bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interaction of Resonances and Yarkovsky Non-Gravitational Effects in The Asteroid Belt
Authors: Vokrouhlický David , Farinella Paolo 
Published: July 2016

The interaction between resonances and dissipative effects has long been investigated in relationship with the dynamics of dust particles or the evolution of planetesimals in the primordial solar nebula. More recently, it has been shown that another important application of this kind of dynamics is the delivery of asteroid fragments (precursors of meteorites and NEAs) to Earth-crossing orbits. The relevant dissipative mechanism, the so-called Yarkovsky effect (Öpik 1951; Peterson 1976; Burns et al. 1979) has been known for a long time, but its “seasonal” and “diurnal” variants, as well as its interaction with the collisional process taking place in the asteroid belt, have been studied quantitatively only in the last few years (Rubincam 1995, 1998; Hartmann et al. 1997, 1998; Farinella et al. 1998; Vokrouhlický and Farinella 1998a,b; Vokrouhlický 1998a,b; Farinella and Vokrouhlický 1998a,b).In the Farinella et al. (1998) paper we have provided a unified discussion of the Yarkovsky effect in both its variants. After computing the rate of the corresponding semimajor axis drift as a function of size and spin rate, and comparing the relevant timescales with those for collisional disruption and spin axis reorientation, we have rediscussed some issues in meteorite science which are put in a new light by the relevance of the Yarkovsky effect. In particular, this mechanism provides a good explanation for the fact that meteorite cosmic ray exposure ages (in particular for irons) are much longer than the dynamical lifetimes of objects delivered to the Earth-crossing region through resonances. Thanks to the Yarkovsky effect, small asteroid fragments in the belt undergo a slow drift in semimajor axis (with a random-walk component related to their rotational state) and therefore have enough mobility to reach the resonances after comparatively long times spent in nonresonant main-belt orbits. Metal-rich fragments have slower Yarkovsky drift rates than stones, but their much longer collisional lifetimes can explain why iron meteorites appear to sample a larger number of asteroid parent bodies compared to ordinary chondrites.
Detailled Study of The Dynamics of Fragments of Comet C/1996 B2 Hyakutake
Authors: Desvoivres E. , Klinger J. , Levasseur-Regourd A.C. 
Published: July 2016

The fragmentation of cometary nuclei is a frequent phenomenon, but the dynamics of the fragments is not yet well understood. During the close approach of comet C/1996 B2 Hyakutake to the Earth (0.1 AU) on late March 1996, images were taken with the 1 meter telescope of Pic du Midi observatory. Bright condensations were observed near the nucleus on images taken between March, 22,1996 and March, 31, 1996. It was suggested that these features were mini-comæ surrounding fragments receding from the nucleus (Lecacheux et al., 1996). A model was developped for the motion of cometary fragments in the orbital plane of the comet, and the simulations were compared with the observations (Desvoivres et al, 1998).In the model, we consider that the nucleus of the comet and a fragment are under the influence of the gravity of the Sun, of their mutual gravity, and of non-gravitational forces (NGF) due the loss of mass induced by solar heating. From an estimation of those NGF, we compute numerically the trajectories of the fragment and of the nucleus with respect to their common center of mass (CoM). Then, the motion of the center of mass is studied in an heliocentric reference frame using the theory of perturbed keplerian motion.
UBV Photometry of RR Lyrae Variables in the Globular Cluster M4
Authors: Cacciari Carla 
Published: July 2016

M4, one of the closest globular clusters to the Sun, presents some peculiar features that make it very interesting to study. The first C-M diagram, published by Greenstein (1939), showed a well populated blue-horizontal branch, a characteristic which usually, but not always, indicates low metal abundance (Hartwick 1968). Kinman (1959) found however that it contains strong lined red giants and classified it as type A, indicating normal metal abundance. More recent C-M diagrams (Moshkalev 1975, Alcaino 1975, Lee 1977, Lloyd Evans 1977) substantially confirmed both these characteristics.One of the major problems in the study of this cluster is the high and possibly non-uni form reddening, due to its location behind the Scorpius-Ophiuchus dark clouds.
Astrometrical and geodetical applications of VLBI “ARC METHOD”
Authors: Dravskikh A. F. , Finkelstein A. M. , Kreinovich V. Ja. 
Published: July 2016

AbstractThe geodetic and astrometric potentialities of radiointerferometric “arc-method” are considered. This method is a logical generalization of differential astrometry method, achieved through the expulsion of all non-invariant with respect to 3 - dimensional rotations and non - constant in time parameters. The brief theory of method is given. An algorithme of processing of radiointerferometric information for the construction of a catalogue on arcs, cited as an example for two - element interferometer, is brought. The question of optimal interferometer’s base orientations and observational regimes has been studied analytically. The estimations of accuracy are given for the determination geodesic and geodynamical parameters through the standard arcs. The question of application of arc - method for verification of relativistic gravitation theories is discussed.
Modern programs of meridian and photographic observations
Authors: Duma D. P. , Polozhentsev D. D. , Potter H. I. , Tavastsherna K. N. 
Published: July 2016

There are 44 active meridian instruments in the world ( 5 great transit instruments, 6 vertical circles, 33 meridian circles), including 8 in the Southern Hemisphere and 16 in the USSR. 10 instruments are new ones - less than 12 years old. We have also more then 20 widefield astrographs which are suitable for catalogue work.There are another 100 astrometric instruments (Danjon Astrolabe, ZT, Time Service TI, PZT and so on) which are used for catalogue purposes.
Imaging with a Coherence Interferometer in Optical Astronomy
Authors: Roddier C. , Roddier F. 
Published: July 2016

In optical astronomy, images are highly degraded by atmospheric turbulence. The diameter of the seeing disk may vary from 0.2 arcseconds to 10 arcseconds or more according to weather conditions. A typical diameter is of the order of 2 arcseconds which is the angular resolution of a 6cm lens at the diffraction limit.Large telescopes have been built for their light collecting capabilities, not for their resolving power which is, in general, of the order of 0.2 arcseconds, that is far from the diffraction limit.
I U E Observations of Circumstellar Lines and Mass Loss from B-Star
Authors: Tarafdar S.P. , Swamy K.S. Krishna , Vardya M.S. 
Published: July 2016

AbstractThe circumstellar lines due to A lΠ - X1Σ transition of CO has been identified for the first time in the spectra of an early type star. The spectrum, taken from the International Ultraviolet Explorer between 1150 - 1900 Å, of 9 Cep, a B2Ib star with E(B-V) = 0.47, shows not only the interstellar absorption lines of CO but also absorption features shifted towards short wavelength relative to the interstellar lines. The amount of shifts towards short wavelength from the 1 - 0, 2 - 0, 3 - 0, 4 - 0, & 6 - 0 interstellar absorption bands of CO has been found to be fairly close and corresponds to a velocity of 450 km sec-1. All attempts to identify these set of lines in a consistent way with atomic or ionic lines have yielded essentially negative results. This has led us to tentatively identify these lines due to circumstellar ∞ around 9 Cep. An estimate of rate of mass loss from the circumstellar ∞-column density leads to a value of Ṁ ≥ 10-11 M⊙ yr-1.
Effects of Flux Tubes on Conventional Chromospheric Diagnostics
Authors: Ayres Thomas R. 
Published: July 2016

AbstractMagnetic flux tubes are usually envisioned as small discrete structures sparsely distributed throughout an otherwise uniform “intertube” medium. An important distinction between the flux tubes and the surrounding atmosphere is the presence of a strong chromospheric temperature inversion at high pressures in the flux tubes, while the intertube component has only a mild, low pressure chromosphere, if any at all. This implies that the flux tubes will be enormously brighter in conventional chromospheric diagnostics than the intertube component. However, the unresolved magnetic elements cover perhaps only 10% of the “quiet” Sun at chromospheric heights. Consequently the intense K and k emission cores are severely diluted. The net result is a weak emission reversal that is not characteristic of either the flux tube or intertube chromosphere. Even in the thermal microwave continuum longward of 100 μm, the flux tubes can contribute significantly to low spatial resolution spectra. Consequently, the spatially averaged microwave emission is also not characteristic of either of the distinct components.If magnetic flux tubes are indeed the dominant class of atmospheric inhomogeneity in the Sun and other cool stars, then single-component interpretations of spatially unresolved data can be completely misleading, especially for inferring important auxiliary quantities, for example chemical abundances, line broadening parameters and chromospheric energy budgets. In the latter case, chromospheric radiative cooling rates derived from empirical mean models could be overestimated by up to an order of magnitude.
The Luminosity Function and Evolution of Cool White Dwarfs
Authors: Liebert James 
Published: July 2016

In the review, I attempt to focus on what we have recently learned from the observations about three general topics of great theoretical interest:
1. evidence for evolution of white dwarf surface abundances,2. the special problems of determining atmospheric parameters and abundances at the cool end of the sequence, and3. evidence for a peaking of the white dwarf luminosity function at Mbol = + 15 ± 1, with possible implications for cooling theory and the history of galactic star formation.
The Formation of White Dwarfs in Close Binary Systems
Authors: Webbink Ronald F. 
Published: July 2016

AbstractThree major modes of interaction in binary systems are identified, corresponding to (I) physical contact, (II) tidal mass loss from a star with a radiative envelope, and (III) tidal mass loss from a star with a convectlve envelope. The qualitative evolution of binary systems in each of these cases is outlined, leading to the formation of single white dwarfs, long-period remnants of quasi-conservative mass transfer, or short-period cataclysmic binaries. The origin of short-period double white dwarfs in a second phase of mass transfer is outlined. Implications for the frequency of different systems of these types, and of planetary nebulae with close binary nuclei, are discussed.
The Automatic Spacecraft Granat
Authors: Sunyaev R. 
Published: July 2016

The participants in the project are:– USSR, by developing the Granat spacecraft (Scientific and Production Association S.A. Lavochkin, G.N. Babakin Research Center) and the instruments in the scientific equipment packages– ART-P, ART-S, KONUS-V, ‘Podsolnukh’ (Sunflower), KS-18M (IKI of the Academy of Sciences of the USSR, Leningrad Institute of Physics and Technology of the Academy of Sciences of the USSR, Nuclear Physics Science and Research Institute of the Moscow State University);– France (CNES), by developing and delivering the gamma ray telescope SIGMA, the high energy spectrometer Phoebus, a memory device with 128 Mbit capacity, and a system for determining the current orientation of the telescope (star sensor);– Denmark (Danish Institute for Space Research), by developing the wide-angle X-Ray telescope VOTCh;– Bulgaria (TsLKI Bulgarian Academy of Sciences), by developing and delivering certain control instruments for the ‘Podsolnukh’ apparatus.
The Hipparcos Mission: Will it be a Scientific Success?
Authors: Perryman M.A.C. 
Published: July 2016

AbstractThe Hipparcos astrometry satellite was launched on 8 August 1989, and after spacecraft and payload commissioning, commenced the routine data acquisition phase on 26 November 1989. Having failed to reach its planned geostationary orbit, major revisions in the mission operations were made, and the post-launch expectations of the mission were strongly degraded with respect to the original goals - principally due to the greatly reduced observational efficiency (caused by the lack of ground station coverage) and the anticipated degraded mission lifetime (as a result of the high-energy particle degradation of the solar arrays in the geostationary transfer orbit).The final astrometric accuracies attainable by the Hipparcos mission will be influenced by the spacecraft and payload performances on the one hand, and by fraction of useful data and mission lifetime on the other. It will be shown that the elemental observational measurements correspond very closely to the predictions, and the data recovery fraction now stands at around 60–70 per cent, so that the ultimate scientific value of the Hipparcos results will be tied directly to the satellite lifetime. A measurement duration of at least 18 months is mandatory if the astrometric parameters (parallaxes and proper motions) are to be decoupled through the data reductions procedures. A somewhat longer lifetime (2.5–3 years) is necessary in order to reduce the errors on the astrometric parameters to the astrophysically-significant accuracies of around 2 milli-arcsec.It will be shown that the present indications of the satellite performances, and the significant progress already made in the data reductions, indicate that the difficulties of the ‘revised’ Hipparcos mission have been largely overcome, and that these target accuracies could still be achievable.
The International Ultraviolet Explorer (IUE)
Authors: Kondo Yoji 
Published: July 2016

AbstractThe International Ultraviolet Explorer (IUE) was launched into a geosynchronous orbit on 26 January 1978. It is equipped with a 45-cm mirror and spectrographs operating in the far-ultraviolet (1150–2000 Å) and the mid-ultraviolet (1900–3200 Å) wavelength regions. In a low-dispersion mode, the spectral resolution is some 6–7 Å. In a high-dispersion echelle mode, the resolution is about 0.1 Åat the shortest wavelength and about 0.3 Åat the longest. It is a collaborative program among NASA, ESA and the British SERC. The IUE is operated in real time 16 hours a day from NASA Goddard Space Flight Center near Washing ton, D.C. and 8 hours daily from ESA’s Villafranca groundstation near Madrid, Spain. By the end of 1989, 1870 papers, using IUE observations, have been published in refereed journals. During the same period, over 1700 different astronomers from all over the world used the IUE for their research.
The Infrared Space Observatory
Authors: Cesarsky C.J. , Kessler M.F. 
Published: July 2016

AbstractThe Infrared Space Observatory (ISO), a fully approved and funded project of the European Space Agency (ESA), is an astronomical satellite, which will operate at wavelengths from 3–200 μm. ISO will provide astronomers with a unique facility of unprecedented sensitivity for a detailed exploration of the universe ranging from objects in the solar system right out to distant extragalactic sources. The satellite essentially consists of a large cryostat containing at launch about 2300 litres of superfluid helium to maintain the Ritchey-Chrétien telescope, the scientific instruments and the optical baffles at temperatures between 2K and 8K. The telescope has a 60-cm diameter primary mirror and is diffraction-limited at a wavelength of 5μm. A pointing accuracy of a few arc seconds is provided by a three-axis-stabilisation system consisting of reaction wheels, gyros and optical sensors. ISO’s instrument complement consists of four instruments, namely: a photo-polarimeter (3–200μm), a camera (3–17μm), a short wavelength spectrometer (3–45μm) and a long wavelength spectrometer (45–180μm). These instruments are being built by international consortia of scientific institutes and will be delivered to ESA for in-orbit operations. ISO will be launched in 1993 by an Ariane 4 into an elliptical orbit (apogee 70000km and perigee 1000km) and will be operational for at least 18 months. In keeping with ISO’s role as an observatory, two-thirds of its observing time will be made available to the european and american astronomical community.
Santa Maria: An Orbiting Multispectral Observatory
Authors: Morales C. , Sabau L. , Gimenez A. , Broadfoot A.L. , Sandel B.R. , Stalio R. , Talavera A. , Bucconi A. 
Published: July 2016

SANTA MARIA is a program of international scope, being a collaboration between scientific groups in Italy, Spain and the United States. The experiment consists of a cooperative space project with the objective of designing, developing, launching, data processing and scientific exploitation of an astronomical satellite under the name of SANTA MARIA.The three research organizations will contribute to the project with tasks shared in the most practical way to guarantee the success of SANTA MARIA.
Cosmic Rays and the Dynamic Balance in the Large Magellanic Cloud
Authors: Fichtel Carl E. , Ozel Mehmet E. , Stone Robert G. 
Published: July 2016

AbstractPresent and future measurement of the Large Magellanic Cloud (LMC) particularly in the radio and high energy gamma ray range offer the possibility of understanding the density and distribution of the cosmic rays in a galaxy other than our own and the role that they play in galactic dynamic balance. After a study of the consistency of the measurements and interpretation of the synchrotron radiation from our own galaxy, the cosmic ray distribution for the LMC is calculated under the assumption that the cosmic ray nucleon to electron ratio is the same and the relation to the magnetic fields are the same, although the implications of alternatives are discussed. It is seen that the cosmic ray density level appears to be similar to that in our own galaxy, but varying in position in a manner generally consistent with the concept of correlation with the matter on a broad scale.
Evidence for Particle Acceleration During Magnetospheric Substorms
Authors: Lopez Ramon E. , Baker Daniel N. 
Published: July 2016

AbstractMagnetospheric substorms represent the episodic dissipation of energy stored in the geomagnetic tail that was previously extracted from the solar wind. This energy release produces activity throughout the entire magnetosphere-ionosphere system, and it results in a wide variety of phenomena such as auroral intensifications and the generation of new current systems. All of these phenomena involve the acceleration of particles, sometimes up to several MeV. In this paper we present a brief overview of substorm phenomenology. We then review some of the evidence for particle acceleration in Earth’s magnetosphere during substorms. Such in situ observations in this most accessible of all cosmic plasma domains may hold important clues to understanding acceleration processes in more distant astrophysical systems.Subject headings: acceleration of particles — Earth — solar wind
Electron-Beam Evolution in Partially Ionized Hydrogenic Plasma with Return Currents
Authors: Syniavskii D. V. , Zharkova V. V. 
Published: July 2016

AbstractThis paper presents the kinetic equation solution for beam electrons injected during solar flares from the corona to the chromosphere, consisting of hydrogenic plasma with partial ionization. The electrons are considered to lose their energy both in collisional processes with the charged and neutral species of ambient plasma and in ohmic heating by return currents induced in the plasma by beam electrons. The evolution of the energy and angular distributions of energetic electrons is calculated as functions of the column density. The bulk of the electron-beam energy stored in low-energy electrons is shown to be lost in the ambient plasma heating, less via Coulomb collisions at the lower corona and more via ohmic dissipation at the upper chromosphere. More energetic electrons with energies above 120 keV can reach the chromospheric levels with a weak ionized plasma, where a decrease of the Coulomb collisions and the induced electric field of a return current produce beams as well directed as on the top boundary. The X-ray bremsstrahlung polarization is shown to be positive in the range 5%-10%. It is very sensitive to the emergent photon energies below 40 keV and to angles of view for all of the X-ray radiation range.Subject headings: acceleration of particles — plasmas — Sun: flares — Sun: X-rays, gamma rays
Electrodynamics of Disk-Accreting Magnetic Neutron Stars
Authors: Miller M. Coleman , Lamb Frederick K. , Hamilton Russell J. 
Published: July 2016

AbstractWe have investigated the electrodynamics of magnetic neutron stars accreting from Keplerian disks and the implications for particle acceleration and γ-ray emission by such systems. We argue that the particle density in the magnetospheres of such stars is larger by orders of magnitude than the Goldreich-Julian density, so that the formation of vacuum gaps is unlikely. We show that even if the star rotates slowly, electromotive forces ( EMFs ) of order 1015 V are produced by the interaction of plasma in the accretion disk with the magnetic field of the neutron star. The resistance of the disk-magnetosphere-star circuit is small, and hence these EMFs drive very large conduction currents. Such large currents are likely to produce magnetospheric instabilities, such as relativistic double layers and reconnection events, that can accelerate electrons or ions to very high energies.Subject headings: acceleration of particles — accretion, accretion disks — MHD — stars: neutron
Evolution of Supernova Remnants with Cosmic Rays and Radiative Cooling
Authors: Dorfi E. A. 
Published: July 2016

AbstractRecent numerical models for SNR evolution are presented, including first-order Fermi acceleration with injection of suprathermal particles at the shock wave, heating due to dissipation of Alfvén waves in the precursor region and radiative cooling of the thermal plasma. The X-ray fluxes obtained from these SNR models show significant differences depending on the acceleration efficiency of cosmic rays. γ-ray fluxes are calculated originating from π0-decay of pions generated by collisions of the high-energy particles with the thermal plasma. Cooling of the thermal plasma and dissipation of Alfvén waves in the precursor are important to determine the final amount of the explosion energy ESN which is transferred into cosmic rays.Subject headings: acceleration of particles — cosmic rays — gamma rays: theory — shock waves — supernova remnants
Polarized One-Quantum Annihilation in Strong Magnetic Fields as a Process for Particle Deceleration in Neutron Star Atmospheres
Authors: Berg D. , Mentzel M. , Wunner G. 
Published: July 2016

AbstractSince several gamma-ray bursts seem to have their origin in the vicinity of neutron stars, where strong magnetic fields are present (B ≃ 108T), electrons and positrons have to be described, in this instance, by relativistic Landau states. As is well known, strong magnetic fields produce important effects: motion perpendicular to the field is quantized, transverse momentum is not conserved, and polarization effects become important. Moreover, in contrast to the field-free case, exotic processes such as 1γ pair-annihilation are not forbidden. With growing magnetic field, the cross section of this process becomes more and more nonnegligible. This cross section strongly depends on the polarization of the electron-positron pairs. Thus the deceleration via annihilation turns out to be a strongly polarization-dependent phenomenon in magnetized electron-positron plasmas.Subject headings: acceleration of particles — gamma rays: theory — polarization — radiation mechanisms: nonthermal — stars: neutron