bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultraviolet Observations of Some Close Binary Systems by the Astronomical Netherlands Satellite-Ans
Authors: Wu Chi-Chao
Published: July 2016

Observations of δ Pic, a β Lyr type of eclipsing binary and seven dwarf novae are reported. The ultraviolet light curves of δ Pic indicate the accumulation of matter at the triangular Lagrangian points L4 and L5, the presence of a hot spot and a higher temperature for the primary star. The implication is that the cooler secondary fills its Roche lobe and is transfering mass to the primary; mass loss to the circumstellar space and possibly to the system may also be appreciable. The temperatures of dwarf novae are derived by comparing their ultraviolet spectral energy distributions with those for normal stars of luminosity classes IV and V. Piecing together observations for different objects, the SSCyg systems have temperatures of 28 500 K, 10 000 K and 9500 K, respectively, when they are at minimum, immediately before outburst and at the beginning of rise to maximum. At maximum, the temperature is 22 500 K or 17 300 K depending on the interstellar reddening correction for AR And. Immediately before outburst, there is a large excess of flux in the far ultraviolet as indicated by the large value of the ratio of flux at 1550 Å to that at 1800 Å. The observations of Z Cam during standstill gives a temperature of 14 900 K. No excess of flux in the far ultraviolet was observed during the maximum of AR And and the standstill of Z Cam.
Coronae Above Accretion Discs
Authors: Icke Vincent
Published: July 2016

A turbulent accretion disc generates acoustic noise which, on propagation upward into the tenuous upper layers, forms shock waves. These give rise to a corona above the disc, thereby providing the possibility to determine observationally the existence (or otherwise) of turbulence in the disc. Models for stationary coronae of this type are calculated on the basis of a simplified thermodynamic cycle in the shocks.
Observations of Gaseous Disks in Close Binaries
Authors: Baldwin B. W.
Published: July 2016

Recent observations of emission lines from circumstellar disks in Algol-type binaries have revealed new facts concerning their structure and evolution. In some cases circumstellar disks are unstable, but the nature of the instability is not known. For U Cep, the emission lines observed during the 1974 outburst can be interpreted as arising from an expanding shell of gas about the primary. Other systems which have displayed emission line variability are RW Tau, SW Cyg, W Del, AQ Peg, and VW Cyg. There is also some evidence to suggest that RY Gem has experienced an outburst similar to that of U Cep. Emission lines observed in the eclipse spectrum of RY Gem by McKellar in 1947 were greatly different in strength and profile from those observed recently and cannot be interpreted as arising from a circumstellar disk rotating about the primary.
Starspot Activities as an Interpretation for the Light Curve Changes of the Close Binary Star XY UMa
Authors: Geyer E. H.
Published: July 2016

The large light curve changes of XY UMa, observed in the last 20 yr, are interpreted as stellar starspot activity of the primary component of this binary.
Evolutionary Status of Massive Algols - a Revision of Classical Theory
Authors: Ziołkowski J.
Published: July 2016

The evolutionary status of Algol systems is examined.
UBV Photometry of the Shortest Period Contact Binary CC COM
Authors: Rucinski S. M.
Published: July 2016

Red colours: B–V=+1.23, U-B = + 1.03 and short period: P=0.2207 days place CC Com at the lower temperature end of the period-colour relation for the W UMa-type binaries. Contrary to the typical behaviour of (B–V) which shows reddening during both minima, the (U–B) index reveals rather large scatter, especially when different nights are intercompared. In addition (U–B) seems to decrease abnormally during some of primary minima when the colours change to B–V = + 1.29 and U–B = +0.99; it is unclear whether the ultraviolet excess δ(U–B) of about +0.11 is not related to these changes. Small night-to-night changes seem to be present in the V-light curve as well.

The large amplitudes of light variations (0.86 and 0.74 mag) and the presence of total eclipses with semi-duration of about 7 deg in phase permit to determine the geometrical elements with rather high accuracy in spite of larger than normal observational errors due to the faintness of the system (V= 11.3-12.2). CC Com belongs to the W-type systems with the relative temperature excess of secondary component X= +0.058 ± 0.002. Other elements are: i = 8806 ± 0.09, q = 0.511 ± 0.009, f = 0.78 ± 0.03 for the assumed Te0 = 4300 K. To obtain a perfect fit to the light curve, the gravity darkening exponent was also varied with the resulting value β = 0.09 ± 0.02.

There are indications that CC Com might belong to the Coma cluster.
Effect of Perturbed Potentials on the Stability of Libration Points in the Restricted Problem
Authors: Bhatnagar K. B. , Hallan P. P.
Published: July 2016

The location and the stability of the libration points in the restricted problem have been studied when there are perturbations in the potentials between the bodies. It is seen that if the perturbing functions involving the parameters α,α1,α2 satisfy certain conditions, there are five libration points, two triangular and three collinear. It is further observed that the collinear points are unstable and for the triangular points, the range of stability increases or decreases depending upon whether the perturbation point (α,α1,α2) lies on one or the other side of the plane Aα + Bα1 + Cα2 = 0, and it remains the same if the point lies on the plane, where A,B,C depend on the perturbations. The theory is verified in the following four cases: (1) there are no perturbations in the potentials (classical problem), (2) only the bigger primary is an oblate spheroid, (3) both the primaries are oblate spheroids, and (4) the primaries are spherical in shape and the bigger is a source of radiation.
New Approach to the Planetary Theory
Authors: Yuasa Manabu , Hori Gen'ichiro
Published: July 2016

A new approach to the planetary theory is examined under the following procedure: 1) we use a canonical perturbation method based on the averaging principle; 2) we adopt Charlier's canonical relative coordinates fixed to the Sun, and the equations of motion of planets can be written in the canonical form; 3) we adopt some devices concerning the development of the disturbing function. Our development can be applied formally in the case of nearly intersecting orbits as the Neptune-Pluto system. Procedure 1) has been adopted by Message (1976).
Semi-Analytical Lunar Ephemeris - the Main Problem
Authors: Henrard Jacques
Published: July 2016

The theory of the motion of the Moon can be approached by two types of methods. In the analytical methods, the solution is usually expanded in formal power series of the small quantities m, e and γ. It is known that the expansions in m are slowly convergent and that, in order to obtain an accuracy of the order of the meter, the expansions have to be carried to very high order (beyond 20) involving several hundred thousands terms.
A Precise Determination of Some Critical Terms in the Solar System
Authors: Chapront Jean , Dvorak Rudolf
Published: July 2016

A new form to determine the contribution of some special small divisors in perturbation theory is presented in this paper. We can avoid to calculate all the kλ+k′λ as it has to be done normally (λ and λ′ designate the mean longitudes of the two regarded planets). For a chosen k and k′ we calculate with a very high precision the contribution to the perturbation of the elements with the aid of the Hansen's coefficients.
The Ephemerides: Past, Present and Future
Authors: Seidelmann P. K.
Published: July 2016

Over the years there has been a continuing trend toward unification of both the annually printed volumes of ephemerides and the fundamental bases for the ephemerides. Thus, from many completely independent national and private publications, which were based on a multitude of theories, there has developed a continually improving agreement on accurate astronomical constants, planetary, lunar and satellite theories and cooperative methods of printing the annual ephemerides in different languages. This trend is continuing, currently, with the adoption of a new system of astronomical constants in 1976, consideration of revisions of nutation, the planned revision of the A.E. (American Ephemeris and Astronomical Ephemeris) for 1981, and the expected introduction in 1984 of new fundamental planetary and lunar ephemerides based on the new constants and on the FK5. Currently the differences between the printed ephemerides and observations sytematically exceed 2″ for Mars at some times and 6″. for Neptune at all times. It is anticipated that a new set of fundamental theories will be introduced which will be based on a consistent set of astronomical constants and in agreement with the available observational data to the printed accuracy.
Observations of Mars 1950-1976 Compared to Ephemerides
Authors: Duncombe R. L. , Kubo Y. , Seidelmann P. K.
Published: July 2016

The present basis for the ephemeris of Mars in the National Ephemerides is the theory of S. Newcomb (1898) as amended by the corrections of Ross (1917). These amendments by Ross, however, are empirical in nature and therefore the present ephemeris of Mars does not have a strictly gravitational basis. In order to provide a gravitationally consistent basis for the ephemeris of Mars, Clemence (1949, 1961) constructed a new general perturbation theory based on the final elements of Mars as derived by Newcomb for the epoch 1850. To test the adequacy and accuracy of this new theory, Clemence compared it against 87 observations from 1802-1839 and 1931-1950. This provided provisional values of the constants (without secular variation) for his new theory. These provisional elements and Clemence's theory were used to produce a heliocentric ephemeris of Mars for the period 1800-2000 (Duncombe and Clemence 1960, Duncombe 1964).
Method of Surface of Section Applied to a Possible Capture Origin of Jupiter's Satellites
Authors: Tanikawa K.
Published: July 2016

The capture of satellites is considered to be a slow process, in which particles approaching the planet lose their energy gradually and fall down into the stable orbits around it. Therefore, in order to investigate the capture problem, it seems to be necessary to clarify the behaviors of orbits near the planet. Recently Hayashi et al. (1977) and Heppenheimer and Porco (1977) found that in the restricted three body problem, particles incident through Lagrange points L1 and L2 revolve always directly around Jupiter as long as the potential windows at L1 and L2 are small. This suggests the impossibility of the capture of retrograde satellites when the potential windows are small.
Planetary Close Encounters: An Investigation on Temporary Satellite-Capture Phenomena
Authors: Carusi A. , Pozzi F. , Valsecchi G.
Published: July 2016

This research is part of a wider one (Carusi & Pozzi, 1978a, b) concerning a detailed study of the dynamics of close encounters between a giant planet and a minor object. A special result of that investigation was the recognization of some satellite-capture events, already found by Everhart (1973). An important remark about this previous work is that all satellite-captures occurred with low inclination objects which orbits were initially near-tangent to the Jupiter's one. Starting from this consideration, a hundred fictitious orbits have been generated in order to study the phenomenon in greater detail. Their initial distribution is shown in fig. 1. The initial angular parameters i, ω, Ω, were chosen to be equal to those of the most interesting case of the previous research. Eccentricities were selected regularly in the range .01-.5, with a step of .01, giving the same value to an object of the upper band and to the next of the lower. The semimajor axes were chosen at random between limits computed so that the aphelion for the lower band, or the perihelion for the upper band, would lie within a distance of 108km from Jupiter's orbit. As the orbital planes do not coincide with that of Jupiter, the minimum distance point between the two orbits does never coincide with the object perihelion or aphelion, but is always close to them. Fig. 2 shows the final situation of this population: we note that in no case a permanent binding occurred. We can do some remarks on this picture. First of all we note that 56% of objects experienced a temporary binding to the planet. Secondly, 67% of objects, bounded or not, had a final orbit lying, on the a-e diagram, on the opposite band with respect to their initial one. This kind of transition is especially significant if compared with the case of observed comets, because it gives a simple mechanism to transform long-period comets in short-period ones, and to transfer comets from one family to another. Actually, on the basis of the computations of Kazimirchak-Polonskaya (1972), we can say that a similar process has been experienced, for example, by comets Whipple, Oterma, Brooks 2, Lexell, Kearns-Kwee and others. A third remarkis that, between the initial and final situations, small eccentricities are increased, as a consequence of the encounter, whilst the great ones are decreased. This phenomenon leads to a clustering of final orbits in the eccentricity range .1-.2.
Dynamics of Gravitating Systems of Colliding Particles in Planetary Discs
Authors: Brahic André
Published: July 2016

During this symposium on the dynamics of the solar system, we have mainly studied the movements of the bodies of the solar system submitted to gravitational perturbations. The next step is to take into account the physical collisions. Indeed, there can be little doubt that collisions between “macroscopic bodies” are of frequent occurence in the Universe. All kinds of quite different objects undergo such collisions: these may range from large interstellar clouds to small solid bodies in the solar system. Collisions have surely played an important role in the formation of planets and satellites and continue to play a central role in the behaviour of the planetary discs. For example for Saturn's rings, one can see intuitively that until the optical depth drops much below unity, the rings are still evolving. Each orbiting particle can be taken as occupying a kind of torus, and collisions will continue until there is only one particle in each such “orbital tube”; this corresponds to a very small optical depth.
Three-Dimensional Distributions of Minor Planets and Comets
Authors: Kresák Ľubor
Published: July 2016

The attitude toward the systems of interplanetary objects is largely different from that accustomed in stellar astronomy. The stellar systems are viewed from the outside, with their shape, population, and internal structure apparent at first glance. The motions are difficult to recognize, if ever, and so the individual orbits are degraded to a background mechanism maintaining the observed organization and rotation of the system. In contrast to this, we dispose of copious information on the dynamics of individual interplanetary objects, but the bodies to which the orbital data refer are sampled under the influence of strong selection effects. Lacking a consistent survey of their systems, we tend to think of them in terms of the biased statistics in the phase-space of orbital elements, rather than in terms of the real three-dimensional distributions. No wonder that we often come across serious misrepresentations: the asteroid belt depicted as a plane ring divided by the Kirkwood gaps like the ring of Saturn; the Trojan clouds as small spherical systems resembling globular star clusters; or the meteor streams as elongated rings of uniform width and population all around. And we seem to receive these gross misrepresentations with surprisingly little annoyance.
The Discovery and Orbit of (2060) Chiron
Authors: Kowal C. T. , Liller W. , Marsden B. G.
Published: July 2016

“Slow-moving Object Kowal” was recognized by the first author on 1977 November 1 on plates obtained with the 122-cm Schmidt telescope at Palomar two weeks earlier (Kowal 1977a). The object, asteroidal in appearance and of photographic magnitude about 18, was found to have moved less than 3′ between similar 75-minute exposures made on October 18 and 19. For something only 8° from opposition this retrograde motion was significantly slower than the 8′-15′ daily motion of normal minor planets at opposition and immediately suggested that the object was located at almost the distance of Uranus. There was a slight possibility that the object was closer and moving almost directly toward or away from the earth, but the fact that the two trails were identical in length to ± 6 percent suggested that this was unlikely. That the object was well beyond the main belt of minor planets was confirmed when Gehrels (1977) succeeded in identifying it close to the extrapolated position near the corner of an exposure obtained with the same telescope on October 11.
Empirical Data on the Origin of “New” Comets
Authors: Delsemme A. H.
Published: July 2016

The different hypotheses proposed so far on the origin of comets have been reviewed in detail last year (Delsemme 1977). In particular, I mentioned why the orbital statistics seem to be consistent with only one hypothesis, namely that comets were accreted at unknown but moderate distances (10 to 1000 A.U.) within the protosolar nebula, and ejected later into a sphere whose radius is some 50,000 A.U., usually called the Oort's cloud. Safronov (1977) and Cameron (1977) have different scenarios to do just that. Even with improvements like that of Dermott and Gold (1978) the choice between these scenarios will remain impossible until we have a convincing model describing the gravitational collapse of an interstellar cloud into a planetary system.
The Shortage of Long-Period Comets in Elliptical Orbits
Authors: Everhart Edgar
Published: July 2016

Based on the number of ‘new’ comets seen on near-parabolic orbits, one can predict the number of comets that should be found on definitely elliptical orbits on their subsequent returns. We show here that about three out of four of these returning comets are not observed.
Mass loss from Eta Carinae
Authors: Andriesse C. D. , Viotti R.
Published: July 2016

This high luminosity (5 × 106 L⊙) star since 1840 is losing mass at the rate of 7.5 × 10−2 M⊙ per year. The large mass loss could be the result of vibrational instabilities produced in the CNO hydrogen burning phase of a very massive (160 M⊙) star. The presence of high excitation lines in the ultraviolet spectrum of Eta Car suggests the idea of a hot zone excited by dissipation of the supersonic turbulent flow.
Stellar outflow: relative motions of nebulae and of stars
Authors: Lynds Beverly T.
Published: July 2016

On the basis of arguments presented by Roberts (1972) and of Shu et al. (1972), Minn and Greenberg (1973) argued that the velocity differences between newly formed hot stars and the surrounding interstellar medium are sufficiently different so that typical H II regions should consist of material which is continually being replaced by the ambient medium and which should therefore possess the velocity of the medium rather than that of the star. Obviously, the critical test of this hypothesis will be a comparison of nebular velocities with the velocities of the exciting stars.
Infrared excesses and mass loss: Implications for OB stars in Carina and the LMC
Authors: Hyland A. R.
Published: July 2016

A method of deriving mass loss rates using near IR excesses is established and applied to OB stars in Carina and the LMC.
The thermodynamic requirements on atmospheric models imposed by observed stellar nonthermal mass-fluxes and by those observed nonthermal features enhanced in Xe stars
Authors: Thomas Richard N.
Published: July 2016

If I understand correctly, this session of the Symposium on Mass-Loss and Evolution of O Stars aims at clarifying the merits and demerits of four “theories” for the observed, nonthermal mass-loss from these stars. Hearn has summarized what he considers to be the essential characteristics of each of the four, especially relative to a set of questions which, he considers, put the observational requirements on the “theories” in focus. Representatives of each of the “radiation-pressure initiated, radiative-equilibrium controlled”, “hot corona”, and “warm corona” alternatives have elaborated on Hearn's summary, to stress what they consider essential. So, now, I would do the same for what we caricature as the “imperfect wind-tunnel” model — not theory, which I assert does not yet exist — both for nonthermal mass-flux, and for other observed nonthermal phenomena, in stellar atmospheres generally, not just in O stars particularly. I assert, that in studying nonthermal mass-flux from O stars, if you limit your attention only to nonthermal mass-flux, and only to O stars, you handicap, a priori, your chance to understand what is required for the general model of a stellar atmosphere, in order to produce this variety of nonthermal phenomena observed, alike in all varieties of stars.
The spectroscopic binary γ 2 Velorum
Authors: Niemelä Virpi S. , Sahade Jorge
Published: July 2016

γ2 Velorum is the brightest binary system with a Wolf-Rayet component; it has been classified as a 09I+WC8 pair (Conti and Smith 1972). The orbital elements of this system were determined earlier by Ganesh and Bappu (1967) from spectrograms of 125 Å/mm dispersion, on the basis of the radial velocities from CIII-IV λ4652 Å emission for the WC component, andon the radial velocities from H absorption only, for the O star.
The distribution in luminosity of OB stars and evolutionary timescales
Authors: Bisiacchi F. , Carrasco L. , Costero R. , Firmani C. , Rayo J. F.
Published: July 2016

We have obtained the observed fraction of supergiant (luminosity classes I and II), giant (III) and dwarf (IV-V) stars of spectral types B2 and earlier. The stellar sample used was formed with all the stars with bi-dimensional spectral classification listed in the Catalogue of Galactic O stars by Cruz-González et al. (1974), the unpublished compilation of B0 and B0.5 stars by J.F. Rayo, and the B1-B2 stars listed by Morgan et al. (1955). The latter sample is by far the least complete one. The results are listed in Table I, together with the total number of stars (in parenthesis) considered in each spectral interval. A prominent conclusion is drawn from the table: The fractions remain approximately constant all over the spectral range considered.
Supergiant mass loss and the Cassiopeia A progenitor
Authors: Lamb Susan A.
Published: July 2016

Observations of the chemical abundances in young supernova remnants may be used, in some circumstances, to place constraints on the evolution of the progenitor stars. For example, if a progenitor was massive (M > 10 M⊙), the presence of high 14N/1H ratios (that is, more than five time the solar value) in the supernova remnant can imply that substantial mass loss took place during the star's early evolution, that is, while it was an early-type supergiant.
Evolution of massive common envelope binaries and mass loss
Authors: Tutukov A. , Yungelson L.
Published: July 2016

A way of treatment of evolution of common envelope binaries based only on the laws of conservation of energy and angular momentum is suggested. It is shown that the final configuration depends on masses of components and initial period of the system, and on parameters describing friction in the envelope, and mass loss by the system. Possible final stages for massive binaries are either a Thorne-Zytkow type object for initially close binaries or a Wolf-Rayet star in pair with a relativistic compact remnant for wider ones. In the course of disruption of the latter system with orbital periods up to several hours very high space velocity (up to 500 km/s) pulsars can arise.
Common envelope binaries and mass loss
Authors: Delgado A.
Published: July 2016

In this work we calculate the evolution of a binary system with a common envelope, which consists of a blue supergiant and a neutron star. We consider as a free parameter the effectivity with which the energy liberated at the orbit produces mass loss from the system.

The evolutionary calculations were made, using various values of this parameter, for a system with mass ratio 25:1. As initial state we choose a model in the phase of Hydrogen-shell burning, before and after the begin of Helium-burning in the core.

We found that, under certain conditions, it is possible for the radius of the orbit and the period of the system to increase; the time scale for the “spiral-in” would be of the order of 104-105 years. Mass loss rates are between 10−3 M⊙/y and 10−4 M⊙/y.
Evolution of O stars and the WR connection
Authors: Conti Peter S.
Published: July 2016

The stellar wind mass loss rates of at least some single Of type stars appear to be sufficient to remove much if not all of the hydrogen-rich envelope such that nuclear processed material is observed at the surface. This highly evolved state can then be naturally associated with classic Population I WR stars that have properties of high luminosity for their mass, helium enriched composition, and nitrogen or carbon enhanced abundances. If stellar wind mass loss is the dominant process involved in this evolutionary scenario, then stars with properties intermediate between Of and WR types should exist. The stellar parameters of luminosity, temperature, mass and composition are briefly reviewed for both types. All late WN stars so far observed are relatively luminous like Of stars, and also contain hydrogen. All early WN stars, and WC stars, are relatively faint and contain little or no hydrogen. The late WN stars seem to have the intermediate properties required if a stellar wind is the dominant mass loss mechanism that transforms an Of star to a WR type.
Disk and spheroidal components of external galaxies: an overview
Authors: Strom S. E. , Strom K. M.
Published: July 2016

A brief review of current theoretical views on how disk and spheroidal galaxies form and evolve provides the background for a summary of recent optical observations of external galaxies. Primary emphasis is placed on a discussion of the large-scale distribution and chemical composition of the stellar and gaseous constituents of relatively isolated galaxies. New studies of halo and disk surface-brightness distributions in spiral and SO galaxies are summarized. The “missing mass” in galactic halos, the relationship between disk size and luminosity, the nonexponential character of disk light distributions and very low-surface-brightness disk systems are highlighted in this section. Next discussed are observations which may provide insight into the factors which regulate the star-forming history of galactic disks and the post-astration appearance of spiral galaxies. Finally, the observed properties of relatively isolated disk galaxies are compared with those located in dense groups. It appears from this comparison that environment plays a significant role in governing the evolutionary history of a galaxy.
Introduction to the session
Authors: Lequeux James
Published: July 2016

The main purpose of this session is to gather observational data which should ultimately yield a better understanding of the relationships between the interstellar matter and the stars in our Galaxy. Ideally we would like to know how the Galaxy evolves in this respect and in particular to understand quantitatively the laws of star formation: What is the relation between star formation and the density of gas? (for a study of this kind see Guibert, Lequeux, and Viallefond, Astron. Astrophys. 68, 1, where Schmidt's law is rediscussed); Does the Initial Mass Function (IMF) vary within the Galaxy? (for recent studies see Burki, Astron. Astrophys. 57, 135, and Puget, Serra, and Ryter, this Symposium). We are obviously still far from being able to give definitive answers to these questions, but I hope that we will obtain at least a better understanding of the basic ingredients: the distribution of interstellar matter and of young stars.
Galactic structure from infrared studies
Authors: Puget J. L. , Serra G. , Ryter C.
Published: July 2016

Star densities on a galactic scale are traced by far infrared emission of dust heated by young stars and by the 2.4 μm radiation of stars in the red giant phase. Coherent results are obtained, pointing to a very strong star formation rate during the last ∼200 My in a ring 5 kpc from the galactic center. A steepening of the initial mass function compared to that observed in the solar vicinity is also suggested.
The density-wave theory confronted by observations
Authors: Wielen Roland
Published: July 2016

Density waves are probably the most general phenomenon producing spiral structure in disk galaxies. The density-wave theory is able to give a rather successful interpretation of the observed spiral structure and of the related kinematics in external galaxies and in our Galaxy. We assume that the reader is familiar with the basic concepts of density-wave theory; for recent reviews see e.g. Kalnajs (1978), Lin (1975), Lindblad (1974), Marochnik and Suchkov (1974), Roberts (1977a,b), Rohlfs (1977, 1978), Shu (1973), Toomre (1977), Wielen (1974a). In Section 2, we discuss the proper theoretical devices which should be used for a meaningful comparison between observations and density-wave theory. The other sections are devoted to a comparison of density-wave theory with some relevant observations, mainly in our Galaxy.
On the maintenance of spiral structure
Authors: W-K. Mark James , Sugiyama Linda , Berman Robert H. , Bertin Giuseppe
Published: July 2016

A concentrated nuclear bulge with about 30% of the galaxy mass is sufficient (Lin, 1975; Berman and Mark, 1978) to eliminate strong bar-forming instabilities which dominate the dynamics of the stellar disk. Weak bar-like or oval distortions might remain depending on the model. In such systems self-excited discrete modes give rise to global spiral patterns which are maintained in the presence of differential rotation and dissipation (cf. especially the spiral patterns in Bertin et al., 1977, 1978). These spiral modes are standing waves that are physically analyzable (Mark, 1977) into a superposition of two travelling waves propagating in opposite directions back and forth between galactic central regions and corotation (a resonator). Only a few discrete pattern frequencies are allowed. An interpretation is that the central regions and corotation radius must be sufficiently far apart so that a Bohr-Sommerfeld type of phase-integral condition is satisfied for the wave system of each mode. The temporal growth of these modes is mostly due to an effect of Wave Amplification by Stimulated Emission (of Rotating Spirals, abbrev. WASERS, cf. Mark 1976) which occurs in the vicinity of corotation. In some galaxies one mode might be predominent while other galaxies could exhibit more complicated spiral structure because several modes are present. Weak barlike or oval distortions hardly interfere with the structure of these modes. But they might nevertheless contribute partially towards strengthening the growth of one mode relative to another, as well as affecting the kinematics of the gaseous component.
Stellar kinematics and interstellar turbulence
Authors: Larson Richard B.
Published: July 2016

It is well known that the velocity dispersion of nearby stars increases systematically with age, and this fact is conventionally explained by postulating that stars are randomly accelerated by encounters with massive gas clouds (Spitzer & Schwarzschild 1951, 1953; Wielen 1977). However, a strong constraint on the possible role of random accelerations is provided by the apparent existence of fairly old moving groups of stars (Eggen 1969, Boyle & McClure 1975). An alternative explanation (Tinsley & Larson 1978) is that the age dependence of the velocity dispersion of stars older than 109yr is produced by a gradual decay with time of interstellar turbulent motions, as predicted by plausible collapse models. This effect cannot account directly for the variation of velocity dispersion with age observed for stars younger than 109yr, but Tinsley & Larson suggested that this could be explained if the velocity dispersion of the youngest stars reflects only the local turbulent motions of the gas, while the velocity dispersion of older stars reflects in addition larger-scale non-circular motions in the galactic gas layer. If the interstellar medium possesses a hierarchy of motions whose velocity dispersion increases with the size of the region considered, older stars which have traveled farther since their formation will sample the gas motions over a larger volume of space, and thus will have a larger velocity dispersion than the younger stars.
A new class of extraordinary HI shell
Authors: Heiles Carl
Published: July 2016

I consider an ordinary shell to be one which can be produced by ordinary means such as a supernova. Good examples are the HI shells associated with the prominent radio loops, discussed today by Prof. Weaver, and the large HI shell in Eridanus (Heiles, 1976). Figure 1 shows the shell which is associated with radio Loop I, made from a consolidation of data from Martha Cleary of Australia, Raul Colomb and Wolfgang Poppel of Argentina, and myself. It changes size with velocity in the manner expected for an expanding shell. The distance is only 100 pc or so. Similar shells should be easily resolvable in the galactic plane, even with a modest telescope, because differential galactic rotation eliminates the confusing effects of foreground and background gas.
Some results from an HI survey of the central region of the galaxy
Authors: Sinha R. P.
Published: July 2016

A complete, high-sensitivity survey of HI (Sinha 1978, in preparation) has been examined for model-independent morphological properties of the distribution of HI in the central region of the Galaxy. The dominant symmetry of the kinematics of HI is evident in Figure 1, where equivelocity contours of the permitted velocity edge (corresponding to 1 K antenna temperature) have been plotted on the longitude-latitude plane. The axis of symmetry is coincident with the Kerr-Sinclair ridge of 20-cm continuum radiation from this region. The positions of the maxima of the absolute velocity in the first and the fourth quadrants are aligned along a line inclined to the line of symmetry indicated in Figure 1. The HI gas, therefore, must have noncircular motion. A similar but not identical symmetry is evident in the distribution of the forbidden velocity edge of the profiles. The absolute magnitude of the velocity peaks and the area under the profiles differ in the two quadrants. The nuclear disk appears to be symmetrical in an angle-velocity diagram in which the angle is measured along the line of symmetry in Figure 1.
Infrared observations of the nuclear region
Authors: Wollman E. R.
Published: July 2016

Infrared observations have provided considerable information about the structure and energetics of the galactic center. The stellar bulge dominates the mass and luminosity of the nuclear region. The luminosity of the bulge is strongly peaked toward the center, even within the central parsec. Dust in the nuclear disk absorbs the power output of the central portion of the bulge and reemits it in the far infrared. Near the center, molecular clouds move in a plane apparently tilted toward the Sun. Within the central few parsecs, or core, the inclination may be as large as 45°. The total power output of the core is about twice that of the bulge population alone. The source of excess luminosity is uncertain, but evidence points to ongoing star formation associated with the Sgr A molecular complex.
Molecular structures of other galaxies compared to that of the galaxy
Authors: Rickard L. J.
Published: July 2016

Of the eleven galaxies with detected CO emission, eight have bright nuclear CO sources: M82, NGC 253, M51, NGC 5236, NGC 1068, Maffei 2 (Rickard et al. 1977a,b), NGC 6946, and IC 342 (Morris and Lo 1978). Two have disk-population CO sources and no detectable nuclear source (M31 and M81, Combes et al. 1977a), and one has no obvious nucleus (LMC, Huggins, et al. 1975). Nuclear maxima thus appear to be the rule for galaxies with extensive molecular components, and such a peak is also seen in our Galaxy (e.g., Bania 1977). In Figure 1, I compare the CO data for the nuclei of M82 and M31 with spectra of the Galactic nucleus as it would be seen at their respective distances. (The Galactic spectra were synthesized from the date of Bania [1977], and assume a uniform z-distribution of 30 pc width.) The Galaxy is roughly intermediate, being about one-fifth the intensity of M82 and more than six times the intensity of M31.
21-cm observations of high-velocity clouds
Authors: Mirabel I. F. , Cohen R. J.
Published: July 2016

(a) Four high-velocity clouds (HVCs) with large negative velocities have been mapped at high sensitivity, with an angular resolution of 12 arcmin and a velocity resolution of 1.8 km s−1 (Cohen & Mirabel, in press). Although these are small isolated clouds they show the same two-component velocity structure that is observed in the large Northern HVC complexes at lower velocity. In addition the cool dense core of one of the clouds is found to be rotating. This rotation, and also the regular velocity patterns within the four clouds, indicates that the clouds are unlikely to be interacting with galactic material. It is interesting that similar observations of the Magellanic Stream do not show narrow velocity components, suggesting that there is a real physical difference between the Stream and other HVCs (Mirabel, Cohen & Davies, in press).
The Magellanic Stream: theoretical considerations
Authors: Fujimoto M.
Published: July 2016

The tidal and the primordial theories for the Magellanic Stream are examined in a frame of test-particle simulation for the interacting triple system of the Galaxy, the Large and Small Magellanic Clouds (LMC and SMC). Difficulties of the radial velocity of the Stream still beset these two theories. Several new models for the Stream and the Clouds are briefly discussed in relation to the bending of the galactic disk, the past binary orbits of the LMC and SMC and also the Local Group and the Local Supercluster of galaxies.
The galactic wake model of the Magellanic Stream
Authors: Bregman Joel N.
Published: July 2016

Tidal interaction models for the origin of the Magellanic Stream have been fairly successful in reproducing the radial velocities of the Stream (Lin and Lynden-Bell 1977, Davies and Wright 1977). However, no investigator has yet attained a self consistent treatment in which (1) the LMC and SMC are bound for at least 5×109 yr, (2) the passing Magellanic Clouds warp the galactic plane, and (3) the Stream velocities are reproduced (Fujimoto and Sofue 1977). Also, Mathewson, Schwarz, and Murray (1977) argue that their 21 cm observations are evidence against the tidal model. To avoid these problems, they suggest that the Magellanic Clouds pass through a hot coronal gas and produce vortices in their wake which radiatively cool to form the HI clouds comprising the Stream.
Numerical Experiments on the Tensor Virial in N-Body Systems
Authors: Miller R. H.
Published: July 2016

Tensor generalizations of the virial theorem were checked in a 100-body integration. The virial theorem was remarkably well satisfied, and the calculation confirmed the generalized Lagrange-Jacobi identities. The potential energy tensor, the kinetic energy tensor, and the virial tensor showed surprisingly long correlation times of about of a crossing time.
Two Recent Developments Concerning the Monte Carlo Method
Authors: Hénon M.
Published: July 2016

This paper consists of two independent parts.

(1)

The Monte Carlo method for computing the evolution of spherical stellar systems has been modified so that the computation can be continued after the time of formation of the central singularity. Results are presented for systems with equal and unequal star masses. The initial core-halo formation is followed by a general expansion of the cluster, while the central singularity absorbs a growing fraction of the total negative energy.

(2)

Theoretical expressions of the ‘diffusion coefficients’, which describe the effect of encounters in a stellar system, contain a factor In(γN) whereNis the number of stars and γ is a constant usually taken to be of the order of 0.4. A reconsideration of the ‘non-dominant terms’ leads to a substantially lower value, of the order of 0.15 for equal masses and 0.075 for unequal masses with a typical distribution. This correction improves the agreement betweenN-body and Monte Carlo simulations of spherical systems.
Dynamical Masses and Mass-to-Light Ratios for Globular Clusters
Authors: Illingworth G.
Published: July 2016

Dynamical masses have been determined for 10 globular clusters. Comparison of the dynamically determined M/L values with those calculated from extrapolations of the observed upper main sequence/giant branch luminosity functions for M3 and M5 indicate that low mass stars (∼0.2 M⊙) comprise a large fraction of the total number.
Crossfertilization Between Plasma, Stellar Dynamics and Hydrodynamics
Authors: Feix M. R.
Published: July 2016

We present results on four different mediums characterised by their ‘density conservation’ in a two dimensional space (phase space for unidimensional plasma and self gravitating systems, configuration space for two dimensional Navier Stokes fluid and guiding center rod plasma).
Integrals of Motion
Authors: Contopoulos G.
Published: July 2016

The properties of conservative dynamical systems of two or more degrees of freedom are reviewed. The transition from integrable to ergodic systems is described. Nonintegrability is due to the interaction of two, or more, resonances. Then one sees, on a surface of section, infinite types of islands of various orders, while the asymptotic curves from unstable invariant points intersect each other along homoclinic and heteroclinic points producing an apparent ‘dissolution’ of the invariant curves. A threshold energy is defined separating near integrable systems from near ergodic ones. The possibility of real ergodicity for large enough energies is discussed. In the case of many degrees of freedom we also distinguish between integrable, ergodic, and intermediate cases. Among the latter are systems of particles interacting with Lennard-Jones interparticle potential. A threshold energy was derived, which is proportional to the number of particles. Finally some recent results about the general three-body problem are described. One can extend the families of periodic orbits of the restricted problem to the general three-body problem. Many of these orbits are stable. An empirical study of orbits near the stable periodic orbits indicates the existence of 2 integrals of motion besides the energy.
Comparison with Observations of Disk Galaxies
Authors: Freeman K. C.
Published: July 2016

We discuss some observational aspects of the structure and dynamics of disk galaxies. Topics include the disk, the bulge, the lens, and the z-structure of the disk.
Galactic Nuclei and Compact Supermassive Objects
Authors: Saslaw W. C.
Published: July 2016

This is a review of the observational evidence concerning compact supermassive objects, their formation and evolution, and their dynamical interaction with dense stellar systems in galactic nuclei.
All these have never yet been seen -But Scientists, who ought to know,Assure us that they must be so…Oh! let us never, never doubtWhat nobody is sure about!Hilaire Belloc, 1910.
The Concentric Shell Method for Relativistic Star Clusters
Authors: Fackerell E. D.
Published: July 2016

The analytic aspects of the Campbell-Hénon method of concentric spherical shells are generalized for application to relativistic spherically symmetric star clusters.
The Green Bank Surveys at 1400 MHz
Authors: Maslowski J.
Published: July 2016

The present 1400 MHz complete pencil-beam survey, made with the NRAO 300-foot telescope, consists of four parts which cover four different regions of the sky, as shown in Fig. 1.
Spectra of Southern Radio Sources
Authors: Bolton J. G.
Published: July 2016

Surveys of the sky between declinations +25° and −90° at 2700 MHz (11 cm) have been in progress for the past 10 years. Excluding some regions close to the galactic plane the whole sky south of +25° has been surveyed to a flux density limit of 0.6 Jy at 2700 MHz and within this area surveys to limits of 0.35, 0.25 or 0.1 Jy have been made covering 3.5 sr. Flux densities have been measured at 5000 MHz for all sources stronger than 0.35 Jy at 2700 MHz. The source positions have an average accuracy of 10″ arc in both coordinates and the positions have been examined for optical identifications on Palomar, ESO or SRC sky survey plates, which now cover 95% of the area. The first part of this paper concerns the relationships between the spectral indices α(2700 to 5000 MHz) and the identifications of the 2300 sources with galactic latitudes greater than 10°. It is a statistically significant sample, since the sources stronger than 0.35 Jy cover 3.5 sr. It is also a representative sample, since no selection was made on the basis of spectral index or identification. It cannot however be claimed as a complete sample, for two reasons. A substantial fraction of sources found in radio surveys at high frequencies are variable - variations of up to a factor of three can occur on a time scale of a year - thus the various sections of the survey are complete only for the relevant epoch. Many of their optical counterparts are also variables - variations of up to a factor of 100 can occur on a time scale of one year. It is hoped to make some assessment of the effect of these two factors in the next two years, when second-epoch Parkes surveys will begin and SRC Schmidt plates will overlap the Palomar Sky Survey.
Absorption Systems in High Redshift QSOs
Authors: Boksenberg A.
Published: July 2016

In addition to the characteristic emission lines, absorption lines frequently are seen in the spectra of QSOs, usually those with high redshift (zem ≳ 1.8). About 10 percent of all QSOs listed in the compilation of Burbidge et al. (1976a) are recorded as having at least one ‘identified’ absorption system, meaning that a pattern of several selected observed lines can be matched with the apparent wavelengths of transitions (generally from the ground level) in a physical plausible group of atoms or ions at the same, although arbitrary, redshift (Bahcall 1968, Aaronson et al. 1975). Identified absorption line redshifts range from being comparable with the associated emission line redshifts, to having very much smaller values with relative velocities exceeding 0.5c in the QSO frame. Added to this, there are many QSOs having absorption lines not yet recognised as belonging to identified systems, both those objects already having one or more identifications, and others with none.
Relations Between Radio and Optical Properties of Radio Sources - Radio Astronomer's Point of View
Authors: Riley J. M. , Jenkins C. J.
Published: July 2016

One particular aspect of the relations between the radio and optical properties of radio sources has been examined for a complete sample of 3CR sources, namely the relation between the radio structure of a source and its optical identification. Possible differences between the radio structures of quasars and radio galaxies are investigated, and the data provide clues as to the optical nature of the unidentified sources.
Progress, Problems and Priorities: A Personal View
Authors: van der Laan H.
Published: July 2016

Half a century after Hubble expansion was recognized and a quarter century after the identification of Cygnus A we must acknowledge that progress in observational cosmology is slow, the efforts are laborious, corrections are subtle and correlations elusive. Part of progress is the realization that there are no short-cuts, no easy methods or quick successes. The result of this awareness has been increasingly careful attention to the completeness of samples, to selection criteria and the hazards of intercomparisons from survey to survey. This week in Cambridge has shown both modest progress and progress in modesty.