bluuebunny/crossref_metadata_2025 huggingface dataset:
Remarks concerning the masses of horizontal-branch A stars
Authors: Davis Philip A. G. , Hayes D. S. , Philip Kristina D.
Published: June 2019

Studies are underway concerning the masses of horizontal-branch A stars. Hayes and Philip (1979) discussed masses determined for seven field HB stars using gravities and temperatures obtained from spectrophotometric scans. They found a mean mass of 0.6 M⊙ ± 0.4 for these stars. However, there was a strong trend of mass with temperature. In the present study four-color measures of over 150 FHB and BHB stars have been dereddened and plotted in the grid relating (b-y), c1 and log g, Teff (Philip and Relyea 1979). If one calculates a mean mass, again the figure of 0.6 M⊙ is obtained. A more detailed look at the data, however, reveals structure in the distribution of points in the various diagrams. A discussion of this result follows.
The H. R.-diagram of central stars of planetary nebulae
Authors: Schönberner D.
Published: June 2019

During the last years some progress has been made in the determination of temperatures of central stars of planetary nebulae (CPN). The main reasons are the successful deployment of space crafts which made the more temperature sensitive spectral region in the UV accessible, and the application of NLTE-spectral analyses (e.g. Mendez et al., 1981). Therefore, a re-examination of the H.R.-diagram of CPN's seems to be in order.
The atmosphere of subluminous B stars
Authors: Heber U. , Hunger K. , Jonas G. , Kudritzki R.P.
Published: June 2019

8 sdB stars have been analyzed for effective temperatures, gravity and helium content by means of LTE and NLTE model atmospheres (Heber et al., 1983). The analyses are based on the following observations:

1.)

B&C IDS spectrograms obtained with ESO's 3.6m and 1.5m telescopes (4250–4800å at 29 å/mm, or, 4000–5000å at 59 å/mm).

2.)

IUE spectra in low resolution (6å) through the large aperture.

3.)

Johnson and Strömgren colours, which are taken from the literature.
Circumstellar dust shells around WN10-11 and WC8-10 stars: An evolutionary sequence?∗
Authors: van der Hucht K.A. , Williams P.M. , Thé P.S.
Published: June 2019

In a recent IR photometric survey of late-type WC and WN stars, it was discovered that not only most WC8-10 stars have circumstellar dust shells, but that two extreme late-type WN stars also have strong IR excesses from circumstellar dust. The latter shells appear to have significantly different density distributions. In this paper the possibility of an evolutionary sequence is suggested.
The interaction of the supermassive object R136a with the interstellar environment
Authors: Feitzinger J.V. , Schmidt-Kaler Th.
Published: June 2019

R136a is the luminous object in the core of the 30 Dor nebula in the LMC, embedded in the extremely young star cluster NGC 2070 with the most recent star forming event less 106 yr ago. R136a-1 (V = 11.08) lies in the center of this cluster. The companion or foreground star R136a-2 (ca. 1.2m fainter than R 136a-1) 0′.5 apart does not impair the dominating role of R136a-1. The light distribution is strongly peaked to the center of R136a and disagrees completely with Moffat and Seggewiss's (1983) description and their interpretation as a dense core of a cluster (Chu and Wolfire, 1983). This is strenghtened by the UV observations (Cassinelli et al. 1981, Feitzinger et al. 1983, Savage et al. 1983): the spatial spread function of the IUE satellite is dominated by an object of extremely small ultraviolet extent, less than that of a gaussian with 1′.5. Speckle observations (Meaburn, 1982; Weigelt, 1981), are discordant in the interpretation of the faint background, but concordant in revealing the existence of a small bright component, with an upper limit of the diameter < 0.02 pc. This is also found, with somewhat lower resolution, by Chu (1934).
Concluding Remarks: Looking Ahead
Authors: Schatzman E.
Published: June 2019

The absence of concensus on several of the problems which have been discussed during the meeting is perhaps the best demonstration of the usefulness of the Symposium.
Expected Use of Lunar Range Data to Determine Modified Nutation Terms
Authors: Bender P. L.
Published: June 2019

The lunar laser range data from the McDonald Observatory in Texas have been used so far to determine major improvements in the lunar ephemeris and librations, to provide a new test of gravitational theory, and to determine single-day UT0 values on about 200 days during the period 1970-1974. The mean uncertainty in the UT0 values is 0.5 msec, and the smallest uncertainty is 0.2 msec (Stolz et al. 1976). The changes in the angular position of the moon with time are believed to be well enough known so that their uncertainty does not substantially degrade the accuracy of the UT0 values.
On the Ellipsoidal Distribution of Density in the Earth's Interior
Authors: Mescheryakov G. A. , Dejneka Y. P.
Published: June 2019

Density within the Earth is expressed by means of generalized Fourier series as a function of the coordinates of a point: its distance from the geocenter, colatitude, and longitude. The following data are used to obtain the coefficients of the series: the parameters of the Earth ellipsoid (assumed to be biaxial), the dynamical flattening of the Earth, the Stokes constants, and the density jumps at four surfaces according to seismological data.

The model of the Earth proposed by the authors is composed of five layers, the density in each layer being expressed as a function of the distance from the center of the Earth by a polynomial of fourth degree. To verify the model, periods of the fundamental modes of spherical and torsion oscillations are derived and compared with observations of the free oscillations of the Earth. The maximum difference is within the errors of the observed periods.
The Love Numbers of the Anelastic Earth
Authors: Zharkov V. N. , Molodensky S. M.
Published: June 2019

We calculate corrections to the Love numbers resulting from the small frequency-dependent variations in the shear modulus, μ, arising from anelasticity in the Earth. The corrections are of the order of a percent, which in some cases exceeds the observational error. We point out the possibility of using these corrections to study the Earth's anelasticity at long (tidal) periods.
Systematics of HII Rotation Curves
Authors: Rubin Vera C.
Published: June 2019

Systematic rotational properties of field spiral galaxies are presented, as a function of Hubble type and of luminosity. Within a Hubble type, radius, nuclear velocity gradient, rotation velocity, mass, and mass density increase with luminosity, while m/L is constant. At fixed luminosity, V(max), mass, density, and m/L decrease from Sa through Sc. These variations are so systematic that it is possible to display them on a single diagram.
Distribution and Motions of Atomic Hydrogen in Lenticular Galaxies
Authors: van Woerden Hugo , van Driel Wim , Schwarz Ulrich J.
Published: June 2019

We report the results of HI observations of eleven gas-rich SO/SOa galaxies with the Westerbork Synthesis Telescope. The majority of these galaxies have most of their hydrogen outside the optical body, in annular configurations with diameters ~2 times the optical. These outer gas rings are often clumped, incomplete, and in approximately circular motion. They may represent the remnants of primordial, often warped, gas disks; or they may have formed from gas (or dwarf galaxies) accreted recently. Optical spectra could discriminate between these possibilities.

A few objects have filled gas disks, and several have inner HI rings with radii ~0.4 × optical. Two objects have peculiar distributions suggesting, respectively, tidal effects and stripping. However, stripping by intergalactic gas appears not to be a major current process.
Global Stability Analysis of an SO Galaxy NGC 3115
Authors: Iye Masanori , Ueda Tatsuo , Noguchi Masafumi , Aoki Shinko
Published: June 2019

The global modal analysis is applied to a family of models which are consistent with recent dynamical data of NGC 3115. A halo component at least as massive as the disk component is required to explain the apparent lack of spiral structures in NGC 3115.
Velocity Structures in the Vertical Extensions of Spiral Arms
Authors: Feitzinger J. V. , Spicker J.
Published: June 2019

Yuan and Wallace (1973) explained the “Rolling motion” in galactic spiral arms by geometrical means as apparent, but not actual motions. Strauss and Poeppel (1976), however, could demonstrate, that these geometrical effects are not sufficiently large to produce the rolling motions. The aim of this investigation is to explain the remaining part of the rolling motion effect with the galactic fountain model (Bregman 1980).
Theories of Warps
Authors: Toomre Alar
Published: June 2019

The large-scale warps of disk galaxies remain a challenge for theorists. Recent speculations about their origins or longevity have tended to focus on the possible benefits of halos. After some remarks about modes, this review will do likewise. It will conclude that any applause even there can as yet be only scattered rather than thunderous.
Photometry, Kinematics and Dynamics of the Barred Galaxy NGC 5383
Authors: Athanassoula E. , Duval M. F.
Published: June 2019

NGC 5383 has often been used as a prototype of SB(s)b type galaxies, particulary in studies of gas flow. We have therefore set out to complement the existing data with surface photometry, velocity measurements in the bar and a dynamical model.
Simulations of Galaxy Mergers
Authors: White Simon D. M.
Published: June 2019

The last few years have seen a considerable amount of effort devoted to the problem of simulating the coalescence of galaxies. After a discussion of the merits and limitations of the N-body techniques that have been used, I summarise the insight this research gives into the mechanisms driving strong interactions in galaxy collisions and into the structure of the remnants such collisions produce.
Galaxy Formation: Some Comparisons between Theory and Observation
Authors: Fall S. Michael
Published: June 2019

Before theoretical ideas in this subject can be compared with observational data, it is necessary to consider the properties of galaxies that are likely to be relics of their formation. Most astronomers would agree that the list of important parameters should be headed by the total mass M, energy E and angular momentum J. Next on the list should probably be the relative contributions to these quantities from the disc and bulge components of galaxies and denoted D/B for the mass ratio. They can be estimated from the median (i.e. half-mass) radius R, velocity dispersion σ and rotation velocity v of each component, either through the virial theorem or through the luminosity L and an assumed value of M/L. As a first approximation, it is reasonable to suppose that galaxies of a given disc-to-bulge ratio or morphological type form a sequence with mass as the fundamental parameter. The comparison of theory with data is further simplified by considering the extreme cases of ellipticals, with D/B << 1, and late-type spirals, with D/B >> 1. The approach outlined below is to explore the consequences of relaxing in succession the constraints that E, J and M be conserved during the collapse of proto-galaxies. In this article I concentrate on theories that are based on some form of hierarchical clustering because the pancake and related theories are not yet refined enough for a detailed confrontation with observations.
The High Energy X-ray Spectra of Supernova Remnants
Authors: Pravdo Steven H. , Nugent John J.
Published: June 2019

We present the results of fitting an ionization nonequilibrium (NIE) model to the high energy (> 5 keV) X-ray spectra of the young supernova remnants Cas A and Tycho. As an additional constraint, we demand that the models simultaneously fit lower energy, higher resolution data. For Cas A, a single NIE component can not adequately reproduce the features for the entire X-ray spectrum because 1) the ionization structure of iron ions responsible for the K emission is inconsistent with that of the ions responsible for the lower energy lines, and 2) the flux of the highest energy X-rays is underestimated. The iron K line and the high energy continuum could arise from the same NIE component but the identification of this component with either the blast wave or the ejecta in the “standard” model is difficult. In Tycho, the high energy data rule out a class of models for the lower energy data which have too large a continuum contribution.
Radio Supernovae
Authors: Weiler K. W. , Sramek R. A. , van der Hulst J. M. , Panagia N.
Published: June 2019

Three supernovae have so far been detected in the radio range shortly after their optical outbursts. All are Type IIs. A fourth supernova, a Type I, is being monitored for radio emission but, at an age of approximately one year, has not yet been detected. For two of the supernovae, extensive data are presented on their “light curves” and spectra and models which have been suggested in the literature are discussed.
Radio and X-ray Emission from Newly Born Remnants
Authors: Salvati Marco
Published: June 2019

Radio and X-ray observations of SN 1979c and SN 1980k offer a unique opportunity of monitoring the transition from supernovae to remnants. By means of the two-frequency radio light curves, we test the hypothesis that these objects are surrounded by circumstellar matter, originated in a pre supernova wind, and derive the relevant parameters. Then we use the absorption-corrected light curves to test the various proposed models. SN 1980 k appears to be powered by a canonical shock, while SN 1979c is a good plerion candidate. An optical pulsar could still be detected at its location.
Neutron Star Cooling: Effects of Envelope Physics
Authors: Van Riper Kenneth A.
Published: June 2019

Neutron star cooling calculations are reported which employ improved physics in the calculation of the temperature drop through the atmosphere. The atmosphere microphysics is discussed briefly. The predicted neutron star surface temperatures, in the interesting interval 300 ≤ t (yr) ≤ 105, do not differ appreciably from the earlier results of Van Riper and Lamb (1981) for a non-magnetic star; for a magnetic star, the surface temperature is lower than in the previous work. Comparison with observational limits show that an exotic cooling mechanism such as neutrino emission from a pion-condensate or in the presence of percolating quarks, is not required, unless the existence of a neutron star in the Tycho or SN1006 supernova remnants is established.
Optical Observations of four Balmer-Dominated Supernova Remnants in the Large Magellanic Cloud
Authors: Tuohy I. R. , Dopita M. A. , Mathewson D. S. , Long K. S. , Helfand D. J.
Published: June 2019

We report the optical identification of four Balmer-dominated supernova remnants (SNRs) in the Large Magellanic Cloud. Both the Balmer-dominated spectra and the presence of a broad Hα component in one remnant can be understood in terms of a very high velocity non-radiative shock encountering gas which is partially neutral, as proposed originally by Chevalier and Raymond to account for the similar spectra of the galactic remnants, Tycho and SN1006. From a consideration of the optical and X-ray luminosities of the SNR with broad Hα emission, we infer that the fraction of neutral gas in the medium is ≲ 30%. Radio observations of the LMC remnants show that their surface brightnesses are anomalously low; this could be intrinsic to the supernova themselves, or a result of their environment. Finally, we argue that the four SNRs all resulted from Type I supernovae, in which case they are the first such remnants to be identified outside the Galaxy.
Keynote: Structure of the Universe
Authors: Oort J. H.
Published: June 2019

A clear keynote for our conference is given by the diagram shown in Figure 1. This year we can celebrate that it is just half a century ago that it was produced by Harlow Shapley and Adelaide Ames. This marvellous picture illustrates nearly all we know about the properties of the Universe, except its expansion. It can teach us practically all the lessons we are still learning today. Most prominent is the Virgo cluster. Also evident are structures on larger scale, such as the appendages on both sides of the cluster, spanning a total length of 20 to 30 Mpc.* They are the kernel of the Local, or Virgo, supercluster. The supercluster has a complicated structure, evident from the clumpiness in the distribution along its axis, but likewise from the arrangement of the galaxies in its environment. The centre of the local supercluster (the Virgo cluster) lies at a distance of about 20 Mpc. The supercluster probably extends somewhat beyond us. However, everything in the Shapley-Ames picture should be considered as connected with this one supercluster. Features marked A, B and C may be independent structures; A lies at a distance of roughly 50 Mpc; C, at a distance of ∼ 70 Mpc, lies similarly well outside the Local Supercluster. The strongly elongated feature B, with an average velocity of 1400 km s−1 and a dispersion of only 300 km s−1, appears also well isolated. All three are roughly 30 Mpc long, and may be considered as separate superclusters.
X-Ray Sources of Cosmological Relevance
Authors: Maccacaro T. , Gioia I. M.
Published: June 2019

The imaging and spectroscopic instruments onboard the Einstein Observatory (Giacconi et al. 1979) have been extensively used to study in detail the X-ray properties of a large variety of astronomical objects. In this paper we will briefly discuss some of the most relevant results on extragalactic astronomy obtained mainly with the Imaging Proportional Counter (IPC).
Search for Small Scale Anisotropy of the 3K Emission of the Universe
Authors: Berlin A. B. , Bulaenko E. V. , Vitkovsky V. V. , Kononov V. K. , Parijskij Yu. N. , Petrov Z. E.
Published: June 2019

One of the greatest mysteries of nature is the absence of any trace of the present structure of the nearby universe in its relict 3K emission.

If we live in an evolving world (which evolves from extremely smooth to extremely structural), our radio telescopes should see observable temperature variations of 3K in practically any world model.
The Southern Cluster Survey
Authors: Abell G. O. , Corwin Harold G.
Published: June 2019

We are searching for clusters of galaxies on photographs taken for the Southern Sky Survey with the U.K. Schmidt telescope at Siding Spring, and we are preparing a comprehensive catalogue of the southern clusters. The purpose is to extend the early cluster survey made from the Palomar Sky Survey (Abell 1958) to full-sky coverage. We are taking special pains to delineate those clusters in the new southern survey that as nearly as possible match those criteria set for the northern survey clusters to be included in a homogeneous statistical sample. It is our expectation, therefore, that there will be a homogeneous all-sky sample of clusters for studying the large-scale distribution of matter in the universe.
Further Investigations on Possible Correlations Between QSOs and the Lick Catalogue of Galaxies
Authors: Nieto J.-L. , Seldner M.
Published: June 2019

We analyze the different contributing factors in a previous study by Seldner and Peebles (1979) who found statistically significant evidence for a correlation between a list of 382 QSOs at |b| > 40°, δ > −23° and the Lick counts of galaxies (m < 19.0), namely, that there are on the average 1.45 ± 0.39 more galaxies within 15′ of a QSO than expected if QSOs were placed at random across the sky. Taking into account these different factors and using a larger sample of QSOs whose detection is not expected to bias our statistical results, we conclude that: i) There is no longer statistically significant evidence for an excess of Lick galaxies close to QSOs from our list considered as a whole. After removing the different possible biases, if there was any excess left in that previous study, it was rather due to radio QSOs and not to optical QSOs. This effect is marginal if we adopt a mean density of galaxies in a ring between 2° and 5°, and null if the mean density is taken between 1° and 2° from QSOs; ii) The whole correlation function w(θ) shows in general a hump between and 2°. This is either an off-set value or a maximum value preceding a slow decrease in w(θ) between and 5°. This feature seems to pertain more to high redshift QSOs (z > 0.4) and to radio QSOs than to optical QSOs. It seems slightly more pronounced at the polar galactic caps and at very low galactic latitudes; iii) Numerical simulations seem to indicate that the error bars determined by assuming that cell numbers are independent are slightly underestimated. They reproduce fairly well some features within 1° from the QSOs and suggest that the hump at would not be as unlikely as indicated by the error bars.
On the Origin of the Voids
Authors: Hoffman Yehuda , Shaham Jacob
Published: June 2019

In the past few years the large scale structure and dynamics of the galaxy distributions have been studied intensively, mainly by means of red-shift surveys. From these surveys it seems that the distribution of galaxies is characterised by large, empty voids of (20–40) h−1100 Mpc in diameter with a typical density contrast of δ ∼ - (0.7–0.8).
Condensations and Cavities
Authors: Occhionero F. , Santangelo P. , Vittorio N.
Published: June 2019

We present a unified algorithm which describes the non-linear growth 1) of condensations surrounded by cavities or 2) of cavities surrounded by condensations (i.e. ridges of higher density) in the Hubble flow. The main idealization is that of pressureless spherical symmetry (Tolman-Bondi solution); overall algebraic details and results for problem 1) are given in previous work (Occhionero, et al., 1981 a and b); results for problem 2) will be given elsewhere (Occhionero, et al., 1982).
Superclusters as Nondissipative Pancakes
Authors: Dekel Avishai
Published: June 2019

The formation of aspherical superclusters (SC's) is studied by 3-D N-body simulations that are confronted with the Local SC (LSC), and a simple model is developed. A nondissipative scenario, in which galaxies are formed from perturbations on smaller scales prior to the collapse of SC's, is found to be successful. It explains the disk-halo structure of SC's, their flattening and their low dispersions, which are nontransient because of the expansion along the long axes. The LSC has collapsed at z≤0.5. The large-scale velocity isotropy and the local 1-D infall indicate Ω<1. The correlation of galaxies on a few Mpc scales grows nonselfsimilarly due to recent pancaking rather than gradual clustering. This may be tested by the lack of clustering among objects at z>1.
The Motion of the Local Group of Galaxies with Respect to the Background of Galaxies
Authors: Davies R. D.
Published: June 2019

A measurement of the motion of the Local Group of galaxies through the Universe provides an indication of their peculiar motion relative to the Hubble flow consequent upon the gravitational influence of the local large scale mass inhomogeneities. This motion can be measured either relative to the cosmic microwave background at z ∼ 1000 or relative to the background or nearby (z ∼ 0.01) galaxies. The interpretation of published measurements is subject to some uncertainty. As an example, the Local Group motion derived from optical studies of nearby galaxies (Rubin et al. 1976) differs from that derived from radio frequency measurements of the dipole anisotropy in the microwave background. (Boughn et al. 1981, Gorenstein & Smoot 1981).
Dynamics of Some Remote Superclusters
Authors: Harms R. J. , Ford H. C. , Ciardullo R.
Published: June 2019

Redshifts of clusters of galaxies have been obtained in four regions of the sky selected as suspected rich superclusters at intermediate redshift (0.1 < z < 0.3). Measurements to date have detected the existence of several superclusters with dimensions up to 50 h−1 Mpc (h = H0/100 k/s/Mpc), irregular shapes, and containing as many as seven rich clusters in the richest supercluster. The velocity dispersions suggest some slowing of the Hubble flow internal to the superclusters. However, the inferred mass densities are low enough to prefer an open universe if the mass-to-luminosity ratios within the best-studied superclusters are comparable to the universal ratio.
Hot Accretion Disks and the High Energy Background
Authors: Kafatos M. , Eilek Jean A.
Published: June 2019

The origin of the high energy (X-ray and gamma-ray) background may be attributed to discrete sources, which are usually thought to be active galactic nuclei (AGN) (cf. Rothschild et al. 1982, Bignami et al. 1979). At X-rays a lot of information has been obtained with HEAO-1 in the spectral range 2–165 keV. At gamma-rays the background has been estimated from the Apollo 15 and 16 (Trombka et al. 1977) and SAS-2 (Bignami et al. 1979) observations. A summary of some of the observations (Rothschild et al. 1982) is shown in Figure 1. The contribution of AGN to the diffuse high energy background is uncertain at X-rays although it is generally estimated to be in the 20–30% range (Rothschild et al. 1982). At gamma-rays, in the range 1–150 MeV, AGN (specifically Seyfert galaxies) could account for all the emission.
Main Sequence Photometry of Kron 3
Authors: Rich R. M. , Mould J. R. , Da Costa G.S.
Published: June 2019

The globular cluster Kron 3 in the Small Magellanic Cloud presents an interesting opportunity to study stellar evolution in a population of intermediate age populous enough to contain many stars in short-lived phases of their evolution. The cluster lies approximately two degrees west of the body of the SMC and just outside the tidal radius of the Galactic globular cluster 47 Tuc.
R127: an S Dor Type Variable Intermediate Between Of and WN
Authors: Stahl O. , Wolf B.
Published: June 2019

On 1982 Jan. 9 a brightening of 0.75 mag of the OIafpe star R127 (=HDE 269858) was detected. Subsequently extensive photometric (optical and infrared) and high resolution spectroscopic (ground-based and IUE) observations covering a period of more than one year have been carried out. These observations have shown R127 to be a new S Dor variable which is hotter than any previously detected and studied variable of this class. For its maximum phase we derived the following basic parameters: Mbol = −10.6, Teff = 16000 K, R* = 150 R⊙. The stellar wind is characterized by a small mean velocity (v = 110 km s−1), a high mass loss rate (M = 6 · 10−5 M⊙yr−1), and a decelerated velocity field. The optical spectra show strong Balmer lines with P Cygni profiles. The He I lines changed within the one year period from strong P Cygni type lines to complex line profiles with extremely wide (FWZI = 3000 km s−1) shallow emission line wings. The IUE spectra are dominated by crowded absorption lines of singly ionized metals. A very complex shell phenomenon is indicated by the multiple substructure of these ultraviolet lines. We suggest that R127 is a massive (M > 60 M⊙) Of star evolving via a short-lived S Doradus phase to a late WN star.
UV Extinction in the 30 Doradus Nebula and the UV Energy Distribution of R136a
Authors: Savage Blair D. , Fitzpatrick Edward L.
Published: June 2019

The properties of ultraviolet interstellar extinction in and near the core of the 30 Doradus Nebula are studied. The pair method is employed using nine reddened stars from within 5′ (80pc) of the core and nine unreddened stars from a variety of locations in the large Magellanic Cloud. All of the 30 Doradus stars examined appear to be reddened by E(B-V) ⋍ 0.12 with an extinction law similar in wavelength dependence to those derived for the LMC by Koornneef and Code (1981) and Nandy et al. (1981). Several of the stars, including R136a, R145 and R147, are found to be additionally reddened by E(B-V) ⋍ 0.18 with an extinction law qualitatively similar in wavelength dependence to the law found in the Orion region. A two-component model, featuring a layer of “LMC foreground dust” which affects all of the stars and a deeper layer of “nebular dust” which affects some of the stars, provides the simplest explanation of the extinction properties. The 2200 Å extinction bump is present in both curves. The wavelength positions of the bump and the bump profiles, when normalized to a linear “background extinction”, are indistinguishable from the average Galactic bump. The strengths of the bumps, relative to E(B-V), are 20–30% weaker than for the Milky Way Curve.
The Magellanic Clouds and Planetary Nebulae
Authors: Peimbert Manuel
Published: June 2019

A review of the statistics, emission line intensities, central star fluxes, radial velocities and chemical compositions of PN in the MC is given. From these data a discussion is made of: a) the distance scale, b) the envelope mass, c) the comparison between the observed chemical abundances and those predicted from stellar evolution models and, d) the effect that intermediate mass stars have on the chemical evolution of the MC and our galaxy.
Solar Oscillator Strengths as a Diagnostic Tool
Authors: Gurtovenko E. A. , Kostik R. I. , Rutten R. J.
Published: June 2019

We briefly review the Kiev program for determining oscillator strengths of Fraunhofer lines from the optical solar spectrum, which has recently resulted in a compilation of solar gf-values for 1958 lines from 40 chemical elements (Gurtovenko and Kostik 1989). These gf-values were determined empirically by fitting solar lines using standard plane-parallel LTE modelling. Errors in this modelling propagate into the gf-values; reversely, the deviations in the latter may serve as diagnostics of the modelling and thus of spectral line formation in the solar photosphere. For a small subset, comparison with reliable laboratory data can be made; for other lines there is information in the differences between fits of the line area and of the line depth.
Theoretical Aspects of Small-Scale Photospheric Magnetic Fields
Authors: Schüssler M.
Published: June 2019

The state of theoretical description of small-scale concentrated magnetic fields in the solar photosphere (excluding oscillations and wave propagation) is reviewed with emphasis on work done since 1982. The processes which probably lead to the formation of strong fields (flux expulsion, convective collapse) are discussed in some detail and the present understanding of the subsequent (quasi-)equilibrium state is summarized. We consider in particular the magnetic and thermal structure of the basic magnetic flux concentrations (magnetic elements) and stress the importance of radiative transfer effects, e.g. the horizontal heat exchange with the surroundings and the effect of radiation from the hot bottom and walls on the upper layers. Velocity fields within and around magnetic flux concentrations are discussed with emphasis on shift and asymmetry of the observed StokesV-profiles which have recently been understood in terms of a downflow in the immediate vicinity outside magnetic structures. Reconnection and instabilities are considered as possible destruction processes for magnetic elements.
Nonlinear Dynamo Modes and Timescales of Stellar Activity
Authors: Belvedere G. , Proctor M. R. E.
Published: June 2019

A simple mean-field model of a nonlinear stellar α-ω dynamo is considered, in which dynamo action is supposed to occur in a spherical shell, and where the main nonlinearity retained is the influence of the Lorentz force on the zonal flow field. The equations are simplified by truncating in the radial direction, while full latitudinal dependence is retained. The resulting nonlinear p.d.e.'s in latitude and time are solved numerically, and it is found that while regular dynamo wave type solutions are stable when the dynamo number D is sufficiently close to its critical value, there is a wide variety of stable solutions at larger values of D. Furthermore, two different types of dynamo can coexist at the same parameter values. Implications for fields in late-type stars are discussed.
Helium in Wolfrayet Spectra(∗)
Authors: Andrillat Y. , Vreux J.-M.
Published: June 2019

The observation of Helium lines in the near-infrared proved to be a powerfull tool to investigate the Wolf-Rayet stars and more particularly the WN.
Intrinsic Variability of Wolf-Rayet Stars from an Observational Point of View
Authors: Moffat Anthony F. J. , Robert Carmelle
Published: June 2019

Evidence is mounting that the dominant random component of variability in single WR stars can be explained by one common phenomenon: stochastic formation, propagation and decay of density enhancements in the winds.
(Intrinsic) Variations of Wolf-Rayet Stars
Authors: van Genderen A.M. , Verheijen M.A.W. , van Kampen E. , Robijn F.H.A. , van der Heiden R. , van Esch B.P.M. , Greidanus H. , le Poole R.S. , Reijns R. A. , van der Hucht K.A. , Schwarz H. E. , de Loore C.W.H. , Kuulkers E. , Spijkstra L.
Published: June 2019

Twenty - two Wolf-Rayet stars (12 of type WN and 10 of type UC) were observed in the years 1986-1990 with the VBLUW photometer of Walraven. Eight (WC and WN) objects appeared to be constant. Five of the in total 14 variable objects will be discussed in the present paper: UR46 (WN3 pec), WR50 (WC6+a), WR55 (WN8), WR86 (WC7) and WR123 (WN8).

Simultaneous spectroscopy is made for WR46 and WR50. These results will be also discussed in short.
Gyroscopics as a Means of Demonstrating Rotational Instability in Stars
Authors: Sastroamidjojo M.S.A.
Published: June 2019

Light-traces of a light bulb fixed on top of the stem of a spinning top were recorded to simulate rotation. It was found that with dissipation of energy the rotational frequency did not decrease monotonically, but showed ‘quasi-periodic’ sequences.
New Wolf-Rayet Binaries
Authors: Niemela Virpi S.
Published: June 2019

Preliminary radial velocity orbits are presented for three binary systems containing Wolf-Rayet stars, namely Sk-71° 34 in the LMC, and WR8 and WR98 in our galaxy. Sk-71° 34 is found to be a WN3 + O6 double-lined binary with an elliptic orbit of period about 34 days. WR8 and WR98 both have WN type spectra with carbon lines. In WR8 the N and C lines appear to move in antiphase, while in WR98 all emission lines have the same orbital motion.
Massive Contact Binary Systems
Authors: Leung Kam-Ching
Published: June 2019

In recent years very massive single stars have been found to be upward of 90 M⊙. Massive contact binary systems have been found among the early-type systems, but their masses are far less than those reported for single stars. The most massive component found is about 60 M⊙.

It is generally believed that no late-type very massive stars have been detected (Humphreys and Davidson). This may be due to the large amount of mass loss from stellar wind. Recently, several extremely long-period late-type binary systems have been found to be contact systems. Two systems, UU Cnc and 5 Cet, have their primary components with masses exceeding 40 M⊙, and K spectra. This result tends to suggest that close or interacting binary stars may be able to preserve the mass loss from stellar wind within the binary systems.
The Light Curve of V444 Cygni
Authors: Hamann W.-R. , Schwarz E. , Wessolowski U.
Published: June 2019

In order to synthesize the eclipse light curve of V444 Cygni, we adopt the following model. The O star revolves round the WR star still within the outer regions of its extended atmosphere. The O star shadows a distinct volume of the WR atmosphere which thus cannot contribute to the total flux seen by the observer. On the other hand, additional radiation emerges from the surface of the O star. Its contribution to the total flux is more or less diminished by absorption when the rays pass through those parts of the WR atmosphere which lie between the O star and the observer. The WR atmosphere is given by our usual models (cf. Hamann and Schmutz, 1987; Wessolowski et al, 1988).
Spectroscopic CCD Study of the Two-Day WN5+O8V Binary CX Cep
Authors: Lewis David , Moffat Anthony F. J. , Robert Carmelle
Published: June 2019

After CQ Cep, the system CX Cep has the shortest orbital period known among Galactic WR+O binaries. However, no definitive spectroscopic study is yet available for CX Cep, probably because of its relatively faint magnitude (B ≈ 13). We have therefore obtained and analyzed some 60 CCD spectra (3700-4900 Å, S/N ⋍ 100, 5 Å/2 pixels) in August and October 1987.
Wolf-Rayet Stellar Wind Theory
Authors: Cassinelli J. P.
Published: June 2019

Two possible solutions to the Wolf-Rayet wind momentum problem are discussed: purely radiation driven wind theory, with multi-line effects, and Luminous Magnetic Rotator theory. Several recently developed radiative processes for enhancing M or v∞ are described, and it is concluded that only the winds of rather hot luminous Wolf-Rayet stars could possibly be driven by radiation. These stars should show evidence of acceleration at large radial distances. For the rapid rotators, it is possible to drive a dense equatorial outflow. Limits are discussed regarding the needed surface magnetic fields. With this model, the wind momentum problem is solved in a piece-wise fashion by having the large radio flux of Wolf-Rayet stars come from the equatorial zone and the broad P Cygni lines, arising in the polar wind. The Luminous Magnetic Rotator model can also be tested through observation, primarily through spectropolarimetry.
On the Chemodynamics of NGC 6888
Authors: Esteban C. , Vilchez J.M.
Published: June 2019

We present preliminary results on an extensive spectroscopical study of the WR Ring nebula NGC 6888. The observations combine high spatial (1.5 arcsec/pixel) and spectral resolution (30 to 50 km s–1) covering most of the optical range - λλ 3600 to 6800 å- at 3 different slit positions along the major axis of the nebula. The spectra of the central parts give an emission system with three different velocities: a) VLSR=-64 km s–1, b) VLSR=+18 km s–1, and c) VLSR=+78 km s–1. Assuming that NGC 6888 is in fact an expanding bubble of gas, as demonstrated by Marston and Meaburn (1988), we can identify components a) and c) as those moving towards us and receeding parts of the shell, while b) could be related to the ambient interstellar ionized gas outside the bubble. We have isolated the spectrum for each component in order to analyse the ionization structure and excitation mechanism, as well as to derive their physical conditions and chemical abundances. The use of diagnostic diagrams indicates that the nebula is basically photoionized, without any significant contribution of shock excitation in the zones studied. The ambient interstellar component shows a spectrum typical of an H II region with nearly solar abundances. In the case of the bubble components, their spectra produce [N II]/Hα line ratios which are outside the H II region box, and entering the extended planetary nebulae locus, suggesting a contribution of ejected nitrogen in the bubble. This fact is evident from the abundance analysis we have performed, finding that, with respect to the values quoted for the ambient gas, the O/H is deficient by a factor 4, N/H is 2.5 times higher, and helium is enhanced by a factor 2. These quoted values clearly indicate that a substantial fraction of the gas in the bubble is processed material ejected from the central massive star.
Metallicity Effects in Massive Star Evolution and Number Frequencies of WR Stars in Galaxies
Authors: Maeder André
Published: June 2019

The results of new grids of models of massive stars with metallicities Z = 0.002, 0.005, 0.020 and 0.040 and mass loss rates depending on Z are shown. When integrated over the mass spectrum, the models enable us to predict number ratios, such as WR/O, WC/WN, WNE/WR, WNL/WR, WCE/WR, WCL/WR, WO/WR as a function of Z in galaxies.

Comparisons between models and observations in galaxies are made and show, as was suggested by Maeder, Lequeux and Azzopardi (1980), that the effects of metallicity on the mass loss rates are the prime agent responsible for the different distributions of massive stars in galaxies.
Convectively Generated Turbulent Pressure: A Possible Cause for η Car - Type Shell Ejections
Authors: Kiriakidis M. , Langer N. , Fricke K.J.
Published: June 2019

A selfconsistent hydrodynamic calculation of a very massive star (MZAMS = 2OOM⊙) including turbulent pressure and energy has been performed. In the contraction phase after core hydrogen exhaustion, the star moves towards cool surface temperatures in the HR diagram (cf. Fig. 1). Consequently, (at Teff ⋍ 8000K) an envelope convection zone developes, and its inner boundery moves inwards with time. First, the envelope remains in hydrostatic equilibrium, with radiation pressure correspondingly decreasing as turbulent pressure increases (gas pressure is small). However, due to the fact, that the gradient of the turbulent pressure is directed inwards at the bottom of the convective zone, this part of the star rapidly contracts. Due to the released contraction energy, the luminosity locally exceeds the Eddington-luminosity. It cannot be transported outwards by convection in the upper part of the convection zone, where convective energy transport is inefficient (▽c ⋍ ▽r) . Thus, the local super-Eddington luminosity leads to the ejection of the overlying layers.
New Results in Evolution in the Upper HRD
Authors: Staritsin E.I.
Published: June 2019

A theoretical interpretation of the observed upper luminosity limit is suggested here. Staritsin (1989) considered the core hydrogen and helium burning stages in a 64 M⊙ star. Mixing in a semi-convection zone in a diffusion approximation (Staritsin, 1987) and mass loss by stellar wind (de Jager et al., 1988) were taken into account. During MS evolution the star looses half of its initial envelope. After MS evolution an intermediate convective zone appears. The hydrogen content in the shell source increases. As a result, the star burns helium in its blue supergiant stage. After the hydrogen content in the envelope has decreased to 10% of its mass, the star looses mass with Wolf-Rayet mass loss rates according to de Jager et al. (1988). The star has a WR character during 5% of its full life time.
The Distance to HD 50896 (EZ CMA)
Authors: Schmutz Werner , Howarth Ian D.
Published: June 2019

The WN5 star HD 50896 lies in the same sightline as the open cluster Cr 121. In order to investigate the possibility of cluster membership, we observed the interstellar Na D lines in the spectra of HD 50896 (=EZ CMa, =WR6) and stars in its neighbourhood (on the plane of the sky) at high spectral resolution (R=80,000 and 105,000). The observations were obtained with the 1.4-m coudé auxiliary telescope and the coudé echelle spectrograph of the European Southern Observatory.

From the strengths and velocity structure of the interstellar features it is immediately clear that HD 50896 is not a member of Cr 121; rather, it is a background object. A comparison with spectra of other background stars shows that the line of sight towards HD 50896 is very similar to those of HD 51854 (B1 V) and HD 50562 (B3 III). From intermediate-band and Hβ photometry the distances to these two B stars are 1.75 kpc and 1.95 kpc, respectively. The most red-shifted absorption component in the spectrum of HD 50896 is displaced only slightly more than that of HD 51854, and a little less than that of HD 50562. We conclude that the the most probable distance to HD 50896 is 1.8 kpc.
A Wolf-Rayet Cluster in IC 4662
Authors: Richter O.-G. , Rosa M. R.
Published: June 2019

An imaging and spectroscopic survey for WR stars in IC 4662 revealed the presence of a cluster consisting of a mix of about 10 WN 7-8 and WC 5 stars plus the equivalent of some 5 OV stars at a projected distance of about 100 pc from the cluster core of the bright central H ii complex.
The Determination of Absolute Magnitudes from Proper Motions
Authors: Luyten W. J.
Published: June 2019

A brief review is given of the several ways in which stellar motions may be used statistically. In the case where the motions of all stars shown on plates of certain regions are measured these are generally used to determine kinematical relations in the Galaxy and only secondarily for the estimation of luminosities; when motions are measured for special groups of stars the solar motion is first determined and then used for the calculation of distances and luminosities.
Absolute Calibration of Stellar Temperatures
Authors: Kienle H. , Labs D.
Published: June 2019

The scale of effective temperatures Teff is based on observed absolute radiation temperatures Tr, which are defined by Planck's radiation law

where TAu designs the absolute temperature of the gold point. A relative scale of radiation temperatures can be derived from spectrophotometric comparisons with a standard star. The absolute calibration of the standard star (α Lyr or Sun) demands a careful comparison with a standard radiation source of well known spectral energy distribution (Black Body or Synchrotron). With ground-based observations atmospheric extinction is to be taken into account; with extraterrestrial observations detectors may be used which are absolutely calibrated in a radiation laboratory under space conditions.
Remarks on the Photometric Criteria of Choice of the Standard Stars
Authors: Golay M.
Published: June 2019

We propose, in several tables, a number of stars selected to be observed both by photometrists, spectroscopists, astrometrists. Properties of selected stars are discussed.
Design and Fabrication of Large CCDs for the Keck Observatory DEIMOS Spectrograph
Authors: Stover R. J. , Brown W. E. , Gilmore D. K. , Wei M.
Published: June 2019

The Keck II Deep Imaging Multi-Object Spectrograph (DEIMOS) is a general purpose, faint object, multi-slit, double-beam spectrograph which offers wide spectral coverage, high spectral resolution, high throughput, and long slit length on the sky. This powerful instrument will be the principal optical spectrograph on the Keck II telescope. DEIMOS is optimized for faint-object spectroscopy of individual point sources, low-surface-brightness extended objects, or widely distributed samples of faint objects on the sky. To obtain high resolution (∼ 1 å) and wide spectral coverage (up to 5000 å) the spectrograph uses wide angle cameras and large CCD detectors with many pixels.

This paper describes some of the work being carried out to obtain the CCD detectors required for the DEIMOS spectrograph. In addition, results are presented on the fabrication and characterization of a 4k × 2k three-side buttable CCD produced by Orbit Semiconductor, a silicon foundry in San Jose, California. This CCD was fabricated to test the ability of Orbit to produce high quality scientific CCDs with the characteristics required for detectors to be used in DEIMOS and other optical instruments of the Keck Observatory.
CCDs in Active Acquisition Systems
Authors: Blecha A.
Published: June 2019

The use of CCD detectors as elements of an active acquisition system is reviewed. In such systems, the CCD image acquisition, data-analysis and the instrument and telescope controls are no longer separated elements whose actions are coordinated by an astronomer and/or operator, but are parts of a global system. The interaction between incoming data (nature of the object, registered flux, current PSF and atmospheric transmission), observer's requirement (S/N, spatial and temporal resolution) and forthcoming CCD exposure characteristics (CCD preparation, exposure time, read-out parameters) is examined. The requirements for the CCD electronics, data acquisition system are evaluated and examples of recent application in imaging, spectroscopy, photometry and auxiliary equipment are given. An attempt is made to analyze future technological trends and possible bottlenecks in such systems and to propose simple rules to adopt when designing CCD hardware and software.
Spectral Classification by Array Detectors
Authors: Corbally C. J.
Published: June 2019

This paper presents the principles, the techniques, and some of the astrophysical potential of spectral classification in the era of array detectors.