bluuebunny/crossref_metadata_2025_split huggingface dataset:
Merits of Space VLBI Missions for Geodynamics
Authors: Adam Jozsef , Mueller Ivan I. 
Published: July 2016

AbstractTwo dedicated space VLBI projects are currently in preparation to launch one or more VLBI radio telescopes in orbit between 1993-1996. One in the Soviet Union called RADIOASTRON is already an approved and funded mission. The second one is a Japanese orbiting VLBI mission called VSOP. There is a Western European mission with NASA participation in Phase A Study at ESA called QUASAT. Although this project was not approved by ESA at the end of 1988, it might still be taken into consideration during the next decade. In the meantime in 1986 a successful demonstration of space VLBI was made at the first attempt using the NASA TDRSS satellite.
Science Observations with the IUE Using the One Gyro Mode
Authors: Imhoff C. , Pitts R. , Arquilla R. , Shrader C. , Perez M. , Webb J. 
Published: July 2016

AbstractThe International Ultraviolet Explorer (IUE) is a geosynchronous orbiting telescope launched by the National Aeronautics and Space Administration (NASA) on January 26, 1978, and operated jointly by NASA and the European Space Agency. The science instrument consists of two spectrographs which span the wavelength range of 1150 to 3200 Å and offer two dispersions with resolutions of 6 Å and 0.2 Å. The spacecraft’s attitude control system originally included an inertial reference package containing 6 gyroscopes for 3-axis stabilization. The science instrument includes a prime and redundant Field Error Sensor (FES) camera for target aquisition and offset guiding. Since launch, 4 of the 6 gyroscopes have failed. The current attitude control system utilizes the remaining 2 gyros and a Fine Sun Sensor (FSS) for 3-axis stabilization. When the next gyro fails, a new attitude control system will be uplinked which will rely on the remaining gyro and the FSS for general 3-axis stabilzation. In addition to the FSS, the FES cameras will be required to assist in maintaining fine attitude control during target aquisition. This has required thoroughly determining the characteristics of the FES cameras and the spectrograph aperture plate as well as devising new target acquisition procedures. The results of this work are presented.
Jupiter Radio Bursts and Particle Acceleration
Authors: Desch Michael D. 
Published: July 2016

AbstractParticle acceleration processes are important in understanding many of the Jovian radio and plasma wave emissions. However, except for the high-energy electrons that generate synchrotron emission following inward diffusion from the outer magnetosphere, acceleration processes in Jupiter’s magnetosphere and between Jupiter and Io are poorly understood. We discuss very recent observations from the Ulysses spacecraft of two new Jovian radio and plasma wave emissions in which particle acceleration processes are important and have been addressed directly by complementary investigations. First, radio bursts known as quasi-periodic bursts have been observed in close association with a population of highly energetic electrons. Second, a population of much lower energy (keV range) electrons on auroral field lines can be shown to be responsible for the first observation of a Jovian plasma wave emission known as auroral hiss.Subject headings: acceleration of particles — planets and satellites: individual (Jupiter) — radio continuum: solar system
Microwave Burst Timescales and Solar Flare Acceleration Processes
Authors: Krüger A. , Kliem B. , Hildebrandt J. , Zaitsev V. V. 
Published: July 2016

AbstractThe occurrence of quite different timescales in solar microwave bursts is considered and possible ways of their physical interpretation are discussed. An interesting feature is the existence of hierarchic time structures, an example of which is provided by the solar event of 1991 March 23.Plasma parameter sets to be invoked for the interpretation of timescales are estimated on the base of different models such as the collisionless conduction front model, the twisted magnetic loop model, the coalescence model, and the electric circuit model. With emphasis on the interpretation of burst fine structures with timescales of a few seconds the coalescence model has been favored. On the other hand, the simultaneous occurrence of a large range of different timescales appears well suited to be described by the circuit model.Subject headings: acceleration of particles — Sun: flares — Sun: radio radiation
Microwave Type III-RS Bursts
Authors: Sawant Hanumant S. , Fernandes Francisco C. R. , Neri José Ângelo C. F. 
Published: July 2016

AbstractA decimetric (1600 ± 100 MHz), high-sensitivity digital spectroscope has been put into regular operation at São José dos Campos, Brazil, since 1991 March. The dynamic spectra are recorded on 35 mm film while 20 frequencies each separated by 10 MHz are digitized with time resolution of 100 ms. So far, about 350 groups of solar bursts have been observed by this system. These have been classified as microwave type and decimetric reverse slope (RS) type III bursts. Here, we report statistical investigations of the properties of the 44 moderately strong groups of decimetric type III-RS bursts. The average total duration of these bursts is ~0.7 s, the drift rate varied between ~400 and 3000 MHz s−1 , and average decay time is ~120 ms. These observed drifts and timescales suggest that decimetric type III-RS bursts are generated by beam plasma interaction at second harmonic in the inhomogeneous chromosphere, and that the acceleration region is located at a density level of ≤109 cm−3 .Subject heading: Sun: radio radiation
Another Clue About Particle Acceleration in Impulsive Hard X-Ray/Microwave Bursts
Authors: Batchelor David 
Published: July 2016

AbstractIn a sample of impulsive bursts with rise times less than 30 s, a correlation between burst rise times and the frequency of maximum microwave emission has been found. The implications for source structure and dynamics are discussed in this paper. Previously evidence was found that such bursts are caused by some propagating disturbance such as a shock wave or thermal conduction front. Combining that evidence with the microwave and hard X-ray spectral information suggests that the most rapid bursts are emitted from the most compact and intensely magnetized sources. The most rapid bursts also exhibited the hardest X-ray spectra, as published previously. These facts are important clues to understanding the physical process responsible for impulsive bursts. A model for the bursts is suggested, based on the observations and inferences described.Subject headings: acceleration of particles — Sun: radio radiation — X-rays: bursts
Evidence for Particle Acceleration in a Magnetized White Dwarf from Radio and Gamma-Ray Observations
Authors: Jager O. C. De 
Published: July 2016

AbstractThe DQ Her-type magnetic cataclysmic variable AE Aqr contains the most rapidly spinning white dwarf ( P = 33 s) in a close binary and can be considered as the “millisecond pulsar” equivalent of white dwarfs. It shows flare-like UV emission on timescales of an hour during which strong QPO activity is seen, as well as flare-like radio synchrotron emission on similar timescales up to frequencies of at least 250 GHz. It is one of the most efficient converters of accretion power to MeV electrons of all X-ray binaries, LMXB, and cataclysmic variables. TeV emission was also reported by two independent groups with a periodic and burst-like behavior similar to that seen in optical. The detection of a period derivative near 10−13 s/s in optical implies that the white dwarf is spinning down at a rate of ~6 × 1033 ergs s−1 which is at least an order of magnitude larger than the quiescent accretion luminosity and a few times larger than the typical UV flare luminosities. This spindown energy is not seen as disk luminosity, and the conditions appear to be favorable for the release of relativistic particles in a pulsar-type mechanism to explain the radio synchrotron emission in magnetic reconnection events, and the acceleration of particles to TeV energies in double layers if conditions are favorable.Subject headings: acceleration of particles — binaries: close — stars: flare — stars: individual (AE Aquarii) — white dwarfs
Model Images of Radio Halos Around Supernova Remnants
Authors: Reynolds Stephen P. 
Published: July 2016

AbstractI present model calculations of profiles and two-dimensional images of the radio synchrotron emission of young supernova remnants, concentrating on observable effects of relativistic electrons diffusing upstream of the shock wave. If the preshock electron scattering mean free path is sufficiently long, observable synchrotron halos outside the bulk of the radio emission can potentially result; their absence can constrain the mean free path from above. If scattering is primarily due, as expected, to Alfvén waves with amplitude δB, the halo is expected to extend a distance of order rg c(δB/B)−2 /vs beyond the shock, where rg is the gyroradius of the electrons emitting at the observed frequency, B is the upstream magnetic field strength, vs is the shock velocity, and the amplitude δB refers to waves with wavelength comparable to rg , of order 1013 cm for typical supernova-remnant parameters. However, the detailed geometry of the halo varies with the assumptions about particle acceleration in the shock wave. I present an atlas of model profiles and images as a function of preshock diffusion length, of aspect angle between the magnetic field and the line of sight, and of other relevant parameters.Subject headings: radiation mechanisms: miscellaneous — shock waves — supernova remnants
Acceleration Processes for Gamma-Ray Bursts
Authors: Mitrofanov Igor G. 
Published: July 2016

AbstractIs it shown that for those astronomical models of cosmic gamma-ray bursts (GRBs) which are associated with galactic neutron stars (NSs), the initial energy of the outburst could be converted to gamma-rays through processes of particle acceleration. The main emission mechanisms are considered for two basic alternatives, when particles are accelerated either by radiative pressure or by an electric field.Subject headings: acceleration of particles — gamma rays: bursts — radiation mechanisms: nonthermal
Cosmic-Ray Transport and Acceleration
Authors: Schlickeiser Reinhard 
Published: July 2016

AbstractWe review the transport and acceleration of cosmic rays concentrating on the origin of galactic cosmic rays. Quasi-linear theory for the acceleration rates and propagation parameters of charged test particles combined with the plasma wave viewpoint of modeling weak cosmic electromagnetic turbulence provides a qualitatively and quantitatively correct description of key observations. Incorporating finite frequency effects, dispersion, and damping of the plasma waves are essential in overcoming classical discrepancies with observations as the Kfit - Kql discrepancy of solar particle events. We show that the diffusion-convection transport equation in its general form contains spatial convection and diffusion terms as well as momentum convection and diffusion terms. In particular, the latter momentum diffusion term plays a decisive role in the acceleration of cosmic rays at super-Alfvénic supernova shock fronts, and in the acceleration of ultra-high-energy cosmic rays by distributed acceleration in our own galaxy.Subject headings: acceleration of particles — convection — cosmic rays — diffusion — shock waves
Relativistic Particle Transport in Hot Accretion Disks
Authors: Becker Peter A. , Kafatos Menas , Maisack Michael 
Published: July 2016

AbstractAccretion disks around rapidly rotating black holes provide one of the few plausible models for the production of intense radiation in AGNs above energies of several hundred MeV. The rapid rotation of the hole increases the binding energy per nucleon in the last stable orbit relative to the Schwarzschild case, and naturally leads to ion temperatures in the range 1012 -1013 K for sub-Eddington accretion rates. The protons in the hot inner region of a steady, two-temperature disk form a reservoir of energy that is sufficient to power the observed EGRET outbursts if the black hole mass is 1010M⊙ . Moreover, the accretion timescale for the inner region is comparable to the observed transient timescale of ~1 week. Hence EGRET outbursts may be driven by instabilities in hot, two-temperature disks around supermassive black holes. In this paper we discuss turbulent (stochastic) acceleration in hot disks as a possible source of GeV particles and radiation. We constrain the model by assuming the turbulence is powered by a collective instability that drains energy from the hot protons. We also provide some ideas concerning new, high-energy Penrose processes that produce GeV emission be directly tapping the rotational energy of Kerr black holes.Subject headings: acceleration of particles — accretion, accretion disks — galaxies: nuclei — quasars: individual (3C 279) — radiation mechanisms: nonthermal
Effect of Advected Fields on Accretion Disk Dynamos
Authors: Mangalam Arun V. , Subramanian K. 
Published: July 2016

AbstractWe present calculations of favored dynamo modes when advection of ambient magnetic fields onto accretion disks is important. These models are relevant for compact binary systems and young stellar objects and can be extended to active galactic nuclei (AGNs). The dynamo equation, including the standard α-effect, is modified to take into account advected magnetic fields. Vacuum boundary conditions are assumed outside the disk and the dynamo number switches sign across the equatorial plane. For the local steady state problem, critical dynamo numbers for various modes are obtained analytically. Our motivation is to investigate whether the dominant dynamo generation of quadrupolar magnetic fields and accretion of dipolar magnetic fields is likely to lead to particle acceleration in the form of jets. The results shown here are for a particular choice of boundary conditions and geometry of the advected field. Besides examining other choices, we shall calculate growth rates for different modes, and the influence of the initial seed field configuration on the evolution of the magnetic fields in subsequent work.Subject headings: acceleration of particles — accretion, accretion disks — binaries: close — galaxies: nuclei — MHD — stars: pre-main-sequence
STARBASE: A Network of Fully Autonomous Telescopes for Hands-on Science Education
Authors: Gelderman Richard , Barnaby David , Carini Michael , Hackney Karen , Hackney Richard , McGruder Charles , Scott Roger 
Published: July 2016

AbstractStudents Training for Achievement in Research Based on Analytical Space-science Experiences (STARBASE) is being established to provide exciting hands-on research opportunities for students. STAR-BASE is a network of networks, consisting of dedicated hardware, universities, professional astronomers, teachers, and students all working together in scientific investigations. Funded through the NASA Office of Space Science, the STARBASE network is working to bring major science research projects to motivated students all over the globe.
RTLinux Driven Hungarian Automated Telescope for All Sky Monitoring
Authors: Bakos Gáspár Á. 
Published: July 2016

AbstractMassive variability searches initiated the design of HAT (Hungarian Automated Telescope), an autonomous observatory. HAT consists of a horseshoe mount similar to the one used in the Automated All Sky Survey (ASAS, Pojmański 1997), a clamshell dome with various utilities, a telephoto lens and a CCD. Expensive hardware elements have been substituted by software running under Realtime Linux: a multitask operating system which can handle processes in real time. A virtual observer – modeled as a finite state machine – is responsible for managing the observatory. The modular structure allows of running virtually any kind of observing program for small telescopes. We describe technical aspects, as well as present test results carried out by HAT1 (Budapest).
RIBOTS: An Automatic Telescope System for Gamma-Ray Burst Follow-Up Observations
Authors: Urata Yuji , Kawai Nobuyuki , Yoshida Atsumasa , Kohama Mitsuhiro , Kawabata Tetsuya , Ayani Kazuya 
Published: July 2016

AbstractWe are constructing a fully automatic observation system named RIBOTS (RIken-Bisei Optical Transient Seeker). We aim to detect optical flashes and early afterglows of Gamma-ray bursts (GRB) with RIBOTS. We are constructing RIBOTS with a small telescope because a quick pointing to the burst is essential for our purpose. RIBOTS is linked to the GRB alert system provided by the HETE-2 satellite.
Spectroscopic Detection of an Extraordinary Flaring-Event on DF Tau
Authors: Li J.Z. , Chen W.P. , Ip W.H. 
Published: July 2016

AbstractAn accretion intrigued flare-like brightening of DF Tau has been recorded spectroscopically, during which spectacular spectral changes took place. We inferred the possible formation of a transient envelope during the process of this episodic mass accretion of DF Tau.
The Ongoing Search for Variables in Young Clusters: Up-to-Date Results and Perspectives
Authors: Pigulski A. , Kopacki G. , Kołaczkowski Z. , Jerzykiewicz M. 
Published: July 2016

AbstractThe goals, results and perspectives of the ongoing search for variables in open clusters and associations of the northern hemisphere, carried out at the Białków Observatory of the Wrocław University, are presented.
An Education Program Using Tera-Byte NEA Observation Data
Authors: Asami A. , Asher D.J. , Hashimoto T. , Isobe S. , Nishiyama S. , Ohshima Y. , Terazono J. , Urata T. , Yoshikawa M. 
Published: July 2016

AbstractThere are three wide-field telescopes at the Bisei Spaceguard Center operated by the Japan Spaceguard Association. These telescopes are dedicated to detect near-earth asteroids and produce several tera-byte data per month. Since these data contain many main-belt asteroids, we will use them for an education program that will allow school pupils and the general public to find new main-belt asteroids. We are now developing a new software for its purpose.
The Humps of KBO’s Size Distribution
Authors: Chen Cheng-Pin , Jiang Ing-Guey 
Published: July 2016

AbstractWe study the possible humps or deviation from the single-power law for the size distribution of the Kuiper Belt Objects (KBOs). Both the current observational data and theoretical simulations show evidence of such humps. We conclude that this is an imprint of the depletion of the outer Solar System in the Kuiper Belt region.
Observation of Comet C/1999 S4 (LINEAR)
Authors: Lin C.Y. , Ip W.H. 
Published: July 2016

AbstractComet C/1999 S4 (LINEAR) with a maximum magnitude of 6 mag was the brightest comet in 2000. The 24” telescope on NCU campus was used to observe its coma behavior in June and July of 2000 as it approached perihelion. The observations were carried out using the comet filters designed by the European Space Agency for the ground-based observational program of Comet Wirtanen (target comet of the Rosetta mission). Comet C/1999 S4 (LINEAR) ended up disrupting into many small fragments near perihelion. We are in the process of analyzing the time variations of the cometary dust coma and dust tail to examine the physical condition prior to the destruction of the nucleus of this intriguing comet. An image processing method will be developed to trace small-scale structures in the dust tail.
The Automated Telescope of Novosibirsk State University
Authors: Nesterenko A. , Nikulin M. , Vyprentsev D. , Zaytsev A. , Nesterenko I. , Prosvetov V. , Tsukanov V. , Valishev A. 
Published: July 2016

AbstractThe current status of the 30 cm automated telescope project at Novosibirsk State University (NSU) observatory with Internet access is presented.
Spatial Structure of Star Clusters by the 2MASS Database
Authors: Chen J.W. , Chen W.P. 
Published: July 2016

AbstractWe present some results of a pilot program to study star clusters with the Two-Micron All-Sky Survey (2MASS) observations. While 2MASS cannot resolve the cores or detect much of the main sequence of globular clusters, the homogeneity and large angular coverages make the database suitable to study young star clusters. We show that member stars are centrally concentrated in open clusters, with a density distribution markedly shallower than that for globular clusters. In NGC2506 (age 3 Gyr) giant stars appear to occupy a smaller region than main sequence stars—a natural consequence of mass segregation.
Magnetic Tubes in Overshooting Compressible Convection
Authors: Jennings R. L. , Brandenburg A. , Nordlund Å. , Stein R. F. , Tuominen I. 
Published: July 2016

AbstractA magnetic tube is introduced into turbulent compressible penetrative convection. After being strongly advected, most of the magnetic flux is stored in the overshoot region. With rotation there are meridional travelling waves.
Waves of Solar Activity
Authors: Proctor M.R.E. , Spiegel E.A. 
Published: July 2016

AbstractWe develop a theory of the sunspot cycle predicated on the assumption that the observed bands of activity are packets of dynamo waves. An approximate equation is proposed to describe the dynamics of these packets, using standard ideas from bifurcation theory. We show that in a certain limit the system can be described in terms of a slowly-evolving solitary wave, and that periodic behavior, like that of the observed butterfly diagram, can easily be found. Generalizations of the theory are discussed.
Non-steady Global Magnetic Fields in Kinematic Theory
Authors: van Geffen J.H.G.M. , Hoyng P. , Zwaan C. 
Published: July 2016

AbstractThe dynamo equation for the mean field ⟨B⟩ contains a random forcing term of unknown magnitude, which is therefore always omitted. The influence of this term is potentially large. To evaluate its effect, we employ ensemble averaging. If an ensemble average is used, there is no random forcing term in the dynamo equation. The effect of fluctuations is that the ensemble members get out of phase, so that ⟨B⟩→0. The damping time of ⟨B⟩ can be found by requiring that the mean energy ⟨BB⟩ remains finite. The eigenvalues к of the dynamo equation then all have negative real parts.Imк determines the period, and −Reк/Imк the relative period stability of the dynamo. We have developed a code to solve the equation for ⟨BB⟩ in a spherical shell (the convection zone), assuming axisymmetry. We report our first results, which do not yet include differential rotation. Using spherically symmetric boundary conditions, we reproduce the well known α2-dynamo, whose behaviour is known analytically. For instance, for an α2-dynamo located in a shell with inner boundary at R/2, we find that ⟨BB⟩ remains finite for R2γ/β=1.48, where β represents turbulent diffusion and γ turbulent vorticity. Taking α = ¼(βγ)½ — a factor of four below maximum helicity — implies that we have a dynamo number Cα ≡ Rα/β = 0.30. Using this value we find a damping time of 6 × 10−2R2/β for ⟨B⟩, which is a measure for the coherence time of B in a single ensemble member. This result implies that the large-scale field of this particular α2-dynamo reorganizes its structure completely on a time scale of only about one year (for solar values of R and β), and it shows the enormous influence of random forcing in general.
Evolution of Large and Small Scale Magnetic Fields in the Sun
Authors: Fox Peter A. , Theobald Michael L. , Sofia Sabatino 
Published: July 2016

AbstractThis paper will discuss issues relating to the detailed numerical simulation of solar magnetic fields, those on the small scale which are directly observable on the surface, and those on larger scales whose properties must be deduced indirectly from phenomena such as the sunspot cycle. Results of simulations using the ADISM technique will be presented to demonstrate the importance of the treatment of Alfvén waves, the boundary conditions, and the statistical evolution of small scale convection with magnetic fields. To study the large scale fields and their time dependence, the magnetic resistivity plays an important role; its use will be discussed in the paper.