bluuebunny/crossref_metadata_2025_split huggingface dataset:
Drift Acceleration at Interplanetary Shocks
Authors: Erdös G. , Balogh A. 
Published: July 2016

AbstractScatter-free acceleration of energetic particles by quasi-perpendicular interplanetary shocks is investigated. A brief review is given on the predictions of the gradient drift acceleration model concerning the energy, time, and angular dependence of the particle flux caused by a single shock encounter interaction. The angular distribution of ions in the energy range 35 keV to 1 MeV has been determined by the low-energy ion spectrometer aboard the ISEE 3 spacecraft at several shock associated events. Reflections of particles from the shock were clearly identifiable by the loss cone in the upstream pitch angle distributions. The measurements were compared to the predictions of the gradient drift acceleration model, showing a qualitative agreement in many respects. However, bidirectional distributions observed at nearly perpendicular shocks cannot be explained in the framework of the single shock encounter mechanism. It is suggested that multiple intersections of the field lines with the surface of the shock, forming magnetic traps on the upstream side, are responsible for the observed bidirectional distributions. Results obtained from numerical test particle simulations are discussed and compared to observations. A qualitative agreement between model calculations and measurements confirms that the energetic particles are trapped and accelerated, due to special field line topology, on the upstream side of the shock. It is also argued that the collapse of the trap by the convection of the field lines through the shock is accompanied by a considerable increase of the particle flux, which may be responsible for the shock spikes.Subject headings: acceleration of particles — interplanetary medium
Strong Double Layers, Existence Criteria, and Annihilation: An Application to Solar Flares
Authors: Volwerk Martin , Kuijpers Jan 
Published: July 2016

AbstractWe present some conditions for the stability of a strong double layer in a warm, current-carrying plasma, which can be extended into the relativistic regime. We apply a model for plasma heating by the electron beam emitted from the double layer and show that this leads to a finite life time of the double layer. We also show that the radio emission accompanying this process can well describe the observed phenomena in Type I radio bursts using a direct emission mechanism, not involving Langmuir waves.Subject headings: plasmas — Sun: flares — Sun: radio radiation
On the Asymmetry of the Distribution of the Anomalous Cosmic-Ray Component in the Heliosphere
Authors: Fichtner Horst , Sreenivasan S. Ranga , Fahr Hans-Jörg , Rucinski Daniel , Grzedzielski Stanislaw 
Published: July 2016

AbstractAn analysis based on a fluid type equation for the spatial diffusion of the anomalous component of cosmic rays in the solar wind is presented. The source distributions of the high-energy particles are related to the pick-up ion flux intensities at the position of the heliospheric shock. Due to the strong asymmetric distributions of the different species of pick-up ions in the heliosphere and a possible aspherical termination shock of the solar wind, the source distributions are expected to exhibit element specific upwind-downwind asymmetries. An analytical treatment of the problem, using boundary conditions derived from observations by the Pioneer and Voyager satellites, leads to an estimate of the asymmetries of the anomalous component in the heliosphere. The investigation is performed in two stages: the problem is solved for an axially symmetric heliosphere in the first instance, and a latitudinal variation of the solar wind velocity as well as in the hydrodynamic diffusion coefficient is incorporated to model the effects of a heliospheric magnetic field in the second.Subject headings: acceleration of particles — cosmic rays — shock waves — solar wind
Positron Annihilation Radiation from the 1991 November 15 Flare
Authors: Kawabata K. , Yoshimori M. , Suga K. , Morimoto K. , Hiraoka T. , Sato J. , Ohki K. 
Published: July 2016

AbstractThe gamma-ray spectrometer on Yohkoh has detected the positron annihilation line at 511 keV produced during the 1991 November 15 flare (X1.0/3B). The 511 keV line fluence, integrated over the time interval of 22:37:50-22:38:14 UT, is (6.7 ± 2.2) photons cm−2 . The time profile of 511 keV line exhibited long decay time compared with the electron bremsstrahlung and prompt gamma-ray line components. From the analysis of time profile of the 511 keV line, we come to the following conclusions: (1) the main source of positrons is deexcitation of 16O *6.052 by e+ – e- pair emisson. (2) β+ −emitting nuclei of 31S, 29P, 27Si, 26mAl, 25Al,23Mg, 19Ne, and 21Na are also important sources of positrons in the decay phase. (3) The density of the positron annihilation region in the photosphere is 1016 cm−3 . (4) Most likely interpretation of the time profile is that at least 50% of positrons annihilate in coronal flare loops with a density of 1012−1013 cm−3 and with a temperature of 106 −3 × 106 K.Subject headings: nuclear reactions, nucleosynthesis, abundances — Sun: flares — Sun: X-rays, gamma-rays
The Flare of 1989 September 9, 09:09 UT: Does Coronal Loop Collision Initiate Efficient Gamma-Ray Emission?
Authors: Aurass H. , Hofmann A. , Rieger E. 
Published: July 2016

AbstractVector magnetogram data and Hα pictures together with data published by Chupp et al. lead us to conjecture that in the presented case a contact between the rising two-ribbon flare current sheet and a coronal loop connecting two nearby plage regions initiates efficient high-energy γ-ray emission.Subject headings: Sun: corona — Sun: flares — Sun: X-rays, gamma rays
Quiescent Microwave Emission from Late-Type Stars
Authors: Güdel Manuel 
Published: July 2016

AbstractA diversity of stellar classes has been detected to be prolific sources of low-level, “quiescent” microwave radiation. This emission is, in most cases, attributed to the persistent presence of mildly relativistic electrons in the coronae. Frequent or continuous particle acceleration is required to maintain a high level of gyrosynchrotron emission. In this paper, observations relevant to our understanding of quiescent microwave emission from stars are reviewed, with emphasis on nondegenerate, late-type stars. Though the nature of the acceleration process remains unknown, a large amount of crucial information is presently available, in particular observations of timescales of slow variations, estimates of particle energies, model calculations based on spectral observations, and correlative studies with soft X-ray emission.Subject headings: acceleration of particles — radio continuum: stars — stars: activity — stars: coronae — stars: late-type — stars: magnetic fields
Unpulsed High-Energy Radiation from the Crab Pulsar and Nebula
Authors: Cheung W. M. , Cheng K. S. 
Published: July 2016

AbstractGenerally, people believe that the unpulsed high-energy gamma rays from the direction of Crab Nebula and pulsar comes from the nebula. But it is entirely possible that the unpulsed high-energy gamma rays from the direction of the Crab Nebula and pulsar are actually emitted from a region extending to a couple of light cylinder radii from the pulsar instead of from the extensive nebula. In this conference paper, we study the possibility that the unpulsed high-energy gamma rays from 100 MeV to 10 GeV are emitted from the extensive nebula. In our model, two pulsed photon beams from two different outer gaps cross each other beyond the light cylinder and result in pair production. Since the pitch angles of these pairs do not correlate with the local magnetic field, and the typical mean free path for pair production is comparable to the local radius of curvature, the subsequent synchrotron radiation and inverse-Compton scattering produce unpulsed X-rays and gamma-rays respectively.Subject headings: acceleration of particles — gamma rays: theory — ISM: individual (Crab Nebula) — pulsars: individual (Crab) — radiation mechanisms: nonthermal
Disk-Accreting Magnetic Neutron Stars as High-Energy Particle Accelerators
Authors: Hamilton Russell J. , Lamb Frederick K. , Miller M. Coleman 
Published: July 2016

AbstractInteraction of an accretion disk with the magnetic field of a neutron star produces large electromotive forces, which drive large conduction currents in the disk-magnetosphere-star circuit. Here we argue that such large conduction currents will cause microscopic and macroscopic instabilities in the magnetosphere. If the minimum plasma density in the magnetosphere is relatively low (≲109 cm−3 ), current-driven micro-instabilities may cause relativistic double layers to form, producing voltage differences in excess of 1012 V and accelerating charged particles to very high energies. If instead the plasma density is higher (≳ 109 cm−3 ), twisting of the stellar magnetic field is likely to cause magnetic field reconnection. This reconnection will be relativistic, accelerating plasma in the magnetosphere to relativistic speeds and a small fraction of particles to very high energies. Interaction of these high-energy particles with X-rays, γ-rays, and accreting plasma may produce detectable high-energy radiation.Subject headings: acceleration of particles — accretion, accretion disks — gamma rays: theory — plasmas — radiation mechanisms: nonthermal — stars: neutron
Electron Acceleration in Short-Lived Radio Transients
Authors: Ball Lewis 
Published: July 2016

AbstractA short-lived (weeks-months) burst of radio emission, assumed to be synchrotron radiation, is sometimes associated with objects detected as soft X-ray transients. The “synchrotron bubble model” which has been applied to these radio transients assumes that the source is initially optically thick, and the model therefore takes no account of the details of the electron acceleration required. The initial increase in the radio flux is attributed to decreasing absorption in the expanding source. Observations of the soft X-ray transient GRS 1124 – 68 (X-ray Nova Muscae 1991) showed, for the first time, the rising phase of such a radio transient. Another radio source, the Galactic Center Transient, was discovered serendipitously in the radio and observed throughout its rise and decay. In both cases the radio flux was a decreasing function of frequency throughout the periods of increasing and decreasing flux, which is not consistent with the optically thick assumption of the synchrotron bubble model. When this assumption is discarded the mechanism responsible for producing the ultrarelativistic electrons, or at the very least the rate at which those electrons become available, must be considered. A generalization of the simple model to include a source which supplies relativistic electrons with a constant energy spectrum is discussed. While such a model can go some way toward matching the observations, it is suggested that the time is ripe for an explicit model of the electron acceleration mechanism. Some of the features such a model may have are presented.Subject headings: acceleration of particles — radio continuum: general — radiation mechanisms: nonthermal — X-rays: bursts
Do Gamma-Ray Bursts Originate from an Extended Galactic Halo of High-Velocity Neutron Stars?
Authors: Hartmann Dieter H. , Brown Lawrence E. , The Lih-Sin , Linder Eric V. , Petrosian Vahé , Blumenthal George R. , Hurley Kevin C. 
Published: July 2016

AbstractThe γ-ray burst brightness distribution is inhomogeneous and the distribution on the sky is nearly isotropic. These features argue against an association of γ-ray bursts with those Galactic objects that are known to exhibit a strong concentration toward the Galactic center or plane. The observed statistical properties indicate a cosmological origin. Circumstantial evidence suggests that neutron stars are involved in the burst phenomenon. Here we consider Population II neutron stars in an extended Galactic Halo (EGH) as an alternative to cosmological scenarios. The BATSE data indicate a small deviation from isotropy near the 2 σ level of statistical significance. If confirmed for an increasing number of bursts, these anisotropies could rule out cosmological scenarios. On the other hand, EGH models require small anisotropies like those observed by BATSE. We consider simple distribution models to determine the generic properties such halos must have to be consistent with the observations and discuss the implications of the corresponding distance scale on burst models.Subject headings: gamma rays: bursts — stars: neutron — stars: Population II — stars: statistics
The NORT: Network of Oriental Robotic Telescopes
Authors: Hajjar Roger , Querci François R. , Querci Monique 
Published: July 2016

AbstractIn this paper, we present the NORT, a network of oriental robotic telescopes originally proposed in 1993 by Querci & Querci to study stellar variability. The NORT project covers all of northern Africa and Asia near the tropic of Cancer. The interest generated among a number of astronomers in countries from the Arab World and Asia offers a solid basis for the rebirth of astronomy and astrophysics and space sciences in developing countries. The number of national projects for telescopes in different countries makes the NORT a framework of choice to coordinate and stimulate these separate efforts by the creation of a NORT steering committee.
High-Speed Photometry of Bright roAp Stars With Small Telescopes
Authors: Kurtz D.W. 
Published: July 2016

AbstractThe rapidly oscillating Ap stars are magnetic peculiar A stars which pulsate in multiple p modes with periods in the range of about 6 to 16 minutes with their oscillation axes aligned with the oblique magnetic axes of the stars. Some of these stars have the richest frequency spectra of any non-degenerate stars other than the sun. This paper shows how photometric observations using small telescopes can be used to work on several astrophysically interesting problems posed by these stars. An example of high precision photometry is shown. The proof of oblique dipole pulsation, the distortion of pulsation modes (probably by the magnetic field), and the determination of asteroseismic luminosities are all discussed. The latter, especially when combined with new theoretical developments concerning magnetic field-pulsation interaction, suggests that Ap stars have lower effective temperatures and/or smaller radii than has been previously thought. It is pointed out that this may be related to the recently discovered extreme discrepancy in effective temperature determined from the wings and cores of the Hα line.
Search for Variable Stars in the Open Cluster NGC 2539
Authors: Choo K.J. , Kim S.-L. , Yoon T. S. , Chun M.-Y. , Sung H. , Park B.-G. , Ann H. B. , Lee M. G. , Jeon Y.-B. , Yuk I.-S. 
Published: July 2016

AbstractWe report on the results of CCD photometric observations of the open cluster NGC 2539. Eight new variable stars have been found in the observed field of this cluster. However, no γ Doradus-type variability was found among the member stars.
Observations of Variable Stars With a Small Telescope at Tabriz University
Authors: Jassur D. M. Z. , Adabi F. , Cham N.A. 
Published: July 2016

AbstractFor more than a decade a small group of Astronomers has been monitoring variable stars of different types. In the present contribution I will present the observations of chromospheric active binaries and near contact binaries and the results obtained from their analysis.
NEOPAT: Near-Earth Object PATrol program
Authors: Moon Hong-Kyu , Chun Moo-Young , Byun Yong-Ik , Han Wonyong , Kim Seung-Lee , Jeon Young-Beom , Kang Yong-Woo 
Published: July 2016

AbstractIn 2000, Korea Astronomy Observatory launched the Near-Earth Object Patrol (NEOPAT) program. NEOPAT has conducted follow-up observations of NEOCP (NEO Confirmation Page) objects and discovered 52 new main-belt asteroids during the observation runs. We initiated collaboration with the Yonsei Survey Telescopes for Astronomical Research (YSTAR) team for NEO search. Wide-field of view, fast read-out time, and fully autonomous data pipeline will enable us to detect and track NEOs with a high efficiency. Scheduled to begin active operations in mid-2001, our survey system is going to be the first network of robotic telescopes for NEO search with automatic access to both hemispheres.
CCD Photometry of Two Asteroids (895) Helio and (165) Loreley
Authors: Woo H.-S. , Kim S.-L. , Chun M.-Y. , Park M.-G. 
Published: July 2016

AbstractWe have presented photometric results for two asteroids (895) Helio and (165) Loreley. The observations were performed from 2000 Oct. to 2001 Jan. using the 61cm telescope installed at Sobaeksan Optical Astronomy Observatory in Korea.
Bright Young Star Candidates in the Rosette Nebula
Authors: Chiang P.S. , Chen W.P. , Li J.Z. , Chu Y.-H. 
Published: July 2016

AbstractWe identified possible optical young stars in the Rosette Nebula by using the IRAS and the ROSAT databases. The previously reported “diffuse” X-ray emission has been resolved into point sources. Forty-seven point sources are detected above 3-sigma of the X-ray background, and twenty-seven of these have stellar counterparts. Some of the young star candidates appear to be associated Herbig-Haro nebular features.
Stable and Unstable Solutions of the Nonlinear Dynamo Problem
Authors: Meinel Reinhard 
Published: July 2016

AbstractA local potential approach to nonlinear dynamo models which allows the use of variational techniques to investigate the problem of stability is introduced. The method applies at least to quasi-kinematic dynamo models, i.e. to models which include the back-reaction of the magnetic field on the fluid motion in a simplified way. A special application leads to a previously investigated one-dimensional dynamo model which shows a coexistence of a periodic solution (limit cycle) with two stable steady solutions of opposite polarities. The inclusion of some small-amplitude noise leads to interesting transition phenomena which may be of relevance to explain the behaviour of astrophysical dynamos. A simple dynamical system with a two-dimensional phase-space is used for illustration.
Nonlinear Nonaxisymmetric Dynamos for Active Stars
Authors: Moss David 
Published: July 2016

AbstractRecent observations seem to have detected large scale nonaxisymmetric structures on active giant stars. These structures are plausibly associated with underlying, dynamo generated, nonaxisymmetric magnetic fields. Such developments have motivated the development of a computer code to solve the nonlinear mean field dynamo equation in spherical geometry with no imposed geometrical symmetries. The nonlinearity is a simple α-quenching. The nature of the stable solutions found depends quite sensitively on the assumed spatial distribution of both α-eflect and differential rotation, and also on the degree of supercriticality of the dynamo. Such a dynamo model with stable, purely nonaxisymmetric solutions is described in this paper.
αΛ-dynamos
Authors: Brandenburg A. , Moss D. , Rieutord M. , Rüdiger G. , Tuominen I. 
Published: July 2016

AbstractIn contrast toαω-dynamos, where the angular velocity is arbitrarily prescribed, we consider hereαΛ-dynamos, for which the differential rotation and meridional circulation are solutions of the momentum equation. The non-diffusive parts of the Reynolds stress tensor are parameterized by theΛ-effect. In earlier investigations we have shown that the turbulent magnetic diffusivity has to be much smaller than the eddy viscosity, otherwise the dynamo is not oscillatory or else the contours of constant angular velocity are cylindrical, contrary to observations. In the present paper we investigate the effects of compressibility.
Λ-effect, Meridional Flow and the Differential Solar Rotation
Authors: Rüdiger G. , Tuominen I. 
Published: July 2016

AbstractRotation laws for the solar convection zone are produced by theΛ-effect in rotating anisotropic turbulence fields. In this paper we use the structure of the turbulence parameters introduced by Rüdiger and Kichatinov (1990), based on a simplified turbulence model. When we neglect the meridional circulation, for small inverse Rossby numbers the angular velocity isolines are spherical, while for increasing inverse Rossby number they approach more and more the helioseismologically derived shape. This simple picture becomes more complicated if the meridional circulation is allowed to act as an angular momentum transporter.
Differential Rotation as an Axisymmetric Resonant Mode of Convection
Authors: Chan Kwing L. , Mayr Hans G. 
Published: July 2016

Recent results from helioseismology (see Goode, these Proceedings) have shown that the inferred contours of the solar angular velocity are more or less radial in the convection region, and the rotation becomes uniform below. These observations contradict the prevailing numerical models of Taylor columns which predict angular velocity contours parallel to the rotation axis of the Sun. Thus, an alternative explanation of solar differential rotation is called for.Presently, it is not feasible to construct a thermally-relaxed, dynamically self-consistent numerical model of the solar convection zone (see Chan and Serizawa, these Proceedings). It is then appropriate to explore simplified models that may shed some light. A number of analytical models have been proposed for the solar differential rotation, and the reader is referred to the book by Rüdiger (1989) for a comprehensive review of this subject. Here, we report on some recent development on the convective resonance model proposed by Chanet al.(1987; hereafter referred as CSM).
Diagnostics of the Solar Dynamo Using the Observed Pattern of Surface Magnetic Fields
Authors: Stenflo J.O. 
Published: July 2016

AbstractThe solar surface represents for the solar dynamo an outer boundary that is directly accessible to observations. The evolutionary and rotational properties of the magnetic fields at this boundary can be empirically determined using existing synoptic magnetograph data. The derived properties provide detailed constraints on the underlying theory, such that an inversion approach to the dynamo problem becomes feasible. Ambiguities in the interpretation may be removed using the independent constraints from helioseismology.
The Large-scale Magnetic Field in the Global Solar Cycle: Observational Aspects
Authors: Makarov V.I. , Sivaraman K.R. 
Published: July 2016

Abstract The global solar cycle is considered as an interaction of 3 types of activity: at low-latitude (sunspots), at high-latitude (polar faculae) and the weak magnetic field. The properties of single and 3-fold reversals of the polar magnetic field are considered. The variation spectrum of the large-scale magnetic field of the Sun is analyzed in the range of 1–30 nHz. A dependence between the rate of a poleward meridional flow and phase of the global cycle is discussed.
Large Scale Patterns on the Solar Surface Indicated by Microwave Observations
Authors: Vršnak B. , Pohjolainen S. , Teräsranta H. , Urpo S. , Brajša R. , Ruždjak V. , Schroll A. , Jurač S. 
Published: July 2016

AbstractA large set of observations of the Sun at 37 GHz is analysed. An association of 99% is found between the regions of brightness temperature depression and the magnetic field inversion lines. Observations indicate a possible existence of “giant cells” with duration of 1-2 years and a longitudinal extension up to 90°.
The History of Activity of the Sun and its Rotational Period on the ZAMS
Authors: Stępień Kazimierz 
Published: July 2016

AbstractThe rotation period of the Sun after it reached ZAMS is estimated from the present rotation rate, average X-ray emission flux and average calcium emission flux. Taking into account all existing uncertainties it is concluded that this initial period was within the range 1–9 days, with the most probable value 2–3 days. Possible influence of the solar activity on evolution of life on the Earth is briefly discussed.