bluuebunny/crossref_metadata_2025 huggingface dataset:
The Quadrantid Meteor Stream: Past, Present and Future
Authors: Hughes David W. , Williams Iwan P. , Murray Carl D.
Published: July 2016

At the present time the orbit of the Quadrantid meteor stream not only intersects the orbit of Earth but also passes very close to the orbit of the planet Jupiter. This causes considerable perturbations. In a series of three papers (1,2,3) the authors replaced the myriad of meteoroids in the stream by ten test particles set at equal intervals of eccentric anomaly around the orbit. The equations of motion of these particles in the solar system were solved using a standard fourth order Runge–Kutta technique with self–adjusting step lengths. The orbits of the test particles were output at ten year intervals going back from the present to the year 300 B.C. and forward into the future to the year A.D. 3780.
Television Observations of the Delta-Aquarid Shower
Authors: Sarma T. , Jones J.
Published: July 2016

The Southern Delta Aquarid meteor shower which is believed to be of relatively recent origin because of its compact photographic radiant, is also possibly associated with the Arietid meteor shower (Kresak and Porubcan 1970). Williams, Murray and Hughes (1979) have studied the orbit of the Quantrantid stream and it is interesting to note that the orbital parameters of that shower approximately 1500 years ago were similar to the orbit of the present day Delta Aquarids.
Observational and Theoretical Aspects of Fireballs
Authors: Ceplecha Zdeněk
Published: July 2016

Recent theoretical concepts of large meteoroid entry into the atmosphere are compared and an evident lack of a theory applicable to all observed fireballs is found. A new empirical criterion separating different fireball groups according to structure and composition of their bodies and containing only values directly obtained by photographic observations is proposed. The complex semi-empirical approach is found to be the best approximation to reality we can achieve for all fireballs at the moment. The interpretation of the fireball differences assuming variations in structure and composition of their bodies is the most natural explanation of the observational facts.
Ultraviolet Albedo of Comet West (1976 VI)
Authors: Feldman P. D.
Published: July 2016

The ultraviolet spectrum of Comet West (1976 VI) in the range 1200-3200 Å was recorded by rocket-borne instruments on March 5.5, 1976. At the time of launch, r = 0.385, Δ = 0.84 and the phase angle was 78°. Longward of 2100 Å the continuum of solar radiation scattered by cometary dust is detected and is found to closely follow the solar spectrum. Since the dust coma is completely included in the spectrometer slit, the ultraviolet albedo can be determined relative to the visible and this ratio is found to be ≈0.3 at 2700 Å. There is evidence for a further decrease in albedo near 2200 Å. Using a visible albedo of 0.2 gives a value of 0.06 for the cometary albedo at 2700 Å, a value similar to that found for the moon and lunar dust in this spectral region.
The Electrostatic Potential of Interplanetary Grains
Authors: Lafon J.P.J. , Lamy P. L. , Millet J. M.
Published: July 2016

A new method is presented for calculating the electrostatic potential of cosmic grains taking into account the plasma sheath and its bulk velocity. Results for various solar wind situations are given.
Micrometeoroid Multiple Foil Penetration and Particle Recovery Experiments on Board Space Shuttle's Long Duration Exposure Facility (LDEF)
Authors: Mandeville J. C. , McDonnell J.A.M.
Published: July 2016

Experiments designed for the investigation of the near-Earth micrometeoroid flux on the Space Shuttle Long Duration Exposure Facility (LDEF) are described. The paper examines, in particular, how two of the experiments deploy a series of multiple layer foil arrays to investigate the physical properties of incident meteoroids and lead to partial recovery of the micrometeoroids for laboratory analysis. Several thousand penetrations are expected to be returned after 12 months' exposure in Space.
Interaction of Lunar Ejecta and the Magnetosphere of the Earth
Authors: Alexander W. M. , Corbin J. D.
Published: July 2016

A significant flux of ejecta from lunar impacts of interplanetary dust particles leaves selenocentric space and enters the magnetosphere of the earth. During favorable lunar phases, 80% of the ejecta enter the magnetosphere where their orbits are determined by electrodynamic as well as gravitational forces. Initial study of the orbital characteristics and perturbations of these magnetosphere ejecta is presented and its implications are discussed.
The Origin of Interplanetary Sectors
Authors: Schatten Kenneth H.
Published: July 2016

The coronal magnetic models of Altschuler and Newkirk (1969), Schatten, Wilcox and Ness (1969), and Schatten (1971) that allowed calculations of the coronal magnetic field from the observed photospheric magnetic field shed light on the origin of sectors. Figure 1 from Schatten's (1971) “Current Sheet Model” is a schematic representation of these similar models. There are three distinct regions in these models where different physical phenomena occur. The photosphere, where the magnetic fields are governed by the detailed motions and currents in the plasma is considered a boundary condition for the model. Above the photosphere, the plasma density diminishes very rapidly with only moderate decreases in the magnetic energy density. This results in the middle region where the magnetic energy density is greater than plasma energy density and hence controls the configuration. One may then utilize the force-free condition, j × B = 0, and in fact make the more restrictive assumption that this region is current free. The magnetic field in this region can be derived from a solution to the Laplace equation.
Mode-Coupled MHD Waves in the Corona and Solar Wind
Authors: Heinemann M. , Olbert S.
Published: July 2016

The purpose of this paper is to outline a model of mode-coupled MHD compressional waves in the corona and solar wind. The eventual aim of this work is to be able to compute how MHD waves propagate through the corona and into the solar wind beginning with a source of Alfven or fast mode waves at the base of the corona. The necessity for consideration of mode coupling arises because of typical scalelengths in the corona. For wave sources, such as supergranulation, with wave periods of about a day, the different modes do no propagate independently, as in the WKB approximation, but are coupled because the ratio of wavelength to scalelength is of the order of one or greater.
An Empirical Relation Between Density, Flow Velocity and Heliocentric Distance in the Solar Wind
Authors: Eyni M. , Steinitz R.
Published: July 2016

Solar wind flow quantities such as matter flux, momentum flux and energy flux, may be closely related to the mechanism responsible for the evolution of the solar wind. In the highly supersonic flow regime their study is facilitated by the fact that the contribution of thermal motions to the momentum and energy fluxes is negligibly small, and thus all three quantities are expressible in terms of proton density n and flow velocity u. If a relation between n, u and heliocentric distance r can be established, the study of these quantities is further simplified. In the following we point out that such a relation does in fact exist, and comment on its implications.
Correlated Variations of Planetary Albedos and Solar-Interplanetary Parameters
Authors: Lockwood G. W. , Suess S. T. , Thompson D. T.
Published: July 2016

The brightnesses of Titan and Neptune have been monitored photo-electrically at 472 and 551 nm since 1972 at the Lowell Observatory, yielding annual mean magnitudes accurate to 0.3 percent (0.003 mag). Both objects increased steadily in brightness until 1976 and declined thereafter (Lockwood 1977, Lockwood and Thompson 1979). The range of variation was about 0.08 mag for Titan and 0.03 mag for Neptune.
Large-Scale Magnetic Field Structure at the Earth's Orbit, Its Correlation with Solar Activity and Orientation and Motion of the Solar System in the Galaxy
Authors: Vassilyeva G. J. , Kuznetsova M. A. , Kotlyar L. M.
Published: July 2016

Interplanetary magnetic field data from the different satellites obtained during the period 1963-1973 at 1 A.U. and compiled by J. King have been analysed in heliocentric ecliptic coordinates. The peculiarities of the background interplanetary magnetic field (BIMF) are discussed in relation to the orientation of the solar system in the Galaxy and the variable helioefficiency of the planets. The results of the direct cosmic experiments are evidence of the solar activity being a complex phenomenon of the solar system as a whole.
Radio Data and Computer Simulations for Shock Waves Generated by Solar Flares
Authors: Maxwell Alan , Dryer Murray
Published: July 2016

Solar radio bursts of spectral type II provide a prime diagnostic for the passage of shock waves, generated by solar flares, through the solar corona. In this investigation we have compared radio data on the shocks with computer simulations for the propagation of fast-mode MHD shocks through the solar corona. The radio data were recorded at the Harvard Radio Astronomy Station, Fort Davis, Texas. The computer simulations were carried out at NOAA, Boulder, Colorado.
Measurements of Mass Flow in the Transition Region and Inner Corona
Authors: Rottman Gary J.
Published: July 2016

A recent sounding rocket experiment has provided high spectral resolution line profiles across the solar disk. The objective of this experiment is to provide information on the systematic velocity fields at the base of the corona by observing the displacement, width and shape of EUV emission lines.
The Association of Type III Bursts and Coronal Transient Activity
Authors: Jackson B. V. , Dulk G. A. , Sheridan K. V.
Published: July 2016

Metric Type III radio bursts are nearly always associated with solar active regions. In particular, the occurrence of Type III bursts within a few minutes of the onset of the solar flares (Wild et al. 1954) is well known. During the Skylab period, a broad peak in the number of isolated Type III bursts occurred about 5 h prior to large Hα solar flares (Jackson and Sheridan 1979).
Recent Very Bright Type IV Solar Metre-Wave Radio Emissions
Authors: Duncan R. A. , Stewart R. T. , Nelson G. J.
Published: July 2016

Stewart et al. (1978) have reported moving Type IV solar metre-wave radio outbursts with brightness temperatures between 108 and 1010 K. We now report Culgoora radioheliograph observations of four more Type IV radio sources, some moving, some stationary, but all with brightness temperatures above 109 K, and one with a brightness temperature above 1013 K. We also describe one of the previously reported events (that of 1977 September 20) in more detail. The interest of these events is that their high brightnesses place great strain upon the gyro-synchrotron theory of radio emission.
The Solar Mass Ejection of 8 May 1979
Authors: Michels D. J. , Howard R. A. , Koomen M. J. , Sheeley N. R. , Rompolt B.
Published: July 2016

This paper describes the main features of the 8 May 1979 solar mass ejection, including the eruption of a polar crown filament to 1.5 R ⊙ during 0810-1036 UT and the passage of material through the outer corona, from 2.6 to 10.0 R⊙, during 1028-1246 UT.
Physical Processes and Models of Interplanetary Responses: Suggested Theoretical Studies
Authors: Cuperman S.
Published: July 2016

Three ways to improve the theory and therefore the understanding of the physical processes in the interplanetary medium (during both quiet and disturbed periods of solar activity) are suggested. They are: (1) the development and consequently the use of higher order moments (fluid) equations as well as of more realistic closure conditions and transport coefficients for the macroscopic description of the solar wind ; (2) the undertaking of computer simulation experiments on the nonlinear collective relaxation process through particle-wave-particle interaction due to the plasma electromagnetic instabilities which may develop under conditions prevailing in the solar wind; and (3) the consideration of collective interactions in the evaluation of the transport coefficients, as deduced from the quasi-linear theory and computer simulation experiments, and their incorporation into the higher order moment equations.
Evolution of Coronal Magnetic Structures
Authors: Steinolfson R. S. , Wu S. T.
Published: July 2016

Several classes or types of coronal transients are believed to originate near the solar surface at the base of pre-existing coronal magnetic loops. These loops often lie beneath an overlying open-field region in a typical coronal- or helmet-streamer configuration. Recent experimental results indicate that these pre-existing magnetic loops may be torn open by the explosive force of the solar phenomena responsible for the transient. Numerical solutions of the time-dependent, two-dimensional, dissipationless, MHD equations of motion (the equations are discussed by Steinolfson et al. (1978)) are used to examine the formation of a coronal streamer magnetic structure and the evolution of the streamer following an explosive solar event in the closed-field region.
Gasdynamics of Impulsive Heated Solar Plasma
Authors: Sermulina B.J. , Somov B.V. , Spektor A.R. , Syrovatskii S.I.
Published: July 2016

Numerical solutions for problem of hydrodynamic response of the inhomogeneous (exponential) atmosphere on impulsive heating by energetic electrons or by very high-temperature thermal fluxes are discussed.
Proposal for an Interplanetary Mission to Sound the Outer Regions of the Solar Corona
Authors: Porsche H. , Volland H. , Bird K. , Edenhofer P.
Published: July 2016

The mission of HELIOS had been started in order to investigate in situ the innermost regions of the interplanetary space. The two spacecraft achieved a perihelion of about 0.3 AU solar distance. Fig. 1 is a sketch of the two orbits. The orbital periods are 190 resp. 186 d.
Solar and Interplanetary Dynamics (Symposium Summary)
Authors: Kuperus M.
Published: July 2016

Solar and interplanetary dynamics comprises dynamic and plasma-physical phenomena in the solar atmosphere, the corona and the interplanetary medium in the broadest sense. In this symposium, however, one has essentially tried to restrict the subject matter to the study of the propagation of a disturbance, produced in the solar atmosphere, through the corona and the interplanetary medium. In studying solar and interplanetary dynamical phenomena we find ourselves in the unique position, with respect to other astrophysical disciplines, to be able to relate solar observations obtained with the highest possible spectral, spatial and time resolution with in situ measurements made in the interplanetary medium. It has now turned out that the two fundamental questions to be answered are:

a) How does the medium in between the sun and the earth and beyond the earth's orbit, the socalled heliosphere, look like? Does a basic undisturbed heliosphere actually exist, and is one able to model its observed magnetic structures and plasma motions with their spatial and temporal variations?

b) How and where in the solar atmosphere are the disturbances generated and what are the characteristic time scales, geometries and energies involved?
Systematic Surveys for Quasars with the Slitless Spectrum Technique
Authors: Osmer Patrick S.
Published: July 2016

Recent results with the slitless spectrum technique are reviewed and the total surface densities from five independent surveys are compared. The observational base for extending the technique to search for quasars with z > 3.5 is now large enough that either the apparent cutoff at z = 3.5 will be confirmed in new surveys or quasars with z > 3.5 will be found.
Evidence for Non-Cosmological Redshifts - QSOs Near Bright Galaxies and Other Phenomena
Authors: Burbidge G.
Published: July 2016

All of the speakers at this meeting except me have assumed, or will assume, without question that redshifts are measures of distance. This reflects a point of view which is not borne out by all of the evidence. I shall attempt to give you some of the flavor of the evidence which so many wish to ignore. It comes from individuals who perhaps not surprisingly, have not been invited to speak.
Standard Candles in QSO's?
Authors: Wampler E. Joseph
Published: July 2016

We present here the current status of a continuing program to investigate the possibility that certain resonance lines in the spectra of QSO's can be used as luminosity calibrators for the spectra.
Optical Identifications of Extragalactic Radio Sources
Authors: Longair M. S.
Published: July 2016

The ability to identify the many tens of thousands of extragalactic radio sources now known depends upon the precision with which the radio positions and structures are known as well as the availability of high quality plate material. For the brightest radio sources, positions with accuracy better than 1 arcsec are now routinely available and radio structures with angular resolution 1–5 arcsec can be readily measured with instruments such as the Westerbork Synthesis Radio Telescope, the Cambridge 5-km Telescope and the VLA. The sensitivity of the VLA is such that these observations can be extended to sources in the flux density range ~ 1–10 mJy.
21-cm Probes of Redshifted Clouds
Authors: Wolfe A. M.
Published: July 2016

21 cm studies, carried out with the 305 m telescope at Arecibo, of absorption-line clouds in QSOs have resulted in the following discoveries: (a) A search for 21 cm absorption in redshift systems selected for exhibiting Mg II/Fe II absorption in radio-bright QSOs resulted in the detection of a z ≈ 0.4 21 cm line in PKS 1229–02; (b) the detection of 21 cm absorption at z ≈ 1.8 in MC3 1331+170; and (c) the discovery of 21 cm emission from regions ~ 100 kpc distant from the ScI galaxy NGC 628, that occurred during a search for outlying H I in a complete sample of spiral galaxies.
Radio Structure of Seyfert Galaxies
Authors: Wilson A. S. , Willis A. G.
Published: July 2016

We have recently mapped about a dozen Seyfert galaxies with the Very Large Array at 5 GHz and obtained less complete structural information on about a dozen more. Most sources are heavily resolved at resolutions near or below 1 arc sec, with linear scales in the range several hundred parsecs to a few kiloparsecs. For 3 galaxies (Mark 3, NGC 1068 and NGC 5548) the structure is double with two components more or less symmetrically placed on opposite sides of the optical nucleus. A third component, when present, coincides with the optical nucleus. This result provides strong evidence that “double radio source machines” also reside in the nuclei of active spiral galaxies as well as ellipticals. Other sources show a more diffuse morphology, but usually also possess a compact radio source associated with the optical continuum nucleus. A close relation between the extended radio emission and the thermal gas in the forbidden line region is indicated since (a) they have similar extents, (b) the radio and forbidden line powers are correlated, (c) the relativistic plus magnetic (B2eq/4π) and thermal pressures (nekTe) are similar and (d) the kinetic energy of the thermal gas and the minimum energy for synchrotron radiation are comparable. For the double sources, the radio emitting plasma is probably ejected from the compact nucleus and slowed by the large quantities of thermal gas in the forbidden line region. Alternatively, radio sources with more diffuse morphology may derive their luminosity from cosmic rays accelerated “in situ” by shock waves associated with the high velocity thermal gas and a magnetic field from a compressed (accreted?) interstellar medium.
Radiation Pressure in Stellar Atmospheres with Application to Solar Spicules
Authors: Grant Athay R.
Published: July 2016

Radiation pressure due to absorption in spectral lines can play an important role in the equilibrium conditions in the outer portions of the stellar atmosphere. In particular, it is suggested that spicules ejected from the upper solar chromosphere as well as other fine structural features of the chromosphere may very likely be a result of radiation pressure from Ly-a. Numerical computation of the radial radiation pressure due to Ly-α in the chromospheric model of Vernazza et al. (1973) gives a maximum outward pressure gradient due to radiation that is 0.06 of the gravitational pressure gradient. The model chromosphere of Vernazza et al. is a spherically symmetric model that reproduces the average Sun Ly-α intensity and profile. Supergranule borders (network), where spicules arise, are known to have a Ly-α brightness some ten times the average Sun brightness. It is suggested, therefore, that in the network areas the pressure gradient due to radiation is comparable to (and oppositely directed to) that due to gravitation and that in local areas of unusual brightness the net pressure gradient is outwards. An estimate of the expected outwards velocity of spicule material driven by radiation pressure was made by equating the kinetic energy flux (½JϱV3) to the Ly-α energy flux. This gives values of v that are comparable to observed spicule velocities. Also, the maximum outwards radiation pressure occurs in the upper chromosphere where the material density in the model of Vernazza et al. is close to the value 4 × 10−14 g cm−3, which is about a factor of two less than the currently accepted value for spicules. Increased density in the network areas could easily remove this minor difference.
Chromospheric Fine Structures near the Solar Limb in Hα
Authors: Bhavilai Rawi
Published: July 2016

The solar limb has been studied visually and photographically in the light of Hα and the combined results are reported. The appearance of a spicule changes with wavelength settings. Effects due to changes of spicule velocities with height and opacity-wavelength relations are indicated. A number of bright spicules seen in the wings are identified with bright mottles seen in the line core. The dark band appears between Δλ=± 1.0 Å and Δλ= ±0.70 Å. Examination of a small mottle cluster in a series of photographs taken in steps from Hα+ 0.85 Å to Hα+ 0.10 Å leads to a three-dimensional model of a typical mottle cluster.
Spicules are Bright and Dark
Authors: Zirin Harold
Published: July 2016

I have tried to understand whether spicules appear dark or bright against the disk in Hα by comparing high resolution pictures in Hα and Ca II K. Since the chromospheric structure is more apparent near active regions, I have first compared the Hα and K fibrils near an active sunspot; these are illustrated in my review paper (this Symposium, p. 161). The elongated fibrils in the active center appear similar to spicules, but much larger and more horizontal. K line pictures show bright features better, while Hα shows dark features better.
Comparison of Hα and CaII H and K Spectroheliograms as a Diagnostic Probe
Authors: Gebbie K. B. , Steinitz R.
Published: July 2016

The line formations of Hα and CaII H and K are compared in order to differentiate the various mechanisms giving rise to observable contrasts in the emergent intensities. Table II summarizes the criteria for distinguishing between horizontal spatial variations in temperature, density, and turbulent velocity.
Fine Structure of the Upper Chromosphere
Authors: Jefferies J. T.
Published: July 2016

The paper contains a review of attempts to understand observational data on the inhomogeneous structure of the upper solar chromosphere, particularly the spicules. Observations over the electromagnetic spectrum from millimetric to the ultraviolet give equivocal results; and in spite of recent progress, models for these inhomogeneous structures still face difficulties in accounting for the observed radiation. New observations in the visible are needed in order to answer even the simplest questions of kinematics, while the interpretation of the line spectra still poses many difficulties. The acquisition of EUV data at high spatial resolution should lead to major progress in the field, just as it already has done in showing the EUV emission to be concentrated over the network boundaries.
A Facula Model and Its Application to Facula Fine Structures
Authors: Wiehr E. , Stellmacher G.
Published: July 2016

In a recent paper Stellmacher and Wiehr (1973) discussed in detail the discrepancies between ‘continuum-’ and ‘line-profile facula models’. Their calculations show that continuum models (e.g. Kuz'minykh, 1962; Schmahl, 1967; Chapman 1970; Wilson, 1971) encounter the problem that the facula contrast increases towards the limb but decreases with wavelength λ. This discrepancy evidently cannot be due to NLTE effects since it concerns the continumm data.
Helical Field Lines in an Erupting Filament
Authors: Vorpahl Joan
Published: July 2016

An example of an erupting filament that exhibited helical structure during a flare on 1971, September 17, was discussed. This sort of event is not rare. Examples of rotational effects in flares, prominences and surges have been reported by others such as Öhman (1968). Accompanied by type II radio emission and the visible flow of Hα gas across 1/2 the Sun's surface, the flare was very interesting in itself. However, here the emphasis is on possible ways in which the observed twist might develop. The latter is important because it yields information about: (1) the state of the subphotospheric field itself, and (2) the possibility of storing flare energy in the twisted filaments.
Excess Heating of Corona and Chromosphere above Magnetic Regions by Non-Linear Alfvén Waves
Authors: Uchida Yutaka , Kaburaki Osamu
Published: July 2016

Excess heating of the active solar atmosphere is interpreted as the decay of MHD slow-mode waves produced in the corona through the non-linear coupling of Alfvén waves supplied from subphotospheric layers. It is stressed that the Alfvén-mode waves may be very efficiently generated directly in the convection layer under the photosphere in magnetic regions, and that such magnetic regions, at the same time, provide the ‘transparent windows’ for Alfvén waves in regard to the Joule and frictional dissipations in the photospheric and subphotospheric layers. Though the Alfvén waves suffer considerable reflection in the chromosphere and in the transition layer, a certain fraction is propagated out to the corona. A large velocity amplitude, exceeding the local Alfvén velocity, is attained during the propagation along the magnetic tubes of force into a region of lower density and weaker magnetic field. The otherwise divergence-free velocity field in Alfvén waves, in such a case, couples with a compressional component (slow-mode waves) which again is of considerable velocity amplitude relative to the local acoustic velocity when estimated by using the formula for non-linear coupling between MHD wave modes derived by Kaburaki and Uchida (1971). Therefore, the compressional waves thus produced through the non-linear coupling of Alfvén waves are eventually thermalized to provide a heat source. The introduction of this non-linear coupling process and the subsequent thermalization of the slow-mode waves may provide a means of converting the otherwise dissipation-free Alfvén mode energy into heat in the corona. The liberated heat will readily be redistributed by conduction along the magnetic lines of force, and thus the loop-like structure of the coronal condensations (or probably also the thread-like feature in the general corona) is explained in a natural fashion. Matter density in the arches is expected to be higher than the ambient density because of the higher temperature and, consequently, greater scale height in the arches.
Report on the Cape Photographic Survey
Authors: Clube S. V. M. , Nicholson W.
Published: July 2016

Since the last report (Clube, 1970), the Cape fourfold overlapping survey of the southern hemisphere has been completed. Approximately one half of the ~6000 plates have now been transferred to Herstmonceux for measurement. The measurement procedure is two staged: initially some 300 of the brightest stars on each of one non-overlapping set of these plates are picked out visually and paper tape listings of rough (x, y) co-ordinates are produced with a D-Mac machine. After some computer editing, these tapes are used to generate search tapes for measuring all the plates on a GALAXY machine. Some 1100 plates have now been measured this way, but the advance to GALAXY measurement has not yet been made on any significant scale. This is because of two difficulties which it is hoped to resolve in the near future, namely the existence of a small astrometric magnitude equation in GALAXY, and the presence on some of the plates of small glass splinters which can damage the ‘nose cone’ of the measurement optics as the plate is tracked beneath it. The technique of reduction and analysis is not described here, but it may be mentioned that the anticipated relative positional accuracy of ~0.″05 is being achieved over fairly wide areas of the sky.
Potentialities of Yale Astrometric Materials
Authors: Hoffleit E. D.
Published: July 2016

A brief summary is given of the plate materials and results obtained at Yale since the advent of photographic astrometry. The distributions of plates not yet measured or reduced are indicated and possible supplementary programmes for their effective utilization are discussed. Interest centres chiefly in the following areas:

(1) The unmeasured parallax plates.

(2) Reduction of the −60° to −70° zone catalogue.

(3) The El Leoncito programmes for the determination of both positions and proper motions relative to faint galaxies.

(4) The feasibility of a search for intrinsically faint nearby stars with the Yale 40-in. at Cerro Tololo and the 20-in. double astrograph at El Leoncito.
Radio and Optical Astrometry
Authors: Wade C. M.
Published: July 2016

Radio positional measurements have achieved an accuracy as high as that of optical astrometry, with uncertainties no greater than a few hundredths of an arc second in each coordinate. Declinations and relative right ascensions are determined absolutely. Since the principal sources of systematic error are different for radio and optical astrometry, radio measurements can be useful in the preparation of future fundamental catalogues.
Proper Motion and Parallax Programmes for Large Telescopes
Authors: Murray C. A.
Published: July 2016

Proper motion work at the present time relies on the availability of plates taken in the past, for which the magnitude limit is generally not fainter than about mpg = 16, apart from Luyten's survey with the Palomar Schmidt. It is very important for future studies to fainter magnitudes in, for example, star clusters, that sufficient time is made available on large telescopes so that plates can be taken now. Consideration should also be given to an extension of proper motion work in Selected Areas.

Ideally, trigonometric parallax observations are best carried out on a dedicated telescope, such as the USNO 61-in. reflector, with a large amount of time available; but if sufficient observational material is to be obtained on faint stars, time must also be taken on other medium sized and large reflectors. With the severe limitation of time available on these telescopes, the criteria for selection of stars for such programmes become of prime importance. Large Schmidt telescopes, with fast automatic plate measurement, may possibly be used for surveys of nearby stars, unbiased by any kinematic or photometric selection effects.
Accurate Optical Positions Using the Palomar Sky Atlas
Authors: Hunstead R. W.
Published: July 2016

Optical positions measured directly on the prints and plates of the Palomar Sky Atlas have been compared with various published lists of precise optical positions. The external comparisons suggest that positional errors ~ ±0″.3 in each coordinate have been achieved. This supports the claimed accuracy and establishes the Sky Atlas as an important astrometric medium for investigating radio-optical associations.
Modern Developments of the Meridian Circle (Invited Paper)
Authors: Høg Erik
Published: July 2016

The successful improvements of meridian instrumentation during the past twenty years have mainly come through electronic devices and computers being applied for facilitating the data handling and for increasing the accuracy. Photographic recording of the circle and of the star has played an important role here, but has for both tasks gradually lost its attractiveness as direct photometric-electronic methods have become available. At the same time new types of the telescope system have been introduced without convincing results as yet, but this field still holds promises for the near future.

The problems of the refraction, the meridian building, the foundation of the instrument and the site selection have been treated in recent years and these efforts will be doubly repaid when the telescope and micrometers become more nearly perfect. Altogether, it need not be long before a few partly automatic instruments produce observations with a mean error of 0″.15 and a systematic error of 0″.03 at a rate of 300 observations per observing night. In addition the limiting magnitude can be mv = 11 or 12, thus 2 mag. fainter than for visual observations. These goals are conservative – most of them have already sometimes been surpassed – and they should be compared to a present day good visual meridian circle giving a mean error 0″.30, a systematic error 0″.10 and 120 observations per night.

The relative roles of meridian and photographic astrometry must be defined anew in the light of the great improvements of both methods.
Instrumental Parameters of the U.S. Naval Observatory's Automatic Transit Circle (ATC)
Authors: Klock B. L. , Gauss F. S.
Published: July 2016

The instrumental constants of the Naval Observatory's Automatic Transit Circle are discussed in conjunction with the transit circle's on-line data acquisition and control system. The reflecting collimators have been designed with CerVit primaries and minified point sources. The mark lens configuration is comprised of a long focal length lens and wedge manufactured from a single piece of fused silica. The on-line data acquisition and control system will permit real time monitoring of these instrumental parameters.
The Influence of the Reduction Model on the Systematic Accuracy of Adjusted Parameters
Authors: Eichhorn H. , Rust A. E.
Published: July 2016

Everybody who deals with the numerical determination of parameters from observations is familiar with the phenomenon that the ‘external’ errors of these parameters are invariably larger than their ‘internal’ ones. This phenomenon is traditionally explained by the presence of systematic errors.

Since it is virtually impossible to use a completely rigorous reduction model in any astrometric problem, an ‘interpolation’ model must normally be employed in which there are fewer parameters (unknowns) than in the rigorous one. It is shown that under these circumstances, the rms errors of the adjustment parameters are always underestimated, which creates the illusion that the results computed with these parameters are more accurate than they actually are.
Modern Dynamical Systems Theory
Authors: Markus L.
Published: July 2016

In order to analyse generic or typical properties of dynamical systems we consider the space of all C1-vector fields on a fixed differentiable manifold M. In the C1-metric, assuming M is compact, is a complete metric space and a generic subset is an open dense subset or an intersection of a countable collection of such open dense subsets of . Some generic properties (i.e. specifying generic subsets) in are described. For instance, generic dynamic systems have isolated critical points and periodic orbits each of which is hyperbolic. If M is a symplectic manifold we can introduce the space of all Hamiltonian systems and study corresponding generic properties.
Stability of Asteroidal Motion in the Hecuba Gap
Authors: Scholl H. , Giffen R.
Published: July 2016

There exist gaps in the frequency distribution of the osculating mean motions of the asteroids. In these gaps, the mean motions of the asteroids are commensurable to Jupiter's mean motion.
The Formation of Disks by Inelastic Collisions of Gravitating Particles. Applications to the Dynamics of the Saturn's Ring and to the Formation of the Solar System
Authors: Brahic A.
Published: July 2016

We integrate numerically the evolution of a three-dimensional system of particles with finite dimensions, which bounce inelastically upon each other. The particles are subjected to the attraction of a central mass; their mutual attraction is neglected. This model is used to study the evolution of Saturn's ring. The first results are presented: such a collision mechanism can flatten very quickly the Saturn's ring and the system tends towards a final equilibrium state.
A Note on a Separation of Equations of Variation of the Elliptic Restricted Three-Body Problem Into Hill's Equations
Authors: Matas V.
Published: July 2016

The equations of variation of the three-dimensional elliptic restricted three-body problem corresponding to the equilibrium solutions (the libration points) have been separated into three Hill's equations. As regards the equation ‘corresponding’ to the motion of the infinitesemal body in the z-axis (perpendicular to the plane of motion of the primaries), the matter is trivial one since the initial equation - as known - reads d2z/dv2 + (Ai + e cosv)/(l + e cosv) = 0 (e, 0<e< 1, and v are the eccentricity and the true anomaly of the relative motion of the primaries) with Ai > 1 for the straight-line libration points Li (i= 1, 2, 3) and Ai=l for the triangular libration points Li, i=4, 5. As concerns the remaining two components, x and y, of the motion of the infinitesimal body (x, y and z are the Nechvíle's variables), in the case of the straight-line libration points, L1, L2 and L3, the corresponding equations of variation have been transformed and separated into two further - mutually independent - Hill's equations without any limitation. In the case of the equilateral triangle libration points, L4 and L5, the separation has been found only when the eccentricity e and the dimensionless mass μ, 0<μ≦1/2 of the ‘minor’ primary satisfy the additional conditions:
Let us write the latter two Hill's equations obtained in the form
where Ik, k= 1, 2, are 2π-periodic even functions of the true anomaly v. The functions Ik, k = 1, 2, are real functions in the case of the straight-line libration points, L1, L2 and L3, without a limitation but in the case of the triangular libration points, L4 and L5, they are real only if
Provided
the functions Ik, k= 1, 2, are complex-valued functions of the real variable v.
The Motion of Comet Encke-Backlund Over 1901–1970
Authors: Bokhan N. A. , Chernetenko Yu. A.
Published: July 2016

The investigation of the 22 apparitions of Comet Encke-Backlund for the time interval 1901–70 was carried out. The integration of equations of motion was performed using the technique devised by Kazimirchak-Polonskaya with automatic step choice, taking into account the perturbations from nine planets (Mercury-Pluto) as well as nongravitational effects.
A Comparison of the Mean-Value and Initial-Value Solutions of the Ideal Resonance Problem with an Application in Rigid-Body Mechanics
Authors: Jupp A. H.
Published: July 2016

A solution of the ideal resonance problem has already been exhibited (Jupp, 1972) explicitly in terms of the ‘mean’ elements; to second order in the small parameter in the case of libration, and to first order in the case of deep circulation. Both representations possess a singularity when the ‘mean’ modulus of the Jacobi elliptic functions is unity; this corresponds to motions on or close to the separatrix of the phase plane of the dynamical system.
The Stability of Triple Stellar Systems
Authors: Agekjan T. A. , Anosova J. P.
Published: July 2016

The motion of triple stellar systems whose components are at rest at the initial epoch is studied. In this study all the components have equal masses, and at the initial epoch the component A is at (-1/2, 0) on the (x, y)-plane, B is at (1/2, 0), and C is anywhere in the region (s) bounded by the positive x-axis, y-axis and a line expressed by (x+1/2)2 + + y2 = 1. By this way all the possible initial configurations are given.
Dynamics and Clusters of Galaxies
Authors: Saari D. G.
Published: July 2016

Under the assumption that the inverse square central force law is a good approximation to the gravitational force, at least for large distances, the different possibilities for the evolution of the Universe are sketched. Several of the possibilities lead naturally to a dynamical classification of clusters of galaxies in an expanding universe. In one of the classifications the galaxies must define configurations which are functions of the masses. The virial theorem approach of determining masses of galaxies in a cluster is briefly examined. Some tentative statements concerning a dynamical explanation of the local hypothesis for quasars are advanced. Finally, the role of mathematical probability in predicting the behavior of the Universe is discussed.
Spatially Resolved X-Ray Spectra of Coronal Active Regions
Authors: Catura R. C. , Acton L. W. , Joki E. G. , Rapley C. G. , Culhane J. L.
Published: July 2016

X-ray spectra from a number of coronal active regions were obtained during ATM support rocket flights carried out by the Lockheed group on June 11 and December 19, 1973. Multi-grid collimators were used to provide fields of view of 40″ diameter and 90″ diameter for a number of scanning crystal spectrometers and a bent crystal spectrometer which employed a position sensitive proportional counter to register the diffracted spectrum. A solar image was produced on film and on a TV camera on board the rocket with the aid of a 1 Å Hα filter. A small part of the X-ray collimator was used to generate a multiple spot diffraction pattern which was superimposed on the Hα image and the composite picture was transmitted to the ground. Pre-launch calibrations allowed the spot corresponding to the X-ray collimator axis to be identified and so the collimator pointing direction on the solar disc was controlled from the ground by means of commands sent to the rocket.
Statistical Methods in the Identification and Prediction of the Solar X-Ray Spectral Lines
Authors: Yousef Shahinaz
Published: July 2016

With the accumulation of numerous identifications of the solar X and XUV spectral lines, the need is felt for systemizing such identification. The results are presented below.
Time Variations in Coronal Active Regions
Authors: Krieger A. S. , Chase R. C. , Gerassimenko M. , Kahler S. W. , Timothy A. F. , Vaiana G. S.
Published: July 2016

The AS&E X-ray telescope experiment on Skylab has obtained images of the solar X-ray corona with a variety of time resolutions ranging from 21/2 s to the regular 12 ± 2 h synoptic observation rate. The form and brightness of coronal active region structures are seen to vary on time scales ranging from seconds, for flare associated changes, to several solar rotations for long term evolution of the regions. The extrapolation of photospheric magnetic fields into the corona, using the potential field approximation, results in a good morphological agreement between the form of the computed coronal field lines and the structure of many of the active regions observed. Thus, in general, the coronal active region structures follow potential field lines and the long term evolutionary changes can be explained on the basis of the spreading of the fields. Short term changes in active region structure frequently take the form of selective brightening or dimming of pre-existing loops due to changes in the pressure of the emitting coronal plasma. In these cases, variations in the non-potential component of the coronal fields supporting and containing the plasma are implied.
On the Thermal Structure of the Flare-Produced Plasma
Authors: Craig Ian
Published: July 2016

Recent flare studies have shown that soft X-ray data are not compatible with simple isothermal models of the source (Herring and Craig, 1973; Craig, 1973; Neupert et al., 1973). With this in mind, the emitting flare plasma has been represented by the temperature-emission measure distribution function,

where ζ(T) is the differential emission measure (cm–3 per 106 K), T is the electron temperature in units of 106 K, T0 is a low temperature cut-off for the distribution, αi are real positive numbers, and Ai are positive coefficients determined from data (for appropriate values of T0 and αi) by a least squares fitting procedure. Such a distribution is suggested by results obtained by the present author using simple delta-function representations for ζ(T) (with n ≤ 4); these discreet multi-temperature models usually indicate that the emission measure decreases with increasing temperature. Also, as discussed by Brown (1974), a power law distribution for ζ(T) is consistent with the observed bremsstrahlung emission in the hard X-ray (> 10 keV) domain. In attempting to find a suitable form for the differential emission measure, a simple empirical function of the type assumed by Chambe (1971) for active regions was also tried, but the fit, as evidenced by the χ2 test was unsatisfactory.
Relationship between Hard and Soft Solar X-Ray Sources Observed by OSO-7
Authors: Datlowe D. W. , Hudson H. S.
Published: July 2016

The UCSD experiment on the OSO-7 satellite has provided hard and soft X-ray observations of a large number of solar flares. Of these a sample of 123 had sufficiently large fluxes to permit analysis of their spectra (Datlowe et al., 1974). The locations of these flares upon the solar disk have been obtained by comparison with Hα flare listings. We find that the soft (5.1–6.6 keV) X-ray bursts, above a threshold of 1000 photons (cm2 s keV)–1, have a relatively flat distribution from center to limb. The frequency of occurrence of hard (20–30 keV) X-ray bursts, as normalized to the longitude distribution of the soft X-ray bursts, shows a statistically insignificant excess of 19±34% in the longitude range 80–90°. Furthermore, the limb flares exhibit a small but statistically significant spectral softening.
Implications of NRL/ATM Solar Flare Observations on Flare Theories
Authors: Cheng C. C. , Spicer D. S.
Published: July 2016

During the Skylab mission, many solar flares were observed with the NRL XUV spectroheliogram in the wavelength region from 150 to 650 Å. Because of its high spatial resolution (∼2″) the three-dimensional structures of the flare emission regions characterized by temperatures from 104 K to 20 × 106 K can be resolved. Thus the spatial relationship between the relatively cool plasma and the hot plasma components of a flare, and the associated magnetic field structure can be inferred. For example, the Fe XXIV plasma (T≃20 × 106 K) observed near the soft X-ray maximum during the 2B (M2) disk flare of 1973, July 15 is elongated perpendicular to the neutral line shown on the photospheric magnetogram, while lines of lower ionization temperatures such as He II–Fe XVI show the familiar double ribbon structures on either side of the neutral line (Widing and Cheng, 1974). The disk flare of 1973, September 5 shows the same spatial structures. The flare was observed at 1831 UT at the X-ray maximum, and shows that the hot Fe XXIV cloud is located spatially between the ribbons of the He II, Fe XIV–Fe XVI emissions. As the flare cools at 1837 UT, the Fe XXIV cloud disappears while the gap is filled with emissions from ions of lower ionization potentials, and exhibit loop structure. Many other flares also show similar spatial distributions in the XUV emissions. The linear dimensions of the Fe XXIV plasmas as measured from the photospheric plates range from 7000 km to 14000 km, and the heights of associated loops range from 10000 to 30000 km. From the spatial distributions of the XUV emissions of the many flares, and the comparisons with the magnetograms, we concluded that the magnetic field configuration for the flares we observed are simple bipolar magnetic flux loops with the hot flare plasma located near the top and the cool plasma component on the footprints of the loop.