bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

A 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

Quantitative 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

Cyclic 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.
Multi–line Zeeman Analysis
Authors: Valenti Jeff A.
Published: July 2016

I present preliminary results of a multi-line Zeeman analysis of the active star ξ Boo A and the inactive star τ Cet. High S/N echelle spectra are compared with LTE model line profiles for 25 Fe I lines to deduce surface magnetic fields.
A New Technique to Measure Magnetic Field Strength in Active Stars
Authors: Almeida J. Sánchez , López R. J.García
Published: July 2016

We 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

We 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

In 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

Using 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

A 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.-
A Comment on the Derivation of the Equation of Transfer in The Presence of Magnetic Fields
Authors: Shore Steven N.
Published: July 2016

The equation of transfer is derived for the case of small Faraday rotation. Applications to line formation in Ap stars are briefly discussed.
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

A discussion is presented on how to ascertain whether certain peculiar star phenomena can be understood as resulting from an enhanced abundance of recently synthesized (< 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

Spectrophotometry 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

A 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

The 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.
A Study of Line Profiles in The Oblique Rotator Model and a Comparison with the Ap Star B Coronae Borealis.
Authors: Freedman R.
Published: July 2016

A study was made of line profiles in left and right circularly polarized light for the Ap stars βCrB. The model adopted for the surface configuration of the magnetic field was that of Wolff and Wolff (1970) who used an oblique rotator offset along the axis of the dipole field. The line profiles were calculated in pure absorption using the method of Rachovsky (1969). Allowance was made for the depth dependence of all relevant physical variables, arbitrary angles of the magnetic field, and the effect of anomalous dispersion. The elements studied were Ce II, Gd II, Mn I and Fe I. In general, weak, unsaturated lines were chosen for analysis. The final profiles were corrected for the effects of rotation.
On the Configuration of the Magnetic Field of β CrB
Authors: Aslanov I.A. , Rustamov Yu.S.
Published: July 2016

Measurements 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.
On the Interpretation of the am Phenomenon
Authors: Böhm-Vitense Erika
Published: July 2016

As it is well known, Am and Ap stars show related peculiarities of their spectra. They both have too strong metallic lines in comparison to the strength of the H lines, both types of spectra show weak Ca II K lines, though this characteristic is more pronounced for the Am stars. For the Ap stars the RE lines are especially strong while this is less pronounced for the Am stars. Since both types appear in the same region of the HR diagram it has been suspected that the reasons for the peculiarities may also be related. If these.peculiar line intensities are attributed to abundance anomalies, the abundances given for Am stars as compiled by Conti (1970) and shown in Figure 1, adapted from Preston (1974), are obtained.
Some Reflections on the Metallic Line Stars
Authors: Stickland D.J.
Published: July 2016

It is a great pleasure for me to attend this meeting to commemorate the hundredth aniversary of the Vienna Observatory, particularly so since I bring with me the greetings from the Royal Greenwich Observatory where we have also been celebrating the anniversary of our founding by King Charles II in 1675. Unfortunately, my aquaintance with the metallic line A stars is a mere seven years old and I feel somewhat presumptuous in giving a review of what is mainly your (the audience's) work. I have decided, therefore, to refer you to Conti's (1970) splendid and comprehensive account together with Preston's (1974) recent updating for the full story, and to content myself with some personal reflections on the state of observational work on the Am stars. This talk will doubtless reveal some of my muddled thinking and misconceptions and I trust you will not let me leave this conference with an incorrect picture of the work you are really doing on this interesting subgroup of peculiar stars.
Statistical Study of the Rotation Effect of Am Stars
Authors: Kodaira Keiichi
Published: July 2016

Excess 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.
A Study of the Lambda Virginis System
Authors: Stickland D. J.
Published: July 2016

The orbital elements of the SB2 λ Vir have been redetermined and the earlier period of 206 days found to be correct. Both stars have been classified as Am although they exhibit rather different ve.sin i's. An abundance analysis confirms the similarity in metallicity of the two components.
Ideal Reference Frames, Concepts and Interrelationships
Authors: Veis George
Published: July 2016

Many 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

The 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

Changes 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

A 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

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

Present 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

Single 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.
A Note on the Origin, Objectives and Programme of Project Merit
Authors: Wilkins George A
Published: July 2016

Project MERIT is a special programme of international collaboration to Monitor Earth-Rotation and Intercompare the Techniques of observation and analysis. It was conceived in 1978 at IAU Symposium No 82 on Time and the Earth’s Rotation and a draft proposal was prepared by a working group set up by the Presidents of IAU Commissions 19 and 31. The proposal was endorsed at the IAU General Assembly at Montreal in 1979 August and at the IUGG General Assembly at Canberra in 1979 December, when the organisation and membership of the Working Group were modified accordingly. The Group is affiliated to the Commission on the International Coordination of Space Techniques for Geodesy and Geodynamics (CSTG), which is sponsored by the International Association of Geodesy (IAG) and by COSPAR. Project MERIT has received the support of the International Council of Scientific Unions and of many national organisations and observatories throughout the world.
Dynamical Constants and Reference Parameters for Mars
Authors: Michael William H. , Kelly George M.
Published: July 2016

Dynamical 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

The 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

A 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

Two-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

The 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.
Radiative Damping of Gravity Waves in the Solar Atmosphere
Authors: Logan Jerry D. , Hill Henry A.
Published: July 2016

The nonlocal character of the radiation field sinnificantly modifies the radiative damping of perturbations in the solar photosphere. Gravity waves are not usually considered to exist in the solar photosphere because the radiative damping time, when based on the Newtonian approximation, is too short. However, this restriction does not apply to low order gravity waves. In fact, with the inclusion of nonlocal effects, the radiative damping for low order gravity waves becomes negative for some region in the photosphere and thus acts as a driving mechanism for gravity waves there.
Nonradial Oscillations: The Cause of Macroturbulence in Late-Type Stars?
Authors: Smith Myron A.
Published: July 2016

A fundamental problem in contemporary stellar atmospheres research concerns the cause of what the spectroscoplst calls “macroturbulence.” Even in so well studied a star as the Sun, it is unclear as to which of the many resolved velocity fields is most responsible for the broadening of the disk-integrated spectrum. There are several uncertainties attached to the identification of this primary velocity field. To cite one, Beckers (1980) indicates in a recent review that the two principal contributors to macroturbulence, convective granulation and the five-minute nonradial oscilltion pattern, each add only an r.m. s. velocity of 1/2 km s at τ5000 = 0.1. According to him, even when they are put together with related unresolved patterns [e.g. subgranulation and short period (<30) oscilltions] the sum of all known velocities seems to fall short of macroturbulence obtained from line broadening studies [~ 3 km s-1; radial-tangential model (Gray 1977, Smith 1978)]. The most recent models of the solar granulation field (Keil 1980) suggest somewhat higher velocities, e.g. 1.1 km s-1 at τ5000 = 0.1, when revised corrections for terrestrial seeing are taken into account. Nonetheless, such corrections must be added to both the convection and oscillation amplitudes, so it is still not clear whether one of these fields dominates the line formation.
Are There Different Types of Variability Among B Stars?
Authors: Sareyan J.-P. , Le Contel J.-M. , Valtier J.-C. , Ducatel D.
Published: July 2016

Almost every survey for β Cephei detection has been restricted to the small area of the HR diagram that contained the 15-20 first discovered. (Table 1). Of course, every new short period pulsating star found in such an a priori limited region has strengthened the impression that an instability box could be derived from the study of the statistics of β Cep variables. That conclusion could have led to the discovery of a β Cep pulsation mechanism related to a particular mass - age internal structure status. On the contrary if the phenomenon is due to a mechanism acting in a wider extension of the HR diagram (and so probably better related to envelope properties) one still has to explain why its detection seems to be easier in the B0-B1 zone. Moreover, even within the “instability box” some classical β Cep could be either in core hydrogen burning phase or others in shell hydrogen burning phase, i.e. with quite different internal structures.
Delta Scuti Stars and Dwarf Cepheids: Review and Pulsation Modes
Authors: Breger Michel
Published: July 2016

Recent developments in the field of Delta Scuti stars are discussed. Considerable progress has been made in determining the multiple-period structure of individual variable stars and in identifying the excited radial and nonradial modes through a variety of methods. This allows an analysis of the change of excited modes as a function of the position in the instability strip.
Nonlinear Calculations for BL Her Stars
Authors: Hodson S. W. , Cox A. N. , King D. S.
Published: July 2016

BL Her Stars are primarily Population II Cepheids with periods between one and three days. On the H-R diagram they are about 1mbrighter than the RR Lyrae variables but below the W Virginis variables. They are not as blue as the so-called anomalous Cepheids. Typically these stars are metal deficient, but notable exceptions are the prototype BL Her and V553 Cen with solar type abundances (Smith, et al. 1978). Their evolutionary status given by Sweigart and Gross (1976) puts them on the immediate post-horizontal-branch stage with energy supplied by both He and H burning shells.
The Effect of Stellar Structure on Supernova Remnant Evolution
Authors: Jones Eric M. , Smith Barham W. , Straka William C.
Published: July 2016

1. Abstract

One-dimensional hydrodynamic calculations have been done of 1E51 erg explosions in 15M⊙ stars. We have appended a steep external density gradient to the pre-supernova model of Weaver et al and find: (1) the outer shock wave decelerates throughout the pre-Sedov phase, (2) the expanding stellar envelope and the shocked interstellar material are Rayleigh-Taylor stable until the Sedov phase, and (3) steep internal density gradients are R-T unstable during the early expansion and may be the source of high velocity knots seen in Cas A.
The ZZ Ceti Stars and the Rate of Evolution of White Dwarfs
Authors: Robinson Edward L. , Kepler S. O.
Published: July 2016

The importance of the ZZ Ceti stars, and indeed the importance of all pulsating stars, derives from the fact that stellar pulsations probe the interiors of stars, and thus they test directly our models of stellar interiors and stellar evolution. The relative value of stellar pulsations as such a probe depends on, among other factors, the number of pulsation modes simultaneously excited in a star, as each additional mode depends on and constrains the properties of the star in a different way. Judged by this criterion, the pulsations of the ZZ Ceti stars should be unusually valuable because all ZZ Ceti stars are multi-mode variables. For example, among the ZZ Ceti stars with well studied light curves, the one with the fewest modes is R548 (= ZZ Ceti itself) with 4 pulsation modes simultaneously excited (Robinson et al. 1976), while some of the other ZZ Ceti stars can have dozens of pulsation modes simutaneously excited (cf. Robinson 1979).
Hydrodynamic Modeling of Mass Loss from Cataclysmic Variable Secondaries
Authors: Gilliland Ronald L.
Published: July 2016

Results of detailed computer simulations of mass loss from a cataclysmic variable secondary are presented. The calculations involve solution of the nonlinear hydrodynamical equations of stellar structure under varying degrees of approximation in an attempt to determine stability of the mass loss process. For comparison with previous theoretical studies dynamical sequences were computed assuming spherically symmetric mass loss from the secondary. The assumption of spherical symmetry is very poor since nearly all of the transferred material is lost within a small region about the inner Lagrangian point. Dynamical sequences treating only the region near the Lagrangian point were constructed in a manner consistent with the assumption of Roche geometry. Finally the effects of mass flow nonorthogonal to the Roche equipotential surfaces were treated in a very simple way. The last generalization produces stable mass loss in a model which was unstable for the less realistic approximation schemes. The finding of stable mass transfer implies that instability of the secondary star is not the mechanism leading to cataclysmic variable outbursts. This conclusion is consistent with published observations of dwarf novae made just prior to outburst.
Herschel and the Construction of the Heavens
Authors: Hoskin Michael
Published: July 2016

The history of astronomy knows great telescope builders, great observers, and great theorists; but only William Herschel falls indisputably into all three categories. When he became a professional astronomer in the summer of 1782, he had already demonstrated his skills in the construction of big reflectors: the mounting of his 20ft still left much to be desired, but otherwise his mirrors, his eyepieces, and his mountings combined to give him a head start over any other astronomer in the examination of distant and therefore faint objects. And in little over a year after his arrival near Windsor Castle where he was to be available on occasion to show the heavens to the Royal Family, he completed one of the great telescopes of all time: his ‘large’ 20ft reflector, with mirrors of 18 inches diameter, and soon to be equipped with a stable ladder-type mounting so that telescope and observing platform could be rotated together by a single workman. This mounting he further improved and refined in the years to come, and meanwhile the telescope was his favourite instrument and in constant use during his twenty-year systematic search of the sky for nebulae. In his extreme old age it was refurbished under his direction by his son John, who resurveyed his father’s nebulae and then took the telescope to the Cape of Good Hope to extend the coverage to the southern skies. John’s General Catalogue of Nebulae and Clusters of Stars (1864) led to the New General Catalogue that astronomers use today.
The Satellites of Uranus
Authors: Cruikshank Dale P.
Published: July 2016

The Uranian satellite system contains five known members, all of which are difficult to study owing to their faintness and proximity to Uranus. The photometry of these objects is not in a satisfactory state, nor is the photovisual spectrophotometry. Infrared observations are in some sense easier and more precise because Uranus itself is faint in the near infrared and interferes but little with the satellite studies. The near infrared work reveals water ice or frost on the satellite surfaces, perhaps in a very pure state. The satellites are most similar to Ganymede in terms of the strength of the ice bands, but subtle differences, now under study, may be present. The diameters and masses of the satellites, while not readily measurable directly, can be estimated from generalizations about the surface geometric albedos, assumed mean densities, and certain dynamical arguments. Most of the data and theories are consistent with bodies with radii in the range 160-520 km (similar to the larger asteroids) and albedos on the order of 0.5, consistent with ice and snow. The mean densities are probably similar to those of the icy Saturn satellites, about 1.3 g/cm3. Uranus’ satellites probably formed after the event that caused the planet to tilt to the presently observed obliquity.
Rings of Uranus: A Review of Occultation Results
Authors: Elliot James L.
Published: July 2016

Since their discovery in 1977 (Elliot 1979), the dark, narrow rings of Uranus have intrigued dynamicists. The main enigma has been how the rings can remain so narrow - only a few km wide - when particle collisions and the Poynting-Robertson effect should cause the particles to disperse. The Uranian rings have posed other problems as well, and have proved to be a unique system for developing dynamical models of rings. The reason for this theoretical interest is the high precision and time coverage of the data available from occultation observations. With occultations we obtain a spatial resolution of 1 km in the position of ring segments and a resolution of 4 km in their structural details. These high-resolution data are available sufficiently often to be useful for dynamical purposes - at the rate of 1-2 events per year. This spatial resolution is somewhat better than that obtained by Voyager imaging of Jupiter’s and Saturn’s rings (Owenet al. 1979; Smithet al. 1981). Ground-based images of the Uranian rings, obtained by Matthews, Nicholson, and Neugebauer (1981), have a spatial resolution of ~50,000 km. Although unable to resolve individual rings, these data have established the mean geometric albedo of the rings at 0.030 ± 0.005.
Uranus Science with Space Telescope
Authors: Caldwell John
Published: July 2016

The Space Telescope Observatory, scheduled for launch in 1985, is described. The advantages of the space environment and the consequent features of ST performance are given, with Uranus observations as examples. The first generation instruments, including two cameras, two spectrographs and a high speed photometer, are discussed. The Space Telescope Science Institute, which will manage the Observatory, is discussed briefly. The potential scientific interaction with the Voyager 2 encounter of Uranus is also considered.
The Astronomical Data Base and Retrieval System at NASA
Authors: Mead Jaylee M. , Nagy Theresa A. , Hill Robert S. , Warren Wayne H.
Published: July 2016

More than 250 machine-readable catalogs of stars and extended celestial objects are now available at the NASA/Goddard Space Flight Center (GSFC) as the result of over a decade of catalog acquisition , verification and documentation. Retrieval programs are described which permit the user to obtain from a remote terminal bibliographical listings for stars; to find all celestial objects from a given list that are within a defined angular separation from each object in another list; to plot celestial objects on overlays for sky survey plate areas; and to search selected catalogs for objects by criteria of position , identification number, magnitude or spectral type.
The Soviet Center of Astronomical Data
Authors: Dluzhnevskaya O. B.
Published: July 2016

On the basis of the current French-Soviet cooperation in science and technology, the Astronomical Council of the U. S. S. R. Academy of Sciences and the Strasbourg Center signed in 1977 an agreement on setting up the Soviet Center of Astronomical Data as its filial branch. The Soviet Center was created on the basis of a computation center at the Zvenigorod station of the Astronomical Council of the U. S. S. R. Academy of Sciences, which had already had considerable experience of working with stellar catalogues. In 1979 the Center was equipped with a EC-1033 computer.
Activities of the Potsdam Data Center
Authors: Schilbach E.
Published: July 2016

In 1968 the Data Centre was established in the Central Institute for Astrophysics of the Academy of Sciences(CIAP) of the German Democratic Republic. Its task was essentially the analysis of astronomical observations and the elaboration of theoretical models for astronomical problems.

In 1974,a cooperation was started between our institution and the Stellar Data Centre at Strasbourg.
The Stellar Data File at Dearborn Observatory
Authors: Buscombe William
Published: July 2016

The majority of entries for MK Spectral Classifications in the Kennedy & Buscombe (1974) catalogue referred to stars brighter than 9th magnitude with H. D. numbers. Accordingly, the file was arranged in sequence corresponding to right ascension for 1900, although the co-ordinates were actually listed for the epoch 2000, in accordance with an earlier precept established in the IAU.
Euronet-Diane, premier reseau europeen de transfert de l'information
Authors: Salle Yvonne
Published: July 2016

Euronet is one of the world's most recent networks created for data transmission. Sponsored by the Commission of the European Communities, Euronet was officially opened for traffic, at the beginning of 1980, in the buildings of the European Parliament in Strasbourg.
The U.K. STARLINK computer network
Authors: Carnochan David J.
Published: July 2016

Six VAX-11/780 computers have been set up at different centres of astronomical research throughout the United Kingdom. These computers are solely for the use of astronomers and they are linked together using special telephone lines. They are proving to be a powerful tool, both in the reduction of astronomical images and in the subsequent data analysis.
New developments in data storage
Authors: Grosbøl P.J.
Published: July 2016

Abstact

It is estimated that up to 100 Gbytes of primary data from digital detectors have to be stored each year. The amount of reduced data is at least one order of magnitude smaller. Although the storage density for magnetic recording can be made higher, only the optical technic can provide a substantial denser medium than the photographic emulsion. It seems likely that optical read-only devices will be developed for archival storage of data in this decade. Magnetic recording of data will still be preferred whenever changing of the information is important.
On Systems of Standards
Authors: Eichhorn Heinrich
Published: July 2016

Rigorous formulations closely following current practice, are proposed for the absolute and the relative estimation of certain target quantities. A system of standards is defined as a set of estimates that has certain properties. This is followed by a discussion of the meaning of “reducing estimates to a specified system“ and certain procedures are suggested for making this process less ambiguous. It is finally shown that relative estimates can be employed for replacing a system which is based on absolute measurements alone by another, more accurate system.
Digital Image Processing and Data Retrieval : The Needs
Authors: Bijaoui A.
Published: July 2016

During the last decenny, Digital Image Processing (D.I.P.) has been introduced in astronomical studies to allow the information extraction.

In a first step, D.I.P. has been used essentially to provide enhanced images (noise reduction, deconvolution, contrast enhancement), to reduce geometrical or photometrical distorsions and to extract rough data. So, a few reference date are needed (some comparison lines for example).
International standards for software structures in astronomy
Authors: Pucillo M. , Santin P. , Sedmak G.
Published: July 2016

The increasing request for astronomical data processing facilities forces the definition of standards for astronomical application software. Separating the application module from the interfaces to the data processing system allows to identify the standard user interaction interface, the standard data storage interface, the standard dedicated subsystems interface and the standard on-line documentation interface. We tested a tentative integrated solution that fulfills these requirements. This solution includes colour graphics and is available to the astronomical community.
INSPEC activities in astronomy and astrophysics
Authors: Collins Mike J.
Published: July 2016

Considers a typical paper from the astronomical literature, shows how it was processed for ‘Physics Abstracts’ and illustrates how it can now be retrieved on-line from the INSPEC database.

“Two-color photoelectric observations of the eclipsing binary BB Peg” by Cerruti-Sola and Scaltriti was published in Astronomy & Astrophysics Supplement Series, Vol. 40, No. 1, p. 85–9 (April 1980). The abstract for this paper appeared as No. 62194 in Physics Abstracts, Vol. 83, No. 1139, p. 4806 (1 July 1980). This particular journal article has been chosen to illustrate the way material is handled by the INSPEC database because apart from the usual bibliographic elements, a designated stellar object (BB Pegasi) is mentioned and numerical data (observation dates) are incorporated.
Editorial policies
Authors: Lequeux James
Published: July 2016

A short summary of the way the main astronomy journals are produced is given. The different ways of publishing a scientific journal are described, their advantages anddrawbacks-are discussed and some projections towards the future are made. We finally deal with a few specific editorial topics : publication of large collections of data, designation of astronomical objects, indexing and retrieval of information.

This paper reflects my opinions concerning what a journal like Astronomy and Astrophysics is presently doing, could reasonably do and will possibly do in the future in order to publish the material submitted by the astronomical community. I have had contacts with Prof. B.J. Tayler, the Managing Editor of the Monthly Notices of the Royal Astronomical Society, and some of his opinions are conveyed here.
A list of standard star designation
Authors: Ochsenbein F. , Spite F.
Published: July 2016

Some rules about star designation have been edicted by Commission 5 of the IAU : they are briefly recalled and discussed. The essential rule, to be kept in mind by every author, is : when quoting a designation of a star, always quote the complete bibliographic reference of the paper defining this star designation. “Standard” designations can be an exception to this rule : it is proposed to publish in the CDS Bulletin a list of designations considered as “standard”; the authors would be relieved of the obligation of quoting the references of these “standard” catalogues and could concentrate on the task of referencing the other catalogues.
On the nomenclature of diffuse fragmentary objects
Authors: Polechova P.
Published: July 2016

For the purpose of Cataloguing diffuse objects in a wide range of dimensions, two alternative proposals are presented.

Problems similar to those discussed in connection with the nomenclature of optical HII-regions may occur with any diffuse objects such as molecular clouds, large reflection nebulae, HI-regions, and, of course, radio HII-regions.

The radio HII-regions are most commonly designated by the galactic numbers “G”. The galactic longitude forms the first part of this number, the galactic latitude the second part, both parts being usually accurate to the first decimal digit and separated by the sign of latitude. This system (also used sometimes for optical objects) was introduced by Mezger and Henderson (1967) in a survey at 5 GHz, with a half power beam width of the telescope of about 6'. The angular dimensions of their objects were in the range from 3 to 11'.
The catalogue of stellar identifications
Authors: Ochsenbein F. , Bischoff M.
Published: July 2016

The evolution of the Catalogue of Stellar Identifications (C.S.I.) developed by the Stellar Data Center (C.D.S.) is summarized in Table 1; a microfiche edition of this fundamental file is described in another paper (Ochsenbein et al, 1981), and recent developements of this file are presented.
Data in Astronomy
Authors: Hauck B.
Published: July 2016

The present situation regarding data for astronomy and astrophysics is dominated by two factors: large increase of data and better accessibility, mainly due to the existence of data centres. An attempt to centralize the information of plate vaults is also presented.