bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Mode Coherent Synchrotron Radiation and Pulsar Models
Authors: Eastlund Bernard J.
Published: June 2019

The radio pulses from pulsars are considered to be formed from the beamed radiation from relativistic electrons. This radiation is in low order harmonics of the gyro frequency, giving pulse shapes and polarisations which agree with observation.

A possible connection between the shapes of radio pulses and the emission of optical pulses, via the electron energy, leads to a suggested means of searching for visible pulsars with improved sensitivity.
Studies on the Galactic Density Wave
Authors: Mark James W.-K.
Published: June 2019

For spiral galaxies, investigations have been made as to the behaviour of density waves at the critical regions of the Lindblad and co-rotation resonances and in particular as to their role in the maintenance and generation of these waves. We shall also discuss the conditions under which an inner resonance ring may be formed. Furthermore, we find that the co-rotation region acts as a wave-amplifier.
Opening of the Symposium
Authors: Schatzman E.
Published: June 2019

The place of stellar physics in Astrophysics is not the same as it were 50 years ago. Stellar evolution theory has been one of the preferred places of numerical calculations, and as a consequence, standard evolution models, from the homogeneous pre-main sequence star to the final stages, white dwarfs, neutron stars, supernovae, has become sort of archetype of numerical analysis and computation, the essence of perfection.
Stellar evolution as evidenced by members of open clusters near the turn-off from the main sequence
Authors: Crawford D. L.
Published: June 2019

In many ways, this paper can be thought of as an introduction to that of Nissen's, and others, which contain high quality, new data for open clusters, particularly for work that includes observations of stars near the turn-off from the main sequence.
The NGC 6752 HR-diagram
Authors: Grenon M. , Blecha A.
Published: June 2019

Deep electronographic photometry has been performed down to mv 21.7 with the 90 mm McMullan camera on the Danish 1.54 m telescope at La Silla. Three exposures per colour were obtained. The plates have been scanned with the Geneva microdensitometer. The selected stars are isolated and are located in the outer corona. The magnitudes are obtained by the profile fitting method, cf. Blecha (1982), which enhances the dynamical range of the plate and reduces the noise due to crowding. The random error appears magnitude independent down to mv = 21 with σ = .05 per colour. Below mv = 20 a number of galaxies were identified and rejected according to their image profiles.
Basic observational constraints on the evolution of massive stars
Authors: Conti Peter S.
Published: June 2019

The sources of information and uncertainties in the intrinsic stellar parameters of luminosity, effective temperature, mass, composition and mass loss rates are discussed. These are used to compare the observed positions of massive stars in the Hertzsprung-Russell Diagram (HRD) with evolutionary tracks. The current status of this effort is briefly reviewed. A short summary of the kinematic properties of massive stars is made. A preliminary but fairly extensive discussion of the distributions and numbers of O-type and Wolf-Rayet stars in the galaxy and other members of the local group is then given.
Apsidal motion in evolved binary systems
Authors: Giménez Alvaro
Published: June 2019

The study of apsidal motions in eclipsing binaries has proven to be one of the best methods to check the internal density concentrations of the stars predicted by theoretical models. During the main sequence phase, we have found a good agreement between the observed apsidal motion rates and computer-constructed stellar models provided that a realistic consideration is made of the evolution between the lower and upper borders of the main sequence (Giménez and García-Pelayo, 1982). An obvious extension of this work is a throughout study of the more evolved evolved systems beyond the TAMS where theoretical models are less accurate and empirical data from different sources are largely needed (see review paper by Zahn in this volume). A preliminary report on such a study is presented.
Constraints on stellar evolution from pulsations
Authors: Cox Arthur N.
Published: June 2019

Consideration of the many types of intrinsic variable stars, that is, those that pulsate, reveals that perhaps a dozen classes can indicate some constraints that affect the results of stellar evolution calculations, or some interpretations of observations. Many of these constraints are not very strong or may not even be well defined yet. In this review we discuss only the case for six classes: classical Cepheids with their measured Wesselink radii, the observed surface effective temperatures of the known eleven double-mode Cepheids, the pulsation periods and measured surface effective temperatures of three R CrB variables, the δ Scuti variable VZ Cnc with a very large ratio of its two observed periods, the nonradial oscillations of our sun, and the period ratios of the newly discovered double-mode RR Lyrae variables. Unfortunately, the present state of knowledge about the exact compositions; mass loss and its dependence on the mass, radius, luminosity, and composition; and internal mixing processes, as well as sometimes the more basic parameters such as luminosities and surface effective temperatures prevent us from applying strong constraints for every case where currently the possibility exists.
HR 7308 (V473 Lyr): The strangest cepheid
Authors: Burki G.
Published: June 2019

The variability of HR 7308 was discovered by Breger (1969), and Percy et al (1979) found this star to be a new cepheid. The correct period and the variation of amplitude were first recognized by Burki and Mayor (1980 a, b). Further studies of this star were published by Percy and Evans (1980), van Genderen (1981), Breger (1981), Fernie (1981), Burki et al (1982) and Henriksson (1983). Here the up-to-date radial velocity observations made with the spectrophotometer CORAVEL are presented.
Convective effects and the RR lyrae instability strip
Authors: Stellingwerf R. F.
Published: June 2019

The effects of nonlinear, nonlocal, diffusive convection have been included in the structure equations of pulsational hydrodynamic analyses of a series of RR Lyrae models. We find a well-defined red edge of the unstable region that depends on mode of pulsation. It is shown that this result has strong implications for the nonlinear behavior of RR Lyrae stars.
B V photometry of RR lyrae variables in M15
Authors: Bingham E.A. , Cacciari C. , Dickens R.J. , Pecci F. Fusi
Published: June 2019

New BV photographic photometry for 56 RR Lyrae variables in M15, combined with original measures by Sandage, Katem and Sandage (1981), yield data of improved precision which enable a rediscussion of the RR Lyrae characteristics and Oosterhoff problem.
On turbulent mixing
Authors: Roxburgh Ian W.
Published: June 2019

Several authors (myself included!) have suggested that turbulent mixing takes place in some, if not all, stars, and in particular that such mixing can explain the low solar neutrino flux. This turbulence is thought to be caused by differential rotation produced by braking due to angular momentum loss in a stellar wind, and/or to the effect of meridional circulation currents in redistributing angular momentum. Whilst such instabilities may exist even in the presence of a stabilizing distribution of chemical composition, they do not necessarily cause mixing. To be effective in mixing, the energy available to the instability be it differential rotation or any other mechanism, has to be sufficient to lift the helium rich matter in the interior of the star to the outer regions. This requires
where Erot is the kinetic energy in rotation, Eg the gravitational energy, τth the thermal time scale and τnuc the nuclear evolution time scale of the star.
M giants at two latitudes in the nuclear bulge of the galaxy
Authors: Frogel Jay A. , Blanco V.M. , Whitford A.E.
Published: June 2019

We are engaged in a long term study of the stellar component in the nuclear bulge of the Galaxy. Regions of low obscuration at different galactic latitudes above the galactic nucleus are surveyed for M giants with a transmission grating and thin prism at the prime focus of the CTIO 4-m reflector. Photographic and infrared photometry are obtained for samples of the stars found. Spectroscopic observations are used to investigate band strengths and radial velocities.
On the Effect of the Scale Value on the Principal Nutation Terms Derived from the ILS Data
Authors: Yablokov E. A.
Published: June 2019

The scale values used in the work of the International Latitude Service are known to be in some cases evidently erroneous. After trying various methods to improve these values, E. P. Fedorov (1963) decided on the one based on the computation of the mean latitudes obtained from observations of the pairs with zenith distances of opposite sign.
Corrections to Some Terms of Nutation Deduced from the Paris Astrolabe Observations
Authors: Capitaine Nicole
Published: June 2019

Any error in the position of the Earth's axis of rotation in space gives an error in the equatorial coordinates of stars used in the reduction of latitude and time observations and consequently gives an error in the results of these observations. This may be due to an error in the classical terms of nutation or to the neglected nutation in space produced by the theoretically predicted nearly-diurnal wobble (Hough, 1895; Poincaré, 1910; Jeffreys, 1949; Molodensky, 1961; Toomre, 1974). A preliminary study of these errors in latitude and time observations was reported in a preceding paper (Capitaine, 1975), which was subsequently corrected for a minor sign error (Capitaine, 1977).
On the Adoption of Empirical Corrections to Woolard's Nutation Theory
Authors: McCarthy D. D. , Seidelmann P. K. , Van Flandern T. C.
Published: June 2019

Commission 4 of the International Astronomical Union has deferred the question of revisions to the constants and theory of nutation in anticipation that there might be recommendations from Symposium No. 78 in Kiev. The present rigid-Earth theory of nutation does not adequately represent current precise astronomical observations for the major nutation terms. Discrepancies between the presently adopted theory and observations can accumulate to 0″1 in right ascension and significantly affect the determination of UT1 and materially influence the derivation of the new fundamental catalog of star positions and proper motions, FK5 There appears to be no obvious choice for a non-rigid-Earth model at present. The analysis of solid-Earth tides shows nutation coefficients in substantial agreement with astronomical observations and these values have been used in the reduction of radio interferometric and laser ranging observations. In the absence of a non-rigid-Earth model which can satisfy all requirements it is suggested that the coefficients found from the investigation of solid-Earth tides be adopted as a working standard until such a model can be adopted as a basis for nutation.
Comparison of Global 21 cm Velocity Profiles with Hα Rotation Curves
Authors: Thonnard Norbert
Published: June 2019

21 cm profiles are compared with high resolution long slit Hα spectra. Asymmetries in intensity and velocity gradient in the spectra are apparent in the global profiles. When measured at 0.5 of peak intensity, the 21cm profile width and optical rotation curve match best.
The Origin of Dwarf Spheroidal Galaxies
Authors: Lynden-Bell D.
Published: June 2019

Two dwarf spheroidal galaxies are associated with the Magellanic Stream with their major axes oriented along it. Evidence suggests that all the dwarf spheroidal satellites of the Galaxy belong to one or other of two streams of tidal debris. If this is true the orbits will give the first reliable determination of the total mass of the Galaxy out to 120 kpc.
Neutral Hydrogen Mapping of three SO Galaxies
Authors: Shane W. W. , Krumm N.
Published: June 2019

Synthesis maps of HI in three SO galaxies are discussed. In one case several companions are observed. An evolutionary sequence based on accretion is suggested.
Relation Between Star Formation and Angular Momentum in Spiral Galaxies
Authors: Carrasco L. , Serrano A.
Published: June 2019

We derive the radial distribution of the specific angular momentum j=J/M, for the gas in M31, M51 and the galaxy, objects for which well observed unsmoothed rotation curves are available in the literature. We find the specific angular momentum to be anti-correlated with the present stellar formation rate, i.e. minima of spin angular momentum correspond to the loci of spiral arms. We find that the stellar formation rate is an inverse function of j. We derive new values of Oort's A constant for the arm and interarm regions in the solar neighborhood.
Morphology, Stellar Kinematics and Dynamics of Barred Galaxies
Authors: Kormendy John
Published: June 2019

A brief review is given of the morphology of barred galaxies, following Kormendy (1981, 1982). The features illustrated include bulges, bars, disks, lenses, and inner and outer rings.

Most of the paper is devoted to a detailed discussion of the absorption-line velocity field of the prototypical SBO galaxy NGC 936. The stars in the bar region show systematic non-circular streaming motions, with average orbits which are elongated parallel to the bar. Beyond the end of the bar, the data are consistent with circular orbits. The bar region also shows large random motions: the velocity dispersion at one-half of the radius of the bar is 1/2–2/3 as large as the maximum circular velocity. The observed kinematics are qualitatively and quantitatively similar to the behavior of n-body models by Miller and Smith (1979) and by Hohl and Zang (1979). The galaxy and the models show similar radial dependences of simple dimensionless parameters that characterize the dynamics. These include the local ratio of rotation velocity to velocity dispersion, which measures the relative importance of the ordered and random motions discussed above. Also similar are the residual streaming motions (relative to the circular velocity) in a frame of reference rotating with the bar. Circulation is in the same direction as rotation in all galaxies studied to date. Thus, except for the fact that NGC 936 has a slightly larger velocity dispersion, both n-body models are good first-order approximations to bars. Thus bars are different from elliptical galaxies, which in general are also triaxial, but which rotate slowly. This study of NGC 936 will be published in Kormendy (1983).

A brief discussion is given of the kinematics of lens components. In both barred and unbarred galaxies, the velocity dispersions in the inner parts of lenses are large. The ratio of rotational to random kinetic energy is ∼ 1/2 at 1/3–1/2 of the radius of the lens. This ratio then decreases to small values at the rim of the lens. Thus at least some kinds of disk components have large stellar velocity dispersions, even in unbarred galaxies.
Theoretical Studies of Gas Flow in Barred Spirals Galaxies
Authors: Prendergast Kevin H.
Published: June 2019

We know far more about the velocity and density distributions of gas in ordinary spirals than in barred spirals. There are several reasons for this : the absence of a nearby barred spiral, the circumstance that several of the best objects lie rather far south, the necessity to map in two dimensions, and the surprisingly low intensity of the emission lines, except in the nucleus and near the ends of the bar. The older literature contains several investigations of radial velocities measured along the bars of barred spirals (cf. Burbidge, Burbidge and Prendergast, 1960 a,b for NGC 7479 and NGC 3504), and it has been known for some time that rotation curves taken in different position angles through the nuclei of barred spirals are not compatible with simple circular motion. It was not until recently, however, that attempts were made to map the velocity fields of barred spirals in two dimensions. Chevalier and Furenlid (1978) studied NGC 7723, NGC 5383 has been mapped by Peterson, Rubin, Ford and Thonnard (1978) in the optical and by Sancisi, Allen and Sullivan (1979) in neutral hydrogen, and NGC 1300 has been mapped by Peterson and Huntley (1980). The most striking result of these observations is that the isovelocity contours are elongated in the direction of the bars, or, put differently, there is no straight line through the center of a barred spiral along which the radial velocity is constant. This is clear proof that significant non-circular motions are present in these galaxies. However, as it is impossible to reconstruct a non-axisymmetric velocity field from radial velocity data alone, there is no analog for barred spirals of the reduction models which are used to estimate local mass densities for ordinary spirals from observed rotation curves.
Structure and Dynamics of Magellanic Type Galaxies
Authors: Feitzinger J. V.
Published: June 2019

In continuation of former work (Feitzinger 1980) the morphological structure of 68 SB(s)m systems, greater than 2!5 on ESO/SRC survey plates, was investigated. Three morphological features should be mentioned:

1.

Stellar bars located asymmetrically with respect to the disk are found in 70% of the cases; the displacement relative to the disk diameter is Λ = 0.1 − 0.35.

2.

The disk is populated in 45 % of the cases by chains of HII regions (spiral arm filaments).

3.

Though not very frequent nearly 25 % of the SBm systems have a dominating HII region near the outer periphery and predominantly near one end of the bar.
Axisymmetric Models of Elliptical Galaxies with Anisotropy
Authors: Petrou Maria
Published: June 2019

It is well known by now that models of elliptical galaxies based on Jeans theorem require the inclusion of a third integral in the distribution function.
Interstellar Matter in Elliptical Galaxies
Authors: Knapp G. R.
Published: June 2019

This contribution concentrates on the properties of the large gas structures in elliptical galaxies, those seen in dust and HI. The distribution and kinematics of ionized gas, which is generally confined to a small region in the center of the galaxy, are discussed at this conference by Illingworth and by Ulrich.
Merger Cross-Sections of Colliding Galaxies
Authors: Sastry K. Shankara , Alladin Saleh Mohamed
Published: June 2019

The velocities of escape of colliding galaxies obtained under the impulsive approximation are compared to those obtained from N-body simulations.
Kinematics of Clusters in M33
Authors: Christian C. A. , Schommer R. A.
Published: June 2019

We have obtained 9.5 A resolution spectrophotometry of 10 clusters in M33 (Cf. Christian and Schommer 1982) with the KPNO 4m telescope. Velocities were derived by comparing the cluster spectra to data for template stars, using the “Fourier quotient” technique described by Sargent et al (1977). The positions and velocities of the clusters are shown schematically in Figure 1, where the HI velocity map (Rogstad, et al 1976) is also indicated. We find that the velocities of younger, bluer clusters are more closely matched to the disk-like motion of the gas, while the older redder clusters have more discrepant values (Table I). As shown in Figure 2, Velocity difference, Vel (HI - cluster), varies smoothly with the integrated (B-V), suggesting a slow smooth collapse of M33 to a disk galaxy. This fall, we intend to increase our sample of measured cluster velocities to probe more completely the history of the cluster and disk formation in M33.
The Expansion of Cassiopeia A
Authors: Tuffs R. J.
Published: June 2019

This paper describes a detailed comparison of radio maps of Cas A obtained with the Cambridge 5 km Radio Telescope in 1974 and 1978. Accurate proper motions and brightness changes are presented for 342 distinct radio peaks, ranging in angular size from 1 arc minute for fragments of the intense ring to less than the resolution limit of 2.0 × 2.3 arc seconds for the compact radio knots.
Consequences of a New Distance Determination of 3C58
Authors: Green D. A. , Gull S. F.
Published: June 2019

In this paper we present new observations that show 3C58 is much closer than has been assumed in the past. This necessitates a reappraisal of many of the quantitative comparisons that have been made between 3C58 and the Crab Nebula or other ‘filled-centre’ remnants.
Hi Shells and Supershells
Authors: Heiles Carl
Published: June 2019

The entire sky has now been surveyed in the 21-cm line with an angular resolution of about 0.5 degree. In the north, above declination −20° or so, the “galactic plane” |b|<10° has been completely sampled Weaver and Williams (1973; 1974). Above declination −30° or so, the sky outside the galactic plane has been almost completely sampled (Heiles and Habing, 1974; Heiles, 1975).
Radio Continuum Observations of Large Supernova Remnants
Authors: Reich W. , Fürst E. , Sieber W.
Published: June 2019

Radio observations of large supernova remnants (SNRs) with high angular resolution have been provided by modern synthesis instruments preferentially at frequencies below 2 GHz. Since these instruments are sensitive mainly to unresolved emission spots, weak extended SNRs usually remain undetected. Besides this, there are numerous physical parameters, which can be studied more properly at higher frequencies. In particular, the polarization characteristics can be more easily analyzed and reduced to the intrinsic magnetic field orientation. In some cases foreground effects substantially disturb the SNR's field structure at low frequencies.
Supernova Remnants With Compact X-Ray Sources
Authors: Clark D. H. , Murdin P. G. , Wood R. , Gilmozzi R. , Danziger I. J. , Furr A. W.
Published: June 2019

More than 3000 radial velocity observations across the face of the Crab Nebula are used to investigate its 3-dimensional properties. In the standard model it consists of a thick hollow shell with synchrotron emission from within. We show that the thick shell is composed of bright inner and faint outer components
X-ray Studies of SS433
Authors: Grindlay J. E. , Band D. , Seward F. , Stella L. , Watson M.
Published: June 2019

Results of Einstein Observations of SS433 are discussed which address both the nature of the diffuse X-ray lobes and the relationships between SS433 and W50 as well as the time variability and nature of the central X-ray source. The diffuse X-ray lobes extend out to the quasi-spherical shell seen in the radio maps of W50 and suggest that the X-ray lobes are powered by the interaction of shock-heating from the SS433 jets and the denser material in the W50 shell. The central X-ray source in SS433 is time variable but only on timescales ≳ 500–1000 sec. Flares, in which the non-thermal spectrum hardens, are detected at two preferred phases in the 13.08 day binary orbit. Constraints on the central X-ray source size as well as a possible eclipse by the companion star suggest the compact object in SS433 may be an ~10 M⊙ black hole.
On the Association Between Pulsars and Supernova Remnants
Authors: Radhakrishnan V. , Srinivasan G.
Published: June 2019

The true nature of the association between pulsars and supernova remnants has remained an intriguing and poorly understood problem even after all these years of research on them. We attempt in this review to marshal all the evidence one has on this question, and to see what conclusions we can draw.
X-ray, Optical and UV Observations of the Young Supernova Remnant in the Irregular Galaxy NGC 4449
Authors: Blair W. P. , Kirshner R. P. , Winkler P. F. , Raymond J. C. , Fesen R. A. , Gull T. R.
Published: June 2019

A powerful young supernova remnant (SNR) similar to Cas A has recently been discovered in the irregular galaxy NGC 4449. We have obtained X-ray, optical and ultraviolet data which allow us to investigate possible models for this object and estimate its age. Several lines of argument indicate a massive star of order 25 M⊙ as the precursor to this remnant. If the x-ray emission is attributed to a reverse shock in the ejecta, the remnant should be ∼ 120 years old.
The Problem of the Redshifts
Authors: Burbidge Geoffrey
Published: June 2019

It is my intention in this brief paper to present once again some of the evidence which appears to show that a major contribution to the redshifts of QSOs and perhaps some galaxies is not associated with the expansion of the universe. The evidence continues to grow and it is of four kinds:

(a)

Evidence concerning galaxies with discrepant redshifts.

(b)

Connections between QSOs and galaxies.

(c)

Statistical information concerning the association of QSOs with galaxies.

(d)

Individual and very striking examples of pairings between QSOs and bright galaxies.
10 to 60 Arcmin Fluctuations in the Cosmic Microwave Background
Authors: Lasenby A. N. , Davies R. D.
Published: June 2019

Considerable astronomical interest attaches to sensitive measurements of temperature fluctuations of the microwave background on scales of a few arcmins to a few degrees. We describe here the first in a series of experiments being carried out at Jodrell Bank which are aimed at providing reliable and repeatable information on these angular scales. The first experiment used the MK II 25m dish at λ6 cm and covered scales from 10 arcmin (the beamwidth) to 60 arcmin (twice the beamthrow). At this relatively long wavelength, the atmosphere has negligible effect on the observations and day to day repeatability consistent with receiver noise alone was obtained. The observations were made in wagging mode near the North Celestial Pole (NCP) so that the two beams alternately traced out a reference circle on the sky, radius 30 arcmin, over the course of 24 hours. The NCP field was chosen since a high sensitivity discrete source survey (Pauliny-Toth et al. 1978) was already available covering the area. This meant that antenna temperatures around the reference circle could be corrected for any source induced effects ≳0.4 mK. In addition control observations were made at positions 30 arcmin East and West of the central field, so that systematic effects due to interaction of telescope sidelobes with objects in the immediate telescope environment, could be monitored and removed.
Large-Scale Anisotropy at Centimeter Wavelengths
Authors: Wilkinson David T.
Published: June 2019

Scientific interest in large-scale anisotropy measurements is now focused on intrinsic effects, which could tell us much about the early Universe. Current experimental precision of better than 10−4 K begins to probe for interesting physical processes. However, at these levels of precision systematic effects and foreground sources present serious difficulties. Some recent results from balloon flights of a maser radiometer (λ 1.2 cm) and a cooled mixer (λ 3 mm) are discussed and interpreted. The dipole effect gives a velocity for the Local Group in the general direction of the Virgo cluster. The Earth's motion is clearly seen. There is no quadrupole detected at a level of ΔT/T ∼ 5 × 10−5.
Large-Scale Anisotropy of the Cosmic Relic Radiation in Spatially Open Cosmological Models
Authors: Lukash V. N.
Published: June 2019

The observed microwave background radiation is a sensitive tool for studying the fundamental features of the universe. A puzzling constancy on the celestial sphere of the temperature, T, of the equilibrium relic radiation coming to us from causally nonrelated regions of space-time points to the global spatial homogeneity and isotropy of the cosmological expansion. On the other hand, a small anisotropy of the relic background can tell a lot about the physics of the beginning of the universal expansion, where primordial cosmological perturbations, which later affect the relic isotropy, formed (see, e.g., [1,2] and other reviews on the early universe). We would like to emphasize another factor that forms mainly the large-scale structure of relic anisotropy: the spatial curvature of the background Friedmann Universe. In the light of the discovery of the large-scale anisotropy of the cosmic radiation [3–5], this problem becomes very important.
Correlation Functions, Microwave Background, and Pancakes
Authors: Bonometto S. A. , Lucchin F.
Published: June 2019

The isothermal theories of galaxy formation encounter serious difficulties in accounting for the existence of large voids (see, e.g., Aarseth and Saslow 1982). The alternative picture of adiabatic fluctuations and pancake collapse (see, e.g., Doroshkevich et al. 1978 and references therein) faces difficulties due to: i) observed correlation functions, and ii) the absence of small-scale fluctuations in the microwave background.
Black Holes and the Fate of a Closed Universe
Authors: Kazanas Demosthenes
Published: June 2019

To date observations have not yet unequivocally determined whether the universe is open or closed. Although for the luminous matter Ω≲0.1, the possibility of existence of non-luminous matter (especially if the neutrino has a non-zero mass) leaves ground for considering that the universe may indeed be closed. In this case the universe is expected to recollapse and become again, at a time to, radiation dominated. Hence R(t) ∼ (tf−t)1/2 ∼ 1/T (t), where tf is the time of collapse to the singularity and T is the temperature. During this new radiation dominated era, a black hole of mass Mo will accrete at a rate

where ρ(t) ⋍ αT4 (t) and r(t) = 2GM(t)/c2. Eq (1) upon integration yields

(All subscript zero quantities are taken at t = to). Eq (2) shows that the mass of the black hole diverges when τo/τ ∼ Mo/4πro2 ρo cρo where τo = tf − to.
The Statistic Study of Lα Absorption Lines
Authors: Jian-Sheng Chen
Published: June 2019

The statistic studies of the absorbing forest in the spectra of high redshift QSOs will provide an important approach to the understanding of the physical properties of the absorbing materials. For this purpose a collection of uniform samples would be very important and urgent. It is very time consuming of the large telescopes to take the high resolution, high ratio-to-noise and wide coverage of wavelength of the QSO's spectra, therefore, an international collaboration in a uniform way would be very desirable.
Relativistic Stellar Dynamics
Authors: Contopoulos G.
Published: June 2019

Three main areas of relativistic stellar dynamics are reviewed: (a) Relativistic clusters, (b) Systems containing a massive black hole, and (c) Perturbed expanding Universes. The emphasis is on the use of orbit perturbations.
The Strong Equivalence Principle and its Violation
Authors: Canuto V. M. , Goldman I.
Published: June 2019

In this paper, we discuss theoretical and observational aspects of an SEP violation. We present a two-times theory as a possible framework to handle an SEP violation and summarize the tests performed to check the compatibility of such violation with a host of data ranging from nucleosynthesis to geophysics. We also discuss the dynamical equations needed to analyze radar ranging data to reveal an SEP violation and in particular the method employed by Shapiro and Reasenberg.
UV-Observations of Young Populous Clusters in the Large Magellanic Cloud
Authors: Geyer Edward H. , Cassatella Angelo
Published: June 2019

The young populous star clusters give evidence for the ‘explosive’ star formation in the Magellanic Clouds which took place in the time interval 5·106 yrs to < 108 yrs agoe. They are also key objects for the understanding of the formation of massive stellar clusters, because they are still situated close to their ‘birthplace’ in the parent galaxy and are dynamically not relaxed (Geyer et al. 1979). Their HRD-morphology shows most of the member stars in the upper Main Sequence range with only a few massive yellow and red supergiants. The lower massive stars are still in the pre-main-sequence evolution phase (‘T-Tauri state’), which cannot be observed at the MC's distances. Thus in the uv-spectral range the blue stars with (B-V) < 0.1 on the upper MS contribute to the uv-fluxes. In the optical spectral regions the bright ‘blue’ globular clusters seem not be embedded in remanent interstellar matter, though neighbouring loose stellar aggregates of similar age are in many cases surrounded by dense HII-regions. This rises the questions wether the starformation process in such massive clusters was so efficient that no remanent matter was left over, or was this material blown away by the uv-radiation of the numerous OB-member stars?
Red Giant Stars: Comparison of Observations and Theory
Authors: Mould Jeremy
Published: June 2019

Recent observations in both the field and the clusters of the Magellanic Clouds suggest a higher mass loss rate during or at the end of the asymptotic giant branch phase than previously supposed. Recent theoretical investigations offer an explanation for the frequency of carbon stars in the Clouds, but a rich parameter space remains to be explored, before detailed agreement can be expected.
Compact X-ray Sources in the IMC: Optical Identifications
Authors: Pakull Manfred W.
Published: June 2019

In addition to the bright sources LMC X-1–X-4 and A0538–66 fifteen EINSTEIN X-ray sources in the field of the LMC appear to be non-extended and have been accurately positioned with the HRI to make optical follow-up studies feasible. At least twelve of these are not associated with the LMC, including one Seyfert galaxy at redshift 0.076 and eleven late-type galactic foreground stars, some showing photometric variability typical for RS CVn and BY Dra stars.

The sources 1E 0524.5–7013 and 0543.8–6823 are identified with variable faint blue stellar objects, the latter has been observed to exhibit variable He II and Balmer emission lines being reminiscent of the low mass X-ray binary LMC X-2. The optical counterpart of LMC X-1 is a highly reddened (V=14.5, E(B-V)=0.61) 0 7–9 type giant with variable He II and N III emission. The IPC source 1E 0501.6–7037 is probably associated with the LMC OB emission line star SK-70 36 which shows ellipsoidal light variations with a period of 6.94 days.

Further possible identifications of IPC sources with stellar objects and globular clusters in the LMC are discussed. The results indicate that only a small fraction of the non-extended X-ray sources are associated with the LMC and that a gap in the X-ray binary luminosity function exists between 1036 and 1038 erg/s.

A full account of this work will be published elsewhere.
Molecules and Dust in the Magellanic Clouds
Authors: Israel F. P.
Published: June 2019

A variety of studies over the last decade has shown molecular hydrogen to be a major constituent of the interstellar medium both in our Galaxy and in other spiral galaxies (Morris and Rickard, 1982). Our Galaxy contains roughly M(H2) = 4 × 109 M⊙; between R = 2 kpc and R = 10 kpc the H2 mass is one to three times that of HI; at the solar circle about 12 per cent of the total disk mass is in the form of H2; most of this mass is in the form of several thousand giant molecular cloud complexes (GMCs) with sizes d > 20 pc and masses M(H2) > 105 MO (Cohen et al, 1980; Sanders, 1981; Dame, 1983). These GMCs mainly consist of clumps with much smaller scales of order a few pc or less (e.g. Bally and Israel, 1983). Apart from their contribution to the total mass of the galactic interstellar medium, molecular clouds are also important as they are the major birthsite of massive early-type stars (see the review by Habing and Israel, 1979).
Models of the Solar Photosphere
Authors: Avrett Eugene H.
Published: June 2019

This review summarizes the main properties of the available theoretical models of the solar photosphere and the semiempirical models based primarily on observed spectra in different wavelength regions. LTE and non-LTE semiempirical models are compared with LTE and non-LTE theoretical (radiative equilibrium) models calculated with and without convective energy transport. Atomic and molecular lines throughout the spectrum affect the model calculations in essential ways. The temperature-minimum region, considered as the upper boundary of the photosphere, is discussed in detail, in view of the substantial non-radiative cooling in this region. Results are shown to illustrate the relationship between average one-dimensional models and Nordlund's three-dimensional convection models.
Bright Features in the Intergranular Region
Authors: Suemoto Z. , Hiei E.
Published: June 2019

There are two kinds of bright threads in spectrograms of the Ca II II and K lines: the ones in the outer line wing are due to enhancements of the continuum inside granules, while the others in the inner wing are due to bright features in the intergranular regions.
Small Scale Motions Over Concentrated Magnetic Field Regions of the Quiet Sun
Authors: Dara H.C. , Alissandrakis C.E. , Koutchmy S.
Published: June 2019

Using a time sequence of filtergrams in the magnetically sensitive λ6103A CaI line (with circular polarization measurements), obtained with the SPO Vacuum Tower Telescope and the universal filter we mapped the line of sight velocity and the longitudinal magnetic field in three quiet solar regions. After elimination of the effect of the 5-minute photospheric oscillations we found in two regions of concentrated magnetic field no association with the line of sight velocity, while the third region was associated with small (<300 m/s) downflows.
Wave Heating in Magnetic Flux Tubes
Authors: Kalkofen Wolfgang
Published: June 2019

The solar chromosphere is identified with the atmosphere inside magnetic flux tubes. In the quiet sun, the layers of the low and middle chromosphere are heated by compressive waves with periods mainly between 2 min and 4 min. These long-period waves probably supply all the energy required for the heating of the quiet solar chromosphere.
Magnetic Flux Concentration by Siphon Flows in Isolated Magnetic Flux Tubes
Authors: Thomas John H. , Montesinos Benjamin
Published: June 2019

Siphon flows along arched, isolated magnetic flux tubes, connecting photospheric footpoints of opposite magnetic polarity, cause a significant increase in the magnetic field strength of the flux tube due to the decreased internal gas pressure associated with the flow (the Bernoulli effect). These siphon flows offer a possible mechanism for producing intense, inclined, small-scale magnetic structures in the solar photosphere.
Asymmetry of Emerging Flux Loops Caused by Radial Differential Rotation
Authors: Marik M. , Petrovay K.
Published: June 2019

Observational and theoretical arguments in favor of a supposed serious asymmetry of magnetic flux loops emerging through the convective zone are briefly summarized. Results from numerical models of flux tubes moving through a differentially rotating upper convective zone are presented (plane parallel geometry, SFT approximation). In most models, especially in the most realistic ones, a remarkable asymmetry of the flux loop is found. It is concluded that in the future observational effects caused by the asymmetry may be used to put quantitative constraints on subphotospheric rotation.
Excitation of Dynamo Modes
Authors: Hoyng P.
Published: June 2019

After the very suggestive results of the early days, the theory of the solar dynamo has now entered a period of re-evaluation. It is clear that our initial expectations have been too high. I shall review some of the recent attempts to formulate nonlinear and stochastic mode excitation theoretically. We now have evidence from synoptic observations that the solar dynamo features many periods. Periods both shorter and longer than the fundamental 22 yr cycle have been claimed. The phase stability of any of these periods is uncertain. The phase memory of the 22 yr period may be as short as ~ 10 cycles, but could also be much longer. Linear mean field theories permit only one marginally stable mode; they predict one period with an infinitely long phase memory. Attempts to explain multiperiodicity and finite phase memory effects fall in two categories:

(1). Nonlinear models. These feature a few nonlinearly coupled variables and may exhibit a multiperiodic or chaotic behaviour; (2). If the number of relevant variables is very high, then the dynamo behaves stochastically. It has been argued that this takes the form of stochastic excitation of many dynamo modes (overtones).
Variation of Even and Odd Parity in the Solar Dynamo
Authors: Brandenburg A. , Meinel R. , Moss D. , Tuominen I.
Published: June 2019

We have studied axisymmetric nonlinear αω-dynamo models taking the interaction between even and odd parities fully into account. It turns out that the dominating type of symmetry is not always determined uniquely, but it can vary on a very long time scale compared to the period of the magnetic cycle. In some cases the frequency of this long term variation is close to the beat frequency of the two solutions with purely dipolar and purely quadrupolar parity. The occurrence of a second frequency is typical of solutions whose trajectory describes a torus in the phase space. We argue that this finding is of relevance for understanding secular variations observed in the Sun. For example measurements of sunspots indicate that the spot number on the northern hemisphere at present exceeds the number on the southern hemisphere. The reverse seems to have been the case at the end of last century.
Self-Ordering of Photospheric Magnetic Fields
Authors: Lawrence J. K.
Published: June 2019

We model the evolution of photospheric field elements by treating them as mean field structures undergoing a nonlinear self-interaction mediated by much smaller-scale, convectively driven plasma turbulence. Distributed fields can gather into discrete, strong elements of a minimum permitted scale. Also studied are the transport of flux from dissolving elements and to growing elements via weak intermediate fields and the cancellation of adjacent emements of opposite polarity.
Some Emission Lines in WCE Stars have Nearly Constant Line Strengths
Authors: Brownsberger Kenneth R. , Conti Peter S.
Published: June 2019

We present empirical measurements of line strengths (Equivalent Widths-EW) of WCE stars (WC4-WC7). Our database presently includes approximately 50 emission lines stretching from the UV to the NIR. We have data for approximately 40 stars, but the spectral range is not complete for each star. At present, there are approximately 10-20 EW measurements for each line in the database. The lines used in the classification of the WC subtypes, along with a few others, show a dramatic dispersion in strength (as expected) within the WCE subtypes. Many other lines of carbon and oxygen ions indicate only a moderate range among the subtypes. We have found that there are several lines that show almost no dispersion in strength from WC4-WC7. These nearly constant lines can be used to give empirical estimates of the brightness ratio of the W-R to companion star in WCE + OB systems, and can also be used to estimate interstellar reddening. The similarity of line strengths among several C III and C IV emission features in WCE stars suggests that the ionization level in the wind is not fundamentally different among WC4-WC7 subtypes. Another parameter (e.g. C/He?) may have a substantial influence on those lines used for the WCE classification.
Physical Parameters of Inhomogeneities in Wolf-Rayet Winds
Authors: Robert C. , Moffat A. F. J. , Seggewiss W.
Published: June 2019

Time-resolved spectroscopy has revealed small, systematically varying features superimposed on the broad emission lines of WR stars. We believe that these structures are due to inhomogeneities of emitting wind material propagating with the general wind. Here we suggest a common, but still unknown, origin for the intrinsic variations observed in WR stars.
Emission Line Variations in γ2 Velorum
Authors: Taylor Mary Jane
Published: June 2019

In this paper, we present results of an intensive search for periodic variations in the strength of the Hell emission line of �2 Vel relative to the nearby continuum. The data were obtained in 1986 and 1988 using an automated optical system located at the Amundsen-Scott South Pole Station. Ten of the data sets have a time resolution between 2 and 3 minutes and consist of 2.3 - 20.4 hours of continuous photometry (Taylor, AJ, in press). Three of the data sets have a time resolution of about 1 minute and span between 1.2 and 6.5 hours.
Ring Nebulae Around Massive Stars
Authors: Chu You-Hua
Published: June 2019

Ring nebulae have been found around WR stars, OB and Of stars, and luminous blue variables. Ring nebulae are formed by the interaction between the central stars and their ambient medium via different combinations of stellar winds, ejecta, and radiation. The spectral properties of the nebulae can be used to diagnose the stellar properties, such as luminosity and effective temperature. Correlations between ring nebulae and their central stars may be used to check scenarios of stellar evolution.
G2.4+1.4: An Extraordinary Mass-Loss Bubble Driven by an Extreme WO Star
Authors: Dopita M.A. , Lozinskaya T.A.
Published: June 2019

The nebula, G2.4+1.4, is shown to be a highly reddened, photoionised, mass-loss bubble of very high excitation powered by WR 102, the most extreme oxygen sequence Wolf-Rayet star known. It lies at a distance of 3±1kpc, and is about 11 pc in diameter. The exciting star, contains neither hydrogen nor helium in its atmosphere, is losing mass at a velocity of 5530 km.s-1, and has the following properties: log (Tion) = 5.20±0.05; log (R/R⊙) = 0.05±0.20; log (L/L⊙) = 5.85±0.20. We conclude that the star is the ~20M⊙ core of a supermassive star (M ≤ 60M⊙) seen near the end of its life.
Warmers
Authors: Melnick Jorge , Heydari-Malayeri Mohammad
Published: June 2019

We present direct observational evidence showing that early type WR stars, and WO stars in particular, are exceedingly hot, and that their ionizing radiation is not fully trapped by their extended atmospheres. We show that extreme WR stars, or Warmers, are found in metal poor as well as in metal rich regions in accordance with theory. Images of HeIII regions around Galactic and Magellanic Cloud Warmers are shown.
Observational Aspects of Stellar Evolution in the Upper HRD
Authors: Leitherer Claus
Published: June 2019

Observational evidence strongly favors an evolutionary relation between Wolf-Rayet (WR) stars and stars with masses above ~ 10 M⊙. The galactic distribution of WR stars closely resembles the distribution of O stars both in the z-direction as well as in the spiral-arm pattern (Hidayat, Admiranto, and van der Hucht 1984, van der Hucht et al. 1988, Conti and Vacca 1990). Lundström and Stenholm (1984) found that the surface density of W R stars increases with decreasing distance from OB associations as well as from young open clusters. The fraction of WR stars in clusters turns out to be about the same as that of O stars. A large number of extragalactic WR stars is situated in giant H II regions, which also contain high numbers of very massive 0 stars (see, e.g., Walborn 1990 for 30 Doradus; Drissen, Moffat, and Shara 1990 for M33). Many WR stars are members of binary systems with well established parameters so that their masses can be determined directly. In several cases, WR-stax masses of M ≥ 10 M⊙ have been derived (Massey 1981, St.-Louis et al. 1987, Schulte-Ladbeck 1989).
The Stellar Association LH 99
Authors: Lortet M.C. , Testor G. , Schild H.
Published: June 2019

The stellar content of this stellar association, related to the supernova remnant N 157B = SNR 0538-691, was up to now unknown, except for three Wolf-Rayet stars and a few red supergiant candidates. A thorough study based on UBV photometry, spectra of 95 stars and nebular spectra will be described elsewhere (see also Schild et al. in these Proceedings).The outstanding properties of this region are :

A. the presence of a shell-shaped supernova, which dominates the thermal radio continuum. It is relatively faint in [OUI], strong in [Sil], [Fe 4658] and He II 4686. The expansion velocity reported by Chu and Kennicutt (1988) is 180 km/s. In addition, many extensions and filaments are found all over a wide area, and possibly there has been more than one supernova responsible.
A Program to Determine an Accurate Trigonometric Parallax for the Hyades Cluster
Authors: Van Altena W. F.
Published: June 2019

A list is presented of very probable Hyades cluster members that are suitable for an accurate determination of the cluster's trigonometric parallax.