bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rotating Stellar Atmospheres and the Energy Distribution of Altair
Authors: Jordahl Peter R. 
Published: July 2016

AbstractModels of rotating stellar atmospheres have been constructed for masses appropriate to middle and late A stars, and some of the photometric properties of these models are discussed. A specific model for the rapidly rotating star Altair has been constructed matching the observed radius, luminosity, and projected rotational velocity. It is found that the energy distribution predicted for the model agrees well with that observed for Altair, after the latter has been corrected for line blanketing.
Fission and the Origin of Binary Stars
Authors: Ostriker Jeremiah P. 
Published: July 2016

AbstractBrief reviews of the classical ‘angular momentum problem’ and the statistics of upper-main-sequence binaries are presented as background for the suggestion that the close, early-type, binaries are produced by fission of rapidly rotating protostars.Next, theoretical sequences of contracting, rotating stars are described. Recent work demonstrates that the zero-viscosity, polytropic sequences, have essentially the same properties as the McLaurin sequence. Thus, fission is possible for centrally condensed stars. Observations of close early-type binaries are compared with theoretical predictions for the minimum angular momentum in binary systems of given total mass; the agreement is excellent.Finally, the existing theoretical objections to the fission hypothesis for the origin of binary stars are reviewed, and it is concluded that, although fission remains unproven, there are now no strong theoretical arguments against the process, and there is considerable observational support for its existence.
Astrometric Application of the Photoelectric Scanning Technique
Authors: Franz Otto G. 
Published: July 2016

AbstractA new photoelectric area scanner, designed primarily for observations of double stars, has been put into routine use at the Lowell Observatory. A description of the scanner and of the associated data acquisition system is given. The procedure of measuring the relative positions of double star components is described and the accuracy obtainable by this method is discussed.This contribution and a subsequent one (p. 170) will appear jointly under the title ‘A Photoelectric Area Scanner for Astrometry and Photometry of Double Stars’ inLowell Observatory BulletinNo. 154. This work has been supported by National Science Foundation Grant GP-6983.
L’observation spectroscopique des couples visuels. (Exposé Introductif)
Authors: Dommanget J. 
Published: July 2016

Le concours de diverses techniques d’observation a toujours été profitable au progrès des connaissances astronomiques.Dans le cas des couples stellaires, l’observation visuelle et l’observation spectroscopique se complètent heureusement: chacune d’elles – lorsqu’elles sont possibles – conduit à la connaissance des éléments orbitaux, sauf que la première ne fournit pas l’échelle de l’orbite en unités astronomiques et laisse subsister une certaine indétermination, relative à la position du nœud ascendant, et que la seconde n’apporte aucune information sur la valeur de l’inclinaison et sur celle de l’angle de position de la ligne des nœuds.
The Measurement of Radial-Velocity Differences Between the Components of Close Visual Binary Systems
Authors: Batten A. H. , Fletcher J. M. 
Published: July 2016

AbstractThe value obtained for the difference in radial velocity between components of a visual binary that is unresolved on the spectrograph slit appears to depend, sometimes, on whether the measurement is made visually with a microscope or by means of an oscilloscopic setting device. This apparent dependence has been confirmed by measurement of artificially produced double-lined spectrograms, and disappears for line pairs separated by more than 1.5 or 2 times the half-widths of their components. The dependence arises from blending of the two line profiles. There is some evidence that the results obtained from visual measures are affected by the scale of the image being measured. For this reason, oscilloscope measures are probably to be preferred; although their errors are sometimes larger, they seem to be more consistent. Errors arising from this sort of blending are not sufficient to explain measures of relative radial velocity of the components of some visual binaries, that differ widely from the predictions made from the visual orbits.
Calcul des Erreurs Moyennes Affectant les Mesures D’Étoiles Doubles Visuelles
Authors: Dommanget J. 
Published: July 2016

Au cours de recherches bibliographiques diverses, nous avons remarqué que bien des observateurs se sont servis et se servent encore de formules par trop approximatives pour calculer – lorsqu’ils le font – les erreurs moyennes affectant leurs mesures.Nous croyons important et opportun de rappeler ici la formule correcte dont nous avons donné une démonstration à une autre occasion (1959).
Photometric Observations of Visual Double Stars by the Area Scanning Technique
Authors: Franz Otto G. 
Published: July 2016

AbstractUBV magnitude differences in visual binaries are presented and their accuracy is discussed. Typical observed image profiles of double stars, including sample profiles of Antares, are shown.This contribution will appear jointly with the earlier one (p. 20) inLowell Obs. Bull., No. 154. The work has been supported by NSF Grant GP-6983.
A Suspected Supernova in A.D. 1181
Authors: Stephenson F.R. 
Published: July 2016

SummaryThe new star which appeared in Cassiopeia in A.D. 1181 attracted considerable attention in the Far East. It was visible for about six months, and its position was carefully recorded by the Chinese and Japanese astronomers. Their observational evidence favours the identification of the star as a supernova of type I. It is proposed that the radio source 3C 58 is the remnant of the new star.
Observed and Theoretical Values of the Nutations
Authors: Vicente R.O. 
Published: July 2016

We are here concerned with the nutations that appear in the motion of the Earth because of the existence of the external forces due to the Sun and Moon, that is, the forced nutations.We can consider the nutations divided in two groups from the point of view of their values and the precision attained by astronomical observations. The first group comprises the nutations that have values greater than 1″ and in this group we have the nutation of period 18.6 yr called the principal nutation and the value of this nutation in obliquity is called the constant of nutation. The second group comprises the nutations with values smaller than 1″ and corresponds to the great majority of all other nutations.
Precession-Nutations and Tidal Potential
Authors: Melchior P. 
Published: July 2016

We have previously established (Melchior and Georis, 1968) the equations connecting the development of precession-nutation with the tesseral part of the tidal potential. These equations are:whereωiAirespectively represent the frequencies and amplitudes of the tidal waves, ω the Earth’s rotation velocity,
Treatment of Close Approaches in the Numerical Integration of the Gravitational Problem of N Bodies
Authors: Bettis D. G. , Szebehely V. 
Published: July 2016

AbstractOne of the main difficulties encountered in the numerical integration of the gravitational n-body problem is associated with close approaches. The singularities of the differential equations of motion result in losses of accuracy and in considerable increase in computer time when any of the distances between the participating bodies decreases below a certain value. This value is larger than the distance when tidal effects become important, consequently, numerical problems are encountered before the physical picture is changed. Elimination of these singularities by transformations is known as the process of regularization. This paper discusses such transformations and describes in considerable detail the numerical approaches to more accurate and faster integration. The basic ideas of smoothing and regularization are explained and applications are given.
The Small-Scale Photospheric Magnetic Field as an Indicator of the Dynamo
Authors: Petrovay K. , Szakály G. 
Published: July 2016

AbstractThe presently widely accepted view that the solar dynamo operates near the base of the convective zone makes it difficult to relate the magnetic fields observed in the solar atmosphere to the fields in the dynamo layer. The large amount of observational data concerning photospheric magnetic fields could in principle be used to impose constraints on dynamo theory, but in order to infer these constraints the above mentioned “missing link” between the dynamo and surface fields should be found. This paper proposes such a link by modeling the passive vertical transport of thin magnetic flux tubes through the convective zone.
Spectrometer-Based Magnetographs
Authors: Jones Harrison P. 
Published: July 2016

AbstractThe techniques and instrumentation for inferring magnetic fields using a spectrometer or spectrograph rather than a narrowband filter are reviewed. With array detectors and/or Fourier transform spectroscopy, the polarimetric data is acquired over the relevant spectral range strictly simultaneously with no possibility of spatial misregistration. Several recent examples of spectrometer-based magnetographs are discussed and compared, and new observations from the NASA/NSO Spectromagnetograph of magnetic flux, velocity field, continuum intensity, equivalent width, and line depth in active regions and the whole sun are shown.
Asymmetric Stokes Q, U and V Line Profiles Observed in Sunspots
Authors: Almeida J. Sánchez , Lites B.W. 
Published: July 2016

AbstractWe present a systematic description of the asymmetric shapes the Stokes line profiles exhibit in sunspots. These asymmetries seem to be caused by gradients of both magnetic field and velocity in the photospheres of sunspots.
High Angular Resolution Stokes V Spectra in Penumbrae
Authors: Almeida J. Sánchez , Pillet V. Martínez , Bueno J. Trujillo , Lites B.W. 
Published: July 2016

AbstractStokes I and V profiles of Fel 630.1 nm and Fel 630.2 nm observed in a sunspot with an angular resolution ≥0.5” are analyzed. We find asymmetric V-profiles whose shapes are in agreement with previous determinations having lower angular resolution (~5”). We also find a correlation between penumbral small scale variations of continuum intensity and velocity. Although it involves smaller velocities, such correlation resembles that existing in the quiet sun as a consequence of convection.
Rapid Variations in Intergranular Space
Authors: Nesis A. , Hanslmeier A. , Hammer R. , Komm R. , Mattig W. , Staiger J. 
Published: July 2016

AbstractSpectrograms of high spatial resolution taken every 15s reveal rapid variations of the continuum intensity and line width. Variations of the latter seem to be related to Doppler velocity gradients.
Hard X-Ray Imaging Observations by Yohkoh of the 15 November, 1991 Flare
Authors: Sakao Taro 
Published: July 2016

AbstractWe present hard X-ray imaging observations by Yohkoh of the 15 November, 1991 flare. The pre-impulsive and the impulsive phase observations are summarized as follows: (1) Hard X-ray sources in the precursor (or pre–impulsive) phase appear in a much wider area compared with the impulsive phase sources and they show clear evolution just before the onset of the impulsive phase. This suggests that some global re-structuring of coronal magnetic fields led to the impulsive energy release. (2) In the impulsive phase, at the peaks of the individual spikes of the time profile, the bulk of the hard X-ray emission (above 20 keV) originates from the footpoints of the flaring loop. At the valleys between the spikes, X-rays below 30 keV are emitted from near the loop top, while higher energy ones (above 30 keV) are still emitted from the footpoints. Such behavior of hard X-ray sources can be explained by the partial precipitation model.
The Reversed Polarity Structures of Chromospheric Magnetic Fields in Active Regions
Authors: Li Wei , Ai Guoxiang , Zhang Hongqi , Chen Jimin 
Published: July 2016

AbstractThe reversed polarity structures of chromospheric magnetic fields are magnetic gulfs and islands of opposite polarity relative to the underlying photospheric fields. In this paper data were analyzed from the Solar Magnetic Field Telescope of the Huairou Solar Observing Station (HSOS) in Beijing. From more than 300 pairs of photospheric magnetograms (in FeIλ5324.19 Å) and relevant chromospheric magnetograms (in Hβλ4861.34 Å), the reality of the reversed polarity structures is demonstrated. According to an analysis of the fine structures of the magnetic fields in the two layers of active regions, we found that there are probably four different types.
Observational Evidence for Magnetic Reconnection in Solar Flares
Authors: Henoux J.C. , Demoulin P. , Mandrini C.H. , Rovira M.G. 
Published: July 2016

AbstractFrom studies of the magnetic topology of flaring active regions, the separator - a region were magnetic reconnection can take place - appears to be magnetically connected to places of intense chromospheric flare brightening. This suggests that magnetic reconnection occurs in the separator region in solar flares. Observational support for magnetic reconnection releasing the energy stored in field align currents systems is presented.
Some Characteristics of the Development and Emissions of May 13, 1981 Flare Related to the Flare Model
Authors: Krivsky Ladislav 
Published: July 2016

AbstractProton flare of May 13, 1981 with various emissions and with registration of loop shaped flare in hard X-ray range above new created flare channel in Hα and Hβ is related with flare loop-model published earlier at IAU Symp. No. 35 in 1967.
Analyses of Vector Magnetograms
Authors: Wang Jingxiu 
Published: July 2016

Abstract(1) Current techniques may now permit an acceptable resolution of the 180 degree ambiguity in determining the direction of transverse fields. (2) The non-potentiality of active regions can be described by parameters of angular shear, source field, line-of-sight current, force-free factor and force-free current. A 2-dimensional description of angular shear is necessary, and an alternative, FFT method of calculating the line-of-sight current seems recommendable. (3) For a sampling region, the degree of non-potentiality quantified by all the parameters shows great enhancement right before a 1M flare, and reduces somehow during the flare. (4) A highly intermittent distribution of force-free factor with fully mixed signs is obtained, consistent with a theoretical approach.
Sunspot Seismology: The Interaction of Solar p-Modes with a Sunspot
Authors: Thomas John H. 
Published: July 2016

AbstractProgress in sunspot seismology is briefly reviewed. New observations of the absorption of p-modes by a sunspot (Bogdan, Brown, Lites, and Thomas 1993) show that the absorption coefficient (averaged over frequency and azimuthal order) increases with horizontal wavenumber to a maximum near k = 0.9 Mm−1 and then decreases monotonically to zero at about k = 1.5 Mm−1. The absorption along individual p-mode ridges shows a sinusoidal-like modulation, which may be an important feature for comparison with theory. Results for the quiet Sun show no net absorption, but do show apparent emission along p1 over the same range of k where the sunspot shows its greatest absorption. This behavior, and the overall decrease in absorption at higher wavenumbers, can be explained as an effect of the decreasing lifetime of p-modes with increasing wavenumber k (increasing mode degree l).
Imaging Spectroscopy of Flows in Active Regions
Authors: Mein P. , Mein N. 
Published: July 2016

AbstractWe use imaging spectroscopy from the MSDP of the VTT telescope in Tenerife (collaboration Paris-Meudon Observatory and Kiepenheuer Institut) to analyse Doppler velocities of arch filaments in Hα and NαD1. The geometry of the magnetic loops is deduced from perspective effects with a simple dynamical model. Velocities are correlated in both lines.Further results are expected from simultaneous observations with other instruments (SVST of La Palma and Huairou magnetograph).
Unsteady Wave-Packets in the Random Ensembles of Magnetic Flux Tubes: Acoustic Halos
Authors: Ryutova Margarita , Priest Eric 
Published: July 2016

AbstractThe propagation of unsteady acoustic wave-packets in a randomly magnetized solar atmosphere is accompanied by specific morphological effects which include the spreading of the energy absorption region over scales much larger than the size of the initial energy source. One of the manifestations of these effects can be acoustic halos. The regions of an efficient energy input and their localization crucially depend on the distribution of magnetic structures in space and over their physical parameters which makes the present study useful for diagnostic goals.
Chaos and Turbulence in Solar Wind
Authors: Buti B. 
Published: July 2016

AbstractLarge amplitude waves as well as turbulence has been observed in the interplanetary medium. This turbulence is not understood to the extent that one would like to. By means of techniques of nonlinear dynamical systems, attempts are being made to properly understand the turbulence in the solar wind, which is essentially a nonuniform streaming plasma consisting of hydrogen and a fraction of helium. We demonstrate that the observed large amplitude waves can generate solitary waves, which in turn, because of some propagating solar disturbance, can produce chaos in the medium. The chaotic fields thus generated can lead to anomalously large plasma heating and acceleration.Unlike the solitary waves in uniform plasmas, in nonuniform plasmas we get accelerated solitary waves, which lead to electromagnetic as well as electrostatic (e.g. ion acoustic) radiations. The latter can be a very efficient source of plasma heating.
Observability of Coronal Heating Processes
Authors: Venkatakrishnan P. 
Published: July 2016

AbstractThe mechanisms that could possibly heat the corona are briefly reviewed with emphasis on their observability. Observing enhanced wave flux at footpoints of active regions would confirm wave heating. Observation of nonthermal electrons in tiny coronal events (nanoflares) would confirm dissipation of current sheets. Presence of large scale flows in coronal arcades would underline the importance of turbulent resistivity for coronal heating. A comparison of Hel absorption in quiet and active regions demonstrates the difficulty of interpreting data that connect chromospheric dynamics with coronal heating. Finally, the implications of the search for observations of coronal heating processes are mentioned.
Dependence of the North-South Component of IMF on the Solar Wind Acceleration
Authors: Felix Pereira B. , Girish T.E. 
Published: July 2016

AbstractThe monthly probability of occurrence of southward component of IMF estimated independent of the sector polarity observed near earth is found to change with the magnitude of solar wind velocity. The above analysis is done for each month during two years around sunspot minima and maxima in cycle 21. The results will be interpreted in terms of association of southward Bz events with solar wind flows of distinct solar origin such as low and high speed solar wind.
A Bimodal Model of the Solar Wind Speed
Authors: Coles W.A. 
Published: July 2016

AbstractUntil the ULYSSES spacecraft reached high latitude, the only means for measuring the solar wind velocity in the polar regions was from radio scattering observations (IPS), and these remain the only way to measure the velocity near the sun. However, IPS, like many remote sensing observations, is a “line-of-sight” integrated measurement. This integration is particularly troublesome when the line-of-sight passes through a fast stream but that stream does not occupy the entire scattering region. Observations from the HELIOS spacecraft have shown that the solar wind has a bimodal character which becomes more pronounced near the sun. Recent observations from ULYSSES have confirmed that this structure is clear at high latitudes even at relatively large solar distances. We have developed a method of separating the fast and slow contributions to an IPS observation which takes advantage of this bimodal structure. In this paper I will describe the technique and its application to IPS observations made using the receiving antennas of the EISCAT incoherent backscatter radar observatory in northern Scandinavia.
Solar Mass Ejections and Coronal Holes
Authors: Bhatnagar Arvind 
Published: July 2016

AbstractIn this paper we present observations of two types of solar mass ejections, which seem to be associated with the location of coronal holes. In the first type, a filament eruption was observed near a coronal hole, which gave rise to a strong interplanetary scintillations, as detected by IPS observations. In the second type, several large scale soft X-ray ‘blow-outs’ were observed in the YOHKOH SXT X-ray movies, in all the cases they erupted from or near the boundary of coronal holes and over the magnetic neutral line. It is proposed that the open magnetic field configuration of the coronal hole provides, the necessary field structure for reconnection to take place, which in turn is responsible for filament eruption, from relatively lower heights. While, in the case of X-ray ‘blow-outs’, the reconnection takes place at a greater height, resulting in high temperature soft X-ray emission visible as X-ray ‘blow-outs’.
Spectroscopic and Variability Surveys for AGN in the Groth Survey Strip
Authors: Sarajedini Vicki 
Published: July 2016

AbstractPreliminary results are presented for a spectroscopic survey of the Groth Survey Strip (GSS), a 30 by 3 arcminute region of the sky imaged with HST, for which several hundred galaxy spectra have been obtained as part of the DEEP project (http://deep.ucolick.org). At least 6 broad-line AGNs (primarily Seyfert 1s) have been detected as well as several narrow-line Seyfert 2 candidates. The seyfert galaxies detected in our survey have integrated absolute magnitudes extending to MB ~-17.5, probing fainter magnitudes and higher redshifts than existing optical spectroscopic surveys. We also discuss a variablity study of the GSS using the original HST images from 1994 and new images obtained in 2001. The high resolution obtained with HST allows us to isolate and measure variable galactic nuclei too faint to be detected from the ground, reaching nuclear magnitudes of MB~-16 in galaxies to z~0.8. The combination of these techniques provide a powerful probe of the population of low-luminosity AGNs at moderate redshifts.