bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar Gamma Rays and their Correlation with Space and Ground-Based Observations
Authors: Fazio G.G.
Published: March 2016

Thus far, only two experiments have detected solar γ-radiation with energy significantly greater than 200 keV. In both events the γ-ray emission occurred during a solar flare. The first observation was in 1958 by Peterson and Winckler (1959), who recorded a burst of radiation that occurred in less than 18 sec from a class-2 solar flare. The radiation spectrum peaked in the 200- to 500-keV region. Recently, Cline et al. (1967) recorded in the OGO-3 satellite three rapid γ-ray bursts in the 80-keV to 1-MeV energy range and measured the integral energy spectrum. The measurements were made on July 7, 1966, during the first high-intensity flare (importance 3) of the new solar cycle. Many attempts have been made to measure higher energy γ-radiation from the quiet Sun and from solar flares, but no flux has been detected; this is primarily due to the fact that no high-energy γ-ray detectors have viewed a major solar flare during the maximum of the optical or microwave burst. However, theoretical estimates of the flux of solar γ-rays, based on a simple flare model, indicate a readily detectable flux from a major flare even to photon energies of 100 MeV. It is therefore important that experiments be performed during the coming maximum of the solar cycle to investigate this region of the electromagnetic spectrum.
Early Stages of the Universe
Authors: Sciama D. W.
Published: March 2016

When I was young theoretical cosmology was more a series of exercises in geometry than a branch of astrophysics. Moreover these exercises were based on little more than the Hubble law of red shifts and a general impression that on a large scale the Universe was roughly homogeneous and isotropic. Now all that has changed. While geometrical considerations retain their importance through the dominant role played by general relativity, cosmology has also become highly astrophysical. As a result we can now say a great deal about the early stages of the Universe. My aim is to give a brief account of our present understanding of this fascinating subject, at the same time highlighting the most important problems that remain.
The Physics of the Interstellar Matter
Authors: Field G. B.
Published: March 2016

Some of the most striking recent discoveries about interstellar matter involve molecules. It has been known for a long time that there are atoms and ions in space - mainly hydrogen and helium, of course - but also heavier elements like sodium and calcium. In addition, there are solid particles of dust, about 10-5cm across, which must be composed of heavier elements, as hydrogen and helium cannot condense under interstellar conditions.

In 1972, the Orbiting Astronomical Observatory-3, which employs an 80-cm telescope at wavelengths between 1000Å and 3000Å, was launched in the United States and put into operation. In the ensuing year, it has demonstrated that much of the interstellar medium is composed of hydrogen molecules. This result, based upon the observation of Lyman-band absorption in the spectrum of early-type stars, had been anticipated by a rocket observation of H2 by Carruthers in 1970.

The same OAO-3 instrument observed resonance lines of many cosmically abundant elements, and found that these elements often appear to be less abundant in interstellar space than in the solar system, relative to hydrogen. As young stars born recently from the interstellar medium do not show this effect, the heavy elements must in fact be present in some other form. Here I will argue that the heavy elements are largely locked up in the form of the dust and, further, that dust is critical for the formation of the molecules in interstellar space.

It is appropriate that the Orbiting Astronomical Observatory-3 which made these discoveries has been named in honor of Copernicus, the Polish astronomer we honor here on the 500th anniversary of his birth. Just as his discoveries were revolutionary for the understanding of the solar system, those made using the Observatory named in his honor have been revolutionary for the understanding of the Galaxy.
The Future of Observational Stellar Atmospheres
Authors: Kuhi L. V.
Published: March 2016

The title of this talk is, of course, a bit absurd since no one in his right mind can possibly predict what will happen in the future over even one year let alone ten. However nothing is impossible for Dick Thomas and having accepted his invitation to present this talk I have to pretend to have a crystal ball and put up a good front. I think that the best way to proceed would be to look at the past few years in observational stellar atmospheres and point out some of the highlights, especially those advances which seem to hold great promise for our understanding of stellar atmospheres in the future. The observer’s work falls neatly into two categories: the collection of data and their subsequent interpretation. The former involves the development and use of instrumentation (usually some type of spectrograph with a photon detection system); the latter is so closely linked to theory that it would be impossible to discuss it without recourse to theoretical assumptions and results. Therefore I would like to first mention a few instrumental developments which I consider to be of great importance and then discuss briefly some of the problems to which they might be applied in the next several years.
Planetary Ephemerides
Authors: Duncombe R. L. , Seidelmann P. K. , Janiczek P. M.
Published: March 2016

At the present time the planetary ephemerides in the Astronomical Ephemeris and in the American Ephemeris and Nautical Almanac (both hereinafter referred to as the AE), the Astronomical Ephemeris of the U.S.S.R. and most other national almanacs have the following basis: For Mercury, Venus, Earth, and Mars the general theories of Simon Newcomb (1898a), the ephemeris of Mars including the empirical corrections determined by Ross (1917); for the five outer planets, the numerical integration of Eckert et al. (1951); the Connaissance de Temps publishes ephemerides of Mercury, Venus, Earth, and Mars based on the theories of Leverrier (1858, 1859, 1861a, b); for Jupiter, Saturn, Uranus, and Neptune the ephemerides are based on Leverrier’s (1876a, b, 1877a, b) expressions as modified by Gaillot (1904,1910, 1913). The ephemeris of Pluto is based on the numerical integration of Eckert et al. In all of the above publications the ephemeris of the Moon is now based on the Improved Lunar Ephemeris which is derived from the theory of Brown (1919). Newcomb’s theories and the numerical integration of the orbits of the five outer planets all rest primarily on the system of astronomical constants and planetary masses adopted at the Paris conferences of 1896 and 1911 {Monthly Notices Roy. Astron. Soc., 1912).
Scans and Narrow-Band Photometry of Late-Type Stars in the One-Micron Region
Authors: Wing R. F.
Published: March 2016

A summary is given of the molecular bands occurring in the near-infrared spectra of cool stars, especially those having sufficient strength and freedom from contamination to be measurable by narrow-band photometry. In some cases useful indices of both temperature and luminosity can be obtained from such measurements. Several bands remain unidentified, including the 9910 Å band in late M dwarfs and at least nine bands in cool S stars.

Three topics of a spectroscopic nature are discussed. (1) In Mira variables, grossly different spectral types are sometimes obtained from zero-volt and excited TiO bands of the same band system. (2) A few M stars have been found to show bands of’ both VO and CN at the same time. They may be the coolest known supergiants, although there remains some doubt as to their luminosities. (3) The first results are given from a program of measuring crude C12/C13 ratios from narrow-band photometry of sensitive points on the profile of the ∆υ = + 2 band sequence of CN. The observations require only a few minutes per star, and the method can be applied to G and K giants and supergiants as well as to carbon stars.
Medium Resolution Stellar Spectra in the Two-Micron Region
Authors: Hyland A. R.
Published: March 2016

The role of medium resolution spectroscopy in the two micron region is discussed. Examples of the spectral features amenable to observation are shown. These include the vibration rotation bands of the important molecules 12C16O, 13C16O, H2O and CN, as well as the By line of hydrogen. Band strength-colour and -luminosity relations for the CO and H2O bands have been derived from observations of approximately 100 stars of spectral types later than G5. The interpretation of these and the outstanding problems (such as the colour dependence of the CO band strengths in carbon stars) are discussed.

Examples of the use of two-micron spectroscopy in the spectral classification of infrared sources, and the infrared components of symbiotic stars, etc., are shown. The extension of this kind of observation to the nuclei of galaxies is briefly discussed in relation to stellar population studies.
Fourier Transform Spectrophotometry and its Application to the Study of K-Giants
Authors: Ridgway S. T.
Published: March 2016

A Fourier Transform Spectrometer has been employed to obtain low and medium resolution spectrophotometry in the range 700 to 10000 cm-1. The method is described briefly and typical data are shown. The technique is applied to a study of 15 K giants, and spectra of 4 and 16 cm-1resolution in the range 4000 to 6500 cm-1 are discussed briefly. CN strong stars are found to be CO strong as well. Five K giants are found to have a relative 13C enhancement over probable primordial abundances.
Stellar Spectroscopy at 1.1 μ
Authors: Zirin H.
Published: March 2016

This is a progress report on the program of stellar spectroscopy at 1.1 μ reported on by Vaughan and Zirin (1968) and by Zirin (1971). About 450 plates of about 200 stars have been obtained, using a magnetically focused RCA image converter with the 144” and 72” Palomar coudé cameras, giving dispersion of 8 and 17 Å mm-1 respectively. Most of the plates were taken at the latter dispersion and cover about 300 Å. In good seeing a star with J = 3 is obtained in about 90 min. A tube with a fibre optic backplate is now in use. Cooling such a tube is difficult because the cathode is held at high voltage. By completely insulating the cold box, we may use dry ice cooling, and 2 h exposures, reaching J = 5, may be made with this ITT tube.

Our principal interest in this region of the spectrum is the He I 10830 line, but there are other features of interest such as Paschen y and a series of CN bands, λ 10830 is of particular interest because it is produced at relatively high temperatures and thus its presence in stars later than B5 can only be explained by the existence of a high temperature corona or chromosphere or of a strong ultraviolet source, which amounts to the same thing. Vaughan and Zirin found the presence of such chromospheres in a number of stars, and I have pursued the matter since then to determine the existence of chromospheric variability. The 10830 absorption in the Sun is very small from the normal chromosphere and is principally due to the presence of active regions. Emission is only found in large flares. Thus cyclic variations in Sun-like stars could be attributed to sunspot cycles. Unfortunately, main sequence stars are near the limit of our observations. Although definite 10830 absorption has been found in such main sequence stars as 61 Cyg A and B, 70 Oph br, K Cet and ε Eri, the absorption is just barely detectable and variation from plate to plate could be explained by variable quality.
The Ages of Stars in the Neighbourhood of the Sun
Authors: de Strobel G. Cayrel
Published: March 2016

This introductory paper is divided into two sections.

In the first section a short summary is given of the IAU Colloquium No. 17 on Stellar Ages held in Paris-Meudon Observatory in September 1972. The summary will concern particularly those subjects relevant to this Joint Discussion.

In the second part the ages of nearby stars located in the subgiant region of the (log Teff, Mbol) diagram are discussed.
The Shell of V603 Aql and the Early Stages of the Nova Event
Authors: Weaver H.
Published: March 2016

Nova V603 Aql 1918 was uniquely suited for studies of the structure of its shell because of the very favorable orientation of the shell in space. Additionally, almost by chance, spectroscopic observations were made in such a way that they permitted derivation of a three dimensional model of the shell.

V603 Aql, as we see from its light curve (Figure 1), was a typical fast nova which showed strong periodic fluctuations in light during the transition stage. The period of fluctuation was approximately 10 days, during which time the visible light changed by roughly 50%.
Exploration of the Planets: An Invited Discourse Presented before the Sixteenth General Assembly of the International Astronomical Union Grenoble, France, August, 1976
Authors: Sagan Carl
Published: March 2016

Until recently the entire astronomical endeavor was restricted to passive observations from the surface of the Earth. Natural experiments — such as stellar occultations, eclipsing binaries, or supernova explosions — might fortuitously arrange themselves, and systematic inventories were performed of information carried by reflected or emitted electromagnetic radiation. But it is only in the last twenty years that our species has been able to carry out in situ experiments on astronomical objects.

Radar astronomy permits a kind of experimentation on solar system objects not too distant from Earth, and has made a number of major discoveries, including the determination of the 3:2 spin/orbit coupling of Mercury, the Earth-locked retrograde rotation of Venus, and major elevation differences on Mars. Radar is the tool of choice for geomorphological mapping of cloud-enveloped Venus, and efforts now underway at the Arecibo Observatory should lead to complete mapping of one hemisphere of Venus down to 10 km resolution. The radar reflectivity of the rings of Saturn has forced a rethinking of the nature of the constituent particles in the rings; and a determination of the radar cross-section of Titan is an experiment which can resolve much of the uncertainty about the atmospheric structure and surface pressure for that enigmatic and fascinating object.
The Evolutionary History of X-Ray Binaries
Authors: van den Heuvel E.P.J. , Savonije G.J.
Published: March 2016

The most important recent observational discoveries in the field of X-ray binaries are probably those of the slow pulsars and of the winds of normal early-type main-sequence stars. These facts yield key information on the evolutionary history of the X-ray binaries and on the rotational slow-down mechanism for a neutron star in a stellar wind, as will be pointed out in section 3. In the theoretical field, the X-ray binaries have triggered much fundamental work, notably on the detailed processes of mass transfer and on tidal evolution, which will be considered in sections 2, 4 and 5.
Accretion Flows in Binary X-Ray Systems
Authors: McCray Richard
Published: March 2016

The subject of accretion flows in binary X-ray systems has been reviewed recently by Lightman et al. (1977), and the subject of accretion disks by Shu (1976). Here I shall emphasize developments that have occurred since those reviews were written, and concentrate on issues concerning the gas flows rather than the radiation mechanisms.
The Magnetic Field of Mercury
Authors: Ness Norman F.
Published: March 2016

The USA Mariner 10 spacecraft encountered Mercury three times in 1974-1975. The 1st and 3rd encounters provided detailed observations of a well developed, detached bow shock wave which results from the interaction of the solar wind. The planet possesses a global magnetic field, and modest magnetosphere, which deflects the solar wind. The field is approximately dipolar, with orientation in the same sense as Earth, tilted 12° from the rotation axis. The magnetic moment, 5×1022 Gauss-cm3, corresponds to an undistorted equatorial field intensity of 350γ, approximately 1% of Earth’s. The origin of the field, while unequivocally intrinsic to the planet, is uncertain. It may be due to remanent magnetization acquired from an extinct dynamo or a primordial magnetic field or due to a presently active dynamo. Among these possibilities, the latter appears more plausible at present. In any case, the existence of the magnetic field provides very strong evidence of a mature, differentiated planetary interior with a large core, Rc ≈ 0.7RM, and a record of the history of planetary formation in the magnetization of the crustal rocks.
Pioneer Images of Jupiter
Authors: Fountain J. W. , Gehrels T.
Published: March 2016

Pioneer 10 flew by Jupiter in December 1973 and Pioneer 11, in a more polar trajectory, one year later. We present some of the pictures of Jupiter made with the spin-scan technique by the imaging photopolarimeter. The pictures are presented here without comment as a detailed description of Jupiter together with references concerning the instrument and its results, and were published in the book, Jupiter, edited by T. Gehrels (University of Arizona Press, 1976).
The Galaxy Content of Clusters
Authors: Oemler Augustus
Published: March 2016

Clusters of galaxies are easily identifiable collections of galaxies, all at the same distance and all observed under similar conditions of galactic obscuration, etc. They are, therefore, very convenient samples with which to study the matter content of the universe. However, clusters are also very particular physical environments, and from this latter point of view it is their atypical character which is of interest. The differences in the contents of one cluster from another, and of each from the contents of small groups and the “field” can teach us much about how the properties of galaxies depend on the environments in which they were born and have evolved.

Because of the interrelatedness of these two points of view, one cannot really understand the galaxy populations of clusters until one also understands the populations of galaxies which are not in clusters. Therefore, while this review will concentrate on the contents of rich clusters of galaxies, it will also be necessary to discuss the properties of non-cluster galaxies.
Velocity Dispersions in Clusters of Galaxies
Authors: Dickens R.J. , Moss C. , Dawe J.A. , Peterson B.
Published: March 2016

31 redshifts have been obtained for A1367, 34 for A262 and 61 for the Centaurus cluster (HMS 1247-4102). Full details of this work have been and will be presented in M.N.R.A.S. Both A1367 and A262 are spiral-rich in Oemler’s classification, while Centaurus is intermediate in type between spiral-rich and poor. In all 3 cases, the distributions of E and L galaxies are centrally concentrated, whilst the spirals are distributed in a more extensive and ragged fashion. The mean corrected redshifts and velocity dispersions for 2 morphological subsets are given in Table I. There is no significant difference in the mean velocities of the 2 subsets for each cluster. However, the velocity dispersions for the spirals are significantly greater than those for the E,L galaxies in both A1367 and A262. The differences in velocity dispersions of the 2 subsets for Centaurus are not statistically significant. Gott and Gunn have suggested that irregular clusters of the sort presently described have not undergone collapse. However, all 3 clusters show morphological separation and are x-ray sources. This is consistent with a collapsed core surrounded by a shell of infailing spirals.
Photometry of the Intergalactic Background Light in the Coma Cluster
Authors: Mattila Kalevi
Published: March 2016

A very faint intergalactic background light component (to be called IBL) was photographically discovered by Zwicky (1957) in the centre of the Coma Cluster. More recently Welch & Sastry (1971, 1972) have mapped the area using isodensity tracings of photographic plates. In order to provide an accurate calibration of the intensity and to determine the colour of the IBL in the Coma Cluster, photoelectrical observations have been made of a region located ˜2′ east of IC 3949 and ˜12′ south-west of the cluster centre. The observations were made using a 60-cm Ritchey-Chretién telescope at the Metsähovi Observatory near Helsinki. The diaphragm size was 115″. In Table I the results of these observations are given together with three other available photoelectrical values for the IBL intensity in clusters. For comparison, the surface brightness due to visible galaxies has been estimated. The resulting values are: IV = 11.6 S10 (≙ 25.1 mag sec-2), IB = 4.6 S10 (≙ 26.1 mag sec−2), and thus the IBL intensity amounts to 25 percent and 39 percent in V and B, respectively, of the light of visible galaxies. For the colour index of the IBL one obtains using the values in Table I: B-V = 0.54 ± 0.18. Two mechanisms have been hitherto proposed in the literature to explain the IBL in the Coma Cluster: (1) light from dwarf galaxies, intergalactic globular clusters or individual intergalactic stars, and (2) thermal bremsstrahlung from a hot intergalactic gas with Te = 0.5 − 10 × 105 K. A third possible mechanism can still be mentioned, namely the scattering of the light of galaxies by intergalactic dust grains.
The Existence of High-Order Clusters of Galaxies
Authors: Kalinkov M.
Published: March 2016

The problem of the existence of high-order clustering of galaxies is a basic one in extragalactic astronomy and cosmology. In a conventional formulation this problem consists of indicating the largest configurations in the spatial distribution of galaxies.

All treatments are carried out generally on the material presented in the catalogues of Abell (1958) and Zwicky et al. (1961-1968). However catalogues of the Jagellonian type (Rudnicki et al. 1973) may turn out to be extremely valuable. The nature of the observational material demonstrates that only statistical methods may be applied effectively. It is already clear that the expected effects are not large even if high-order clustering is a basic property in the Universe.
Radio Sources in Clusters of Galaxies
Authors: McHardy Ian
Published: March 2016

Sixty-five radio sources in the 4C catalogue lie within 0.3 of the radius, Rc, defined by Abell (1958), of the centre of an Abell cluster of galaxies. Statistically few of these are expected to be chance coincidences and hence they provide a well defined statistical sample of sources in rich clusters of galaxies. Over the last 6 years sources from this sample having declinations greater than 10° have been observed with high resolution using the Cambridge One-Mile telescope by Slingo (1974(a) and (b)), Riley (1975) and by myself (1977, in preparation). The number of sources observed and the number expected by chance at different distances from the cluster centre are shown in Table I; the radio positions used are from the 4C catalogue.
Some Research Programmes Into Galactic Structure at the Galactic Caps Under Way at the Royal Greenwich Observatory
Authors: Jones D. H. P.
Published: March 2016

The R.G.O. has a continuing programme to investigate both the density and motions of the stellar content of the solar neighbourhood. Gaps in current knowledge are wider for the fainter stars which are found in proportionally greater numbers near the galactic poles. Our approach divides naturally into two questions: (i) What are the proportions of red dwarfs to giants at each apparent magnitude? and (ii) What are the corresponding total numbers of red stars?

Question (i) was first tackled by a narrow-band photometric search for M dwarfs (Jones 1973). This approach is continuing and a progress report has been delivered (Jones 1976). To push the search deeper 41 stars in the South Galactic Cap (mostly fainter than V = 15) selected by P.S. Thé from a survey with the Lembang Schmidt as being M2 or later were observed with the Robinson-Wampler Scanner on the 150-inch A.A.T. The Na D lines, CaH and the band at λ5500 tentatively identified by Pesch with CaOH have been measured. Column density calculations of CaOH for giants and dwarfs of different temperatures support Pesch’s identification. Nearly all the stars are dwarfs but only seven appear in proper motion catalogues, (Thé and Staller 1974). At the galactic caps most stars brighter than V = 12 are giants and fainter dwarfs. The transition zone is only 10-14.
Galactic Mass Density in the Vicinity of the Sun
Authors: Joeveer M. , Einasto J.
Published: March 2016

It is possible to estimate the galactic mass density in the solar neighbourhood either directly by summing up the mass densities of individual subsystems of stars and interstellar matter or indirectly from dynamical considerations.

Observational data on the number density of visible stars lead to mutually consistent results on the stellar component of the mass density. The mean of different estimates is ⍴stars=0.052±0.010 Mʘpc−3. By adding the probable contributions of intrinsically faint undetected objects and of interstellar matter the value ⍴=0.09±0.02 Mʘpc−3 has been obtained for the total mass density.
The Gravitational Field of the Galaxy in the Z Direction
Authors: Griffin R. F.
Published: March 2016

This is a progress report of a project designed to find the component, perpendicular to the Galactic plane, of the gravitational potential of the Galaxy. The principle is to measure the radial velocities and distances of a large number of K-giant stars near the North Galactic Pole. My student G. A. Radford is masterminding the project; collaborating with us are Drs. J. E. Gunn of the Hale Observatories and L. Hansen and K. Gyldenkerne of Copenhagen.

We have measured the radial velocities of all the HD stars of type KO and later, and many of the G5 stars, within 15°of the Galactic Pole, using the Cambridge photoelectric spectrometer. In addition, we have observed all the stars classified as K giants by Upgren in his declination zones 25° to 31°, using the spectrometer on the Hale telescope. There are about 900 stars observed altogether, including about 200 Upgren stars, running down to twelfth magnitude or so, which are not in the Henry Draper Catalogue. To determine the distances of all these stars we are now trying to determine the absolute magnitudes by narrow-band photoelectric photometry in the Copenhagen system. Most of the observations have been made, thanks largely to the very generous grants of observing time given by the Hale Observatories earlier this year; but the reductions have only been completed for about 300 stars (including 244 K giants) which were observed last year at Kitt Peak, and the present, very preliminary, discussion is based on those stars alone.
A New Program to Determine K(z) from Main Sequence Stars
Authors: Upgren A. R.
Published: March 2016

Recently Dessureau and Upgren (1975) redetermined the velocity distribution of giant stars in the north galactic pole direction using Upgren’s (1962) catalogue and Oort’s (1960) determination of K(z). The velocities were assumed to be represented by n Gaussian distributions with no further constraints imposed. The velocities are well represented by three such distributions whose properties disagree with those found by Oort. A larger number did not improve the stability of the solution. Without radial velocities, however, they could not redetermine the K(z) force itself.
Concluding Remarks Part II
Authors: Blaauw A.
Published: March 2016

In research in the galactic polar caps we may roughly distinguish two categories:

I. Research on problems concerning the galactic population at large distances from the plane, including the density and velocity distribution and the field of force at large z.

II. Research on problems concerning the population in the immediate neighbourhood of the sun; at high galactic latitudes it is easier to discriminate the nearest stars than at low latitudes - see, for in stance the investigations of the M dwarf population.

Most of the papers presented in part II of this Joint Discussion deal with the first category, and of these, the distances reached are mostly within a few Kpc. Classical investigations, some of them dating from more than thirty years ago, have provided our current knowledge of the force K(z) perpendicular to the galactic plane up to about 1500 pc and the large scale features of the density distribution. What emerges from recent and current work, is attempts to improve the knowledge of K(z) and to extend it to greater distances; and refinement of the density and velocity investigations by more and more detailed discrimination of population types. The dominating problem is that of the separation of the stars according to two basic parameters: age and chemical composition. Kinematic and space distributional properties for subgroups according to these two parameters will be the necessary elements on which a theory of the (local) evolution of the Galaxy is to be built. The vague notion, that metal abundance may be taken to be an equivalent of age is abandoned and replaced by the recognition that at any epoch, star formation may have occurred with a considerable spread in the resulting stellar metal abundances.
Competition Between Diffusion Processes and Hydrodynamical Instabilities in Stellar Envelopes
Authors: Gérard  , Vauclair Sylvie
Published: March 2016

Since the work of Michaud (1970), the abundance anomalies observed in the peculiar Ap and Am stars are increasingly believed to be a consequence of diffusion processes in stellar atmospheres or stellar envelopes. A number of the problems that seemed at first sight insoluble within the framework of diffusion processes have now been solved by it. Diffusion processes can, for example, account for anonalous helium isotopic ratios (Vauclair et al, 1974 (b)) and mercury isotopic ratios (Michaud et al, 1974). Quantitative results on abundance variations due to diffusion processes have been obtained (Michaud et al, 1976; Michaud, this conference; Alecian, 1976). They show that, in general, the relative abundance anomalies obtained from computation are close to the observed ones. It is now well established that the largest abundance anomalies observed in Ap stars (for rare earths) can be interpreted by diffusion processes with a satisfactory time scale, in a completely stable atmosphere. However, the predicted absolute abundance variations often exceed the observed ones, as in the case of Am stars. This suggests that the assumption of stability is not completely valid for the stellar gas: some kind of macroscopic motion, such as a meridional circulation or turbulence or both, must be at work and slow down the diffusion.
Mixing between Burned Core Material and Surface Layers
Authors: Schwarzschild Martin
Published: March 2016

Dr. Pagel has given us a fine summary of the observations relevant to the topic I am to cover. Drs. Michaud and Vauclair have described in detail the potential effects of diffusive processes which might well explain, at least in part, the apparent abundance anomalies observed in the peculiar A stars and the magnetic A stars. In the paper following mine, Dr. Boesgaard will present the observational evidence regarding the abundance of the light elements lithium, beryllium and boron, and relate these observations to the theory of stellar envelopes. With these important topics expertly covered I shall restrict myself to the single question: How do some reasonably common types of stars, such as the carbon stars and the S stars, manage to show off at their surfaces, for us to observe, a fair sampling of the products of the nuclear burning going on deep in their cores?
Flows in Magnetic Flux Tubes
Authors: Durrant C. J.
Published: March 2016

Harvey has reported in this discussion observations of mean downflows in magnetic elements that increase in speed with depth. It is therefore pertinent to ask what role such flows may play in the production and maintainance of the flux concentrations.

Equilibrium Models

The first thing to be said is that such flows cannot directly influence the horizontal momentum balance, i.e. their dynamic pressure is negligible.

A steady internal flow such as that proposed by Ribes and Unno (1975) for chromospheric concentration would require supersonic flows with very large curvature at photospheric levels. There is no evidence for transverse flows of such magnitude.
An Atlas of Ultraviolet Stellar Spectra
Authors: Code A. D.
Published: March 2016

Ultraviolet stellar fluxes have been presented for 140 bright stars in the spectral region from 1200 A to 3600 Å in a graphical and tabular form (A. D. Code and M. R. Meade, 1976). The spectra represent a subset of 0A0-2 spectrometer data on file at the National Space Science Data Center. The monochromatic flux is given in units of ergs cm−2 sec−1 Å−1 with a spectral resolution of about 22 Angstroms in the region from 3600 Å to 1850 Å and approximately 12 Angstroms from 1850 Å to 1160 Å.

The monochromatic flux, Fλ, is based upon the absolute calibration described by Bless, Code and Fairchild (1976).
The Near Ultraviolet Spectrum of FE III as a Classification Criterion
Authors: Faraggiana R. , Lamers H. J. G. L. M. , Burger M.
Published: March 2016

The Utrecht Orbiting Ultraviolet Stellar Spectrophotometer S59 on board the ESRO TD-1A satellite has observed ultraviolet spectra of about 200 stars in the wavelength regions 2060–2160 Å. 2490–2590 Å and 2770–2870 Å with a resolution of 1.8 Å (cf. de Jager et al., 1974). The spectra are analyzed in order to find UV criteria for stellar classification. Particular attention has been given to Fe III lines since no strong lines of this ion occur in the visible part of the spectrum. As one of the most striking results, it is found that the feature at 2078 Å, which is mainly due to Fe III, is very sensitive to luminosity.
The Role of General Relativity in Astronomy: Retrospect and Prospect
Authors: Chandrasekhar S.
Published: March 2016

My last attendance at a meeting of the International Astronomical Union was forty-four years ago when it met in Paris in 1935. I do not doubt that my being asked to give an invited discourse at this meeting is a personal courtesy extended to me by your distinguished President recalling, perhaps, the years when he and I were colleagues together at the University of Chicago.

I am aware that associated with my absence from these meetings for nearly half a century is the fact that during most of this period - if not all of it - my interests, at different times, have been outside whatever may have been the prevailing trends in the mainstream of astronomy. I am afraid that on this account, the point of view I shall present - retrospectively and prospectively - will not be in conformity with the trends currently prevailing. I must therefore begin by asking for your patience and for your forbearance.

Dr. Blaauw, when he invited me to give one of the three discourses at this meeting, suggested that in selecting a topic I might wish to take into account the fact that this year is the centennial of Einstein’s birth. The subject of my discourse is in accordance with that suggestion.
A Formalism for Differential Rotation
Authors: Durney B. R. , Spruit H. C.
Published: March 2016

One of the approaches for dealing with the differential rotation of the Sun is to separate the flow in the convection zone into an axisymmetric steady part (differential rotation plus meridional circulation) and a “turbulent” part comprising all smaller scales of motion. In the equations of motion and energy the effect of the small scales is then represented by a turbulent viscosity and conductivity. Theories of this type at present belong to either of two categories:

a)

Theories stressing the role of an anisotropic turbulent viscosity. Due to the presence of gravity as a preferred direction the velocity distribution in the turbulent flow is different in the horizontal and vertical directions. This implies that the turbulent viscosity is also anisotropic. Biermann (1951) showed that as a result, the convection zone cannot rotate as a solid body. Theories based on this idea were developed by Kippenhahn (1963) and Köhler (1970).

b)

Theories using a latitude dependence of the efficiency of turbulent transport of heat. In the deeper layers of the convection zone the influence of rotation on convection is strong because the convective turnover time is comparable to the rotation period. Since the angle between gravity and the rotation axis varies with latitude, this influence must also vary with latitude. This produces a temperature variation between the pole and the equator which drives a meridional circulation. Since the Coriolis force dominates over the viscous force in most of the convection zone, there is a strong differential rotation associated with this circulation (quasi geostrophic flow). This type of theory has been developed by Weiss (1965), Durney and Roxburgh (1971) and Belvedere and Paterno (1977).
Radio Continuum Emission from the Nuclei of Normal Galaxies
Authors: van der Hulst J. M.
Published: March 2016

During the last few years detailed and sensitive observations of the radio emission from the nuclei of many normal spiral galaxies has become available. Observations from the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO1), in particular, enable us to distinguish details on a scale of ≤100 pc for galaxies at distances less than 21 Mpc. The best studied nucleus, however, still is the center of our own Galaxy (see Oort 1977 and references therein). Its radio structure is complex. It consists of an extended non-thermal component 200 × 70 pc in size, with embedded therein several giant HII regions and the central source Sgr A (˜9 pc in size). Sgr A itself consists of a thermal source, Sgr A West, located at the center of the Galaxy, and a weaker, non-thermal source, Sgr A East. Sgr A West moreover contains a weak, extremely compact (≤10 AU) source. The radio morphology of several other galactic nuclei is quite similar to that of the Galactic Center, as will be discussed in section 2. Recent reviews of the radio properties of the nuclei of normal galaxies have been given by Ekers (1978a,b) and De Bruyn (1978). The latter author, however, concentrates on galaxies with either active nuclei or an unusual radio morphology. In this paper I will describe recent results from the Westerbork Synthesis Radio Telescope (WSRT, Hummel 1979), the NRAO 3-element interferometer (Carlson, 1977; Condon and Dressel 1978), and the VLA (Heckman et al., 1979; Van der Hulst et al., 1979). I will discuss the nuclear radio morphology in section 2, the luminosities in section 3, and the spectra in section 4. In section 5 I will briefly comment upon the possible implications for the physical processes in the nuclei that are responsible for the radio emission.
Star Formation in the Nuclei of Normal Galaxies
Authors: Biermann Peter
Published: March 2016

For the purpose of this talk, I define all those galaxies as normal whose nuclear regions are not known to be dominated by a compact source. Thus I will exclude N galaxies, Seyfert galaxies and radio galaxies, but include galaxies like M81 and M82 which have weak compact nuclei. My review is organized in three parts, (i) tracers of star formation, (ii) star formation in the nuclear regions of observed galaxies, and (iii) the theoretical attempts to interpret the observational material.
Ultraviolet Spectroscopy of Chemically Peculiar Stars
Authors: Leckrone David S.
Published: March 2016

This discussion focuses on high dispersion spectroscopic observations of chemically peculiar (CP) stars of the upper main sequence, classical HgMn, Si and SrCrEu stars, obtained with the IUE. Two subjects will be emphasized - the confirmation of composition anomalies previously identified in ground-based spectra and evidence relating to the validity of the diffusion theory for the production of chemical pecularities.

The gallium anomaly occurs primarily in the hotter Mn stars (Cowley 1975). Model atmospheres analyses of Mn stars yield overabundances of Ga as large as 2×105 relative to the solar value (Heacox 1979). The identification of the Ga peculiarity and estimates of Ga abundances are based upon a few high excitation lines observed in the blue. Figure 1 illustrates the resonance line of GaII, λ1414.44, observed in six Mn stars. The feature is strong and broad in the hotter stars, к Cnc and μ Lep. It is present but weaker in 46 Dra (A+B). It is absent in the cooler stars г CrB, χ Lup and HR 4072. The sharp feature seen near λ1414.4 in the latter three stars is probably Mnll and is also seen in normal stars. The Gall λ1414.44 line varies in strength from star-to-star in the same manner as the blue Gall lines. The absence of the blue Gall lines in cool Mn stars cannot be an excitation effect, since the resonance line is also absent in these stars. Neither can the presence of the blue Gall lines in hotter Mn stars be due to non-LTE effects, because the resonance line is also abnormally strong in these stars. The IUE observations confirm the Ga peculiarity as a genuine abundance anomaly.
Stellar Coronae
Authors: Vaiana G. S.
Published: March 2016

The standard theory of stellar coronae requires the presence of vigorous surface convection. In consequence, the expectation of such a theory is that stellar x-ray emission — if due to a corona — should be limited to a subset of stars (principally those of main sequence spectral types F and G), and therefore should be relatively rare. This theory also makes detailed predictions about coronal heating, which are subject to test if spatially resolved coronal data are available. We are now in a position to subject the standard coronal scenarios to observational scrutiny on both counts: Skylab and later observations have supplied us with spatially resolved data of the solar corona, while the succession of high-energy x-ray astronomy satellites, culminating with EINSTEIN, now gives us a long-awaited glimpse of stellar x-ray emission throughout the K-R diagram.

I will maintain that these new data imply that coronal x-ray emission dominantly derives from plasma structure confined by stellar surface magnetic fields; that coronal heating is likely to be non-acoustic in character and involves the confining magnetic fields; that stellar x-ray emission is not well correlated with the level of surface convection activity. These results of course cast serious doubt upon the viability of the standard theory of stellar coronal formation. In the following, I will try to very briefly summarize the solar and stellar data, to present the context in which they were initially obtained, and very briefly sketch the new coronal picture we are pursuing. The results presented here are excerpted from lectures presented by R. Rosner and myself recently at Erice, Italy (viz. Vaiana 1979) and from the preliminary results of the EINSTEIN Stellar Survey (Vaiana et al. 1979). The latter, part of a larger effort in x-ray astronomy led by R. Giacconi, involves the work of many people, including F.R. Harnden, L. Golub, P. Gorenstein, R. Rosner, F. Seward, K. Topika at CFA, as well as a number of EINSTEIN guest investigators.
Types of Stellar Instabilities
Authors: Ledoux P.
Published: March 2016

Aside from violent phenomena, regular forms of motions originate often in instabilities and the linear theory with terms ∞ exp (st) yields already significant information. The system, here a spherical star, will be the seat of an instability if R (s) > 0. In general, s will be complex as both conservative (adiabatic) and non-conservative (non-adiabatic) factors are present. However if the latter (small) are neglected, the eigen-values s2 often denoted -σ2 are real. If at least one σ2 < 0, then the star is dynamically unstable.

Radial perturbations. If an appropriate average value Γ1 > 4/3, then all σ2 are positive. If Γ < 4/3 (formation phase: ionization; late evolution: nuclear equilibrium; degeneracy in white dwarfs and neutron stars or radiation in very large masses plus general relativistic effects) the fundamental eigenvalue of only becomes negative.
Solar Pulsations
Authors: Severny A. B. , Kotov V. A. , Tsap T. T.
Published: March 2016

Oscillations of the Sun with the period of 160m first observed in Crimea in 1974 and described in a set of papers by Kotov, Severny and Tsap (Severny et al. 1976, 1978; Kotov et al. 1978) were observed also by Brookes et al. (1976) and have been afterwards observed during the last three years in Stanford (Scherrer et al. 1979) and Kitt Peak (Snider et al. 1978). This fact excludes possible instrumental origin of the effect. Moreover, the phase coherence (after elimination of integer number of 160m-periods) between these four observatories makes the assumption of Earth atmospheric origin of the oscillations (Fossat and Grec 1978) very unlikely. Besides that, (1) the dependence of amplitude of oscillations on the phase of solar rotation and (2) slow, synchronous (at Crimea and Stanford) drift of the phase of maximum from year to year, pointing to a true period slightly higher 160m (160m 0.1), make the “telluric hypothesis” of the effect completely inconsistent.
Planetary Nebulae Formation
Authors: Tuchman Y. , Sack N. , Barkat Z.
Published: March 2016

It is a well accepted idea that Planetary Nebulae ( P.N. ) formation is due to mass ejection from red giant envelopes.

According to the original model, as was proposed by Roxburgh and Lucy in 1967, and established about a year later by Paczynski and Ziolkowski (1968), red giant envelopes become dynamically unstable above a certain boundary luminosity, while their total energy, including the ionization energy, which should be available upon expansion, is positive. This energy is sufficient for ejecting the entire envelope with a velocity similar to those observed in P.N.

In the light of these facts, it was quite natural to look for “one shot” ejection mechanisms in unstable red giant envelopes, using full non-adiabatic dynamical codes. This has been done several times since the adiabatic analysis carried out by Paczynski and Ziolkowski (1968), but with minor success, at least in those cases where natural initial conditions were used.

It was found that as soon as the radial expansion of the envelope becomes comparable to its initial radius, the entire radiative zone, which is located above the partial ionization zone, turns to be almost completely transparent. Thus, most of the released recombination energy is radiated directly out of the star, instead of pushing mass shells outwards. Since this energy leakage is very fast, motion is quickly reversed without resulting in any mass loss. Nevertheless, it was pointed out by Smith and Rose (1972) and later by Wood (1974) that there is a possibility for some mass ejection due to shocks generated within the contracting envelope.
Chromospheres, Coronae and Mass Loss in Solar and Late-Type Stars
Authors: Jordan Carole
Published: March 2016

Until observations in the EUV spectral region became available the existence of hot extended envelopes aroung latetype stars was inferred from the presence of visible and near infrared region lines which cannot be formed in radiative equilibrium within the stellar photospheres. The traditional indicators of stellar chromospheres have been the Ca II H and K lines, particularly the presence of emission components, the He I 10830 A triplet, the He II 4686 A line and emission in various hydrogen Balmer and Paschen lines. When observations from rockets and satellites become possible the strong lines of Mg II at 2800 A and the H Lya line at 1216 A could also be included in the modelling of stellar chromospheres. The new spectra from IUE allow not only stellar chromospheres to be studied but also stellar transition regions, should hot coronae exist.