bluuebunny/crossref_metadata_2025 huggingface dataset:
A Cocoon Transparency and the 3C 345 Low Frequency Variability
Authors: Matveenko L.I.
Published: July 2016

The structure of the quasar 3C 345 is studied at λ = 49cm. The core has a low-frequency cut off spectrum and α ≃ 3. The brightest knot is in the nearest part of the jet. The cocoon wall absorbs low-frequency emission and changes the polarization orientation, RM = 3500 rad m–2, B|| ≃ 100 μG at the core region.
The Spectral and Spatial Decomposition of Extragalactic Radio Sources
Authors: Rudnick L. , Katz-Stone D.M.
Published: July 2016

We have developed a new set of techniques for extracting information from maps of synchrotron emission. Some of these methods are used to determine the shape of the spectrum and then to isolate the contributions of the number and energy of relativistic electrons and the local magnetic field strength to the total intensity images. These are discussed in Katz-Stone, Rudnick & Anderson (1993), Katz-Stone & Rudnick (1994), and Rudnick, Katz-Stone & Anderson, (1994). Here, we describe a method - called spectral tomography - to remove confusion from various features along the line of sight. We find that both structural and spectral confusion are commonplace, and therefore our dynamical and radiative models of extragalactic sources need significant revision.
First Results from the VLA FIRST Survey
Authors: Becker R.H. , Gregg M.D. , Helfand D.J. , Cress C.M. , Mcmahon R. , White R.L.
Published: July 2016

The VLA FIRST survey is now in its second year. We have completed mapping over 1500 deg2 of the North Galactic Cap and present here the catalog of the 138,000 radio sources detected therein. We discuss the statistics of this new catalog including the two-point angular correlation function for all radio emitters, present our optical identification of 24,000 sources using the APM catalog, and report followup studies on radio variability, X-ray source identification, and our bright quasar sample.
Virtual and spurious surface structure on Ap stars
Authors: Stift M.J.
Published: July 2016

Modelling of magnetic Ap type stars has a long and distinguished history. The Oblique Rotator Model (ORM) – a dipole inside the star, its axis not aligned with the rotation axis – proposed by Babcock (1949a) provides a simple yet flexible enough paradigm for the modelling both of the magnetic and the spectral line variations of these stars. Deutsch (1958) developed a method to derive surface composition distributions from magnetic field measurements in conjunction with line strength variations but subsequent investigators concentrated either on the magnetic field or on the abundance distributions. Hardly ever was the question of consistency between field and composition mapping addressed – Landstreet (1988) constitutes the exception. In abundance mapping, Doppler imaging (Vogt et al. 1987) has meanwhile replaced most other approaches and is credited with fairly reliable results. But can one really carry out such mapping, as done by Hatzes (these proceedings) without accounting for the magnetic field and can these zero-field abundance maps and their relation to the magnetic configuration be compared to the predictions of diffusion theory? Did Landstreet ever have a real chance of disentangling magnetic and abundance effects using intensity (Stokes I) profiles only? What is the probability of obtaining spurious surface structure from intensity Doppler imaging of Ap stars?
Chromospheric emission line mapping
Authors: Neff James E.
Published: July 2016

Throughout its eighteen years of operation, the International Ultraviolet Explorer has afforded us the opportunity to make many new discoveries regarding the nature of the outer atmospheres of magnetically active, late-type stars. High-resolution spectra obtained continuously throughout the rotational cycle of rapidly-rotating stars have been used to map the spatial structure of the magnetic active regions in stellar chromospheres. The RS CVn-type binary system AR Lacertae has been observed intensively at 3 epochs, with additional observations with less complete phase coverage was obtained at 4 other epochs. Taken together, we are able to probe the evolution of atmospheric structure of AR Lac over a 13-year timeline. I briefly review techniques of chromospheric emission line mapping, and I summarize the IUE results for AR Lac, V711 Tau, EI Eri, V1794 Cyg, and TY Pyx. I conclude with a description of chromospheric imaging programs (present and future) that make use of the Hubble Space Telescope.
Differential interferometry imaging
Authors: Petrov R. G. , Lagarde S. , Van KY M. N'GUYEN
Published: July 2016

Differential Interferometry (DI) combines high spectral and high spatial resolution. On non resolved objects, it yields the angular variation of the source photocenter as a function of wavelength which has been shown theoretically and experimentally to complement very usefully both interferometric and spectroscopic data in a large number of astrophysical problems. This paper presents the general characteristics of DI which are likely to allow improvements of the Doppler images of stellar surface structures as soon as interferometers with large apertures and baselines approaching 100 m are available.
Long-term stellar activity: three decades of observations
Authors: Donahue R.A.
Published: July 2016

Knowledge of the solar sunspot cycle extends back to the mid-19th century with the work of Schwabe (1843) and Wolf (1856). The mean cycle period of the Sun is 11 years, however, individual cycle lengths range from 7 to 13 years (Eddy 1977). In this century, however, the length of the solar cycle has been closer to 10 years (Donahue and Baliunas 1992a). A complete explanation of the solar magnetic activity and its variations has not yet been produced, although a hydromagnetic dynamo is frequently posited as the source of solar (and therefore stellar) magnetic activity. Empirical measurements of those stars in the H-R Diagram which have convective zones and surface magnetic activity provide the boundary conditions and the range of behavior which must be explained by any all-encompassing theory explaining stellar magnetic activity, and activity cycles.
Distribution of starspots on cool stars A Model Based On the Dynamics of Magnetic Flux Tubes
Authors: Schüssler M.
Published: July 2016

A theoretical study of storage, instability and rise of magnetic flux tubes in the outer convection zone of a cool star is presented. Special emphasis is laid on their emergence latitudes at the surface of magnetically active stars. We apply the ‘solar paradigm’ and assume toroidal magnetic flux tubes to be stored in force equilibrium within the overshoot layer underneath the convection zone. A non-axisymmetric (undulatory) instability leads to the formation of flux loops, which rise through the convection zone and emerge at the surface to form bipolar magnetic regions and starspots. Our approach combines the analytical determination of the linear stability properties of flux tubes with numerical simulations of the nonlinear evolution of the instability and the rise of magnetic flux tubes through the convection zone. It is found that for sufficiently rapidly rotating stars the magnetic flux emerges at high latitudes since the Coriolis force leads to a poleward deflection of rising flux loops. The latitude distribution of the emerging flux is determined for a number of stellar models along the evolutionary sequence of a star with one solar mass, from the pre-main sequence evolution up to the giant phase. Rapid rotation and deep convection zones favour flux emergence in high latitudes. Starspots right at the stellar (rotational) poles form either directly by flux eruption from small stellar cores (as for T Tauri stars or giants) or by a poleward slip of the sub-surface part of the flux tube after flux emergence in mid latitudes. The latter process explains the simultaneous existence of polar spots and spots at intermediate latitudes as observed on some stars.
Observational evidence for polar spots
Authors: Strassmeier Klaus G.
Published: July 2016

“Are results from ill-posed problems, like Doppler-imaging, conclusive at all?” and “Could polar spots be simple image-reconstruction artifacts?” are often asked questions. Although I can not definitively answer them, I will present observational evidence for the existence of cool starspots at or very near a stellar rotation pole.
Chromospheric dynamics
Authors: Rutten Robert J.
Published: July 2016

This brief review advertises a breakthrough in solar dynamics: the identification of chromospheric Ca II K2V “grains” as manifestations of acoustic shocks. The successful numerical reproduction of the intricate spectral characteristics of K2V grain formation by Carlsson & Stein shows that the non-magnetic solar chromosphere is pervaded by outward traveling shocks to such extent that static modeling is no longer acceptable. Dynamical modeling should soon reconcile the long-standing Ca II/CO dichotomy. The chromospheric dynamics of the magnetized regions remains enigmatic.
Coronal loops and their modeling
Authors: Van Den Oord G.H.J. , Zuccarello F.
Published: July 2016

We discuss the theory of quasi-static coronal loops, introducing a phase plane representation to study loop solutions independently of specific boundary conditions. Emphasis is put on the effects of loop expansion, heat input and gravitational stratification on the differential emission measure, and on the intrinsic limitations of spectroscopic observations for deriving loop parameters. We show that certain classes of published loop solutions cannot actually exist. For expanding loops new classes of loop solutions, with rather special properties, are presented. Special attention is paid to loops in binary systems and on rapidly rotating stars.
A new opacity-sampling model atmosphere program for arbitrary abundances
Authors: Kurucz Robert L.
Published: July 2016

I have developed a new opacity-sampling version of my model atmosphere program called ATLAS12. It recognizes more than 1000 atomic and molecular species, each in up to 10 isotopic forms. It can treat all ions of the elements up through Zn and the first 5 ions of heavier elements up through Es. The elemental and isotopic abundances are treated as variables with depth. At present ATLAS12 reads atomic line data from Kurucz CD-ROM 1 and diatomic molecular data from Kurucz CD-ROM 15. For each line the wavelength, identification, lower energy level, gf, radiative, Stark, and van der Waals damping constants are packed into 16 bytes. At each wavelength point in a frequency integration the Voigt profiles of all the significant nearby lines are computed and summed. The H, He, and auto-ionizing lines are treated with the appropriate profile functions.

The fluxes predicted by ATLAS12 are not accurate in intermediate or narrow bandpass intervals because the sample size is too small. A special stripped version of the spectrum synthesis program SYNTHE is used to generate the surface flux for the converged model using the line data on CD-ROMs 1 and 15. That high resolution spectrum can be used directly or can be instrumentally broadened to compare to low resolution observations.

ATLAS12 can be used to produce improved models for Am and Ap stars. It should be very useful for investigating diffusion effects in atmospheres. It can be used to model exciting stars for H II regions with abundances consistent with those of the H II region. These programs and line files will be distributed on CD-ROMs.
Absolute Determinations of Star Declinations From Pole to Pole
Authors: Naumov V.A.
Published: July 2016

The most widely spread method of determination of star declinations is Bessel's method. Alhough it gives good agreement between star declinations obtained from observations of stars in upper and lower culminations, it leads to great systematic errors if the system of the instrument has an error of the type

such as flexure or errors of divided circle. Besides, in the determination of correction of latitude (Δφ) and refraction (Δμ) considerable correlation between them exists.
The FK4 Orientation Parameters Derived From Photographic and VLBI Observations of Radio / Optical Objects
Authors: Gubanov V.S. , Kumkova I.I. , Solina N.I.
Published: July 2016

The photographic and VLBI positions of 59 quasars are used for determination of the FK4 orientation parameters with respect to the radioastrometrical system (RAS).
Equator and Ecliptic FK5 Positions on the Basis of Sun and Planets Observations by the Ertel-Struve Vertical Circle at the Kislovodsk Mount Station
Authors: Devyatkin A.V. , Gnevysheva K.G.
Published: July 2016

The classical Ertel-Struve vertical circle of the Pulkovo Observatory was astablished at the Kislovodsk Mount Station. From 1984 to 1989 we have obtained 566 declinations of the Sun, 230 of Mercury, 413 of Venus, and 207 of Mars. Observations were visual, and the reductions were differential in the FK5 system. Only day-time observations of reference stars were used.
Modified Method of Krejnin and Murri for the Determination of Absolute Declinations
Authors: Tolchelnikova-Murri S.A.
Published: July 2016

Krejnin and Muni's method (1973) enablesenables one to derive absolute declinations of stars in a narrow equatorial zone |δ| < 10′ from observations near the Earth's equator |ϕ| < 10′. Some systematic effects, including the errors of the value of the micrometer screw for two equatorial instruments (or the scale error if one of the instruments is a PZT), might be determined if a global reduction is used for the original observations from the equator and from those of an astrolabe at latitude |ϕ| ∼ 20° to 23°. Astrolabes—especially photoelectric ones (Hu 1988) are considered to be the most efficient for determination of absolute declinations of stars and absolute latitudes of the instruments in Tolchel'nikova-Murri (1985).

In Izv. GAO No. 206 the method will be published as well as the criterion for estimating the efficiency of different programs, which is required to improve planning in astrometry.
The Celestial Reference System in Relativistic Framework
Authors: Chun-Hao Han , Tian-Yi Huang , Bang-Xin Xu
Published: July 2016

The concept of reference system, reference frame, coordinate system and celestial sphere in a relativistic framework are given. The problems on the choice of celestial coordinate systems and the definition of the light deflection are discussed. Our suggestions are listed in Sec. 5.
The Celestial System of the International Earth Rotation Service
Authors: Arias E.F. , Feissel M.
Published: July 2016

The celestial system of the International Earth Rotation Service (IERS) is materialized by the J2000.0 positions of more than 250 extragalactic compact radio sources observed by VLBI. The source coordinates are evaluated from the combination of individual celestial frames obtained by the Goddard Space Flight Center, the Jet Propulsion Laboratory and the U.S. National Geodetic Survey.

The combination model and the maintenance algorithm are described. To free the IERS celestial frame from inconsistencies due to the inaccuracy of the IAU conventional models for precession and nutation, it is implemented on individual frames which have been obtained in parallel to the adjustment of corrections to the direction of the celestial pole.

The IERS celestial reference frame is consistent with FK5 at a few milliarcsecond level. To be made denser and more accessible for astronomical uses, it will be related to the HIPPARCOS stellar frame.
The Computation of Mean Positions and Proper Motions
Authors: Cole Carl S.
Published: July 2016

This paper investigates the estimation of mean positions and proper motions given independent solar-system barycentric positions observed at different epochs, reduced to the same equator and equinox and freed of systematic errors. Past practices are reviewed and the relative quality of the data is studied to determine the appropriate form of the model.
Can We Define an Inertial Reference System?
Authors: Linghuai Li , Fu Tong
Published: July 2016

The topic (Seidelmann, 1986) is one of the unresolved questions in the field of celestial mechanics because the definitions of an inertial system are all controversial (Mach, 1893; Eichhorn, 1984). Eichhorn's definition enlarges its connotation and is not acceptable either. Connotation of a concept is endowed through defining it. One of the reasons why the existing definitions of an inertial system are all controversial is that the connotations that are endowed by them are not unique, in other words, they do not draw up the same area of ideas. Taking the interplay of all of them for its connotation is an acceptable solution.
Precision of Studies From Astrometric Observations: Recent Progress and Future Prospects
Authors: Li Z. X.
Published: July 2016

Recent progress of precision in astrometric studies is summarized and the weights of systematic errors in astrometric observation are analysed.
Corrections to the IAU 1980 Nutation Series From Lageos Observations
Authors: Tarady V.K.
Published: July 2016

The attempt was made to determine the corrections to the coefficients of the IAU 1980 nutation series together with other geodesical and geodynamical parameters by the use of the Kiev-Geodynamics-3 program complex for LAGEOS laser data analysis. This complex is based on the MERIT standards and on numerical integration techniques for satellite orbit computation. An integration is carried out in cartesian coordinates by the Adams method of variable step and order.
The Program Complex “Kiev — Geodynamic R1”
Authors: Medvedsky M. M.
Published: July 2016

The software for the reduction of the VLBI observations of the Main Astronomical Observatory of the Ukrainian Academy of Science is described.

Our program complex has three parts:

1) calculation of geometrical delay τ,

2) calculation of required corrections to values of τ,

3) data analysis procedures.

This software has been tested using the NGS VLBI data for the obtaining of corrections to the ERP. The parameters of the clock were derived. Our results were compared with similar results, which were published by Shanghai observatory (China) and IRIS bulletin.

The differences between our results and the data given in the IRIS bulletin are within 5 mas, and for UT are within 0.1 ms.
Determination of Nutation Based on Observations With the Pulkovo Polar Tube
Authors: Kotreleva O.V.
Published: July 2016

Since 1953 regular observations have been carried out with the Polar photographic tube at Pulkovo [1, 2, 3]. A detailed description of the observational procedure, the data reduction technique, and error sources were given by Potter [4].
On the Calculation of Low Frequency Oscillations of the Earth's Core
Authors: Dyakonov S.V.
Published: July 2016

The problem of calculation of low frequency oscillations of an ideal rotating compressible fluid is investigated. An original method of solving such a problem, based on using characteristic functions of the Poincaré operator is proposed. An efficient scheme of calculating the characteristic numbers and functions of the Poincaré operator is worked out. The high speed of convergence of the method is shown. An essential influence of compressibility on the theoretical nutation amplitude is found.
On the Astrometrical Methods
Authors: Shkodrov V. , Ivanova V.
Published: July 2016

In this paper some problems are discussed concerning the connection between the highly accurate optical and radio observations in the case when the waves propagate in an anisotropic medium.
Dynamical Reference Frames in the Planetary and Earth-Moon Systems
Authors: Standish E. M. , Williams J. G.
Published: July 2016

We summarize our previous estimates of the accuracies of the ephemerides. Such accuracies determine how well one can establish the dynamical reference frame of the ephemerides. Ranging observations are the dominant data for the inner four planets and the Moon: radar-ranging for Mercury and Venus; Mariner 9 and Viking spacecraft-ranging for the Earth and Mars; lunar laser-ranging for the Moon. Optical data are significant for only the five outermost planets. Inertial mean motions for the Earth and Mars are determined to the level of 0.″003/cty during the time of the Viking mission; for Mars, this will deteriorate to 0.″01/cty or more after a decade or so; similarly, the inclination of the martian orbit upon the ecliptic was determined by Viking to the level of 0.″001. Corresponding uncertainties for Mercury and Venus are nearly two orders of magnitude larger. For the lunar mean motion with respect to inertial space, the present uncertainty is about 0.″04/cty; at times away from the present, the uncertainty of 1′/cty2 in the acceleration of longitude dominates. The mutual orientations of the equator, ecliptic and lunar orbit are known to 0.″002. The inner four planets and the Moon can now be aligned with respect to the dynamical equinox at a level of about 0.″005.
The Main Stages of the Construction of AE89—The Numerical Ephemeris of the Planets and the Moon
Authors: Belikov M. L. , Boyko V. N. , Glebova N. I. , Eroshkin G. I. , Rumyantseva L. I. , Sveshnikov M. L. , Sveshnikova E. S. , Smekhacheva R. I. , Trubitsyna A. A. , Fursenko M. A. , Chunaeva L. I. , Shiryaev A. A.
Published: July 2016

The realization of theoretical and applied researches in the domain of ephemeris astronomy, connected with analysis of precision of existing planetary and lunar theories, the construction of an inertial coordinate system and investigation of physical properties of space-time, necessitated the elaboration in ITA of the numerical theory of the motion of heavenly bodies suitable for calculation of high-precision ephemerides at large time-spans, and fit also for the maintenance of space experiments.
Fluctuations of the Earth's Rotation by Stellar Occultations
Authors: Jordi C. , Rossello G.
Published: July 2016

Observations of lunar occultations made between 1800 and 1955 are analyzed in order to determine the fluctuations of the Earth's rotation before the International Atomic Time was established. The reduction is made on the basis of the DE200/LE200 ephemeris and the FK5 system. The analysis of the fluctuations shows a main period of 11.7 lunations caused by the error in the stars places.
Hipparcos and Reference Systems
Authors: Mignard F. , Cerga O.C.A.
Published: July 2016

The Sphere determined from the observations carried out by the ESA satellite Hipparcos will have a residual rotation with respect to distant extragalactic sources. The alignement of the two systems of reference will be made at the mission completion. The procedure to be applied is discussed along with its expected accuracy.
Space Astrometry and the HST Wide Field/Planetary Camera
Authors: Seidelmann P. K.
Published: July 2016

The launch of the Hipparcos spacecraft marked the beginning of space astrometry. Hopefully, this will be followed in the near future by the launch of the Hubble Space Telescope, which is not primarily an astrometric instrument, but has astrometric capabilities which will be described in this paper. In addition, there are plans and proposals for future astrometric spacecraft. These include the launch of a radio antenna, which combined with Earth-based antennae would provide a very, very long base line interferometer (Levy, 1986, 1988). There are proposals for launching optical interferometers, such as POINTS (Reasenberg et al 1988). There are also proposals by York and Gatewood (Gatewood et al., 1986; Gatewood 1987, 1989) for launching astrometric instruments using gratings and detectors. Thus, the future holds the prospects for a whole new capability in the field of astrometry.
Correction to Absolute Proper Motion Using the IAS-Galaxy Model
Authors: Ratnatunga Kavan U.
Published: July 2016

The IAS-Galaxy model (Ratnatunga, Bahcall and Casertano 1989) is a software interface between theoretical models of the Galaxy and observed kinematic distributions. It has been developed for analysis of many kinematic catalogs to study global galactic structure. In addition, the IASG model can be used to estimate corrections needed to derive absolute parallax and absolute proper motion by evaluating, on a star-by-star basis, the expected mean motion of the reference stars.

A theoretical Galaxy model is defined on an inertial coordinate frame. Proper motions are measured in a reference frame defined by a fundamental catalog. The observed distribution of proper motions in star catalogs can be directly compared with the expected distributions evaluated using IASG to check the accuracy of the adopted reference frame in realizing the inertial coordinate frame in the sky.
Realization of the Local Inertial Geocentric Frame in Relativity
Authors: Miao-Fu He , Cheng Huang
Published: July 2016

There are two kinds of geocentric frames: local inertial and non-inertial geocentric frames. Ashby et al successfully constructed a local inertial geocentric frame in the neighborhood of the gravitating Earth. In the frame with origin at the Earth's center, the gravitational effects of the sun and of planets other than the Earth are basically reduced to their tidal forces, with very small relativistic corrections.

However, the spatial base vectors of the local inertial frame essentially experience the geodesic (or deSitter) precession with respect to the solar system barycentric frame. Hence the realization of the local inertial frame requires that the general precession should exclude the geodesic precession. This requirement is inconsistent with the convention that the amount of geodesic precession is included in that of the general precession given by Lieske et al.
Astrometry With the Tautenburg Schmidt Telescope
Authors: Steinert K.-G.
Published: July 2016

The realization of an optimum astronomical reference frame depends on well-defined connection between the systems of optical and radio positions of objects. For this the physics of radio objects are to be studied carefully. Besides this it is necessary to investigate how to get accurate positions of the optical counterparts of these objects as benchmarks for establishing a radio-optical reference frame. As the optical sources are very faint, photographic telescopes with robust light-gathering power are to be used.

For 15 years research work has been done using plates of the 134/200/400 Tautenburg Schmidt telescope for determinations of photographic positions of stars and extragalactic objects. An overview of some special results obtained at Dresden Lohrmann Observatory and Potsdam Central Institute of Astrophysics of the GDR Academy of Sciences will be given.
Comparison of Astrometrical Accuracy of Big Schmidt Telescopes
Authors: Schilbach E. , Hirte S. , Heudier J.-L.
Published: July 2016

The measurements of AGK3 stars carried out with the automated measuring machine MAMA in Paris were used for the estimation of the accuracy of stellar positions on Tautenburg and CERGA plates. The results show good coincidence of stellar positions derived with both Schmidt telescopes. The achieved accuracy is high enough to use combined observations for improving present positions in the catalog AGK3.
CCD Parallaxes for Faint Southern High Proper Motion Stars
Authors: Anguita C.A. , Ruiz M.T.
Published: July 2016

In April 1985, we started a program to measure trigonometric parallaxes for faint southern high proper motion stars, using a CCD at the Cassegrain focus of the Cerro Tololo Interamerican Observatory (CTIO) 1.5-m telescope. The program stars (mR > 16; μ ≥ 1 arcsec/year) were selected from the LHS Catalogue and the University of Chile proper motion program.

The X and Y positions of the stellar image centroids were obtained using the algorithms of DAOPHOT program packages. The precision of the measurement of one stellar image is about 6 milliarcseconds (0.02 pix). For stars with 16 < mR < 19.5 a precision of 2 milliarcseconds in the parallax determination can be obtained in a one year period. Trigonometric parallaxes for some stars common to other parallax programs are given, showing an agreement with those results within the quoted mean errors.

Several technical aspects of the present program are also discussed.
An Astrometric Catalog of Four Million Stars
Authors: Nesterov V. V. , Kisliuk V. S. , Potter H. I.
Published: July 2016

The goal of the present study is

(1)

Completion of a general reduction of the Carte du Ciel astrophotographic catalogs, measurement of the positions in them on modern astronegatives, derivation of proper motions and compilation of a catalog of stars to magnitude 12.5.

(2)

Copying the data of all 272 volumes of astrophotographic catalogues onto magnetic tapes (all together 8.5 million measurements).

(3)

Measurement of modern astronegatives on FON-OBZOR-S and FOKAT-Y programs.

(4)

Studies of the magnitude equation of the AGK3 catalog and other catalogs which will be presumably used as reference catalogs.

(5)

Development and comparative studies of several methods of determination of equatorial coordinates on the basis of full information on astronegative measurements. Application of these methods to compilation of the catalog of 4 million stars.
Modernization of Chinese Photoelectric Astrolabes and Improvement of Optical Reference System
Authors: Dong-Ming Li , Hong-Qi Wang , Gang Zhao , Ze-Zhi Wang , Rui Wang
Published: July 2016

The features of the astrolabe are that:

(1) a span of 6 hour of R.A. of star positions can be tied in a group of observation of 2 hours, all-night observation can cover more than half of the sky, and

(2) the declination system can be set up with high precision without the need of a precise circle (Li 1987).
Locating the Seat of the Solar Dynamo
Authors: Choudhuri Arnab Rai
Published: July 2016

By analyzing the hypothesis that the solar dynamo operates in a thin layer at the bottom of the convection zone, we conclude that this hypothesis can fit observational facts only if there is turbulence with the length scale of a few hundred kilometers in and around the dynamo region.
Helioseismological Determination of Stratification and Dynamic Processes in the Solar Core
Authors: Kosovichev A.G.
Published: July 2016

Helioseismology provides a powerful tool for investigating stratification and dynamics of plasma in the Sun's interior. The observed frequencies of the 5-min oscillations depend on density, sound speed, chemical abundances and angular velocity distributions inside the Sun. These parameters are estimated using inversion techniques.
Stokes Parameters for Thomson Scattering in Magnetized Plasma
Authors: Chou Chih-Kang , Chen Hui-Hwa
Published: July 2016

The effect of a superstrong magnetic field on neutron stars or white dwarfs is studied for Thomson scattering in a fully ionized collisionless. plasma. The equation of motion for an electron in the presence of both the induced electric field of the plasma and a static uniform external magnetic field is used to determine the acceleration of the electron. The collective plasma effects due to the field and density fluctuations are investigated by using the test-particle picture. The scattering of a photon by a plasma is a function of the acceleration of particles by the electric field of the incident wave and the static external magnetic field Assuming that the electrons are distributed with density the radiation field far from the scattering center is

where the delta function indicates that all quantities are to be evaluated at the retarded time and δλ is the angle between the wave vector and the Poynting vector, which is given by
Linear and Nonlinear Convection with an Aligned Magnetic Field
Authors: Rudraiah N. , Shivakumara I S , Geetavani P
Published: July 2016

The effect of horizontal magnetic field on the onset of three-dimensional convection in a horizontal fluid layer is studied. It is found that the two-dimensional solutions are unstable to three-dimensional disturbances. A detailed bifurcation study is reported.
Waves in Magnetic Flux Tubes
Authors: Roberts B
Published: July 2016

The basic aspects of wave propagation in a magnetic flux tube are reviewed, with particular emphasis on the types of flux tube that occur in the solar atmosphere. Two fundamental speeds arise naturally in a description of wave propagation in a flux tube: the slow magnetoacoustic (cusp) speed cT, which is both subsonic and sub-Alfvénic, and a mean Alfvén speed ck. Both surface and body modes are supported by a tube. It is stressed that a flux tube may act as a wave guide, similar to the guidance of light by a fibre optic, or sound in an ocean layer, or seismic waves in the Earth's crust.
Resonant Absorption of P-Modes by Sunspots
Authors: Chitre S.M. , Davila Joseph. M.
Published: July 2016

A substantial amount (≲50%) of solar acoustic (p-mode) absorption in sunspot regions has been reported by Braun, Duvall and LaBonte (1988). A number of suggestions have been advanced to account for the observed p-mode absorption in sunspots (see review by Davila in these proceedings). These include processes involving resonance absorption, radiation damping, and non-dissipative mechanisms. The main purpose of the present work is to demonstrate that any dissipative process like radiative, viscous, or resistive dissipation leads to the resonant absorption of acoustic waves incident on the sunspot tube and that the resultant heating rate can be shown to be consistent with the observed absorption of the p-mode power impinging on an isolated inhomogeneously structured sunspot.
Recent Advances in Acoustic Heating
Authors: Ulmschneider P.
Published: July 2016

Turbulent surface convection zones of stars generate acoustic waves which contribute to the heating of chromospheres and coronae. The dissipation of limiting strength acoustic shock waves agrees well with the empirically determined chromospheric radiation loss rates. Acoustic waves with frequency and energy required for the chromospheric heating are observed in the solar atmosphere. Acoustic heating can explain the basal chromospheric emission of slowly rotating stars and constitutes a weak background in faster rotating stars; it can not explain the emission-rotation correlation and the surface variation of emission which are due to magnetic heating.
Fabry-Perot Interferogram Profiles in λ5303 in Relation to Coronal Structures: 1980 and 1983 Eclipses
Authors: Desai J.N. , Raju K.P. , Chandrasekhar T. , Ashok N.M. , Pasachoff J.M.
Published: July 2016

Fringe profiles of Fabry-Perot interferograms taken in the λ 5303 line during the total solar eclipses of 1980 and 1983 are studied in relation to coronal structures observed in white-light pictures. Evidence for doppler-shifted discrete components and large random velocity components in specific regions is presented here.
The Evolution of a Sheared Potential Magnetic Field in the Solar Corona
Authors: Karpen J. T. , Antiochos S. K. , DeVore C. R.
Published: July 2016

Several theoretical studies have proposed that, in response to photospheric foot-point motions, current sheets can be generated in the solar corona without the presence of a null point in the initial potential magnetic field. In these analytic models, current sheets form wherever the coronal field dips down and is parallel to the photosphere. A fundamental assumption in these analyses — commonly referred to as the line-tying assumption — is that all coronal field lines are anchored to a boundary surface representing the top of the dense, gas-pressure-dominated photosphere. In theoretical arguments presented elsewhere (Karpen, Antiochos, and DeVore 1989), however, we show that line-tying is not valid for “dipped” coronal fields, and hence that the conclusions of the line-tied models are incorrect. We contend that current sheets will not form if the photosphere-corona interface is represented by a physically valid model. Here we summarize a numerical investigation of the response of a “dipped” potential magnetic field in a hydrostatic-equilibrium atmosphere to shearing motions of the foot points. Our results show that, in the absence of artificial line-tying conditions, a current sheet indeed does not form at the location of the dip. Rather, the dipped magnetic field rises, causing upflows of photospheric and chromospheric plasma.
Plasma Processes in Solar Flares
Authors: Tomozov V.M.
Published: July 2016

A rationale is presented for a conception that appearance of flares in active regions is due to the interaction of large-scale convective elements. Such an interaction gives rise to shear motions in the vicinity of the inverse polarity line of the photospheric magnetic field which generate vortical motions leading to non-equilibrium state of the magnetic configuration. Modern concepts of manifestations of turbulent plasma processes are described in terms of theoretical models for solar flares. Plasma effects arising at propagation of electron beams and thermal fluxes in the solar atmosphere are considered. Their role in the interpretation of hard X-ray and type III radio bursts is pointed out. The role of the turbulent Stark effect for diagnostics of collective plasma processes in solar flares is emphasized.
Magnetic Field-Chromospheric Plasma Interaction and the Problem of the Braking Force in Surge Dynamics
Authors: Dermendjiev V.
Published: July 2016

An important stage in the evolution of solar flares is the generation of a number of dynamic phenomena, greatly varying in size and velocity, but actually representing plasma ejections. They are responsible for the transport of mass and energy and are usually considered to be result of the development of local magnetic features accompanied by a magnetic energy increase in the solar atmosphere. One of these phenomena is the surge prominence. In this contribution, we propose a possible explanation for the nature of the braking force acting in the decelerated ascending phase of surge dynamics. The possibility of structuralization of the chromospheric plasma during surge formation and the plasma action on the external, colimating magnetic field is taken into account.
Density Diagnostics of Solar Emission Lines from the Nitrogen-like Mg VI Ion
Authors: Raju P.K. , Vasundhara R.
Published: July 2016

The variation of theoretical line intensity ratios with electron density for Mg VI ion are presented. This study indicates that the line intensity ratios for Mg VI can be used to infer electron density for solar plasma.
Relationship of Coronal Mass Ejection Events with Solar Flares and Coronal Holes
Authors: Verma V K
Published: July 2016

We present an analysis of the relationship between coronal mass ejection (CME) events with solar flares and coronal holes. Out of 79 CME events whose location and span are known, 10 CME event circles contain solar flares. On the other hand out of 71 CME events (selected for the study with coronal holes) 40 CME event circles contain coronal holes. We have examined the above associations by calculating the Yule's coefficients of association and found that the CME events and solar flares are statistically not associated while CME events and coronal holes are statistically associated. This does not necessarily indicate that CMEs come from coronal holes as claimed by Hewish and Bravo (1986).
Diagnostics of the Solar Plasma Using Radio Observations with the RATAN-600
Authors: Gelfreikh G.B.
Published: July 2016

This paper summarises the methods and main results of studying physical parameters and processes in different structures of the solar atmosphere from the chromosphere to the outer corona as based on the observations with a 600-meter radio telescope the RATAN-600 (1975-1989). Diagnostics of the solar plasma have been made using the spectral-polarization measurements in the wavelength range 0.8-32 cm with high spatial resolution. The most important results concern the structure and strength of the magnetic fields at different levels of the solar atmosphere and detection of localized regions of long-lasting (several days) energy release in the lower corona.
VLA-Phoenix Observations of a Narrow-Band Decimetric Burst
Authors: Willson Robert F. , O. Benz Arnold
Published: July 2016

We discuss observations of a highly-circularly polarized multiply-impulsive microwave burst detected by the Very Large Array and the Phoenix Digital Radio Spectrometer. The VLA was used to resolve the burst in two dimensions, while PHOENIX provided high time resolution information about its spectral properties. During part of the burst, positive frequency drifts were detected, suggesting inwardly propagating beams of electrons emitting Type III-like radiation.
Recent Results on Associations: Anatomy of CMa OB1 and Mon OB1
Authors: Herbst William
Published: July 2016

Three types of associations are presently recognized. These are OB, R, and T, and represent, respectively, concentrations of O and B type stars, reflection nebulae, and T Tauri stars, in certain regions of the sky. OB and T associations are identified on objective prism plates; R associations may be found using direct plates such as those of the Palomar Sky Survey. All associations are intimately connected with what appear optically as dark clouds and are now detected as sources of molecular line emission and known as molecular clouds. Often, all three types of associations are found within the same cloud complex (eg, Mon OB1). However, there are also examples of T associations (Taurus) and R associations (Mon R2) which are not connected with recognized OB associations.
Abundance Variations Among Young Clusters and Associations
Authors: Nissen Poul E.
Published: July 2016

The aim of this paper is to give a review of our knowledge of the chemical composition of young groups of stars in the Galaxy, i.e. open clusters and associations with ages less than about 109 years. In particular I shall discuss if abundance differences between these groups of stars do occur, and how large these possible differences can be. Such information is important in many astronomical fields. Thus, abundance differences between star clusters complicate the determination of their distances by ZAMS-fitting, and make the distance scale in the Universe more uncertain. Comparisons between theoretical isochrones and cluster sequences in color-magnitude diagrams with the purpose of testing the theory of stellar structure and evolution are also much more difficult if differences in abundances have to be taken into account. On the other hand the determination of abundances of clusters and associations as a function of their ages and places of formation give important information on the chemical evolution of our galaxy, in particular because abundances, ages and space velocities for clusters and associations can be determined much more accurate than for single stars.
The Present Data Situation for Stars in Open Clusters. II
Authors: Mermilliod J.-C.
Published: July 2016

The present state of astrometric, spectroscopic and photometric data for stars in 63 open clusters nearer to the Sun than 750 pc is summarized. Table I reports the limits of the available data in terms of the apparent V magnitude, in the same way as the previous version (Mermilliod 1977). Information on the apparent V magnitude of the brightest main sequence star (Vbr) and on the number of stars brighter than V=10 (n∗) has been included. In addition, the bluest spectral type on the main sequence has been used as an age estimator (TS).
N-Body Simulations of Open Clusters
Authors: Terlevich Elena
Published: July 2016

The dynamical evolution of open star clusters has been followed by numerical N-body simulations. These computations have been done considering both the interactions between stars in the cluster, and the effect of a linearized galactic tidal field, assuming circular orbits in the solar neighbourhood. Models have been studied for 250, 500 and 1000 stars, and two initial mass spectra (α=2.35 and α=2.75). We adopt a mean mass and a mass ratio of 50:1 between the heaviest and the lightest star. A simple scheme for instantaneous mass-loss from stellar evolution (neutron stars and white dwarfs) is incorporated into the models using published parameters. The models with 250 stars are found to be relatively insensitive to the adopted value of (the virial theorem scale factor) in the range of pc. The disruption half-lifes (T1/2) are about 1.7 × 108y for models with 250 stars, and 4.6 × 108 y for 1000 stars and α=2.75. Preliminary work including successive encounters of clusters with interstellar clouds appears to give shorter disruption times. Two effects play an important role in the dynamical evolution of the cluster: the formation of one or two massive and energetic binaries (≃50 per cent of the total energy) during the first few crossing times, and their disruption by mass-loss.
Open Clusters and Stellar Evolution
Authors: Harris Gretchen L.H.
Published: July 2016

Several topics relevant to the study of stellar evolution through open clusters are discussed. These include composite color-magnitude diagrams, the need for thorough studies of populous clusters, parameters affecting the core helium burning stage, and the potential importance of initial conditions and dynamical evolution on the cluster color-magnitude diagram.
Distant Galactic Open Clusters
Authors: Christian C. A.
Published: July 2016

The motivation for studying distant open clusters primarily arose out of a desire to gain some understanding of star formation processes in the general context of galactic structure. Of specific interest are faint open clusters (c.f. Alter, Balázs and Ruprecht 1970) near the galactic anticenter which are part of a larger survey of objects which may be located in the “periphery” of the Galaxy. Table I contains a sample of results from broad-band photometric studies for clusters near ZII=180°, bII=0°. The characteristics of these clusters are consistent with other investigations, which suggest that the disk of the galaxy extends to large galactocentric distances; for example, deep surveys of blue stars (Chromey 1979; McCarthy and Miller 1974) and investigations of the rotation curve of the galaxy (Blitz 1979; Knapp, Tremaine and Gunn 1978), to mention a few. There is also a considerable amount of evidence that the distributions of distant objects basically reflect the locations of local absorbing clouds and low absorption “windows” (Westpfah1 and Christian 1979), rather than distant galactic structure. Therefore, in this study, emphasis is being placed on the determination of ages, abundances and luminosity functions of clusters, rather than considering them as “spiral tracers”.
Polarization of Stars in the Field of NGC 3372
Authors: Marraco H. G. , Forte J. C.
Published: July 2016

BV polarimetry of about 60 stars belonging to the clusters Tr 14, Tr 16 and Coll 228 as well as some luminous stars of the surrounding field is presented.
Radial Velocities and Rotational Velocities of Late-Type Stars in the Coma Ber Cluster
Authors: Mayor M. , Mermilliod J. C.
Published: July 2016

Stars with spectral types later than or equal to F5V in the Coma Ber cluster have been measured from 1977 to 1979 with the spectrometer CORAVEL (A. Baranne et al. 1980). The aims of this investigation were to clarify the membership based on radial velocity for some faint stars, to study the binarity of the low mass stars of the cluster, and to obtain the distribution of the rotational velocities for the red dwarfs. 391 measurements have been made for 34 stars. The average dispersion over the mean VR of each star is 0.6 kms−1.
A Search for HI in Nine Southern Galactic Clusters
Authors: Olano C. A. , Pöppel W. G. L. , Vota M. D.
Published: July 2016

The results of a search for HI features in nine galactic clusters are reported. The clusters were selected from the catalog of Alter et al. (1970) with galactic latitudes in order to reduce the galactic background radiation. The clusters are listed together with some of their newer optical data in Table 1. Column 1 gives the cluster's designation; 2 and 3 their galactic coordinates; and 4 and 5 their distances and mean angular diameters. Only two of the clusters have a measured radial velocity.