bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical simulations of the accretion of Uranus and Neptune. II. Effect of low velocity encounters
Authors: Brunini A. , Fernández J.A. 
Published: July 2016

AbstractNew numerical simulations of the accretion of the outer solar system were carried out by means of a symplectic integration code developed by the authors. By contrast with our previous numerical experiments, we now pay special attention to the treatment of low relative velocity encounters between planetesimals. Our new results corroborate, in general, a marked radial drift of the accreting outer planets, and that less than 50% of the solid material originally present in the system contributes to the accretion process. The results confirm that mean motion resonances play a major role during the accretion of the outer solar system.
Šumava meteoroid − was it a small comet?
Authors: Nemtchinov I.V. , Kuzmicheva M.Yu. , Shuvalov V.V. , Golub' A.P. , Popova O.P. , Kosarev I.B. , Borovička J. 
Published: July 2016

AbstractŠumava event was one of the brightest bolides detected by the European Network. At the altitudes from 75 to 59 km its light curve shows four major maxima. Low strength appears the evidence of its cometary origin, while spectrum is consistent with a chondritic composition. The velocity of impactor lateral expansion is higher than that caused by simple aerodynamics. We consider some probable models of meteoroid disruption.
Detection of a high density meteoroid on cometary orbit
Authors: Spurný P. , Borovička J. 
Published: July 2016

AbstractWe report a detection of a unique fireball photographed at three Czech stations of the European Fireball Network on June 1, 1997. The main exceptionality of this fireball is given by its retrograde heliocentric orbit (i= 138°) typical for comets and, at the same time, a behavior in the Earth’s atmosphere typical for the hardest component of the interplanetary matter. The spectrum of the fireball is unique by the absence of the sodium line. With the entry velocity of 65 km s−1, the meteoroid of an estimated initial mass of 0.2 kg (diameter of several centimeters) penetrated down the altitude 65 km, i.e. significantly deeper (about 25 km) than cometary meteoroids of a comparable velocity and mass. A comparison with a typical cometary meteoroid is demonstrated on anηAquarid fireball photographed one month before.The event reported is unique in decades-long records of the fireball networks. The origin of the meteoroid in the asteroid belt is highly improbable owing to the orbit. The possibility that comets contain centimeter sized compact stones is therefore suggested.
The O–C diagrams of minor planets − a new approach to modelling the rotation
Authors: Szabó Gy. , Sárneczky K. , Kiss L.L. 
Published: July 2016

AbstractA widely used tool in studying quasi-monoperiodic processes is the O–C diagram. This paper deals with the application of this diagram in minor planet studies. The main difference between our approach and the classical O–C diagram is that we transform the epoch (=time) dependence into the geocentric longitude domain. We outline a rotation modelling using this modified O–C and illustrate the abilities with detailed error analysis. The primary assumption, that the monotonity and the shape of this diagram is (almost) independent of the geometry of the asteroids is discussed and tested. The monotonity enables an unambiguous distinction between the prograde and retrograde rotation, thus the four-fold (or in some cases the two-fold) ambiguities can be avoided. This turned out to be the main advantage of the O–C examination. As an extension to the theoretical work, we present some preliminary results on 1727 Mette based on new CCD observations.
Are there two populations of comets based on polarimetric properties of dust particles?
Authors: Kiselev N.N. 
Published: July 2016

AbstractA critical analysis of attempts to classify comets on the basis of their polarimetric properties is given. It was shown that a degree of polarization depends strongly on the gas-to-dust ratio of comets and bandpass of filters. At present, there are no rigorous polarimetric evidences for two taxonomic classes of comets.
CCD photometry of high inclination faint asteroids and Kuiper belt objects
Authors: Ivanova A. , Ivanova V. , Tsvetkova A. 
Published: July 2016

AbstractA new program for CCD photometric observations of Kuiper belt objects and high inclination faint asteroids with the 2m RC telescope of Rozhen National Observatory, Bulgaria, started at the beginning of 1998. We present our observations andV-composite lightcurve of 863 Benkoela.
Approaches of stars to the Sun
Authors: Dybczyński P.A. , Kankiewicz P. 
Published: July 2016

AbstractClose approaches of stars to the Solar System perturb comets from the Oort cloud so that they pass into the planetary system − the gravitational impulse changes the distribution of observable comets. This paper presents the results of calculations of the motion of stars in the solar neighbourhood in the past and future. The main results for each star are: the time of the encounter and the minimum distance between the Sun and the star. They are calculated using three different methods: a straight line motion model, a model with a Sun − star Keplerian interaction, and the numerical integration of the equations of motion with galactic perturbations included. In the last case, two models of the Galactic potential are used: a simplified potential of the Galactic disk and the more complex potential of the Galaxy by Dauphole and Colin. Coordinates and velocities of nearby stars are taken from several different catalogues: the Gliese catalogue, the Hipparcos catalogue, and the Barbier-Brossat catalogue of Radial Velocities.
From Jupiter-family comets to objects in Encke-like orbits
Authors: Valsecchi G.B. 
Published: July 2016

AbstractNumerical integrations of the orbital evolution of objects in orbits resembling the peculiar cometary orbit of 2P/Encke have allowed the identification of the dynamical paths connecting these orbits to the possible source regions and to the possible end states. A certain degree of concentration of the longitudes of perihelion of objects in Encke-like orbits has led to the idea that 2P/Encke and the asteroidal objects in nearby orbits all come from the recent fragmentation of a giant progenitor. However, the fact that the majority of Earth-crossing asteroids are discovered when passing near the Earth induces a correlation between the date of discovery and a range of possible longitudes of perihelion. By combining this correlation with the variable rate of asteroid discoveries over the year, it is possible to show that the discovery of asteroids on orbits of given semimajor axis and eccentricity is favoured if their longitudes of perihelion fall within certain intervals. A question still open is the efficiency of the dynamical path linking the Jupiter family to Encke-like orbits; nongravitational forces seem to play an important rôle in this respect.
Covering of cometary nucleus by refractory crust and its evolution into asteroid-like body
Authors: Ibadinov Kh.I. 
Published: July 2016

AbstractFrom the established dependence of the brightness decrease of a short-period comet dependence on the perihelion distance of its orbit it follows that part of the surface of these cometary nuclei gradually covers by a refractory crust. The results of cometary nucleus simulation show that at constant insolation energy the crust thickness is proportional to the square root of the insolation time and the ice sublimation rate is inversely proportional to the crust thickness. From laboratory experiments resulted the thermal regime, the gas productivity of the nucleus, covering of the nucleus by the crust, and the tempo of evolution of a short-period comet into the asteroid-like body studied.
Solar Flare Spectral Diagnosis: Present and Future
Authors: Antonucci Ester 
Published: July 2016

AbstractNew perspectives in solar diagnosis have been opened in recent years with the advent of high-resolution soft X-ray spectroscopy for plasmas forming at temperatures above 107K. The spectra obtained with the soft X-ray spectrometers flown during the last solar maximum on the major space missions dedicated to flares have allowed detailed studies of the hydrodynamic response of coronal loops to impulsive energy deposition and of the formation of the high-temperature plasma as a consequence of such dynamic effects. These studies are possible since high-resolution spectrometers give an accurate measure of both line intensities and profiles in important spectral regions, covering the emission of highly ionized heavy ions, which allow a direct determination of most of the crucial plasma parameters in the flare region. In response to the impulsive energy release in the flare region, while the intensity of soft X-ray lines increases, line profiles show large non-thermal broadenings and strong blue-asymmetries.There have been important contributions in the understanding of the formation of the flare high-temperature plasma, as an effect of the hydrodynamic response of the solar atmosphere to impulsive chromospheric heating. On the other hand, the attempts to investigate the primary energy release and transport, on the basis of the soft X-ray spectral data, have not yet been entirely successful. Significant differences in the emitted spectra are expected at the very onset of flares for different energy deposition and transport processes, but the sensitivity of the present experiments is still insufficient to detect with good statistics the early stage of flares and, therefore, to allow a reliable discrimination. It is expected that future experiments with higher sensitivity will be of great importance for relating with less ambiguity the observed flare evolution in soft X-rays to the primary energy deposition in the flaring coronal loops.
Solar Flares: The Impulsive Phase
Authors: Dennis Brian R. , Schwartz Richard A. 
Published: July 2016

AbstractOnly during the previous solar cycle have systematic observations begun to be made with the sensitivity and time resolution, and the continuous coverage required to catch the impulsive phase and measure the rapid variations present in many wavelength ranges. Observations in X-rays, gamma-rays, UV, Ha, and radio wavelengths all reveal rapid variations during the impulsive phase and have contributed to our understanding of the different phenomena involved. Results have been obtained from several spacecraft, from rocket and balloon flights, and from ground-based observations. These are reviewed in the context of a simple single loop flare model with a view to showing what results are consistent with this model and what the major problems are in our understanding of the impulsive phase. New instrumentation planned for observations during the present Cycle 22 will provide a concerted attack on the impulsive phase as part of the Max'91 program.
Preflare Activity
Authors: Gaizauskas V. 
Published: July 2016

AbstractMagnetic reconnection at current sheets or in current-bearing arches in the solar atmosphere is generally accepted as the mechanism responsible for the sudden energy release in solar flares. Attempts have so far been unsuccessful to isolate from the observations some unique preconditions which would be necessary and sufficient to ensure rapid conversion of energy by this process. Here we survey recent multi-wavelength observations which illustrate the variety of preflare activity. Multiple structures are now believed to participate in the energy release. Dynamic global coupling of the magnetic fields between a flaring site and the rest of an activity complex is seen from the data to be an important aspect of preflare activity.
Simultaneous Multi-Frequency Imaging Observations of Solar Microwave Bursts
Authors: Kundu M. R. , White S. M. , Schmahl E. J. 
Published: July 2016

AbstractWe review the results of simultaneous two-frequency imaging observations of solar microwave bursts with the Very Large Array. Simultaneous 2 and 6 cm observations have been made of bursts which are optically thin at both frequencies, or optically thick at the lower frequency. In the latter case the source structure may differ at the two frequencies, but the two sources usually seem to be related. However, this is not always true of simultaneous 6 and 20 cm observations. The results have implications for the analysis of non-imaging radio data of solar and stellar flares.
Solar and Stellar Magnetic Fields and Structures: Observations
Authors: Linsky Jeffrey L. 
Published: July 2016

AbstractThis review of stellar magnetic field measurements is both a critique of recent spectral diagnostic techniques and a summary of important trends now appearing in the data. I will discuss both the Zeeman broadening techniques that have evolved from Robinson's original approach and techniques based on circular and linear polarization data. I conclude with an ambitious agenda for developing self-consistent models of the magnetic atmospheres of active stars.
Mass Motions Associated with Solar Flares
Authors: Martin Sara F. 
Published: July 2016

AbstractMass motions are a principal means by which components of solar flares can be distinguished. Typical patterns of mass motions in Ha are described for chromospheric flare ribbons, remote chromo-spheric flare patches, flare loops, flaring arches, surges, erupting filaments and some expanding coronal features. Interrelationships between these phenomena are discussed and illustrations of each are presented.
The Importance of Solar White-Light Flares
Authors: Neidig Donald F. 
Published: July 2016

AbstractThe basic results of white-light flare (WLF) photometric and spectrographic observations are reviewed. WLFs represent the most extreme density conditions in solar optical flares and are similar to stellar flares in many respects. It is shown that WLFs originate in the low chromosphere and upper photosphere, and that their huge radiative losses remain difficult to explain within the context of known mechanisms of energy transport.
Long-Duration Solar and Stellar Flares
Authors: Poletto Giannina 
Published: July 2016

AbstractAccording to one of the most popular classifications, solar flares may be assigned either to the category of small short-lived events, or to the category of large, long-duration two-ribbon (2-R) flares. Even if such a broad division oversimplifies the flare phenomenon, our knowledge of the characteristics of stellar flares is so poor, that it is worthwhile to investigate the possibility of adopting this classification scheme for stellar flares as well. In particular we will analyze Einstein observations of a long duration flare on EQ Peg to establish whether it might be considered as a stellar analogy of 2-R solar events. To this end we apply to EQ Peg data a reconnection model, developed originally for solar 2-R flares, and conclude that stellar observations are consistent with model predictions, although additional information is required to identify uniquely the physical parameters of the flare region. Application of the model to integrated observations of a 2-R solar flare, for which high spatial resolution data are also available, shows, however, that future integrated observations may allow us to solve the ambiguities of the model and use it as a diagnostic tool for a better understanding of stellar flares.
Polarimetry of Stellar Active Regions and Flares
Authors: Tuominen I. , Huovelin J. , Efimov Yu. S. , Shakhovskoy N. M. , Shcherbakov A. G. 
Published: July 2016

AbstractObservations of regular and irregular polarimetric variability in late-type stars are reviewed, and the related physical and geometrical effects are discussed. There are indications that the irregular part of the variability could be caused by transient events, possibly associated with flares. Polarimetric observations during flares are reviewed, and preliminary results of new observations of a well-known flare star, YY Geminorum, are presented. The results show that the small flare in YY Gem did not cause any significant variations in linear polarization, while the binary eclipse evidently causes an enhancement in the polarization. The reasons for the difficulties in stellar flare polarimetry are discussed. Finally, future prospects for the observations of flaring stars and for the utilization of linear polarimetry as a complementary method to other techniques of surface imaging of stellar activity and flares are presented.
Computer Controlled Pulse Counting Photometry
Authors: Nielsen R. Florentin 
Published: July 2016

I wish to present some aspects of a computer controlled pulse counting system for general photoelectric photometry.The pulse counting technique applied in astronomical photoelectric photometry has yielded significant improvements as to telescope efficiency, especially in connection with the measurement of very faint light sources. This is achieved through the advantages inherent in the pulse counting technique over the conventional charge technique, that is:
A Digitized Microphotometer and Some Applications
Authors: Gratton L. , Martini A. , Martino E. , Natali G. , Viotti R. 
Published: July 2016

Despite the great progress which is being continuously made towards direct photoelectric recording, it is almost certain that for many years to come photographic plates will remain the most common means for detecting images of stars and stellar spectra, whether directly or through the intermediary of an image intensifier.The photographic image of the spectrum of a star contains an enormous wealth of information whose utilization is one of the most important tasks of observational astrophysics. To achieve this task many difficult problems must be solved, the first being to express the information in a form which lends itself to further processing.This is usually done by means of two different kinds of instruments.
Coherence Problems in High-Resolution Microdensitometry
Authors: Parrent G. B. 
Published: July 2016

My background is neither astronomy nor instrumentation but rather image analysis. Hence, I am not going to describe new equipment nor new astronomical findings, but rather some difficulties which have arisen in other fields where images must be interpreted and manipulated, and which are sure to arise in astronomy as well.I shall limit my attention to problems arising from coherence of the radiation in the analysing instrument and attempt to isolate their source and give guidance on how to recognize them and avoid them.
Calculation of Equivalent Widths via an Interactive Display Device
Authors: Klinglesmith Daniel A. 
Published: July 2016

AbstractThis paper describes a computer program used to compute equivalent widths via an IBM 2250 attached to an IBM 360/75J.The measurement of stellar equivalent widths is a long tedious procedure and the final results depend to a large extent on where the stellar continuum is drawn. Therefore, a method which permits the continuum to be redrawn and the equivalent width remeasured quickly is desirable. An interactive CRT display device is an ideal instrument for allowing an astronomer to adjust the continuum level and the other parameters that are involved in equivalent width measurements. The display device discussed in this paper is an IBM model 2250 used in conjunction with a IBM 360/75J.The “2250” consists of a 12 inch (30 cm) square CRT display tube plus a 32 function key box, an alphanumeric keyboard and a light pen which can be pointed at any illuminated spot on the screen. Thus, there are 34 interrupts that can be sensed by the program controlling the “2250”. The program that has been used communicates with the astronomer via messages and questions displayed on the CRT screen. The main program remains in a wait state until one of the 34 possible interrupts occurs, whereupon it branches to the designated subroutine and executes the procedures necessary to satisfy the interrupt.
Spectral Changes in the Grygar Variable HBV 475
Authors: Mammano A. , Righini G. M. 
Published: July 2016

Photovisual and spectroscopic observations of HBV 475 in the range λλ 3800–11 000 Å by means of S-20 and S-1 Carnegie Intensifies and prismatic cameras (dispersion 60 A/mm at Hγ), made in 1969 through 1971, have revealed the simultaneous presence of hot and cold sources of radiation, both variable.In 1969 when the magnitudes were B = 12.45, V = 12.05, U = 11.40 the hot source gave origin to a quite strong ultraviolet continuum and to emission lines among which the most intense are due to: HI (H16 to Hα and P14 to P7); OI 8446; Fell (mult. 27, 37, 38, 42, 48, 49); [NII] 5755; Hel (4471, 5876, 6678, 7065, 10 830 very strong); [OIII] (5007, 4959, 4363); [NeIII] (3869, 3968); Hell 4686 weak.
High-Frequency Stellar Oscillations. The Cerro Tololo Search for Luminosity-Variable White Dwarfs
Authors: Hesser James E. , Lasker Barry M. , Kunkel W. 
Published: July 2016

AbstractThe techniques and procedures of time-series monitoring and Fourier analysis which are used at Cerro Tololo to search for luminosity variations in white dwarfs are summarized. Further null results from this program, which are applicable to the problem of defining the region of white-dwarf variability in the HR-diagram, are considered; and the properties of the four known variables are reviewed as possible archetypes of a group.
The Evolution of a Contact Binary
Authors: Hazlehurst J. , Meyer-Hofmeister E. 
Published: July 2016

Test calculations have been made to study the effects of central hydrogen depletion, luminosity exchange and mass exchange on the evolution of a contact binary. The Munich Henyey programme was adapted to allow the study of both components in a time-dependent way.The first model considered was that of LUCY (Ap. J. 151, 1126) in which entropy is assumed to be at all times uniform throughout the adiabatic portion of a common convective envelope. This model was found to be unstable, in the sense that mass flows from the primary to the secondary in a time short compared with the nuclear time-scale.
Observations of Faint Globular Clusters
Authors: Rosino L. , Pinto G. 
Published: July 2016

The present communication reports some results of observations made at Asiago on three faint globular clusters discovered on Palomar Sky Survey plates (Abell 1955).Palomar 2 (4h43.m1, + 31 °23’, 1950; l= 170°, b= -9°). This cluster was studied some years ago by McCarthy and Treanor (1964) on infrared plates taken with the Schmidt telescope of the Vatican Observatory. After an extensive discussion the authors concluded that the object was either a peculiar globular cluster at an estimated distance of 63 kpc or an old galactic cluster at a distance of the order of 16 kpc.
Planetary Nebulae, Globular Clusters and the Galactic Halo
Authors: Bergh Sidney Van Den 
Published: July 2016

AbstractPlanetary nebulae are used as a tracer for halo Population II stars. A comparison of the number of planetary nebulae in the galactic pole caps (|b| ≥ 45°) with the number of planetaries in globular clusters suggests that (to within a factor of 2 or 3) the galactic halo has a luminosity LB ⋍ 2 × 108L⊙. From the work of Oort it is estimated that the galactic halo has a mass of at least so that for the galactic halo.
Variable Stars In NGC 4590
Authors: Terzan A. , Rutily B. , Ounnas CH. 
Published: July 2016

AbstractThe globular cluster NGC 4590 has been observed at Haute Provence Observatory (photographic photometry, 80-cm reflector, F/6) and at the European Southern Observatory (image-tube, 152-cm reflector, F/15).
– A sequence of red magnitudes, mr (λett ≅ 6400 Å) has been established around the cluster. It comprises 28 stars with magnitudes between 11.66 and 16.50.– Five new variable stars were discovered in a one square degree field, centered on the cluster.– Four other variable stars (No. 39, 40, 41, and 42) were discovered in the cluster.