bluuebunny/crossref_metadata_2025_split huggingface dataset:
The transition between long period comets, short period comets and meteoroid streams
Authors: Hughes David W. 
Published: July 2016

It has long been realised that Jovian perturbation is the dominant cause of the transition of long period comets (Period > 200 yr) into short period ones (P < 200 yr). When the differences in the detectability of comets in the two groups are taken into account it is clear that the present day flux of long period comets is sufficient to provide the present collection of short period comets in the inner solar system.The fact that meteoroid streams are produced by decaying short period comets was first recognised around 1866 (see Hughes 1982a). The magnificent display of Leonids in that year enabled the radiant position and time of maximum rate to be easily calculated. Assuming the orbital period to be 33.25 yr Le Verrier (1867) and Schiaparelli (1867) published orbits for the meteoroid stream. The orbit of comet 1866 I, which had been discovered by Guillaume Tempel, from Marseilles on December 19, 1865 and independently by Horace P. Tuttle from Harvard, Massachusetts on January 5, 1866, has been calculated and published by Oppolzer (1867a). Almost to a man Peters (1867), Schiaparelli (1867) and Oppolzer (1867b) realised that the comet and the stream had similar orbits. Since that time many more examples have been put forward, two famous ones being the Perseids and comet Swift-Tuttle (1862 III) and the Eta Aquarids and Orionids both of which have comet Halley (1910 II) as their parent. For more details see Cook (1973).
The long-term evolution project
Authors: Carusi A. , Kresák L. , Perozzi E. , Valsecchi G.B. 
Published: July 2016

AbstractThe Long-Term Evolution Project (LTEP), realized in collaboration by the IAS-Reparto di Planetologia (Rome, Italy) and the Astronomical Institute of SAV (Bratislava, Czechoslovakia), has been developed with the aim of giving a general insight into the dynamical evolution of short-period comets. The motion of all the known short-period comets has been investigated over a long time span (over 800 years) taking care, as far as possible, to eliminate the sources of possible discrepancies within the computations. An internally consistent data-set and an atlas of orbital evolutions are the first outputs of this project. The main characteristics of the LTEP are discussed, together with some general remarks on its importance for cometary studies, its limitations and the future developments.
One of the problems of long-term integrations of cometary orbits
Authors: Carusi A. , Perozzi E. , Pittich E.M. , Valsecchi G.B. 
Published: July 2016

AbstractOne of the problems of the numerical integrations of cometary orbits is that of their numerical stability. For those bodies which undergo close encounters with the giant planets the problem has a specific feature. Apart from the numerical instability of integrations in the mathematical sense, there is an additional source of instability due to the inaccuracy of initial data, i.e. the orbital elements. An example of this case is presented in this paper by the numerical integration of the motion of comet P/Shajn-Schaldach over an interval of 368.4 years, within which six close encounters with Jupiter occurred. The inaccuracy of the starting orbital elements of this comet is modelled by changes in the last digit of each element of the central orbit, determined by the set of the best orbital elements. In the process of integration, eight model orbits experience differential perturbations with respect to the central orbit. The numerical instability, caused by the inaccuracy of starting orbital elements and represented by the dispersion of these orbits, tends to increase abruptly beyond each encounter with Jupiter. It is shown that, with the attainable accuracy of the osculating elements representing the observations, one or two approaches to within 1 AU from Jupiter can make the orbit entirely indeterminate.
Review of studies on capture of comets by neptune and its role in the dynamic evolution of cometary orbits
Authors: Kazimirchack-Polonskaya E.I. 
Published: July 2016

AbstractA historical review of investigations on encounters of minor bodies with outer planets is presented. The dominating role of Jupiter in the capture of comets and in determining their secular evolution is emphasized. Participation in the above process of Saturn, Uranus and, especially, Neptune is investigated. In the present paper are considered five fictitious comets, penetrating into the depths of Neptune’s sphere of action, where they undergo large orbital transformations and capture by Neptune. Two near-circular orbits are transformed into elliptical ones, their perihelia being moved inside the planetary system; one hyperbolic orbit is transformed into a transplutonian one, another into a typical short-period orbit of the Neptune’s family with a perihelion accessible to terrestrial observers. One fictitious comet is captured by Neptune as a stable satellite.
The problem of the 1/a-distribution and cometary fading
Authors: Bailey M.E. 
Published: July 2016

AbstractThe background to the problem of explaining the frequency distribution of cometary 1/a-values is briefly reviewed and it is emphasised that the explanation in terms of the Oort Cloud model relies on an ad hoc fitting function - the fading/disruption probability per revolution. Assuming an underlying steady-state Oort Cloud and the integral equation formalism developed by Oort and Yabushita to predict the 1/a-distribution for an arbitrary fading probability, we have been able to constrain the unknown fading function by comparison with observations. In agreement with previous work we find that the tendency for fading or disruption should be strong at small 1/a-values and weak at large 1/a-values. The mean fading probability per revolution, k(x), is found to lie within a factor roughly of order 2 about k(x) ≈ 0.3(1+(x/4 × 10−3)2)−3/2, where × is 1/a in units AU−1. A physical model for fading which might qualitatively account for this behaviour is tentatively proposed. This depends on the thermal shock experienced by a long-period comet nucleus around perihelion passage. It is emphasised that until a viable model for fading has been found, the validity of the steady-state primordial hypothesis remains unresolved.
The selection of comets for future space missions
Authors: Yeomans D.K. 
Published: July 2016

AbstractThe criteria used to select a short period comet for possible future rendezvous space missions are stated and the selection process is outlined. For the time period 1900 - 2000, several candidate comets offer opportunities for spacecraft rendezvous. Two of the best candidates are periodic comets Kopff and Wild 2.
Zodiacal Light, Gegenschein and Sky Background
Authors: Maucherat A. , Llebaria A. , Gonin J.C. 
Published: July 2016

AbstractResults from photometers on board the D2B satellite (1975) for the whole sky in ultraviolet and blue light, are combined to generate a very well defined empirical representation of the zodiacal light and Gegenschein. The sky background is then obtained by subtraction of this model from the data.
Some Remarks on the Density of Interplanetary Dust Grains
Authors: Lamy P.L. 
Published: July 2016

AbstractThe relevance of the bulk density as a physical parameter characterizing interplanetary dust grains is discussed. The various measurements which lead to a determination of this parameter are reviewed. The specific case of the collected interplanetary dust grains is considered.The bulk density of interplanetary dust grains has been and is still a matter of controversy. This quantity cannot, in general, be directly measured; it is used to relate the mass and the size of a grain. This duality stems from physics itself as there are interactions sensitive to the mass (e.g., gravitational forces) while others are sensitive to the size or the cross-section (e.g., light scattering, radiation pressure, gas and plasma interactions). The measuring technics of the grains reflect this duality as, for instance, impact sensors are generally sensitive to the kinetic energy and thus to the mass, while optical sensors are sensitive to the cross-section. One sees that the density is not strictly speaking the relevant parameter, but what is needed is a relationship between mass and average cross-section.
Cosmic Ray Exposure Age Determinations of Cosmic Spherules from Marine Sediments
Authors: Yamakoshi Kazuo 
Published: July 2016

AbstractThe cosmic ray exposure ages of deep sea metalic lie spherules were determined by various methods; low level countings (Ni-59), neutron activation analysis (Mn-53), high energy accelerator mass spectrometry (Be-10, Al-26) and mass spectrometry (K isotopes). The exposure ages of 0.3 - 50 Ma were obtained. According to Poynting-Robertson effect, the starting points (supplying sources) are located at inner region of the orbit of Saturn.
Cosmic Spherules, Asteroid Collisions and the Solar Constant
Authors: Parkin D.W. 
Published: July 2016

AbstractIn 1980 (Phil. Trans. Roy. Soc. 297, 495) and in 1983 (Geophys. Jour. Roy. Astr. Soc. 75, 473) it was proposed that cosmic spherules are formed as splash ejecta in asteroidal collisions. The Poynting-Robertson effect size-sorts the spherules as they spiral to Earth in circular orbits. The time taken in My is given byΔt = 3.5 × 10−7 Dδ (a2 − 1)where a (in AU) is the collision distance from the Sun, D (in um) is the diameter of the spherules and δ (in kg/m−3) its density. In the 1983 paper, we tested the hypothesis by plotting the size of all the iron spherules (≥ 43 μm diam.) against time for two dated N. Pacific cores. Sloping lines, giving a ~ 2.1 AU, could be discerned; but their existence could be disputed - see figure 6.In current work, all the spherules from core V21-65 have been cracked open to find δ. Out of 220 spherules, 65 have rusted metal globules and these (Dδ) points give a confused plot, because of inaccurate δ-values. However, 66 spherules have their metal globules well preserved. Since globule diameter and %Ni can be accurately measured, δ can be calculated. These (Dδ) points show two sloping lines with some clarity, giving a ~ 3.4 AU; also, there are vague lines, giving a-values well within the main asteroid belt.To establish the hypothesis, wide cores are needed, giving an abundance of undamaged spherules. To obtain accurate a-values, the Robertson formula requires correction because of the spherule’s “hummocky” oxide surface. Also, any waviness in the sloping lines could be a measure of a variable solar constant.A new kind of iron spherule was found because of the cracking; 13 enclose opaque beads of true glass (rich in Fe, Ni and Si, no Mg) instead of metal globules. Crushed bits are deep ruby-red and nonmagnetic.
Cometary Dust and the Periodicity of Rainfall Singularities
Authors: Kviz Z. 
Published: July 2016

AbstractPeriodicity in rainfall singularities in the U.S.A. corresponds to the periods of two comets whose orbits are sufficiently close to Earth’s orbit. These effects are connected with the position of a stratospheric jet stream over the territory of the U.S.A. This investigation indicates that some processes, so far not properly understood, could be responsible for the influence of cometary dust on the triggering of atmospheric precipitation.
Optical Detection of Large Meteoroids in Space
Authors: Zook H.A. , Potter A.E. 
Published: July 2016

AbstractCCD sensors placed across the focal plane of large Schmidt telescopes have great potential for detecting and measuring the very low flux in space of meteoroids with diameters larger than 1 meter. With the Palomar “Big Schmidt”, a detection rate of 1.4 per hour is obtained for meteoroids between 0.6 and 200 meters in diameter. For the Baker-Nunn “Satellite Tracking Camera”, the corresponding rate is about 0.8 per hour. The key to obtaining such high detection rates derives from approximately setting the sensor integration time equal to the time it takes a meteoroid to cross a pixel field of view. This minimizes signal to noise problems and is accomplished, in practice, by multiple summing of short integration time data records to obtain data records of longer effective integration times.
Meteoroid Orbits Determined by Southern Hemisphere Radar
Authors: Steel D.I. , Baggaley W.J. 
Published: July 2016

AbstractA radar meteor orbit facility of novel design has been developed at the University of Canterbury. Synchronous digital noise averaging,impulse suppression and meteor echo recognition using a microprocessor system, along with high gain antennas, allow a limiting radar magnitude of about +13 to be achieved, making this the most sensitive meteor orbit radar to’ date. An exhaustive survey of faint sporadic meteors will be carried out, along with an investigation of the little-known Southern showers. Since the observatory is ideally located with respect to the Eta Aquarid radiant, a programme of observations during the Comet Halley perihelion epoch is planned.
Dust-Plasma-Gas Interactions in the Heliosphere
Authors: Fahr H.J. , Ripken H.W. 
Published: July 2016

AbstractSeveral, different forms of how neutral gases and dusty media can interact with a plasma have been discussed in the Literature. Common to all of these interactions is that they in principle lead to changes in both the composition and dynamical state of all interacting media. The most important scenarios in the heliosphere involving these kinds of interactions are described in this paper. Special emphasis is placed on the solar wind interaction with the zodiacal dust. In regard to the dust, this leads to severe complications with respect to its dynamics due to the plasma Poynting- Robertson effect and due to Lorentz scatterings. As for the plasma, this causes the appearance of dust-generated neutrals and secondary ions. An influence on the plasma dynamics, at least in the present solar system, can be neglected. The surface chemistry of the plasma-dust reactions is described in some detail here, and the densities and fluxes of exotic, dust-generated ions not originally belonging to the coronal solar wind are calculated. Observabilities of these neutrals and ions are investigated and it is discussed how physical, chemical, and dynamical parameters of the zodiacal dust cloud could be derived from these observations.
Computer Calculation of Collision Cascades by Energetic Particles Penetrating Dust Grains
Authors: Rössler K. , Eich G. 
Published: July 2016

AbstractThe penetration of energetic particles from stellar winds, cosmic rays and fast moving gas clouds in interstellar dust grains induces a variety of physical and chemical changes. Detailed information on penetration ranges, number of secondary projectiles produced by knock-on and their energy distribution is obtained from computer simulation of collision cascades with the program MARLOWE. Model targets are polycrystalline H2O-ice, NH4Cl, and SiO2, projectiles are lo2 - lo4 eV H, He, and C. Depending on the energy and the projectile/ target mass ratio up to lo2 secondary projectiles are created per primary impact with energies ranging from a few to some lo3 eV. In composite grains, condensed gases and ice mixtures the energetic secondaries can undergo hot chemical reactions leading to a series of precursors for larger organic and biomolecules.
A New Approach to Evaluate Planetary Perturbations on a Cloud of Dust in Low Eccentricity Heliocentric Orbits
Authors: Gustafson Bo. Å. S. 
Published: July 2016

AbstractDynamical perturbations on ensembles of particles in heliocentric orbits of low eccentricity are integrated over time. The dust is perturbed by radiation pressure, Poynting-Robertson drag, their corpuscular counterparts, and by gravitation due to any number of planets. A dust cloud is represented by a set of centroids and orbital dispersions (about the centroids). Gravitational perturbations on the centroid are derived from a single matrix, valid for any planet, in the appropriate frame of reference. After transformation of the time derivatives to a common coordinate system, the perturbation rates are summed up and integrated. The time dependence of the planets’ orbital elements are evaluated inside the time integral.
The Proposed Columbus Mission: High and Low Resolution Spectroscopy in the 100–2000 Å Spectral Region
Authors: Linsky Jeffrey L. 
Published: July 2016

For the past year a Joint Working Group of NASA and ESA scientists and engineers has been defining the scientific objectives and instrument parameters for a proposed satellite to obtain far and extreme ultraviolet spectra of stars, interstellar gas, solar system objects, and galaxies. The project, now called Columbus, incorporates the scientific goals of the previously proposed NASA Far Ultraviolet Spectrograph Explorer (FUSE) and ESA Magellan missions.The prime spectral range of Columbus, 900–1200 Å, cannot be observed by IUE or Space Telescope. In this spectral range Copernicus was able to observe bright stars (mv ≤ 6) with high resolution and the Hopkins Ultraviolet Telescope (HUT) will observe faint sources at low resolution, but Columbus will be the first instrument capable of high spectral resolution observations of faint sources (mv ≈ 17). High resolution spectra in the 900–1200 Å region will permit studies of the Lyman lines of atomic H and D, the molecules H2 and HD, resonance lines of C III and O VI, and other species listed in Table 1. Columbus also is being designed to observe the 1200–2000 Å spectral region at high resolution, permitting measurements of many stages of ionization for the same atom (i.e. N I, II, III, V; C II, III, IV; and S II, III, IV, VI). The broad coverage of ionization states is essential for the analysis of interstellar and stellar plasmas where the ionization balance can be quite complex.
Collision Strengths and Line Strengths for Transitions from the ls23ℓ, Levels to the ls2ℓ'3ℓ" Levels in Li-Like Ions
Authors: Sampson D.H. , Goett S.J. , Petrou G.V. , Clark R.E.H. 
Published: July 2016

It is well known that radiation from the levels of the ls2ℓ2ℓ' and ls2ℓ3ℓ' configurations of Li-like ions form satellites of spectral lines from He-like ions that are of high interest for plasma diagnostic purposes. Recently Sampson et al (1984) have made calculations of the collision strengths for innershell excitation to these upper levels from the ls22s and ls22p levels for a large number of Li-like ions using a Coulomb-Born-exchange method. Here we consider the alternative mechanism for populating the ls2ℓ3ℓ' levels by collisional excitation from the ls23s, ls23p and ls23d levels. Although the poDulations of the ls23ℓ levels are lower than those of the ls22ℓ levels, this is at least partially compensated for by the fact that the collision strengths for the ls23ℓ − ls2ℓ'3ℓ" transitions are considerably larger on the average than those for the ls22ℓ − ls2ℓ'3ℓ" transitions. The method of calculation is the same as that used by Sampson et al (1984), where all possible configuration mixing, parentage mixing and intermediate coupling type mixing among the states in a complex (the states having the same n values, parity and J values) was included. Also the present application is sufficiently simple that after summation over J values for the initial level the results for the collision strength Ω can be expressed in a simple manner in terms of the Z scaled hydrogenic collision strengths Z2ΩH and analogous to Eqs (8)-(15) of Sampson et al (1984). The appropriate formulae and the numerical results for both excitation to upper fine structure levels and to upper energy terms for 19 Li-like ions have been submitted for publication to Atomic Data and Nuclear Data Tables. Here we give only the pertinent formula and sample numerical results for transitions between energy terms in Li-like iron. This formula iswhere due to configuration mixing neither ℓ need equal ℓ" nor ℓa need equal ℓ'. The recommended values for σ and σe are zero for transitions involving ls−2s and are −0.5 and 0.3, respectively, for transitions involving ls−2p. Numerical values for the coefficients A and Ae for Li-like iron are given in Tables I-III. Values for Z2ΩH and for impact electron energies up to 15 times threshold are given in Golden et al (1981) and Clark et al (1982) and are repeated in Table IV for convenience. Finally we note that the line strengths S for transitions involving ls−2p are obtained by multiplying the corresponding value for A(ls−2p) by the scaled hydrogenic line strength 1.665 and dividing by (Z-σ)2.
Spectral Line Intensities for Δ N = 0 (L-Shell) Transitions of N, O, and F-Like Ions
Authors: Lee Y.T. , Reed K. 
Published: July 2016

Many laboratories are actively investigating radiation spectra emitted from high temperature/high density plasmas produced using gas-puff Z-pinch machines and high power lasers. Spectral-line intensities from these plasmas can be useful temperature and density diagnostics. In a well-diagnosed plasma, information on the emission spectrum can also be used to test the accuracy of theoretical rate coefficients.Recently time-resolved spectra from an oxygen-like argon plasma produced in a gas-puff z-pinch were measured in the wavelength range 150–200 Å . Over this wavelength range the spectrum contains mostly the Δn = 0 (L-shell) transitions in ArX-ArXIV and some weak transitions for n = 3 to n = 4 of ArVI-ArVIII. The measured spectra show the predominance of 0-like Ar L-shell transitions.
The Physics of Supernovae
Authors: Woosley S.E. , Weaver Thomas A. 
Published: July 2016

AbstractPresupernova models of massive stars are presented and their explosion by “delayed neutrino transport” examined. A new form of long duration Type II supernova model is also explored based upon repeated encounter with the electron-positron pair instability in stars heavier than about 60 M⊙. Carbon deflagration in white dwarfs is discussed as the probable explanation of Type I supernovae and special attention is paid to the physical processes whereby a nuclear flame propagates through degenerate carbon.
The Early Evolution of Supernova Remnants
Authors: Fransson Claes 
Published: July 2016

In his review in 1972 Woltjer [1] divided the evolution of supernova remnants into three different phases, the free expansion phase, the adiabatic Sedov phase and the radiative phase, when cooling of the gas becomes important. The first of these was only briefly discussed and little connection between the supernova explosion and the remnant phase was made. The reason for this is also easy to understand in view of the difficulty of determining the type of explosion even for well-known, young remnants like Cas A, Tycho, Kepler and the Crab remnant.This situation has changed considerably during the last five years or so, mainly due to observations with new instruments like VLA, IUE and Einstein. With these, as well as large optical and infrared telescopes, the information about the supernova explosion and the early evolution of the supernova remnant has increased dramatically, and a more or less new picture of the explosion has emerged. Instead of a free expansion into a virtual vacuum, with few observational consequences, the supernova undergoes a complex interaction with its immediate surroundings, with a wealth of observational information. In this stage both the structure of the supernova ejecta and the circumstellar medium is crucial for the observational properties. Perhaps, the most interesting aspect of it is that we in this way can bridge the gap between the supernova explosion and the remnant stage.