bluuebunny/crossref_metadata_2025 huggingface dataset:
Helium Abundances in Gaseous Nebulae
Authors: Clegg R.E.S. , Harrington J. P.
Published: July 2016

New collision strengths, from a 19-state quantum calculation for He I, are used to derive revised He/H ratios in planetary nebulae (PN). Empirical formulae are given, for the correction of He I recombination line fluxes for collisional effects, and for the calculation of the population of metastable helium (He I 23S) in gaseous nebulae. The revised He abundances for PN, for four samples of published line fluxes, show a mean ratio He/H = 0.100 ±0.007 if nebulae with neutral He and Type I PN are excluded. The mean reduction due to collisional effects is only 10% for Galactic PN. It is shown that the hypothesis, that He/H should be independent of nebular temperature and density, is better satisfied when collisional effects are allowed for. The new He abundances indicate that there is very little He enrichment in Galactic PN of Types II, III, and IV, and that the enhancement of Type I PN in He over H II regions is reduced from earlier values by one third.
Some Statistics of Nebular Chemical Compositions
Authors: Aller L. H. , Keyes C. D.
Published: July 2016

Data from a survey of 51 planetary nebulae (PN) observed with the image tube scanner on Shane Telescope at Lick Observatory are combined with those for a comparable number of objects previously reported. For nearly all of the PN included in the later program, it was possible to obtain adequately accurate plasma diagnostics and line intensities to derive ionic concentrations for He, N, O, Ne, S, Cl, and Ar. To get ionization correction factors we calculated theoretical nebular models to fit the excitation level and the intensities of individual important lines. Final model parameters include the stellar radius, emergent flux, Fv(*), from Husfeld et al. (1984, Astron. Astrophys., 134, 139), nebular size, the optical depth at the hydrogenic Lyman limit, and chemical abundances. Many PN do not appear to be optically very thick in the Lyman continuum.
Effect of Density Variations on Elemental Abundance Determinations in Gaseous Nebulae
Authors: Rubin Robert H.
Published: July 2016

When there are changes in gas density within a nebula, various methods of determining the electron density Ne can give different results. Irrespective of differences in ionization structure, there will be deviations in derived values of Ne due to the physics of populating the energy levels. To focus on Ne variations, the electron temperature is held constant. For two cases presented, the values of Ne inferred range over a factor of ten from nine species (line pairs); in order of increasing Ne, they are N+(122/204 μm), O++(52/88 μm), S+(6716/6731 A), S++(18.7/33.5 μm), 0+(3726/3729 A), Ne++(15/36 μm), Ar+3 (4711/4740 A), Ar++(8.99/21.8 μm), and C++(1906/1909 A). This is basically a progression from lower to higher critical densities, Nc, for the lines involved, although other factors are involved. The above order can change somewhat for different mixes of densities.
The Continuum Emission from Planetary Nebulae
Authors: Viegas-Aldrovandi Sueli M.
Published: July 2016

The study of nebular continuum emission is important for several reasons (Pottasch 1984, Planetary Nebulae, Dordrecht: Reidel). First of all, it can provide information about the temperature and the density of the nebula, when the object is large enough, or when the central star is weak enough, so that the nebular continuum is easily observed without interference from the stellar continuum. On the other hand, for small planetary nebulae, both the central star and the nebula contribute to the observed continuum. In this latter case, in order to obtain the stellar continuum the theoretical nebular emission must be used. Thus, studies of the evolution of planetary nebula nuclei through the HR diagram rely on a good calculation of the theoretical nebular continuum.
New Identifications of Faint Central Stars in Extended PN
Authors: Kwitter K. B. , Jacoby G. H.
Published: July 2016

As the first step toward assessing the high-mass end of the PNN (and hence, WD) mass distributions, we report here on new PNN found in extended, low surface brightness PN. Our ultimate goal is to obtain luminosities and temperatures for these stars and to compare them with evolutionary calculations to derive stellar masses. Based on studies of a local sample of PN, Schönberner (1981, 1983) and Schönberner and Weidmann (1983) infer that the PNN mass distribution is sharply peaked near 0.6 M⊙, and that 80% of PNN have masses < 0.61 M⊙. Their sample was necessarily chosen for the existence of photometric data for both the nebulae and their central stars, criteria that excluded small bright PN whose central stars are masked by nebular emission, and large faint PN for which there is little photometric data for the nebulae and/or the central stars. Acknowledging these selection effects, those authors have urged further investigation, especially of low luminosity PNN.
Evolution of Magellanic Cloud Planetary Nebulae
Authors: Meatheringham Stephen J. , Dopita Michael A. , Wood Peter R. , Webster B. Louise , Morgan David H. , Ford Holland C.
Published: July 2016

New evolutionary correlations have been discovered to apply to the population of Planetary Nebulae (FN) in the Magellanic Clouds. Firstly, the age of the nebular shell is found to follow a relationship τ = 890[(Mneb/M⊙) (Vexp/km s−1)]0,6 yr, which is shown to be consistent with a model in which the total energy of the ionised and swept up gas drives the expansion down the density gradient in the precursor AGE wind. Secondly, a tight correlation is found between the expansion velocity and a combination of the Excitation Class and the Hβ flux. This appears to be determined by the mass of the planetary nebula nuclear star. These correlations provide strong observational support for the idea that the PN shells are ejected at low velocity during the Asymptotic Giant Branch phase of evolution, and that they are continually accelerated during their nebular lifetimes.
Stalled Winds: Interactions Between Nebulae and Stellar Winds
Authors: Kaler J. B. , Feibelman W.A. , Shaw R. A. , Henrichs H.
Published: July 2016

Spectra of the nuclei of two planetaries show what appear to be features caused by fast stellar winds as they encounter the surrounding nebulae. Superimposed upon the high velocity (3670 km s−1) ultraviolet P Cygni profiles of Abell 78 are low velocity absorption lines that likely arise from a density enhancement in the wind as it brakes and builds up against the inner edge of the nebula. The deepest portions of these narrow absorptions fall at −78 km s−1 for N V and O V and −26 km s−1 for C IV, which implies a gradient in the decelerating wind, as does the profile of the strongest C IV line. The lower value may be related to the expansion velocity of the inner helium-rich nebulosity, which we associate with a sharp absorption feature. Another density enhancement, evidenced only by absorption lines, appears at −250 km s−1, and may be caused by a rebound shock of the sort envisioned by Kahn (IAU Symposium No. 103, Planetary Nebulae, 1983, 305) and Okorokov et al. (Astr. Ap., 1985, 142, 441).
Optically Thick Wind from Post-AGB Stars and Formation of Planetary Nebulae
Authors: Kato Mariko
Published: July 2016

Self-consistent mass-loss solutions are computed for post-AGB stars, and the evolution of the central star is followed by utilizing the sequences of the steady mass-loss and the static solutions. The mass loss is driven by the radiation pressure gradient and the matter is accelerated in the inner region to the photosphere. The optically thick wind occurs when the H-burning luminosity is larger than the Eddington limit at the surface region. Such a situation is realized in the low-temperature region of the H-R diagram. Therefore no wind solution exists when the surface temperature becomes high enough.
The Spatial Structure of Planetary Nebulae with Binary Central Stars
Authors: Kolesnik I. G. , Pilyugin L. S.
Published: July 2016

The planetary nebulae formation in the detached binaries is considered.
The Position of the Central Stars of PN on the HR Diagram
Authors: Pottasch S. R.
Published: July 2016

Central stars can be placed on the HR diagram if their effective temperature (Teff) and radii are known. Knowledge of the radius can sometimes be replaced by another indication of the luminosity. The distance, which always plays an important, really critical role, is not well known. This is the essential reason that there is so much uncertainty about the position on the HR diagram.
The Evolution of the Common Planetary Nebula
Authors: Köppen J.
Published: July 2016

When we look at evolutionary aspects of PNe, we hope to test our ideas and understanding of the origin of PNe -i.e. why and how gas is expelled from the progenitor star - and of the processes relevant in the evolution of the nebula as well as the central star.
Common Envelope Evolutions of Binary System and Formation of Planetary Nebulae
Authors: Hachisu Izumi , Kato Mariko
Published: July 2016

The more massive component star evolves faster than the less massive one. When it fills its inner critical Roche lobe at the red-giant stage or at the asymptotic-giant-branch (AGB) star stage, the mass transfer begins from the more massive to the less massive component. Since the separation decreases with the mass being transferred, the more massive component star eventually overfills its outer critical Roche lobe. The mass outside the outer critical Roche lobe flows out of the system and the outgoing matter carries away the orbital angular momentum. As a result, the separation of the binary shrinks and the size of the outer critical Roche lobe drops. This shrinkage of the Roche lobe enhances the systemic mass outflow. This process is almost dynamically unstable because the deep convective envelope responses the loss of the envelope mass in an almost dynamical time scale. This dynamical process will stop when most of the hydrogen-rich envelope of the more massive component is lost and its radius becomes less than the radius of the outer critical Roche lobe.
Theoretical Models for the Evolution of Planetary Nebulae Nuclei Tested by Observations
Authors: Tylenda Romuald , Stasińska Grażyna
Published: July 2016

We compare theoretical evolutionary tracks of planetary nebulae nuclei with observational data on over a hundred planetary nebulae in the (log L, log Teff, log texp) space. The simultaneous use of the three coordinates eliminates some interpretation that might be proposed when looking at the (log L, log Teff) plane and at the (Mv, log texp) only. The inconsistencies which we find between theory and observations could be partly removed by adopting a different distance scale.
Comments on the Applications of Planetary Nebulae Research
Authors: Peimbert Manuel
Published: July 2016

A discussion is given about some of the implications that advances in the study of PN are having in other areas of research such as: atomic physics, stellar formation rates, stellar evolution models, dust production, chemical evolution of galaxies, pregalactic helium abundance, stellar dynamics and the extragalactic distance scale.
Rotation Curves in the Outer Parts of Galaxies from HI Observations
Authors: Salpeter Edwin E.
Published: July 2016

21cm observations at the Arecibo Observatory for 9 edge-on spiral galaxies are described. Flat rotation curves are found in most cases.
The Large-Scale Radio Continuum Structure of Spiral Galaxies
Authors: van der Kruit P.C.
Published: July 2016

This review concerns the large-scale structure of radio continuum emission in spiral galaxies (“the smooth background”), by which we mean the distribution of radio surface brightness at scales larger than, say, 1 kpc. Accordingly the nuclear emission and structure due to spiral arms and HII regions will not be a major topic of discussion here. Already the first mappings of the galactic background suggested that there is indeed a distribution of radio continuum emission extending throughout the Galaxy. This conclusion has been reinforced by the earliest observations of M31 by showing that the general emission from this object extended over at least the whole optical image. More recently, van der Kruit (1973a, b, c) separated the radio emission from a sample of spiral galaxies observed at 1415 MHz with the Westerbork Synthesis Radio Telescope (WSRT) into a nuclear, spiral arm and “base disk” component, showing that the latter component usually contains most of the flux density. This latter component is largely non-thermal and extends over the whole optical image (see also van der Kruit and Allen, 1976). Clearly it is astrophysically interesting to discuss the large-scale structure of the radio continuum emission.
The Dynamics of the Spiral Galaxy M81
Authors: Visser H.C.D.
Published: July 2016

The spiral galaxy M81 is a challenging object for testing a density-wave theory. It is of large angular size and favourably inclined to the line of sight; radio observations of neutral atomic hydrogen showing well defined spiral arms with noncircular motions are available (Rots and Shane 1975), and there is evidence from surface photometry for density waves in the old disk population (Schweizer 1976). Can these observations be unified in one density-wave model?
Radio Observations of Molecules in Nearby Galaxies
Authors: Whiteoak J.B.
Published: July 2016

The observation in 1965 of absorption due to the 18 cm ground-state transition of OH in the direction of Cas A (Weinreb et al., 1963) marked the first occasion on which a molecular cloud was detected at radio wavelengths. However, it was not until the later discovery of high-intensity OH emission (Weaver et al., 1965) that attention turned to nearby galaxies. Unfortunately, searches for OH emission in the Magellanic Clouds (McGee et al., 1965; Radhakrishnan, 1967) and in more distant galaxies (Roberts, 1967) were unsuccessful. The first detection of an OH transition, in absorption against the radio continuum of NGC 253 and 3034 (Weliachew, 1971), went almost unnoticed because the results were unconvincing. However, Whiteoak and Gardner (1973) and Nguyen-Q-Rieu et al. (1976) confirmed the existence of the absorption.
Interacting Galaxies: The Kinematics of NGC 4038/39 and the HI Bridge Between M81 and NGC 3077
Authors: van der Hulst J.M.
Published: July 2016

Computer simulations of galaxy encounters (Toomre 1974 and references therein) have strongly supported the idea that the luminous bridges and tails in many multiple galaxies are a result of gravitational interaction. The need for an observational test of the kinematics of these models has prompted observations of NGC 4038/39 (the “antennae”) in the 21 cm line of neutral hydrogen (HI) with the Westerbork Synthesis Radio Telescope (WSRT) at an angular resolution of 100″×150″ (α×δ). A detailed description of the observations and data reduction is given elsewhere (van der Hulst, 1977). Neutral hydrogen is definitely associated with the tails as was already indicated by the filled aperture observations of Huchtmeier and Bohnenstengel (1975) at the lower resolution of 8′.7. The distribution of HI column density is shown in Figure 1 superposed on a print of a plate obtained by F. Schweizer with the 4 m telescope at Cerro Tololo. Owing to the low declination of the object (−19°) the WSRT map is affected by several sidelobes; the main effect is an attenuation of extended east-west structures, for which reason the HI along the southern tail in Fig. 1 shows a gap. Computer experiments and a comparison with the filled aperture observations show that the WSRT data are entirely consistent with an HI distribution which is uniform along this tail and increases with about a factor 2 at the extreme end, where the tail is very blue and small HII regions are present (Schweizer, elsewhere in this volume). The tails contain 2.9 × 109M⊙of HI (assuming a distance of 20 Mpc), 85% of which is in the southern and more prominent tail. About 1.1 × 109M⊙of HI is associated with the galaxies which are not spatially resolved at the present angular resolution.
Equidensitometric determination of angular diameters and mean surface magnitudes of compact galaxies
Authors: Högner W. , Richter N.
Published: July 2016

In a previous publication (1975) we showed that it is possible to determine the maximum diameters of galaxies on photographic plates by means of the photographic equidensity method. This method was applied especially to 235 members of the Coma cluster. On Tautenburg plates it was possible to determine for these objects equidensitometric angular diameters down to 10 arc sec.
On the tidal origin of M51-type systems
Authors: Vorontsov-Velyaminov B.
Published: July 2016

We established M51 systems as a class of interacting pairs of galaxies in 1959. in 1975 I showed that among 160 systems with this appearance the ratio of luminosities (and hence masses) of the components varies from 1:1 to 1:0.01. in the latter case, the companion is comparable in mass and dimension to an isolated H II region. the number of such M51-type systems increases as the luminosity of the companion decreases. Small companions cannot draw spiral arms from the primary companions by means of tides. Yet, they are observed at the tips of spiral arms. Thus, they must originate at the same time as the spiral or form within them. in some cases, these companions emanate from the spiral arm, as is shown by comparison of observations and calculations.
Extended radio emission in clusters of galaxies: recent Westerbork observations
Authors: Valentijn E.A. , van der Laan H.
Published: July 2016

Whether galaxy clusters, in addition to a number of radio sources associated with individual cluster members, have an extended radio emitting region designated as cluster halo is in an interesting way related to several questions concerning cluster characteristics:
Clusters with extended radio emission at high frequencies
Authors: Wielebinski R.
Published: July 2016

The existence of ‘haloes’ in clusters of galaxies was deduced by Ryle and Windram (1968) for the Perseus cluster and by Willson (1970) for the Coma cluster at 408 MHz by comparing total flux measured by a single dish with the sum of fluxes of radio sources found in the field. A direct measurement of the extended source Coma C was made by Jaffe et al. (1976) at 610 MHz. the failure to detect the halo of Coma at higher frequencies is attributed by all authors to a steep spectrum of this extended component.
An analogy between simulated and actual clusters of different kinds
Authors: Paál G.
Published: July 2016

A study of clusters is presented by means of the function Nm(θ), i.e. the total number N of members heavier than a limiting mass m, as a function of the limiting projected angular distance from the centre θ. As a rule such a function is found to possess a well-defined maximum change of slope - an apparent Ȝdeflectionȝ - if the limiting mass is large enough (see Figure 1 a-g). Some possible definitions of this deflection and the corresponding special Ȝcore radiusȝ of the cluster are described elsewhere (Astrofizika, 7, 435, 1971). the typical occurrence and rather regular behaviour (systematic temporal variations) of this deflection in a sample of 17 configurations simulated by S.J. Aarseth and S.D.M. White for different conditions prove this feature to be a natural consequence of the gravitational interaction of many bodies in a statistical sense; it is apparently a characteristic of core formation and the evolution of clusters. in the case of computer data the existence of such deflections cannot possibly be due to any observational error or uncertainty or erroneous personal judgement. the corresponding diagrams, Nm(θ) for clusters of galaxies (see also loc. cit.) are found to be practically indistinguishable from those of star clusters and simulated systems. They show the very same type of deflection, the same remarkably small dependence on the choice of the limiting mass, that of the Ȝcentreȝ, the field correction etc. As simulations give just the same diagrams as have been obtained observationally it is plausible to regard also these observational findings as dynamically necessary and not chance coincidences, unless the actual clusters of galaxies are stabilized by some continuously distributed intergalactic Ȝhidden matterȝ instead of the masses of observable discrete bodies themselves. However one can hardly accept a radically different explanation for the apparently identical phenomenon in the case of systems of galaxies on the one hand and those of stars on the other. Estimates of the crossing time tc of the systems together with morphological arguments and numerical experiments indicate that actual “rich” clusters of galaxies might typically be near a particular epoch of very rapid systematic cosmological evolution. A considerable decrease of the aforementioned “core radii” (a transition between two nearly constant values) with the other characteristic sizes of the systems almost unchanged (Figure 1 a-d). the corresponding phenomena were detected earlier observationally and consequently these empirical data, together with their consequences, now seem to be once again corroborated (see e.g. Astron. Nachrichten, 297, 311, 1976). These remarkable analogies suggest that a similar mechanism is responsible for the formation and evolution of conspicuous cores of clusters and a similar solution of the somewhat controversial situation with regard to mass segregation both for clusters of galaxies and open star clusters (e.g. by properly choosing the initial conditions).
Radio emission of Abell clusters in the GB and GB2 regions
Authors: Michalec Adam , Machalski Jerzy
Published: July 2016

The observational material is based upon pencil-beam surveys made with the NRAO 300-ft radio telescope at 1400 MHz. the GB survey (Maslowski 1972) covers 0.1586 sr in the zone 7h15m ≦ α ≦ 16h20m, 45°.9 ≦ δ < 51°.8. the GB2 survey made by Machalski in 1975 was carried out in the region defined by 7h08m ≦ α ≦ 16h58m, 31°.8 ≦ α 39°.6 (0.2828 sr).
The Distribution of Masses and Radii of White-Dwarf Stars
Authors: Shipman Harry L.
Published: July 2016

The status of determinations of white dwarf radii by model atmosphere methods is reviewed in this paper. Details will appear elsewhere (Shipman 1978). In brief, the results are that (i) the mean radius of a sample of 95 hydrogen-rich stars with parallaxes is 0.0131 R⊙; (ii) the mean radius of a sample of 13 helium-rich stars is 0.011 R⊙, indistinguishably different from the radius of the hydrogen-rich stars; and (iii) that the most serious limitation on our knowledge of the mean radius of white dwarfs is the influence of selection effects. An estimate of the selection effects indicates that the true mean white dwarf radius is near 0.011 R⊙.
Horizontal-Branch Stars in the Log Teff, Log G Diagram
Authors: Philip A. G. Davis
Published: July 2016

A review of the available Strömgren four-color data concerning horizontal-branch (HB) stars is presented. Several observers have studied seven globular clusters (with [Fe/H] values from −2.2 to −1.3) and more than 100 HB stars in fields at high galactic latitudes over the last ten years at Kitt Peak, Cerro Tololo, Mt. Wilson and Steward Observatories. The predictions of model atmospheres (Kurucz, 1976) allow one to calculate atmospheric parameters such as θeff, log g, and MV(Philip, Miller and Relyea, 1976). These parameters then can be compared with the predictions of evolutionary models (Sweigart and Gross, 1976).

A comparison of the observed data with evolutionary tracks indicates that within the rms error of observation and the computational error of the models the data and the tracks agree quite well. This matches the case for Population I stars, where a similar analysis shows a good match between observational data and evolutionary tracks (Philip,et al. 1977).
Physical Properties of Cepheids and RR Lyrae Stars
Authors: Pel J. W. , Lub J.
Published: July 2016

At the Leiden Southern Station a large program on galactic pulsating variables has been carried out with the Walraven five-channel photometer. For 170 Cepheids and 100 RR Lyrae stars south of δ =+15° there are now available 30000 VBLUW measurements (Walravenet al., 1964; Pel, 1976; Lub, 1977b). These data are used to derive physical properties of the variables. A general discussion of the VBLUW system and its calibration for A-G stars by means of the theoretical fluxes of Kurucz (1975) has been given by Lub and Pel (1977). Following this calibration, reddening and blanketing corrections, as well as effective temperatures, gravities, and their cyclical variations were determined, and luminosity and radius curves were derived (Cepheids: Pel, 1977; RR Lyrae stars: Lub, 1977a). We will present here some interesting results that have been obtained from these data. A more detailed discussion is in preparation.
The Use of Praesepe for the Definition of the Lower Part of the Zero-Age Main Sequence
Authors: Golay M.
Published: July 2016

In an attempt to determine the Hyades distance (Golay, 1973), it was assumed that stars of the same “photometric 0m.01 box” (see Golay, 1977a) have the same visual absolute magnitude. The large amount of photometric data in the UBV B1B2V1G photometric system allows a discussion on this hypothesis (Golay, 1977b). We have 60 “photometric 0m.01 boxes”, each containing a central star of known trigonometric parallax and at least one Praesepe star. We select the 16 boxes (Table I) containing single stars or binaries with an estimated mass ratio, a relative probable error < 30% for the parallaxes and a standard deviation for colors <0m.007. The UBV B1B2V1G colors, the indices (B-V), (B2-V1) and the magnitude mVare taken from theSecond Catalogue(Rufener, 1976) and the internal catalogue of the Geneva Observatory. The color index (B-V) is taken from Johnson (1952, 1957), Johnson and Knuckles (1955), the trigonometric parallax from Jenkins (1952, 1963) and Gliese (1969) and the spectral type for Hyades stars from Morgan and Hiltner (1965). The listings of all 0m.01 photometric star boxes in the UBV B1B2V1G system are given by Golay (1977c). The parallax obtained for Praesepe is π(0″.001) = 6.175 ± p.e. 0.1, i.e. a distance modulus (m-M) = 6m.05 and a distance of 162 parsecs. Golay (1977c) published the differences of the distance moduli for pairs of clusters having stars in the same box. The distances of these clusters is given in Table III, assuming a distance of 162 pc for Praesepe. The accuracy of this method is independent of both the distance magnitude and the chemical composition of the stars of a cluster since the stars have to be in the same box as a star with a known trigonometric parallax. The main sequence of Praesepe and a sample of Hyades stars, in the same photometric box with a Praesepe star is given in Table II. The depth effect in Praesepe being very small, the main sequence is very thin and the main sequence fitting procedure is better starting from Praesepe than from the Hyades.
The HR Diagram of Abnormal A-Type Stars
Authors: Mendoza Eugenio E.
Published: July 2016

We have observed over a hundred A-type stars in the ∝ (16) ∧ (9)-photometric system defined by Mendoza (1976a, b; 1977). These stars also have UBVRI measurements. Sixty five stars have been observed in the thirteen color-photometric system (Mendoza 1971, and Johnson and Mitchell 1975).
The Evolution of the Integrated Colors of Globular Clusters and Elliptical Galaxies
Authors: Ciardullo R.B. , Demarque P.
Published: July 2016

The purpose of this paper is to show the first results of a program designed to construct population models of stellar systems on the basis of theoretical data of stellar evolution. Synthetic HR diagrams were obtained using the isochrones and luminosity functions of Ciardullo and Demarque (1977). This last work is based on the stellar models of the Yale - IBM research group (Mengel, Sweigart, Demarque and Gross 1978; Sweigart and Gross 1976; 1978). The conversion from the theoretical HR diagram to observable parameters is made with the help of theoretical model stellar atmospheres principally due to Kurucz (1976), Relyea (1976) and Bell and Gustafsson (1975). The program provides a synthetic C-M diagram and integrated properties for the system given the following parameters: the chemical composition in terms of the (Y,Z) pair, the age, the total number of stars, the initial mass function (IMF) and the law of mass loss from stars in the system. In this brief paper, we shall concentrate on theintegratedproperties of theoretical star clusters and then remark on some interesting consequences for the color evolution of elliptical galaxies.
Nucleosynthesis in Massive Population II Stars
Authors: P. Dearborn David S. , Trimble Virginia
Published: July 2016

According to the conventional wisdom, the first stars formed in our Galaxy, including the massive ones responsible for most heavy element synthesis, must have had metal abundances much lower than solar. They may also have had somewhat lower helium abundances, corresponding to an enrichment ΔY/ΔZ = 2.7 ± 1.0 over the history of the Galaxy, a larger ratio than is readily accounted for by standard (Arnett-type) supernovae (Hacyan et al. 1977) or by mass shed from lower mass stars (Gingold 1977). But early nucleosynthesis must have occurred in stars with Pop II compositions. Several authors (Ezer and Cameron 1969; Cary 1974; Chiosi and Nasi 1974; Trimbleet al. 1973) have modelled and evolved such stars, but none of the studies followed the stars far enough from the main sequence to be able to say anything very quantitative about their contribution to galactic chemical evolution. We address here the question of the effects of initial composition upon helium and heavy element production in massive stars.
Microturbulence as a Third Dimension in the G-K Giant Region of the HR Diagram
Authors: Foy R.
Published: July 2016

The structure of the HR diagram in the G-K giant region is complex, because of the funneling effect and of the intersection of evolutionary tracks for different stellar masses. Therefore it is impossible to derive the age of a cool giant from its location in the HR diagram alone. To remove this indeterminacy a third dimension is needed, and we suggest microturbulence as the appropriate observational parameter.
A Revised Classification System in the Red for S Stars
Authors: Ake Thomas B.
Published: July 2016

A classification scheme in the red spectral region for the S stars is described. For those stars exhibiting both ZrO and TiO bands, a modified version of the Keenan (1954) system is used for the assignment of temperature subtypes. For the pure S stars, a new system is introduced utilizing ZrO band strengths and the sodium D lines. Comparisons between the revised types and photometric colors have been made. In addition a new abundance index is proposed based on the relative strength of YO compared to ZrO and TiO. The revised system provides a connecting link between the M and C systems so that all red giants may be classified consistently from the strengths of TiO, ZrO and Na D.
Optical and Infrared Properties of the Newly Formed Stars in CMa R1
Authors: Herbst William , Racine Rene , Warner John W.
Published: July 2016

UBVRIJHKL photometry and MK spectral types have been obtained for stars illuminating nebulae in the CMa R1 association. Five stars, including the two classical Herbig-emission-stars Z CMa and HD 53367, have (K-L) excesses and/or emission line spectra indicating the presence of circumstellar matter. A number of stars also have (V-K) indices larger than expected on the basis of their spectral types and (B-V) indices, suggesting that a steeper than normal extinction law applies to these stars. The color-magnitude diagram for the association is unusual; many stars over the entire spectral range of the association (B0 to A1) lie more than 1 magnitude above the ZAMS in V. The middle and early type B stars with this property are all variable stars and most have rotationally broadened spectra and/or shell indicators. No stars later than B5 are on the main sequence, making CMa R1 probably the youngest stellar group yet identified. It suggests an age of ~3 × 105years, compatible with the suggestion that a supernova explosion triggered star formation in this region. A comparison is made between the observations and theoretical models of pre-main sequence stars. A bolometric luminosity of Mbol< −4m.3 is derived for Z CMa implying a core mass of M > 10 M⊙, and a spectral type of ~B1, if the star is on the ZAMS.
A new catalogue of quasi-stellar objects
Authors: Hewitt A. , Burbidge G.
Published: July 2016

We have prepared a new catalogue of QSOs and BL Lac objects containing approximately 3400 entries. A complete update of the Hewitt-Burbidge (1980) catalogue has been made with approximately another 2000 objects with known redshifts added. The references to discovery, magnitudes, redshifts, color, spectra and polarimetry have been updated for the objects listed in 1980, and complete new references are included for the new objects. In addition to the basic optical information, the new catalogue also contains X-ray, radio and infrared information for all objects. Absorption redshifts are listed when they are available. A supplementary catalogue which is now in preparation will contain similar information for objects described variously as Seyfert galaxies, N systems and AGNs. In doubtful cases we have used the operational dividing line ƶ = 0.1. All objects with ƶ < 0.1 are put in the supplementary catalogue unless their discoverers have unambiguously defined them as QSOs. With approximately twice as many objects included it is interesting to note that:

a)

There are still very few genuine BL Lac objects, ∼100.

b)

The largest number of additions has come from identifications using the objective prism-grism techniques.
Observations of QSOs and related objects with EFOSC, the ESO faint object spectrograph and camera
Authors: D'Odorico S. , Cristiani S. , Clowes R.G. , Keable C.J.
Published: July 2016

EFOSC is a standard ESO instrument operating at the Cassegrain focus of the 3.6 m telescope since April 1st, 1985. A description of its optical design and operating modes is given in Enard and Delabre (1982) and Dekker and D'Odorico (1985). Briefly, it is a focal reducer with spectroscopic capability. The collimator produces a collimated beam with a diameter of 40 mm which passes through a filter and/or grism. The f/2.5 camera focusses the beam on the detector which is at present a thinned, back-illuminated RCA CCD with 320×512 pixels. The pixel size is 30 μm which corresponds to .675″ on the sky. There are three remotely controlled wheels in the instrument: the aperture wheel in the focal plane of the telescope, with long slits of different widths, a filter and a grism wheel with 12 positions each. The instrument can be operated in four different modes: direct imaging, slit spectroscopy, grism or multiple object spectroscopy with specially made aperture plates.
X-ray to Infrared Continua of optically selected quasars
Authors: Elvis Martin
Published: July 2016

X-ray to infrared continuum data for nine optically selected (PG) quasars show a form which can be simply described in terms of two components — a power law of slope ∼1 joining smoothly the 1–10 μm infrared with the 0.1–10 keV x-ray points and superimposed on this, a ‘big bump’ of optical-uv emission. The ‘big bump’ can be interpreted as thermal emission from an accretion disk. In a unique case where this ‘big bump’ extends to soft x-rays the accretion disk parameters can be constrained interestingly.
A statistical analysis of the radio properties of a large sample of 374 optically selected quasars
Authors: Krishna Gopal , Steppe H. , Ghosh T. , Saripalli L.
Published: July 2016

Using a large, unbiased sample of 374 optically selected QSOs, of which 54 are radio detected, we have computed for different redshift ranges the probability distribution function φ (R) of R defined as the ratio of monochromatic luminosities at 15 GHz and 2500 Å in the QSO's rest frame. A significant variation of φ (R) with redshift is noticed. At small redshifts (z < 0.5), the distinctive feature of φ (R) is a peak near R∼102, arising due to the QSOs having steep radio spectrum(αr<−0.5).
Observations of 3C273 with high north-south resolution
Authors: Cohen M. , Biretta J. , Schaal R. , Comoretto G. , Bååth L. , Nicholson G.
Published: July 2016

The quasar 3C273 lies at a declination of +2°. Maps made with northern hemisphere VLBI Networks clearly show superluminal motion, but the north-south resolution is poor and details cannot be seen. We have now made two observations at 10.7 GHz with the Itapetinga Radio Observatory in Brazil, and one at 5.0 GHz using the Hartebeesthoek Observatory in South Africa along with the European and U.S. VLBI Networks (Biretta et al. 1985).
High resolution VLBI observations of the nuclei of bright galaxies and quasars at 327 MHz
Authors: Ananthakrishnan S. , Kulkarni V.K.
Published: July 2016

An intercontinental VLBI experiment at 327 MHz involving the Ooty Radio Telescope and telescopes at Jodrell Bank, Westerbork, Torun and Crimea was carried out during December 8–12, 1983. The purpose of the experiment was to (i) establish the feasibility of performing MKII VLBI observations from India and (ii) to study the low frequency structure of nearby galaxies, quasars and some other well known radio sources at metre wavelengths. The sources observed were NGC 262, 315, 1052, 1068, 1265, 1275, 4151, 4486, 7674 and 3C 120; PKS 1055+018, 1148−001 and CTA 102; 3C 237 and SS 433. The bright NGC galaxies chosen were selected from an Interplanetary Scintillation survey of 150 nearby galaxies (Bagri and Ananthakrishnan 1983); they were found to have a flux density greater than about 0.2 Jy in subarcsec components at 327 MHz and have high frequency VLBI observations. The quasars chosen are amongst the most compact sources known at metrewavelengths. The other objects were the well known sources which have been studied extensively at higher frequencies.
The core and halo structure of the quasar 4C18.68
Authors: Gower Ann C. , Hutchings J.B.
Published: July 2016

We present new VLA observations of this complex low redshift quasar, which was previously modelled as a precessing twin-jet nucleus. A new 2cm map fails to show the predicted curvature near the nucleus. B and C configuration maps have been obtained, to study the halo of the source. These results suggest that the radio source is not very old, and appears to have undergone two major changes of orientation in its < 107 year history.
The peculiar radio structure of quasar 1320+299
Authors: Cornwell T.J. , Saikia D.J. , Shastri P. , Feretti L. , Giovannini G. , Parma P. , Salter C.J.
Published: July 2016

The radio source B2 1320+299 is associated with a 20m QSO. Apart from the core component, it has two outer components on the same side of the QSO; it was therefore classified as of the one-sided (‘D2’) type. The radio structure is unusual in that the three slightly non-collinear components are apparently unconnected and the projected linear size for any plausible redshift is large for a ‘D2’ source (Feretti et al. 1982, Astron. Astrophys.115, 423). The radio structure has now been mapped with the VLA (λ20 & 6 cm, B array and λ20, 6 & 2 cm, A array; Figs.1a, b).
A study of one-sided radio quasars
Authors: Saikia D.J. , Shastri P. , Cornwell T.J. , Salter C.J.
Published: July 2016

Although most powerful extended radio quasars have lobes of radio emission on opposite sides of the nuclear component, a significant number appear to have extended emission on only one side. We have observed ∼40 such sources (mostly from the compilation of Kapahi 1981) with the VLA, to confirm their classification and study their properties.
Wind-type flows in quasars
Authors: Ferrari Attilio , Trussoni Edoardo
Published: July 2016

Jets are found in many astrophysical phenomena, from young stellar objects and collapsed stellar cores to quasar and radiogalaxies. Therefore they must represent a common dynamical phenomenon, while different morphological characteristics arise from the interaction with specific environments (Ferrari and Tsinganos 1985). In order to investigate the basic aspects of jet dynamics and morphologies, we have proposed a simple analytical treatment based on the fluid theory of stellar winds (Parker, 1063), which allows a direct test of different physical effects (Ferrari et al. 1985, 1986). We discuss here implications for the physical theories of quasars.
Models of steady thick accretion discs around a Schwarzschild hole
Authors: Anderson M. R.
Published: July 2016

An outline is given of a project to model thick accretion discs around a black hole. A simple shear viscosity is assumed and the effects of radiation transport and thermal conduction neglected. Preliminary results are given for the equatorial structure of the model discs.
Evolution of the Luminosity Function
Authors: Green Richard F.
Published: July 2016

In this review, the currently published, complete, spectroscopically identified samples of quasars are assembled to produce a composite luminosity function, independent of evolutionary assumptions. Two interpretations of the change with cosmic time provide reasonable fits to the data. Luminosity evolution implies a fixed population of host objects, with nuclear luminosity that fades with advancing cosmic time; some dependence of the timescale on intrinsic luminosity is required. Density evolution traces objects of comparable luminosity to find the change in space density, without a requirement of long lifetime. The change in co-moving volume density depends on luminosity; newer data suggest that somewhat stronger evolution is required at the low luminosity end than the models of Schmidt and Green allowed. Caution is advised in drawing direct physical conclusions about the evolution of individual quasars from mathematical representations of ensemble properties.
Noncosmological Redshifts
Authors: Narlikar Jayant V.
Published: July 2016

Although the majority of astronomers interpret the redshifts of quasars according to Hubble's law, there are isolated cases as well as detailed studies indicating that the redshifts of quasars and even some galaxies may have noncosmological components. The evidence discussed here will be on two counts: (i) the periodicities in redshift distributions, (ii) the associations between discrepant redshifts objects. In addition, theoretical constraints on physical models based on the cosmological hypothesis will be briefly mentioned.
Optical brightness monitoring of the twin QSO Q0957+561 A,B
Authors: Schild R.
Published: July 2016

The gravitationally lensed QSO 0957+561A,B has been monitored from 1979 to the present with CCD cameras. We believe that the arrival time difference is 1.2 ± 0.2 years.
Absorption spectrum of the z=3.78 QSO 2000-330 at high resolution
Authors: Hunstead R.W. , Murdoch H.S. , Blades J.C. , Pettini M.
Published: July 2016

The forest of absorption lines observed in all high-redshift QSOs at wavelengths shorter than Ly α emission is generally accepted as being due to a population of intergalactic hydrogen clouds. In order to study the physical properties of these clouds and possible changes in the properties with redshift it is first necessary to establish the true continuum level. The difficulty in defining continuum levels in the Ly α forest region is readily acknowledged in the literature but only rarely do published spectra show the adopted continuum.
Rocket Experiment to Search for the Near-Infrared Extragalactic Background Light
Authors: Matsumoto T. , Akiba M. , Murakami H.
Published: July 2016

A rocket experiment was carried out to search for the extra-galactic background light at 1–5 μm. After subtracting the foreground radiation, there still remains an appreciable amount of isotropic diffuse radiation with a complex spectral feature which is possibly attributed to extragalactic origin.
A Study of the Hubble Flow
Authors: Wampler E. Joseph
Published: July 2016

It is found that the Hubble diagrams for quasars and giant radio galaxies are very similar. Either the evolution of giant branch stars in the galaxies closely matches the evolution of the quasar nonthermal emission or the cosmological deceleration parameter qo is close to 3.
Distance Moduli from the Tully-Fisher Relation
Authors: Giraud E.
Published: July 2016

When the Bottinelli et al. version of the Tully-Fisher relation is applied to derive distances, and when the observed parameters are used to predict the Malmquist bias at a given distance, the observed variation of the Hubble ratio as a function of kinematic distance is about 2.5 times the predicted variation.
A New Measurement of the Geometry of Space
Authors: Loh Edwin D.
Published: July 2016

This paper discusses the recent measurement of the number of galaxies vs. redshift and flux and presents new results pertaining to the two dimensionless geometrical quantities that describe the geometry of the conventional big-bang cosmology, the density parameter Ω and the dimensionless form λ = Λ/(3H02) of the cosmological constant. In contrast to the classical redshift-magnitude test as applied to the brightest galaxies in clusters, this new method is able to separate the effects of evolution from geometrical effects and is therefore able to measure the geometry of space. The 95% confidence limits are Ω - λ = 0.9−0 5+0 7 and −1.5 < Ω + λ < 7.1. The principal conclusions are these: (1) For both λ = 0 and inflationary models of the universe, this measurement and primordial nucleosynthesis imply a large density of nonbaryonic matter. (2) Hubble's constant H0 and the age of the universe τ are constrained by 0.60 < H0τ < 0.88 (95% confidence).
The Angular Size - Redshift Relation as A Cosmological Tool
Authors: Kapahi V.K.
Published: July 2016

The angular size - redshift (θ - z) relation can in principle be used to discriminate between world models because the angular size subtended by a rigid rod is quite a sensitive function of cosmology, specially at z ≳ 0.5. The test is simpler to apply to objects for which a metric diameter is measured than to objects with isophotal diameters (Sandage 1961). It was first suggested by Hoyle (1958) at the Paris symposium on Radio Astronomy, that the separation between the two lobes of extragalactic radio sources such as Cyg-A, could be used for performing such a test. In an Einstein-de Sitter Universe sources like Cyg-A cannot have angular sizes ≲ 15 arcsec (the minimum occuring at z = 1.25) whereas in the Steady State Universe their sizes should asymptotically approach a value near 4 arcsec at large redshifts. It was not until the early seventies that the test was actually applied to samples of radio quasars with redshifts of upto ∼ 2 (Legg 1970; Miley 1971; Wardle & Miley 1974). The angular sizes were found to show a large scatter due to a wide distribution of physical sizes and the projection effects associated with the essentially linear radio structures. The upper envelope to the θ -values (which would be expected to show much less scatter) nevertheless appeared to fall off monotonically with increasing z, more or less like the Euclidean relation θ ∝ z−1. The θ - z test thus appeared to be incompatible with the predictions of uniform world models in which the linear sizes of quasars are independent of epoch.
Simulations of Large-Scale Structure Compared to Abell Cluster Distribution
Authors: Batuski David J. , Melott Adrian , Burns Jack O.
Published: July 2016

The amount of structure present among the Abell clusters out to redshift z = 0.085 has been compared with numerical supercomputer simulations (with 643 particles) of the isothermal, neutrino, and cold particle models for large-scale structure, assuming a flat universe and H = 50 km sec−1 Mpc−1. High-density clusters of particles were identified in each simulation. Correlation and percolation tests were then used to compare the spatial distribution of these high-density points with the apparent superclustering among Abell clusters. While all of the models had some small superclusters (the neutrino model has too many), none came very close to possessing the extremely extensive structures found in the Abell clusters (generally, disagreement by 2σ or more).

A second set of simulations used the cold particle model with Ω = 0.2 and 0.5. The structures found in these simulations were certainly larger than those of the Ω = 1.0 cold particle case, but still > 2σ too small in comparisons with the Abell clusters.