bluuebunny/crossref_metadata_2025 huggingface dataset:
SAS-2 gamma ray observations related to a galactic halo
Authors: Fichtel C. E. , Simpson G. A. , Thompson D. J.
Published: July 2016

An examination of the intensity, energy spectrum, and spatial distribution of the diffuse γ radiation observed by SAS 2 away from the galactic plane in the energy range above 35 MeV has revealed no evidence supporting a cosmic ray halo surrounding the galaxy in the general shape of a sphere. The diffuse γ radiation does consist of two components. One component is related to the galactic disk on the basis of its correlation with the 21-cm measurements, the continuum radio emission, and galactic coordinates. Further its energy spectrum is similar to that in the plane, and its intensity distribution joins smoothly to the intense radiation from the plane. The other component appears isotropic, at least on a coarse scale, and has a steep energy spectrum. The degree of isotropy which has been established for the “isotropic” radiation and the steep energy spectrum, which distinguishes it from the galactic disk radiation, place strong constraints on galactic halo models for the origin of this component. Theoretical models involving a galactic halo have generally postulated a halo with dimensions of the order of the Galaxy and hence a radius, at least in the plane, of about 15 kpcs. Since the Sun is about 10 kpc from the galactic center, if such a halo exists and is responsible for the γ rays (through, for example, black body Compton radiation), a very marked anisotropy would be seen, with the γ ray intensity from the general direction of the galactic center being much larger than that from the same latitudes in the anticenter direction. In fact, no such anisotropy is seen; specifically the ratio of the average intensity in the (300° < ℓ < 60°, 20° < |b| < 40°) region to that in the (100° < ℓ < 250°, 20° < |b| < 40°) region was found to be 1.10±0.19 compared to a calculated value for a model with a uniform cosmic ray sphere with a 15 kpc radius of 2.85. The ratio between the average γ-ray intensity from regions with |b| < 60° to that from 20° < |b| < 40° is found to be 0.87±0.09. If the region is assumed to be spherical, but with a larger radius and a uniform cosmic ray density, the upper limit (2σ) set for the anisotropy demands that the radius be at least 45 kpc. An extragalactic origin for the isotropic component currently appears to be a more plausible explanation.
The Magellanic Stream: Observational Considerations
Authors: Mathewson D. S. , Ford V. L. , Schwarz M. P. , Murray J. D.
Published: July 2016

The Magellanic Stream is an arc of neutral hydrogen which nearly follows a great circle and which contains the Magellanic Clouds - hence its name (Mathewson, Cleary and Murray 1974). This great circle passes within a few degrees of the south galactic pole and lies close to the supergalactic plane. Mathewson and Schwarz (1976) argued that this indicates that the Magellanic Stream and Magellanic Clouds are not bound to the Galaxy. To reinforce this argument, they pointed out that around the supergalactic plane there is a similar systematic variation in the velocities of the Local Group and those of the Stream which may be due to the reflection of the motion of the galactic center if the velocity of rotatior of the Sun is 225 km s−1; if it is 290 km s−1 then the grounds for this argument would disappear.
The Magellanic Stream as a probe of the galactic halo
Authors: Cohen R. J. , Davies R. D. , Mirabel I. F.
Published: July 2016

Recent observations of the Magellanic Stream can be used to set limits on a possible hot halo surrounding the Galaxy. The observations are described in detail elsewhere (Mirabel, Cohen & Davies, submitted to Mon. Not. R. astr. Soc.). Briefly, the neutral hydrogen in the northern end of the Magellanic Stream is concentrated in narrow filaments which contain small elongated clouds of typical size 0°.4 × 0°.6. These clouds have a large velocity halfpower width (25 km s−1 and are gravitationally unstable, unless there is a massive low luminosity stellar component. If we consider only the observed gas the expansion age of a typical cloud is 6 × 105 D years, where D is the distance in kpc from the Sun, and this falls at least a factor of ten short of the age of the Stream predicted by current models. This strongly suggests that some containment mechanism is operating.
Structure of the Hyades Cluster
Authors: Pels G. , Oort J. H. , Pels-Kluyver H. A.
Published: July 2016

H. A. Pels and J. H. Oort have discussed the results of a search for fainter Hyades that had been made by G. Pels. The search extended over a region of about 15° radius around the Hyades centre. It was made from proper motions determined from a comparison of Astrographic Catalogue positions with those on plates taken with the 34-cm Leiden refractor. The data extend to about 13m. In part of the field comparisons were also made with plates taken for the Astrographic Charts, in order to extend the luminosity distribution to somewhat fainter magnitudes.
Dynamical Friction in the Coma Cluster
Authors: Lecar M.
Published: July 2016

If the galaxies composing the Coma Cluster were initially ‘Ostriker-Peebles’ galaxies (i.e., isothermal spheres extending to 250–500 kpc), the hidden mass is likely to be tidally torn-off halos. Owing to dynamical friction, the remnant cores tend to spiral in to the center of the cluster. This happens as long as the hidden mass, whatever its origin, consists of objects much less massive than galaxies.
On the Formation of Elliptical Galaxies
Authors: Gott J. R.
Published: July 2016

Simple collapse and violent relaxation models produce sharply cut off envelopes with ϱ(r) ∝ r–4, whereas actual elliptical galaxies have more extended envelopes approximately given by ϱ(r) ∝ r–3 as implied by Hubble's Law. Numerical models are presented, showing that when cosmological infall effects are included, galaxies are produced with more extended envelopes having a ϱ(r) ∝ r–2.8 dependence in excellent agreement with Hubble's Law. We have also computed a realistic rotating model of an E5 galaxy which includes infall effects and where the angular momentum of the galaxy is gained through tidal interactions with neighboring protogalaxies. The envelope displays a Hubble dependence but at great distances shows a cutoff due to the tidal effects. The model is compared to the E5 galaxy NGC 4697 and provides an outstandingly good fit to the observations. Except for simple scaling, this excellent fit is produced without the use of any free fitting parameters.
Problems Associated with the M-Dwarf Population
Authors: Schmidt M.
Published: July 2016

The existence of a rich population of late M-type dwarfs with small peculiar velocities is discussed on the basis of the work of Weistrop, Murray and Sanduleak, Pesch and others. These stars probably supply the ‘missing’ mass in the solar neighborhood. Their small peculiar velocities create problems related to the stability of the galactic disk.
Interim Report on the Texas Survey
Authors: Douglas James N. , Bash Frank N.
Published: July 2016

The University of Texas Radio Astronomy Observatory (UTRAO) is engaged in a survey of the entire sky north of −35° declination at various frequencies in the range 335-380 MHz. Primary goals are (i) determination of accurate (∼1″) positions for about 50,000 sources, followed by (ii) optical identification of the sources on the basis of exact radio-optical position coincidence; (iii) provision of rough structure models for all listed sources; and (iv) monitor the sky for variable sources on the time scale of 1 to 2 years. The survey is not expected to be a reliable source of absolute flux density information except for those sources known to be unresolved from other work.
Surveys of Radio Sources at 5 GHz
Authors: Pauliny-Toth I. I. K.
Published: July 2016

A number of surveys have been carried out at a frequency of 5 GHz at the National Radio Astronomy Observatory (NRAO) and at the Max-Planck-Institut für Radioastronomie (MPIfR), with the aim of determining the number-flux density relation for the sources detected and also of obtaining their radio spectra and optical identifications. The surveys fall into two categories: first, the strong source (S) surveys, which are intended in due course to cover the whole northern sky and to be complete above a flux density of about 0.6 Jy; second, surveys of limited areas of sky down to lower levels of the flux density.
The Angular Size - Flux Density Relation
Authors: Kapahi Vijay K.
Published: July 2016

The relation between angular size and flux density depends on the world model and more strongly on evolution in radio source properties with epoch. I shall consider here the simplest forms of evolution that explain the observed θ-S relations (Swarup 1975; Kapahi 1975a,b; Ekers, this symposium).
The Present Status of 3CR Identifications
Authors: Kristian Jerome
Published: July 2016

This paper is a partial and preliminary report on a review of the optical and radio properties of 3CR sources (Kristian, 1977). It will treat the overall status of the identifications and a few of the optical properties of the identified sources, including evidence for a faint magnitude cutoff in the apparent brightness of 3CR quasars. A summary of the status of 3 CR identifications as of early 1976 has been prepared by Smith, Spinrad, and Smith (1976). The present work includes new data on several dozen sources, as well as a systematic reevaluation of previous identifications.
Identifications from the WSRT Deep Surveys
Authors: Katgert J. K. , de Ruiter H. R. , Willis A. G.
Published: July 2016

The WSRT yields samples of radio sources which are well suited for systematic identification work for the following reasons:

a)

The surface density is high: at 1415 MHz an average of 10 to 30 sources can be detected within 0°.55 from the field centre; at 610 MHz the numbers are 40 to 100 within 1°.0. In any given field, most sources will fall within the boundaries of plates for the present generation of optical telescopes.

b)

The positional accuracy is, on the whole, rather high. One can thus propose identifications based on positional agreement only, avoiding selection effects present when selecting “on type”.
Relations Between the Optical and Radio Properties of Extragalactic Radio Sources
Authors: Burbidge E. M.
Published: July 2016

Correlations between the radio and optical properties of radio sources have proved elusive and the main conclusion to be drawn from this is that there is a great variety of objects in the universe that emit nonthermal radiation, so that attempts to use these objects for cosmological purposes can be frustrated unless one can find some way of selecting objects that do have common intrinsic properties. Despite this, the search for relations and correlations is interesting quite apart from cosmology, because such correlations should provide a groundwork for a physical theory or theories of what is really happening in sources of nonthermal radiation.
Cosmological Interpretation of Redshift Data on Quasars through the V/VMaxTest
Authors: Schmidt M.
Published: July 2016

The ultimate aim of statistical studies of redshift, magnitudes and flux densities of quasars is to derive the general luminosity function Φ(z, Fopt, Frad, α, …) which describes the space density as a function of redshift, intrinsic optical luminosity, intrinsic radio luminosity, spectral index, etc. We assume throughout that the emission-line redshifts z of quasars are cosmological. The function Φ contains information that will be pertinent for any theory of the formation and evolution of quasars.
Microwave Background Spectrum - Survey of Recent Results
Authors: Robson E. I. , Clegg P. E.
Published: July 2016

For those enamoured of the primaeval fireball, the relict radiation has proved a tantalising mistress. Since the famous discovery in 1965, by Penzias and Wilson, of an excess antenna temperature consistent with cosmological expectations, many observers have succeeded in measuring a flux consistent with a thermodynamic temperature of ∼3K. Until recently, however, no direct spectral measurements had been made at wavelengths shorter than the Planckian peak corresponding to radiation at this temperature. At such wavelengths atmospheric emission and absorption are overwhelming from even the highest mountain site and observations must be made from at least balloon platforms. The pioneering broadband rocket and balloon measurements covering this wavelength region produced consternation when excessively high fluxes were reported; successive flights gradually eliminated the excess, emphasising the practical difficulties of such observations. A review of this phase of the pursuit is given by Blair1. Nevertheless, it is upon direct submillimetre measurement of the spectral density Iν that confidence in the interpretation of the longer wavelength results must reside. The outcome of the first such measurement, by Queen Mary College in 1974, seemed completely to justify such confidence. Unfortunately, the subsequent observations by Berkeley, although leading to the same conclusion about the value of the thermodynamic temperature, were so discrepant in detail from those of QMC as once again to raise doubts. We have since been eagerly awaiting the results of observations by independent groups but these have been frustrated by instrumental failures. We attempt here to assess the present situation. We conclude that although present measurements indicate a flux not inconsistent with a Planckian spectrum corresponding to a temperature of ∼3K, they do not demand such an interpretation. Moreover, because we may not actually expect a Planckian curve from a fireball, very much more detailed information is needed to obtain a view of the early thermal history of the universe.
Non-Explosive Mass Loss
Authors: Woolf N. J.
Published: July 2016

The various mechanisms whereby stars might lose matter are considered, together with the observational evidence of the mass loss rates associated with these mechanisms. The results are shown in a diagram giving the fractional mass that a star loses by various mechanisms as a function of initial mass.
Evolution of Stars with M8 M⊙
Authors: Massevitch A. G. , Tutukov A. V.
Published: July 2016

A review of research in the field of evolution of massive stars during the last three years is presented. The analysis of computed stellar models in the helium-burning stage provides evidence for the existence of neutrino emission predicted by the theory of universal Fermi-interaction. The criterion for convective stability in the zone of variable molecular weight still remains uncertain despite several possibilities for a unique choice of the stability criterion that were recently suggested.

Evolutionary computations of massive star models in the carbon, oxygen, neon and silicon-burning stages provide opportunities to obtain models of presupernovae of different types and to investigate the cause of instability responsible for the implosion as a function of the initial mass of the star.

If the neutrino emission is included in computations the core of a star with M≳90 M⊙ loses stability due to the positron-electron pair formation in the oxygen-burning stage. A star with 16 M⊙ ≲ M ≲ 90 M⊙ collapses because of photodissociation of the iron nuclei but a core of a star with 9 M⊙ ≲ M ≲ 16 M⊙ collapses due to neutronization of silicon or iron nuclei.

Attention is paid to the possibility of circulation mixing of matter within the boundary of a carbon-oxygen core, due to the fast rotation of the core in advanced stages of evolution, if the angular momentum is conserved in the course of evolution. As the molecular weight barrier is low in late stages of chemical evolution, it can not prevent the penetration of circulation flows outside the convective core.

Difficulties of the present theory of convection in stars are stressed and the necessity of a two-dimensional approach to the solution of the stellar constitution equations is emphasized.
FG Sagittae: The s-Process Episode
Authors: Langer G. E. , Kraft Robert P. , Anderson Kurt S.
Published: July 2016

The spectrum of the supergiant FG Sge has been studied from a series of high dispersion 120-in. coudé spectrograms obtained during the interval 1969–72, thus continuing the work of Herbig and Boyarchuk (1968). The star, of effective temperature about 6500 K in 1972, is cooling at the rate of 250 K yr-1; it is known to have ejected a still visible planetary nebula some 6000 years ago (Flannery and Herbig, 1973). Abnormally strong absorption lines of Y ii, Zr ii, Ce ii, La iiand other s-process species began to appear in the spectrum of the central star some time after 1967 and have progressively strengthened. Present abundances per gram of these elements are about 25 times the solar value. There is little doubt that the atmosphere of the star has been enriched in these elements during the past seven years, but the rate of enrichment now appears to be slowing down.
Evidence for Instability Among Sub-Luminous Stars
Authors: Greenstein Jesse L.
Published: July 2016

A programme of spectroscopic study of sub-luminous stars has been in progress at Palomar, using the coudé spectrograph. Various types of objects have been studied and some preliminary results are available. Certain other programmes will, when completed, be relevant to the subject-matter of this Symposium. A survey of possible velocity variations in sub-dwarfs of spectral types A to G is in progress. So far I can report that no emission lines have been found, and that there are very few spectroscopic binaries in this group. In another programme, the depth of the late-type absorption lines in the composite spectra of SS Cygni stars will be used to estimate the luminosities of the hot components near their minima. Spectra of old novae are also being obtained with a dispersion of 38 å/mm. Plates obtained thus far show that complex structure still exists in the emission bands.
Variable Stars and Problems of Stellar Formation
Authors: Kukarkin B. V.
Published: July 2016

The possibility of discovering phenomenologically similar objects either located in different stellar systems, or in totally different (according to their origin and age) parts of some complex stellar system (as, for instance, our Galaxy) is of extreme importance. The detection of such objects permits us to confirm that, in spite of different initial conditions and evolutionary paths, stars of quite different origin pass in the course of their evolution through the same stages.
The Instability of Sub-Giants in Close Binary Systems
Authors: Kopal Zdeněk
Published: July 2016

I should like to open my subject by attempting to answer the following question: how many parameters are necessary and sufficient for a complete specification of the form of both components in close binary systems? Their shape should, in principle, be specified by the nature of forces acting on their surfaces, and (provided that the free period non-radial oscillations of both components are short in comparison with that of their orbits) their distortion should be governed by the equilibrium theory of tides. The level surfaces of constant density then coincide with those of constant potential, and the boundary of zero density becomes a particular case of such equipotentials.
Photometric Evidence of Instability in Eclipsing Systems
Authors: Wood Frank Bradshaw
Published: July 2016

Many eclipsing variables exhibit characteristics that indicate lack of stability. Physically, these systems range from certain short-period dwarfs, which show irregular brightness fluctuations unexplainable by any normal eclipse hypothesis, to systems such as AO Cassiopeiae: class O super-giants whose periods, velocity curves, and light curves have shown remarkable variations. Included are systems having one Wolf-Rayet component and probably one old nova. Many eclipsing binaries show erratic changes of period that are difficult to explain on any concept of a stable system. Indeed, when we consider the physical conditions which must prevail when two stars are located with their surfaces only a few hundred thousand miles from each other, perhaps we should be surprised that the irregularities are not larger.
B. The Non-Linear Calculations for Pulsating Stars
Authors: Christy Robert F.
Published: July 2016

(Ed. note: The custom in these Symposia has been to have a summary-introductory presentation which lasts about 1 to 1.5 hours, during which discussion from the floor is minor and usually directed at technical clarification. The remainder of the session is then devoted to discussion of the whole subject, oriented around the summary-introduction. The preceding session, I-A, at Nice, followed this pattern. Christy suggested that we might experiment in his presentation with a much more informal approach, allowing considerable discussion of the points raised in the summary-introduction during its presentation, with perhaps the entire morning spent in this way, reserving the afternoon session for discussion only. At Varenna, in the Fourth Symposium, several of the summaryintroductory papers presented from the astronomical viewpoint had been so full of concepts unfamiliar to a number of the aerodynamicists-physicists present, that a major part of the following discussion session had been devoted to simply clarifying concepts and then repeating a considerable amount of what had been summarized. So, always looking for alternatives which help to increase the understanding between the different disciplines by introducing clarification of concept as expeditiously as possible, we tried Christy's suggestion. Thus you will find the pattern of the following different from that in session I-A. I am much indebted to Christy for extensive collaboration in editing the resulting combined presentation and discussion. As always, however, I have taken upon myself the responsibility for the final editing, and so all shortcomings are on my head.)
D. The Line Spectrum of Pulsating Variable Stars
Authors: Kraft R. P.
Published: July 2016

(Ed. note:Encouraged by the success of the more informal approach in Christy's presentation, we tried an even more extreme experiment in this session, I-D. In essence, Kraft held the floor continuously all morning, and for the hour and a half afternoon session, serving as a combined Summary-Introductory speaker and a marathon-moderator of a running discussion on the line spectrum of cepheids. There was almost continuous interruption of his presentation; and most points raised from the floor were followed through in detail, no matter how digressive to the main presentation. This approach turned out to be much too extreme. It is wearing on the speaker, and the other members of the symposium feel more like an audience and less like participants in a dissective discussion. Because Kraft presented a compendious collection of empirical information, and, based on it, an exceedingly novel series of suggestions on the cepheid problem, these defects were probably aggravated by the first and alleviated by the second. I am much indebted to Kraft for working with me on a preliminary editing, to try to delete the side-excursions and to retain coherence about the main points. As usual, however, all responsibility for defects in final editing is wholly my own.)
C. Prediction on the Velocity Field Coming from Convective Overshoot in a Layer Overlying a Convectively Unstable Atmospheric Region
Authors: Moore Derek W.
Published: July 2016

Böhm has described the problems associated with the interior of the convection zone. My task is to say something about those fluid motions of the region just above the top of the convection zone which occur as a result of convective overshoot.
Contribution Apportée par les Marées Terrestres Dans L'étude de la Rotation de la Terre
Authors: Melchior P.
Published: July 2016

Three aspects of the experimental study of earth-tides present a direct interest for the study of the rotation of the earth. These are (1) the experimental determination of the Love numbers and the dynamical effects of the liquid core on nutations of the principal axis of inertia; (2) the delay of earth-tides; and (3) the drift of horizontal pendulums.
Sur L'utilisation des Différences de Longitude Pour la Détermination du Pôle Instantané
Authors: Gougenheim A.
Published: July 2016

To determine the position of the instantaneous pole one may use, in addition to calculations, a graphical method, which is described.
10. Spectral studies of meteors at the tokyo astronomical observatory
Authors: Hirose H. , Nagasawa K. , Tomita K.
Published: July 2016

Our program of meteor research has been changed since November, 1963, by introducing spectral photography at the Dodaira branch station of the Tokyo Astronomical Observatory, in addition to the direct photography at the Mitaka Station. Observations at these two stations are basic, and they have been supplemented in case of need by observations at the temporary station at Tatebayashi, situated about 40 km Northeast of Dodaira. Double- or triple-station observations were carried out mainly during the active period of the major streams, such as Quadrantids, Perseids, Leonids or Geminids, with the purpose of the dynamical and physical studies of meteors. The coordinates of these three stations are as given in Table 1.
19. Evaporation and deceleration of small meteoroids
Authors: Lebedinec V. N. , Šuškova V. B.
Published: July 2016

Knowledge of altitude and ionization curves of faint meteors is of great importance for the calculation of meteor detectability during radar observations (Greenhow and Hall, 1960; Lebedinec, 1963). Greenhow (1963), using the simplest physical theory of meteors (Herlofson, 1948) for altitude calculations, arrived at a conclusion that radar observations of very faint meteors were impossible for practically any radar power. The simplest physical theory of meteors is used for calculations of radar-meteor detectability by almost all the authors. Lebedinec (1963) has shown that this theory is inapplicable in the case of faint meteors since one should take into account energy losses caused by thermal radiation from the meteoroid surface.
20. The ablation of solid meteoroids
Authors: Kaiser T. R. , Jones J.
Published: July 2016

Ablation profiles for compact meteoroids have been obtained which take account of the effects of thermal radiation, conduction, meteoroid heat capacity and deceleration, while retaining the simplifying assumption that the onset of massive ablation occurs at a well-defined temperature.

The dependence of the air density, ρa, at the onset of ablation on the initial meteoroid radius, R0, is in agreement with the results of Ceplecha and Padevět (1961). For a meteoroid of given composition, velocity and zenith angle there are four critical values for the radius, R1, R2, R3 and R4. R1 is the micrometeorite limit such that if R<R1, the ablation temperature is not reached. For R1<R<R2 the onset of ablation is delayed due to thermal radiation and occurs at air density ρa1, which is substantially independent of radius. If R2<R R3 the meteoroid develops a marked thermal gradient and, if it is brittle, will fragment before ablation commences. The smallest fragments will ablate at the air density ρa1, which is shown to be close to the experimental result of Jacchia et al. (1967) for photographic meteors. If such a particle survives fragmentation, the molten droplet will fragment due to distortion if R > R4 (Lebedinec and Portnjagin, 1966); it is shown that R4 is not substantially different in magnitude from R3. Meteoroids in the size range R2<R<R3 produce underdense meteor trains and experimental measurements of echo decay as a function of echo amplitude are in agreement with the expectation that ρa2 ∝ m0n where n ~ 1/3 (Poole and Kaiser, 1967). This would support the view that the bulk of radio meteors are produced by compact particles and that the fragmentation observed with photographic meteors may be a result of thermal shock.

The ablation profiles have been computed for initial meteoroid velocities between 20 and 70 km sec−1 and radii between R1 and R3; the deceleration and residual size (at the end of ablation) have also been calculated. Even quite close to the micrometeorite limit, the residual particle is small compared with the initial size. Hence, meteoroids with R > R1 will make negligible contribution to the micrometeorites reaching the Earth's surface, except, perhaps, where a significant proportion of the mass of larger meteoroids fragments into particles with radius less than R1. By neglecting deceleration, it is possible to arrive at an analytic expression for the ablation profile; this is found to be in good agreement with the computed profiles except for particles near to the micrometeorite limit.
23. On the structure and chemical composition of meteor bodies of cometary origin
Authors: Kramer E. N.
Published: July 2016

Possible origins for hyperbolic meteor orbits are noted, and photographic evidence on the nature of meteoroid structure is discussed.
41. On the width of the Geminid shower at faint radio magnitude
Authors: Forti G.
Published: July 2016

A search for major streams has been performed among the orbits of meteors observed with the six station meteor radar of the Harvard-Smithsonian Radio Meteor Project at a limiting radio magnitude of about + 10 on the visual scale.

The analysis of the Geminid shower from observations made in December 1961, 1962, 1963 and 1964, shows some evidence that meteors belonging to this stream are detected at an earlier date than the bright photographic meteors. From observations made on December 28–31 of the same years during the hours in which the Geminid radiant is within the collecting area of the six station system, 15 orbits were identified as possible members of the shower.

It is suggested that the stream might be active for a period longer than the previous observations indicated.
42. Radar observations of the Leonids in 1965–66
Authors: Plavcová Z.
Published: July 2016

Hourly rates of meteor echoes are presented, and it is shown that the peak activity occurred at solar longitude 234°. 457 in 1965, and 234°. 466 in 1966 (mean equinox 1950·). The exponent s is calculated from distribution of echo durations and its variation with date is given.
43. Observations of the Leonid meteor shower in November 1966 in the U.S.S.R.
Authors: Bronšten V. A.
Published: July 2016

In connection with the expected passage of the Earth through the densest part of the Leonid meteoric stream in November, 1966, the Commission on Comets and Meteors of the Astronomical Council of the U.S.S.R., and the All-Union Astronomical-Geodetic Society, organized visual, photographic and radar observations of the shower at many points in the Soviet Union.
Planetary Nebulae as a Part of the Galaxy
Authors: Perek L.
Published: July 2016

Planetary nebulae form one of the most important subsystems of the Galaxy. If we knew more about this subsystem, an important gap in our ideas about the galactic structure would be filled. Very briefly, we are facing the following situation:

Population I, which contributes to the total mass of the Galaxy by hardly more than 7 %, can be tracked almost over the entire Galaxy thanks to the radio observations of neutral hydrogen at 21 cm wavelength. Other data, for a wide solar neighbourhood, follow from observations of Cepheids and early-type stars.
Transition Probabilities for Forbidden Lines
Authors: Garstang R.H.
Published: July 2016

A compilation is given of transition probabilities of forbidden lines which occur in the spectra of gaseous nebulae.
The Ionization of Planetary Nebulae
Authors: Williams Robert E.
Published: July 2016

The ionization of the most abundant elements in planetary nebulae has been determined for a number of models of nebulae at different epochs in their expansion. The values used for the temperatures and radii of the central stars and the sizes and densities of the shells have come from Seaton's evolutionary sequence. The ionizing radiation field has been taken from model atmosphere calculations of the central stars by Gebbie and Seaton, and Böhm and Deinzer. Emission-line fluxes have been calculated for the models and compared with observations of planetary nebulae by O'Dell, Osterbrock's group, and Aller and his collaborators. Results indicate that the central stars have strong He+ Lyman continuum excesses, similar to those predicted by Gebbie and Seaton. The mean abundance determinations for the nebulae made by Aller are confirmed, with the exception of nitrogen, which appears to be 3 or 4 times more abundant than his value. It is also seen that the electron temperatures of the nebulae are higher than previous theoretical determinations, providing better agreement with empirically derived values.
The Atmospheres and Spectra of Central Stars
Authors: Böhm K.H.
Published: July 2016

After a brief discussion of the determination of the effective temperature, the surface gravity and the chemical composition of the central stars, we describe the typical problems arising in the computation of static and dynamical models of the very hot atmospheres of these objects. Special attention is paid (1) to the strong non-greyness of the atmosphere, (2) the electron-scattering contribution to the source function, (3) the contribution of the higher ions of C, N, O and Ne to the absorption coefficient, (4) the importance of radiation-pressure effects. The application of the computed energy distribution to the determination of the ionization stratification of the nebula and to the calculation of the bolometric correction is discussed.

A formation of emission edges due to the Schuster effect does not seem to occur in any of the static non-grey model atmospheres which have been computed so far. The reason is that the steep temperature gradient in the uppermost layers of these models strongly favors the formation of absorption edges. Using very simple dynamical models by Schmid-Burgk (1967) we discuss the possibility of a considerable flattening of this temperature gradient by a hydrodynamic outflow driven by radiative acceleration. We argue that the Schuster effect may be much more important, if these atmospheres are not in hydrostatic equilibrium.

The position of central stars of different spectral type in the Teff-g plane is discussed.
A Method of Determination of the Temperature of Nuclei of the Planetary Nebulae
Authors: Khromov G.S.
Published: July 2016

I would like to make a few comments on the problem of the determination of the temperatures of nuclei of planetary nebulae.

It can be shown that in a high-excitation planetary nebula two independent Strömgren zones of heavy elements can be found. The first is a He III zone; the second corresponds to a zone of the luminescence of Ne V forbidden lines and originates due to combined absorption by the heavy ions Ne IV, O V and N V. If so, a relatively independent method of the determination of the color temperature of nuclei can be suggested.
Long-Period Variables and Planetary Nebulae
Authors: Menzel Donald H.
Published: July 2016

The occasional appearance of a red giant or long-period variable in planetary nebulae poses a problem for theoretical astrophysics. Such a cool nuclear star would not ordinarily provide a source of ultraviolet radiation necessary for the excitation of the spectrum of a gaseous nebula.

One possible solution of this problem postulates the existence of intense magnetic fields in the star. Second, the star itself has a structure resembling that of a miniature, highly compressed planetary, with a high-temperature nuclear star at the centre and a distended atmospheric shell enveloping chiefly the stellar equator.

The magnetic field induces a sort of pumping action that creates the tire-shaped envelope from matter ejected near the poles. As this shell grows denser, it radiates like a stellar photosphere at low temperature. Eventually the shell becomes unstable and disperses outward to form and maintain the nebula. A quasi-periodic situation occurs, which explains the variation of light. Ultraviolet light absorbed during the minima, when the shell has vanished, adequately accounts for the nebular excitation. A wide variety of such symbiotic stars occurs, including repeating novae as well as the long-period variables.
Dynamical Instability of the Envelopes of Red Supergiants and the Origin of Planetary Nebulae
Authors: Paczyński B. , Ziółkowski J.
Published: July 2016

Deep convective envelopes of the red supergiants with masses smaller than 4 M⊙ are found to be dynamically unstable for the luminosities in the range of 4 × 103–5 × 104L⊙. The total energy of the envelopes is positive when the recombination energy of the ionized hydrogen and helium is taken into account, and is sufficient to expel a typical envelope up to infinite distance at a speed of 30 km/sec. We suggest that planetary nebulae are formed in this way.
Evolution of Central Stars of Planetary Nebulae Theory
Authors: Salpeter Edwin E.
Published: July 2016

Before discussing observational inputs and actual model calculations, I want to give a very elementary review of the relevant parts of stellar evolution theory. We shall only be dealing with stellar masses M below the Chandrasekhar limiting mass Mch(~1·2–1·45 M⊙, depending on chemical composition). The inequality M<Mch implies that relativistic effects are not of overriding importance and I will not mention them further (however, all quantitative model calculations which I will mention later include all the relativistic corrections to the equation of state, including radiation pressure which is also not very important). Let us try to estimate how the central temperature Tc and (total bolometric) luminosity L varies with central density ρc or radius R(ρc~MR−3) for a star of fixed mass.
On the Evolution of the Central Stars
Authors: Deinzer Willi
Published: July 2016

A most puzzling feature of the evolution of the central stars of planetary nebulae is their rapid contraction (O'Dell, 1963; Seaton, 1966); assuming homologous contraction, an enormous amount of gravitational energy is released therefore. For reasons of hydrostatic equilibrium a large part of this energy must be radiated away. As this does not show up in the luminosity of the central stars it must either leave them by some other means – e.g. neutrinos (Vila, 1966) – or it does not originate from the outset; in other words, the actual contraction must deviate strongly from the homologous way. I should like to discuss briefly the second possibility.
Physical Processes
Authors: Osterbrock D.E.
Published: July 2016

When Dr. Seaton asked me to chair the epilogue session of our conference I could not help but wonder if it were to be considered an example of type-casting. He told you that when an Englishman is asked to give a prologue, he immediately begins thinking of quotations from Shakespeare, so I must tell you that when an American is asked to deliver an epilogue, his thoughts turn naturally to Ernest Hemingway. I therefore suggest to you as the theme for our symposium the closing words of the main character of To Have and Have Not, which may for publication here be bowdlerized to read “One man alone ain't no —, — good at all.” Over and over again in the last week we have seen that discussions between astronomers have provided new insights, have opened up new fields for investigation, have revealed unsuspected connections between apparently unrelated problems. I believe this has been a very fruitful conference because there have been so many fruitful discussions among the participants. I shall therefore try to summarize briefly my impressions of the things we have learned and the things we may reasonably hope to learn in the next few years about physical processes in planetary nebulae, and then five of our colleagues will summarize the other sessions of our conference. We invite discussion from all of you after each of these summaries, and also during the general discussion at the close.
The balance of magnetic fluxes in active regions
Authors: Stenflo Jan Olof
Published: July 2016

According to modern theories of the solar cycle, active regions on the Sun are caused by a magnetic disturbance penetrating the solar surface from below. Sunspots, filaments, flares and other conspicuous events in an active region seem to be only secondary phenomena, the basic feature being the magnetic field itself.
Last phases of development of active regions
Authors: Bumba V. , Kleczek J. , Olmr J. , Růžičková-Topolová B. , Sýkora J.
Published: July 2016

A close relation of filament feet to the supergranular structure has been found. Green corona brightness, 1420 MHz flux, and the location of quiescent filaments depend upon the distribution of the photospheric magnetic fields. The development of polar maxima of the green corona and their relation to the following polarity have been studied.
The migration of sunspot activity along solar meridians and parallels
Authors: Dezsö L. , Gerlei O. , Kovács Ágnes
Published: July 2016

The places of local maxima of sunspot activity, i.e. the formation of solar active regions, seem to follow in a definite sequence of tracks over the Sun's surface. These sequences of activity apparently represent distinct continuous streams, whose duration may be of the order of magnitude of 1 year.
Sunspots and magnetohydrodynamic flows
Authors: Anderson G. F. , Menzel D. H.
Published: July 2016

Theoretical techniques are developed to study compressible, steady-state, magnetically aligned gas flows in sunspot regions. The flows are adiabatic and occur in a known streamline configuration. The non-linear parabolic partial differential equation describing the flow reduces to an ordinary linear differential equation. The solutions are briefly discussed.
The intensity, velocity, and magnetic structure in and around a sunspot
Authors: Beckers J. M. , Schröter E.H.
Published: July 2016

An observational study of the fine structure in a sunspot region led to the following results: (a) The photosphere around a sunspot is covered with the so-called Magnetic Knots. These features have a diameter of 800 km and a magnetic field of up to 1400 gauss. Although they coincide with dark, intergranular spaces, they are distinctly different from pores. We estimate some 300 to surround the sunspot. The magnetic field of the smallest pores were found to be 1500 gauss. (b) For the Umbral Dots we find a lifetime of 25 min. Their colour, as derived from simultaneous observations at 4700 Å and 6400 Å, was found to be identical to that of the photosphere. Assuming their brightness to be photospheric we derive a diameter of 160 km.
Chromospheric heights in active regions
Authors: Bappu M.K.V. , Sivaraman K. R.
Published: July 2016

Spectra, with a radial slit in the K and Hα lines, of a sunspot close to the limb are used to determine chromospheric heights in an active region. Equidensity contours obtained with the Sabattier effect are used to measure the values of h* for different positions in the line core and wings. The spectra have also been utilized to determine similar heights in two very restricted regions of Ca+ emission which show an arched emission structure in K232 with bright continuum emission. At the K-line centre, unit tangential optical depth in the umbra, umbra-penumbra interface, and penumbra are at 1310, 1610, and 2330 km respectively. The corresponding value for the umbra in the Hα-line centre is 1080 km. The arches have a value of h = 3000 km at Δλ = 0 for the K line.
The ‘detwisted’ prominence of September 12, 1966
Authors: Valniček Boris
Published: July 2016

The eruptive prominence of September 12, 1966, is described. Detwisting of two filaments is demonstrated and compared with similar phenomena and with tornado prominences. A short discussion of mechanisms of the origin and subsequent development of the phenomenon is given.
Flare activity and spotgroup development
Authors: Bumba V. , Křivský L. , Martres M. J. , Soru-Iscovici I.
Published: July 2016

The flare activity of all active regions having ten or more flares from August 1959 until December 1961 was investigated. We constructed flare-activity curves drawn with the aid of Kleczek's q-index. The characteristic magnetic situation on the Mt. Wilson synoptic charts of photospheric magnetic fields in which the flare-rich active regions developed is described. A flare activity rate ‘quantization’ was found. From the CSSAR magnetic observational material we studied the reorganization of the magnetic fields of active regions which correlated with sudden changes in the rate of flare activity.
A study of the localization of flares in selected active regions
Authors: Martres M. J. , Michard R. , Soru-Iscovici I. , Tsap T.
Published: July 2016

From the material gathered during the ‘Cooperative Study of Solar Active Regions’, we studied the flare locations in AR magnetic structure, and flare relations to changes in the magnetic fields and spot configurations. Besides a confirmation of previous results, we find that flares are often associated with two features of the spot configuration evolving in opposite senses, one growing, the other declining.
Evolution of Ca plages of the CSSAR active regions
Authors: Godoli G. , Monsignori Fossi B. C.
Published: July 2016

For each plage of the CSSAR period the daily projected areas have been determined and plotted versus time. Also the correction for foreshortening has been taken into account.

Daily fluctuations, of the plage corrected areas, certainly greater than the errors, have been found. Also area fluctuations of shorter periods have been observed.
La composante lentement variable des rayons X solaires en relation avec la structure des centres d'activité
Authors: Michard R. , Ribes Mme E.
Published: July 2016

The slowly varying component of solar X-rays has been studied through records of the satellite Explorer-30 instrumented by the U.S. Naval Research Laboratory. Correlations with plage areas, and flux at radiofrequencies have been studied. High flux values in the 8–20 Å and, still more, the 1–8 Å bands are related to specific ARs, also characterized by great flare productivity, high intensities on 3 cm, and anomalous magnetic structure.
A model of solar flares
Authors: Sturrock P. A.
Published: July 2016

A model of solar flares is proposed in which the preflare state comprises a bipolar magnetic-field structure associated with a bipolar photospheric magnetic region. At low heights, the magnetic-field lines are closed but, at sufficiently great heights, the lines are drawn out into an open structure comprising a bipolar flux tube containing a ‘neutral sheet’ or ‘sheet pinch’. Such a sheet pinch is probably related to a coronal streamer. The energy stored in the closed-field region is derived from photospheric motion whereas energy stored in the open-field region is derived from the non-thermal energy flux which heats the corona and drives the solar wind.

The flare itself is identified with reconnection of magnetic field by the tearing-mode resistive instability. If the thickness of the sheet pinch is determined by resistive diffusion and a growth time of the bipolar region of order 1 day, the transverse dimension will be about 104 cm. The rise time of the tearing-mode instability is then a few seconds, compatible with the characteristic time of Type-III radio bursts. One can understand that the time-scale of the reconnection process is of order 102–103 sec if reconnection proceeds by the Petscheck mechanism, with the modification that resistive diffusion is replaced by the more rapid Bohm diffusion.

The evolution of a flare, according to this model, appears to fit a number of the observational characteristics of flares.
The occurrence and possible meaning of the ‘nimbus’
Authors: Houtgast J.
Published: July 2016

There are few observations of cases in which a nimbus has developed around a solar flare of major importance. Speculations have been made about the nature of this obscuring cloud. We shall give here some consequences of the assumption that we have to do with scattering by a cloud of electrons, ejected together with the protons during the formation of the flare.