bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Abundance of Helium in Stellar Interiors
Authors: Faulkner John 
Published: March 2016

From the titles of the other contributions to this morning’s session, one deduces that the hard facts of theory are to be sandwiched between the loose speculations of direct observation. I shall therefore feel free to discuss theoretical implications from stellar structure unencumbered by what are, after all, but peripheral considerations.I should, however, begin with an apology. It is impossible to do even minimal justice to the vast number of investigations which have contributed to our present understanding (or lack of it). The choice of topics has been dictated in part by history, in part by current relevance, but mainly by personal whim. While much of the discussion centres, for obvious reasons, on Population II work, one or two problems associated with Population I will also be considered. Reference may be made to the exhaustive review article of Iben (1967) and also to the Warner Prize Lecture by Demarque (1968) for background and a more complete discussion of some of the points which will be touched upon here.I shall assume today that the ‘normal’ helium content of stars is of the order of 25±5% by mass. This leaves me free to pay particular attention to systems which do not appear to adhere to this generalization, systems for which abnormally high or low helium contents have been claimed. The main point of my talk is that there is no really convincing, concrete evidence from stellar interiors alone for helium contents far removed from normal. During the course of the past decade, this has come to be largely accepted. It is in a way sad to see the radicalism of one’s youth become the orthodoxy of middle age.
Helium Production in the Different Cosmological Models
Authors: Doroshkevich A. G. , Novikov I. D. , Sunyaev R. A. , Zeldovich Ya. B. 
Published: March 2016

The aim of the present report is to emphasize the role of the helium problem as the key one for different aspects of cosmological speculations. This is not surprising, because the processes which produce the helium and other elements in primordial matter take place during the first stages of the cosmological expansion of the Universe.The theory gives three critical values of the He4 abundance in pre-stellar matter, depending on assumptions about the behaviour of the Universe near the singularity. The three critical values are:(1) practically no He4 at all;(2) about 25% of He4 by mass;(3) practically entirely He4.Although intermediate values of He4 are in principle possible, the cosmological models permitting such values are highly improbable. It is obvious that the helium abundance is less than 100%, and that even rough estimates of whether the stellar matter consists almost entirely of hydrogen, or if it has a significant part of He4, are of tremendous importance. The much-more-difficult determination of traces of primeval He3, D, Li6, would be of great help in making definite cosmological conclusions.
Helium in the Universe: Final Summary
Authors: Burbidge G. 
Published: March 2016

It is my task to summarize for you what we have learned today about the helium problem. Before attempting this, let me first very briefly outline the problem as it appears to us in 1970. It amounts to the questions: What is the fractional abundance of helium in different regions in the universe, is it the same in all places, and how did it originate?The simple answers to these questions which appealed to many and seemed to have a reasonable basis in fact a few years ago were:The He/H ratio is of ~ 25-30% by mass; the ratio is the same everywhere, and the helium was most probably synthesized in the early stages of a primordial fireball in which the universe began. However, for some time it has been clear that the situation is more complicated than this, as I pointed out in an article published last year in Comm. Astrophys. Space Sci.
Interstellar Molecules - The Optical Region
Authors: McNally D. 
Published: March 2016

Considerable attention has recently been given to the observation of interstellar molecules by radio methods. Interstellar molecules have also been given a boost because of excitation by the 3K black body radiation field (to use a convenient description). Nevertheless optical studies of interstellar lines have reached a very low ebb and, with brighter moments, have remained so since the work of Adams (1949).The years 1937-1942 were the exciting period for optical studies of interstellar molecular lines. It is interesting to note that it was not molecular lines as such that led to the suspicion that molecules might exist in interstellar space but it was the discovery of the diffuse features at 5780, 5797, 6284 and 6614 by Merrill (1934) that led Russell (1935) to speculate on the possibility of their existence. It was Swings and Rosenfeld (1937) who stressed that likely interstellar molecules would be CH, OH, NH, CN and C2. Dunham, Adams and McKellar did much of the work of identifying interstellar lines in the period 1937-1940 and indeed McKellar (1941) had derived an excitation temperature of 2-3 K for CN - a value subsequently rediscovered.
The Interpretation of Xuv Solar Radiation
Authors: Goldberg Leo 
Published: March 2016

Solar ultraviolet and X-radiation arriving at the Earth is emitted mainly by highly-charged ions in the outer layers of the Sun, where departures from thermodynamic equilibrium are extreme. Hence the diagnosis of physical conditions from spectral intensities entails the use of accurate cross sections for a variety of physical processes governing the excitation and ionization of emitting ions. Now that the full potential of satellites for solar data acquisition has begun to be realized, the need for atomic data of all kinds is more acute than ever before. In this review, I shall illustrate the importance of laboratory and theoretical investigations for the analysis of solar ultraviolet and X-ray data by referring to five problems to which space experimenters are currently devoting a great deal of attention:(1)the temperature minimum at the interface between the photosphere and the chromosphere,(2)the temperature and density profiles of the low chromosphere,(3)the transition zone at the chromosphere-corona interface,(4)the corona,(5)solar flares.
The Electron Excitation Rate for the Green Coronal Line at 5303 Å
Authors: Petrini D. 
Published: March 2016

The collision strengths for transitions between levels of Fexiv have been calculated using the close coupling and the Coulomb-Born I methods. It is shown that the Coulomb-Born I approximation gives reliable results for highly ionized ions.The electron excitation rate coefficient for the transition in the 3s2 3p configuration, giving rise to the green coronal line, has been investigated in detail. The quantum defect method, which takes into account the excitation via autoionization levels of FeXIII, has been used. This process greatly increases the excitation rate for low energies of the incident electron.The statistical equilibrium populations of the FeXIV levels have been calculated under coronal conditions, and the effective excitation rate coefficient for the green coronal line is given for a wide range of temperatures and densities.
The Relevance to Astrophysics of the Results of Recent Experiments With Colliding Charged-Particle Beams
Authors: Dolder K. T. 
Published: March 2016

AbstractA summary is given of some recent measurements of the ionization and excitation of positive ions by electrons, and the detachment of electrons from H− by proton and electron impacts. The results are discussed and compared with theory. Conclusions are drawn which are relevant to atomic collision processes which occur in astrophyscial plasmas.
Pressure Broadening of UV Lines
Authors: van Regemorter H. 
Published: March 2016

Most of the lines in the UV spectra are lines of ions which are formed in high temperature regions where the pressure broadening is caused by electrons and protons. This is the case in O and B type stars for which the theoretical calculation of the width of all the strong UV lines is important in determining both the blanketing effect and the abundances of the elements.The cores of these strong lines are formed in non-LTE layers near the surface where the electron density is very low. The wings of some of the lines are more easy to interpret, being formed in deeper layers of the star, where one can assume LTE and where the electron density - or in the Sun, the neutral hydrogen density - is such that the pressure broadening is much more important than the natural width.Two opposite approximations have been applied to the line broadening problem; the impact approximation is generally valid for electrons when the perturbations are so rapid that the collision timeτcis very small compared to the typical time, Δω-1, of importance in computing the profile at the frequencyΔω = ω – ω0measured from the line centre. On the contrary, whenτc≫Δω−1the quasi static approximation may be assumed. Both of these approximations have been considerably improved and efforts have been made recently to develop a unified theory valid from the impact regime to the static regime.
On the Polarization and Anisotropy of Solar X-Radiation During Flares
Authors: Elwert G. , Haug E. 
Published: March 2016

From the spectral intensity distribution of solar X-radiation one can conclude that there is a non-thermal contribution, which is effective during the initial phase of a flare. It is reasonable to suppose that the electrons producing the non-thermal radiation have a non-isotropic velocity distribution. Indeed, one should assume that the electrons, during their acceleration, obtain a preferred direction and that only afterwards does their velocity distribution become Maxwellian by means of collisions. Hence the short-wavelength continuous X-radiation in the initial phase of a flare, consisting mainly of bremsstrahlung, should be polarized and should have a non-isotropic angular distribution.In papers presented to the IAU-Symposia in Budapest 1967 (Elwert, 1968) and in Leningrad last May, the polarization of X-radiation from electrons of a few keV accelerated in solar flares has been calculated using energy distributions based on the observations of Pounds et al. obtained with the satellites Ariel I and OSO-4.
Geodetic Applications of Grazing Occultations
Authors: Dunham D. W. 
Published: March 2016

Up to about a century ago, occultations were often used to measure differences in geographical longitude. Extensive geodetic surveys, accurate chronometers, telegraphic communications, and later short-wave radio time services obviated the geodetic need for occultation observations, which are affected by geodetically severe uncertainties of stellar and lunar positions, lunar limb irregularities, and observers’ personal equations. More sophisticated methods of observation would be needed before the Moon could again be useful to geodesy.During this century, cinematography of Bailey’s beads and the flash spectrum during total solar eclipses have been used to obtain the relative apparent position of the Sun and Moon to an accuracy which could be useful to geodesy. But observational opportunities were rare and few results of geodetic significance have been obtained.
Seeing Effects on Occultation Curves
Authors: Young A. T. 
Published: March 2016

‘Seeing’ affects the light-curve of a stellar occultation by the Moon in two ways: the diffraction pattern on the ground is smeared out by atmospheric turbulence, and the pattern also suffers random displacements. These effects are analogous to the familiar image blur and image motion, respectively. However, there is a major difference between ordinary astronomical seeing and the effect on the lunar diffraction pattern: the former is the seeing looking up at the sky from the bottom of the atmosphere, but the latter corresponds to the seeing looking down through the atmosphere at the surface of the Earth.This downward-looking seeing is of concern to people engaged in aerial photography and satellite reconnaissance, and has been studied theoretically from this point of view. It also enters into the theory of stellar scintillation, because the seeing blurs out the scintillation shadow pattern just as it blurs out the occultation diffraction pattern.
Photoelectric Observations of Occultations in Japan
Authors: Sinzi A. M. 
Published: March 2016

In Japan, photoelectric observations of occultations were made for the first time in 1951.For about ten years after that, observations were made partly for geodetic purposes in order to determine the position of Japan with reference to islands in the Pacific, Phillippine and Taiwan.The geodetic datum of Japan, which is currently adopted, suffers seriously from the vertical deflection. The amount of this deflection is supposed to be about 10″ in latitude and 20″ in longitude.This project of occultation geodesy was, however, not so successful, because of the following two reasons: (1) Poor efficiency of data acquisition due to weather. We need good weather at two stations; the distance between them is usually over 1000 km. (2) Difficulty of correction for the Moon’s limb. For geodetic purposes, the atlas of the Moon’s limb by Dr Watts is still insufficient.Therefore, the project of occultation geodesy was replaced by satellite geodesy.
A Preliminary Analysis of Photoelectric Occultation Measurements
Authors: Pansch E. , de Vegt Chr. 
Published: March 2016

AbstractPhotoelectric occultation traces of 5 stars are discussed which have been obtained with the 60 cm refractor of the Hamburg-Observatory during 1969/70. All traces show remarkable deviations from the usual Fresnel point-source pattern. Most details of these traces can be interpreted assuming the stars to be unresolved doubles. A short description of the equipment and the observational procedure is given.
Some Recent Observations of Occultations by the Moon
Authors: White Nathaniel M. 
Published: March 2016

A program for the measurement of diffraction patterns resulting from the lunar occultations of stars was begun at the Lowell Observatory by Rakos (1964), resumed by him in 1967 and continued by Pettauer through the summer of 1969. The expected results were accurate timing of occultations and hence accurate position measurements, the discovery of close double stars, and the determination of stellar diameters. The author is continuing the program using new equipment designed by R. E. Nather of the University of Texas.The equipment was built at the Lowell Observatory and put into operation on its new 42-in. reflector in March, 1970.
Occultation Studies at the Dominion Astrophysical Observatory
Authors: Morbey C. L. , Hutchings J. B. 
Published: March 2016

During the last year studies of lunar occupations have begun at the Dominion Astrophysical Observatory. Since the acquisition of a Fabri-Tek (model FT 1074) signal averager and analyser, twelve occultations have been observed but only one has been reduced and a comparison made with a theoretical model. The observed diffraction pattern for this occultation was found to correspond with an almost point source model.The exposure meter photomultiplier (EMI type 6094) on the 48 in. telescope has been used for all observations to date. A preamplifier mounted close to the photomultiplier housing directs the amplified signal to a circuit which controls the D.C. level of the signal before being applied to the signal averager.
Remarks on the Role of Pulsars in Cosmic Ray Production
Authors: Ginzburg V. L. 
Published: March 2016

This discussion is concerned with the production of cosmic rays in supernova explosions. In particular, we are discussing the role of pulsars (which we all believe to be neutron stars) in this process. I should like first to recall that (so far as I am aware) the idea that neutron stars form in supernova explosions, and that this phenomenon is relevant to cosmic rays, was first proposed by Baade and Zwicky in 1934. The argument was originally based on energy considerations, and further estimates indicated that supernovae could indeed be the main source of cosmic rays (ter Haar, 1950). When radioastronomical data later showed that supernova remnants definitely contained large numbers of relativistic electrons, there could be no doubt that they were sources of cosmic rays as well (and it became quite probable that they were indeed the major source of such particles). The growth of these ideas can be studied in historical perspective in Rosen’s (1969) compilation of papers on cosmic ray origin theories. As is so often the case, this subject has developed in a cyclic and repetitious fashion. I wish to make this point because I feel that my own contribution to these theories has sometimes been overestimated - though I hope I cannot myself be blamed for this.It would not be appropriate to consider cosmic ray origins in detail during this discussion. I have in my case given my present views elsewhere (Ginzburg, 1969, 1970). The following remarks will deal specifically with the role of pulsars.
The Absolute Magnitudes of the RR Lyrae Stars
Authors: Woolley Richard 
Published: March 2016

The absolute magnitudes of pulsating variable stars, both RR Lyrae stars and Cepheid variables, may be assessed from observation in three ways: by the classical method of statistical parallaxes, by their occurrence in star clusters whose distance is otherwise known, particularly by ascertaining the position of the main sequence in the HR diagram, and by the Baade-Wesselink method of determining stellar diameters.As regards the first of these, the method of statistical parallaxes, the RR Lyrae stars lend themselves to this better than do the Cepheid variables, because the velocities relative to the Sun are so much larger. RR Lyrae radial velocities are frequently as high as 200 km/sec or even 300 km/sec, and as many of the stars lie at distances between 1000 and 1500 pc the proper motions of the transverse velocities may be expected to be as high as 0”.050 per annum. And, indeed, many investigations have been made recently, among which one may mention those by Plaut, by van Herk, and by the Royal Greenwich Observatory.
Ultraviolet Astronomy
Authors: Wilson R. 
Published: March 2016

Ultraviolet astronomy is in a phase of very rapid development and any review of the new techniques involved is necessarily conditioned by the fact that most of the work is in a preparatory stage. This paper, therefore, will not be restricted to a discussion of those techniques which have undergone the ultimate test of their effectiveness, i.e., an actual space mission, but will include a consideration of those techniques which are still under development. Some omissions are therefore inevitable.The presentation is divided into three categories: (a) the vehicle and its stabilisation (if any), (b) the optics, and (c) detectors. Category (a) presents the major new technological problems and contributes the greater part of the total cost. Experience in the other categories of optics and detectors had, of course, reached an advanced and sophisticated level at the time of the advent of the rocket, but new and difficult problems have been posed mainly by their operation in a space environment, but also by their use in the ultraviolet region of the spectrum.
X-Rays Radiation of a Neutron Star as a Result of Gas Accretion
Authors: Zel’dovič Ja. B. 
Published: March 2016

The accretion of gas on the surface of a neutron star is a source of energy, which can be converted into X-rays radiation. Accretion can ascertain a far greater lifetime of an X-ray star than the radiation of internal energy.The source of gas could be a cloud of intergalactic gas. If the neutron star is a component of a binary system, the gas could come from the other (non-neutronic) star.The idea of accretion and evaluation of energetic balance were given by Zel’dovič (1964) and Zel’dovič and Novikov (1964, 1965) and Salpeter (1964). Shortly the idea of accretion was mentioned by Šklovskij (1967).The motion of gas and radiation spectra idealised case of spheric symmetry are studied now by N. Shakuro and Zel’dovič.
The AGK3, SRS and Related Projects
Authors: Scott Francis P. 
Published: March 2016

This report consists of a brief summary of the status of a number of programs of an international nature which are now in progress at various observatories of the world. These programs have received strong endorsements from Commission 8 of this Union, as well as from a number of international organizations interested in accurate positions and motions of the stars to the 9th magnitude of brightness. Among the organizations and conferences which have explicitly endorsed the programs are:(1) The Symposium on Coordination of Galactic Research, Groningen, 1953.(2) Conference on the Problems of Astrometry, Evanston, 1953.(3) Astrometric Conference, Pulkovo, 1954.(4) Conference on Astrometry, Brussels, 1955.(5) International Union of Geodesy and Geophysics, 1954 and 1963.(6) International Astronomical Union, 1955.(7) Second Astrometric Conference, Cincinnati, 1959.(8) First Inter-American Conference on Astronomy, La Plata and Cordoba, 1959.(9) Meeting on Problems of Astrometry and Celestial Mechanics, La Plata, 1960.(10) Committee on Space Research, COSPAR, 1966.
Études sur l’emploi de Recouvrements de Plaques pour l’établissement de Catalogues Photographiques
Authors: Lacroute P. 
Published: March 2016

Le but de cette étude est la recherche des possibilités et des limites de l’emploi des recouvrements de clichés.Le travail n’est pas terminé. Un travail plus complet sera publié dans quelques mois.
On the Origin of the Algol Systems
Authors: Plavec M. 
Published: March 2016

The 4th edition of the Finding List for Observers of Eclipsing Variables (Koch et al, 1963) contains 145 sufficiently well-observed eclipsing binaries brighter than 8·5m at maximum light. Among them, 59 binaries, or 41%, are systems with both components on the main sequence. The second largest group, 52 binaries or 36% of all systems, are systems similar to Algol. These can be characterized as follows:
(1)The primary (more massive) components are main-sequence stars, fitting well into the mass-luminosity relation defined by visual binaries and by eclipsing binaries with both components on the main sequence (detached systems).(2)The secondary components are of later spectral type than the primaries, and can be best characterized as subgiants. They are overluminous for their mass as well as for their spectral class.(3)As a rule, the secondary components fill their respective critical Roche lobes (innermost Lagrangian surfaces).
Arguments Indicating that Ap and Am Stars are Evolved Spectroscopic Binaries
Authors: van den Heuvel E.P.J. 
Published: March 2016

Roughly three types of evolution of spectroscopic binaries may occur:Case (a): the primary fills its Roche limit already before the end of core hydrogen burning;Case (b): the primary fills its Roche limit after core hydrogen exhaustion but before the onset of helium burning, andCase (c): the primary does not fill its Roche limit before the end of core helium burning.Since long-period variables of Population I as well as Population II may reach radii of 10 AU, case (c) will occur in systems with periods up to 100 years. Since about 50% of the A and B stars are spectroscopic binaries, many evolved spectroscopic binaries are expected to occur in the galactic system. Computations show that, using the mass-ratio distribution of unevolved systems derived by Kuiper, the number of systems with one evolved component is expected to be at least as large as the number of unevolved systems, in the spectral regions A and B.