bluuebunny/crossref_metadata_2025 huggingface dataset:
Redshift Distribution & Nature of μ-Jy Radio Sources
Authors: Hammer F. , Crampton D. , Lilly S. , LE Fèvre O.
Published: July 2016

During the preliminary deep imaging phase of our large spectroscopic survey of faint field galaxies (CFRS), one of our fields (10 arcmin × 10 arcmin) was chosen to coincide with the Fomalont et al (1991, A.J. 102,1258, hereafter FWKK) radio source field, including 36 S≃ 16μJy radio sources of their complete sample. All sources but two have been identified to V < 25 and/or IAB ≤ 24, and/or KAB ≤ 21.

The microJy population is mainly constituted of three distinct populations of galaxies with different redshift regimes: early-type galaxies at z > 0.75 with a low powered AGN in their cores, post-starburst galaxies at intermediate redshifts (z = 0.375 to z = 0.8 or slightly > 1), and emission-line galaxies at z < 0.45 containing AGNs. The fraction of μJy sources with z > 1 could be as high as 30%. Most of the μJy radio sources (> 50%) are likely associated to AGNs, conversely to what is found at mJy levels (mostly starburst galaxies, Benn et al, 1993, MNRAS, 263, 98). Only one galaxy in our sample has a classical starburst spectrum.

The strong decrease of the radio spectral index from sub-mJy to μJy counts appears to be due to a combination of three factors: (1) the emergence of an elliptical population at high redshifts with moderate radio emission (2) an increasing fraction of narrow emission-line AGNs (Seyfert 2 and LINER); (3) a higher contribution of the thermal radiation to the radio emission from spirals, and the almost complete disappearance of starburst galaxies. Details of the results summarized here can be found in Hammer et al (1995, MNRAS, 276, 1085).
High-Redshift Milli-Jansky Radio Galaxies
Authors: Dunlop J. , Peacock J. , Windhorst R. , Spinrad H. , Dey A. , Waddington I.
Published: July 2016

The study of radio galaxies selected at mJy flux levels has the potential to resolve two important issues in observational cosmology provided redshifts can be determined or reliably estimated for complete samples of such sources. First, the deep flux limit, combined with the shape of the radio luminosity function means that the redshift distribution of such samples provides a much more powerful test of the existence of a high-redshift cutoff for radio sources (Dunlop & Peacock 1990) than can be provided by further studies of brighter radio samples. Second, as a consequence of selection from bright radio surveys, the detailed study of galaxies at z > 2 has to date been confined to objects of extreme radio power (e.g. 4C41.17, Chambers et al. 1990; B2 0902+34, Eales et al. 1993), and it has now become clear that the ultraviolet-infrared properties of such sources are strongly contaminated by processes connected to the AGN (Eales & Rawlings 1993; Dunlop & Peacock 1993). Being 100-1000 times less radio luminous than these extreme sources, mJy radio galaxies at comparable redshifts should provide much more representative probes of the formation and evolution of elliptical galaxies in general.
The R-Band Hubble Diagram for GPS Galaxies
Authors: Snellen Ignas , Bremer Malcolm , Schilizzi Richard , Miley George , Van Ojik Rob
Published: July 2016

The Hubble diagram of GPS galaxies has a low dispersion and a steep slope compared with that for 3C galaxies. The relative faintness of GPS galaxies at high redshift may be due to the absence of the aligned optical/uv component seen in high redshift 3C galaxies. The GPS Hubble relation is too steep to fit with evolution models for passively evolving ellipticals. This could be caused by the dynamical evolution of the GPS galaxies.
Doppler imaging of stellar surfaces
Authors: Rice J.B.
Published: July 2016

The process of recovering the geometric information encoded in the time varying line profiles of rotating stars to obtain maps or images of the surface features on those stars has come to be known in stellar astronomy by the title “Doppler imaging”, although other titles have been used. The principles of Doppler imaging are fairly well known, but the extent of application has been less than might have been expected given the ready availability now of the electronic detectors, the large telescopes and the computing power needed to undertake this sort of imaging.
Stellar magnetic imaging from spectropolarimetric data
Authors: Donati J.-F.
Published: July 2016

In this paper, I will review the capabilities of magnetic imaging (also called Zeeman-Doppler imaging) to reconstruct spot distributions of surface fields from sets of rotationnally modulated Zeeman signatures in circularly polarised spectral lines. I will then outline a new method to measure small amplitude magnetic signals (typically 0.1% for cool active stars) with very high accuracy. Finally, I will present and comment new magnetic images reconstructed from data collected in 1993 December at the Anglo-Australian Telescope (AAT).
Starspot modelling from broad-band photometric and radio light curves
Authors: Budding E.
Published: July 2016

The concept of starspots or maculation is well established. There is indeed such a variety of corroborative evidence for those stars associated with ‘activity’ effects that we cannot imagine photospheric maculation not being a factor. The subject was reviewed by Eaton (1992), and a comprehensive background recently provided by Eker (1995), while relevant papers continue to be presented at more or less annual cool stars symposia. Even so, confidently testifying to more than the mere existence of starspots is non-trivial.
Interferometric imaging of stellar surfaces
Authors: Mozurkewich D.
Published: July 2016

Until recently, all study of stellar surface structure, except for the sun, has been limited to indirect methods. This state of affairs is rapidly changing. With the introduction of interferometric techniques to optical astronomy, direct imaging of stellar surfaces is finally possible. Within a few years we will have images with sub-milliarcsecond resolution and 10 or more resolution elements across the stellar surface.

In this talk, I will describe the technique of optical interferometry and explain how it can be made to work through the earth's turbulent atmosphere. I will show some actual data and describe what can be expected in the near future.
Particle transport and surface abundance inhomogeneities
Authors: Michaud G.
Published: July 2016

The various mechanisms leading to the appearance of horizontal inhomogeneities at the surface of ApBp stars are critically reviewed. The effect of magnetic fields is essential but is it more to control locally, on the surface, the appearance of anomalies that are caused by the vertical transport of particles, or is it to create directly the horizontal inhomogeneities by horizontal transport? The time scales for horizontal and vertical transport will be discussed in this context.

The processes discussed include: a) ambipolar diffusion of protons and hydrogen in the presence of magnetic fields; b) the guiding of diffusion by magnetic fields; c) the horizontal component of radiative accelerations; d) mass loss; e) light induced drift.
Goddard-HRS observations of variability in the RS CVn system V711 Tau (HR 1099)
Authors: Dempsey R. C. , Neff J. E. , Linsky J. L. , Brown A.
Published: July 2016

Through examination of line profile asymmetries and their phase-dependent behavior at high-resolution and high S/N we can determine the spatial structure (i.e., size, location, temperature, magnetic field distribution) of atmospheric inhomogeneities on stars other than the Sun (Vogt & Penrod 1983; Walter et al. 1987; Neff et al. 1989). In an effort to simultaneously probe several lines in addition to Mg II we observed the RS CVn V711 Tau (HR 1099, Prot = 2.d8, G5 IV + K1 IV) with the GHRS in the fall of 1993. Ultraviolet observations were obtained with HST's GHRS over a one week interval beginning 1993 September 14. Full details can be found in Dempsey et al. (1996; see also Wood et al. 1995). In this paper we present results of detailed modeling of the the Mg II emission profiles. Line fluxes and profile models for the emission lines were calculated using least-squares gaussian fits as described in Neff et al. (1989).
Next generation model atmospheres
Authors: Avrett Eugene H.
Published: July 2016

Continued progress in the physical interpretation of solar and stellar observations, the increased speed of computing now available, and new highly efficient numerical procedures have all led to significant advances in stellar atmospheric modeling. This review attempts to summarize recent progress in the field and to describe the many interrelated physical processes that should be taken into account in next-generation modeling programs.
The Origin of Celestial Coordinates
Authors: Murray C. A.
Published: July 2016

In 1978, Guinot proposed that, for studies of Earth rotation, the zero point of the apparent “right ascension” coordinate on the true equator should be so chosen that the rate of change of its hour angle is exactly proportional to the inertial rate of rotation of the Earth. It has been subsequently suggested that this concept of the “non-rotating origin” supersede the equinox quite generally as the origin of celestial coordinates. Since this proposal was first put forward, there has been much discussion, and some criticism, from Aoki and his colleagues, both published and in private correspondence. Some of the arguments for and against Guinot's proposal are discussed, as a contribution to the wider debate on reference systems now being carried out under the auspices of the IAU.
Complex Geodynamical Investigations in the Area of the USSR Academy of Sciences Central Astronomical Observatory at Pulkovo
Authors: Abalakin V. K. , Bogdanov V. I. , Boulanger Yu.D. , Naumov V. A.
Published: July 2016

For astronomical, geodetical and geodynamical investigations as well as for practical applications the inertial coordinate system is widely used which is based on the Fundamental Star Catalogue FK5 together with local coordinate systems in observation stations on the Earth's surface which are intrinsically connected with the geometry of the gravitation field.
Pulkovo Programme for the Photographic Observations of Satellites of Planets
Authors: Kisseleva T. P. , Bobylev V. V. , Bronnikova N. M. , Dementjeva A. A. , Kalinichenko O. A. , Kisselev A. A. , Potter H. I. , Tolbin S. V. , Shakht N. A.
Published: July 2016

The satellites of Mars, the Galilean satellites of Jupiter and the first eight satellites of Saturn have been observed with the 26-inch refractor, the normal astrograph at Pulkovo and with the luni-planet telescope at the Ordubad station of the Pulkovo observatory since 1972.
Density Function of the FK4 Systematic Errors
Authors: Gubanov V. S. , Solina N. I.
Published: July 2016

A notion of density function of systematic errors of astrometric catalogues distributed on the unit sphere as a simple layer is introduced. Components of the catalogue errors in any direction are determined as partial derivatives of layer potential in the same direction. For example, the density function of FK4 errors is computed as an expansion of spherical harmonics.
Contribution of Soviet-Bolivian Astronomical Observatory in the Construction of the Inertial Coordinate System
Authors: Polozhentsev D. D. , Potter H. I. , Yagudin L. I. , Zelaya J. A. , Zalles R. F.
Published: July 2016

The work on photographic astrometry in Bolivia begun in 1983, when an expeditional astrograph was put there (D=23 cm, F=230 cm, working field of 4°x4°). The main purpose of the observations with this telescope is extending the inertial coordinate system to different classes of stars. For this purpose we have carried out and are currently carrying out the following observational astrometric programs:

1. The preliminary catalog of precise positions of 200 000 southern stars to mag 11 with declination in the range from 0° to −90° was created. Each star was observed four times with displacement of the photoplate by 2° in δ and by 8 secδ in α. The exposure time is from 4 to 12 minutes. The accuracy of the preliminary catalog is ±0.247 arcsec and the final one is ±0.15 arcsec.

2. We are not far from finishing the work on a catalog of 1900 bright stars (−90° < δ; 0°, m ≥ 6.05). Each star was observed not less than 2 times for different positions of a special filter which diminished the light of bright stars.

3. The work on astrometry of equatorial stars to mag 12 in the range of declination from −20° to +20° was begun. From the beginning of the observations on 1 May 1987, 1150 astroplates were obtained. On the whole it is necessary to obtain 3840 photoplates. All three programs use the reference catalog SRS, compiled by Pulkovo and Washington astronomers, in the FK5 system.
Relativistic Reference Frames of Local Observer and Space Radiointerferometer
Authors: Alexandrov A.N. , Parnovsky S.L. , Zhdanov V.I.
Published: July 2016

In a considerable number of works on relativistic astrometry (see, e.g. Kovalevsky and Brumberg 1986) the reference frames (RFs) are introduced either by means of coordinate representation of a space-time metric, such as using harmonicity conditions (Brumberg and Kopejkin 1989), or on the basis of invariant constructions like Fermi coordinates (Synge 1960; Ashby and Bertotti 1986; Boucher 1986). Both approaches must, probably, be combined in applications. We consider the local observer RFs (LORFs) based on the Fermi coordinates and on the optical ones (Synge 1960), which are rigorously defined for a general metric and are directly related to observable quantities. In particular, the optical RF operates with the observed direction of the light source, whereas the Fermi RF seems to be a natural generalization of the classical Cartesian RF.
The Determination of the Principal Nutation Terms From the Observations With ZTF-135 in 1948.7-1989.0
Authors: Glebova L.A. , Kostina L.D. , Malkin Z.M. , Persiyaninova N.R.
Published: July 2016

A re-reduction of observations made with ZTF-135 in Pulkovo during 1948.7-1989.0 (all together about 87 000 observations) has been carried out with the aim of determing the amplitude of the principal terms of nutation in longitude and obliquity. The derived coefficients of nutation M=6.“8445±″0033 and N=9.”2028±0.″0025 are in good agreement with similar astrometric determinations.
The Mean Pole of the Moon's Rotational Axis and General Selenocentric Coordinate System
Authors: Barkin Yu.V.
Published: July 2016

One of the fundamental problems of lunar astronomy is the reduction of the coordinates of the Moon's surface, found by astronomical methods, to its mean pole. The instantaneous poles of the rotation axis and the instantaneous equator move in the Moon's body. The unstable position of this equator does not allow one to use in selenodesy the instantaneous spherical coordinates which have not been preliminarily transformed into some unified system of coordinates. Such a reduction can be made to the system of coordinates connected with the mean pole—to be definite, we shall speak about the Moon's North pole.
Ancient Chinese Astronomical Observations Related to the Stellar Background on the Sky
Authors: Shouxian Wu , Ciyuan Liu
Published: July 2016

Ancient Chinese astronomers had special interest to measure positions of celestial bodies. “Shishi Xingjing” including at least 115 stars was produced in the 4th century BC. By the 11th century, the measure of stellar coordinates was in full swing and 5 detailed measures were carried on in only 100 years. So several ancient stellar catalogs have been retained up to now. As an ancient reference system, many astronomical phenomena have been recorded on it. This is meaningful for modern astronomers to do some modern research.
Dedicated Soviet VLBI-Network “Quasar”
Authors: Finkelstein A.M. , Golubchin G.S. , Gorodetsky V.M. , Grachev V.G. , Gubanov V.S. , Ipatov A.V. , Kaidanovsky M.N. , Korkin E.I. , Nikolaev E.I. , Smolenzev S.G. , Stotsky A.A. , Umarbaeva N.D. , Yatskiv Ya.S.
Published: July 2016

The radiointerferometrical network “QUASAR”, composed of six dedicated VLBI stations linked via a geostationary satellite channel with the Center of Operations, is under construction in the Soviet Union. It is proposed to construct “QUASAR”-stations abroad, in China, Bulgaria and India. A short review of basic scientific and technical features of the project is given in this paper.
A New Approach to the Construction of a Compiled Catalogue of Positions of Extragalactic Radio Sources
Authors: Yatskiv Ya.S. , Kuryanova A.N.
Published: July 2016

An attempt of the realisation of the radio reference frame was undertaken. For this purpose a new approach to the construction of a compiled catalogue from observation catalogues of extragalactic radio sources was used. As a numerical example a compilation catalogue of primary radio sources based on the three individual catalogues (GSFC, JPL, and NGS) was constructed. Comparison of this catalogue with recent compiled catalogues led to the conclusion that their r.m.s. differences were about 1 mas.
On the Improvement of the System of Fundamental Catalogues Based on Asteroid Observations
Authors: Duma D.P. , Fedij P.M.
Published: July 2016

The question concerning the influence of the consideration of asteroid mutual perturbations on the calculated positions of 20 selected minor planets as well as on the fundamental catalogues systematic corrections is discussed.
The Lomonosov Project for Space Astrometry
Authors: Nesterov V.V. , Ovchinnikov A.A. , Cherepashchuk A.M. , Sheffer E.K.
Published: July 2016

The lomonosov project is aimed at developing a high-accuracy coordinate system of the entire sky to be used for sufficiently long period of time (30 to 50 years) in order to ensure the solution of a variety of applied and basic scientific tasks. This goal can be feasible as a result of comprehensive work, the basis of which is the space experiment, i.e., observations of stars with a telescope on board the Earth satellite. This method can be instrumental in overcoming the distortions characteristic of terrestrial astrometric observations performed through the atmosphere, and to achieve a high degree of efficiency. The other part of the lomonosov project involves international backing of the space experiment through preparation of the input catalogue for 400 000 stars, and organization of high-precision ground observations of stars and other celestial objects in accordance with special programs.
On the Role of Star Catalogues for Autonomous Space Navigation
Authors: Ivashkin V. V.
Published: July 2016

The questions connected with constructing modern systems of autonomous navigation for spacecraft are considered. Increasing importance of these systems is shown, which is due to: a sharp increase in a number of spacecraft launches and congestion of on-ground control centers; and a necessity to provide more accurate and timely determination of motion parameters and motion control of spacecraft during their flights to the Solar System's celestial bodies. Importance of the star sighting and angular measurements connected with stars for adequate solution of space navigation problems is shown. Thus the star catalogues play a significant role for constructing navigational algorithms.
Systematic Differences Instrument Minus FK5 in the Southern Hemisphere
Authors: Carrasco G. , Loyola P.
Published: July 2016

Observations of Fundamental Faint Star Catalogue (FKSZ) stars, made with the Repsold Meridian Circle at Cerro Calán National Astronomical Observatory, began in 1979 and finished in 1988. Today International Reference Star (IRS) observations are in progress. These observations correspond to the second epoch of the Santiago 67 Catalogue (Carrasco and Loyola 1981) and they are going to be used for determining the proper motions of these stars.
Effect of the FK5-FK4 Catalogue Corrections for the Observations of the Photoelectric Astrolabe at Shanghai Observatory
Authors: Xu T. Q. , Li Z. X.
Published: July 2016

On the basis of the observational materials of the photoelectric astrolabe from 1976 to 1977 at Shanghai Observatory, the possible increase improvement in observational precision after adopting the FK5 catalogue is estimated. The calculation proves that the improvements are about 6 per cent and 9 per cent in the right ascension and declination respectively.
Differences in Changes of Borowiec Geographical Coordinates Caused by the Replacement of FK4 Catalogue by FK5
Authors: Lehmann M.
Published: July 2016

Astronomical observations of time and of geographical latitude carried out by means of Danjon's astrolabe OPL No. 31 in the years 1982-1988 have been reduced to the system FK4. After the introduction of the FK5 catalogue in 1989, the earlier observations were re-reduced. The geographical latitude results, before and after introducing the FK5 catalogue, are given.
Faint Reference Stars
Authors: Corbin Thomas E. , Urban Sean E.
Published: July 2016

Three major reference star projects have been completed recently at the USNO: the Southern International Reference Stars (SIRS − 19, 827 stars) the southern part of the Faint Fundamentals (1,169 stars) and the Astrographic Catalog Reference Stars (ACRS - 325,416 stars). The compilation of the mean positions and proper motions of each is discussed. Reports on the progress of the USNO's Pole-to-Pole Fundamental Program and the Working Group on Star Lists are also presented.
Determination of Absolute Proper Motions by Use of Automated Measurements of Tautenburg Plates
Authors: Scholz R.-D.
Published: July 2016

From measurements of Tautenburg Schmidt plates with the APM in Cambridge positional accuracies per plate of 0.″05 for stars and of 0.″10 for galaxies were achieved. With 0.″3/100a accuracy in a single stellar proper motion we obtained the absolute proper motion of the M3 globular cluster in good agreement between the two pairs of plates used.
The System of the PPM Catalogue
Authors: Roeser Siegfried
Published: July 2016

The coordinate system of the Catalogue of Positions and Proper Motions (PPM) was constructed as an extension of the FK5 sytem to higher star densities and fainter magnitudes. Zonal deviations from the FK5 were minimised on scales of 7 × 7 square degrees via AGK3R and CMC catalogues. Compared with these catalogues, no magnitude equation was found for stars brighter than m(pg) = 10.5.
Torino Programme on Radiosources Astrometry: Progress Report
Authors: Chiumiento G. , Lattanzi M. G. , Massone G. , Morbidelli R. , Pannunzio R. , Sarasso M.
Published: July 2016

Measurements of precise positions of optical counterparts of extra-galactic radio-sources, with the aim to compare them with VLBI positions, is in progress at Torino Observatory. The Carlsberg Automatic Meridian Circle Catalogue (CAMC) is used for plate reductions. Presently, about 40% of the plate material required to complete the project has been taken and some significant improvements have been made both in the material and the reduction methods. Improvements are also due to the publication of a new volume of the CAMC catalogue that significantly increases the number of stars in the fields.
Occultation of Radio Sources for the Linkage of Radio and Stellar Reference Frames
Authors: Sôma Mitsuru , Miyamoto Masanori , Aoki Shinko
Published: July 2016

The right ascension of the radio source 3C273B, which serves as a right ascension zero point in radio astrometric work, has been determined from lunar occultations and photographic observations.

We re-analyze here the lunar occultations of 3C273B using the recent precise lunar ephemeris and obtain its right ascension referred to the FK5 equinox at J2000.0. The obtained right ascension is 12h29m06s.6946±0s.007 at its mean observation epoch of 1963.62.

Predictions of occultations of radio sources by the Moon and planets are also given. Observations of them are encouraged in order to improve the accuracy of the linkage between radio and stellar reference frames.
Comparison of Proper Motions of Stars From AGK3 and Special Compiled Catalogue in Regions With Galaxies
Authors: Rybka S.P.
Published: July 2016

The procedure of construction of special compiled catalogue is presented. The compiled catalogue is based on 6 catalogues obtained following the KSZ plan. The mean error of proper motions of stars is ±0.″009 per year. AGK3 proper motions compared with those in the compiled catalogue yield precession corrections Δk=-0.″0046 ± 0.″0010, Δn = +0.″0045 ± 0.″0010. Systematic differences between these catalogues are represented by a series development using products of Hermite polynomials, Legendre polynomials and Fourier terms.
Internal Large-Scale Toroidal Magnetic Field of the Sun
Authors: Krivodubskij V.N.
Published: July 2016

The evolution of the large-scale toroidal magnetic field Bϕ of the Sun generating in the radiative zone by acts of differential rotation on the relict radial magnetic field Bϕ is investigated regarding the magnetic buoyancy and ohmic dissipation.
Magnetic Buoyancy with Viscosity and Ohmic Dissipation and Flux Tube Formation
Authors: Kuznetsov V.D.
Published: July 2016

In the framework of the magnetohydrodynamic equations with dissipative terms in the form of turbulent viscosity (Vt) the linear stage of the instability of a subphotospheric field with respect to magnetic buoyancy is considered. For an exponential in z, isothermal plane-parallel atmosphere with a constant Alfvenic velocity

the perturbations of the form

are described by differential equation with constant coefficients. The qualitative dependence of the growth rate of instability on transverse wave number is determined (see Figures 1 and 2) and characteristic scales of the magnetic tubes are evaluated at the linear stage of instability (Kuznetsov, 1987, 1988).
Propagation and Oscillation of Neutrinos with Magnetic Moment inside the Sun
Authors: Sivaram C.
Published: July 2016

The VVO mechanism suggests that the existence of a neutrino magnetic moment would lead to variations of the observed solar neutrino flux with the magnetic activity of the Sun. The MSW mechansm suggests neutrino oscillations in the dense plasma solar interior. Assuming a non-vanishing neutrino magnetic moment and a magnetic field gradient increasing towards the solar core as required in some dynamo models, the combined effect of the oscillation and the flipping on neutrino propagation in the solar interior is studied. The effect of charge screening in scattering cross-section is also considered.
Classical Treatement of the Compton Collision in General Relativity
Authors: Paillere Pierre
Published: July 2016

A systematic development of the photon 4-momentum in the non-quantic perspective of General Relativity is very difficult to find in the scientific litterature. However, the photon 4-momentum is a fundamental concept if one wants to study relativistic transport theory or Compton collision formulae. For these reasons, a coherent formalism has been elaborated. It sysmetically allows one to formulate these problems the criterion of validity being the fact that in the case of the Minkowski metric, the general formulae give the classical results of the Special Relativity.
Self-Organization Processes on the Sun: The Heliosynergetics
Authors: Krishan V. , Mogilevskij E.I.
Published: July 2016

Abstract Non-linear interactions between small fluid elements, magnetized or otherwise, in an energetically open nonlinear system facilitate the formation of large coherent stable structures. This is knwon as self-organization. We interpret solar granulation on all scales and the formation and evolution of some structures in solar active regions to be the result of self-organization processes occuring in a turbulent medium.
Nonlinear Waves in Flux Tubes
Authors: Ryutova M.
Published: July 2016

Some results of nonlinear studies of flux tube oscillations are summarized showing that each step made towards the real conditions of the solar atmosphere opens the existence of qualitatively new effects which form the basis of strongly nonlinear dynamics. Among these effects are, for example: explosive instability in the presence of negative energy waves which leads to an efficient and fast energy release; the generation of secondary plasma flows and current drive which strongly influence the evolution of magnetic flux tubes and their stability conditions; formation of shocks and solitary waves, temporal brightening of flux tubes and others.
Nonlinear Surface Alfvén Wave Propagation in Solar Atmosphere
Authors: Ruderman M.S.
Published: July 2016

The paper deals with the surface wave propagation in the solar atmosphere. The plasma motion is supposed to be described by magnetohydrodynamic equations. In the first part of the paper the surface wave propagation on a single magnetic interface in the solar corona is considered. The plasma is assumed to be cold. Using the reductive perturbation method we derive the equation governing the evolution of nonlinear small-amplitude surface waves as follows

This equation is written in a coordinate system moving with the phase velocity of linear waves. Dimensionless variables are used. The symbol H denotes the Hilbert transform. The shape of the interface is defined by the equation z = h(t,x) in the Cartesian coordinates x, y, z. The Reynolds number R determines the relative contributions of nonlinearity and viscosity. We take a source radiating a sinusoidal wave. Then the wave evolution is calculated numerically. We get that at large R the wave steepening takes place. This steepening leads to a strong increase of wave damping.
Density Irregularity of the Inner Corona determined from Simultaneous Measurements of the XUV and the K Coronal Brightness
Authors: Guhathakurta M. , Rottmann G.J. , Fisher R.R. , Orrall F.Q.
Published: July 2016

In this paper we report preliminary results from a study of the inner corona based on the direct comparison of XUV resonance emission line λ174.53 FeX with that of the white-light emission from the K corona. The data sets were obtained 17718th of March, 1988, during a total solar eclipse of the sun and consists of co-spatial and co-temporal measurements of these two quantities as a function of position angle and height above the solar limb. The local emission of a coronal resonance line is proportional to the electron density squared, the chemical abundance, and the electron kinetic temperature, while the white-light emission (arising from Thomson scattering by electrons) depends directly on the electron density and the local radiation field. Taken together these measurements yield an estimate of the quantity where n is the electron density. This quantity, called “X the coronal irregularity factor” by C.W. Allen, is found to be >1.
Calcium K Line Profiles as a Function of Latitude and Solar Cycle Phase
Authors: Singh Jagdev
Published: July 2016

The sun as a star has been studied by many observers by monitoring the calcium K line profile. Skumanich et al (1984) proposed a three component model of the solar cycle variability of calcium K emission using extant contrast and fractional area parameters for (1) cell (2) network and (3) plage components. The computed line profile agreed well with the observed one at the solar minimum by taking the contribution of only cell and network features and using extant limb-darkening laws. The occurrence of plages during the growth of the solar cycle was found to be insufficient to account for the increase in K emission and therefore, they introduced an additional network component, ‘Active network’ in excess of the quiet sun value to explain the observed excess emission during the maximum phase.
On the Existence of Hydromagnetic Interface Waves at a Structured Atmosphere
Authors: Somasundaram K. , Manthiramoorthi S. , Narayanan A. Sathya
Published: July 2016

The conditions under which the hydromagnetic interface waves can exist at a magnetic interface is deduced. Using these conditons, it is shown that a slow interface wave with a phase velocity about 5Km/s and a fast interface wave with a phase velocity 6.5 to 8km/s at the photospheric level can exist.
Acoustic Wave Generation in Vertical Magnetic Fields
Authors: Yun H.S. , Lee J.W.
Published: July 2016

We extended Stein's hydrodynamic theory of acoustic wave generation to accommodate the effect of a vertically uniform magnetic field. It is shown that in the presence of a uniform vertical field with pure horizontal field fluctuations the acoustic waves are produced both from a non-magnetic monopole source of the Reynolds stress and by the magnetic field fluctuations. The computed acoustic flux is found to be confined to the topmost of the spot's convection zone with a small range of depth.
Structure and Equilibrium of Coronal Magnetic Fields
Authors: Van Ballegooijen A. A.
Published: July 2016

In “closed” magnetic structures (i.e., coronal loops) the random shuffling of magnetic footpoints in the photosphere causes twisting and braiding of field lines in the corona. If the motions are sufficiently slow, the coronal field evolves through a sequence of force-free equilibrium states. Numerical simulations are presented for a simplified model in which the overall curvature of the coronal loop is neglected. It is shown that magnetic fine structures develop on spatial scales significantly smaller than those of the imposed “photospheric” velocity field.
Stability of a Massive Current Sheet Supported by a Two-Dimensional Potential Magnetic Field
Authors: Aly J.J. , Colombi S.
Published: July 2016

Necessary and sufficient criteria of linear ideal magnetohydrodynamic stability are derived for a massive current sheet - idealizing a solar prominence - supported against gravity by a two-dimensional potential magnetic field.
The Quasi-Static Evolution of Magnetic Structures on the Sun and Their Topological Reconstruction
Authors: G. Matyukhin Yu. , Tomozov V.M.
Published: July 2016

We have considered the problem of quasi-static evolution of a magnetic configuration as it is affected by shear motions at field line footpoints. It is found that, with a certain character of the shear motions at the field line footpoints, topological reconstruction will, by necessity, occur in the magnetic configuration. A pattern of magnetic field lines during the course of configuration restructuring is constructed.
Fast Solar Flare Proton Acceleration by MHD Turbulence
Authors: Smith Dean. F.
Published: July 2016

Proton acceleration by short-wavelength Alfven (A) waves resonant at the first harmonic of the proton gyrofrequency is reconsidered, taking into account nonlinear wave-wave interactions, collisionless wave losses, and wave escape losses in the geometry of a model coronal loop. It is shown that for the A wave levels required for acceleration in the transrelativistic regime in the 1982 June 3 flare and for acceleration in the nonrelativistic regime in the 1980 June 7 flare, the nonlinear wave interaction of scattering on the polarization clouds of ions will be important. This interaction rapidly isotropizes the A waves which divide their energy with fast magnetosonic (M) waves with a negligible change in their frequency spectrum. Because of electron Landau damping and escape losses, the M waves are confined to two narrow cones about the magnetic field and the total (A+M) wave distribution is still highly anisotropic. The total (A+M) wave spectrum has the same acceleration efficiency as a pure A wave spectrum. There are two principal problems with models of this type. The first is that a large wave energy density is required in a fairly narrow range in k-space. The second is that the protons are effectively bottled up. This makes very impulsive behavior as in the 7 June 1980 flare difficult to explain because proton precipitation is relatively slow.
Acceleration, Transport of and Radiation by Electrons in Impulsive Phase of Flares
Authors: Petrosian Vahé
Published: July 2016

I review here results of works that we have carried out over the past few years in connection with various manifestations of the impulsive phase of solar flares. The primary goal of this work has been the determination of the characteristics of the accelerated electrons. We take into account various possible interactions that electrons suffer as they traverse the flare plasma and evaluate the expected radiation via several mechanisms. The comparison of these with the observed x-ray, gamma-ray and radio emissions allows us to set constraints on the characteristics of the accelerated electrons and on some properties of the flare plasma. I will describe some of the results we have derived from comparisons with SMM and other observations of flares during the past solar cycle. In particular, I will show that we can set limits on the range and distribution of the accelerated electron spectrum and pitch angle distribution, and on the column depth and field convergence rate of the flaring loop. More complete data and high spatial resolution and polarization observations could be very useful for furthering this kind of work.
Relationship between Solar Flares and Solar Cosmic Rays
Authors: Vahia M N
Published: July 2016

We discuss the possibility that the plasma trapped inside the solar magnetic loop region may be the principal arbitrator in deciding whether a given active region will release particles into the interplanetary medium or will remain a solely electromagnetic event. We analyze the particle abundance patterns and show that the particle selection occurs in a cool region much below the corona. We discuss the particle acceleration in time varying magnetic field and show that the betatron process can be very effective under solar conditions. We then show that the electron density in the flare region may be the critical parameter in deciding the evolution of the active region. Finally we show that direct observations of flares in the interplanetary medium agrees well with this suggestion.
Analysis of Prognoz - 9 Solar Flare Hard X-ray Data-support for the Non-thermal thick target Model
Authors: Rausaria R. R. , Bakaya Ranjana , Khosa P.N.
Published: July 2016

Solar flare hard X-ray data obtained by Prognoz-9 spacecraft (Abrosimov et al 1988) in the energy range 10-200 keV are analysed. In examples of events which we consider here, high energy X-ray pulses appear earlier than low energy ones, which is contrary to many other events where the low energy X-ray peak emission takes place earlier. The variation of the spectral index was dynamical.
Millimeter and Microwave Activity of the Sun
Authors: Kundu M. R. , White S. M.
Published: July 2016

The emission of solar flares at millimeter wavelengths is of great interest both in its own right and because it is generated by the energetic electrons which also emit gamma rays. Since high-resolution imaging at gamma-ray energies is not presently possible, millimeter observations can act as a substitute. Except for that class of flares known as gamma-ray flares the millimetric emission is optically thin. It can be used as a powerful diagnostic of the energy distribution of electrons in solar flares and its evolution, and of the magnetic field. We have carried out high-spatial-resolution millimeter observations of solar flares this year using the Berkeley-Illinois-Maryland Array (BIMA), and report on the preliminary results in this paper (Kundu et al 1990; White et al 1990). We also report some recent results obtained from multifrequency observations using the VLA (White et al 1990).
Absorption of Electromagnetic Waves in Astrophysical Plasmas
Authors: Gangadhara R.T , Krishan V
Published: July 2016

We study Parametric Decay Instabilities(PDI) using the kinetic description, in the homogeneous and unmagnetized plasmas. These instabilities cause anomalous absorption of the incident electromagnetic (e.m)radiation. The maximum plasma temperatures reached are functions of luminosity of the non-thermal radio radiation and the plasma parameters.
Star Clusters as Touchstones for Theories of Galactic Evolution — A Few Examples
Authors: van den Bergh Sidney
Published: July 2016

Observations of NGC 5128 (Cen A) show that this giant elliptical galaxy contains few globular clusters. The fact that the number of globular clusters per unit luminosity in E galaxies has a range of ∼ 102 indicates that different ellipticals were formed in differing physical environments. It is pointed out that more data on the frequency with which globular clusters occur in elliptical galaxies might place interesting constraints on theories of galaxy clustering.

Intercomparison of the Local Group galaxies IC 1613 and the SMC shows that differences in the frequency of cluster formation also occur among Irregular galaxies.

It is pointed out that globular clusters associated with distant galaxies probably start to outnumber galactic stars for B > 31.

The discovery that the LMC supernova remnant N63A is situated in the small association N2030 shows that this object must have been formed from a star with a main sequence mass > 30 M⊙.

Finally we show that E3, which is one of the faintest known galactic globular cluster, was decimated by tidal forces. Due to the interplay of equipartition and tidal effects this cluster has been severely depleted in single stars while retaining many (presumably binary) blue stragglers.
The Galactic Distance Scale: Globular Clusters
Authors: Harris William E.
Published: July 2016

A new compilation of distance data for the Galactic globular clusters is used to estimate the distance to the Galactic center, RO. Three different ways of using the space distribution of the clusters lead to RO = (8.5 ± 1.0) kpc. The problem of the space distribution of the clusters in the Galactic nuclear region is briefly discussed.
Hyades Distance and Chemical Composition From the Competitive use of Astrometry, Photometry, Spectroscopy, and Internal Structure Computation
Authors: de Strobel G. Cayrel
Published: July 2016

An analysis of observational astrometric, photometric, spectroscopic data for the Hyades cluster is performed in order to compare Hyades G dwarfs to the sun. Internal structure computations are also used to compare the solar ZAMS with the Hyades ZAMS and to discuss the constraints existing between distance and chemical composition for the cluster.
2.3 GHz Radio Emission From Sco OB2
Authors: Baart E.E. , de Jager G. , Mountfort P. I.
Published: July 2016

The Sco OB2 Association is convenient for investigation as it has a high galactic latitude and is therefore remote from the confusion of the galactic plane. Its distance is accurately known and this permits fairly precise estimates to be made of the Lyman continuum photon fluxes responsible for the radio emission. It includes the ρ Ophiuci dark cloud where star formation is occurring.
Chemical Evolution of the Galactic Disk. II. Gradients of Chemical Composition
Authors: Chiosi C. , Matteucci F.
Published: July 2016

In this paper we propose a model for the chemical evolution of the solar neighbourhood and the galactic disk as well. The model takes into account the inflow of primordial gas, and the time scale associated with the process of disk formation. We follow the same physical description and formalism adopted by Chiosi (1979). However, by releasing the approximation of instantaneous recycling, we are able to describe the chemical history of the galactic disk in much better detail than in Chiosi (1979). A set of eight elements (H,D,He3,He4,c+0,N,n-rich, heavy) is used to describe the chemical composition of the galactic gas and inflowing material. The disk is supposed to be represented by several independent shells, whose surface mass density is thought to depend on radial distance from the galactic center and age of the galaxy. The rates of mass accretion and star formation follow the formulation of Chiosi (1979). To better approximate the results from dynamical models of disk galaxies, we have taken into account the known fact the time scale of disk formation varies with the distance from the galactic center, being of the order of 1×109 y in the innermost, and up to 10×109 y in the outermost, regions of the disk. From the body of solutions we have explored, we can derive the following results, which are shortly summarized for the case of our best model of chemical evolution of the disk only.
The Hyades Cluster — Solar Metallicity?
Authors: Flower Phillip J.
Published: July 2016

Some simple comparisons have been made between models of main sequence (MS) stars and the Hyades main sequence with the aim of investigating the effects of small changes in the stellar opacities, the zero point of the temperature scale and the assumed distance modulus for Hyades cluster have on the inferred metallicity of the Hyades. Three grids of MS models were constructed using the Cox and Stewart (1970a,b) opacities. Furthermore, taking a rather conservative view with regard to future changes in opacity compilations, another grid was constructed with opacities 20% higher than the Cox-Stewart opacities. Following the procedure outlined by Gough and Weiss (1976), the mixing length required for constructing a solar model was found to be 1.36. Because recent photometric and spectroscopic work (Barry et al. 1978; Hardorp 1978) suggests that the sun may be redder than traditionally believed, i.e., (B-V)⊙ = 0.66–0.67 instead of 0.63 mag, two temperature scales have been used to transform the MS models to the CM diagram.
A Computer Based Catalogue of Open Cluster Data
Authors: Lyngå Gösta , Lundström Ingemar
Published: July 2016

The catalogue contains data for 1130 galactic clusters. Each cluster has 255 available storage places. Most of these are reserved for positional, descriptional and physical parameters. In the present version the following items are included:

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Cluster name, OC1 No. (Alter et al. 1970)

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R.A., Dec (1950.0), R.A., Dec. (2000.0), precession for 10 years, galactic longitude, galactic latitude

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Data on peculiar stars (Feinstein 1979): Type, number, references

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Part of Dixon's (1976) catalogue: POSS chart type, chart No., coordinates for chart centre (R.A., Dec), position on chart, largest published angular diameter, magnitude of brightest star, Trumpler class, nebulosity

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Part of Bochum-Strasbourg catalogue (Kluke et al. 1975): Selected angular diameter, distance, magnitude of brightest star, spectral class, total magnitude, colour excess

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Buscombefs (1978) compilation: Radial velocity, distance, colour excess, total apparent magnitude, total absolute magnitude, linear diameter, age, mass

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Basel data (Becker and Fenkart 1971; Fenkart and Binggeli 1979): Photometric system, colour excess, interstellar extinction, distance, spectral type of hottest star, colour type of bluest star, linear diameter, type of observation

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van den Bergh-Hagen (1975) data: Angular diameter, richness

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Lyngå (1979) compilation: Selected angular diameter, references (various other parameters with references will be included later).
The Structure of h and χ Persei
Authors: Meurers J.
Published: July 2016

Well known methods for analyzing stellar distributions have been refined and new methods developed. Their application to h and χ Persei is demonstrated.
A Spectroscopic and Statistical Study of Collinder 140
Authors: FitzGerald M. Pim , Harris G.L.H. , Miller M.
Published: July 2016

Spectra of 140 stars in a 1.36 square degree field centered on the open cluster Collinder , 17 outside this field, and 125 in two neighbouring fields of the same total area, have been classified on the MK system. Twenty of these were classified on slit spectra in the manner described by FitzGerald et al. (1979) and the balance on objective prism plates obtained at Cerro Tololo with a disperson of 280 A mm−1. All spectra were classified at least twice, usually by more than one author. The internal accuracy was ±0.9 spectral sub-classes and ±0.4 luminosity classes. Comparison with the Michigan 10° classes of Houk (1979) for 34 stars in common gives the difference (Houk-FHM): 0.2 ± 0.2 (s. e. mean) for spectral classes and −0.1 ±0.1 for luminosity classes. All stars brighter than V=14.35-0.65 S were classified in the above regions, where S is a numerical representation of the spectral class ranging from 2.0 to 6.7 for BO to M7 stars respectively. Members are shown in Figure 1.