bluuebunny/crossref_metadata_2025 huggingface dataset:
Singly-Ionized Iron Emission Lines in the Spectra of Early Type Stars
Authors: Viotti R. , Koubský P.
Published: July 2016

The appearance of singly ionized iron emission lines in the spectra of early type stars is studied, and the results of a spectroscopic investigation of EW Lac and other Be stars are given. We also discuss the atomic processes of excitation of Fe ii in the stellar envelopes using a two-parameter diagram W, NeT−1/2e.
Be Stars as Rotating Stars: Observations: (Review Paper)
Authors: Slettebak Arne
Published: July 2016

The classical rotational hypothesis for Be stars is reviewed and discussed. Methods of measuring rotational velocities are considered and the particular difficulties that Be stars pose in this respect are pointed out. Several tests of the rotational hypothesis are discussed and shown to support this idea. New observations of Balmer emission-line widths in the spectra of 46 Be stars show a correlation with rotational velocity, also in support of the rotational hypothesis. The very large emission widths found for some Be stars are discussed and possible reasons for the broadening are presented.
Hα and Hβ Measures as Related to Be Star Rotation
Authors: Feinstein Alejandro
Published: July 2016

Photometric data for the hydrogen lines in 80 southern and 55 northern Be stars give evidence of a constant ratio for the emission in α and β in stars of similar spectral type. In an (α, β) diagram the intersection of this emission-line ratio with the standard relation for non-emission stars gives lower values than those corresponding to standard stars of the same spectral type. This may be due to rotational effects. A correlation of the variation in the β index with the V magnitude is also given.
The Near Ultraviolet Spectrum of ζ Tau
Authors: Delplace A. M. , Van Der Hucht K. A.
Published: July 2016

By using several ultraviolet spectrograms in the λ 2100–2800 Å wavelength range, the absorption features and the flux values of ζ Tau have been determined and compared to different early type stars.
Photographic Infrared Spectroscopy and Near Infrared Photometry of Be Stars: (Review Paper)
Authors: Swings J. P.
Published: July 2016

As the title indicates two topics will be tackled in this presentation: spectroscopy and photometry. Let us therefore define first what ‘infrared’ means for these two subjects. I chose the following definitions:

– photographic infrared spectroscopy: wavelengths Hα ≤ λ < 1.2 μ

– near infrared photometry: wavebands: 1.6 μ ≤ λ ≤ 20 μ
Motions in the Shells and Atmospheres of V923 Aql and Ew Lac and Their Manifestation in the Spectrum
Authors: Vojkhanskaya N. F.
Published: July 2016

The stars V923 Aql (HD 183656) and EW Lac (HD 217050) are marked in the General Catalog of Variable Stars (Kukarkin et al., 1969) as unique, similar objects with shells. The two stars have quasiperiodic variations in brightness (Lynds, 1960; Walker, 1953). It is assumed here that the variation of brightness is caused by an inhomogeneous distribution of brightness over the surface of the star. A consideration of the literature data on the radial velocities Vr which we have carried out has shown that the variation of Vr is different (Figure 1).
The Possible Role of Radiative Acceleration in Supporting Extended Atmospheres in Be Stars
Authors: Kurucz R. L. , Schild R. E.
Published: July 2016

A detailed calculation of the radiative acceleration in B-type stars shows it to be a double-peaked function of effective temperature at small optical depths. The two peaks are shown to coincide approximately with peaks in the distribution of mean Hα emission strength as a function of B - V color in Be stars. These facts suggest that radiation may play an important role in the support of the Be star extended atmosphere.
Final Remarks on the Binary Hypothesis for the Be Stars
Authors: Plavec Miroslav
Published: July 2016

The hypothesis that a significant fraction of Be stars are interacting binaries is discussed in general terms. The author believes that the observed Be stars are a mixture of three different types of objects. The weakest point of the single-star hypothesis is probably the difficulty in explaining the quasi-periodic V/R variations; the weakest point of the binary hypothesis appears to be the statistical expectancy of a fairly high number of eclipsing systems among them.
Gravitational Radiation and the Evolution of Low Mass Binaries
Authors: Faulkner John
Published: July 2016

Gravitational radiation of energy and angular momentum can modify and in some cases, control the evolution of a close binary system. The region of interest is briefly delineated. Recent work of the author and colleagues of relevance to this area is discussed, including theoretical studies of accretion, mass loss and mass transfer, and an observational study of a system, HZ 29 where gravitational radiation may dictate its behaviour.
Energy Transfer in Contact Binaries
Authors: Moses A. P. , Smith R. C.
Published: July 2016

The anomalous mass-luminosity relation for the components of a contact binary system is usually explained by postulating strong energy transfer from the primary to the secondary. It has been assumed that the transfer occurs in the common convective envelope surrounding the two stars, but so far the only attempt at a model for the energy transfer has been the sideways convection model of Hazlehurst and Meyer-Hofmeister (1973), which assumes a large-scale circulation of material between the two components.

Any detailed discussion of the dynamics in the common envelope must take account of the predominantly vertical motions associated with normal thermal convection, of Coriolis forces and of viscosity. We have constructed an approximate model for the horizontal transfer of energy between the two components, using a mixing-length approach and taking all three factors into account. The major factors are the vertical convection and the Coriolis forces, which together prevent a large-scale circulation of the type proposed by Hazlehurst and Meyer-Hofmeister. Instead, the flow breaks up into smallscale eddies whose horizontal scale is determined by the interaction of convection, Coriolis forces and viscosity. This has the important qualitative consequence that horizontal energy transfer will occur only if the mean horizontal pressure gradient between the two stars exceeds a certain minimum value. This condition can easily be satisfied in the adiabatic zone of the envelope, but may be an important restriction in the super-adiabatic zone.

Using our model, we were able to estimate the entropy difference between components which is required to transfer enough energy to explain the observed mass-luminosity relation. We found that equal entropy models are possible only if the contact is deep. Unequal entropy models are possible for any degree of contact, so long as the contact extends down as far as the adiabatic zone. If, as has been suggested, the depth of contact increases during evolution then zero-age models must have shallow contact and hence unequal entropies. Deep contact equal entropy models would then form as a result of evolution.

A difficulty is that in our model insufficient energy transfer can occur in the super-adiabatic zone to produce WUMa light curves for the unequal entropy models. This may mean that further work is needed on the exact surface conditions in these stars.
Introduction
Authors: Marsden B. G.
Published: July 2016

IAU Symposium No. 81, “Dynamics of the Solar System”, was held at the Hydrographic Office, Tokyo, Japan, during 23–26 May 1978. The Symposium was cosponsored by COSPAR and IUTAM, and generous financial support was also provided by the Japan Society for the Promotion of Science. IAU sponsorship was through Commissions 4, 7 and 20, and the Scientific Organizing Committee consisted of the current Presidents, Vice Presidents and immediate Past Presidents of these Commissions: V. K. Abalakln,
R. L. Duncombe, Y. Kozai, L. Kresfik, B. G. Marsden (Chairman), P. J. Message, A. M. Sinzi, G. Sitarski and V. G. Szebehely.
Introductory Address
Authors: Hagihara Yusuke
Published: July 2016

The aim of celestial mechanics is to derive all solutions of the differential equations of the three- and n-body problems and to reveal the interrelation among all such solutions with various values of the masses and initial conditions, not only to predict the positions of celestial bodies at any instant but to think over the cosmogony of stellar systems and to ascertain the law of universal gravitation in view of the time-space picture of physical theory.
On Non-Stationary Problems of Celestial Mechanics
Authors: Omarov T. B.
Published: July 2016

Some non-stationary problems of celestial mechanics can be described in an inertial system of right-angled coordinates with gravitational potential of the form:

where is a sufficiently arbitrary function of time and is the meaning of in the initial epoch For example, in a two-body problem of variable mass we have:
Construction et Precision de Nouvelles Theories Planetaires
Authors: Bretagnon P. , Chapront J.
Published: July 2016

At the Bureau of Longitudes the construction of planetary theories have been developed in three directions: A general theory of the motion of the four largest planets in the solar system is in the course of development at the Faculty of Sciences at Lille by L. Duriez (1977) following the methods of V. A. Brumberg and J. Chapront (1973). Theories of the classical type with secular variations of the motions of all of the planets from Mercury to Neptune are being completed at the Bureau of Longitudes. They are constructed by P. Bretagnon and J. L. Simon (1975, 1978). The numerical complement to all of these studies, numerical integration, a representation of the solution by Tchebychev series, are being carried out by P. Rocher as concerns the motions of minor planets, and by J. Piranx for the action of Pluto on Uranus and Neptune in the framework of theories with secular variations.
The Rotation of the Mars Planet
Authors: Borderies N. , Balmino G.
Published: July 2016

In a non-inertial reference frame, of which the motion is given, the differential equations describing the rotation of a planet around its center of mass can be derived either under the form of Euler type equations, or from certain relations between angular velocity vectors or even angles. Unfortunately these equations are not well adapted to an analytical integration. Nevertheless, with some simplifications, Ward (1973), and Christensen (1977), by considering the motion of the spin axis in a non-inertial reference frame attached to the moving orbital plane, have found very large periodic variations in the obliquity of the Mars planet over a period of the order 1.2 10+5 years, which would be of great importance to the climatic history of the planet.
Theories of Resonant Satellite Pairs in Saturn's System
Authors: Jefferys W. H. , Ries L. M.
Published: July 2016

Upcoming missions to the outer planets have made evident the need for better theories of their satellites. We have been involved in an effort to provide better satellite theories through new observations (Abbot, Mulholland and Shelus 1975; Mulholland, Shelus and Abbot 1976; Mulholland and Shelus 1977; and Benedict, Shelus and Mulholland 1978), and new analytical theories (Jefferys and Ries 1975; Jefferys 1976. Hereinafter these are denoted Paper I and Paper II, respectively). In this paper we report on our incorporation of new and old observations into our theories, and on our progress on the theoretical front.
Asteroidal Motion at Commensurabilities Treated in Three Dimensions
Authors: Schubart Joachim
Published: July 2016

This paper consists of a review about work done on three-dimensional motion at commensurabilities of either the mean motions, or of secular periods, and of a report on the author's recent results on some special cases. Real and fictitious asteroidal orbits and the corresponding long-period effects are the main subject of interest. At first, methods are listed.
Recent Work on the Origin of the Kirkwood Gaps
Authors: Scholl H.
Published: July 2016

The frequency distribution of the asteroidal mean motions shows the well known Kirkwood gaps which are found near the commensurabilities 3/1, 5/2, 7/3, and 2/1. The number of asteroids in the gaps is significantly smaller than those in the corresponding regions around these commensurabilities. In the outer part of the asteroidal belt, the frequency distribution is reversed: The number of asteroids at the commensurabilities 3/2, 4/3, and 1/1 is much larger than in the region around these commensurabilities.
Evolution of Orbits in the Outer Part of the Asteroidal Belt and in the Kirkwood Gaps
Authors: Froeschlé C. , Scholl H.
Published: July 2016

It is well known that the semi-major axes of the asteroids between the orbits of Mars and Jupiter are not uniformly distributed. The depleted regions in the outer part and the Kirkwood gaps in the inner part of the belt represent singularities in the frequency distribution of the asteroidal semi-major axes. The question whether these depleted regions and the Kirkwood gaps are due to gravitational perturbations of Jupiter or due to cosmogonic effects has not yet been solved and the discussion is still continuing.
Characteristics of Single Encounters of Long-Periodic Comets With Jupiter
Authors: Nakamura Tsuko
Published: July 2016

Original nearly parabolic orbits of comets are known to be evolved toward short-periodic elliptic orbits as statistical results of hundreds of encounters with Jupiter. There seems to be two methods to handle the process, namely, the method by exact numerical integrations for each orbit (Everhart, 1972) and random walk approach by using probability distributions of perturbations after single encounters (Lyttleton and Hammersley, 1963; Shteins, 1972). Since both methods need a great number of input parabolic comets to have only a few tens of short-periodic ones, the second method may save time compared with the first one, which is in turn more accurate. The purpose of this paper is to clarify the characteristics of single-encounter effects, in order to develope the second method more elaborately and extensively.
On the Effect of Binary Encounters
Authors: Shimizu Tsutomu
Published: July 2016

The effect of binary encounters is examined by restricting considerations to a sphere of finite radius R, instead of an infinite one assumed hitherto. The sphere is centered at an assigned test-particle with velocity ∇o. The corresponding modified assumption is that particles lying outside the sphere are scattered randomly with an average number density n and their velocity distribution is Maxwellian with an r.m.s. of in the space velocity. As for the particles' masses the same M is presumed.
H alpha variations in two mass losing stars
Authors: Vreux J. M. , Andrillat Y.
Published: July 2016

The aim of this paper is to report quite preliminary results obtained with a new multichannel detector put into operation at the Haute Provence Observatory. The observations have been made at the Cassegrain focus of the 1.93 m. The dispersion of the spectrograph was 17 Å. mm−1 at Hα and the slit was 300μ wide. The detector was a cooled SIT TV camera tube commercially available under the name of “Nocticon”. Details on the observing technique have been given elsewhere (Adrianzyk and al., 1978). We will only point out that all the wavelengths are recorded simultaneously : this recording technique is different from the scanning technique the result of which have been recently reviewed by Lacy (1977).
Mass loss effects in the spectrum of the O 6.5f binary HD 153919
Authors: Hammerschlag-Hensberge G.
Published: July 2016

Apart from the known P-Cygni profiles of Hβ, HeI 5876, 4471 in the spectrum of HD 153919, also HeII 3923 and a line at 3759 A which is tentatively identified as OIII show an emission component. These lines indicate that the Of star is losing mass at a high rate. A detailed analysis of the radial velocities obtained from 76 spectrograms indicates that the outflow of the wind is not spherically symmetric: at the side where the Of star faces its companion the velocity of the wind has increased.
O VI in stellar winds
Authors: Morton Donald C.
Published: July 2016

The region of the O VI resonance doublet around 1030 Å has been observed in 9 stars with the high resolution (0.051 Å FWHM) detector on the Copernicus satellite spectrometer. Although the spectra are confused with interstellar Lyman β and H2 absorption, P Cygni profiles or shifted absorption lines indicating mass flow were found in ζ Pup (O4If), 15 Mon (O7V), HD 151804 (O81af), 10 Lac (09.4V), υ Ori (BOV) and τ Sco (BOV). However, no O VI could be seen in ρ Leo (BlIab) or γ Ara (BlIb). The O VI profiles display a considerable variety that is not correlated with spectral type. Zeta Pup has a broad emission and deep absorption ranging over all velocities to about −2800 km s−1 while HD 151804 has only narrow absorption from −1060 to −1660 km s−1, and 15 Mon has a narrower feature from −1700 to −2100 km s−1. Both 10 Lac and τ Sco have broad relatively shallow absorptions extending from positive velocities to −1380 and −1000 km s−1 respectively. In contrast, the absorptions are narrower with steeper wings in ζ Oph and υ Ori. The latter star also has emission, while in ζ Oph the absorption is split into two components from about −1550 to −1280 and −1280 to −980 km s−1.
C IV resonance line profiles in O stars
Authors: Parsons S. B. , Wray J. D. , Henize K. G. , Benedict G. F.
Published: July 2016

The S-019 experiment on Skylab (cf. Henize et al. 1975; “Paper I”) recorded far UV spectra in about 160 4° x 5° fields, covering 10% of the sky, on 101 film with a 15 cm aperture objective-prism telescope. Several hundred early-type stars were observed in the vicinity of 1550 Å with a resolution between 3 and 4 Å, as well as thousands of stars at longer wavelengths and correspondingly lower resolution. An atlas of spectra for types 04 to B5 is illustrated in Paper I. That figure shows that the P Cygni profile is a characteristic of all supergiants earlier than B3 and main sequence stars earlier than 08.
Temperatures and radii of O stars
Authors: Underhill A. B. , Divan L. , Doazan V. , Prévot-Burnichon M.L.
Published: July 2016

Angular diameters have been estimated for 18 O and 142 B stars using absolute intermediate-band photometry in the near infrared and they have been combined with integrated fluxes to yield effective temperatures. The effective temperatures of the O stars lie in the range 30000 K to about 47000 K. For a given subtype, the luminosity class I stars have lower effective temperatures than the main-sequence stars by about 1000 K. The absorption-line spectral types of the supergiants of types O and B reflect electron temperatures which are higher than can be maintained by the integrated flux which flows through the stellar atmosphere. Distances have been estimated for all the stars and linear diameters found. The average radius for an 08 to 09.5 supergiant is about 23.3 R⊙; the radii for luminosity class III and Class V O stars lie in the range 6.8 to 10.7⊙ R.
The Hα profile in Zeta Puppis
Authors: Van Blerkom David
Published: July 2016

The Hα profile in the spectrum of Zeta Puppis is shown in Figure 1 (Conti and Frost 1977). It is of the P Cygni type, with a violet displaced absorption component that extends to about 300 km s−1 from line center. An unusual feature is the broad wing emission which can be seen out to 1500 km s−1 on both sides of the line. Of the roughly 2.5 Å equivalent width of Hα, 1.8 Å is due to velocity displacements |δv| > 300 km s−1. The presence of wing emission shortward of the violet absorption edge has been noted before in a Wolf-Rayet star, where it is attributed to non-coherent electron scattering (Castor, Smith and Van Blerkom 1970). In the present case, an optical depth in electrons of nearly 1.5 is required to produce the extensive wings by scattering a normal P Cygni profile. This exceeds by a factor of three the electron scattering optical thickness through the entire envelope, assuming published values of the mass loss rate, terminal velocity of the wind and photospheric radius. Thus an alternative explanation is required.
The mass loss rate of γ Velorum
Authors: Noerdlinger Peter D.
Published: July 2016

The CIII λ 1909 absorption feature (deepest at V=−1600 Km s−1) in this star, observed by Burton et al (1975) and Johnson (1978), was predicted by Castor and Nussbaumer (1972). It implies a copious flow of CIII ions, because the oscillator strength is only fik = 1.6× 10−7.
Binary frequency among the O-type stars
Authors: Garmany Catharine D.
Published: July 2016

A great deal of work has been done on the theory of mass loss and evolution in close binaries, and numerous individual systems have been discussed in this connection, but the general question of the binary frequency of O-stars, and in particular, the initial binary mass ratio frequency or distribution of secondary masses, has not been completely answered. In general, we know that about half of all O-type stars are binaries; the most recent determination by Conti, Leep and Lorre (1977) found 58% of their sample to be certain or probable binaries. However, many of these stars were judged to be variable on the basis of only a few spectra from different sources, and therefore require further study. Another point to be examined concerns the binaries with available orbits: two thirds of these are double line systems. Figure 1 shows a plot of the semi-amplitude versus orbital period for all known systems, along with some theoretical curves for different mass ratios. Not only is the lack of single line systems obvious, but low amplitude systems are almost completely missing. This would appear to be only an observational selection effect, although it is to be noted that low amplitude double line Wolf-Rayet systems have been detected. If the effect is real, it implies that O-type binaries with mass ratios (m1/m2) greater than about three do not exist.
Contact binaries of spectral type O
Authors: Leung Kam-Ching , Schneider Donald P.
Published: July 2016

The eclipsing binaries UW CMa, AO Cas, and V729 Cyg have been systems of great interest for over fifty years. The light curves are complex and suffer significant changes on a time scale of months, but the primary attraction of these systems is that both components have O-type spectra; thus they present us with some of the few possibilities for direct measurement of absolute dimensions of very massive stars. Much effort has been expended on these systems, but no really consistent model has emerged.
The binary orbit of HD 92740
Authors: Niemelä Virpi S.
Published: July 2016

HD 92740 is a star located in the Carina nebula showing a Wolf-Rayet spectrum of type WN7. Faint absorption lines of the upper Balmer series of hydrogen, and also of the Pickering series of Hell are present in the spectrum, in addition to the WN emissions. Although absorption lines present in a Wolf-Rayet spectrum are generally assumed to arise in a companion OB star, a previous study (Niemelä 1973) of the radial velocities of HD 92740 showed that the absorption and emission lines followed the same orbital motion. Subsequent spectral observations of this star have been carried out at the Cerro Tololo Inter-American Observatory, Chile, and at the Córdoba Observatory, Argentina, during four years; the observational data are listed in Conti, Niemelä and Walborn (1978). These observations showed that the true period is 8 times longer than the initially derived period of 10 days, and that doubtlessly the absorption lines belong to the WN star.
Critical rates of stellar mass loss
Authors: Dearborn D. S. P. , Blake J. B.
Published: July 2016

Many of the effects of mass loss on OB stars have now been explored. Mass loss will cause a star to be overluminous for its mass (though less luminous than a star of its original mass) and, for moderate mass-loss rates, the luminosity decreases at the same rate as the mass contained in the convective core decreases causing the main sequence lifetime to remain unchanged (Chiosi and Nasi 1974, 1978, Deloore, DeGreve and Lamers 1977, Dearborn, Blake, Hainebach and Schramm 1978). Mass loss can also expose layers where 14N has been enhanced via the CNO tricyle (Dearborn and Eggleton 1977) and, in extreme cases, can produce a stripped helium core resembling a Wolf-Rayet Star (Hartwick 1967). While many of these phenomena (in particular the composition change) are more sensitive to the total mass removed than the formalism used to represent the mass loss, significant differences will result for the same average mass-loss rate depending on whether the mass was removed early (near the ZAMS), or late (near core hydrogen depletion). In addition, there appears to be a critical mass loss rate which depends on initial mass and separates those models which continue to evolve in a relatively normal (though subluminous) manner, and those models which evolve to a Wolf-Rayet configuration.
The galactic WN7/WN8 stars as massive O stars in advanced stages of evolution
Authors: Moffat A.F.J. , Seggewiss W.
Published: July 2016

It is shown from various observational contraints that WN7/WN8 stars tend to occupy a class of their own set apart from other Wolf-Rayet subclasses. They probably evolved by stellar-wind mass loss from Of stars with original masses greater than ~35 m⊙, whether single or component of a binary. Two WN7/WN8 stars may be runaways in the second WR phase. One, HD 197406, is situated over 1000 pc from the galactic plane and has a low-mass, overluminous companion which is eclipsed by the WN7 component.
Radio studies of the distribution of ionized gas
Authors: Lockman Felix J.
Published: July 2016

Although radio recombination line and continuum observations are very useful for investigating galactic structure, it is well to remember their limitations. First, they only provide measurements of coordinates and velocities; a kinematic model is needed to derive the distance and thus the actual location of every nebula. In some directions, particularly all longitudes from ℓ=0°, kinematic distance estimates are prone to systematic errors arising from velocity crowding or uncertainties in the rotation curve, and are of little use in quantitative studies. I will only discuss the distribution of radio nebulae in the inner ∼100° of the galactic plane, since in this area kinematic analyses can give reasonable results and, in any case, here we must rely on radio observations for most of our information.
Gamma-ray observations and the large scale structure of the galaxy
Authors: Paul J. A.
Published: July 2016

Within the last few years, γ-ray astronomy has shifted from the discovery phase to the exploratory phase, thanks to the SAS-2 and COS-B satellites. The strongest feature of the γ-ray sky is the overwhelming emission of the galactic disc; even the radiation observed away from the galactic plane appears to be predominantly galactic, on the basis of its latitude dependence (Fichtel et al., 1978). Nevertheless, extragalactic γ-ray astronomy is not hopeless: the γ-radiation of the nearby quasar 3C273 has been very recently detected (Swanenburg et al., 1978). A brief summary of the present status of the galactic γ-ray astronomy follows.
Unstable spiral modes in the Milky Way system
Authors: Lau Y. Y. , Haass Jon
Published: July 2016

Discrete spiral modes of density waves have been calculated for models of the Milky Way system. The calculation is based on a fluid dynamical formulation. (See Lau and Bertin, 1978.) The equilibrium assumes a rotation curve given by Schmidt in 1965. The surface density σ of the active disk is less than the projected value implied by the Schmidt model, because of the presence of the spheroidal component and of the finite thickness of the disk. One such model (left figure) supports a spiral mode with a pattern speed of 13.6 km/sec/kpc. The spiral pattern (right figure) is very similar to that calculated earlier by Lin and Shu (1967) who used only the short wave. The perturbation density on the contours shown equals 1/5 of the maxima. There are other unstable modes. The modes are sensitive to the assumed Q profile. The superposition of these modes opens the way to the explanation of the complicated features observed but not well explained by the single spiral pattern computed earlier.
On the use of the WKBJ density wave theory at the Inner Lindblad Resonance region of our galaxy
Authors: Athanassoula E.
Published: July 2016

I have tested the reliability of certain approximations involved in the asymptotic WKBJ density wave description of the inner Lindblad resonance (=ILR) of our galaxy.
The circular velocity at the sun
Authors: Knapp G. R.
Published: July 2016

The galactic rotation velocity at the Sun, , can be derived several ways, none of them direct and unambiguous - (1) the solar velocity can be found relative to the halo population (the RR Lyrae stars, globular clusters etc.), but may contain an unknown contribution from possible systematic rotation of the halo system (2) the product Ro ω(Ro) = Ro (A-B) can be calculated but is uncertain because of large uncertainties in each of these three quantities (3) the motion of the Sun with respect to the center of the Local Group can be found but includes the motion of the galactic center of mass and (4) the velocity-longitude dependence of the outer HI boundary can be examined to deduce the most likely value of . The incorporation of new data into analyses using methods (1) and (3) gives essentially the same answers as older studies. Examination of the accumulated current evidence suggests that the best values for the solar rotation velocity and the galactocentric distance Ro are 220 km s−1 and 8.5 kpc respectively.
A statistical study of local interstellar matter based on the Nancay 21-cm absorption survey
Authors: Crovisier J. , Kazès I.
Published: July 2016

The survey of 21-cm galactic absorption towards 819 extragalactic sources, recently carried out with the Nancay radio telescope (Crovisier et al. 1978) provides a sample of absorbing neutral hydrogen clouds which is an order of magnitude larger than those resulting from other available surveys (Hughes et al. 1971, Radhakrishnan et al. 1972, Lazareff 1975, and Dickey et al. 1978). A statistical study of this sample offers insight into the properties of local interstellar matter.
General physical characteristics of the interstellar molecular gas
Authors: Turner B. E.
Published: July 2016

The interstellar medium may be characterized by several physically rather distinct regimes: coronal gas, intercloud gas, diffuse clouds, isolated dark clouds and globules (of small to modest mass), more massive molecular clouds containing OB (and later) stars, and giant molecular clouds. Molecules first appear in the denser diffuse clouds, and occur everywhere that AV ≳ 1m. Values of temperature, density, ionization fraction, mass, size, and velocity field are discussed for each regime. Heating and cooling mechanisms are reviewed. Nearly all molecular clouds exceed the Jeans criteria for gravitational instability, yet detailed models reveal no cases where observations can be interpreted unambiguously in terms of rapid collapse. The possibility that clouds are supported by turbulence, rotation, or magnetic fields is discussed, and it is concluded that none of these agencies suffice. Comments are made about fragmentation and star formation in molecular clouds, with possible explanations for why only low mass stars form in low mass clouds, why early-type stars form only in clouds with masses ≳ 103 M⊙, and why O-stars seem to form near edges of clouds. Finally, large-scale interactions between molecular clouds and the galactic disk stellar population are discussed.
The coldest molecular gas in our galaxy
Authors: Zuckerman B.
Published: July 2016

Galactic CO emission surveys such as those carried out by Gordon and Burton (Ap. J., 208, 346, 1976) and references cited therein are sensitive only to CO with J = 1 → 0 excitation temperature ≳ 5 k “Cold” molecular (H2) gas with CO excitation temperature ≳ 5 k would go undetected in such surveys. Low Tex could be due to either low kinetic temperature or low H2 density. Evidence for the possible existence of substantial amounts of cold gas (Tex ∼ 3 K) towards the galactic center is apparent in spectra of Liszt et al. (Ap. J. 213, 38, 1977 and 198, 537, 1975) in the form of narrow gaps, suggestive of self-absorption, at velocities of 0, −30 and −55 km/s with respect to the LSR.
Global physical characteristics of the HI gas.
Authors: Baker P. L.
Published: July 2016

The interstellar HI is best discussed in temperature categories because the requirement of pressure equilibrium leads to gross differences between hot and cold gas. The temperature of the hot (6000K) neutral gas has been measured by five techniques while the cold (60K) gas is visible mainly in 21cm absorbtion. There is evidence for warm (200K to 1000K) gas. Because of emission line blending, the small scale structural morphology is undetermined; however, there is evidence it is filamentary. With few exceptions, spatial sizes observe a lower limit of about 5 pc. On a larger scale, the gas is organized into sheets which reflect the recent history of cloud formation.
Chemical evolution of the galactic interstellar medium: abundance gradients
Authors: Peimbert Manuel
Published: July 2016

Recent abundance determinations of galactic H II regions and planetary nebulae are reviewed. The presence of O/H and N/H abundance gradients is well established; there is observational evidence indicating the presence of N/S, He/H and C/H abundance gradients. Some implications of these results are discussed.
HI in the inner few kiloparsecs of the galaxy
Authors: Burton W. B. , Liszt H. S.
Published: July 2016

After reviewing the available observational material, we describe here a simple model of the distribution and kinematics of HI gas within 1.5 kpc of the galactic center. According to this model, most of the inner-Galaxy gas is smoothly distributed in a tilted disk, within which the perceived kinematics are consistent with axisymmetric rotation and expansion of approximately equal magnitude. The model subsumes in a coherent way many observed spectral features which were previously studied separately, without requiring important density enhancements or anisotropic ejection from the nucleus.
Carbon monoxide and the 3-kpc arm feature
Authors: Bania T. M.
Published: July 2016

First isolated using the 21-cm HI spectral line, the 3-kpc arm exhibits the largest non-circular motion of any large-scale gaseous structure in the Galaxy (see e.g. Rougoor, 1964). Carbon monoxide observations best delineate the 3-kpc arm because the CO features are both narrower in velocity and also less confused with emission from more local gas than are HI observations. Because CO is a tracer of molecular hydrogen, the HI and CO data can in principle provide a good estimate of the total gaseous mass of the 3-kpc arm. A previous CO study of the inner Galaxy (Bania, 1977) suggested that, unless it is significantly tilted with respect to b=0°, the 3-kpc arm cannot be a continuous ring structure because emission at extreme positive velocities which should be produced by ring segments lying farther than 10 kpc from the Sun is absent. Consequently, the latitude distribution of CO in the 3-kpc arm has been studied by surveying 12CO emission over the region 350°<ℓ<25° at b=0° and ±0°.33. The survey positions are separated by Δℓ=1°. This coarse angular sampling resolution is deemed sufficient because the typical 3-kpc arm CO cloud has a linear dimension of 100 pc (Bania, 1977). Such clouds will subtend ∼0°.4 at the maximum line-of-sight distances expected for the extreme positive velocity 3-kpc arm emission (∼14 kpc).
“Three-integral”, collision-free statistical mechanics and stellar systems
Authors: Innanen K. A.
Published: July 2016

In a recent paper, Innanen and Papp (1977) have introduced and discussed the behaviour of a function they called the “super angular momentum,” ht2. This quantity, although not formally an integral of motion in the classical definition, is nevertheless a straightforward generalization of the classical total angular momentum. The super angular momentum, together with the other two classical invariants, the total energy E, and the Z component of the angular momentum hZ lead to the introduction for each homogeneous stellar system of a new collision-free distribution function

and fo, β and γ are constants. The function f satisfies the fundamental equation of stellar dynamics and shows that the velocity dispersions of stellar systems cannot be isotropic, but rather that

(a)

the velocity dispersion in the radial direction is constant (i. e. “isothermal”) and

(b)

the velocity dispersions in the tangential directions follow the law

That is, the tangential components are “isothermal” at the centre of the system, and decay according to the above equation so as to leave a purely radial distribution in the outer parts.
Is there a composition gradient in the halo?
Authors: Kraft Robert P. , Trefzger Charles F. , Suntzeff N.
Published: July 2016

We define “metals” as consisting of the elements at and near the Fe-peak, and review several methods by which the metal-abundance gradient of stars in the halo can be obtained. In the inner halo (galactocentric distance R ≲ 8 kpc), the Basel RGU photometry should allow the derivation of the shapes and dimensions of the iso-abundance contours. For the outer halo to R ∼ 30 kpc, we review techniques based on Δs-measurements of RR Lyraes (Lick) and intermediate band-pass photometry of globular-cluster giants (Searle and Zinn, Palomar). Both methods suggest little change in mean [Fe/H] between 10 and 30 kpc; however, both may be biased against the discovery of very metal-poor objects. The conclusion that the outer halo has no abundance gradient may be somewhat premature.
Gamma-ray evidence for a galactic halo
Authors: Stecker F. W.
Published: July 2016

γ-ray data favor a cosmic-ray propagation halo comparable with the thickness of the primary radio emission disk of our Galaxy and the halo seen around NGC891.
Introduction to the session
Authors: Verschuur G. L.
Published: July 2016

The generic label “high-velocity cloud” is a very unspecific term that tells us only that there are clouds of hydrogen gas moving with velocities which are anomalous for their position on the sky, if we assume that we live in a flat, uniformly rotating galaxy. If one attempts to explain them all away in one fell swoop we might draw an analogy with the situation extant in the 19th century, when optical astronomers were aware of patches of emission that were called nebulae. We now know that there are extragalactic as well as galactic nebulae, all quite different from one another. They were recognized to be so different as soon as the quality of data on these objects improved sufficiently. We may be in a similar, somewhat frustrating, position with regard to the high-velocity clouds. Soon after their discovery in 1963 it was believed that the clouds were mostly at negative velocities and that they were very local. Now we know of many more clouds at both positive and negative velocities. The models proposed for their existence cover a range of distances. We still have local (infall and explosive event) models, while other models place the clouds on relatively nearby spiral arms, in the high-z extension or warp areas of distant arms, in the outskirts and immediate neighborhood of the Galaxy, at the distance of the Magellanic Clouds, and even beyond. There may well be some truth in all of these models.
High-velocity clouds: review of observational properties
Authors: Hulsbosch Aad N.M.
Published: July 2016

Earlier extended surveys with moderate resolution and sensitivity had shown that high-velocity gas can appear as small clouds (∼2°) either isolated, or in elongated complexes with lengths of up to 30°. The profiles were rather broad (halfwidths of 25 km/s). While the brightest HVC's were found in the northern galactic hemisphere, the highest negative velocities were found in the southern latitudes. The only known high-positive velocity objects were a few at low latitudes between 1 = 245° and 330°.
Our galaxy as a member of the Local Group∗
Authors: van den Bergh Sidney
Published: July 2016

Galaxies are like people. When you get to know one well it always turns out to be peculiar in some way or other. In many cases such peculiarities appear to be inherent whereas in others they seem to result from the environment in which a galaxy has evolved. Very few galaxies live in total isolation; most are members of cluster families. The purpose of the the present paper is to introduce the known members of the Local Group to you in the hope that a closer acquaintance with our closest relatives in space will ultimately lead to a deeper understanding of the structure and evolution of our own Milky Way system.
The galaxy in perspective - an observer's synopsis
Authors: van Woerden Hugo
Published: July 2016

As mentioned already in Morton Roberts' fine introduction, two features were striking in this Symposium's programme: the broad spectral range of observational data, and the strong emphasis on comparisons with external galaxies. I shall return to the latter item towards the end of my summary. Let us first review the spectral panorama, then scrutinize what it has taught us about our Galaxy.
Correlation Functions for the Gravitational Force
Authors: Cohen L.
Published: July 2016

Spatial and time correlations of the force acting on a star are derived for finite gravitational systems. It is shown that their behavior is qualitatively different than that for infinite mediums.

The dissolution time for a binary system is considered. We explain why Chandrasekhar's dissolution time differs from that given by Ambartsumian and Oort in that it does not depend on the velocities of the field stars. We show that the difference lies in the definition of what constitutes ‘relative change in velocity’ of the two stars in the binary. Indeed, using the general approach of Chandrasekhar and von Neumann (appropriately modified) we derive a velocity dependent dissolution time.
Dynamics of Star Clusters: Comparison of Theory with Observations and Simulations
Authors: Wielen R.
Published: July 2016

Stellar dynamical theories for collisional systems are tested by numerical N-body simulations of isolated star clusters with N up to 500. For the dynamical evolution of the density distribution in star clusters, good agreement is found between Monte Carlo results and N-body models. There remains a discrepancy between theory and simulations in the rate of stellar escape from clusters and/or in the mechanism by which escapers are produced. Simulations of non-isolated star clusters are compared with observations of open clusters. The observed age distribution of open clusters can be explained by the dynamical dissolution of clusters. Stars of low mass do not escape relatively more frequently than stars of average mass.
Dynamical Models of Elliptical Galaxies
Authors: Wilson C. P.
Published: July 2016

Self-consistent dynamical models of elliptical galaxies have been constructed using a modification of the Prendergast-Tomer algorithm. They reproduce many of the observed properties of elliptical galaxies.
On the Sensitivity of the Behaviour of Stellar Orbits to the Parameters of Simple Galactic Mass Models
Authors: Martinet Louis
Published: July 2016

Some conjectures are given about the sensitivity of the behaviour of the stellar orbits (appearance of resonant orbits, possible interaction of resonances etc.) to the set of parameters characterizing a simple realistic ‘spheroid + nucleus’ mass model of our Galaxy. Connections with a systematic exploration of orbits in Schmidt mass models are mentioned. Finally we present arguments in favour of the existence of a third integral for the whole solar neighbourhood old stellar populations, independently of the chosen model.
Resonant Stellar Orbits in Spiral Galaxies
Authors: Vandervoort P. O.
Published: July 2016

This paper reviews a series of investigations of the orbits of stars in the regions of the Lindblad resonances of a spiral galaxy. The analysis is formulated in an epicyclic approximation. Analytic solutions of the epicyclic equations of motion are obtained by the method of harmonic balance of Bogoliubov and Mitropolsky. These solutions represent the resonance phenomena exhibited by the orbits in generally excellent agreement with numerical solutions.
Global Instabilities of Disks
Authors: Bardeen J. M.
Published: July 2016

Current understanding of the stability of gas and stellar disks suggests very strongly that local stability to axisymmetric modes is not sufficient for global stability. A global instability to a bar mode will develop unless the rotational kinetic energy is sufficiently small compared with the random kinetic energy for the system as a whole. A disk as cool as the galactic disk near the Sun can survive only if most of the mass of the Galaxy is in a ‘hot’ component, such as a central bulge and/or an extended halo. We review the theoretical evidence for this conclusion coming from analytic results for simple gas and stellar disks, from numerical simulations of stellar disks, and from numerical calculations of the stability of gas disks. Some new results on the precise form of dynamic bar instabilities of gas disks with and without halos are reported.
The Rotation Curves of Galaxies
Authors: Roberts M. S.
Published: July 2016

Currently available data on rotation curves are reviewed. For curves derived from optical measurements the distribution of the ratios: the last measured point on a rotation curve to the optical radius of the galaxy has a median value of if Reference Catalogue radii are used and if Holmberg radii are used. It is the absence of easily measurable H II regions that so severely limits the extent of these rotation curves. Accordingly, little can be said of the dependence of Vc on R for large R, where R is comparable to a Holmberg radius. The assumption that a rotation curve approaches a Keplerian curve after passing its peak rotational velocity implies a strongly concentrated and limited extent of the mass distribution within a galaxy. This assumption is not supported by 21-cm observations of the velocity field within a galaxy. Because of the greater extent of H I compared to measurable optical (blue) surface brightness, rotation curves may be defined to much larger radii from 21-cm observations. The median value of the above ratio for 14 galaxies is 1.3. At least 7 of these galaxies show an essentially constant rotational velocity at large R, while 5 galaxies have a slowly decreasing Vc(R). For both types of curves, a significant surface mass density at large R is required, and a large (≳ 100) mass-to-luminosity ratio is indicated. Such values are consistent with a late dwarf M star population (the most common type of star in the solar neighborhood) in the outer regions of a galaxy.