bluuebunny/crossref_metadata_2025_split huggingface dataset:
Millimeter, Microwave, Hard X-Ray, and Soft X-Ray Observations of Energetic Electron Populations in Solar Flares
Authors: Kundu M. R. , White S. M. , Gopalswamy N. , Lim J. 
Published: July 2016

AbstractWe present comparisons of multiwavelength data for a number of solar flares observed during the major campaign of 1991 June. The different wavelengths are diagnostics of energetic electrons in different energy ranges: soft X-rays are produced by electrons with energies typically below 10 keV, hard X-rays by electrons with energies in the range 10-200 keV, microwaves by electrons in the range 100 keV-1 MeV, and millimeter-wavelength emission by electrons with energies of 0.5 MeV and above. The flares in the 1991 June active period were remarkable in two ways: all have very high turnover frequencies in their microwave spectra, and very soft hard X-ray spectra. The sensitivity of the microwave and millimeter data permit us to study the more energetic (>0.3 MeV) electrons even in small flares, where their high-energy bremsstrahlung is too weak for present detectors. The millimeter data show delays in the onset of emission with respect to the emissions associated with lower energy electrons and differences in time profiles, energy spectral indices incompatible with those implied by the hard X-ray data, and a range of variability of the peak flux in the impulsive phase when compared with the peak hard X-ray flux which is two orders of magnitude larger than the corresponding variability in the peak microwave flux. All these results suggest that the hard X-ray-emitting electrons and those at higher energies which produce millimeter emission must be regarded as separate populations. This has implications for the well-known “number problem” found previously when comparing the numbers of nonthermal electrons required to produce the hard X-ray and radio emissions.Subject headings: Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays
Gamma-Ray Spectral Observations with Yohkoh
Authors: Yoshimori M. , Suga K. , Morimoto K. , Hiraoka T. , Sato J. , Kawabata K. , Ohki K. 
Published: July 2016

AbstractWe present gamma-ray observations of the 1991 October 27, November 15, and December 3 flares with the Yohkoh gamma-ray and hard X-ray spectrometers. The October 27 flare (X6.1 /3B) shows significant gamma-ray line emission, and the temporal evolution of the gamma-ray line-to-bremsstrahlung flux ratio indicates that protons and electrons were complicatedly accelerated during flare. The December 3 flare (X2.0/2B) shows a strong bremsstrahlung continuum extending to 10 MeV and indicates that electrons were preferentially accelerated to 10 MeV. A line feature at 420 keV was observed from the November 15 flare (X1.0/3B). This is most likely due to a compound of redshifted nuclear deexcitation lines of Be (429 keV) and Li (478 keV) resulting from He-He reactions. The spectral feature indicates that the accelerated He nuclei suffer strong pitch-angle scattering in the corona and form a downward-peaked distribution. Furthermore, the November 15 flare exhibits evidence of positron annihilation line at 511 keV. The positron production processes and the electron density of the annihilation region are discussed on the basis of the temporal characteristics of 511 keV line emission.Subject headings: line: identification — Sun: flares — Sun: X-rays, gamma-rays
Weightiness of the Dispersive Rate in Stochastic Acceleration Processes
Authors: Pérez-Peraza J. , Gallegos-Cruz A. 
Published: July 2016

AbstractWe present analytical solutions to the transport equation of the accelerated particles that are valid over the entire energy range (nonrelativistic, transrelativistic, and ultrarelativistic) for the time-dependent and equilibrium cases. On the basis of these overall spectra, we have studied the relative importance of the term of average (systematic) energy increase and the term of diffusion (spread) in energy that define the evolution of accelerated particles within the frame of a simplified diffusion-convection transport equation, when the particle distribution functionN(E, t) is assumed to be independent of spatial pitch-angle diffusion (isotropic). Since in some astrophysical works, only the term of average energy increase in the simplified transport equation in energy space is considered to be leading directly to a power-law-type spectrum, we have established the conditions under which such an approximation may be justified. The analysis is illustrated for acceleration by two different kinds of turbulence: MHD and Langmuir waves. The omission of the term of energy spread leads, in general, to an important depletion or overproduction of the accelerated particle flux that must be seriously considered in any calculation of the flux of secondary radiation produced by the accelerated particles. The presented analytical spectra may be of particular relevance to gamma-ray, neutron, and pion production in solar flares as well as in other astrophysical sites.Subject headings: acceleration of particles — MHD — Sun: general — turbulence — wave motions
Particle Orbits, Trapping, and Acceleration in a Filamentary Current Sheet Model
Authors: Kliem Bernhard 
Published: July 2016

AbstractTest particle orbits in the two-dimensional Fadeev equilibrium with a perpendicular electric field added are analyzed to show that impulsive bursty reconnection, which has been proposed as a model for fragmentary energy release in solar flares, may account also for particle acceleration to (near) relativistic energies within a fraction of a second. The convective electric field connected with magnetic island dynamics can play an important role in the acceleration process.Subject headings: acceleration of particles — MHD — plasmas — Sun: corona — Sun: flares
Radio Evidence for Nonthermal Particle Acceleration on Stars of Late Spectral Type
Authors: Lang Kenneth R. 
Published: July 2016

AbstractRadio evidence for nonthermal particle acceleration on stars of late spectral type (G, K, and M) is reviewed, including the pre-main-sequence T Tauri stars, the dwarf M flare stars, and the RS CVn binary stars. Both the long-lasting radio emission and the transient radio flares can be attributed to nonthermal electrons accelerated in magnetically confined coronae, radiating by either incoherent gyrosynchrotron radiation or by coherent processes. Related observations of the Sun provide the framework for interpreting the radio emission of late-type stars. We review recent VLBI observations of single and binary stars, observations of rapid acceleration and dynamic spectra of dwarf M flare stars, and models for long-lasting radio emission from dwarf M flare stars and RS CVn stars. The VLBI data provide evidence for nonthermal particle acceleration in large-scale magneto-spheres several times larger than the stellar radius for T Tauri and RS CVn stars. In contrast, rapid radio flares on dwarf M stars require sources much smaller than the visible star in size, and this is consistent with the VLBI data.Dynamic spectra suggest particle acceleration by relativistic electron beams on dwarf M stars. The long-lived radio radiation of dwarf M stars and RS CVn stars requires more-or-less continuous particle acceleration over periods of hours, perhaps by persistent low-amplitude flaring.Subject headings: acceleration of particles — binaries: close — radio continuum: stars — stars: flare — stars: late-type — stars: pre-main-sequence
Pulsar Studies with Comptel
Authors: Bennett K. , Busetta M. , Carramiñana A. , Diehl R. , Lichti G. , Schönfelder V. , Strong A. , Hermsen W. , Kuiper L. , Connors A. , Ryan J. , Buccheri R. 
Published: July 2016

AbstractThe Compton Gamma-Ray Observatory (C-GRO) has completed a full-sky survey during which the number of known γ-ray pulsars has more than doubled. COMPTEL has observed the classical pulsars Crab and Vela on several occasions and has derived detailed pulse patterns and spectral parameters in the 0.7-30 MeV energy interval. The new C-GROγ-ray pulsars have different properties in terms of energy spectra and light-curve shapes, and, in fact, only the Crab is seen by all four C-GRO instruments. This raises intriguing questions about the particle acceleration processes and beaming taking place in the neutron magnetosphere. We have examined the COMPTEL data to add information on these objects in the 0.7-30 MeV energy interval and present evidence for the detection of one of them, PSR B1509-58. We have also undertaken a search for candidate radio pulsars whose ephemerides are well defined. The results of these analyses are presented.Subject headings: gamma rays: observations — pulsars: general
Gamma-Ray Burst Theory: Back to the Drawing Board
Authors: Harding Alice K. 
Published: July 2016

AbstractGamma-ray bursts have always been intriguing sources to study in terms of particle acceleration, but not since their discovery two decades ago has the theory of these objects been in such turmoil. Prior to the launch of Compton Gamma-Ray Observatory and observations by BATSE, there was strong evidence pointing to magnetized Galactic neutron stars as the sources of gamma-ray bursts. However, since BATSE the observational picture has changed dramatically, requiring much more distant and possibly cosmological sources. I review the history of gamma-ray burst theory from the era of growing consensus for nearby neutron stars to the recent explosion of halo and cosmological models and the impact of the present confusion on the particle acceleration problem.Subject headings: acceleration of particles — gamma rays: bursts
High-Energy Gamma-Ray Observations of Active Galaxies
Authors: Fichtel Carl E. 
Published: July 2016

AbstractDuring the period from 1992 May to early 1992 November, the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory obtained high-energy gamma-ray data for most of the sky. A total of 18 active galaxies have been seen with high certainty, and it is expected that more will be found in the data when a more thorough analysis is complete. All of those that have been seen are radio-loud quasars or BL Lacertae objects; most have already been identified as blazars. No Seyfert galaxies have been found thus far. If the spectra are represented as a power law in energy, spectral slopes ranging from approximately −1.7 to −2.4 are found. A wide range of z-values exists in the observed sample, eight having values in excess of 1.0. Time variations have been seen, with the timescale for a significant change being as short as days in at least one case. These results imply the existence of very large numbers of relativistic particles, probably close to the central object. Although a large extrapolation is required, their existence also suggests that these active galactic nuclei may be the source of the extragalactic cosmic rays.Subject headings: acceleration of particles — galaxies: active — gamma rays: observations — quasars: general
High-Energy Radiation From Active Galactic Nuclei
Authors: Sikora Marek 
Published: July 2016

AbstractTwo recent findings concerning high-energy radiation properties of active galactic nuclei—discovery of breaks in hard X-ray spectra of Seyfert galaxies, and discovery of huge fluxes of hard gamma rays from blazars—seem to press us to change our standard views about radiation production in these objects. I review briefly the existing radiation models, confront them with the newest observations, and discuss newly emerging theoretical pictures which attempt to account for the discoveries.Subject headings:galaxies: active — galaxies: nuclei — radiation mechanisms: nonthermal
The Whole Earth Telescope: An International Adventure in Asteroseismology
Authors: Kawaler Steven D. 
Published: July 2016

AbstractToday, we are beginning to probe the interior of stars through the new science of stellar seismology. Certain stars, ranging from our own Sun to white dwarfs, undergo natural vibrations that can be detected with sensitive time-series photometry and/or spectroscopy. Since the signal we seek is an unbroken time-series to allow determination of the vibration frequencies, data from a single-site is usually incapable of uniquely identifying the pulsation modes, no matter how large the telescope being used. In many cases, the observational goals can be achieved using small-ish telescopes in well-coordinated global networks. Here, I briefly describe the work of one such international network of observatories and scientists known as the Whole Earth Telescope (WET). With the WET, we have sounded out the interiors of a large number of nonradially pulsating stars. Over the past 14 years, WET has observed dozens of stars in 20 separate observing campaigns. Our team has wide span of interests, and has observed several other classes of objects such as delta Scuti stars, CV stars, pulsating sdB stars, and rapidly oscillating Ap stars.
Early Results from HETE-2
Authors: Kawai N. , Yoshida A. , Tamagawa T. , Matsuoka M. , Shirasaki Y. , Ricker G. , Crew G. , Doty J.P. , Levine A. , Vanderspek R. , Villasenor J. , Monnelly G. , Atteia J.-L. , Vedrenne G. , Olive J.-F. , Boer M. , Fenimore E.E. , Galassi M. , Issler J.-L. , Colongo C. , Hurley K. , Jernigan J.G. , Lamb D.Q. , Graziani C. , Pizzichini G. , Woosley S. , Takagishi K. , Hatsukade I. , Yamauchi M. , Cline T. 
Published: July 2016

AbstractThe High Energy Transient Explorer 2 is a small scientific satellite designed to detect and localize gamma-ray bursts (GRBs). The coordinates of GRBs detected by HETE-2 will be distributed to interested ground-based observers within seconds of burst detection, thereby allowing detailed observations of the initial phases of GRBs. HETE-2 was launched successfully on October 9, 2000. The GRB positions will start to be delivered after a few months of the complete testing and calibration of the spacecraft system and the science instruments.
A Spectrograph for Prompt Observations of Gamma-Ray Bursts with a 1-m Telescope
Authors: Kawabata Tetsuya , Ayani Kazuya , Fujii Mitsugu , Urata Yuji , Kawai Nobuyuki , Ebizuka Noboru 
Published: July 2016

AbstractWe are developing a new slit-less spectrograph for gamma-ray bursts (GRBs) at Bisei Astronomical Observatory. We can quickly point the 1-m telescope to the GRB coordinates provided by HETE-2 via the GRB Coordinates Network. The pointing is readjusted when the position is refined to 5” accuracy by the small optical telescope RIBOTS using the optical image of the GRB, and we then take an exposure immediately with the slit-less spectrograph.
Optical and Near-IR Monitoring of Symbiotic Binary Systems
Authors: Mikołajewska Joanna 
Published: July 2016

AbstractSymbiotic stars are long-period interacting binary systems in which an evolved red giant star transfers material to its much hotter compact companion. Such a composition places them among the most variable stars. In addition to periodic variations due to the binary motion, they often show irregular changes due to nova-like eruptions of the hot component. In some systems the cool giant is a pulsating Mira-type star usually surrounded by a variable dust shell. Here, I present results of optical and IR monitoring of symbiotic systems as well as future prospects for such studies.
A Near Infrared Camera Refrigerated by Two Stirling Machines – an Alternative to Robotic Telescopes
Authors: Ishitsuka I. José K. , Wada Takehiko , Ieda Fumihiko , Tokimasa Noritaka , Kuroda Takehiko , Morimoto Masaki , Miyaji Takeshi , Omodaka Toshihiro , Ueno Munetaka , Hasegawa Wataru , Narusawa Shin-ya , Waki Yoshifumi 
Published: July 2016

AbstractWe have developed and tested a new near infrared camera equipped with a 512 × 512 PtSi CCD and cooled by two independent Stirling Cycle refrigerators. The camera, installed on the 60 cm reflector telescope of the Nishi-Harima Astronomical Observatory (NHAO) since April 2000, has begun regular observations toward infrared objects. Since the reasonable cost and lower maintenance needs of the camera make it more attractive, we introduce it as an alternative to robotic telescopes.
Revealing Variety of Comets by Long-Term Monitoring Observation with a 50-cm Telescope
Authors: Watanabe Jun-ichi , Fukushima Hideo 
Published: July 2016

AbstractWe have been monitoring comets using the 50-cm telescope at the Mitaka campus of the National Astronomical Observatory, Japan since 1996. Over 20 comets, including bright ones such as comet C/1995 O1(Hale-Bopp), have been observed over long-term periods, namely over large heliocentric distance scales. Our samples show variety of comets in terms of both morphological and temporal variations. Several typical examples of various morphology, probably due to dust, are shown to emphasize the importance of long-term monitoring of comets.
INTEGRAL and Small Telescopes
Authors: Mowlavi Nami , Kretschmar Peter , Türler Marc , Produit Nicolas 
Published: July 2016

AbstractThe future INTEGRAL satellite, to be launched in 2002, will observe the universe in gamma-rays. Parallel observations in other wavelengths are desirable for many gamma-ray objects, the most famous being certainly the gamma-ray bursts.In this article, we present the INTEGRAL mission and its scientific objectives. We then give three examples of astrophysics fields for which combined gamma ray and optical observations are recommended. Small telescopes would be ideally suited for many of the studies.
Russian/Former Soviet Union Experience in Small Telescope Usage for Investigation of Interstellar Matter (ISM) and Nebulae
Authors: Bochkarev N.G. 
Published: July 2016

The deepest tradition in ISM study in the optical range was built in Russia/FSU by V.Fessenkov, the founder of Fessenkov Astrophysical (Aph) Institute (AFIF, Kazakhstan) and G.Shain (Crimean Aph.Obs. - CrAO, Ukraine). The tradition was handed over to SAI (Moscow) by I. Shklovski and S.Pikelner, to Abastumani Aph. Obs. (AAO, Georgia), where a catalogue of dark nebulae (Khavtassi, 1960) was produced, and to Byurakan Aph. Obs. (BAO, Armenia).For a long time 0.3-0.7 m telescopes were used for determination of interstellar extinction in the Galaxy by the standard technique (SAI; Engelhart Astron. Obs. of Kazan Univ., Russia; AAO; BAO and others. The most sophisticated investigations were carried out in Lithuania (e.g. Straizys, 1977; Sudzius, 1974).
Asymptotic Methods in the Nonlinear Mean-field Dynamo
Authors: Sokoloff D.D. , Shukurov A. , Ruzmaikin A.A. 
Published: July 2016

AbstractWe discuss the methods and results of analysis of nonlinear mean-field dynamo models based on α-quenching in two asymptotic regimes, namely for weakly and highly supercritical excitation. In the former case the spatial distribution of the steady-state magnetic field is close to that given by the neutrally stable eigenfunction of the corresponding kinematic dynamo. In the latter case the magnetic field distribution within the main part of the dynamo volume is presumably determined by the balance between the Lorentz and Coriolis forces while near the boundaries boundary layers arise in which the field adjusts itself to the boundary conditions. The asymptotic behaviour of the highly supercritical αω-dynamos is sensitive to the particular form of dependence of the mean helicity on magnetic field while α2-dynamos are less sensitive to this dependence.
The Prolonged Minima and Maxima of Solar Activity
Authors: Dermendijev V.N. , Buyukliev G.T. , Shopov Y.Y. 
Published: July 2016

Abstract We study a new indirect index of solar activity – the Intensity of Luminescence of Cave Flowstone Microzones. This index correlates directly with the solar activity. Using a time series of the index with resolution 4-5 pixels/year we study some of the statistical properties of the solar activity cycle during 28 prolonged minima and 21 prolonged maxima.
The Longer Term Evolution of Magnetic Field and Mass Flow in a Decaying Active Region
Authors: Zhang Hongqi , Ai Guoxiang , Wang Haimin , Zirin Harold , Patterson Alan 
Published: July 2016

During September 24-29, 1987, the longitudinal magnetic fields of a decaying active region (AR 4855) were observed almost continuously at Big Bear and Huairou Solar Observatories. The target consisted of an αp sunspot and surrounding enhanced network. We achieved a 75-hour coverage with 4 night-time gaps of six to eight hours. The images were then combined to made a continuous movie.The BBSO Videomagnetograph (VMG) System was originally developed by Leighton and Smithson and has been improved in recent years (Zirin, 1985). This system has made it possible to study very weak photospheric magnetic structures.
Fe I Line Asymmetries and Shifts Caused by Pressure Broadening
Authors: Kršljanin V. , Vince I. , Erkapić S. 
Published: July 2016

AbstractIn order to test the validity of the usual neglect of pressure line shifts in investigations of Fe I line asymmetries and shifts, we calculated synthetic line bisectors and shifts of 96 moderate and weak photospheric lines, taking into account both hydrogen- and electron-impact shifts and neglecting the velocity fields. Absolute pressure line shifts obtained are less than or appr. equal to 50 m/s and the largest relative shifts along the bisectors are about 40 m/s. We found pronounced dependences of both shifts and bisectors on the energy of the upper level in transitions and on the transition array.
The Differential Rotation and Evolution of Spots on UX Arietis from a Sequence of Doppler Images
Authors: Vogt Steven S. , Hatzes Artie P. 
Published: July 2016

AbstractWe present a sequence of three Doppler images of the spotted RS CVn star UX Arietis obtained over a 5-month interval from August 1986 through January 1987. The spot distribution was quite complex and consisted of a large stable polar spot, a spot near the equator, and several other spots at intermediate positive and negative latitudes. The time intervals between successive images were small enough that we were able to reliably track the evolution of the spot distribution, measuring accurate longitudes, latitudes, and areas of the major spots, as well as their drift rates in longitude and latitude. The longitudinal drifts of spot features at equatorial, intermediate, and high latitudes yielded an accurate measurement of differential rotation. We find that the spotted primary of UX Arietis is indeed rotating differentially and in the sense opposite to that of the Sun, i.e. the poles rotate faster than the equator. The equator is synchronized to the orbital angular velocity, and the angular velocity increases towards either pole. The angular velocity distribution can be expressed as Ω(°/day) = −55.91 + 1.09(±0.09) sin2∅, where ∅ is the latitude. The amount of differential rotation, parameterized as the ratio of the difference between the equatorial and polar angular velocities to the equatorial angular velocity, is then α = −0.020(±0.002), as compared to a value of α = +0.2 for the Sun.
Chromospheric Surface Structures on EI Eridani and HD 199178
Authors: Neff James E. 
Published: July 2016

Several groups at this meeting are presenting maps of the spatial distribution of either brightness or effective temperature in the photospheres of rapidly-rotating, late-type stars. It is generally believed that structure seen in these maps traces the magnetic topology, in analogy with the Sun. We expect the structure of the outer atmospheres (i.e., chromosphere and corona) of these stars to be even more directly tied to the magnetic topology; the magnetic structure is three-dimensional. In order to probe the radial dimension of stellar atmospheres, we need to combine maps of the spatial distribution of emission from chromospheres and coronae with these detailed photospheric maps.Along with collaborators at Armagh, Catania, Boulder, Paris, Helsinki, and Stony Brook, I have been obtaining high-dispersion ultraviolet spectra of several rapidly-rotating, late-type stars using the IUE spacecraft. I discuss results for two stars, El Eridani and HD 199178, for which photospheric maps are presented elsewhere at this conference.