bluuebunny/crossref_metadata_2025 huggingface dataset:
Quasar Clustering at Intermediate Redshifts
Authors: Drinkwater Michael
Published: June 2019

This paper summarizes recent results from a study of quasar clustering based on a survey of U.K. Schmidt objective prism plates using the Automatic Plate Measuring facility at Cambridge. New procedures have been developed to detect quasars, eliminate contamination and measure accurate redshifts from the (see Drinkwater, M.J. 1987. Mon. Not. R. astr. soc., submitted). The redshift identifications are 90% reliable with an error (rms) of Δz = ±0.019 for quasars to a limiting magnitude of Bj = 19.5. Some 600 quasars from 6 U.K. Schmidt fields in the redshift range 1.8 < z < 2.6 have been analysed for weak clustering using power spectrum analysis (Webster, A. 1976. Mon. Not. R. astr. soc.175, 61). Plots of the statistic Q′ for 2-D and 3-D (4 fields only) projections of the data are given in the figure below. The ±1σ expectation values of Q′ calaulated for random simulations of the data (including non-uniform redshift selection and plate sensitivity) are indicated by vertical bars.
The Environments of Optically-Selected QSOs
Authors: Boyle B. J. , Shanks T. , Yee H.
Published: June 2019

In recent years much attention has been focussed on the environments of low redshift QSOs. In particular, Yee and Green (1987) have found that the average environment of radio-loud QSOs at z ≃ 0.6, as measured by the QSO-galaxy spatial covarience function, is over three times richer than that of radio-loud QSOs at z ≃ 0.4. This strongly indicates that there has been a steep evolution in the numbers of QSOs in rich clusters over a period of 109 years. This observation is therefore inconsistent with pure luminosity evolution models, which preserves QSO number with epoch, currently employed by a number of authors (see e.g. Boyle et al. 1987) to explain the observed redshift dependence of the QSO luminosity function. However, since over 90% of QSOs are radio-quiet, the main test concerning the validity of pure luminosity evolution is to look for similar evolutionary effects in the preferred environments of optically-selected QSOs.
Radio Galaxies as Large-Scale Cosmological Probes
Authors: Peacock J.A. , Miller L. , Collins C.A. , Nicholson D. , Lilly S. J.
Published: June 2019

We are working on an all-sky sample of radio-selected elliptical galaxies to provide a powerful probe of clustering & streaming velocities on 10–100 Mpc scales. Our eventual sample will have the limits (i) S>0.5 Jy at 1.4 GHz; (ii) 0.01<z<0.1; (iii) |b| >15°; about 400 galaxies satisfy these criteria. We are pursuing an optical programme to obtain (i) B & I CCD frames for all galaxies; (ii) spectra for the galaxies without accurate redshifts; this is now about 30% complete. Accurate optical luminosity indicators exist for radio galaxies, without needing to measure velocity dispersions (using the correlations with optical core radius and radio central-component luminosity: Hoessel 1980: Ap. J. 241, 493; Fabbiano et al. 1984: Ap. J. 277, 115). We therefore expect to provide an accurate test of the Rubin-Ford effect, and to extend such studies to higher redshift. We also have a preliminary result for the 3D two-point correlation function of radio galaxies (see Figure). This strong clustering signal is seen only from galaxies in the decade of radio power below the Fanaroff-Riley division. These objects are known a priori to lie in cluster environments of average Abell richness 0 (Longair & Seldner 1979: MNRAS 189, 433). This result therefore provides confirmation of a trend of clustering with richness independent of optical selection effects in choosing a cluster sample.
Spatial Correlation Functions of Bright Radio Galaxies
Authors: Zhou You-yuan , Jing Yi-peng
Published: June 2019

Because of their large separation bright radio galaxies characterize the structure of the universe on the scales of clusters and superclusters. In order to calculate the spatial correlation function we choose radio galaxies in radio surveys, for which the redshift values have been measured. One is from Bright Radio Sources at 178 MHz (Liang, Riley and Longair 1983), and another is from All-Sky Catalogue of Bright Extragalactic Radio Sources at 2.7 GHz (Wall and Peacock 1985).
Explosions in pancake models of galaxy formation
Authors: More J.G. , Heavens A.F. , Wilson M. J. , Trew A.S.
Published: June 2019

We have investigated the consequences of galaxies in pancakes releasing large quantities of energy, in the spirit of explosion models.
On dynamical analysis of hydrostatic self-gravitating sphere: application to galaxy clusters
Authors: Sadat R. , Gerbal D.
Published: June 2019

Consider an hydrostatic self-gravitating sphere. The gravitational field is generated by 2 components: a visible (o) and an unseen (x). The resolution of the equations yields global quantities such as the mass (observed, unseen or total) of matter in the configuration Mo,x,t the ratio of unseen mass to visible one R = Mx/Mo, the mean quadratic velocity computed on the configuration V2o,x, Cv=V2x/V2o the relative concentration indicator of kinetic energy, and the relative concentration indicators of x-matter and x-potentiel energy Ci and Cx.
On the Possibility of a Higher Baryonic Contribution to Dark Matter
Authors: Dominguez-Tenreiro Rosa , Yepes Gustavo
Published: June 2019

The most stringent constraint against baryonic dark matter is provided by primordial nucleosynthesis. Agreement between theory and observations is reachedonly for a limited range of the baryon-to-photon ratio ‘LR, namely , which implies that, in standard cosmological frameworks, the universe cannot be closed by baryons.
A New Approach To Traditional Chinese Astronomy
Authors: Kistemaker J. , Zhengzong Yang
Published: June 2019

We have made a systematic investigation of the traditional Chinese stellar sky, using Yi-Shitong's precise stellar maps at the Amsterdam Zeiss Planetarium, reproducing the positions of pole, hour circles and equator for any epoch between 1000 and 3000 BC at the latitude of Xian.

The right ascensions of the 28 boundary hour circles of the traditional lunar lodges, as well as the declinations of the various determinative stars, give insight into the possible original meaning of star names and ages. The four cardinal directions along the celestial equator (α Hya, η Tau, β Aqr and Sco) fit best with 2250±50 years BC.
Past, Present, And Future Of Photographic Surveys
Authors: Maury Alain
Published: June 2019

Surveying the entire sky requires very efficient instrumentation, if the project has to be done in a relatively short period. In this is a review of the existing photographic surveys, it is demonstrated that photography, because of its very large format, is still the best existing technique for survey purposes.
Fundamental Catalogues
Authors: Gliese W.
Published: June 2019

The first plates for the great enterprise, the Carte du Ciel or the Astrographic Catalogue, were taken in 1891. At that time no fundamental system existed which was usable as a basis for reference stars over the whole sky and was commonly accepted by the astronomical community. Therefore reference stars were taken from available catalogues, sometimes updated to the epoch of the plates by application of proper motions. Other observatories used their own reference stars specially observed on transit circles. For the last-mentioned method the work at the Cape Observatory is an instructive example which was described by Sir David Gill, an experienced observer, in a catalogue of Astrographic Standard Stars (Gill, 1906). The methods of observation are fully described in the volumes of the Cape Meridian Observations. For the derivation of proper motions southern catalogues dating from 1835 to 1900 were used, applying Newcomb's values for precession. The determination and elimination of serious systematic errors played an important role. “Eye-and-Ear” observers had their personal errors which even changed with the years for the same person, occasionally even during tiresome long watches in a single night. Further sources of errors include: None-reversible instruments, zenith discontinuities, magnitude equations, possible changes of flexure, pivot errors and their variations, and unsufficient knowledge of the polar motion in old catalogues. Many of these questions were investigated and described in extended introductions to observational catalogues but in some cases such problems were only incompletely explained. Reference stars for the Astrographic Catalogues were observed on various “fundamental system” if fundamental at all.
David Gill And Celestial Photography
Authors: Murray C. A.
Published: June 2019

In this centenary commemoration of the Paris Astrographic Congress it is appropriate that we should recall the very significant role played by David Gill, Her Majesty's Astronomer at the Cape of Good Hope, in pioneering the application of photography to mapping the sky, and in the planning of the great Carte du Ciel project itself.
The Guide Star Catalog. III. Structure And Publication, Status and Plans
Authors: Jenkner Helmut , Russell Jane L. , Lasker Barry M.
Published: June 2019

The current structure and content of the Guide Star Catalog (GSC), as well as future enhancements in this area are described. An overview of the forthcoming publications is given, both with regard to scientific papers and electronic media.
Linking Hipparcos To Extragalactic Reference Frame (Task Of Input Catalogue Subgroup 2130)
Authors: Argue A.N.
Published: June 2019

A review is given of methods that have been proposed for linking the HIPPARCOS Catalogue of star positions to Extragalactic Reference Frames. The methods to be used by the data reduction consortia are outlined briefly.
Radio Mapping
Authors: Deul E.R. , Burton W.B.
Published: June 2019

The mapping discussed in this paper is based on observations obtained from the 21–cm emission line of neutral atomic hydrogen. We will give an overview of the existing large surveys and present a homogeneous datacube that contains the most important surveys. This datacube was created by regridding the original observations, for the surveys included, onto a common denominator grid. Presenting a three dimensional dataset of intensities in one single image is impossible, therefore we made a film that displays in a time sequence a set of cuts (position–velocity maps) through the datacube. The advantage of showing the third coordinate in time is that the eye can now catch continuities in this coordinate that were previously hidden in the data.
The Compared Efficiency Of Centering Algorithms
Authors: Bienaymé O. , Motch C. , Crézé M. , Considère S.
Published: June 2019

The purpose of this study is to compare the quality of three digital image centering algorithms; 1) the fit of marginal distributions by Gaussian, 2) the maximum of the Autocorrelation of a stellar image by its symmetrical, 3) the 2–dimensional fit of stellar images by a mean stellar Profile.

The two main conclusions are: 1) the 3 centering methods give the same accuracy if the star is isolated, bright and unsaturated. But as soon as one of these conditions fails, fast algorithms lack robustness and the only reliable method is the 2-d profile fit, 2) preliminary tests on Schmidt plates digitized with the MAMA (Machine Automatique à Mesurer pour l'Astronomie) show that under the above restrictions, the centering algorithms do not alter the final astrometric accuracy, neither do the digitizing machine.
Paris Full Pupil Astrolabe And Danjon's Prism Astrolabe. A Statistical Comparison In Terms Of Time-Magnitude-Colour Equation
Authors: Bougeard Mireille L.
Published: June 2019

Through multivariate statistical methods, we are trying to detect and separate some “outstanding errors” in visual astnometric data, especially in terms of time, magnitude, colour effects. The methods are illustrated by their application to the Paris Astrolake data.
A Prototype Detector For The Astrometric Telescope Facility
Authors: Gatewood G. , Castelaz M.W. , Levy E.H. , McMillan R.S. , Nishioka K. , Scargle J.D. , Stein J.W.
Published: June 2019

The Multichannel Astrometric Photometer (MAP) now in use in the Allegheny Observatory astrometric program is the detector chosen for the strawman design of the Astrometric Telescope Facility (ATF) proposed for the U.S. Space Station. Extrapolation of ground based performance to above atmosphere observing conditions indicates an approximate precision of 0.00001 arc seconds per annual normal point.
The Tautenburg Part Of The Programme Studying The Main Meridional Section Of The Galaxy
Authors: Schilbach E.
Published: June 2019

The programme for the determination of proper motions with reference to galaxies for 6000 stars on 17 fields near the main meridional section of the Galaxy is presented. For each field there are 2 or 3 first-epoch plates taken with the Tautenburg Schmidt-telescope before 1970. In preliminary investigations the mean error of an individual proper motion was found to be per century both for bright (8m–12m) and for faint (16m–18m) stars.
The JPL 1986–3 Extragalactic Reference Frame
Authors: Sovers O.J. , Edwards C.D. , Jacobs C.S. , Lanyi G.E. , Treuhaft R.N.
Published: June 2019

Intercontinental dual-frequency radio interferometric measurements were carried out during 1978 to 1985 between NASA's Deep Space Network stations in California, Spain, and Australia. Analysis of 6800 pairs of delay and delay rate observations made during 51 sessions produced a catalog of positions of 106 extragalactic radio sources, fairly uniformly distributed over the celestial sphere between −45° and +85° declination. Almost all of the resulting source positions have formal uncertainties between 0.5 and 3 milliarcseconds, with their distributions peaking somewhat below 1 mas. Root-mean-square uncertainties are 2.1 and 2.0 mas for RA and declination, respectively. Evidence is found for a long-term drift of the Earth's rotation axis in inertial space, relative to the 1984 IAU precession and nutation models. Tests for time variability of positions of 32 frequently observed sources place limits at the 1 mas/yr level. Comparisons with independently determined source catalogs of comparable quality show differences of positions of common sources that amount to a few mas, and may indicate the level of systematic errors in VLBI source position measurements.
Proper Motions Of 47 TUC And NGC 362 Relative To The Small Magellanic Cloud
Authors: Tucholke H.-J.
Published: June 2019

The proper motions of the galactic globular clusters 47 Tuc and NGC 362 are currently being measured relative to the background of the Small Magellanic Cloud. This paper reports on the reduction routines developed so far for the simultaneous computation of several thousands of stellar proper motions. A preliminary result for NGC 362 is given.
The Planetary Nebula in the Galactic Cluster NGC 2818
Authors: Dufour R.J. , Hack E.C.
Published: June 2019

The planetary nebula PK 261+8°1 is of special interest due to its apparent physical association with the galactic cluster NGC 2818 (Tiff, Connally, and Webb 1972, M.N.R.A.S., 158, 47). During 1975–76 we obtained spectrophotometric observations (both photographic and photoelectric) and interference filter photographs (Hβ, [OIII], [NII], and [SII]) of this object at Cerro Tololo. The nebula has a rather smooth bilaterally symmetric “hourglass” structure in the Hβ and [OlII] photographs, while several bright filaments appear in [NII] and [SII]. The spectrum of PK 261+8°1 is very rich in lines characteristic of both low ionization ([OI], [OII], [NI], [NII], [SII]) and high ionization (He II, [OIII], [NeV]) regions. Using the photo electric observations, we derive Te = 14,500 ± 1500°K from the [Olli] lines and Te = 11,000 ± 1300°K from the [OIII] lines and Te = 11,000 ± 1300°K from the [NII] lines. The λ6717/λ6730 [SII] ratio suggests that Ne ≤ 800 cm−3 in the regions where S+ exists. Additional information μ the density and temperature structure of the nebula derived from the deep photographic spectra will also be presented. Due to the complicated ionization structure, an accurate abundance analysis of PK 261+8°1 is difficult. Consequently, we will present the quantitative results from a variety of abundance calculation techniques. We conclude that He/H = 0.14 ± 0.01, N is substantially enriched relative to H and 0 (N/H ≥ 0/H = 4 × 10−4), while the abundances of 0, Ne, S, Ar, and Cl relative to H are similar to values typical of galactic planetary nebulae. Other characteristics of the nebula derived from its association with the cluster NGC 2818 and its spectral similarity to Henize 97 in the Large Magellanic Cloud will be discussed. This research was supported in part by a grant from the Research Corporation.
Planetary Nebulae: Advances in Radio Observations
Authors: Terzian Yervant
Published: June 2019

The most recent review on planetary nebulae at radio wavelengths appeared in 1974 by Thompson. Previous summaries were given by Terzian (1968) and Higgs (1973). Major advances in this subject include extensive continuum observations at 5 GHz of southern planetary nebulae; the highly successful aperture synthesis observations providing brightness temperature distributions with a resolution of a few arc seconds; the high sensitivity observations of radio recombination lines which have allowed the unambiguous detection of collisional broadening in NGC 7027; the very recent detection of molecular CO emission from NGC 7027, IC 418 and NGC 6543, and CO and OH emission from possible proto-planetary nebulae.
Medium Resolution Spectroscopy of NGC 7027 from 16 to 38 Microns
Authors: McCarthy J.F. , Forrest W.J. , Houck J.R.
Published: June 2019

NGC 7027 was observed on two nights, 1976 May 18–19 and 20–21, using the 36″ telescope of the KAO. A medium resolution, two channel, Helium-cooled grating spectrometer was used to observe the bands, 16-23μ (Δλ = 0.5) and 20-38μ (Δλ = 1.2). The beam size was 30″. A nearly flat smooth continuum over the entire band was observed with a peak intensity of 7 ×10−16 W/cm2μ between 20 and 25μ.
Observations of Infrared Fine-Structure Lines: [S III]
Authors: Greenberg Lawrence T.
Published: June 2019

Recent observations of the 18.7 ym fine-structure line of S++ in NGC 7027 and BD+30°3639 (Greenberg, Dyal and Geballe, 1977 Ap.J.(Letters), 213, L74) allow the first determination of an ionic column density in ionized nebulae. The line ratios 18.7 μm/A9532 and λ6312/λ9532, besides yielding both electron density and temperature in the S++ region, have been used to indicate that the fine-structure levels of S++ are collisionally saturated. In this case the 18.7 ym surface brightness directly measures the column density of S++ ions with little dependence upon nebular structure, the major uncertainty being the experimental error. This research has been partially supported by NASA Grants NGR 05-003-511 and NGL 05-003-272.
Observations of Infrared Fine Structure Emission
Authors: Lacy J.H. , Baas F. , Beck S. , Townes C.H.
Published: June 2019

A new spectrometer has been built for use in the 10μm atmospheric window which is substantially more sensitive than previous instruments for observations of 10]im emission and absorption features narrower than about 0.25 cm−1. Measurements have been made of fine structure emission lines in planetary nebulae as well as in galactic and extragalactic H II regions. The spectrometer consists of a liquid Helium cooled grating with a resolution of 1–4 cm−1 and a liquid Nitrogen cooled Fabry-Perot spectrometer which is scanned across the grating bandpass, resulting in a resolution of 0.1 − 0.2 cm−1. The system NEP is about , resulting in a minimum detectable line flux of about 10−19 w/cm2, with a 6″ aperture on the Lick 3m telescope.
Echelle Studies on the Symmetrical Stratified Planetary Nebula NGC 3918
Authors: Dopita M.A.
Published: June 2019

Coudé échelle studies of the symmetrical planetary southern nebula NGC 3918 at a resolution of 20 km/sec have shown a high degree of stratification of velocity of expansion with ionisation. The greatest velocity of expansion, 28 km/sec is observed in the [Mgl] line at 4751 Å
Theory of Evolution of the Central Star
Authors: Shaviv Giora
Published: June 2019

The fundamental feature of the evolution of the central star of planetary nebulae (CPN) is the cooling of the core towards a white dwarf. The basic observations were made by O'Dell (1963), Seaton (1966), and Harman and Seaton (1964); namely, they discovered a correlation between the linear size of the nebula and the position of the CNP in the HR diagram. Typical values for the velocity of expansion are 10–30 km/sec and the largest size observed for a nebula is ∼0.6 pc and hence the lifetime is 2–6 × 104 years. From a theoretical point of view the important fact about the Harman-Seaton sequence (HS) is the implication on the evolution of the central star. The star first heats up, L and Te increase, then L decreases. But Te keeps increasing until finally Te decreases also (shown schematically in Figure 2). Thus the HS is an evolutionary sequence and not a locus of stars.
Theory of Evolution of Central Stars of Planetary Nebulae
Authors: Paczyński B.
Published: June 2019

Young central stars of planetary nebulae burn hydrogen and helium in the shell sources. Within less than 104 years nuclear fuel is exhausted and old central stars cool off at almost constant radius to the white dwarf stage.

Young, i.e., luminous central stars should follow complicated loops on the H-R diagram as a result of helium shell flashes. FG Sagittae is the example. This should be a typical behaviour and a systematic search for light variations on a time scale of years or decades among other luminous entral stars should be undertaken. Because of rapid evolution of their nuclei many planetary nebulae may be far from the ionization equilibrium. This should be taken into account when the effective temperature and bolometric luminosity of the central stars are estimated.
Central Star of NGC 3132: A Visual Binary
Authors: Kohoutek L. , Laustsen S.
Published: June 2019

A faint companion to HD 87892 (V=10.07, B-V=+0.09, U-B=+0.10, Sp.A2) has been discovered with the 3.6 m telescope (prime focus) of the European Southern Observatory at La Silla having the following parameters: separation ψ = 1″.65, position angle θ = 226°.3. The companion was detected on plates taken in the U system (IIIa-J baked + UG1) and appears to be about ΔmU ≃ 4.5 mag fainter than the main component; it is almost invisible in the nearly visual system having Δmvis ≃ 4.8 mag. Contrary to the eccentric position of HD 87892 the companion lies in the axis of symmetry of the nebula. For the given reason the companion can be considered as the actual planetary nucleus. Assuming that its temperature is approximately T* ≈ 105 °K and the distance of the nebula d ≃ 0.9 kpc, the following parameters of the nucleus were estimated: L*/L ≃ 110, R*/R ≃ 0.035. The physical association of HD 87892 with its visual companion is probable. (Paper will appear in Astronomy and Astrophysics.)
Hydrogen- and Helium-Shell Flashes and FG Sagittae Phenomenon
Authors: Sugimoto D. , Fujimoto M.Y. , Nariai K. , Nomoto K.
Published: June 2019

Evolution of an electron-degenerate carbon-oxygen star of 1.08 M0 was computed assuming that hydrogen-rich gas was accreted at 1.58 × 10−7 M0y−1. Such a star mimicks the evolution of FG Sge, if a part of the ejected mass accretes back onto the central star. When a hydrogen envelope of 4 × 10−6 M0 was formed, a hydrogen-shell flash began. Succeeding 300 hydrogen-shell flashes were suppressed artificially to compute the growth of helium zone. After 8100 years of accretion, helium-shell flash began. Helium convection zone was found to reach the bottom of the hydrogen envelope, because the entropy barrier was low for the thin envelope. Protons were mixed into the helium zone, which produced neutrons and s-process elements. The mixing triggered also the hydrogen-she11 flash. Hydrogen convection zone reached a mass shell of 10−8 M0 measured from the surface. After the helium-shell flash ceased, the hydrogen envelope expanded greatly and a deepening surface convection dredged up the s-process elements. (Paper to be submitted to Publ. Astron. Soc. Japan.)
Ultraviolet Photometric Variations in the Central Star of IC 418
Authors: Gilra D.P. , Pottasch S.R. , Wesselius P.R. , Van Duinen R.J.
Published: June 2019

Ultraviolet photometric observations of IC 418 taken with the Netherlands Astronomical Satellite (ANS) indicate variability in the central star brightness. The variations occurring on the time scales of 5 hours are only 4% at 3300 Å but increase to about 15% at 1550 Å. The observations were not made frequently enough to determine a periodicity, if one exists. There are also 5–10% changes in brightness observed in A78 and NGC 6543, these are probably due to spectral changes in the central star spectra. About 10% type variations were found in VV 1–7 and He 2–131 but their interpretation is not clear.
The Position of Central Stars in the Hertzsprung-Russell Diagram
Authors: Pottasch S.R. , Wesselius P.R. , Wu C.-C. , Van Duinen R.J.
Published: June 2019

The determination of total luminosity and effective temperature recently reported on sometimes (but not always) differ in a substantial way from the determination of these quantities from Hell Zanstra method. For example, differences in luminosity exceeding a factor of 10 have been noted. The resultant effect on the Hertzsprung-Russell diagram is presented and discussed. (Paper will appear in Astronomy and Astrophysics.)
Some Aspects of Chemical Abundance Determinations in Planetary Nebulae
Authors: H. Aller Lawrence
Published: June 2019

The determination of the chemical compositions of gaseous nebulae in general and of planetary nebulae in particular is a difficult undertaking. The zeroth-order approximation is straightforward, the first approximation is challenging, and the second approximation is almost intractable.
The Structure of NGC 6720: The Ring Nebula in Lyra
Authors: Atherton P.D. , Hicks T.R. , Reay N.K. , Worswick S.P. , Smith W. Hayden
Published: June 2019

New observations have been made of the [OIII] 5007Å ine profile from the central and outer regions of 6720 in order to study in detail the radial velocity structure of the nebula. This data was obtained using a Fabry-Perot Interferometer working at a resolution of 67,000. The line profile is clearly s p l i t in the centre indicating the presence of a gaseous envelope surrounding, and in radial expansion from, the central star at avelocity of 25 ±5 km/sec. Irregularities in the emission intensities indicate local patchiness in this shell.
Origin of Planetary Nebulae
Authors: Roxburgh Ian W.
Published: June 2019

My interest in the origin of planetary nebulae goes back to 1967 when I proposed that the envelopes of giants with degenerate carbon-helium cores were dynamically unstable and would be completely ejected to form a planetary nebula. Essentially the same proposal was made almost simultaneously by Lucy (1967) and Paczyński (1967). For some years after that I worked on the dynamical ejection with W. van der Reijden, but for the last few years my interests have been in other areas, principally solar physics and gravitation theory. What then can I contribute to a discussion on Planetary Nebulae? Not a detailed review of work in this area; for that, the reader is referred to review articles by Salpeter (1971), Osterbrock (1973) and Miller (1974).
Planetary Nebulae and Related Objects
Authors: Panagia Nino
Published: June 2019

This symposium is explicitly devoted to Planetary Nebulae which are associated to “dying” stars of moderate mass. All other bright nebulae in the Galaxy can be considered to be related to planetary nebulae in the sense that they are similar to planetary nebulae in many respects. However, in most cases, these “relatives”-nebulae correspond to astro-physical situations (as characterized by the evolutionary stage, chemical composition, physical parameters, etc.) which are completely different. A large variety of nebulae can be found in the sky. One goes from point-like objects like K3-50, which is a very compact HII region, or V1016 Cyg, possibly a proto-planetary nebula, through moderate size nebulae like the Crab Nebula (the famous supernova remnant, 5′ size) or the Orion Nebula (the famous HII region around the Trapezium stars, 3′ core), to large nebulae like the Trifid (HII region of 20′ size) or NGC 6888 (which is associated to a WN6 star, about 30′) and extremely large like the North America Nebula (NGC 7000, an emission-reflection nebula of about 2° size) and the Gum Nebula (probably a supernova remnant of approximately 36° diameter). We see that not only might they be different in size but also, and drastically, different in their physical nature. It is interesting to note, however, that as a rule nebulosities are found to accompany stars only in the early phases and in the very late phases of evolution. At this stage of the symposium we should have learned enough about nebulae related to old stars. Therefore, I have decided to talk about nebulae related to stars at the other end of evolution, that is classical HII regions. For convenience, I will use here the term “HII region” meaning implicitly an ionized nebula associated to, and ionized by, a young and massive star. By definition, these nebulae are interesting because they represent the first manifestation of new-born stars of high mass. In fact, in many cases one can detect an HII region (in the radio and/or in the infrared) well before being able to directly observe the exciting star.
The Herbig-Haro Objects - Breakup of Protostellar Cocoons
Authors: Dopita M.A.
Published: June 2019

From a large body of data gathered on the 3.9 metre AAT and the 2 metre and 76 cm telescopes at Mount Stromlo including absolute photometry, quantitative spectrometry and studies of internal velocity fields, the Herbig-Haro objects are shown to be radiating shock fronts in the ISM. Physical conditions are found by comparison with theoretical models of plane-parallel shock fronts. Shock velocities in the range 30–150 km/sec are observed, and the densities in the interstellar clouds in which the objects are embedded found to be 80–400 cm". Extinction at Hg ranges up to 4.4 mag. Parameters are found to be consistent with the radiation pressure driven breakup of a dust cocoon around a newly formed B-type star.
Model Analysis of 108–76°1
Authors: Balick Bruce , Boeshaar G.O.
Published: June 2019

108–76°1 was discovered by Boeshaar and Bond (1977, Ap. J., 213, 421) to be a member of the galactic halo component. Herein are presente the results of a computer model analysis of these observations and those of Hawley and Miller (this volume). Models producing the 23% of helium in the doubly-ionized state required by the Hell X4686 line strength utilized the 95,000°K, non-gray, spherical atmosphere model of Cassi-nelli (1971, Ap. J., 165, 265) for the central star. Even 100,000°K plane-parallel atmospheres gave less than half the needed He++. The results for model 1 (homogeneous sphere) and model 2 (Gaussian shell) show good agreement with observed fluxes, even for [OH] X3727. The abundance values
Changes in Emission Line Intensities of HBV475
Authors: Tamura Shin'ichi
Published: June 2019

Some of the results in the spectroscopic observation of HBV475 are presented.
Density Distribution and Chemical Abundances in NGC 7027
Authors: Preite-Martinez Andrea , Panagiat Nino
Published: June 2019

The data available on permitted and forbidden line intensities of the planetary nebula NGC 7027 have been analyzed in terms of non-constant density models. The significance of the derived density distribution is discussed. Some implications to the determination of the chemical abundances are also discussed.
Results on the Large Scale Distribution of Extragalactic Objects Obtained by the Method of Statistical Reduction
Authors: Rudnicki Konrad , Zieba Stanislaw
Published: June 2019

The phenomenon of clustering of galaxies was known earlier than the nature of the so called extragalactic nebulae. It was discovered as early as the end of XVIII century by W. Herschel and confirmed by his followers. After the introduction of Schmidt cameras into astronomy, Zwicky suggested that all galaxies participate in clustering. After the discovery of extragalactic radio sources some astronomers have been trying, in different ways, to apply the concept of clustering to them also.
Observations of the large scale distribution of galaxies
Authors: Tifft W. G. , Gregory S. A.
Published: June 2019

It has long been assumed that clusters of galaxies merge into a smooth “field” of isolated galaxies. Early estimates put 50% of all galaxies into the field. Using new redshift surveys over large areas we find the real distribution of galaxies to be very different. Nearly all galaxies are in clusters or groups covering a range of at least 1000 in mass and richness.
Remarks on the angular distribution of Markarian galaxies
Authors: Flin Piotr , Urbanik Marek
Published: June 2019

Lists I-IX of Markarian galaxies have been used as the basic observational material. An attempt has been made to form a statistically complete sample. Two regions (region I 6h.8 < α < 14h.2, 41° < δ < 77°, region II 6h.8 < α < 13h.9, 5° < δ < 32°) which appeared to be roughly complete have been carefully examined. After preliminary tests the first two hours in R.A. of the region II were removed from the analysis. the method of statistical reduction (Flin et al. 1974, A. Zieba 1975) and the maximum likelihood estimate of the number-magnitude counts (Crawford et al. 1970) were applied as a combined test in their practical version (Urbanik 1976, 1977). We have examined the whole region, as well as a number of smaller sub-regions varying in size and position. the angular sizes investigated ranged from 1° up to 30°. Our analysis of 15 galaxy sets led to the following conclusions.
The autocorrelation analysis of deep galaxy samples
Authors: Phillipps S.
Published: June 2019

The two point correlation function w(θ) has been evaluated for the galaxies measured by the COSMOS machine at the Royal Observatory, Edinburgh, in an area of about 2 square degrees on a 2 hour exposure J plate and a 2 hour exposure R plate (Phillipps, S., Fong, R., Ellis, R.S., Fall, S.M. and MacGillivray, H.T., 1977, Mon. Not. R. astr. Soc., in press). in each case w(θ) is found to be in agreement with the form w = Aθ−0.8 found previously by Peebles and coworkers. Since the samples are not magnitude limited the selection function, i.e. the distribution in distance, was determined by using models of the galaxy distribution to fit the observed angular diameter counts. However, when these selection functions are used to scale the amplitudes found for our samples, the amplitudes are found to be lower than those expected from Peebles' results by a factor of about 3. We consider that this is likely to be due to a lack of clusters in the small area of sky which we have studied: analysis of further areas should show whether this is the case.
The Surface Density of Quasars
Authors: Bolton J.G. , Savage Ann
Published: June 2019

A knowledge of the surface density of quasars as a function of magnitude is important for two reasons. Firstly it is necessary in order to assess the possible statistical significance of close pairs of quasars or the association between quasars and bright galaxies. Secondly it is a necessary step in the determination of the space density or luminosity function of QSOs. We have carried out what we believe to be currently the most comprehensive investigation into the surface density of quasars. Three techniques have been used in this investigation. These are
Cosmological Information from X-Ray Observations
Authors: Gursky Herbert
Published: June 2019

The fact that x-ray astronomy could yield cosmological information was apparent in the earliest rocket flights carried out in 1962 and 1963 (Giacconi et al, 1962, Bowyer et al, 1963). These flights established that diffuse radiation was present around the sky; indeed one of the first theoretical papers commenting on the x-ray results was by Fred Hoyle (1963) showing that the observed background flux was below that predicted for the hot, steady-state universe. A few years later, the first discrete source was credibly identified with an external galaxy (Byram, et al. 1966).
Orientation of spiral galaxies as a test of theories of galaxy formation
Authors: Jaaniste J. , Saar E.
Published: June 2019

The cosmological turbulence theory and the theory of adiabatic fluctuations predict different orientations of galaxies in clusters and superclusters. the first theory favours the alignment of the planes of galaxies with the supergalactic plane, whereas the planes of spiral galaxies formed according to the second theory are perpendicular to the plane of a supergalaxy.
The Distribution of Young Stars in Nearby Galaxies
Authors: Freedman W. L.
Published: June 2019

Although luminous stars are relatively rare, they can potentially be studied out to large distances. In our own Milky Way, this advantage is offset by obscuration due to dust in the plane of the Galaxy. In addition, distances to these individual stars are extremely difficult to determine. The study of external galaxies allows a panoramic view of the system and its individually brightest stars which are all at a common distance. The spatial distribution of star forming regions is immediately apparent, and the effects of obscuration are minimized. Nearby resolved galaxies therefore provide a rich resource for examining the properties of the intrinsically brightest stars and their relation to other components of the galaxy.
Synthetic HR Diagrams for Luminous Stars: A Test of Stellar Evolution Theory
Authors: Nasi Emma
Published: June 2019

The composite HR diagram for luminous stars in our galaxy by Humphreys and McElroy(1984) is the only source which provides enough data for the comparison with the results of massive stars theoretical models. The luminosity limit for completeness of Humphreys' and McElroy's catalog(l984) is about MBol=−8 mag, when restricted to 3 Kpc from the Sun. Inside these limits there are 378 luminous stars in galactic associations and clusters, whose distances are known with sufficient reliability. The correspondent observational HR diagram is reproduced in Fig. 1. Synthetic HR diagrams for massive stars were constructed with the aim of reproducing the observed features for galactic luminous stars. By means of a Montecarlo technique, stars were randomly distributed in the MBol−Log Teff plane, weighted on the Salpeter's initial mass function and with a constant star formation rate.
A Low-Dispersion, Near-Infrared Survey for Galactic M Supergiants
Authors: MacConnell D. J. , Wing R. F. , Costa E.
Published: June 2019

While there have been many surveys for luminous, blue galactic stars and their numbers can be considered somewhat complete, such is not the case for red supergiants (see e.g. Humphreys and McElroy 1984). One result of this incompleteness is that the ratios B/R and WR/R, often used as diagnostics for evolutionary models of massive stars and the variation of the ratios with galactocentric distance, are not well known for the Galaxy. In an attempt to improve the statistics, the first author began an objective-prism survey within 6 deg of the southern galactic plane using I-N plates. The dispersion is 3400 A/mm at the A-band, and the spectra cover the range 6800–8800 A; the deepest plates reach ir mag ∼13. The detection of possible M supergiants on such plates was first discussed by Nassau, et al. (1954) and depends on the presence of TiO at 7054 A and a spectrum sharply tapered to the blue. For supergiants, this shape results from integration of interstellar dust over a long path-length, but any sample of red stars with tapered spectra contains M giants in heavily-obscured regions and S stars; thus follow-up observations of the candidate stars are necessary.
Bolometric Corrections and Magnitudes of WR+O Stars
Authors: Hellings Paul
Published: June 2019

Bolometric corrections and absolute magnitudes for WR stars have been evaluated by various authors. A review of the results may be found in De Jager (1980). The calibrations, relating BC or Mv with the spectral subtype, however strongly differ from author to author. Moreover, even with the same observational method a large scatter is found for the same subtype, as was recognised by Conti et al. (1983). The only trend found is the increase of Mv with the subtype from WN3 to WN7, and for the WC subtypes. In this study BC and Mv are computed for a number of WR+O binaries.
On the Occurrence of WR+O Binaries
Authors: De Greve J. P. , Hellings P. , van den Heuvel E.P.J.
Published: June 2019

Using stellar evolution models of two different kinds, one with convective cores determined by the Schwarzschild criterion, one with enlarged convective cores, we discuss the masses of the WR stars in a number of double-lined WR binaries. For the main group of systems the mass of the WR-star is between 10 and 20 M.
Infrared Spectroscopy of Southern P Cygni Stars
Authors: McGregor P.J. , Hyland A.R. , Hillier D.J.
Published: June 2019

Investigations of the 1.0–2.5 μm spectra of high luminosity p Cygni stars reveal the presence of several new emission features. All stars measured show emission in the Brackett and Paschen lines of H I, but the emission strengths of He I 1.083, 1.700, and 2.058 μm relative to the H I lines show large variations. Emission lines of [Fe II] are seen at 1.257 and 1.644 μm in several stars and are particularly strong in HR Car. An interesting subset of these stars show the first-overtone CO bands in emission. The presence of this molecular component associated with hot P Cygni stars has not been inferred from previous optical or UV spectroscopy.
Effects of Convective Overshooting, Mass Loss (and Chemical Composition) across the HR Diagram
Authors: Chiosi C.
Published: June 2019

The far reaching consequences of convective overshooting during the core H and He-burning phases of stars in the mass range 1.3 M⊙ to 100 M⊙ are discussed. In addition to this, the effects of mass loss in luminous stars of all spectral types, and in the red giant and asymptotic giant branch stars are briefly outlined. Furthermore, the effects of the novel 12C(α γ)16O reaction rate are also illustrated. The main purpose of this review resides however in lending convincing support to the idea that convective cores of real stars are greater than commonly supposed in classic models. To this aim, several observational embarrassments that could not be explained by classic models are reanalyzed in the light of the new ones. Since a much better agreement between theory and observations is now possible, we are inclined to conclude that convective overshooting may be of paramount importance in stellar structure theories and that convective cores in real stars ought to be larger by approximately one pressure scale height than predicted by classic models.
Consequences of Rotational Mixing in late Type Massive Stars
Authors: Sreenivasan S.R. , Wilson W.J.F.
Published: June 2019

We have examined further the consequences of mixing induced by rotation in massive stars (Pop I composition: X = 0.7; Y = 0.27) in the mass range 40–100 M⊙. The basic physics and a detailed examination for a 60 M⊙ model has recently been published (Sreenivasan and Wilson 1985b), as has a detailed examination of supergiants without such mixing (Sreenivasan and Wilson 1985a). We shall therefore not go into the background of our computation here, but merely summarize our present findings.
The Dynamical Evolution of Expanding HI Shells and Initial Mass Function of OB Associations
Authors: Silich S.A.
Published: June 2019

The evolution of expanding supershells produced by SN explosion in OB associations is considered. The expansion velocities of the shells and OB associations IMF spectral index are obtained. The results agree well with observational data.
Metallicity Effect on Absolute Magnitude Determination
Authors: Dubois P.
Published: June 2019

In our Galaxy, it is possible to determine the absolute magnitude of a star by mean of the intensity of the hydrogen lines, if we know the spectral type of the star or its temperature (see for instance Petrie, 1965; Hutchings, 1966; Balona and Crampton, 1974; Crawford, 1973, 1978; …).
Bright Stars in Five LMC Star Clusters
Authors: Kontizas E. , Xiradaki E. , Kontizas M.
Published: June 2019

The bright stars of five LMC clusters were classified for deriving the distribution of various spectral types. The studied clusters are very young (NGC 2093) young (NGC 1818, NGC 2157) intermediate (NGC 1831) and old (NGC 1806) (Van den Bergh 1981). The spectral classification of the stars was carried out using film copies of the 1.2 m Schmidt telescope objective prism plates. Medium dispersion (830 Å at Hγ) unwidened YJ and widened UJ and low dispersion (2440 Å at Hγ) UJ were examined by means of a binocular microscope. Details of the criteria used for the classification are described by Kontizas et al (1985).
Convective Overshooting: New Integrated Colours vs Age Relations for Star Clusters
Authors: Bertelli G. , Bressan A.G. , Chiosi C. , Nasi E. , Pigatto L.
Published: June 2019

If the integrated colours of a star cluster mainly depend on chemical composition and age, then theoretical calibrations of colours as function of age for different chemical compositions are very useful to obtain quantitative determinations of the age and composition of individual clusters, and thus to trace the chemical history of nearby galaxies. Several calibration curves exist in the literature which rest on the standard theory of stellar evolution. However, a growing amount of observational evidence seems to indicate that overshooting from convective cores may be an important phenomenon in stellar evolution. In fact models computed with overshooting are significantly different from the standard ones. The aim of this preliminary investigation is to study the effects of convective overshooting on the integrated colours of clusters whose turnoff mass is in that range in which convective overshooting is effective.
Cooling Flows and the Formation of Dark matter
Authors: Fabian A. C. , Arnaud K. A. , Thomas P. A.
Published: June 2019

The distribution of matter condensing out of cooling flows in clusters of galaxies and individual elliptical galaxies has been studied using X-ray data and is found to resemble the expected mass profiles of the underlying galaxies. Most of the cooled gas must create objects of high mass-to-light ratio, although some more normal stars are produced. Cooling flows provide an observable mechanism for the continual formation of dark matter around galaxies. Since the conditions at galaxy formation are similar to those in cooling flows if the gas reaches the virial temperature, we suggest that they are local models of galaxy formation.
Formation of Galactic Halos in the Cold Dark Matter Universe: Computer Simulations
Authors: Quinn P. J. , Salmon J. K. , Zurek W. H.
Published: June 2019

We simulate the formation of structure on the galactic scale in the cold dark matter, Ω=1 universe.
Formation of Large Scale Structure in the Explosion Scenario
Authors: Saarinen S. , Dekel A. , Carr B.J.
Published: June 2019

This is a progress report on a study of the formation of large scale structure in the explosive amplification scenario, using N-body simulations. The simulations start when galaxies of the last generation form. The galaxies are distributed at random in expanding shells around random seeds. They start with an expansion velocity 20% larger than the Hubble velocity, in accordance with the similarity solution that was valid before the gaseous shells fragmented into galaxies. The galaxies are treated thereafter as softened point particles that interact only gravitationally, embedded in an N-body background representing inter-shell gas and dark matter (in variable amounts).