bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheres of Central Stars
Authors: Hummer David G.
Published: June 2019

This review begins with a brief summary of atmospheric models that are of possible relevance to the central stars of planetary nebulae, and then discusses the extent to which these models accord with the observations of both nebulae and central stars. Particular attention is given to the significance of the very high Zanstra temperature implied by the nebular He II λ4686 Å line, and to the discrepancy between the Zanstra He II temperature and the considerably lower temperatures suggested by the appearance of the visual stellar spectrum for some of these objects.
Peculiar Central Stars and Related Objects
Authors: Lutz Julie
Published: June 2019

Results are presented of a spectroscopic survey of sixteen peculiar central stars (i.e., central stars which have absorption spectra and continuua which are too cool to account for the superimposed emission line spectrum). Classifications on the MK system are presented for the absorption spectra. Intensities relative to H are presented for some of the strongest emission lines. The relationships between peculiar central stars and other types of emission line objects such as Be stars, symbiotic stars and P Cygni stars will be discussed. Three interpretations for peculiar central stars will be considered: 1) Some of them are binary nuclei of planetary nebulae, 2) Some of them are manifestations of the protoplanetary nebula phase, 3) Some of them are not related to planetary nebulae. (Paper will appear in Astronomy and Astrophysics.)
Morphology of Planetary Nebulae
Authors: R. Capriotti Eugene
Published: June 2019

When we look at planetary nebulae, we are by definition looking at similar objects and yet, the pictures which we exhibit show many dissimilar features. In fact, individual planetary nebulae have names that are associated with their peculiar features. There are, for example, the Helix, the Dumbbell, the Ring and the Eskimo.
The Filamentary Structure of the Ring Nebula
Authors: Goad L.E.
Published: June 2019

Image-tube photographs taken through narrow-band interference filters have been used to obtain monochromatic surface brightnesses of the Ring Nebula (NGC 6720) in the strongest emission lines of H I, He I, He II, [N II], [O I], [O II], [O III], and [S II]. These data have been used to analyze the spatial distribution of the various ionized species within the nebula. The bulk of the observed emission is shown to arise from a network of neutral filaments whose inner surfaces are ionized by the incident stellar radiation. The filamentary network is embedded in a low-density, high-temperature medium which is the source of most of the observed high-excitation lines. The ionization structure of several prominent filaments is examined in detail and comparisons are made to recent ionization structure calculations.
Dynamical Effects of Radiation Pressure in Evolved Planetary Nebulae
Authors: Tarter C.B. , Weisheit J.C.
Published: June 2019

We have investigated the dynamical effects of radiation pressure occurring in evolved planetary nebulae, for a wide range of central star and nebula parameters. Detailed model atmosphere calculations of the incident stellar flux were used to determine the temperature, ionization structure, and radiative acceleration throughout the nebula. Our computations included the effects of dust, a provision for charge exchange reactions, and all bound-bound, bound-free, and free-free processes that contribute significantly to the total radiation pressure. We have estimated the effects of the radiative force on nebular condensations and, as an example, have applied the results to the problem of the numerous radial filaments in NGC 7293. This work was supported by the U.S. ERDA under contract No. W-7405-Eng-48.
Are Light DA White Dwarfs the Progenitors of Planetaries?
Authors: Finzi Arrigo
Published: June 2019

According to a model presented elsewhere the progenitors of plane-taries are fully degenerate stars with hydrogen-rich outer shells and internal temperatures lower than those of observed white dwarfs. Apparently, these stars have gone through the white dwarf stage and evolved into invisible black dwarfs. This suggests that some among observed white dwarfs may be stars with hydrogen-rich envelopes that have still to go through the planetary stage. Tentatively, we identify these stars with light white dwarfs of DA spectra and consider possible tests of this tentative identification:
A Single Star Model for V 1016 Cygni
Authors: Ahern F.J. , FitzGerald M.P. , Marsh K.A. , Purton C.R.
Published: June 2019

We present a model of the emission object V1016 Cygni consistent with the current optical, infrared and radio observations. V1016 Cygni is 4.2 ± 1.0 kpc from the sun. It was originally an M star which ejected ∼0.017 M0 at 35 kms"1 over a period of ∼600 years producing a neutral nebula with an r"2 density distribution. This process ceased in 1961.3 ±3.0 when the nebula detached from a remnant hot core (T> 80,000K, R< 1.5 Rg). By 1964 0.1 ± 0.3 the nebula was ionized by the UV radiation from the core, producing the observed emission line spectrum. The infrared energy excess comes from two dust components of M000°K and ∼250°K, which absorb UV photons from the star. The dust is concentrated into clumps which 1) provide high density areas on their inner side, allowing strong [OHI] X4363 to remain; 2) shield the regions on their outer side permitting low excitation lines to be present; 3) explain the observed emission line structure. A stellar wind of 105 km/s helps to keep the centre of the ejected nebula hollow. We suggest V1016 Cygni is an example of a low mass planetary nebula in the formation stage.
Planetary Nebulae and White Dwarfs
Authors: Weidemann V.
Published: June 2019

The present-day birth rate of planetary nebulae, 5·10−12 PN/pc3yr according to Cahn and Wyatt (1976), seems somewhat high compared to white dwarfs, for which a redetermination, including the statistics of Sion and Liebert (1977), yields 2·10−12 WD/pc3yr to within a factor of two. However, an increase of the distance scale for PN by a factor of 1.3 compared to Seaton (1968) - necessary in order to shift the extremum of PN radial velocities to the distance of the galactic center (9 kpc), and to increase the luminosities of the central stars from the position given by Pottasch et al. (1977) to a minimum value compatible with evolutionary constraints (Weidemann, 1977a) - brings birth rates of PN and WD into almost complete agreements.
Symposium Conclusions II
Authors: Field George B.
Published: June 2019

Dr. Osterbrock has given a comprehensive summary of the Symposium. I will discuss a few topics which seemed particularly interesting to me as a non-specialist: dust, the fate of pre-planetary ejecta, and inhomogeneities. Let me begin by describing a simple model of the planetary nebula (PN) phenomenon, which is suggested by the discussions we have heard at this Symposium, and which provides the framework for my other comments.
The structure of the Hercules supercluster
Authors: Tarenghi M. , Tifft W. G. , Chincarini G. , Rood H. J. , Thompson L. A.
Published: June 2019

Counts by Shane and Wirtanen detected a cloud of Galaxies - the Hercules Supercluster - centered at about α = 16h02m; δ = 17°00m. It is unclear whether there is a physical connection with another cloud located to the south for which no radial velocities are yet available and with the system A2197/A2199 located to the north. the latter is at slightly smaller redshift (velocities between 8000–11,000 km sec−1) than the Hercules cluster.
Superclustering of galaxies
Authors: Kalinkov M. , Dermendjiev V. , Staikov B. , Kaneva I. , Tomov B. , Stavrev K.
Published: June 2019

A new type of catalogue of extragalactic objects is nearing completion in our department. the catalogue is on magnetic tape and is a compilation of data for galaxies and cluster of galaxies, together with references, and for counts of galaxies. At present this Metacatalogue contains about 3 × 105 entries - Abell and Zwicky clusters, Zwicky galaxies, Lick counts, Jagellonian counts and some others. the first two files of the catalogue can be obtained on request from the Centre de Données Stellaire at Strasbourg.
Quasars and Cosmological Evolution
Authors: Schmidt Maarten
Published: June 2019

The first evidence that quasars exhibit a non-uniform distribution in the universe was obtained ten years ago from a sample of 33 quasars in the 3CR catalogue. Much larger samples of radio quasars are now available and we will discuss the results in terms of an exponential decrease of quasar numbers with cosmic time. Only a few samples of optically selected quasars exist. We will show that their counts indicate a non-uniform space distribution, even if the redshifts are non-cosmological.
The internal structure of protoclusters and the formation of galaxies
Authors: Doroshkevich A. G. , Saar E. M. , Shandarin S. F.
Published: June 2019

We give a short review of the general picture and main features of the formation of galaxies and clusters of galaxies on the basis of the adiabatic theory. Detailed discussions of these questions are published in references 1–6. Some related problems of the formation and development of large scale structure in the Universe according to the same theory are considered in Zeldovich's report.
Evidence for the gravitational instability picture in a dense Universe
Authors: Davis Marc
Published: June 2019

The statistical nature of the galaxy distribution is in a sense remarkably simple. the two-point correlation function ξ(r), which measures the count of galaxies at separation r in excess of that expected for a random distribution, varies as ξ∝;r−1.8 for ξ>1(r ≲15 Mpc). At larger separations ξ apparently decreases more rapidly. the power law behavior is observed in different galaxy catalogs of varying depth and positions in the sky. What is the explanation of this universal behavior of ξ(r), and what do correlation functions tell us about the initial conditions at the recombination epoch and/or the value of Ω?
Brightest Stars in Galaxies as Distance Indicators
Authors: Sandage Allan
Published: June 2019

The current status of the absolute magnitude calibration of the brightest blue and red supergiants in galaxies of different absolute magnitudes shows trends of M(star) with M(parent galaxy). Red supergiants show a more shallow correlation than the blue stars for galaxies brighter than MB = −14. For fainter galaxies, the red supergiant method appears to become totally degenerate.

Four areas of application of the brightest star data are discussed as (1) determining MB of the Eddington limit to be ∼−10 for blue supergiants, (2) calibration of MB(max) = −20.0±0.4 for type I supernovae, leading to a Hubble constant of HO = 43±10 km s−1 Mpc−1, (3) detection of the deceleration of the cosmological expansion by the Local Group leading to a Local Group mass of 4×1011 M⊙ and a mass-to-blue light ratio of 3, and (4) use of the brightest stars to map the Virgo cluster velocity perturbation of the Hubble flow.
A Stellar Content Study of NGC 2403 with the automated Plate Scanner
Authors: Manley Thomas R.
Published: June 2019

In this poster we illustrate how the Minnesota Automated Plate Scanner (APS) is being used to study the luminous stellar content of NGC 2403. Presented are a brief description of the APS, examples of photometric calibration, separation of stellar and non-stellar images, and a preliminary color-magnitude diagram. The eventual goal is to study the evolution of massive stars via color-magnitude diagrams, luminosity functions and star formation rates.
IRAS Observations of the Cool Galactic Hypergiants
Authors: Stickland D. J.
Published: June 2019

It is still a matter for some debate as to how far the most massive stars ever get towards the right-hand side of the HR diagram during the course of their evolution. The apparent absence of very luminous red stars suggests either that stars never reach this region at all, or that if they do, their sojourn there is very brief indeed. If the latter is the case, one might expect to see an increase in mass-loss activity with luminosity among the brightest stars that we actually do see - the cool galactic hypergiants. An attempt has been made to search for one of the signatures of mass-loss - thermal reemission from ejected dust - using recently released data from the InfraRed Astronomical Satellite (IRAS).
The absorption feature at 1920Å in the spectra of early-type supergiants in the Small Magellanic Cloud
Authors: Morgan D.H. , Nandy K. , Thompson G.I.
Published: June 2019

The 1600–2500Å spectra of many early-type supergiants are dominated by a broad depression of the continuum near 1920Å. This depression, often called the 1920Å feature, was detected in S2/68 (TD-1) spectra of early B stars (Thompson et al. 1974) and was shown to be strongly luminosity dependent. It was also shown that its profile could be matched by the cumulative effects of FeIII absorption lines.
Voyager Observations of Hot Luminous Stars
Authors: Polidan Ronald S. , Stalio Roberto
Published: June 2019

This is a progress report on a study of the far-UV spectra of hot stars observed with the Voyager ultraviolet spectrometers (UVS); we discuss UV flux distribution and variability of a set of early type high luminosity stars.
Parameters of Wolf-Rayet Stars
Authors: Conti Peter S.
Published: June 2019

Wolf-Rayet (W-R) stars are objects with strong emission lines in the optical region due to a substantial stellar wind. They are found among the extreme Population I stars which are the topic of this Symposium and also this talk, and as central stars of planetary nebulae which I will not discuss here. The mass loss rates, Ṁ, are typically several 10−5 solar masses per year. W-R stars come in two major subtypes, the WN, in which strong lines of helium and nitrogen are seen, and the WC, in which strong lines of carbon and oxygen are found, along with the helium ions. In a few WN stars hydrogen appears to be present but the spectra of W-R stars are notable for the absence of this element. Absorption lines are generally not found in W-R stars, except in some instances due to a binary companion, or a more distant companion, or as a P-Cygni profile associated with certain emission features. An absorption spectrum appears to be an intrinsic feature in a very few WN stars.
Two Possible Wind Models for Wolf-Rayet stars
Authors: Nugis T.
Published: June 2019

Frequently the models proposed to explain some observational data are in conflict with the other observational data. Our purpose was to find out the empirical models of the envelopes of WN5 and WN6 stars which are not in conflict with the continuum runs in the IR spectral region and with the emission line intensities and profiles. In our recent study (Nugis, 1984) we proposed for Wolf-Rayet stars the spherically symmetric outflow model having an increasing velocity zone (with some coronal heating near the stellar surface) which is followed by the decreasing velocity zone extending up to the distance where the matter starts flowing with constant velocity. Let us call this model the AD-model (Acceleration-Deceleration).
Wolf-Rayet Stars in M31
Authors: Shara M.M. , Moffat A.F.J.
Published: June 2019

We have completed a survey of the closest giant spiral galaxy beyond our own for Wolf-Rayet stars, using narrow band imaging techniques (cf. Moffat and Shara 1983, Ap. J., 273, 544). About 90% of the main body of M31 has been thoroughly searched to B ≅ 21.5 (MB ≅ −3.5) to a level of emission line equivalent width We(HeII 4686 A) ≳ 60 A. We do not expect interstellar extinction to be a limiting factor in the detection of WR stars, except possibly in the localized neighborhoods of massive HII regions. The mean extinction for stars in the disk is estimated to be AB ≲ 0.9 mag. Although some weak-line WN stars will have escaped detection, the survey should be complete for WC stars.
The WR/OB Number Ratio within 2.5 kpc from the Sun
Authors: Vanbeveren D.
Published: June 2019

Comparing the observed and theoretical HR diagram for massive stars, it is concluded that at least 34 % of the stars within 2.5 kpc from the sun with initial ZAMS mass larger than 35 MO have not yet been detected. It is argued that the number of core helium burning pop I WR stars within 2.5 kpc from the sun may be as low as 26. If the progenitors of WR stars have initial ZAMS masses larger than 35 MO, one then concludes that the observed number ratio (core helium burning pop I WR stars) / (WR progenitors) within 2.5 kpc from the sun ranges between 0.05 and 0.09.
IRAS Observations of Wolf-Rayet Stars
Authors: van der Hucht K.A. , Jurriens T.A. , Olnon F.M. , Thé P.S. , Wesselius P. R. , Williams P.M.
Published: June 2019

IRAS PSC. LRS. and CPC observations of Wolf-Rayet stars are used as diagnostics of hot circumstellar dust shells, cool dust in WR ring nebulae, the Ne/He abundance ratio, and the interstellar extinction. In two cases the IR energy distributions are indicative of a WR planetary nucleus status rather than a Population-I WR status.
The Formation of Nitrogen and Carbon Lines in HD 50896(WN5)
Authors: Hillier D. J.
Published: June 2019

Although considerable progress has been made in understanding Wolf-Rayet (WR) stars, the basic mechanisms for producing the nitrogen and carbon emission lines, which characterize a WR's spectrum, are unknown. To determine the mechanisms giving rise to these lines we are currently studying the formation of N and C emission lines in the WN5 star HD 50896.
Binary Evolution in the Upper HRD
Authors: De Greve J.P. , de Loore C.
Published: June 2019

The importance of close binaries in the domain of luminous objects is examined. The group of unevolved massive stars of O- and B-type, the groups of Wolf-Rayet binaries and X-ray binaries are discussed, and limits on the mass ratios, masses and periods are listed, as well as the average values. The connections between these various groups are investigated, and relations among subgroups are established.
Star Formation in NGC 5128
Authors: Pennington Robert L.
Published: June 2019

Star formation in the dust lane of NGC 5128 (Cen A) has been studied using digitized CTIO 4m plates. The digital images were calibrated to the standard U, B and V passbands using photoelectric photometry (van den Bergh 1976). Ages for the dominant stellar component were derived by de-reddening each pixel along an R = 3.3 reddening law to its intercept with a theoretical cluster evolution track in the U-B, B-V plane (Davis 1979). The HII regions of Hodge and Kennicutt (1983) were used as tracers for the most recent star formation.
Oscillating Star Formation
Authors: Bodifee G.
Published: June 2019

As a consequence of positive feedback effects in interstellar chemical and star forming processes, a star formation region may undergo nonlinear oscillations.
The Evolution of Massive Close Binaries with Mass Loss and Overshooting. An Application to V729 Cyg (=BD+40 4220)
Authors: Sybesma Christiaan H. B.
Published: June 2019

The evolution of massive close binaries is altered if the effects of mass loss through a stellar wind and overshooting from the convective core are taken into account. The occurrence of mass transfer as well as the extent of the mass transfer itself differs from the classical case (Doom and De Greve 1983, Doom 1984). The main-sequence widening due to the enlargement of the convective core results in an enhancement of the frequency of case A of mass transfer. It occurs for initial periods much longer than in the classical case. A cosiderable number of early-type systems will therefore undergo this type of mass transfer (Sybesma, 1985b). Systems with primary masses larger than 35 M will most likely not undergo mass transfer at all as these stars do not form red supergiants if overshooting is coupled to the effects of mass loss through stellar wind. These systems will only be able to undergo case A of mass transfer, and then only for initial periods below 2–3 days.
Tidal Radii and Masses of the Clusters in the LMC
Authors: Kontizas M. , Chrysovergis M. , Kontizas E. , Hadjidimitriou D.
Published: June 2019

Masses and tidal radii of star clusters in the LMC have been derived by means of star counts from U.K. Schmidt plates. Two groups of clusters according to their distance from the rotation centre of the LMC were measured. The tidal radii of the central clusters vary from 58 to 85 pc and those of the most distant clusters from 33 to 86 pc whereas masses were found to vary from 105 to 4×105M⊙ and from 104 to 2×105M⊙ respectively.
Non-LTE Analysis of Massive Stars in the Magellanic Clouds
Authors: Gehren T. , Husfeld D. , Kudritzki R.P. , Conti P.S. , Hummer D.G.
Published: June 2019

The massive stars of the Magellanic Clouds are of considerable current interest with regard to questions of initial mass function, star formation mechanisms, stellar evolution with mass loss and the chemical evolution of galaxies. The effective temperatures, surface gravities and helium abundances of 6 main sequence O-type stars, obtained by fitting non-LTE model atmospheres to high quality spectra, are presented here; these are the first results from a long-term program to determine accurately the parameters and chemical abundances of massive stars in the Magellanic Clouds. The program stars were selected to be main sequence objects, according to the classification of Conti et al. (1985, in prep.), with He II λ 4686 Å in absorption, and to have minimal reddening and nebular emission. Spectra were obtained in 1984 December with the Cassegrain echelle spectrograph (CASPEC) and a CCD detector at the ESO 3.6 m telescope. A preliminary analysis of these spectra has been carried out by fitting the equivalent widths of He I λ 4471 Å and the profiles of Hγ and the Pickering lines (for details of the technique, see Kudritzki, 1980). The resulting values of effective temperature and gravity are given in Table I, along with the identification, spectral type and mv, of each star.
Convective Overshooting: The Upper Mass Limit for Stars undergoing Core He-Flash
Authors: Bertelli G. , Bressan A.
Published: June 2019

With classic models of stars, in which overshooting from convective cores is not taken into account, the transition mass, Mtr, separating stars which undergo core He-flash from stars which ignite He-burning nonviolently in a non degenerate core, is set around 2.2 M⊙ (Iben 1967) for Pop I chemical composition (X = 0.700, Z = 0.020). This value is known however to depend on the chemical abundances, being lower at increasing Y and decreasing Z (Wagner 1974; Sweigart and Gross 1978). However, in recent years many independent arguments have indicated that convective overshooting from the central cores may play an important role in stellar evoluion (Bertelli et al 1985). In order to assess the dependence of Mtr on overshooting, we have computed evolutionary sequences of 1.4 M⊙, 1.5 M⊙ and 1.6 M⊙ with chemical composition X = 0.700 and Z = 0.020 adopting the description of convective overshooting formulated by Bressan et al (1981) for their parameter λ = 1/Hp = 1. As shown in the Tc vs pc diagram of Fig 1, while the tracks of 1.4 M⊙ and 1.5 M⊙ stars deeply penetrate into the region of high degeneracy and likely undergo core He-flah, the 1.6 M⊙ star succeeds in igniting helium in non degenerate conditions. This means that the classic value of 2.2 M⊙ for Mtr is now lowered to the mass range 1.6 to 1.5 M⊙. The HR diagram of the 1.4 M⊙, 1.5 M⊙ and 1.6 M⊙ stars in presence of convective overshooting is shown in Fig 2. The region of stationary core He-burning for the 1.6 M⊙ and the extension of the red giant branches for the 1.4 M⊙ and 1.5 M⊙ stars are also indicated.
The Final Fate of Massive Stars
Authors: Schild H.
Published: June 2019

The cluster membership of Wolf-Rayet stars, supernova remnants and pulsars is used to study the late stages of stellar evolution of massive stars.
Dark Matter: Key Issues
Authors: Faber Sandra M.
Published: June 2019

Key outstanding questions regarding dark matter are formulated, as a backdrop to the upcoming discussions at this meeting. A major issue involves how many species of dark matter there are, and whether both baryons and non-baryons are implicated in cosmological dark matter. How is dark matter distributed relative to baryons on all scales? Are voids really empty? And finally, is there high-amplitude structure in the matter distribution of the universe on scales ∼100 Mpc, and, if so, how can it be accounted for in terms of known, plausible physical processes?
Seen and Unseen Matter in the Galactic Disc
Authors: Robin Annie , Bienaymé Olivier , Crézé Michel
Published: June 2019

We use a Galaxy model including three components for the ‘seen’ stellar matter (Robin, Crézé, 1985). A scenario of star formation and evolution in the disc constrains the age distribution within each spectral type and luminosity range. The model fits available star counts. We add the ‘seen’ interstellar matter with local density 0.04 M⊙ pc−3 and scale height 140 pc. Thus the total observed local density is 0.085 M⊙ pc−3.
The Local Galactic Escape Velocity
Authors: Carney Bruce W. , Latham David W.
Published: June 2019

From a new photometric and spectroscopic survey of high proper motion stars, combined with previously published work, we find that the local value of the escape velocity from the Galaxy exceeds 500 km s−1. This gives direct dynamical evidence that the total Galactic mass exceeds the mass inside the solar orbit by a factor of at least five.
Mass Determinations and Dark Matter at Intermediate Scales
Authors: Ostriker J. P.
Published: June 2019

The issue of “dark matter” in astronomy is extremely confusing. Difficulties exist on two levels. First there are the, in principle, straightforward scientific questions of measurement. A certain region of space is studied, and by some technique, the mass within it is determined. Separately the energy output in some wavelength band from the region is measured and then, with due allowance for distance uncertainties, a “mass-to-light” ratio is determined. These measurements are difficult, with the results affected both by small number statistical uncertainties (as when using globular clusters to determine the mass of the galactic halo), measurement errors (as with binary galaxies), and systematic questions of interpretation (as with X-ray emitting gas around galaxies). Ultimately, with patience and skill these problems have been reduced and, as we shall see in subsequent sections of this report, there exists moderate agreement among observers concerning the large mass (∼ 1012 M⊙) and high mass-to-light ratio (M/LB > 100 M⊙/L⊙) for material integrated over distances in the range (30 kpc < r < 300 kpc) from the centers of giant galaxies.
The Mass of the Binary Galaxies NGC 4038/39 (The “Antennae”)
Authors: Mahoney J. M. , Burke B. F. , van der Hulst J.M.
Published: June 2019

The binary galaxies NGC 4038/39 have extended filamentary arms generated by tidal interactions (Toomre and Toomre, Ap. J. 178; 623, (1972)(TT)). The velocity field was determined by HI observations taken with the VLA (a facility operated by the NRAO under contract with the NSF), and the combined velocity and morphological information was used to constrain the allowed orbital parameters, halo characteristics, and dynamical friction. TT-type calculations were carried out with central masses and rings of test particles, and the calculated results compared with the data. Using disk orientations derived from optical data (Rubin et al., (1970) Ap. J. 160 81), and solving for the six remaining orbital parameters, central potential softening constant (representing the halo), and frictional relaxation time, a good fit between the model and the radio data was found. The best model is shown in Figure 1, and is superimposed on an HI column density map in Figure 2. The orbit is well-determined, and must be nearly parabolic; the pair are interacting for the first time, and if the galaxies have extensive massive halos much larger than their discs, then their tidal arms would be shorter and stubbier than observed. More limited halos are allowed; each galaxy could have up to 80% of its total mass in a halo, but the halos cannot be much larger than the discs. A halo several times larger than the disc, with 10 to 20 times the disc mass, is not permitted by the data.
Clustering on a Scale of 1018 M●
Authors: Brent Tully R.
Published: June 2019

This discussion represents an update of an article submitted for publication in The Astrophysical Journal that describes the concentration of Abell clusters to the supergalactic equator. Since that article was written, our sample of Abell-class clusters has been augmented by 44% to now total 309 clusters within a redshift of 0.1c. The distribution of those clusters with distance from the supergalatic equator is illustrated in the accompanying figure. The normalized histogram includes an attempt to correct for the diminished unobscured area in planes off the supergalactic equator. Within 4 bins on the equator (i.e., within 80/h75 Mpc) there are 105 clusters, rather than the 48 clusters that would be expected with a random distribution. The 57 excess clusters represents a 4.6 σ signal.
Parameters for Dark Halos
Authors: Freeman K. C.
Published: June 2019

What are the characteristic scale lengths and densities for the dark halos of galaxies, and the typical ratios of dark to luminous mass? For elliptical galaxies, the best estimates come from X-ray data which will be discussed in a later session. For spirals, the best estimates come from rotation curves. I will concentrate on the halo parameters for disk galaxies. At the end, there will be a few comments on stellar dynamical data for ellipticals, and on the unique information available for the dark halo of our Galaxy.
HI and Mass Distribution in the Dwarf “Regular” Galaxy UGC 2259
Authors: Carignan C. , Sancisi R. , van Albada T.S.
Published: June 2019

HI synthesis observations of the dwarf “regular” galaxy UGC 2259 are presented. This system turns out to be most suitable for our purpose of studying the mass distribution in late-type spirals. It has a symmetrical HI distribution extending over 2 D25 and a regular velocity field which shows no sign of departure from axial symmetry. Despite the fact that UGC 2259 is fainter than most other objects of the same morphological type, its HI properties are typical of what is expected from an Scd galaxy with a MH/LB = 0.43.
X-Rays from Galaxies and Clusters of Galaxies: Observations and Phenomenology
Authors: Canizares C. R.
Published: June 2019

X-Ray observations of galaxies and clusters can, in principle, trace the binding mass in these systems. I review some of the relevant work. The mass of hot gas in rich clusters is comparable to or exceeds the mass in visible stars. This proportion of gas to stellar material could be universal, although there is no direct evidence that it must be. Studies of the distribution of the gas indicate the presence of dark matter in the envelopes of some dominant cluster galaxies, most notably M87. The M/LB values increase with radius to values of ∼ 400–600 M⊙/L⊙. Uncertainties in the temperature distribution of the gas have hampered these analyses and have made it difficult to draw definitive conclusions about the binding mass in clusters. Recent work on Coma suggests that M/L is falling with radius and the total M/L for the cluster may be as low as ∼ 120. Studies of early type galaxies show that many contain hot gas with temperatures ∼107 K. There is evidence for the existence of cooling flows, and gravity rather than supernovae may be the dominant source of energy that heats the gas. The deduced binding masses for several bright galaxies are uncertain because of the unknown temperature profiles. Values of M/LB ≃ 20–30 within ∼ 30–40 kpc are indicated if one assumes isothermality, but values as low as 5 and as high as 100 are allowed. With better models one may be able to reduce these uncertainties.
X-Ray Halos in Galaxies and Clusters of Galaxies: Theory
Authors: Sarazin Craig L.
Published: June 2019

X-ray measurements provide an excellent method to determine the amount and distribution of the dark matter in clusters. Unfortunately, accurate temperature profiles, necessary to this method, are currently not available. However, if the intracluster gas is assumed to have a monotonically decreasing temperature, one finds that the dark matter is strongly concentrated to the cluster center, and has a mass which only exceeds the known baryonic mass by a factor of about three. On a second topic, cooling flows are shown to be a very common feature of cluster central and normal elliptical galaxies. The cooling gas is probably ultimately converted into low mass stars.
Filamentary Nebulosity Surrounding M87
Authors: van den Bergh S. , Pritchet C. J.
Published: June 2019

Recently we have obtained both Hα + [NII] and broad-band red exposures of a number of galaxies with an RCA 320 × 512 CCD at the prime-focus of the 3.6 m CFH Telescope. Figure 1 shows the difference between Hα and red exposures (each with a total integration time of 60 min) of M87 = NGC4486.
N-Body Results on Dark Matter
Authors: White Simon D. M.
Published: June 2019

The structure of the dominant “dark” component of the Universe may evolve primarily under the influence of gravity. A number of models for the evolution of the Universe make specific predictions for the statistical properties of density fluctuations at early times. N-body simulations can follow the nonlinear development of such fluctuations to the present day. A major difficulty arises because we cannot observe the present mass distribution directly. Recent N-body work has concentrated on models dominated by weakly interacting free elementary particles. Neutrino-dominated but otherwise conventional cosmologies pass rapidly from a smooth distribution to one dominated by lumps with masses greater than those of any known object. Cosmologies dominated by “cold dark matter” produce mass distributions which fit the observed galaxy distribution (i) if Ω = 0.1–0.2 and galaxies follow the mass distribution, or (ii) if Ω = 1, HO< 50 km/s/Mpc and galaxies form preferentially in high density regions. In the latter case, clumps form with flat rotation curves with about the amplitude and abundance expected for galaxy halos.
Cold Dark Matter: Galactic Halos
Authors: Frenk C. S.
Published: June 2019

A flat universe dominated by cold dark matter (CDM) is an attractive arena for the formation of galaxies and large scale structure. Current upper limits on anisotropies of the cosmic microwave background and the standard theory of primordial nucleosynthesis are both compatible with such a universe. Furthermore a flat CDM model in which galaxy formation is biased towards high density regions provides a good match to the observed distribution of galaxies on Megaparsec scales. In collaboration with M. Davis, G. Efstathiou and S.D.M. White, we have carried out a high resolution N-body simulation which shows that this model can also account for the abundance and characteristic properties of galactic halos. The initial conditions for this simulation were based on the results of our previous work which gave both the scaling and overall normalisation of the initial CDM fluctuation spectrum appropriate to the biased galaxy formation model. We simulated a cubic region of present size 14 Mpc (H0 = 50km/s/Mpc) from a redshift of 6 to the present day, with a resolution of 2kpc initially and 14 kpc at the end. We found that by a redshift of 2.5 about 20 clumps with circular speeds exceeding 100 km/s had collapsed near high peaks of the initial linear density field. Between Z = 2.5 and the present most of them remained isolated and accreted extensive outer halos, while others merged into larger systems. The rotation curves of the final smooth systems were impressively flat at large radii resembling the measured rotation curves of spiral galaxies. Furthermore, the abundance of clumps with circular velocities larger than 150 km/s was about the same as the abundance of galaxies brighter than M33 expected in a volume the size of our simulation. Significant transfer of angular momentum to surrounding material occurred as large subclumps merged. Most of this angular momentum was originally invested in the orbital motions of the subclumps. As a result, the central regions of merged objects showed little rotation.
Embedding of Galactic Systems in Extended Neutrino Clouds
Authors: Cowsik R. , Ghosh P.
Published: June 2019

In an expanding universe neutrinos of mass 10eV form condensates with typical mass 1016 M⊙ and size ∼0.5 Mpc. Visible matter like galaxies and stars are embedded in these and assuming a Maxwellian distribution and collisionless nature of these systems we solve the self consistent Poisson-Vlasov equations. These solutions correctly predict the profiles of luminosity of clusters of galaxies, dwarf, elliptic and spiral galaxies as well as their rotation curves; the embedding picture is supported by M∼R33 relation for astronomical systems as below.
Massive Black Holes in Galactic Halos?
Authors: Lacey C. G. , Ostriker J. P.
Published: June 2019

We consider the idea that galaxy halos are composed of massive black holes, as a possible resolution of two problems: the composition of dark halos, and the heating of stellar disks. Scattering of disk stars by halo black holes with mass MH, velocity dispersion σH and number density nH causes the stellar velocity dispersion to increase with time t as σ≈(Dt)1/2 for t large, where D α nHM2H in Λ/σH, and in Λ is the Coulomb logarithm. This time-dependence is in good agreement with observations, as is the prediction for the axial ratios of the velocity ellipsoid σu: σv: σw. To account for the magnitude of the disk velocity dispersion in the solar neighbourhood, we require MH≈2 × 106M⊙. The stellar distribution function is predicted to be approximately isothermal at low epicyclic energies, in the Fokker-Planck regime in which the effect of the many distant, weak encounters dominates, but with a power-law tail at high energies produced by the relatively rare close encounters. This tail has the form N(E)αE−2, where E is the horizontal or vertical epicyclic energy, and N(E) is the number of stars per unit area of the disk, per unit E. The fraction of stars in this power-law tail depends only on the value of in Λ, and is about 1% for typical values. This provides a possible explanation for the high velocity A stars found in the solar neighbourhood. This disk heating mechanism can also account for the approximate constancy of the disk scaleheight with radius that is observed in other spiral galaxies, although this does not result as naturally as the other properties.
Prospects for Axion Detection
Authors: Moody John
Published: June 2019

Axions are a natural consequence of the only known solution of the ‘Strong CP Problem.’ The axion represents a minimal U(1) extension to the standard SU(3) × SU(2) × U(1) model of the strong and electroweak interactions and furthermore appears very frequently in the contexts of SUSY GUTs, Kaluza-Klein, Superstring, Technicolor, and other unified models. As such, the axion is perhaps the best motivated conjectured particle.
CCD photometry with small telescopes
Authors: Walker Alistair R.
Published: June 2019

CCD photometry with small telescopes often complements the use of such detectors on larger telescopes and in addition it is ideally suited to projects, such as determining variable star light curves, that require considerable amounts of observing time. Following a discussion of some of the techniques found useful for producing accurate CCD photometry, the results of several projects carried out with the SAAO 1m CCD camera are presented.
An automated South Pole stellar telescope
Authors: Chen K-Y. , Esper J. , McNeill J. D. , Oliver J. P. , Schneider G. , Wood F. B.
Published: June 2019

An 8-cm optical telescope is constructed for use at the south pole. It is designed to make photoelectric observations of selected stars continuously through an austral winter. The automated operation is controlled by a computer. The aim is to study the variability of the star γ2 Velorum as well as the condition of the polar sky and the performance of the instrument.
Construction of a 32cm Cassegrain photoelectric telescope
Authors: Hickey David
Published: June 2019

This paper describes the building of a 32cm telescope which had been designed from the beginning to undertake high precision photoelectric photometry.
Black Birch Astrometric Observatory
Authors: Robinson D. , Dick S. , Stone R. , Loader B.
Published: June 2019

The seven inch transit circle near Blenheim, New Zealand is intended in conjunction with the six inch circle at Washington, to produce a fundamental catalogue and to re-observe the Southern Reference Stars.
A simultaneous two channel photometric system
Authors: Sullivan D. J. , van der Peet A.
Published: June 2019

A photometric system capable of simultaneous dual channel operation has been developed for use in NZ. The photometer head unit, developed and constructed by the University of Texas at Austin, permits simultaneous observation of two stars using suitable optics and mechanically coupled photomultiplier systems. The instrumentation and control system is centred around a DEC micro/PDP-11 computer and incorporates general purpose hardware and software developed specifically for the system.
Asteroids
Authors: Schober H. J.
Published: June 2019

Using a number of different conventional observing methods of astronomy like spectrophotometry, polarimetry, IR-radiometry and UBV-photometry, physical properties of asteroids can be derived, such as diameters, spectral reflectivity and albedo. Based on observable parameters a classification in terms of taxonomic types can be made and the mineralogy of the surface can be determined and compared with meteoritic analogues. UBV-photometry at different phase angles can reveal something about surface properties and diameters, whereas from accurate photometry during different phases of the rotational cycles we are able to derive rotation periods, geometric irregularities of the asteroid-body and topographic features on the surface. If observations of lightcurves are obtained during several oppositions at different ecliptic positions, the orientation of the spin axis in space and sometimes the sense of rotation can be derived. Observations of asteroids are especially well suited to small and medium-sized telescopes, as most of the programmes need long telescope runs. In addition there is a definite need for a large number of observations of asteroids in the magnitude range 12–15 mag.
Coordinated programs for comet Halley
Authors: A'Hearn Michael F.
Published: June 2019

Because comets are so difficult to observe, it is essential to coordinate observations from a variety of telescopes in order to fully understand their behavior. The apparition of Comet Halley represents a unique opportunity for coordinated programs because this is the only predictable comet which is routinely bright enough for the many observational programs desired. The International Halley Watch is playing an advocacy and coordinating role in the observations of Halley. Coordinated photographic observations will provide a record of the development of jets in the coma and of the motion of features in the tail. Coordinated photometry will provide both the heliocentric variation in vaporization and also the details of the outbursts thought to occur in most comets. Coordination with larger optical telescopes and with radio and infrared telescopes will allow a more complete understanding of the physical and chemical processes occurring in comets. Examples, of course, must still be drawn from observations of previous comets but they illustrate the results expected from Halley.
Research programmes, productivity, and usage statistics for the 0.9m telescopes at Kitt Peak
Authors: Jacoby G. H.
Published: June 2019

Current research programmes using the smaller telescopes at Kitt Peak include spectroscopy, photometry, and imaging of clusters, variable stars, nebulae, and extragalactic objects. Their scientific productivity is competitive with the 4m and 2.1m telescopes. Subscription rates indicate that when advanced instrumentation is made available on a small telescope, the demand will increase significantly.
Surface photometry surveys of galaxies with small telescopes
Authors: Djorgovski S.
Published: June 2019

Surface photometry of relatively bright galaxies is now becoming almost an exclusive province of small telescopes equipped with CCDs. I give a brief review of the scientific possibilities and problems of interest in this field. Small telescopes become tools of observational cosmology: they can provide large amounts of data necessary for the further understanding of fundamental properties of galaxies, clues to their formation, and their interactions with environment.
Cometary astrometry with the Sydney Observatory astrograph
Authors: Bembrick Col , Byron Jeff , Phipps David
Published: June 2019

The New South Wales Branch of the British Astronomical Association is currently making use of the Sydney Observatory astrograph for cometary astrometry. Astrometric plates (16 × 16 cm) of P/Halley are being taken at a plate scale of 116 arcsec/mm with a field of 5 × 5 degrees. Plate measuring is accomplished by means of a mechanical single screw Hilger measuring machine. Plate reduction utilises the program supplied by the International Halley Watch organisation. Measurement and reduction is facilitated by the machine readable catalogue and plotting routines supplied by the United States Naval Observatory. Currently the BAA observing team is working towards achieving a 24 hr turnaround for plate reductions. This will enable useful contributions to be made during the critical pre-encounter periods.
Stellar activity
Authors: Duncan D. K.
Published: June 2019

We have been monitoring the CaII H and K emission in late-type giant stars using the Mt Wilson 60-inch telescope. It is a continuation of work that Olin Wilson began almost 20 years ago. As a result not only have starspot cycles been detected (equivalent to the solar sunspot cycle), but rotation periods have now been measured.
Arc-second infrared imaging of the BN-KL star formation region
Authors: Woodward C. E. , Moneti A. , Pipher J. L. , Forrest W. J.
Published: June 2019

Infrared images of the BN-KL region in Orion obtained with the Univ. of Rochester IR Array Camera on the Mees 0.6-m (2.5“/pixel) and the Kitt Peak 1.3-m telescopes (1”/pixel) are presented. These images demonstrate the utility of small telescopes for infrared studies of star formation regions.
Measurement of line profiles
Authors: Gray David F.
Published: June 2019

The basic requirements for high precision spectral line profile measurements are reviewed, with the observatory at the University of Western Ontario serving to illustrate several of the points.
10 μm heterodyne spectroscopy at telescopes with 1m aperture
Authors: Rothermel H. , Schrey U. , Käufl H.U. , Drapatz S.
Published: June 2019

Heterodyne spectroscopy combines high instrumental transmission with virtually unlimited spectral resolution. For 250 K bodies like Mars and Venus resolution is limited to 107 (= 30 m/s) because of photon statistics whereas for solar measurements the cm/s velocity range, desirable for study of solar oscillations, is feasible. Since a single heterodyne receiver is conserving its etendu, smaller collecting area results in larger field of view. The signal remains unchanged as long as the source is large enough to fill the beam. For Mars, Venus and the Sun heterodyne observation with 1m aperture is competitive.
FAGS - a fast astronomical grating spectrometer
Authors: Denby B. , Dalglish R. , Meadows V. , Taylor K.N.R.
Published: June 2019

A fast astronomical spectrometer is described using commercially available photographic lenses and a CCD detector. The size and weight of the instrument have been kept to a minimum to allow it to be used on telescopes as small as 0.6m.