bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical Characteristics of V 1016 Cygni
Authors: Ciatti F. , Mammano A. , Rosino L.
Published: July 2016

Short description of the spectral phenomena of V 1016 Cyg.
The Outburst of CI Cygni in 1973
Authors: Belyakina T. S.
Published: July 2016

Description of photometric and spectroscopic observations of CI Cyg during the 1973 outburst.
The Binary X-Ray Stars – the Observational Picture
Authors: Gursky Herbert , Schreier Ethan
Published: July 2016

When X-ray sources in the galaxy were discovered in 1962 (Giacconi et al., 1962) it was only possible to speculate on their nature, which centered on supernova and cosmic-ray phenomena since these were the only very energetic events known. In particular, the discovery of an X-ray source associated with the Crab Nebula led to the idea that the emission might be the thermal radiation from the surface of a hot, neutron star. However, it was soon demonstrated (Bowyer et al., 1964) that a neutron star could not be responsible for the bulk of the X-radiation from the Crab, and it was not possible to exclude highly pathological conditions in otherwise ordinary stellar systems as being responsible for the X-ray sources (cf. Hayakawa and Matsuoka, 1964).
Linear Polarization Observations of Some X-Ray Sources
Authors: Shakhovskoy N. M. , Efimov Yu. S.
Published: July 2016

Multicolour linear polarization of optical radiation of the X-ray sources Sco X-1, Cyg X-2, Cyg X-1 and Her X-1 was measured at the Crimean Astrophysical Observatory in 1970–1973. These observations indicate that polarization of Sco X-1 in the ultraviolet, blue and red spectral regions appears to be variable. No statistically significant variations of polarization were found for the other three sources observed.
A Model for the Double System Containing the X-Ray Pulsar Her X-1
Authors: Bisnovatyi-Kogan G. S. , Komberg B. V.
Published: July 2016

A model for the double system with the X-ray source Her X-1 is considered. It is supposed that the central star has a sufficiently strong magnetic field for the outflow of the matter to occur in jets. When the neutron star is in the jet the optical depth τx attributable to the X-ray emission due to Compton scattering is greater than unity and the solid angle of the emitted X-radiation is broad, ∼ 180°. In the opposite case, τx < 1, there is a narrow angle of emission and the radiation falls on to the star and is not observed on the Earth. The motion of the neutron star relative to the jet is due to nonsynchronization between the orbital motion and rotation of the central star. If the duration of the whole orbit around the central star is 35 days and the dimension of the jet is about 1/3 of the orbit, then such a model explains features connected with the 35-day cycle.
Spectra of Type II Cepheids
Authors: Evans T. Lloyd
Published: July 2016

Spectra of over 100 stars classed as type II Cepheids of short period (BL Her-type) or long period (W Vir-type) or RV Tauri stars have been obtained. A range of metallic line strength and hence presumably metal abundance is present at all periods, those having weak lines being found especially in the globular clusters and the central bulge of the Galaxy. Stars which have enhanced Carbon molecular features (CH, CN and sometimes C2) occur at all periods but are probably distributed differently in space from the other stars.
Introductory Address
Authors: Plavec Miroslav
Published: July 2016

The early history of the studies on Be stars is reviewed. The importance of keeping in mind a basic model of a Be star is emphasized, and the binary star model is suggested as one serious possibility at least for some Be stars.
Spectra and Photometry of Be Stars: (Review Paper)
Authors: Hutchings J. B.
Published: July 2016

My task is to review the spectroscopy and photometry of Be stars. In the wide range of topics this covers, I will naturally be biased by my own interests and knowledge. I hope however at least to mention all forms of observed behaviour within these limitations, but note that as we have specific sessions on energy distributions, rotation, observations at unusual wavelengths (i.e., not from 3500 to 6700 Å), and polarisation, I shall deal less thoroughly, if at all, with these topics. I shall also attempt to incorporate the results of the speakers who follow in this session, in order to save duplication of individual introductions and allow the later presentations to concentrate more on the relevant discussions. I shall deal with nine aspects of Be stars behaviour, under the headings below.
A Study of Be Stars in Clusters
Authors: Schild R. , Romanishin W.
Published: July 2016

Calibrated spectrograms at Hα of 566 stars in 29 young galactic clusters led to the detection of 41 Be stars in clusters. Using cluster membership we have inferred ages and intrinsic (B – V) colors of Be stars to permit a discussion of their evolutionary states.

Rotating stars can become Be stars in their early hydrogen burning evolution away from the main sequence. Both the fraction of stars showing hydrogen emission and the strength of emission appear to vary little during the first 80% of post main sequence evolution. However, at the onset of gravitational core contraction, both the fraction of stars showing emission and their mean emission strength undergo a fourfold increase. Many stars in the core contraction phase develop an intrinsic (B – V) excess of 0.15 mag. due to the H− free-bound continuum radiation. Because of the great strength of Hα emission and the short time duration of the effect, the extreme Be stars would be excellent probes for studies of spiral structure and would also serve as probes for studies of ages and distances of extragalactic systems.

Analysis of the corrected colors of the Be stars in clusters suggests that the Lucy and Solomon (1970) mechanism for reduction of effective surface gravity by ultraviolet resonance line scattering is probably important for the hotter Be stars. However, a discrepancy exists for the cooler stars between the predicted and observed colors.
Emission Features of Several Be Stars as Related to Their Luminosity Class and Spectral Type
Authors: Hubert H. , Chambon M. Th.
Published: July 2016

At the Haute Provence Observatory, a survey of the Be stars brighter than the seventh magnitude was initiated by Herman and her collaborators twenty years ago.
Rapid Variations in the Spectra of o and, γ Cas, and χ Oph
Authors: Doazan V.
Published: July 2016

o And is a shell star which has lost its shell characteristics several times since 1897. It exhibits short time scale light variations with a period of about one day. Its binary nature is doubtful according to Olsen (1972). We have detected rapid spectroscopic variations in October 1973 when o And had no envelope, that is, when it appeared as a ‘normal’ B star. Spectrograms of 7.2 Å mm−1 dispersion were obtained at the Haute Provence Observatory with exposure times ranging from 12 min to 52 min.
Ultraviolet Si IV/C IV Ratios for Be Stars
Authors: Henize Karl G. , Wray James D. , Parsons S. B. , Benedict G. F.
Published: July 2016

The intensities of the very strong lines of C IV λ 1549 Å and Si IV λλ 1394, 1403 Å observed in spectra obtained with Skylab experiment S019 provide a sensitive discrimination of spectral type between B0 and B2. Eye estimates of the Si IV/C IV ratio are tabulated for 33 B0-B2, class III-V stars of which 11 are emission-line stars. Seven of the emission-line stars show significantly smaller ratios than normal stars of the same MK class. The most outstanding examples are 60 Cyg, o Pup, η Cen, and Ara.
Si II Lines in the Shell of ζ Tau
Authors: Heap Sara R.
Published: July 2016

Non-LTE strengths of Si II lines were computed in an effort to reproduce the observed strengths of Si II lines in the shell spectrum of ζ Tau. This effort was unsuccessful, probably because it assumed that the shell could be represented by a finite, plane-parallel slab. The main conclusion of this study, then, is that in order to understand the shell spectra of Be stars, a more realistic geometry must be assumed, in which the shell is represented by a thick disk.
Models for the Circumstellar Envelopes of Be Stars: (Review Paper)
Authors: Marlborough J. M.
Published: July 2016

A survey is presented of the theoretical attempts to determine the structure of the circumstellar matter around Be stars. The general equations describing the structure and dynamics of Be star envelopes are given. The complications introduced by various physical phenomena are briefly discussed and initial attempts to solve restricted problems are considered. The various ad hoc models proposed for Be stars are discussed and comparisons of the observations with predictions of these models are illustrated. The strengths and weaknesses of these models are evaluated and areas where progress is being or should be made are considered.
Theoretical Wavelength Dependence of Polarization in Early-Type Stars
Authors: Haisch Bernhard M. , Cassinelli Joseph P.
Published: July 2016

We have examined the theoretical wavelength dependence of linear polarization produced by electron scattering and modified by an absorptive opacity in the extended, distorted atmospheres of Be and Wolf-Rayet stars. A model atmosphere representing a Wolf-Rayet star recently calculated by Cassinelli and Hartmann was used. This model takes into consideration the subsonic portions of a radial, steady-state flow together with the requirement of radiative equilibrium. The model was then scaled down in temperature to approximate the cooler Be stars, again assuming radiative equilibrium. There were four models altogether, one WR star, and three Be models. All the atmospheres are quite extended by radiation pressure.
Late Stages of Close Binary Systems
Authors: Van Den Heuvel E. P. J.
Published: July 2016

The expected final evolution of massive close binaries (CB) in case B is reviewed. Primary stars with masses ≳ 12–15 M⊙ are, after loosing most of their envelope by mass exchange, expected to explode as supernovae, leaving behind a neutron star or a black hole.

Conservative close binary evolution (i.e. without a major loss of mass and angular momentum from the system during the first stage of mass transfer) is expected to occur if the initial mass ratio q0 = M20/M10 is ≳ 0.3. In this case the primary star will be the less massive component when it explodes, and the system is almost never disrupted by the explosion. The explosion is followed by a long-lasting quiet stage (106–107 yr) when the system consists of a massive main-sequence star and an inactive compact companion. After the secondary has left the main-sequence and becomes a blue supergiant with a strong stellar wind, the system becomes a massive X-ray binary for a short while (2–5 × 104 yr).

The numbers of Wolf-Rayet binaries and massive X-ray binaries observed within 3 kpc of the Sun are in reasonable agreement with the numbers expected on the basis of conservative CB evolution, which implies that several thousands of massive main-sequence stars with a quiet compact companion should exist in the Galaxy. About a dozen of these systems must be present among the stars visible to the naked eye. During the second stage of mass exchange, large loss of mass and angular momentum from the system is expected, leading to a rapid shrinking of the orbit. The supernova explosion of the secondary will in most cases disrupt the system. If it remains bound, the final system will consist of two compact stars and may resemble the binary pulsar PSR 1913 + 16.

In systems with q0 ≲ 0.2–0.3 large mass loss from the system is expected during the first stage of mass exchange. The exploding primary will then be more massive than its unevolved companion and the first supernova explosion disrupts the system in most cases. In the rare cases that it remains bound, the system will have a large runaway velocity and, after a very long (108–109 yr) inactive stage evolves into a low-mass X-ray binary, possibly resembling Her X-1.
The Observational Situation in Regard to Black Holes
Authors: Wilson Robert E.
Published: July 2016

Accumulated evidence on the existence of collapsed stars (black holes) in X-ray and non-X-ray binaries is considered. At present Cyg X-1 is the only strong case. The determinacy of solutions for mass ratios and other parameters of X-ray binaries is discussed, and some effects of tidal distortion and X-ray heating on measured radial velocities and ellipsoidal light curves are described.
The Algols, Red Spectra, Be Stars, and Even Neutrinos
Authors: Plavec M. , Polidan R. S.
Published: July 2016

The introduction of image tubes makes spectroscopic studies in the red and near infrared spectral regions much more efficient. Work currently done at the Lick Observatory by the Los Angeles binary star investigators is reported. Preliminary results on element abundances in the subgiant in U Sagittae indicate that there may indeed exist systematic abundance anomalies of potential relevance to the problem of the solar neutrino flux. Emission at Hα has been observed in many systems, and several types of circumstellar features are indicated. It is suggested that some Be stars and shell stars are interacting binaries. The possibility of observing very deep stellar eclipses is discussed.
A Cyclic Thermal Instability in Contact Binary Stars
Authors: Flannery Brian P.
Published: July 2016

Contact binary stars coupled by a common convective envelope in which the entropy is constant, the Lucy model, are unstable against mass exchange: if either component begins to transfer mass, it will continue to do so. A detailed sequence of models is calculated which follows the thermal evolution of a 2M⊙ contact binary of normal Population I abundances (X=0.70, Z = 0.02), starting at nearly equal mass. The initial instability develops into a cyclic mass-exchange with the mass fraction oscillating between 0.56≤m2/(m1 + m2)≤0.62 with a period of ~107yr. Throughout the cycle the component stars are not in thermal equilibrium. The instability is of a general nature, and such oscillating systems can satisfactorily populate the short period, red region of the period color relation for WUMa stars.
Statistics of Binary Stars: Semi-Major Axes
Authors: Trimble V. , Cheung C.
Published: July 2016

We have examined the distribution of the semi-major axes of the binary systems in the Sixth Catalogue of the Orbital Elements of Spectroscopic Binary Systems (and its extensions) and the correlation of semi-major axis with other properties of the systems. The total distribution has a single peak near asini=107km. Evolved systems have wider separations and smaller mass ratios than unevolved systems. Among each type separately, the distribution of mass ratios is bimodal and small mass ratio is correlated with large separation. These data appear to show evidence of two mechanisms of binary system formation and of the process of mass transfer in close binaries.
A Note as to a Perturbation of Hill's Curves
Authors: Matas V. R.
Published: July 2016

Let us consider motion of an infinitesimal body in the gravitational field of two homogeneous spheroids with coinoident equatorial planes. Let mass of the infinitesimal body M - a material point - be negligible if compared with masses of the spheroids S1, S2 respectively. We will study the motion of M in the common equatorial plane provided that the spheroids move along circular orbits (in an inertial frame of reference) - see Kondurar', 1952.
Topology of the Negative Energy-Manifold of the Kepler Motion
Authors: Yoshida Junzo
Published: July 2016

The motion of a particle of mass m according to the central force of Newton, is denoted bywhere K is a constant. x=0 corresponds to singular points of this equations. The domain of (1), denoted by= (R3−{0})×R3, is called the phase space of the Kepler motion. In the sequel we set m=K=1 for simplicity and also transform the independent variable from t to s by dt =|x|ds (x≠0), then the Kepler motion in the phase spaceis written asFurther, we shall confine the following discussion to the case of the negative energy value, except the preliminary discussion.
An Extension of Newton's Equation of Motion
Authors: Cheon Ki Jae
Published: July 2016

Classical mechanics failed to solve two problems in own defensive area, namely the motion of Mercury's perihelion, and the high-velcity motion of a charged particle. Today it is generally believed that the concepts of classical mechanics are completely invalid in a treatment of these problems. In this paper, however, we discuss these problems throughly with the concepts of classical mechanics — Euclidean space-time, point of mass and central force. Thereat we introduce a new concept “absolute mass variation”, with which we extend the Newton's second law of motion. In following chapters we show that this extended equation explains the motion of Mercury's perihelion, and that it throws new light on the atomic physics. We also make a study of reconstruction of internal structure of mechanics. We discuss the possibility of the revival of the principal frame of Newton's mechanics.
Formule d'Inversion de Lagrange et Son Application a La Theorie Des Perturbations
Authors: Inoue Takeshi
Published: July 2016

The article studies the application of the Lagrange series inversion formula to perturbation theories. One of the main problems is to generalize the Lagrange formula to several variables. The article also shows the need for introducing some operators to simplify the notation. To terminate, an application to the Von Zeipel-Brouwer satellite theory is given.
Astronomical Measurements and Coordinate Conditions in Relativistic Celestial Mechanics
Authors: Brumberg V. A.
Published: July 2016

The differences between the Newtonian theory and the general relativity appear both in the “relativistic effects,” such as the advance of perihelion, and in the deflection of light beams that modifies the astronomic observations and the radar reflection measurements.
Ephemeris of Mars
Authors: Kinoshita Hiroshi , Nakai Hiroshi
Published: July 2016

Newcomb's (1898) Tables of Mars with Ross's corrections have been used to compute its ephemeris in national ephemerides. Clemence (1949 and 1961) constructed a more precise theory of Mars and determined preliminary mean elements using a limited number of observations. Laubscher (1971) compared Clemence's theory with about 11000 observations by meridian circles from 1851 through 1969 and about 800 observations by radars and derived an improved set of mean elements. Duncombe and Kubo (1977) compared the ephemeris of Mars, in which Clemence's theory and Laubscher's elements were adopted, with the observations made by the meridian circle at Washington in 1972 and found large systematic residuals, which were larger than residuals by Newcomb's theory. Therefore, Duncombe and Kubo suspected that Laubscher's treatment of data was erroneous. On the other hand we had undertaken a reconstruction of Clemence's theory. In the meantime Kubo and Seidelman independently have found Laubscher's error in the determination of the inclination.
The Rings of Planets and Cosmogony of the Solar System
Authors: Vsekhsvyatskij S. K.
Published: July 2016

It is shown that the hypothesis that comets originate in the vicinity of each of the giant planets is consistent with the idea that these planets possess rings. It is suggested that the rings of Uranus, the probable gaseous ring around Jupiter and the clouds surrounding Io are rapidly evolving phenomena - the same may also even be true of Saturn's rings - which is to be expected of agglomerations of cometary meteoroids losing their icy constituents by sublimation.
Secular Perturbations of Asteroids and Comets
Authors: Kozai Yoshihide
Published: July 2016

In 1962 the author published a paper on secular perturbations of asteroids with high eccentricity and inclination (Kozai, 1962) and found that for such asteroids the secular perturbations are more complicated than those estimated by the classical linear theory. Before that the author(Kozai, 1954) tried to extend the classical theory to include terms of squares of disturbing masses, eccentricities and inclinations in expressions of secular motions of angular variables and found that the sum of the longitudes of the perihelion and the ascending node is not as stable quantity as the classical theory predicted, and, therefore, it cannot be used to estimate the ages of asteroid families. Then Williams(1969) and Yuasa(1973) extended the classical theory further.
Dynamical Problems in the Preparation of the Catalogue of One-Apparition Comets
Authors: Sitarski G.
Published: July 2016

Subtle effects influencing the results of orbit determination have to be taken into consideration when recomputing the cometary orbits for the Catalogue. It is very important to apply the numerical integration method, taking into account the specific conditions of the comet's motion, which almost eliminates a cumulation of numerical errors of integration. In this point of view the recurrent power series integration is adapted for cometary orbital computations. The optimal value of step-size of integration according to the required accuracy is calculated at every integration step. The method gives excellent results for “normal” comets as well as in the cases of close approaches of a comet to the Sun and to the planets.
Recent Dynamical History of the Six Short-Period Comets Discovered in 1975
Authors: Rickman Hans
Published: July 2016

In 1975 a remarkably large number of short-period comets were discovered - only the most recent number from 1977 is comparable. While the average discovery rate has been 0.8-1.0 new short-period comets per year (Kresák 1974), in 1975 there were six discoveries. In five of the cases IAU Circulars soon afterwards contained indications that close encounters with Jupiter had recently taken place (Marsden 1975, Kastel' 1975). For two of the comets, P/Kohoutek and P/Smirnova-Chernykh, also pre-encounter orbital elements were outlined, suggesting that substantial reductions of the perihelion distances had occurred.
Long Propagation Periods of Residuals in the Motion of a Comet
Authors: Kiang T.
Published: July 2016

P/Halley In a previous paper (Kiang 1973), I derived a differential equation which governs the behaviour of the residual O - C in the time of perihelion passage of a comet. The work was stimulated by the discovery (Brady 1972) that a long periodicity of about 600 years seemed to be present in the residual for P/Halley. The derivation was based on the following assumptions:

1.

The system consists of only the Sun, Jupiter and P/Halley, and Jupiter is assumed to move in a circular orbit with a period P′ = 11.8614 yr.

2.

P/Halley is assumed to move in a fixed Keplerian orbit with a period P = (13/2) P′ exactly, so that the whole system is strictly recurrent with a period Po = 13 P′ = 154.198 yr.
On the Orbit Mechanics of Cometary Dust Particles
Authors: Kimura H.
Published: July 2016

It is generally believed that the structure of dust tails of comets can be described in terms of the mechanical theory. The basic parameters of this theory are the repulsive force and initial emission velocity of particles. However, the effect of initial velocity does not seem to have been considered seriously in the discussion of the overall structure of dust tails. Finson and Probstein (1968) have recently proposed an elaborated method to analyse the tail brightness profiles by introducing the distribution function of particles. The initial velocity effect was, however, taken into account only in an approximate way. They assumed that a group of particles are emitted isotropically with a single speed, and afterwards forms a spherical shell expanding uniformly in time. The isotropic emission is suggested by the fluid-dynamical considerations on the gas-dust interaction in the inner head region, but the subsequent spherical expansion implies merely a simplification for the calculation to obtain the line-of-sight integrals analytically. Due to this simplification, the validity of the Finson-Probstein method is seriously limited, particularly when a tail after perihelion passage is concerned.
Short term variability of line strengths in some of and WR Stars
Authors: Weller W. G. , Jeffers S.
Published: July 2016

In recent years many observations of short time scale variability in a variety of spectral classes have been published. Some of these observations relate to phenomena which are reasonably well understood, as for example the Beta Canis Majoris stars, which are short period pulsators. In other cases, such as the Of and WR stars, the mechanism responsible for the variation is not fully understood. Models proposed to explain this variability include:- the binary hypothesis which ascribes the variations to fluctuations in gas streams in and around the members of a close binary system, and:- the pulsation hypothesis, which ascribes the variation in line strength to the presence of pulsational instability of massive carbon burning cores of evolved objects. The choice of the correct model is made difficult by the lack of an extended set of homogeneous observations. We must fulfil two conditions before making this choice. It is necessary to observe individual objects over extended periods of time at high dispersion to establish whether or not all WR's are binary systems. It is also required firmly to establish the temporal nature of the variations, since short term periodicities would tend to favor the core pulsation model.
The theory of mass loss from hot stars
Authors: Hearn A. G.
Published: July 2016

Although some evidence had been available earlier, it was the work of Morton (1967) that proved that the OB Supergiants are losing mass. He obtained spectra with a rocket borne spectrograph of the three stars in Orion's belt, δ, ε and ζ Orionis. These stars are all supergiants of spectral type 09.5 or BO. The spectra showed resonance lines of ions such as C III, C IV, Si IV, N V with P-Cygni type profiles. The deepest part of the absorption profile corresponded to a velocity away from the star of 1400 km s−1, and the absorption profile extended out to wavelengths corresponding to velocities of 2000 km s−1 away from the star. Since these velocities are much greater than the escape velocities from the surface of these stars, it is clear that matter is escaping from them. With a number of simplifying assumptions Morton deduced that the rate of mass loss is about 10−6 M⊙ yr−1. This order of magnitude has remained unchanged by the many high quality observations made since that time.
The domain of radiatively driven mass loss in the H-R diagram
Authors: Abbott David C.
Published: July 2016

Previous work by Castor, Abbott, and Klein (1975) presented a self-consistent model of a steady-state stellar wind. They also showed qualitatively that for O stars at least a static atmosphere could not exist. This paper extends that result by calculating in detail the minimum luminosity as a function of effective temperature required for the line radiation force to exceed gravity. Within the observational and theoretical uncertainty there is a one-to-one correspondence between a star's calculated ability to self-initiate a stellar wind by radiation pressure alone and the observed presence of outflowing material in the UV resonance lines.
Synthetic line profiles in early-type stellar winds. I. H and He+
Authors: Kunasz P. B.
Published: July 2016

Statistical equilibrium calculations for the first ten levels of H and He+ were carried out for several model atmospheres of a star with Teff = 40,000 K and log g = 3.5, using the method of Mihalas and Kunasz (1978). Atomic level populations and line profiles were computed for “model C” calculated by Klein and Castor (1978) and for variants of this model in which material density and mass loss rates were scaled down by factors of 2.0, 2.2, 2.5 and 4.0. We will refer to these variant models as D, E, F, and G. The resulting line profiles are discussed. Two variants of the Klein-Castor model C are generally successful and produce He II λ4686 in emission with λ3204 in absorption. All normal Of stars observed with He II λ4686 in emission have λ3204 in absorption. In one of the models, Hα is in emission, while Hβ and the higher Balmer lines remain in absorption, as is commonly observed in Of spectra.
The nature of the runaways: old disk population OB stars?
Authors: Carrasco L. , Bisiacchi G. F. , Costero R. , Firmani C.
Published: July 2016

We propose that most of the OB runaway stars are Old Disk Population objects in the same evolutionary phase as the hot UV-bright stars in globular clusters. Bimodal Gaussian fits to the peculiar radial velocity distribution are computed for 386 O-type and 1093 B-type stars. Both samples independently yield one Gaussian with σ ≃ 13 km s−1, a value typical of extreme Population I objects, and a second one with σ ≃ 28 km s−1 which is characteristic of the Old Disk Population. The fraction of stars under the high velocity-dispersion distribution (HVD stars) is 47% of the 0 and 23% of the B stars. We analyze the kinematics of the sample of OB stars divided into low peculiar radial velocity, |Vrp|<20 km s−1, and high-velocity stars, |Vrp|> 45 km s−1. The results for the solar motion and mean peculiar velocity of the groups are the expected ones for the extreme Population I objects in the case of the low-velocity group (U⊙= 9.1±0.1;V⊙= 14.8±0.1 km s−1) and an asymmetric drift of approximately 20 km s−1 for the high velocity stars (U⊙=2.7±1.4; V⊙= 32.7±1.4 km s−1). This lag behind circular motion also corresponds to Old Disk Population objects.
Evolution of single stars with mass loss
Authors: de Loore C.
Published: July 2016

A.

Mass loss has been observed by means of UV, optical, IR and radio observations.

B.

There exists also indirect evidence that stars lose matter during their evolution.
The role of rotation in the evolution of massive stars losing mass
Authors: Sreenivasan S. R. , Wilson W.J.F.
Published: July 2016

The role of differential and solid body rotation in the evolution of massive stars undergoing mass loss is discussed. The implications for Of, WR, β Cephei stars and shell stars are brought out.
Mass conservation and rapid mass loss on the main sequence
Authors: Mazurek T. J.
Published: July 2016

The rapid mass loss observed in O stars can affect their evolution dramatically if it takes place during core hydrogen burning on the main sequence. Conti has suggested that this is the case for the brightest Of stars, and that these stars evolve into Wolf-Rayet (WR) stars. Support for this scenario comes from the similarity in the spectra of the Of and WR stars, and from the observed helium enrichment of Wolf-Rayet WN stars along with the correlation of the latter with the most luminous O stars. If the most massive Of stars evolve to WN stars of relatively low mass, one needs to determine the range of zero-age stellar masses where such an evolution occurs. This communication abstracts some observational evidence that bears on the question of the minimum zero-age mass for rapid mass loss on the main sequence. It then summarizes the author's investigation of a model for mass loss where photospheric acoustic waves control the flow rate.
Evolution of binary stars with mass loss
Authors: Ziółkowski Janusz
Published: July 2016

Three situations involving mass loss from binary systems are discussed. (1) Non-conservative mass exchange in semi-detached binaries. No quantitative estimate of this mechanism is possible at present. (2) Common envelope binaries. There are both theoretical and observational indications that this phase of evolution happens to many systems, even to some that are not very close initially (orbital periods ~ years). (3) Stellar winds in binaries. Observational evidence suggests that stellar winds from components of close binaries (especially semi-detached) are significantly stronger than from single stars at the same location in the H-R diagram. Theoretical arguments indicate that in some cases stellar wind may stabilize the component of a binary against the Roche lobe overflow. In some cases there is weak evidence of an anisotropy in the stellar wind.
The influence of stellar wind mass loss on the evolution of massive close binaries.
Authors: Vanbeveren D. , De Grève J.P. , de Loore C. , van Dessel E.L.
Published: July 2016

It is generally accepted that massive (and thus luminous) stars lose mass by stellar wind, driven by radiation force (Lucy and Solomon, 1970; Castor et al. 1975). For the components of massive binary systems, rotational and gravitational effects may act together with the radiation force so as to increase the mass loss rate. Our intention here is to discuss the influence of a stellar wind mass loss on the evolution of massive close binaries. During the Roche lobe overflow phase, mass and angular momentum can leave the system. Possible reasons for mass loss from the system are for example the expansion of the companion due to accretion of the material lost by the mass losing star (Kippenhahn and Meyer-Hofmeister, 1977) or the fact that due to the influence of the radiation force in luminous stars, mass will be lost over the whole surface of the star and not any longer through a possible Lagrangian point as in the case of classical Roche lobe overflow (Vanbeveren, 1978). We have therefore investigated the influence of both processes on binary evolution. Our results are applied to 5 massive X-ray binaries with a possible implication for the existence of massive Wolf Rayet stars with a very close invisible compact companion. A more extended version of this talk is published in Astronomy and Astrophysics (Vanbeveren et al. 1978; Vanbeveren and De Grève, 1978). Their results will be briefly reviewed.
BE 381: WN9 or O8 Iafpe?
Authors: Bohannan Bruce
Published: July 2016

As John Hutchings summarized at the opening of this symposium the most easily detected symptom of mass loss in hot stars is emission at Hα. Some years ago I made a survey of the Large Magellanic Cloud for stars with Hα in emission (Bohannan and Epps 1974) and since then have obtained low resolution spectra of some of these stars to establish their spectral identity. I would like to talk today of one of these objects, BE 381, which displays spectroscopic features of both the extreme Of and low excitation WN Wolf-Rayet classifications.
Giant molecular clouds in the galaxy: distribution, mass, size and age
Authors: Solomon P. M. , Sanders D. B. , Scoville N. Z.
Published: July 2016

Millimeter wave observations of emission from the CO molecule have become, over the past eight years, the dominant method for determining the physical properties of dense interstellar clouds, composed primarily of molecular hydrogen and for exploring the structure and kinematics of the galactic disk. In this paper we briefly review the CO survey results in the literature (Section 2) and then present new results (Section 3-7) of an extensive 13CO and 12CO survey of the galactic distribution, size, mass and age of molecular clouds. The interpretation of this survey leads to a new picture of the interstellar medium dominated by very massive stable long-lived clouds which we refer to as Giant Molecular Clouds. We find that Giant Molecular Clouds (GMC's) with M = 105–3 × 106M⊙ are a major constituent of the galactic disk, the dominant component of the interstellar medium in the galaxy interior to the sun and the most massive objects in the galaxy. We find that the interstellar medium and star formation are dominated by massive gravitationally bound clouds in which stars and associations are forming but at a very low rate in comparison to the free fall time. The galactic distribution of the molecules as traced by CO emission is interpreted as the distribution of GMC's. As the most massive objects in the galaxy they are also basic to the dynamics of the disk.
Line and continuum surveys of the galactic plane with the 100-m telescope
Authors: Downes D.
Published: July 2016

A new continuum survey of the galactic plane has been made with the Effelsberg 100-m telescope at a frequency of 4.875 GHz with a beamwidth of 2°.6. The data are available in the form of radio contour maps covering ℓ = 357°.5 to 60°, b = ±1°, together with a list of 1186 radio sources. (Altenhoff, Downes, Pauls and Schraml, 1978, Astron. Astrophys. Suppl. 35, 1).
The distribution of young stars, clusters and cepheids in the Milky Way and M33 - a comparison
Authors: Humphreys Roberta M.
Published: July 2016

Ever since the pioneering work by Morgan and his collaborators (1952, 1953), it has been well known that the distribution of the associations of young stars, HII regions, and young clusters defines the optical spiral features. Although considerable progress has been made in spiral structure studies during these past 25 years, the basic picture of optical spiral structure has not been significantly altered. The three spiral features first described by Morgan are still recognized. Modern work on the various optical spiral features has strengthened and improved the definition of the optical features, especially to larger distances. Most of the improvements and any additions to the basic three-arm pattern have resulted primarily from observations of the spiral tracers in the Southern Milky Way. Specifically, the Sagittarius feature is now generally recognized as the Sagittarius-Carina arm which may indeed be a major arm of the Galaxy. It can now be traced optically to very large distances, up to 6 kpc or more in the direction ℓ = 290°. The Local arm (Cygnus-Orion) probably extends to 4 kpc in the direction of Puppis (ℓ ≅ 240°), and most astronomers would probably agree that our local spiral feature is not a major arm, but an inter-arm feature.
Pulsars as a galactic population
Authors: Taylor Joseph H.
Published: July 2016

Recent pulsar surveys have increased the number of known pulsars to well over 300, and many of them lie at distances of several kpc or more from the sun. The distribution of pulsars with respect to distance from the galactic center is similar to other population I material such as HII regions, supernova remnants, and carbon monoxide gas, but the disk thickness of the pulsar distribution is rather greater, with
≈350 pc. Statistical analysis suggests that the total number of active pulsars in the Galaxy is a half million or more, and because kinematic arguments require the active lifetimes of pulsars to be ≲5×106 years, it follows that the birthrate required to maintain the observed population is one pulsar every ∼10 years (or less) in the Galaxy.
On a mechanism that structures galaxies
Authors: Lynden-Bell D.
Published: July 2016

By considering the interaction of a single stellar orbit with a weak cos 2Φ potential it is shown that in the central regions of galaxies with slowly rising rotation curves, the elongations of the orbits will align along any potential valley and oscillate about it. This effect is more pronounced for elongated orbits. In such regions any pair of orbits will naturally align under their mutual gravity and so a bar will form. The gravity of this bar will drive a spiral structure in the outer parts of the galaxy where differential rotation is too strong to allow the orbits to be caught by the bar. The spiral structure carries a torque which slowly drains angular momentum from the bar, gradually making its outline more eccentric and slowing its pattern speed. In the outer parts of the bar only the more eccentric orbits align with the potential valley; the rounder ones form a ring or lens about the bar. As the pattern speed slows down, the corotation resonance and outer Lindblad resonance, which receive the angular momentun, move outwards. The evolution of the system is eventually slowed down by the weakness of these outer resonances where the material is rather sparse.
Observations of CO in the Perseus arm
Authors: Yuan C. , Dickman R. L.
Published: July 2016

Observations of the 2.6-mm line of C12O16 were made in the galactic plane from 1=105° to 150° at 1° intervals. The total velocity coverage is 83.2 km s−1 centered at −40 km s−1 with resolution equal to 0.65 km s−1. The observations were made first in June 1976 and confirmed in October 1977 after some improvement of the observing facilities at the Aerospace Corporation. The integration time in each direction is 15 minutes, giving 30-noise dispersions of 0.9K. Among the 46 directions, there are 18 CO detections. Twelve of them have CO components moving with the velocities typical of those expected for the Perseus Arm. Most of them are situated in or near the 0 associations or HII regions in the Perseus Arm, while the others lie in the regions rich in young star clusters. All the velocities observed are in excellent agreement with those expected in the post-shock region in the context of the shock formation model of the spiral density-wave theory. These molecular clouds may be viewed as being formed in the compression phase of the cloud medium as the individual clouds enter the shock front of the intercloud medium. Their line-of-sight velocities are in general a few km s−1 more negative than those of the HII regions, the young star clusters, and the O associations in the Perseus Arm. This suggests that these young objects may be formed prior to the observed CO clouds. The CO velocities are in agreement with those of the HI ridge. One CO cloud is observed at 1=148°, although it is well known that all the tracers of the spiral arm come to an abrupt stop at 1=140°.
RR Lyrae variables in Baade's window
Authors: Blanco B. , Blanco V. M.
Published: July 2016

In his pioneer study of the RR Lyrae variable stars near NGC 6522, in the relatively unobscured window close to the galactic center (1 = 0.9, b = −3.9), Baade (1963) was limited by the high zenith distance of the galactic center as seen from Palomar, and suggested that southern hemisphere observations would be of value. Subsequent studies of the region have been based on the variables found in Baade's original search. Southern hemisphere plates were taken by Hartwick et al. (1972), and their re-analysis of a sample of Baade's variables showed many periods to be in error. They did not, however, search the plates for new variables. Plaut (1973) re-analyzed all the variables but no search for new variables was done.
An outward motion of young stars with respect to old stars
Authors: Upgren Arthur R.
Published: July 2016

Space motions are calculated for 145 dK2-M2 stars with radial velocities and with parallaxes and proper motions determined and published at the Van Vleck Observatory. The stars are divided into young and old disk components kinematically and also according to the age-sensitive CaII emission intensities. Rigorous solutions for the solar motion and velocity ellipsoid were calculated for each population group using three methods of weighting errors in parallax, proper motion and radial velocity. All methods show a mean motion of the young stars outward away from the galactic center of about ten km/sec when referred to the old stars. Details are presented by Upgren (1978). The conclusion appears to confirm an outward motion suggested by Kerr (1962) from 21-cm observations. It is reasonable to inquire whether a similar outward motion can be seen in the space motions of other stars. Unlike the Van Vleck parallaxes combined with the most rigorous of the weighting methods used here, earlier results may be too insensitive to measure such a motion. Nonetheless a search of some of the existing literature shows that a small outward motion is consistent with sources so far examined. Of the motion solutions listed by Delhaye (1965) only two involve space motions of stars covering most of the main sequence. For stars with velocity dispersions similar to ours, both studies show a small outward motion of the order of five km/sec (for the A dwarfs relative to the generally older F and G dwarfs). The A dwarfs brighter than 5m.5 (Eggen 1965) have a planar motion distribution very similar to our young dK-M stars and both groups possess a mean motion close to the basic and standard solar motions. These last are mostly based on young stars and the solar motion should be reexamined relative to stars of all ages. It might be worthwhile to redetermine the mean motions of stars for which age-dependent parameters are now available, such as the F-stars with uvby measures or the giants with DDO photometry, since the local standard of rest appears to be a function of stellar age. This study was supported by grant AST77-26554 of the National Science Foundation.
Energy balance in the interstellar medium
Authors: Salpeter E. E.
Published: July 2016

A large number (approximately 7) of different components or phases are needed to describe the interstellar medium. The neutral intercloud medium is probably a composite of (a) “lukewarm, substandard” clouds (heated by grain photoeffect and shockwaves), (b) the interfaces between clouds and coronal gas and (c) some “phase 2” gas heated by soft X-rays. Ionizing UV photons are mainly produced by OB-stars and are responsible for most of the average electron density. Bulk kinetic energy for “stirring” the medium and soft X-rays are mainly produced by supernova remnants, less by O-star stellar winds.
A new look at the galactic magnetic field
Authors: Kronberg P. P. , Simard-Normandin M.
Published: July 2016

We have measured the linear polarization of a new large sample of extragalactic radio sources, and by combining these with polarization values already in the literature, we have been able to compute a large number of rotation measures, with improved quality. We have also investigated the depolarization properties of these sources and as a result have been able to identify most sources with a large internally generated Faraday rotation. Figure 1 shows the rotation measures of 475 extragalactic radio sources on an equal-area projection, after “cleaning out” the extragalactic effects to first order.
Galactic center pulsar as a test of black hole existence and properties
Authors: Paczyński B. , Trimble V.
Published: July 2016

There is a reasonable chance of finding a (probably X-ray) pulsar in a short-period orbit around the galactic center. Such a pulsar can provide a test distinguishing a central black hole from a supermassive object or spinar. It also makes available a good clock in a region of space in which GM/Rc2 is much larger than solar system values, thus allowing strong-field tests of general relativity.
Theoretical overview - Interactions among the galaxy's components
Authors: Tinsley Beatrice M.
Published: July 2016

The structure and evolution of the Galaxy are reviewed in terms of interactions among various components, including its immediate surroundings. Emphasis is given to the large-scale processes responsible for star formation and chemical evolution, which are seen to be controlled by interactions between the ISM and other components and by gas flows. A model for formation of the Galaxy is outlined, in which the spheroidal component results from mergers of former small galaxies, and the disk has been accreted from outlying diffuse matter.
The mass and light distribution of the galaxy: a three-component model
Authors: Ostriker J. P. , Caldwell J. A. R.
Published: July 2016

The galaxy is represented schematically by a three-component model: a disc having the form of a modified exponential distribution, a spheroidal (bulge + nucleus) component and a dark halo component which, following the nomenclature of Einasto, we call the corona. The shapes of these components, chosen on the basis of observations of other galaxies, are consistent with imperfect knowledge of the Galaxy; values of the adjustable parameters are chosen by a least square minimization technique to best fit the most accurate kinematical and dynamical galactic observations. The local radius, circular velocity and escape velocity are found to be (R⊙, V⊙, Vesc) = (9.05 ± 0.33 kpc, 247 ± 13 km/s, 550 ± 24) quite close to the values determined from observations directly. The masses in the three components are (MD, MSp, MC) = (0.78 ± 0.13, 0.81 ± 0.09, 20.3) × 1011 M⊙ for a model with coronal radius of 335 kpc. If the quite uncertain coronal radius is reduced to 100 kpc the model is essentially unchanged except that then MC = 6.65 × 1011 M⊙. The disc and spheroidal components have in either case luminosities (in the visual band of (LD, LSp) = (2.0, 0.2) × 1010 L⊙. The galaxy is a normal giant spiral of type Sb-Sc similar to NGC 4565.