bluuebunny/crossref_metadata_2025 huggingface dataset:
External and Internal Solutions for the Twisted, Flux Tube, Prominence Model
Authors: Cartledge N. , Hood A. W.
Published: July 2016

We consider a model for the support of a prominence sheet in a twisted magnetic flux tube. Solutions for the equilibrium of the sheet in a constant current density force-free field, as given by Ridgwayet al. (1991) are considered and extended to include a current sheet of finite height.

Next we consider the internal region of the prominence by “stretching” the sheet to a finite width. We can analytically select solutions for the field in this region that match onto the external force-free solutions at the edge of the prominence.

Horizontal and vertical force balance for this internal region then determines profiles for the pressure and density and the corresponding temperature may be evaluated.
Tall Coronal Jets Seen Occasionally in Hα
Authors: Rompolt B.
Published: July 2016

Some features of tall coronal jets observed at rare occasions in Hαabove the solar limb after the prominence eruptions are discussed. The jets usually reach the height of a few hundred thousands kilometers above the solar surface and exibit filamentary structure.
Wave-Based Heating Mechanisms for the Solar Corona
Authors: Malara F. , Velli M.
Published: July 2016

Dissipation of MHD waves generated in the lower solar atmosphere has long been proposed as a means to heat the solar corona. Because of the extremely low dissipation coefficients of the coronal plasma large gradients are necessary to efficiently dissipate such waves. Interactions with the inhomogeneities of the background medium may represent a way to create small scale structures, phase-mixing and resonant absorption being important examples. The generalization of such ideas to propagation in complex geometries (e.g., containing X type neutral points) and the extension to nonlinear effects are paramount to the development of wave-heating theories.
Coronal Mass Ejections and the Rise Profiles of 0.3 MeV Electron Events
Authors: Kahler S. W. , Stolpovskii V. G. , Daibog E. I.
Published: July 2016

There is some evidence to suggest that relativistic electrons observed in interplanetary space may be produced in coronal shocks. If so, the rise phases of such events may be longer than those not arising in shocks. To test this possibility, we examined the rise profiles ofE< 0.3MeVelectron events observed on the Helios spacecraft. First we compared rise times of electron events associated with short-duration X-ray flares to events with long-duration X-ray flares. The latter events are more likely than the former to be associated with coronal shocks and coronal mass ejections (CMEs). For a smaller group of electron events we determined the rise times as a function of the speed of the CME observed with the NRL Solwind coronagraph to see whether higher shock speeds resulted in longer event rise times. The data show a weak indication that event rise times increase with CME presence and with CME speed, thus suggesting a role for shock acceleration.
Interactions of Coronal Streams
Authors: Odstrčil D.
Published: July 2016

The two-dimensional hydrodynamic model is used to investigate some details of interaction of fast and slow coronal streams. Shock pair structure is formed due to collision of streams and a cocoon is formed due to deflection of compressed fast-stream plasma. Relatively small amplitudes of pressure modulation at the inner boundary have relatively large consequences: shock wings are gradually formed and they become stronger for larger heliocentric positions. Boundaries between the fast and slow coronal streams are stable against small random fluctuations and against small introduced disturbances and the Kelvin-Helmholtz instability is not initiated.
The Corona Electropolarimetry during July 11, 1991 Solar Eclipse
Authors: Kulidzanishvili V. , Mayer A. , Mayer V. , Danik S.
Published: July 2016

The electropolarimetry of July 11, 1991 eclipse solar corona using the new photoelectric polarimeter of Abastumani Astrophysical Observatory of the Georgian Academy of Sciences, equipped with the IBM computer, is described in this paper.

By means of measurable values the isopolarization lines were constructed, which turned out to be stretched along the coronal streamers. The polarization plane has, entirely, radial direction; however, small but real deviations from radiality were established. The errors of measurements of intensity, polarization degree and polarization plane direction are evaluated.
Fine Structures of the Inner Corona Observed at the 1991 Total Solar Eclipse
Authors: Takeda A. , Kurokawa H. , Kitai R. , Ishiura K.
Published: July 2016

Extended Abstract

The Kwasan and Hida Observatories team (three of the authors but A. T.) observed the total solar eclipse of 11 July, 1991 with the multi-channel telescope at UABCS (Universidad Autonoma de Baja California Sur) campus in La Paz, Baja California Sur, Mexico. The primary purpose of our obsevation is to get high-resolution images of the inner corona at the wavelength of coronal emission lines and continuum shown in Table 1. Thanks to the clear sky and good seeing condition, we successfully got many images of high spatial resolution with photographic cameras and video recorders. Details of the observation have already been published by Kurokawaet al. (1992). In this paper, we present the results obtained from the photographic data reduction on fine structures of the inner corona. The procedure of photometrical measurement and image processing are fully described in another paper (Takeda, 1993).

There have been published several observational works on the temperature structure of the coronal loops. Some authors proposed that hot coronal loops have cool cores (Foukal, 1975; Hanaokaet al., 1988), but others denied such coaxial models (Chenget al., 1980; Dere, 1982). Our high-resolution images obtained at the eclipse enables us to compare the positions of the loops seen in different emission lines of different ionization temperatures more precisely than any other previous observations. Main results are summarized as follows.
Hα Limb Evolution around the 1990 and 1991 Total Solar Eclipses
Authors: Bücher A. , Noëns J.-C.
Published: July 2016

At the periods of the total solar eclipses of July 1990 and 1991 a survey in the Hαlight was performed at Pic-du-Midi. Maps of the limb evolution are described and discussed.
Very High Resolution Analysis of the Dynamics of a Coronal Plasmoid
Authors: Bouchard O. , Koutchmy S. , November L. , Vial J.-C. , Zirker J. B.
Published: July 2016

We present the results of the analysis of a movie taken over a small field of view in the intermediate corona at a spatial resolution of 0.5“, a temporal resolution of 1 s and a spectral passband of 7 nm. These CCD observations were made at the prime focus of the 3.6 m aperture CFHT telescope during the 1991 total solar eclipse.
Colour Photometry of the Solar Corona of July 11, 1991
Authors: Alexeyeva I. V. , Kroussanova N. L. , Streltsova M. V.
Published: July 2016

The results of photometry of colour positives of the solar corona of July 11, 1991 are presented. Observations of the white corona were made without radial niters in Jojutla (Mexico). Dependences of coronal brightness on distance in the red (640 nm) and blue (420 nm) wavelength intervals are deduced for different coronal structures up to 3.0-3.5R⊙. The effect of ”reddening“ is noted. The excess of the red emission to the blue one (I640nm/I420nm) is found to be 1.20 and 1.17 at distance of 2.2R⊙for the N-E helmet streamer (P ≃ 37°) and the N-W region of low brightness (P ≃ 339°), respectively.
Equation of State of Stellar Plasmas
Authors: Rogers Forrest J.
Published: July 2016

The equation of state (EOS) of astrophysical plasmas is, for a wide range of stars, nearly ideal; with only small non-ideal Coulomb corrections. Calculating the EOS of an ionizing plasma from a ground state ion, ideal gas model is easy, whereas, fundamental methods to include the small Coulomb corrections are difficult. Attempts to include excited bound states are also complicated by plasma screening and microfield phenomena that weaken and broaden these states. Nevertheless, the high quality of current observational data, particularly seismic, dictates that the best possible models should be used. The present article discusses these issues and describes how they are resolved by fundamental many-body quantum statistical methods. Particular emphasis is placed on the activity expansion method that is the basis of the OPAL opacity code. Some comparisons with standard methods are given.
A Comparative Study of Hydrogen Equations of State
Authors: Saumon D.
Published: July 2016

The numerous complexities underlying large tables of thermodynamic quantities act as a deterrent to a careful evaluation of their reliability. As a consequence, equations of state are often used as black boxes. To clarify this situation, some of the more critical issues of equation of state physics are discussed from the point of view of the user. They are illustrated by a comparison of four equations of state for hydrogen. The flaws and disagreements thus brought into light are explained and evaluated with simple physical arguments.
Strongly Coupled Ionic Mixtures and the H/He EOS
Authors: DcWitt Hugh E.
Published: July 2016

This paper summarizes recent work on the strongly coupled OCP and Binary Ionic Mixture equation of state and other thermodynamic quantities in white dwarf interior conditions for both fluid and solid phases with the assumption of a uniform background. Conditions for phase separation of different elements in fluid or solid phases is strongly dependent on deviations from the linear mixing rule which gives the equation of state as an additive function of the OCP equation of state. These deviations turn out to be small (a few parts in 105) and always positive including the case where the fraction of the higher Z component approaches 0. Also the equation of state of strongly coupled light elements (H and He particularly) obtained from simulations with a linear response description of the electrons is given for conditions appropriate to brown dwarf star interiors. Recent Livermore work on a band structure calculation of the enthalpy of H and He mixtures under jovian conditions is discussed. This work leads to a prediction of a high temperature (15000 °K) for miscibility of He in ionized H at 10 Mb.
Towards A Helioseismic Calibration of The Equation of State of The Plasma in The Solar Convective Envelope
Authors: Vorontsov S. V. , Baturin V. A. , Gough D. O. , Däppen W.
Published: July 2016

We report the results of a nonlinear inversion of solar oscillation data that enable us to detect nonideal Coulomb interactions between particles, including pressure ionization, in the solar convection zone.
Thermal Cyclotron and Annihilation Radiation in Strong Magnetic Fields
Authors: Bezchastnov V.G. , Kaminker A.D.
Published: July 2016

The cyclotron and the one-photon annihilation emissions are investigated for a strongly magnetized thermal electron-positron plasmas. The annihilation spectral component is significant when the particle number density N exceeds some critical value, Ncr(T,B). For T ~ 108 − 109 K and B ~ 1012 − 1013 G, this condition can be fulfilled at N < 1022 cm−3, which is realistic for neutron star magnetospheres.
Time and Latitude in South Africa
Authors: Hers J.
Published: July 2016

In South Africa the modern outlook towards time may be said to have started in 1948. Both the two major observatories, The Royal Observatory in Cape Town and the Union Observatory (now known as the Republic Observatory) in Johannesburg had, of course, been involved in the astronomical determination of time almost from their inception, and the Johannesburg Observatory has been responsible for the official time of South Africa since 1908. However the pendulum clocks then in use could not be relied on to provide an accuracy better than about 1/10 second, which was of the same order as that of the astronomical observations. It is doubtful if much use was made of even this limited accuracy outside the two observatories, and although there may – occasionally have been a demand for more accurate time, it was certainly not voiced.
Time and Latitude Results of the Danjon Astrolabe Program at Santiago
Authors: Angulta C. , Noël F.
Published: July 2016

A brief report is given of the Danjon astrolabe program of Santiago de Chile, a description of the observation method, the reduction system and the Instrumental equipment. By means of the latitude and time determination a study of the variation of the latitude and earth rotation during the period 1966-1967, is made.
The Attachment of PZT’s to FK4
Authors: Tanner R. W.
Published: July 2016

The photographic zenith tube (PZT), observing a narrow band of generally faint stars in the zenith, obtains latitude and time results of high precision in the system of its catalogue. It is desirable that this system coincide with the fundamental system, as represented by FK4; to this end, other instru ments observe both the FK4 stars and the fainter PZT stars. I here consider some questions raised by the results of one such program of observation.
Secular Motion of the Pole and Changes in Geographical Coordinates
Authors: Markowitz Wn.
Published: July 2016

Changes in geographical coordinates due to station – drift must be separated from changes due to the secular – motion of the pole. A simplified PZT has been designed to aid in the study of these effects.
The Interaction of Rotation with Convection
Authors: Durney Bernard R.
Published: July 2016

The equations for a rotating convective spherical shell are solved in the Herring approximation as an initial value problem. The main results are

(1)

The most unstable modes (those that maximize the heat flux) correspond to convective cells stretching from pole to pole.

(2)

The calculations of the Reynolds stresses show transport of angular momentum towards the equator. That is, differential rotation sets in with equatorial acceleration.

(3)

The convective heat transport is maximum at the equator. This would give rise to an equator-pole flux difference.

(4)

If convection is non-axisymmetric (as in the most unstable modes) there are no time independent solutions. The time dependence is oscillatory and of the form ωt + mφ.
Étoiles doubles révélées par leurs mouvements propres communs
Authors: Deutsch A. N.
Published: July 2016

L’observatoire de Poulkovo a publié dans plusieurs mémoires les mouvements propres des 50000 étoiles jusqu’à la 15-me grandeur photographique obtenus par l’astrographe de la Carte du Ciel. Dans la présente étude nous avons utilisé 74 aires de Kapteyn et 25 autres aires ayant au centre les amas stellaires, les nébuleuses planétaires, les Novae etc. Nous avons profité en outre de résultats du catalogue de Radcliffe [9] qui nous a fourni 41 aires de Kapteyn de plus. Donc on peut admettre que nous avons examiné 200 degrés carrés c’est à direde la sphère céleste.
Contribution à la mesure des binaires visuelles au moyen de la camera électronique Lallemand
Authors: Laques P.
Published: July 2016

En 1961, au cours du Symposium IAU sur ce même sujet, M. Rösch avait déjà annoncé l’intérêt que pourrait présenter l’utilisation d’un convertisseur d’image de type Lallemand pour la photographie des étoiles doubles. Des essais prometteurs avaient déjà été faits sur le réfracteur de 60 cm du Pic-du-Midi. Depuis, et surtout à partir de 1965, un programme a été poursuivi, au moyen du nouveau réflecteur de 106 cm de cet Observatoire. Plus d’une centaine de plaques ont pu être prises. Ce sont l’exposé de cette nouvelle méthode photographique, et les résultats des mesures obtenues, que nous avons l’intention d’aborder ici.
Photovisual Magnitude Differences of Double Stars
Authors: Strand K. Aa.
Published: July 2016

Differences in magnitudes between the components of 874 double stars have been derived from visual estimates on several series of multi-exposure photographic plates. The plates were obtained with long focus refractors primarily for the purpose of determining the relative positions of double stars according to the well-known Hertzsprung method.
Close Binaries: Theoretical Computations
Authors: Paczyński B.
Published: July 2016

There is a number of review articles concerned with the theory of evolution of close binaries. Plavec (1968) has given a thorough description of the development of the theory. There is also a short review of the recent advances in this field by Weigert (1969). I would like to restrict myself today to those phases of evolution of close binaries that are reasonably well understood. I would like to emphasize the most important assumptions made in the model computations, and to discuss the limitations imposed on our studies by those assumptions.
Gains Realized with Electronic Observing and Measuring Instruments at the Hale Observatories
Authors: Dennison Edwin W.
Published: July 2016

During recent years it has often been stated that the introduction of automatic electronic equipment can provide two benefits for the astronomical observer. The first is that he can make observations which he could not make with older methods. The second is that he can do the same job more rapidly, more thoroughly, and more efficiently than he had been able to do previously. The first benefit has obviously been realized with many pieces of equipment and I will not concentrate on this point. The second has been a very real one also, and I would like to report on some of the gains which have been made at the Hale Observatories by the introduction of modern electronic equipment. Because of the power which can be brought to bear on astronomical observing problems by the use of digital electronic techniques, almost all of the equipment which I will describe is in one way or another digital in nature.
Common Proper Motion Stars in a Southern Zone Catalogue
Authors: Hoffleit Dorrit , Paranya Katharine
Published: July 2016

In the recent Yale Zone Catalogues star charts have been included showing 20,000 year changes in star positions indicated by the proper motions of the catalogued stars. An inspection of such charts (e.g. Figure 1) reveals some widely scattered stars which seem to share large proper motions. In the Zone Catalogue for -40° to -50°, just published as Vol. 30 of the Transactions of the Yale University Observatory, we have indicated some fifty pairs or groups of stars appearing to have closely the same proper motions exceeding 0.”100. The numbers of stars represented in each group range from two to fifty. In general, the largest groups correspond to the smallest motions, where the uncertainties are also the greatest. The average number of stars per group decreases from eleven for proper motions between 0.”100 and 0.”200, to three between 0.”300 to 0.”500, to two for proper motions exceeding 0.”500.
Effective Temperatures of White Dwarfs
Authors: Oke J. B.
Published: July 2016

Of all the fields of stellar astronomy, the study of white dwarfs has been most influenced by work done on proper motions. From proper motion studies, particularly by Luyten and Giclas in recent years, many white dwarf candidates have been found. These candidates have been studied intensively, particularly by Greenstein who has obtained spectra and Eggen who has measured magnitude and colors. As a result, many new white dwarfs have been discovered, and we now have many examples of most types of white dwarfs. It is, therefore, possible to study each group separately and to find relationships between the various types of white dwarfs.
Can the Fundamental System be Replaced by a Reference System of Galaxies
Authors: Fricke Walter
Published: July 2016

Quasistellar objects with and without radio emission have recently given unforeseen and vigorous impetus to astrometry. Great effort has been made in the search for the optical counterparts of radio sources. For the purpose of identifications accurate positions were demanded, optical as well as those by radio techniques. Optical positions of radio sources are also needed to serve as calibrators for radio positions. In all cases the objects under consideration are optically much fainter than those ever used previously in high precision astrometry. Finally, methods have been developed for the absolute measurement of radio positions to an accuracy which competes with that known from fundamental observations of bright stars.
First Results of the Lick Proper Motion Program
Authors: Vasilevskis S. , Klemola A. R.
Published: July 2016

Photography of the second epoch of the Lick Proper Motion Program (Wright 1950) was started in 1968. The original plan (Vasilevskis 1954) was modified in several respects. It was decided to carry out a pilot program first, before the start of a full coverage of the sky accessible from Lick. It was also decided to make use of the new lens corrected for yellow light (Vasilevskis 1964), in addition to the blue lens used for the first epoch. The aims of the pilot program were formulated: (1) carry out the necessary error investigations, (2) develop methods and procedures to a stage of routine, (3) derive proper motions of stars measured, and (4) attempt to arrive at some astronomical conclusions based on these motions. The program was limited to 97 fields nearly uniformly distributed over the sky north of -23° all these fields were photographed, measured and reduced, 78 of them contain a sufficient number of galaxies for proper motion reference. This report will be limited to presenting a few results obtained from the first crude analysis of proper motions that became available only a week ago. These results, therefore may change significantly in the process of further analysis.
Use of the Overlap Method for the Connexion of Proper Motions to Galaxies Problems of the Zone Without Nebulae
Authors: Lacroute P.
Published: July 2016

There are two methods for connecting the proper motions to the galaxies. The one used under the direction of A. N. Deutsch at Pulkovo, and the other method at the Lick Observatory.

Only the method used by the Lick Observatory allows the use of overlapping plates. It is the only one which will be dealt with in this first part.
Theoretical Computations on the Efficiency of the Overlap Method in the Lick Program
Authors: Lacroute P. , Valbousquet A.
Published: July 2016

The theoretical computations suggested in section 5 of the preceeding paper have now been done.

It is necessary to do many approximations in order that the successive values of ∑β2 give the limit. We have done as many as 8. After that the computation becomes too difficult.
IAU Colloquium No. 8: Experimental Techniques for the Determination of Fundamental Spectroscopic Data
Authors: Shore Bruce W.
Published: July 2016

The last ten years have brought significant changes to the venerable disciplines of astronomy and spectroscopy. Traditionally astronomers sought wavelength catalogues of identified spectra lines. Under this impetus spectroscopists laboured to provide very accurate wavelength measurements and estimates of emission line intensity. Physicists and astronomers alike are now recognizing interest not only in such properties of isolated atoms as energy levels (or spectral-line wavelengths) and oscillator strengths, but also those atomic properties which depend upon the surroundings of a radiating atom: spectral-line profiles, excitation rates, and level populations. In turn, new uses of lasers and interferometers, fast time resolution, and simple but significantly different absorption and emission samples are altering experimental spectroscopy almost beyond recognition. The present colloquium, chaired by A.H.Cook (University of Edinburgh) and held at Imperial College, London, on September 1-4 1970, aimed to identify the means by which astronomers can now obtain fundamental atomic data.
Exact Statistical Mechanics of a One-Dimensional Self-Gravitating System
Authors: Rybicki George B.
Published: July 2016

The statistical mechanics of an isolated self-gravitating system consisting ofNuniform mass sheets is considered using both canonical and microcanonical ensembles. The one-particle distribution function is found in closed form. The limit for large numbers of sheets with fixed total mass and energy is taken and is shown to yield the isothermal solution of the Vlasov equation. The order of magnitude of the approach to Vlasov theory is found to be 0(1/N). Numerical results for spatial density and velocity distributions are given.
Evolutionary Models of Nucleosynthesis in the Galaxy
Authors: Truran J. W. , Cameron A.G.W.
Published: July 2016

A model of the galaxy is constructed and evolved in which the integrated influence of stellar and supernova nucleosynthesis on the composition of the interstellar gas is traced numerically. Our detailed assumptions concerning the character of the matter released from evolving stars and supernovae are guided by the results of recent stellar evolutionary calculations and hydrodynamic studies of supernova events. Stars of main sequence mass in the range 4 ≤M≤ 8 M⊙are assumed to give rise to supernova events, leaving remnants we identify with neutron stars and pulsars and forming both the carbon-to-iron nuclei and the r-process heavy elements in the explosive ejection of the core material. For more massive stars, we assume the core implosion will result in the formation of a Schwarzschild singularity, that is, a black hole or ‘collapsar’. The straightforward assumptions (1) that the gas content of the galaxy decreases exponentially with time to its present level of ~ 5 % and (2) that the luminosity function characteristic of young clusters and the solar neighborhood is appropriate throughout galactic history, lead to the prediction that ≈ 20% of the unevolved stars of approximately one solar mass (M⊙) in the galaxy today should have metal compositionsZ ≲0.1 Z⊙. As Schmidt has argued from similar reasoning, this is quite inconsistent with current observations; an early generation dominated by more massive stars – which would by now have evolved – is suggested by this difficulty. Many of these massive stars, according to our assumptions, will end their lives as collapsed black hole remnants. It is difficult to visualize an epoch of massive star formation in the collapsing gas cloud which formed our galaxy which would enrich the gas rapidly enough to account for the level of heavy element abundances in halo population stars; we have therefore proposed a stage of star formation which is entirely pregalactic in character. We suggest that the Jeans’ length-sized initial condensations in the expanding universe discussed by Peebles and Dicke may provide the appropriate setting for this first generation of stars. Guided by these considerations, and by the need for a substantial quantity of ‘unseen’ mass to bind our local group of galaxies, we have constructed a model of the galaxy in which this violent early phase of massive star formation produces both (1) approximately 25 % of the level of heavy elements observed in the solar system and (2) an enormous unseen mass in the form of black holes. The implications of our model for other features of the galaxy, including supernova nucleosynthesis, the cosmic ray production of the light elements, and cosmochronology, are discussed in detail.
On Combined Operational Method for Transfer Problems in Homogeneous, Spherical Media
Authors: Kho T. H. , Sen K. K.
Published: July 2016

In this paper, the Combined Operational Method developed by Busbridge (1961) in connection with the radiative transfer problems in plane-parallel atmospheres has been extended to similar problems in isotropic scattering, homogeneous spherical media. The relevant auxiliary equation has been formulated, the scattering function defined and the integro-differential equation for such function deduced. For a medium having radial distribution of source in addition to the incident flux at the outer surface, the integro-differential equations for source function and emergent intensity have been established.
Doppler Motions in Active Regions and in the Surrounding Photosphere
Authors: Bumba V. , Klvaňa M.
Published: July 2016

We present the preliminary results of photoelectric measurements of line-of-sight motions in the quiet and active photosphere. We show the topology, amplitudes and signs of Doppler motion distribution in active regions and their surroundings. We pinpoint the different characters of both topologies.
Polarimetric Measurements of the Fine Structure of a Sunspot Penumbra
Authors: Hofmann J. , Deubner F.-L. , Fleck B. , Schmidt W.
Published: July 2016

Observations of a fairly regular sunspot penumbra near disk center have been carried out using a Stokes V polarimeter at the German Vacuum-Tower-Telescope in Izaña, Tenerife. We obtained two-dimensional spectral data by scanning the limb oriented sector of the penumbra in steps of 1” with the slit parallel to the solar limb. From Stokes V and Stokes I spectra of four magnetic sensitive lines (Fe I 5247.1, Cr I 5247.6, Fe I 5250.2, and Fe I 5250.7) obtained with 1024 × 1024 pixel CCDs we have determined Doppler shifts and several magnetic parameters. The results of a correlation analysis point out a clear relation between continuum brightness and magnetic field inclination in the sense of steeper field lines in the bright penumbral filaments. There is also a doubtless connection between intensity and Doppler shift. We did find indications for a correlation between field strength and brightness which is not uniform across the penumbra, though.
Field Strength Vs. Temperature Relation and the Structure of Sunspots
Authors: Solanki S.K. , Walther U. , Livingston W.
Published: July 2016

The relationship between the magnetic vector and the temperature of a large symmetric sunspot is studied on the basis of 1.56 µm spectra. From this relation we estimate the shape of the τ = 1 surface. i.e. the Wilson depression, as a function of radial distance in the sunspot. We find that the Wilson depression is relatively small throughout the penumbra and changes by 200–500 km at the umbral boundary. We also estimate the magnitude of magnetic gradients and curvature forces.
Evershed Effect in Sunspots and their Canopies
Authors: Solanki S.K. , Montavon C. , Livingston W.
Published: July 2016

An analysis of Stokes I and V profiles of 1.56 µm lines of sunspots near the solar limb shows that the magnetic field continues outside the visible contours of sunspots in the form of a low-lying superpenumbral canopy. We also find that the V profiles formed in the canopy exhibit the Evershed effect (with line shifts of 1–2 km s−1), while the matter below it shows no sign of a flow. Therefore, the Evershed effect definitely is present beyond the visible sunspot boundary. However, if we interpret the line shifts in terms of stationary flows, then only a small fraction of the matter seen to be flowing outwards in the penumbra can be accounted for by the outward flow in the superpenumbral canopy. Therefore, although the Evershed “flow” does not stop at the boundary of the spot, most of the flowing matter stops or disappears there.
Velocity Fields in the Filament Regions: Structure and Evolution
Authors: Ioshpa B. , Kulikova E.
Published: July 2016

The velocity structure in the photosphere under the Hα-filaments is analyzed. The results bring to suggestion that the velocity structure are connected with the stability and the type of the filament.
The Distribution of Sunspot Decay Rates
Authors: Pillet V. Martínez , Moreno-Insertis F. , Vázquez M.
Published: July 2016

The distribution of sunspot decay rates is studied using the Greenwich Photoheliographic Results (GPR). The decay rates are seen to be lognormally distributed. An analysis of the lognormal distributions associated to each sunspot group type and for isolated spots is presented. As a remarkable property of the decay process, we show that it happens at a constant total to umbral area ratio.
Delta-Sunspots and X Class Flares in Solar Cycle 22
Authors: Shi Zhongxian , Wang Jingxiu
Published: July 2016

A sample of 221 active regions with δ magnetic configurations from 1986 to 1991 in Solar Cycle 22 is used to investigate the characteristics of δ-sunspots and the relationship between the δ-sunspots and X class X-ray flares.
Computational Modeling of Solar Magnetic Fields
Authors: Sakurai Takashi
Published: July 2016

Modeling techniques for solar magnetic fields are discussed. As an extension of the source surface model for large scale solar magnetic fields, a method based on the Green’s function approach to the Laplace equation is proposed. In the force-free field modeling, a proper definition of the boundary condition is an important but still unresolved problem. A condition based on the continuity of the Maxwell stress is newly proposed.
Thermal and Hall-Current Instabilities in a Current Sheet and the Triggering of two Ribbon Flares
Authors: Jae Li Sang
Published: July 2016

Thermal stability of a current sheet is investigated when the magnetic field is not perfectly anti-parallel at the sheet. If the effect of Hall electric current is taken into account, a new instability (the Hall instability) appears. The result is applied to the activation of dark filaments often seen prior to solar flares. The growth time of the instability is evaluated and found to be consistent with the observed time scale of the filament activation.
On the Inference of Magnetic Field Vectors from Stokes Profiles: A Generalization of the Weak-Field Approximation
Authors: Qu Zhong-Quan , Ding You-Ji , Xuan Jia-Yu , Ye Shi-Hui
Published: July 2016

A generalization of Jefferies et al’s weak-field approximation for the inference of the strength and polar angle of magnetic field vectors from Stokes profiles is obtained while the inference of azimuthal angle follows a relationship derived by Landi Degl’Innocenti’s perturbative solutions to the transfer equations in which the magneto-optical effect is taken account. It is found that the weak-field condition (ΔλH / ΔλD ≤1) is not necessary for the new method when the fitting is done in the line wings.
Numerical Simulation of the Explosive Events in the Solar Atmosphere
Authors: Jiu Shu-Ping
Published: July 2016

Explosive events are the earliest indicators of flare activity and potentially predict the imminent occurrence of a flare at a specific location. They are highly energetic small-scale phenomena which are frequently detected throughout the quiet and active sun. The observations show that explosive events are related to emerging magnetic flux and tend to occur on the edges of high photospheric magnentic field regions. The cancellation of photospheric magnetic flux are the manifestation of explosive events, so that they are identified as the magnetic reconnection of flux elements. We assume that emerging flux are convected to the network boundaries with the typical velocity of intranetwork elements. Two-dimension (2D) compressible MHD simulations are performed to explore the reconnection process between emerging intranework flux and network field. The numerical results clearly show the cancellation of magnetic flux and the acceleration of the plasma flow.
Progress in the Measurement of Solar Magnetic Fields
Authors: Ai Guoxiang
Published: July 2016

The historical development of optical instruments for solar physics is outlined, from white light to unpolarized and polarized monochromatic light, to Stokes profiles and simultaneous fields of view, from points to lines, plane to cube. An evolutionary series and classificaton of instruments for the solar magnetic field is described. As a next step the 2-D real time polarizing spectrograph has been proposed. The planned instruments in China for measurements of solar magnetic and velocity fields are briefly introduced.
SIMURIS: High-Resolution Solar Physics
Authors: Rutten Robert J. , Damé Luc
Published: July 2016

The magnetic fields of the Sun provide the major incentive to do solar physics. The small spatial extent of the magnetically constrained structures and processes in the solar atmosphere provide the major incentive for high resolution solar telescopes. The visibility of the outer solar atmosphere in the ultraviolet and X-ray domains provide the major incentive for solar space telescopes. Cost provides the major incentive to use interferometric techniques. SIMURIS employs short-wave interferometry from space to measure solar structures and processes with high resolution.
Solar Radio S-Component Variation with the Magnetic Field of Active Regions
Authors: Zhao Ren-Yang
Published: July 2016

According to an active region model proposed in the present paper, i.e. three-dimensional and continuous distributions of the three plasma parameters (electron temperature, electron density, and magnetic field) from the active region to the quiet region, and using the combined mechanisms of gyroresonance radiation and bremsstrahlung, we have researched the solar radio S-component (i.e. the slowly varying component or SVC) variation with the magnetic field of active regions.
Solar Activity Observed with the New Nobeyama Radioheliograph
Authors: Enome Shinzo , Nakajima Hiroshi , Shibasaki Kiyoto , Nishio Masanori , Takano Toshiaki , Hanaoka Yoichiro , Torii Chikayoshi , Sekiguchi Hideaki , Kawashima Susumu , Bushimata Takeshi , Shinohara Noriyuki , Irimajiri Yoshihisa , Koshiishi Hideki , Kosugi Takeo , Shiomi Yasuhiko , Sawa Masaki , Kai Keizo
Published: July 2016

The new Nobeyama Radioheliograph was completed in March 1992 after two years of construction. It is a T-shaped array operating as a multiple spacing grating-type radio interferometer at 17 GHz and is dedicated to full disk solar observations. Routine observations began in late June, 1992, after three months of system integration, fine tuning, and test observations. During the course of test observations it was shown that major items of the system performance exceeded the designed values, and that the image quality or the dynamic range of the images is better than the designed value. In the three months of routine observations two X-class flares, several M-class flares and a number of small flares were observed. In this report we present a summary of initial observational results and preliminary comparisons with YOHKOH HXT and SXT observations.
Flows, Evolution of Magnetic Fields, and Flares
Authors: Wang Haimin
Published: July 2016

This paper reviews observations on the evolution of magnetic fields and flows in active regions which produce major flares. It includes the following topics: (1) Relationship between magnetic shear and flares; (2) Relationship between electric currents and flares; (3) Flows in active regions, particularly the emergence of new flux inside sheared penumbrae, and the mixed magnetic polarity nature of this kind of flux emergence; and (4) Changes of magnetic structure immediately before and after major solar flares; in particular, I will describe some recent findings that shear may increase after major flares.
Observations of X-Ray Jets Using Yohkoh Soft X-Ray Telescope
Authors: Shibata K. , Ishido Y. , Acton L. , Strong K. , Hirayama T. , Uchida Y. , Mcallister A. , Matsumoto R. , Tsuneta S. , Shimizu T. , Hara H. , Sakurai T. , Ichimoto K. , Nishino Y. , Ogawara Y.
Published: July 2016

Time series of SXT (Soft X-ray Telescope) images have revealed many jet-like features in the solar corona. Typical size of the “jet” is 5 × 103 – 4 × 105 km, the typical projected velocity is 30 – 300 km/s, and the kinetic energy estimated to be 1025 – 1028 erg. Many of the jets are associated with flare-like bright points or sub-flares. Three typical examples are discussed, including an X-ray jet identified with an Hα surge. It is suggested that magnetic reconnection is one of the possible mechanisms to produce these X-ray jets.
Statistical Characteristics of Solar Proton Flares
Authors: Wang Jia-Long
Published: July 2016

An investigation of the statistical behaviour of solar flares responsible for the proton events detected at the earth orbit would be of significance for solar physics and sun-earth research. Based on the data given by Kunches (1992) and other relevant data, we study the statistical behaviour of solar proton flares. The asymmetry of distributions, special property of hard X-ray bursts and relation to the large scale mean magnetic field of the proton flares are given in this paper.
A Statistical Study of Flares as Self-Organized Critical Phenomena
Authors: Nakagawa Yoshinari
Published: July 2016

The statistical property of flares is examined in terms of the number of flares versus its magnitude, i. e. the “Importance” reported in the IAU Quarterly Bulletin of Solar Activity for 1961–1983. It is shown that the number of flare and its magnitude follow a power law relationship indicative of the self-organized critical phenomenon, regardless of the phase of the solar cycle.
Solar Flares in Centers of Activity with No Spots
Authors: Šeršeň Michal
Published: July 2016

This paper presents a study of 9 “spotless” flares of H-alpha importance 1 or more which occurred in the years 1981-1990. The flares occurred in positions where no active region has been reported. All the flares were found to occur in evident and well-localized plages, large and diffusive plages as well as in regions where no plage was observed. Only one of all the flares studied in the paper was reported to be accompanied by the filament activity.
Nonlinear Mode Coupling of Resistive Instability and the Flares of February 4 and 6, 1986
Authors: Deng X.H. , Wang S.
Published: July 2016

In this paper, we propose a mechanism of solar flare based on the 3-D nonlinear mode coupling of resistive tearing instability. The results show that the nonlinear coupling of tearing modes leads the rapid destabilization of some high modes. Furthermore, tearing mode turbulence is formed and anomalous resistivity is produced, which in turn, quickens the development of tearing instability and accelerate the magnetic reconnection process. It is suggested that the fast magnetic reconnection as a mechanism of solar flare may be associated with this self-excited process caused by the nonlinear mode coupling of tearing instability in the solar corona. Using our model, we successfully explain all the main typical characters of the flares of February 4 and 6, 1986.
Calcium K-Line Profiles as a Function of Latitude and Solar Cycle Phase
Authors: Singh Jagdev
Published: July 2016

Astract

High resolution spectra are being taken in ionized calcium K-line at different latitudes and integrated over the visible 180 degree longitude. These have been analysed to study the variability of the line parameters as a function of latitude. These spectra are being obtained on a regular basis and large data base will be used to study chromospheric rotation, differential rotation in chromosphere, activity and variability of K-line parameters as function of latitude and solar cycle phase. Further, an optical arrangement has been worked out to obtain the spectra along the latitudes of the solar image in the light integrated over longitudes. This involves the unidirectionally focusing of the image in N-S direction.
Magnetic Field Topology in Solar Active Regions
Authors: Seehafer N.
Published: July 2016

In solar active regions, over extended periods of time the plasma-magnetic field configuration evolves quasistatically through a sequence of nearly force-free equilibrium states. This evolution may be understood as the continual distortion of an existing equilibrium by wavelike disturbances propagating upward from the photosphere and subsequent fast relaxation to a new, neighbouring equilibrium. In the present paper the build-up of magnetic energy, which is presumably necessary for flares and other explosive events, during a quasistatic evolution is considered. If during the slow evolution the magnetic energy is increased, then the relaxation processes represent inverse cascades of energy. We study the conditions under which such cascades are possible within the framework of mean-field MHD. In contrast to the convection zone, where the dynamo for the global magnetic field of the Sun works, the solar atmosphere is convectively stable and the first order smoothing approximation justified. It turns out then that current helicity (B.∇ × B) is an important quantity decisive for whether magnetic energy can be built up.
Effect of Sheared Flow on Resistive Tearing Instability and the Triggering of Flare
Authors: Deng X.H. , Wang S. , Chen J.M. , Zhang H.Q. , Ai G.X.
Published: July 2016

The nonlinear evolution of tearing modes in the presence of sheared mass flow is studied in the cylindrical geometry. It is demonstrated that a sufficient large sheared mass flow can destabilize the development of resistive tearing instability. It is suggested that the coupling of sheared mass flow with shear magnetic field may be a triggering of solar flares.
Hα Surge Activity at the First Stage of Magnetic Flux Emergence
Authors: Kurokawa Hiroki , Kawai Goro
Published: July 2016

We present a new observational evidence of the magnetic field reconnection in emerging flux regions (EFR). Our observations show that Hα surges are the first active manifestation of emerging magnetic field in some EFRs. We call them EFR-surges. Examining their morphological and evolutionary characteristics, we conclude that they are produced by the magnetic field reconnection between the EFR and the pre-existing surrounding region.
The Sun’s Rotation Near the Interface Between its Convective and Radiative Zones: 1986 to 1990
Authors: Goode Philip R.
Published: July 2016

The Sun’s rotation rate near the base of its convection zone might be expected to vary over the solar cycle because of related changes there in the magnetic field. Helioseismic analyses have taught us that much of the Sun’s convection zone rotates with surface-like differential rotation and a transition toward solid body rotation beneath. For a review of what we know about the Sun’s internal rotation, see Goode, et al.(1991). We now have sufficient solar oscillation data to look for changes in the internal rotation near the base of the convection zone. The relevant data are from the 1986, 1988, 1989 and 1990 Big Bear Solar Observatory( BBSO) sets, Libbrecht and Woodard(1992, private communication). These four datasets were gathered at the same site for roughly the same number of days, reduced in the same way and span the same temporal and spatial frequency ranges—the differences between the sets should arise primarily because they were obtained in different years.
Coronal Transients in Radio and X-rays
Authors: Kundu Mukul R.
Published: July 2016

We present a summary of several studies of transient coronal phenomena based upon high spatial resolution radio imaging data along with Yohkoh SXT and HXT observations. In addition to normal flares the studies also involve such exotic events as active region transient brightenings (ARTB) and coronal jets and bright points. We provide evidence of nonthermal processes in flaring X-ray bright points from spatially resolved meter-wave data, existence and propagation of type III burst emitting electrons in coronal jets, radio signatures of ARTB’s, and beaming of electrons producing microwave and hard X-rays. The implications of these observations are discussed.
Disconnection of Coronal Field Lines Due to the Emergence of New Photo-Spheric Flux as the Cause of CMES & Interplanetary Shocks
Authors: Bravo S.
Published: July 2016

A scenario is presented whereby CMEs and interplanetary shocks are consequences of a large scale rearrangement of the coronal magnetic field induced by the disconnection of field lines from the solar surface due to the emergence of flux with opposite polarity. In this scenario the CME is the mass released from the previously closed structure and the interplanetary shock is formed by the injection of faster solar wind from an extended or newly created coronal hole which results from the opening of the field lines. Here CMEs and interplanetary shocks are associated events, but not cause-effect related. Observational and computational evidence supporting this view is provided.
Coronal Disconnection Events and Metric Radio Emission
Authors: Gopalswamy N.
Published: July 2016

We review the existing literature on the coronal disconnection events (CDEs) and discuss the importance of these events in understanding coronal structures. We discuss the possible radio signatures of the CDEs and how they may be observed by radio instruments.