the simultaneous measurement of many spectral lines and synthetic spectra to improve the accuracy of rotational half-widths.

The natural desire for simplicity of such models has often resulted in erroneous values for stellar parameters. This is particularly the case for the most rapidly rotating stars generally of early spectral type, but may also be present in some giants and supergiants where rapid rotation is difficult to detect. Finally, we will comment on the possibilities of improving the quality of both the measurement and interpretation of this important stellar rotation parameter.
Absolute Wavelength Shifts — A New Diagnostic for Rapidly Rotating Stars
Authors: Dravins Dainis
Published: July 2016

Accuracies reached in space astrometry now permit the accurate determination of astrometric radial velocities, without any use of spectroscopy. Knowing this true stellar motion, spectral shifts intrinsic to stellar atmospheres can be identified, for instance gravitational redshifts and those caused by velocity fields on stellar surfaces. The astrometric accuracy is independent of any spectral complexity, such as the smeared-out line profiles of rapidly rotating stars. Besides a better determination of stellar velocities, this permits more precise studies of atmospheric dynamics, such as possible modifications of stellar surface convection (granulation) by rotation-induced forces, as well as a potential for observing meridional flows across stellar surfaces.
New Homogeneous v sin i Determinations for B Stars in Galactic Open Clusters
Authors: North P. , Royer F. , Melo C. , de Medeiros J. R. , do Nascimento J. D. , Mermilliod J.-C. , Grebel E. K. , Maeder A. , Mathieu R.
Published: July 2016

We present new observations of projected rotational velocities of main sequence B stars in the galactic clusters NGC 2439, NGC 3293, NGC 3766, NGC 4755, NGC 7160 and h & χ Persei. 257 stars have been observed with three instruments, 207 of which are presented here. Projected rotational velocities have been determined by least-squares fit to synthetic spectra. Our v sin i scale is compared with that of Slettebak et al. (1975).
Metallicity and v sin i of B Stars in Galactic Open Clusters: is there any Correlation?
Authors: Royer F. , Melo C. , Mermilliod J.-C. , North P. , do Nascimento J. D. , de Medeiros J. R. , Grebel E. K. , Maeder A.
Published: July 2016

We discuss the v sin i distributions of main sequence B stars in galactic clusters in relation to stellar luminosity and to cluster metallicity. We show that evolutionary effects and/or dependence of initial v sin i distribution on stellar mass are important, so that a much larger sample and a wider metallicity range are required to detect any possible metallicity effect beyond doubt.
Direct Observations of Rotationally Distorted Stars
Authors: van Belle Gerard T. , Ciardi David R. , Thompson Robert R. , Akeson Rachel L.
Published: July 2016

We present infrared interferometric angular size measurements for rapidly rotating stars which indicate non-circular projected disk brightness distributions. For the A7IV-V star Altair, assuming that the apparent oblateness of the photosphere is due to the star's rapid rotation, a rigorous evaluation of the observation data in the context of a rigidly rotating Roche model shows that an estimate of v sin i = 210 ± 13 km s–1 can be derived that is independent of spectroscopic techniques. Altair is the first main sequence star for which direct observations of an oblate photosphere have been reported, and the first star for which v sin i has been established from observations of the star's photospheric geometry. Future prospects for this technique are considered, and a prospective catalog of 67 rotationally oblate targets is presented.
Probing rotation in pulsating stars from space
Authors: Matthews Jaymie M.
Published: July 2016

At the time of the last Stellar Rotation symposium in 1969, the map of known pulsators in the H-R Diagram covered a lot less territory, being confined mainly to the classical instability strip. Among the new classes of pulsators are the strongly magnetic roAp (rapidly oscillating Ap) stars whose pulsation amplitudes and phases are modulated with their rotation periods. Among the classical pulsators, the δ Scuti stars are now known to show many more eigenmodes and frequency splitting than was ever recognised three decades ago. Both are examples of the diagnostic potential and severe challenges to detect and interpret correctly rotational fine structure in the pulsational frequency spectrum. In a pulsating star, rotation can perturb the structure or dynamics, and it can split degeneracies to serve as a diagnostic of pulsational modes. One tool which should help us exploit the potential and overcome the challenges of studying the interaction between rotation and pulsation is Canada's MOST (Microvariability & Oscillations of STars) microsatellite. MOST is a small optical telescope and ultraprecise CCD photometer designed to detect and characterise acoustic (p-mode) oscillations with periods of minutes and amplitudes as low as 1 micromagnitude in bright stars. While customised to conduct asteroseismology of solar-type stars, the MOST mission will also include roAp stars as prime targets and eventuallly δ Scutis as secondary targets. I present here simulations of MOST observations of such targets with different rotation periods, in advance of the real data expected in the months after the scheduled 30 June 2003 launch.
CNO abundances in Early Type Be Stars
Authors: Frémat Y. , Zorec J. , Levenhagen R. , Leister N. , Hubert A.-M. , Floquet M. , Neiner C.
Published: July 2016

High dispersion spectra in the visible range were obtained for field Be Stars in both hemispheres. As Be Stars form a class of Main Sequence fast rotators, we are intended to test how their chemical composition can be affected by rotation.
Lithium and Rotation in Pop I stars
Authors: Mallik Sushma V.
Published: July 2016

Lithium abundances have been determined for 130 stars sampled on the basis that they have just about completed depletion of Li on the main sequence and have not yet begun their ascent on the red giant branch. The main goal is to study the effects of rotation on Li depletion. Analysis of the data reveals that fast rotating stars have suffered little depletion whereas slowly rotating stars have both low and high Li abundances. No one-to-one correlation appears to exist between Li abundance and the present v sini. The large observed spread in Li abundance is perhaps a consequence of an initial range in rotational velocities in stars spinning down to low values on the main sequence. An attempt is made to study the Li evolution as a function of age, mass and rotation against the backdrop of the evolutionary tracks on the HR diagram.
Rotation and Lithium Abundances in Evolved Stars
Authors: Lèbre A. , de Laverny P. , do Nascimento J.D. , de Medeiros J.R.
Published: July 2016

For a sample of 57 evolved stars (spectral type from F5III to G5III), typically stars located near and along the Hertzsprung gap, we derived lithium abundances from spectral synthesis method compared to new high resolution spectroscopic data. Lithium is detected for about half of this large sample stars and high Li-contents (ALi > 2.8) are reported for 8 stars. We examined the Li abundances along Teff, v sin i, the single/binary status and along the stellar mass and the evolutionary status (inferred from the HIPPARCOS data).
Angular Momentum Transport and Mixing by Magnetic Fields
Authors: Spruit H. C.
Published: July 2016

Magnetic fields can be created in stably stratified (non-convective) layers in a differentially rotating star. A magnetic instability in the toroidal field (wound up by differential rotation) replaces the role of convection in closing the field amplification loop. A dynamo model is developed from these ingredients, and applied to the problem of angular momentum transport in stellar interiors. It produces a predominantly horizontal field. The process is found to be more effective in transporting angular momentum than the known hydrodynamic mechanisms, with the possible exception of transport by internal gravity waves.
A Comparison of O Spectral Types with Nonrotating and Rotating Evolutionary Models
Authors: Walborn Nolan R. , Lennon Daniel J.
Published: July 2016

A calibration of the O spectral types and luminosity classes has been plotted onto evolutionary tracks and isochrones for both nonrotating models and models with an initial rotational velocity of 300 km sec–1. Differences in the physical interpretation of the spectral types between the two cases have been investigated.
Presupernova Evolution of Rotating Massive Stars and the Rotation Rate of Pulsars
Authors: Heger A. , Woosley S. E. , Langer N. , Spruit H. C.
Published: July 2016

Rotation in massive stars has been studied on the main sequence and during helium burning for decades, but only recently have realistic numerical simulations followed the transport of angular momentum that occurs during more advanced stages of evolution. The results affect such interesting issues as whether rotation is important to the explosion mechanism, whether supernovae are strong sources of gravitational radiation, the star's nucleosynthesis, and the initial rotation rate of neutron stars and black holes. We find that when only hydrodynamic instabilities (shear, Eddington-Sweet, etc.) are included in the calculation, one obtains neutron stars spinning at close to critical rotation at their surface – or even formally in excess of critical. When recent estimates of magnetic torques (Spruit 2002) are added, however, the evolved cores spin about an order of magnitude slower. This is still more angular momentum than observed in young pulsars, but too slow for the collapsar model for gamma-ray bursts.
A CFH12K Survey of Red Giant Stars in the M81 Group
Authors: Durrell Patrick R. , DeCesar Megan E. , Ciardullo Robin , Hurley-Keller Denise , Feldmeier John J.
Published: July 2016

We present the preliminary results of a wide-field photometric survey of individual red giant branch (RGB) and asymptotic giant branch (AGB) stars in the M81 group, performed with the CFH12K mosaic camera of the CFHT. We use deep VI images of 0.65 sq. deg. of sky to map out the two-dimensional distribution of intragroup stars and to search for stars associated with the many HI tidal tails in the group. We place an upper limit on the presence of metal-poor RGB stars in a field located 50-80 kpc from M81, and derive an ‘intragroup’ fraction of < 2%. In a field sampling the M81-NGC3077 HI tidal tail, we find blue stars associated with some of the tidal features, including 2 clumps which we tentatively describe as tidal dwarf candidates. These objects are ~ 1 kpc in size, and, based on their color-magnitude diagrams, have formed stars as recently as ~ 30 – 70 Myr ago, long after the group's most recent interactions.