bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Topological Model of the Solar Magnetic Field Reversals
Authors: Benevolenskaya E.E. 
Published: July 2016

The phenomenon of a three-fold reversal of the solar polar magnetic field in both hemispheres has not been observed during the last 115 years. Such three-fold reversals took place in the southern hemisphere alone in the even cycles Nos 12 (1885.8), 14 (1908.4) and in the northern hemisphere alone in solar cycles Nos 16 (1928.5), 18 (1949.0), 20 (1970.6). The single reversal took place in the odd cycles, the only exception is the solar cycle No 19 (Fig. 1).There are periods of 1.7-2.5 years in the variation of background magnetic fields (Makarov et al., 1985). It determines the quasi-period of the high-frequency component and corresponds to a time interval between the zones of alternating polarity of the magnetic field. This enables us to show topologically that single and three-fold polarity reversals of the solar magnetic fields can result from interaction of two types of magnetic fields: a low-frequency component with period of the order of 20 years and a high frequency component with period of order of 1.7-2.5 years (Benevolenskaya and Makarov, 1990).
Solar Rotation over Solar Cycle 21
Authors: Ribes Elisabeth , Vince Istvan , Mein Pierre , Ferreira Eduardo Neto 
Published: July 2016

Abstract Having measured the rotation rate of sunspots through solar cycle 21, from 1977 to 1983, we have found that the mean differential rotation averaged over this seven year record is similar to the grand average differential rotation determined by Howard et al. (1984) over the period 1921-1982. However, the rotation rate does change from year to year. These changes are evidenced by a steepening or a flattening of the mean differential rotation profile, as well as significant changes in the equatorial rate. The presence of a time-dependent pattern of azimuthal rolls inferred from the meridional circulation pattern of the sunspots offers a qualitative explanation of the observed rotation rates. The amplitude of the changes is almost one order of magnitude larger than that of the torsional oscillations found by Howard and LaBonte (1981).
The HeI λ10830 Å Line as an Indicator of the Chromospheric and Coronal Activity of the Sun
Authors: Shcherbakov A.G. , Shcherbakova Z.A. 
Published: July 2016

AbstractThe behaviour of the HeI λ10830 Å line profile in spectra of solar features is reviewed. The connection of line characteristics with various phenomena on the solar disc, such as plages (faculae), sunspots, jets, prominences, coronal holes, flares, fine structure and emission above the solar limb, is discussed. We present a short summary of the mechanisms for helium excitation in the solar chromosphere. Time variations of the line profile, observed in quiet and active regions, and HeI λ10830 Å absorption in the Sun as a star are discussed and compared with other indexes of solar activity. It is shown that the equivalent width of the helium line varies in an 11 year cycle and reflects the 27 day periodicity of the rotation of the Sun. It is also shown that the HeI line is a more sensitive index of activity than K-index.
Temperature Variations on the Surface of the Si-star CU Virginis
Authors: Ryabchikova T.A. 
Published: July 2016

AbstractA hot region with an increase of effective temperature of 700 K was found on the surface of Si-star CU Vir, based on the analysis of the available photometric and spectroscopic observations. This hot region is located near the phase of negative magnetic extremum and can explain both hydrogen line and infrared light variations.
Starspot Activity on Short-period RS CVn Stars
Authors: Zeilik Michael 
Published: July 2016

We have yet to understand the magnetic activity cycles of cool close binary systems of sunlike stars. Mutual tidal interactions, as well as magnetic ones, may result from a regime of dynamo models not yet tested, because these have been developed for single stars. To arrive at the basic physics, though, requires that we first examine the phenomenology of magnetic activity for binary systems. In particular, we would like to discover if such activity has a clearly-defined cycle, such as the sun exibits.Among the proxy indicators of magnetic activity are the Ca II H and K lines. Strassmeier et al. (1988) used the strength of these lines as the primary criterion for the inclusion of systems in The Catalog of Chromospherically Binary Stars. Of the RS CVn stars in the catalog, 12 have orbital periods of one day or shorter; 9 are eclipsing systems. As part of a decade-long program, we have focussed our observations and models on eight of the short-period group (Hall, 1976): XY UMa, UV Psc, SV Cam, RT And, CG Cyg, ER Vul, BH Vir, and WY Cnc. These close systems are tidally-locked in synchronous rotation and tidally-distorted into Roche lobe configurations.
Variations in Spottedness of Photosphere and Chromosphere of the Flare Star EV Lac
Authors: Gershberg R.E. , Ilyin I.V. , Shakhovskaya N.I. 
Published: July 2016

AbstractQuantitative analysis of the variations of EV Lac as being caused by spottedness leads to the conclusion that the total areas of starspots vary strongly – up to two or threefold – from one season to another but the starspot temperatures remain constant.
On the Existence of Solar-type Activity in the Secondary Components of Cataclysmic Variables
Authors: Dmitrienko E.S. 
Published: July 2016

AbstractCyclic variations of the parameter O-C (the difference between observed and calculated times of the light minimum in eclipse) have been detected for Nova 1934 DQ Her in the U BV RI-bands during 1982-89 with a recurrence time of about 5-6 years and amplitudes of about 2-4 min. No O-C oscillations for the nova-like AC Cnc have been discovered with the resolution of 45 sec in 1985-89. Both systems consist of a white dwarf and a late-type dwarf component. Some possibilities to explain their O-C-behaviour are discussed.
A New Technique to Measure Magnetic Field Strength in Active Stars
Authors: Almeida J. Sánchez , López R. J.García 
Published: July 2016

AbstractWe explore the use of the flux difference between the lines Fe I 5250 Å and Fe I 5247 Å as a technique to measure photospheric magnetic fields in late-type stars. The technique developed takes into account all the LTE physics of the problem, assuming a radial and homogeneous magnetic field distribution over the stellar surface. Some test calculations, in order to prove the feasibility of the method, are shown.
Magnetic Flux Determination in Late-Type Dwarfs
Authors: Rίpodas P. , Almeida J. Sánchez , López R. J. García , Collados M. 
Published: July 2016

AbstractWe present a very preliminary and simplified analysis designed to measure photospheric magnetic fields in late-type stars, using the FeI 5247.06 Å and 5250.22 Å lines. We show how the use of the equivalent widths of the lines and differences in their depth can give a rapid estimation of the magnetic flux.
Magnetic Fields and Filling Factors in Late-Type Stars: Predictions from Dynamo Theory
Authors: Montesinos B. , Fernández-Villacañas J.L. , Jordan C. 
Published: July 2016

AbstractIn this paper we examine the link between observed magnetic fields and filling factors in main-sequence stars of types G and K, and the results obtained for these parameters from a simple dynamo model. We explore how the predicted magnetic fluxes, fB, for a selected sample of stars, vary with rotation, adopting two theoretical approaches to estimate the filling factor, and considering different expressions for the variation of the stellar angular velocity, ω, with depth.
Hα and NaD Line Variability in RY Tauri
Authors: Petrov P. , Vilhu O. 
Published: July 2016

AbstractUsing high resolution spectroscopy of the T Tau star RY Tau in the regions of Hα and Na D lines, we discovered line profile variability, which is interpreted by a hypothesis of stellar ’prominences’: cool gas clouds are moving inside the stellar wind, ascending and descending on a time scale of a few days. These clouds are supposed to be controlled by the magnetic field of the star. The range of radial velocities of the clouds (−100 to +100 km/s) is twice as large as the rotational velocity (v sin i) of the star. The form of variability of the Hα profile suggests the existence of two components: the (variable) stellar wind and the circumstellar disc.
The Age Evolution of Ca II Emission in Late Type Stars
Authors: Trigilio C. , Catalano S. , Marilli E. , Reglero V. , Umana G. 
Published: July 2016

It has been widely demonstrated that chromospheric emission is dependent on rotation rate (Hartmann and Noyes, 1987, Catalano, 1990, for recent reviews). Since the rotation decays with time, the chromospheric activity of single main sequence stars is also dependent on age. Catalano and Marilli (1983) suggested that the chromospheric emission of solar mass stars decays exponentially with the square root of the time, as recently confirmed by Barry (1988). Magnetic activity depends also on the convection parameters, i.e. on the mass. Since the evolution of surface rotation is faster for lower mass stars (Catalano et al., 1988), the internal rotation distribution, and therefore the dynamo action, should change with time in a different way for different masses.In order to get insight into the evolution of dynamo action we have studied the CaII chromospheric emission as a function of mass and age. Here we present some preliminary results of observations of late type stars in young clusters and old moving groups.
Flare Rate Spectra as a Possibility of Diagnostics of Convection Zones in Stars
Authors: Pustil’nik L.A. 
Published: July 2016

AbstractA theoretical interpretation is offered for the power-law dependence of the flare occurrence rate in red flare dwarfs. Flares on red dwarfs are regarded as being physically akin to solar flares, with the energy source being the magnetic field. A power law flare energy relation then emerges naturally. Model estimates of the corresponding spectral index β fit the observed values in most flare stars. Within the bounds of the interpretation offered the energy dependence of a flare event is determined by the character of the turbulence in the convection zone. The observed parameters of the dependence can be used to diagnose the character of the turbulence in the convection zones of flare stars.-
Actinide Lines in the Spectra of Peculiar Stars: the Search for Evidence of Recent r-Process Events
Authors: Blake J.B. , Schramm D.N. 
Published: July 2016

SummaryA discussion is presented on how to ascertain whether certain peculiar star phenomena can be understood as resulting from an enhanced abundance of recently synthesized (&lt; 109years ago) r-process material. The actinides Th and U are shown to be powerful probes. The possible lack of odd-even abundance effects does not lower the probability of r-process material being present. The recent uranium isotopic measurements of Cowley and Adelman (1975) also are discussed.
The Broad Continuous Absorption Features and Atmospheric Structure of Peculiar A Stars
Authors: Adelman Saul J. , Shore Steven N. , Wolken Pamela R. 
Published: July 2016

SummarySpectrophotometry of peculiar A stars shows that their flux distributions match those of main sequence stars in a gross sense in the optical region λ 3300-7100 although many magnetic peculiar A stars possess broad continuous absorption features not seen in the main sequence stars. In an attempt to explain these features, locations of bound-free discontinuities were computed using known energy levels for the relevant atomic species of those elements which are known to be overabundant. Most of these possible candidates can be eliminated as contributors.
A Working Report on Hd 203006 (θ1 Mic)
Authors: Schober H.J. 
Published: July 2016

A rapid spectrum scanner is a suitable instrument for a direct photometric study of spectral features. As an example HD 203006 was selected to report on the possibility to get useful information from spectrum scanner observations.The cool Ap star HD 203006 (θ1Mic, HR 8151), spectral type A 2 p and V = 4m.81, was first observed to show a variable magnetic field by Babcock (1958). He also stated strong Cr I and II, Eu II and Sr II lines and a reversal of the magnetic polarity after about one day. Morrison and Wolff (1971) observed this star in the uvby system and got a 1dperiod (1d.062 or 0d.941). A relatively strong scatter in the v-band during the m maximum phase they attributed to a variability in the Hδ-line.
Are All Blue Stragglers Ap Stars?
Authors: Pendl E.S. , Seggewiss W. 
Published: July 2016

SummaryA list of open clusters with blue stragglers studied for Ap characteristics is presented. In addition to previously published results new spectroscopic data are given of blue stragglers in the open cluster IC 4756 derived from ESO spectrograms taken in 1973. Preliminary conclusions concerning the status of Ap stars and blue stragglers are drawn.
The HgMn Stars
Authors: Wolff Sidney C. , Wolff Richard J. 
Published: July 2016

SummaryThe properties of the HgMn stars, including their rate of occurrence as a function of temperature and their rotational velocity distribution, are discussed. It is shown that there must be some normal, slowly rotating stars; slow rotation is a necessary but not sufficient condition for the formation of a HgMn star. The relationship of the HgMn stars to other peculiar stars, including the Am and He-weak stars, is discussed.
On the Configuration of the Magnetic Field of β CrB
Authors: Aslanov I.A. , Rustamov Yu.S. 
Published: July 2016

SummaryMeasurements of the radial velocities and magnetic field strength of β CrB were carried out. It is shown that there is a variability with the rotation period different for various elements. The curve of the magnetic field variation measured from lines of 5 different elements: FeI, CrI, CrII, TiII, ScII and CaI has a complex shape specific for each element. This may be due to the presence of magnetic spots on the stellar surface. A comparison with the radial velocity curves suggests the presence of a least 4 spots of Ti and Cr coinciding with magnetic spots. A change of the magnetic field with optical depth is shown. The curve of the Heffvariation with the rotation period is given. A possibility of secular variations of the magnetic field is shown.
Statistical Study of the Rotation Effect of Am Stars
Authors: Kodaira Keiichi 
Published: July 2016

SummaryExcess of [m1] index of Am stars, relative to normal stars, is statistically found to be correlated with rotation velocity; the coefficient is estimated at ∆׀m1׀ /∆V(km/sec) ˜ - 0.0007 among Am stars. This result supports the general view that slow rotation is essential for Am phenomena.
Ideal Reference Frames, Concepts and Interrelationships
Authors: Veis George 
Published: July 2016

AbstractMany problems of geodynamics depend on spatial relationship of points and their temporal variations. To solve these problems it is convenient, but not necessary, to use a reference frame. To use a reference frame, a scheme is needed by which the coordinates of any point expressed in this frame could be obtained. Coordinates are hardly ever measured directly. Instead, they are computed from measurements of other quantities within the framework of a theory that relates the measured quantities with the coordinates. Such a scheme will be called a reference system. Reference systems have been realized using simple theories and reducing the measurements with the best available, but not always complete, theories. This geometric (static) method has been used to a great extend to define astronomic reference systems (star catalogues) and geodetic reference systems (geodetic datums), With space techniques, a method can be used based on dynamic principles. A space object moving according to a certain theory (assumed to be known) defines in a time dependent way the representative points. A reference system of this type is the WGS 72.
Relativistic Effects in Reference Frames
Authors: Moritz H. 
Published: July 2016

AbstractThe impact of relativistic theories of space, time and gravitation on the problem of reference systems is reviewed.First, the concept of inertial systems is discussed from the point of view of the special and the general theory of relativity. Then, relativistic corrections of Doppler, laser and VLBI, and similar effects are reviewed; they are usually on the order of 10-8. Finally, the problem of a possible variation of the gravitational constant G (on the order of 10-11/year) is outlined; such a variation does not occur in special and general relativity, but is implied by certain generalized field theories which are less commonly accepted.
Reference Coordinate System Requirements for Space Physics and Astronomy
Authors: Mulholland J. D. 
Published: July 2016

AbstractChanges in reference coordinate systems have major implications well beyond the realm of Earth dynamics. Definitions that serve geodynamic convenience may cause considerable effects for other disciplines. After presenting some typical areas in which coordinate frame definitions are important, recommendations are given for criteria to be considered as boundary conditions in discussing changes. These cover such qualities as observability, complexity, stability, internal coherence and uniqueness.
On Reference Coordinate Systems Used in Polar Motion Determinations
Authors: Kołaczek B. , Teleki G. 
Published: July 2016

AbstractA short review of the reference pole presently used in polar motion determinations by classical astrometric methods is followed by a discussion of the systematic differences between systems of polar coordinates and the influence of the mean latitude of stations on pole position. The importance of homogenous processing astrometric data is stressed.
Determination of ‘Decade’ Fluctuations in the Earth’s Rotation 1620-1978
Authors: Morrison L V , Stephenson F R 
Published: July 2016

Abstract:The ‘decade’ fluctuations in the Earth’s rotation in the period 1620-1978 are derived from astronomical observations. The torques on the mantle which produce these fluctuations attain a magnitude of 1018Nm (1025 dyn cm) around 1900.
Some Considerations in the Use of Very-Long-Baseline-Interferometry to Establish Reference Coordinate Systems for Geodynamics
Authors: Robertson Douglas S. 
Published: July 2016

AbstractPresent knowledge of the number, distribution, proper motion and structures of extragalactic radio sources indicates that there should be no problem in defining a celestial reference frame with stabilities of a few milliseconds of arc over time spans of the order of a decade. One of the limiting factors appears to be the structure of the sources. By measuring and monitoring these structures, the stability could probably be improved by as much as one or two orders of magnitude. Even without this improvement, a network of properly distributed fixed observatories making regular interferometric observations of these radio sources could be used to define a terrestrial coordinate system that could be maintained at the few centimeter level over indefinitely long time periods. Such a stable terrestrial reference system would be useful for a host of modern geodetic and geodynamic applications, including, in particular, studies of the time varying deformations and relative motions of lithospheric plates. The National Geodetic Survey has already begun work on a three station base network of permanent observatories under project POLARIS as a first step toward implementing the new celestial and terrestrial reference frames. It is hoped that others will join in the effort and make the new reference frames a reality by the middle of this decade.
Use of Gravity Measurements in Defining and Realizing Reference Systems for Geodynamics
Authors: Boulanger J. D. , Pariisky N. N. , Pellinen L. P. 
Published: July 2016

AbstractSingle measurements of gravity cannot give sufficient information about the position of measuring points with respect to some terrestrial reference system. Only a set of gravimetric stations all over the Earth combined with a determination of their coordinates allows one to determine (from the solution of Molodensky’s problem) the heights of these stations with respect to a level ellipsoid with center at the geocenter. Given in addition their heights above some reference ellipsoid, whose position in the Earth’s body is fixed through a set of reference points on its surface, the position of the geocenter in the same reference system may be obtained.
Dynamical Constants and Reference Parameters for Mars
Authors: Michael William H. , Kelly George M. 
Published: July 2016

AbstractDynamical constants and other fundamental reference parameters for Mars have been derived from analyses of Viking lander ranging and Doppler tracking data covering a time span of nearly four years. Precise values have been obtained for the coordinates of the spin axis and for the rotation rate, suggesting that these Viking-derived values are definitive and are suitable for adoption by the IAU. Preliminary results have been obtained for a small seasonal variation in the rotation rate, and progress has been made toward a direct determination of the precession constant.
Definition and Practical Realization of the Reference Frame in the FK5 - The Role of Planetary Dynamics and Stellar Kinematics in the Definition
Authors: Fricke Walter 
Published: July 2016

AbstractThe formulation of the fundamental reference system to be represented by the FK5 includes the determination of the equinox and equator on the basis of planetary dynamics and the application of the new expressions for the general precession in longitude adopted in the IAU (1976) System of Astronomical Constants. The role of hypotheses which entered the determination of the lunisolar precession is explained. Results are presented for the equinox and equator of the FK5 which are based on observations of the Sun, planets, and lunar occultations.
Dynamical Equinox and Analytical Theory of the Sun
Authors: Krasinsky G.A. , Sveshnikov M.L. 
Published: July 2016

AbstractA concept of dynamical equinox and its relation to the analytical form of the adopted theory of the Sun is discussed. Connection between the FK4 equinox and the dynamical equinox is determined by comparing two analytical theories of the Sun (the adopted Newcomb’s theory and a new one (AT-1) constructed at the Instituted of Theoretical Astronomy) with solar meridian observations made at US Naval Observatory (1911-1971 yr.). Corrections Δα to the FK4 right ascensions, Δδ to declinations and Δε to the angle between the equator and the ecliptic are:Secular variations in Δα and Δε may be explained by improvement of observational conditions after reconstruction of the telescope pavilion in the forties.
Two-Dimensional Radiation-Hydrodynamics Calculations of the Formation of 0-B Associations in Dense Molecular Clouds
Authors: Klein Richard I. , Sandford II Maxwell T. , Whitaker Rodney W. 
Published: July 2016

AbstractTwo-dimensional calculations of ionization-shockwave propagation into a curved molecular cloud are presented. Density enhancement occurs due to the combined effects of cloud curvature and radiation flow. The star formation process is expected to be enhanced near the edges of irregularly shaped molecular clouds.
Numerical Simulation of the Solar Granulation
Authors: Cloutman Lawrence D. 
Published: July 2016

AbstractThe solar granulation has been simulated by numerical solution of the multidimensional, time-dependent, nonlinear Navier-Stokes equations applied to the solar atmosphere. Granules may be explained as buoyantly rising bubbles created at the level where T = 8000 K, and which have collapsed into vortex rings. The calculation is in quantitative agreement with observations and has a number of implications for solar physics and convection theory.