bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigations of DDDM 1; The Fourth Halo Planetary Nebula
Authors: Shchelkanova A. Yu.
Published: July 2016

Spectral (λλ 4100 - 7300 A) and photoelectric observations of DDDM 1 (61 + 41°1; δ1950 = +38°48′) were made in 1985–86 on Crimean Station of Sternberg State Institute. Photographic absolute H3 flux is found to be F(Hβ) = (3.0±0.57) 10−12 erg cm−2 s−1, angular radius φ = 1″.0±0″.5. Interstellar reddening E(B-V) for the object is found to be less than 0″.02. Integrated flux from central star and gaseous nebula was measured in UBV-filters V = 14m.71, B-V = 0m.12, U-B = −0m.9.
Oxygen Depletion Variations in Planetary Nebulae and Shells Ejected from Luminous Population I Stars
Authors: Dufour Reginald J.
Published: July 2016

Recent studies by the Peimberts have noted an anticorrelation between 0 and N abundances in the Type I He- and N-rich PN, such that N+) is approximately constant. We report observations of the spectra and composition of several “planetary nebula-like” shells surrounding more luminous population I O- and WR-stars, which indicate that this 0-N anticorrelation extends upwards in the HR diagram to among the most luminous stars known, with O/H values in the shells ranging down to −2 dex below Solar. We report optical and UV spectrophotometry of the shell nebulae NGC 2359, NGC 6164-5, NGC 6888, NGC 7635, AG Carinae, and the condensations around Eta Carinae, which generally support this anticorrelation trend. We also discuss variations in other elements such as He, C, S, and Ar in these shell nebulae, and compare the compositional variations to the expectations from stellar evolution and nucleosynthesis models of intermediate and massive stars.
Abundances of C, N and O in Planetary Nebulae
Authors: Nikitin A. A. , Kholtygin A. F. , Sapar A. A. , Feklistova T. H.
Published: July 2016

The abundances of C, N and O in planetary nebulae must correspond to the evolutionary status of their progenitor red giant stars. The best spectral features for abundance determination of these elements are the recombination lines, which depend weakly on the variations of Te and ne. The abundance ratio of the ions A+ and H+ can be given by [1–3].
Electron Densities in Planetary Nebulae
Authors: Stanghellini Letizia , Kaler James B.
Published: July 2016

A large sample of forbidden lines -[O II], [S II], [Ar IV], and [N I]- have been analyzed to obtain electron densities for 134 planetary nebulae.
Comparison of Different Treatments of the Radiation Transfer in Model Calculations of Planetary Nebulae
Authors: Bässgen G. , Bässgen M. , Grewing M.
Published: July 2016

A method of Radiation Transfer treatment (Global Shell Model (GSM)) has been developed, different from the On the Spot Approximation (OSA), taking into account all diffuse reemission from radiative recombination of hydrogen and helium in the nebula itself. For optically thick and optically thin nebulae the method automatically reproduces the On the Spot Approximation and the models without any Radiation Transfer, respectively.
The Origin of the Zanstra Discrepancy: UV Excess in the Central Star Continuum?
Authors: Henry R. B. C. , Shipman H. L.
Published: July 2016

The temperature of a planetary nebula central star (CPN) may be determined by observing the nebular flux in an H I or He II recombination line and the stellar flux in a continuum band. The former measures the integrated UV stellar continuum blueward of the ionization edge of the recombined ion. By assuming a continuum shape (usually a blackbody), the ratio of these two fluxes yields an effective temperature for the CPN. This particular method, first introduced by Zanstra (1931), has an advantage over others in that the observables are relatively straightforward to obtain. However, this method also carries a troublesome ambiguity with it: CPN temperatures determined using He II recombination lines. This Zanstra discrepancy is reviewed by Kaler (1985) and Henry and Shipman (1986). Examples of He II and H I temperatures for numerous CPNs are given in Pottasch (1984), where it is shown that the He II Zanstra temperature often exceeds the H I temperature by several times 104K.
Are Zanstra Temperatures Always Real?
Authors: Aller L. H.
Published: July 2016

The classical Zanstra method compares a H Balmer line or He II λ4686 with flux from a limited region of the planetary nuclear (PNN) spectrum to obtain the central star temperature T(PNN). Long ago it was found that generally T(He II) > T(H I), a result attributed to differing optical depths at the Lyman limits of He II and H I; T(He II) often was regarded as the “real” temperature. Much attention has been paid to discordances between Zanstra temperatures and those found by other means, such as the energy-balance (EB) method. (see e.g., Preite-Martinez and Pottasch 1984).
A Search for Cool Companions of Planetary Nebula Nuclei
Authors: Bentley A. F.
Published: July 2016

At present only a small number of planetary nebulae are known to possess binary nuclei. Since approximately 2/3 of main sequence stars are members of binary or multiple star systems, one might expect a large fraction of PN central stars to have gravitationally bound companions. Additionally, late-type stars are more numerous, and due to their low luminosities would be difficult to detect by visual observational methods at distances where PN are typically found (≧ 1 kpc). (Only 5 known PN are thought to be nearer than 0.5 kpc). It is thus possible, and in our view probable, that a significant number of PN nuclei possess cool companions, hitherto undetected.
The Nature of the Hot Companion of the G8 IV Nucleus of Abell 35
Authors: Grewing Michael , Bianchi Luciana
Published: July 2016

The nucleus of the large, low surface brightness planetary nebula Abell 35 (Abell 1966) belongs to the small group of objects which are known to have a binary nucleus. From his photometric and spectroscopic study of the object, Jacoby (1981, Astrophys. J. 244,903) found the star SAO 181201, a G8 IV star, to be located near the apex of the parabolic region of enhanced [O III] emision which is completelely absent in H∝. The G8 IV star can clearly not be the ionising source for this nebulosity nor the larger scale nebulosity of the PN proper. Jacoby concluded that the central object must be a binary and suggested a hot subdwarf as the second component, which is masked in the optical by the bright SAO star. This interpretation is supported by the analysis of the DDO and UBVRI photometry, which shows that the observed colour indices can be fitted if one assumes a 50.000 K blackbody companion.
Planetary Nebulae in Galaxies Beyond the Local Group
Authors: Ford H. C. , Ciardullo R. , Jacoby G. H. , Hui X.
Published: July 2016

Planetary nebulae can be used to estimate the distances to galaxies and to measure stellar dynamics in faint halos. We discuss surveys which have netted a total of 665 candidate planetary nebulae in NGC 5128 (Cen A), NGC 5102, NGC 3031 (M81), NGC 3115, three galaxies in the Leo Group (NGC 3379, NGC 3384, NGC 3377), NGC 5866, and finally, in NGC 4486 (M87). Radial velocities of planetaries in M32 have shown that its halo velocity dispersion is most likely isotropic. Radial velocities of planetaries in M31 show that ∼ 2/3 of the nebulae with projected radii between 15 and 30 kpc are members of a rotating thick disk with slight asymmetric drift, while ∼ 1/3 belong to a slowly rotating halo. Velocities of 116 nebulae in NGC 5128 reveal pronounced rotation and a slowly declining velocity dispersion in the halo out to 20 kpc. The [O III] λ5007 luminosity functions (PNLFs) in NGC 5128, M81, and the three Leo Galaxies have the same shape over the first magnitude. The highly consistent distances derived from the brightnesses of the jth nebula and the median nebula in different fields in the same galaxy and from different galaxies in the same group lend strong support to the suggestion that planetaries are an accurate standard candle in old stellar populations. Comparison of theoretical luminosity functions to the observed PNLFs shows that there is a very small dispersion in the central star masses.
Chemical Abundances in Magellanic Cloud Planetary Nebulae
Authors: Monk D. J. , Barlow M. J. , Clegg R. E. S.
Published: July 2016

Optical spectroscopic data for 71 Planetary Nebulae (PN) in the Large and Small Magellanic Clouds have been analysed. The line fluxes have been used to determine nebular temperatures, densities, and the abundances of He, N, O, Ne and Ar, relative to H. In our sample there are 12 nebulae with N/O ≥ 0.5, resembling Peimbert's Type I PN; 6 low excitation (LE) objects (1 ≤ I(5007)/I(Hβ) ≤ 4); and 4 very-low-excitation (VLE) nebulae (I(Hβ) > I(5007), similar to the Galactic VLE class. Mean abundances have been calculated for the nebulae not in these special groups.
Carbon Stars as Planetary Nebula Progenitors
Authors: Knapp G. R.
Published: July 2016

Molecular line observations show that some planetary nebulae are still only partially ionized and are surrounded by the remains of the mass loss envelope shed by the preceding AGB star. The mass loss rates and outflow velocities of these envelopes are similar to those of the cool winds from luminous AGB stars. Both the kinematics of carbon stars and observations of the molecular envelopes around young planetaries show that the carbon star progenitors have a wide range of ages and of mass loss rates. There is increasing evidence that a significant fraction of AGB stars are carbon stars and that these provide a substantial contribution to the total mass returned to the interstellar medium.
Proto-Planetary Nebulae: Models and IRAS Observations
Authors: Volk K. , Kwok S.
Published: July 2016

A number of high-galactic latitude supergiant stars of intermediate spectral types have been suggested to be proto-planetary nebulae (PPN), such as the 89 Her and R CrB stars. A number of these stars along with some IRAS sources expected to be PPN -either sources with IRAS low Resolution Spectra (LRS) showing features which may indicate unusually cool dust shells or unusually red IRAS sources for which CO emission from a circumstellar envelope has been observed- where chosen for study. The IRAS 12/25 and 25/60 μm colours of 32 such stars from 3 groups on a colour-colour diagram. Class I show colours similar to ordinary stars; Class II have a 60 μm excess but have normal 12/25 μm colours; Class III are much redder than ordinary stars.
Some Comments on Radio Observations of Spiral Arms
Authors: Shane W.W. , Bystedt J.
Published: July 2016

If we view spiral structure in galaxies as a manifestation of some dynamical process which we wish to understand, then the observer can distinguish two facets of the problems. In the first place he must consider the observable consequences suggested by theoretical developments. In the second place he must endeavour to interpret the available observations in terms of realistic physical models, where such models may require detailed information beyond that required for an understanding of spiral structure as a dynamical phenomenon. We shall consider these two aspects in turn.
On Peripheral Dynamics
Authors: Toomre A.
Published: July 2016

A review of the observed facts and the observed theories of distortions of the outer parts of galaxies.

[Manuscript not received]
Galaxies with Long Tails
Authors: Schweizer François
Published: July 2016

Today I would like to show you some animals from the zoo of Alar Toomre. These animals are all characterized by long tails and belong to two subspecies: The first consists of animals which always huddle in pairs, each individual having one long tail. The second, rarer subspecies comprises those strange animals which live alone but have two tails!
High Velocity Clouds: Galactic or Extragalactic?
Authors: Giovanelli Riccardo
Published: July 2016

While most of the sky has been surveyed in the 21 cm line at velocities within a few hundred km/s with respect to the LSR, the coverage is highly inhomogeneous in sensitivity, angular and spectral resolution and velocity extent. As interesting information has recently become available on the structure of the clouds, however, inferences on the dynamical and thermal state of the gas have become possible. Here, we shall concentrate on the direction in which this structural information influences the dichotomy stated in the title of this paper.
Nearby Small Groups of Galaxies
Authors: Tully R. Brent , Fisher J. Richard
Published: July 2016

To date, our view of the universe has largely been two-dimensional. Velocity data, the basis for a look in the third dimension, have been too incomplete and uneven in quality to provide a clear picture. Nonetheless, the pioneering work by de Vaucouleurs (1975) has given us a rough idea of what the universe is like locally. At least a good fraction of galaxies are improbably close to their nearest neighbours compared with expectations based on statistical fluctuations of a random distribution. Our vocabulary to describe these associations includes the words: binary, group, cloud, cluster and supercluster. Does the real universe indeed have characteristic scales that make these terms meaningful? Or, as Peebles and his co-workers (Davis, Groth & Peebles 1977, and reference therein) would have us believe, is there structure on all scales, at least up to about 15 Mpc? and associated galaxies aside, are there galaxies truly randomly distributed: are there field galaxies? Looking two-dimensionally, it has been possible to arrive at remarkably different conclusions. Turner & Gott (1975) concluded that roughly 40% of all galaxies are randomly distributed while Soneira & Peebles (1977) set an upper limit of 18%. It was roughly this latter figure that de Vaucouleurs (1975) derived with his early look into the third dimension. So we ask: (1) what are the characteristic scales and densities of galaxy associations, and (2) what are the scales and densities of the voids?
Three dimensional analysis of groups of galaxies
Authors: Materne Jürgen
Published: July 2016

A systematic and automatic classification of groups of galaxies has been made only in two dimensions up to now (Turner and Gott, 1976). They investigated the projected density of galaxies at the sky. in this analysis one can correct for foreground and background galaxies and superimposed groups only statistically. the properties of the groups and their member galaxies will often not be recognized correctly. Therefore, a three dimensional analysis is proposed.
Detection of an optical halo surrounding the spiral galaxy NGC 4565
Authors: Hegyi Dennis J.
Published: July 2016

A halo surrounding the edge-on Sb giant spiral galaxy NGC 4565 has been detected in the spectral band 3800–8600 A using a new photometric instrument, an annular scanning photometer. the halo is brightest close to the galactic nucleus and decreases in brightness until it reaches a level of 1 part in 1000 of the sky at a galactic radius of 6.1 arc minutes or 43 kpc from the galactic center. Because the scan path of the ASP is circular, this point corresponds to a distance of 34 kpc from the galactic plane. For comparison, the Holmberg radius of NGC 4565 is equal to 7 arc minutes or 50 kpc. Preliminary V-I photometric data indicate that the halo becomes redder with increasing galactic radius, exceeding V-I = 1.9. Based on a variety of possible origins for the light, it is concluded that the light is due to stars.
Photoelectric surface photometry of the Coma Cluster
Authors: Melnick Jorge , White Simon , Hoessel John
Published: July 2016

A photoelectric search is presented for light from a smooth intergalactic background in the Coma cluster of galaxies.
Large Scale Clustering in the Universe
Authors: Peebles P. J. E.
Published: July 2016

In 1924 Hubble presented the first generally convincing evidence, from the identification of variable stars, that some of the brightest “spiral nebulae” are galaxies of stars well outside the bounds of our own Galaxy. This led him to reconsider the idea that the faint “spiral nebulae,” which were known to be much more abundant than bright ones, might be similar objects at greater distances.
The isotropy of the universe on scales exceeding the horizon
Authors: Grishchuk L.
Published: July 2016

I would like to describe in a few words work which was done by Zeldovich and myself. It gives some restrictions on the amplitude of possible very large-scale density fluctuations mentioned by Peebles. the main question investigated in this work is the following. What can be said, using known observational data and some general hypotheses, about structure of the Universe beyond the region accessible for observation at the present epoch? in fact we consider density fluctuations (as well as rotational perturbations and gravitational waves) with wavelengths larger than the horizon. We use the observational fact that the quadrupole-type anisotropy of the microwave background radiation is absent at the level of δT/T < 10−4. It is interesting to know if it may happen that, at the present epoch, there exists a significant density of perturbations (say, with the dimensionless amplitude of the order of 10−1) which we do not even suspect because the corresponding wavelength is very long and therefore direct observation of the entire perturbation is not possible. Such a direct observation will be possible only in the remote future when the horizon becomes equal to the corresponding wavelength. To answer the question we make a natural but very important assumption. Namely, we assume that the harmonic perturbations of different wavelengths are not correlated in any particular way. Otherwise, they might fit together in such a way that all perturbations (and, therefore, δT/T) would be especially small within the horizon while significant perturbations could take place just beyond the horizon. A situation of this kind would imply that an observer at the Earth occupies a unique position in the Universe. We assume, on the contrary, that all observers are equivalent. All of them, even causally unconnected observers, could detect similar restrictions on the anisotropy of the microwave background, δT/T < 10−4. Nevertheless, the question still exists whether small perturbations unnoticeable by every observer within his horizon can represent different parts of a significant long wavelength limit. the main result of this investigation can be formulated in the following way. the observational data on δT/T in combination with the natural hypothesis on the statistical independence of different harmonics leads to the conclusion that in the Universe there are no significant (i.e. with the amplitude exceeding δT/T) density fluctuations on any spatial scale larger than the horizon. (The paper will be published in Astr. Zh. U. S. S. R. j November-December, 1977.
Statistical HR Diagrams for One Hundred and Fifteen Thousand Proper-Motion Stars
Authors: Luyten Willem J.
Published: July 2016

Since regular HR diagrams require apparent magnitudes, colors or spectra, and parallaxes, and such complete data are available for relatively few stars, there may be some advantage in making up diagrams which utilize proper motions instead of parallaxes, and are thus statistically similar to an HR diagram. The reduced proper motion, first used by Hertzsprung, is defined as H = m + 5 + 5log μ, but may also be written as H = M + 5log T, where T is the tangential velocity, and is expressed in astronomical units per year. A diagram plotting H against color will thus contain the considerable dispersion in tangential velocity which is a serious disadvantage. However, this is outweighed by two practical advantages. First the one and the same person who does the proper motion survey can, and does also determine the other two quantities needed. Second, when using data obtained from such a proper motion survey one deals, statistically, with all the stars within a given distance and the results, therefore, are much more representative of the real situation in space than many HR diagrams which often contain an unrealistic preponderance of giants.
Hertzsprung-Russell Diagrams and Color-Luminosity Diagrams for the Stars Nearer than Twenty-Two Parsecs
Authors: Gliese W.
Published: July 2016

Observational data for stars in the solar neighborhood received before January 1969 were included in theCatalogue of Nearby Stars(Gliese, 1969) which contains more than 1800 objects, single stars and components of binaries, nearer than 22 pc. Since then more than 8 years have gone by and many new data have been published, especially new trigonometric parallaxes as well as photometric distance determinations. Today we know more than 2000 stars with parallaxes measured to be greater than 0m.044. But many of these distances are still very uncertain and for a considerable number of objects, especially the faint ones, spectral classificiation is lacking or the photometry is still not satisfactory.
Spectrophotometry in Stellar Associations
Authors: Gutiérrez-Moreno A. , Moreno H.
Published: July 2016

When analyzing the spectral energy distributions of early type stars as measured at Cerro Calán, we find that many of them have a feature which we have called ΔD (Gutiérrez-Morenoet al., 1968); the internal error of the measure of ΔD for a single star is ±0.02. An analysis of the spectrum scans and the energy distributions shows that this feature may be interpreted as an emission in the Balmer continuum. A few stars have values of ΔD<0, and a comparison of their scans with those of normal stars (ΔD=0) suggests an absorption larger than normal in the Balmer continuum.
A Photometric Study of Ara OB1
Authors: Herbst William , Havlen Robert J.
Published: July 2016

Photoelectric and photographic UBVRI photometery have been obtained for over 700 stars in the field of Ara OB1, including many in the central cluster NGC 6193. Association members were identified mainly on the basis of their reddenings. The association sequence is well populated blueward of (B-V)O= −0m.10, (U-B)O= −0m.35. Beyond this “turn-up” point stars lie only above the ZAMS. There are clear gaps in the color magnitude diagrams just redward of the turn-up points. The width of these gaps is 0.07 mag. in (U-B). They cannot be easily explained by pre-main sequence models involving only gravitational contraction or by those involving3He burning. The difficulty of identifying the faint pre-main sequence stars (if they exist) amidst the field stars is discussed and a limiting luminosity function for the association is derived.
The Hyades Cluster — Too Distant?
Authors: Flower Phillip J.
Published: July 2016

Theoretical zero age main sequences (TZAMS) from Flower (1976) are compared with two observed zero age main sequences (ZAMS) in Fig. 1.: ZAMS40, based on a distance of 40 pc (Sandage 1957) and ZAMS46 on a distance of 46 pc (see Flower 1977 for Teff: (B-V): BC scales). Although ZAMS46 lies above any TZAMS, the TZAMS can be shifted in luminosity by changing the chemical composition.
Observations of CO and OI in Stars in Globular Clusters
Authors: Wallerstein George , Pilachowski Catherine
Published: July 2016

During the past decade it has been evident that the morphologies of globular cluster color-magnitude diagrams cannot be described by only two parameters, age and metal abundance (Sandage and Wildey 1967, Hartwick 1968). The third parameter is unlikely to be helium because a normal helium abundance is needed to explain the pulsation of RR Lyrae stars (Deupree 1977) and because the helium abundance of the planetary nebula in the metal-poor cluster M15 is normal (O'Dellet al. 1964).
The Expected Morphology of Zero Age Horizontal Branches
Authors: Castellani Vittorio
Published: July 2016

On the basis of available theoretical evaluations of the H-burning evolutionary phases of Population II stars, it is at present quite simple to predict the expected location of Zero-Age Horizontal-Branch (ZAHB) stars for assumed values of the age and original chemical composition. A result of such a computation is disclosed in Fig. 1, for the labelled values of the assumed evolutionary parameters.
HR Diagrams of Galaxies: Ages and Stages of Evolution
Authors: Tinsley Beatrice M.
Published: July 2016

Baade (1944) based his concept of stellar populations in galaxies on the HR diagrams that he inferred from the magnitude at which their brightest stars could be resolved. His type I population had bright blue supergiants like those in the disk of the Milky Way, while the brightest stars in type II were the red giants found in globular clusters. He postulated that the Hubble sequence of galaxy types from irregulars to ellipticals contained increasing proportions of Population II relative to Population I, and that similar differences characterized nuclear bulges of spirals relative to their disks. A very important revision of this picture came with the discovery by Morgan and Mayall (1957; Morgan, 1956, 1959) that the integrated blue light of the nuclear bulges of M31 and the Galaxy is dominated by strong-lined CN giants, not by the weak-lined type found in globular clusters. On the basis of integrated spectra of galaxies, Morgan developed a revised population scheme, in which the extreme types are a young-star rich population, like Baade's extreme Population I, and a young-star deficient population, analogous to Population II but generally metal-rich. Different proportions of these two types are still thought to represent the main differences among stellar populations in different regions of galaxies.
A New Kind of HR Diagram?
Authors: Evans David S.
Published: July 2016

When the system of correlations between stellar parameters that we know as the HR diagram was discovered, the physical basis for them was unknown and remained essentially unknown during four decades of eager application.
Comparison Between Observational and Theoretical (log Teff, Mbol) Diagrams
Authors: de Strobel G. Cayrel , Perrin M.N.
Published: July 2016

In a paper by Perrinet al. (1977), we have constructed an empirical HR diagram for 138 nearby F, G and K stars, for which we had: i) an effective temperature and a metal content derived from a detailed analysis; ii) a reliable bolometric magnitude obtained from an absolute magnitude My, based on a large parallax and a rather small bolometric correction.
The Colors of G and K Giant Stars
Authors: Bell R.A. , Gustafsson B.
Published: July 2016

In previous papers, we have discussed the calculation of model atmospheres for metal-deficient and solar-abundance giant stars and have presented a grid of such models. We have now carried out synthetic spectrum calculations at a resolution of 0.1 Å between 3000 and 7200 Å for most of the models of this grid. We have also computed synthetic spectra at wavelengths up to 12000 Å for some of the grid models. The calculations allow for the presence of thousands of atomic and molecular lines. Examples of these spectra are shown in this paper.
Peculiarities in Some Cluster Color-Magnitude Diagrams
Authors: McNamara Bernard J. , Sanders W.L.
Published: July 2016

There has existed for some years a generally accepted conceptual scheme of stellar evolution as reflected in HR diagrams. Such evolutionary sequences are normally only apparent in stellar clustering where, in the first order at least, coeval formation is assumed. Such observational evidence of evolutionary sequences is directly dependent upon the identification of cluster membership. Only in very recent years have the necessary high precision and full membership based independently upon proper motion become available for a significant sample of clusters. The result of these studies for some sample cluster C-M diagrams are discussed and some possible difficulties with our evolutionary scheme are evidenced.
Angular Diameters of Cool Stars Measured by the Method of Lunar Occultations
Authors: White Nathaniel M.
Published: July 2016

Given the angular diameter and total energy flux of a star, its effective temperature can be determined. Until recently, there were few well-determined angular diameters of cool stars, and effective temperature calibrations rested on angular diameter measurements of several not necessarily “normal” stars. The number of measured angular diameters of stars cooler than about spectral type G is steadily being increased by using the method of photoelectric observations of lunar occultations.
Counts of quasars at faint magnitudes: a new complete sample
Authors: Zamorani G. , Zitelli V. , Marano B.
Published: July 2016

We present results on a new sample of optically selected quasar candidates. The “standard” multicolor technique for selecting quasar candidates has been applied to all the objects brighter than J = 22.0 in a field of 0.69 square degrees. Additional candidates have been selected from a search on grism plates obtained in the same area. Spectroscopy for all the candidates brighter than J = 20.9 has provided a sample of 22 confirmed quasars. The redshift distribution of these objects is essentially flat from z = 0.6 up to z = 2.8. Three out of the eight quasars with redshift larger than two were selected from the grism plates and were missed by our color selection. This result, although based on a small number of objects, suggests that the luminosity functions computed in this redshift range from samples which are only color selected might have to be increased by a factor up to 1.5. On the other hand, these possible losses of the multicolor search technique are negligible (of the order of 15% only) for the estimates of the integral number counts at magnitudes of the order 20–21.
QSO search by slitless spectroscopy
Authors: Hoag A.
Published: July 2016

Sandage and I have obtained “grism” plates that redundantly cover one square degree fields centered on ten Selected Areas. We used a grating-prism in the converging beam of the Mayall 4-meter telescope prime focus to photograph 1580 A·mm−1 slitless spectra to a limit of about B = 21.5 (cf. Hoag and Smith 1977).
The radio emission from optically selected quasars
Authors: Peacock J.A. , Miller L. , Mead A.R.G.
Published: July 2016

We describe models which try to account for the incidence of quasar radio emission in terms of two populations. One is effectively radio quiet, with radio powers P2.7 ≤ 1022 WHz−1 sr−1 characteristic of type I Seyferts. These are presumed to lie in spiral host galaxies. The other population is the classical radio-loud quasars with P2.7 ≥ 1024 WHz−1 sr−1. Apparent correlation of radio and optical powers can arise without any real effect being present because the two populations in general have separately-evolving luminosity functions.
Results from a monitoring program of low frequency variable sources
Authors: Padrielli L. , Fanti R. , Ficarra A. , Gregorini L. , Mantovani F.
Published: July 2016

The flux variability of extragalactic radio sources at decimetric wavelengths (Low Frequency Variability LFV) is mostly associated with the nuclei of compact radio sources. But is a not yet well understood phenomenon. The main question still is: where does this phenomenon take place?
The radio morphology of quasars at high redshift
Authors: Barthel P. D.
Published: July 2016

The mapping at kpc-scale resolution of the radio sources associated with quasars is fascinating, since it provides us with morphological information on a population of objects during 1010.3 y evolution of the universe, as well as information on a possible epoch dependence of the influence of the ambient medium on the properties of these objects.
The extended radio structures of quasars and radio galaxies
Authors: Leahy J.P. , Stephens P.W. , Muxlow T.W.B.
Published: July 2016

We have observed 20 classical double radio galaxies and quasars with MERLIN at 151 MHz. We discuss the systematic variation of the bridge structures with radio power and the nature of the identification.
B2 quasars and relativistic motion
Authors: Ruiter H.R. de , Rogora A. , Padrielli L.
Published: July 2016

Relativistic motion has been established with a certain degree of confidence only on VLBI scales, but its application to larger scales has encountered severe difficulties (see e.g. De Young, 1984).
X-ray studies of Seyfert galaxies and quasars
Authors: Canizares Claude R. , Kriss Gerard A. , Kruper John , Urry C. Megan
Published: July 2016

We present results of studies carried out with the imaging instruments on the Einstein Observatory. We summarize a statistical analysis of the X-ray properties of optically selected, radio quiet quasars including nine new high redshift quasars detected in two deep X-ray surveys. We find that the X-ray to optical luminosity ratio of optically selected quasars decreases with increasing optical luminosity. It depends only weakly, if at all, on redshift. However, the distribution function does not properly account for the properties of the X-ray selected Medium Sensitivity Survey sample (MSS). We note that part of the discrepancy could be due to the presence of red, low luminosity quasars in the MSS but not in the optically selected samples. We also summarize some results from a detailed study of the X-ray properties of 64 Seyfert galaxies. None of the spectral fits performed for the brightest 20 required unusually steep spectra, although in many cases the spectral indices were not well constrained. Of the ten objects with good measurements of the absorbing column density, three showed excesses above the galactic value while the remaining seven gave excess columns generally less than 2 × 1020 cm−2 and consistent with zero. Variability studies of the full Seyfert sample showed three objects to be variable on timescales of a few hours. One of these is the Seyfert II Mkn 78.
A statistical study of the relationship between X-ray, optical and radio luminosity for a sample of QSOs
Authors: Worrall D.M. , Giommi P. , Tananbaum H. , Zamorani G.
Published: July 2016

Our statistical study finds that the X-ray luminosity, lx for an average QSO of given optical luminosity, lo is an increasing function of radio luminosity, lr. An average QSO of given lo and lr has higher lx if the radio spectrum is flat than if it is steep. The correlation between lx, lo and lr appears to be improved if lr refers only to core emission, lrcore. Assuming an average radio-loud QSO is a radio-quiet QSO with a separate component which produces lrcore and Ixcore, lxcore/lrcore is larger if the core is that of a QSO with extended radio structure than if that of a compact flat-spectrum QSO.
Emission-line kinematics as a probe of the central engine in QSOs
Authors: Wandel Amri
Published: July 2016

We investigate the constraints on dynamic models for the line-emitting regions in quasars and AGN. The parameters characterising the central energy source (Mass, efficiency, accretion rate) are calculated in terms of the physical conditions in the line emitting gas. In a large sample the central mass (calculated assuming the emission-line clouds are bound) is proportional to the continuum luminosity. We find typical values of L/LE∼10−2±0.5, e∼0.1-l%, and Ṁ/ṀE∼1–10.
Spectrophotometry of 3C 232 and 3C 249.1
Authors: Dultzin-Hacyan D.
Published: July 2016

We find indication of variability of the ratio Mg II 2934/2798 for 3C 232 and discuss the excitation mechanism of Mg II 2934. For 3C 249.1 we identified the following new lines: [Ne V] 3346, [Ne V) 3426 and He I 3884. Comments are made on continuum shapes; in both cases optical continuum variability is confirmed.
The Electron-Positron Cauldron and the Formation of the Hard Radiation of Quasars and AGN
Authors: Kardashev N.S. , Novikov I.D. , Stern B.E.
Published: July 2016

Active Galactic Nuclei (AGN) and quasars have unique physical parameters among all the objects in the Universe. Undoubtedly it is the uniqueness of the physical conditions in these systems that gives rise to the peculiar physical processes in them.
Decolimation of a jet due to spacetime curvature
Authors: Kapoor R.C.
Published: July 2016

Central cores of compact radio sources are believed to contain supermassive black holes accreting material from their vicinity which produce fast moving plasma in the form of directed beams (jets), with apparent opening angles ≥5° (Rees et al. 1981). In case, the jets are produced and their collimation is established on scales few times the SchwarzschiId radius (2m; m=GM/c2) of the central engine, deflection in particle trajectories in the curved spacetime () would be large enough to widen the beam and thereby reduce the particle density and effective luminosity in the beam (Fig.1).
The statistics of radio galaxies & quasars at high redshift
Authors: Peacock J.A. , Dunlop J.S.
Published: July 2016

Evidence is now accumulating that the most powerful extragalactic radio sources display a cutoff in comoving density at relatively low redshift. For both radio galaxies and quasars, the luminosity function falls by a factor ≥ 3 between z = 2 and 4. We describe the data which lead to this conclusion, and discuss the prospects for studying the behaviour of low-luminosity active galaxies at high redshift. The strong evolution of highly luminous radio-quiet quasars at z > 2 may be an artifact of gravitational lensing.
Quasar Pairs
Authors: Shaver P. A.
Published: July 2016

This paper summarizes various uses which have been made of QSO pairs. Statistical studies using pairs show that the sky distribution of QSOs of arbitrary redshifts is random, and that QSOs of similar redshifts are clustered on a linear scale similar to that of galaxies today. Close pairs are used to set limits on the masses of QSOs. And absorption line studies of QSO pairs support the extrinsic hypothesis for the origin of the narrow absorption lines and the cosmological interpretation of the redshift, they demonstrate the presence of absorbing matter around QSOs, and they set limits on the sizes of the absorbers.
The association of galaxy clusters with moderately-high-redshift quasars
Authors: Yee H. K. C. , Green Richard F.
Published: July 2016

CCD images of quasars having redshifts between 0.3 and 0.65 are analyzed to study the association of galaxies with quasars. Average luminosity functions (LF) of the excess galaxies associated with the radio-loud quasars are determined. It is found that for the sub-sample with z>0.55, there is a significant brightening of the characteristic magnitude M*, if qo is assumed to be 0. Comparing computed quasar-galaxy spatial-covariance amplitudes, we can conclude, at the 0.025 significance level, that the spatial-covariance amplitudes of the sub-sample with z>0.55 are greater than those of the lower redshift quasars. This indicates that there has been a strong evolution of preferred sites for bright radio-loud quasars, implying some number-density evolution of quasars has taken place, and that some rich clusters at z∼0.6, in comparison with the local rich clusters, have significantly different physical conditions.
Gravitational Lensing — Models
Authors: Narayan Ramesh
Published: July 2016

Qualitative features of gravitational lensing are discussed in terms of a scalar framework based on Fermat's principle. The lensing action of galaxy-like models with spherical and elliptical mass distributions are described. The elliptical model has three distinct regimes of lensing, of which two correspond to lensing with three images and one with five images. One of the three-image geometries has been frequently explored in the past. Models proposed for 0957+561 correspond to this. The five-image geometry has been invoked for 1115+080. Some general model-independent properties of gravitational lensing are listed. If image parities were available, it might be possible to make statements about the lensing mass even when it is made up of dark matter.
Gravitational lenses as probes of the distribution of dark matter in the universe
Authors: Cowsik R. , Ghosh P.
Published: July 2016

Studies of the characteristic properties of gravitational lensing by clusters of galaxies suggest that the dark matter in them is probably smoothly distributed on the scale of the cluster itself, rather than being clumped into halos around individual galaxies.
QSO Absorption Lines: Heavy Elements and Lyman-α Clouds
Authors: Peterson Bruce A.
Published: July 2016

The absorption lines in QSO spectra may be produced in material surrounding the QSO, in intergalactic clouds and in the interstellar gas of galaxies along the line of sight to the QSO. The intergalactic clouds produce weak Lyα absorption lines. The intervening galaxies produce absorption line systems with heavy element abundances and ionizations similar to the H i clouds in the halo of our galaxy. The material surrounding the QSO produces broad absorption troughs. Evidence suggests a continuity in spatial correlation and heavy element abundances for the Lyα clouds and intervening galaxies.
High resolution spectroscopy of absorption lines in the Z = 1.7 BL Lac object 0215+015
Authors: Blades J. Chris , Hunstead Richard W. , Murdoch Hugh S. , Pettini Max.
Published: July 2016

We describe the various absorption systems in 0215+015, and present results from our new, high-resolution studies at 10 km/sec (FWHM).
The Cosmic Microwave Background
Authors: Partridge R. B.
Published: July 2016

This review summarizes recent observational work on the cosmic microwave background, or 3 K radiation. Recent measurements of its spectrum and large-scale angular distribution are described, as well as searches for small angular scale fluctuations on arcsecond to degree scales. A few of the consequences of these measurements and upper limits for cosmology, astrophysics, and theories of galaxy formation are touched on here.
The Cosmic Distance Scale
Authors: Tammann G.A.
Published: July 2016

The zero-point of the extragalactic distance scale, defined by about two dozens of nearby, late-type galaxies, has remained nearly unchanged for the last decade, in spite of the advent of new techniques and great efforts. The distances are essentially tied to trigonometric parallax stars and hence independent of the Hyades modulus; they are consistent with RR Lyr stars. The mean zero-point is therefore probably secure to better than 10%.

All known secondary distance indicators are still affected by zero-point errors, by problems in the definition of their relation between distance indicator and absolute magnitude (or linear size), and/or by selection bias. The effect of the very important selection bias (Malmquist effect), which causes a seemingly non-linear expansion field, is illustrated by two examples. To test for any true deviations from a linear expansion the Hubble diagram of nearly bias-free first-ranked cluster galaxies and supernovae Ia is shown; this imposes stringent limits on any non-linearity of the Hubble flow within v<5000 km s−1.

After freeing the available distances of field galaxies from selection bias and after reducing them to a common zero-point, one finds HO=55–65. Several distance indicators require a best Virgo cluster modulus of (m-M)=31.60, which implies for the Coma cluster (m-M)=35.38 and, with v(Coma)=7217 km s−1, HO=60. Supernovae Ia and first-ranked cluster galaxies out to large distances give HO (global)=53. Thus the evidence from clusters and field galaxies is best satisfied by HO=55; the assigned mean error of ±7 is to indicate a 3σ range of 35<HO<75.

Purely physical methods to determine extragalactic distances have modest weight yet; they will contribute eventually much to the determination of HO.

If HO were as large as 100, several paradoxa would arise. The Milky Way would have a very high supernova frequency, our Galaxy and M31 would be oversized, the baryon density would fall short to bind clusters, and Friedman universes were excluded.

Because all systematic errors have conspired and probably still conspire to measure HO too high, the true value could well be 40. Until new, decisive evidence becomes available, it is suggested for all practical purposes to use HO=50.
Distribution of IRAS Galaxies
Authors: Rowan-Robinson Michael
Published: July 2016

Infrared wavelengths are free of several of the problems that plague optical galaxy surveys. At high galactic latitude ≥99% of 60μ sources in the IRAS Point Source Catalog, after deletion of obvious stars, are galaxies. At lower latitudes care has to be taken to avoid confusion with emission from interstellar dust (the ‘cirrus’). IRAS galaxies have been used to determined the direction of the gravitational acceleration acting on the Local Group due to galaxies and clusters within about 200 Mpc. This agrees well with the direction of the microwave background dipole. The density of matter in the universe, distributed like IRAS galaxies, needed to account for the observed velocity of the Local Group, corresponds to Ωo = 1.0 ± 0.2. In the standard hot Big Bang model, 90–95% of this matter would have to be non-baryonic.

IRAS galaxies are significantly less clustered than optically selected galaxy samples.
Galaxy Formation: Confrontation with Observations
Authors: Silk Joseph
Published: July 2016

The implications for galaxy formation of inflationary cosmology are reviewed. In particular, I explore some implications of the hypothesis that galaxies form from adiabatic, gaussian density fluctuations in a cold dark matter–dominated universe. Topics discussed include protogalaxies and the epoch of galaxy formation, Lyman alpha clouds, dark halos and dwarf galaxies. Finally I describe how environmental biasing may arise as a consequence of tidally induced star formation in protoclusters.
Alternative Cosmologies
Authors: Narlikar Jayant V.
Published: July 2016

This review highlights some of the cosmological theories proposed as alternatives to the standard hot big bang model. Specific ideas discussed here are the matter - antimatter symmetric cosmologies, the empirical two-component model, the G-varying cosmologies, the chronometric cosmology and a simplified quantum cosmology. It is argued that many alternative cosmologies have contributed useful concepts and offered observational tests that have enriched the field of cosmology as a science.
Redshift Asymmetries and the Missing Mass
Authors: Byrd Gene G. , Valtonen Mauri J.
Published: July 2016

We study the existence of missing mass in the outermost regions of galaxies not accessible to study by rotation curve methods. We consider binary galaxies, groups and clusters of galaxies. Arp has previously explained redshift asymmetries in pairs or groups with “non-Doppler redshifts”. Instead, we propose the asymmetries indicate contamination by optical pairs or by members which are not gravitationally bound to the group or pair. The group samples which are commonly used to justify very high missing mass values in spiral galaxies (>> the mass detected by rotation curves) also exhibit significant redshift asymmetries. From this and other information, we conclude that spiral galaxies do not possess very massive halos. Only the rare giant elliptical galaxies, such as the binary pair in the center of the Coma Cluster of galaxies, apparently possess extremely massive halos. Dynamical effects of such giants lead to overestimates of the mass of clusters. The evidence indicates that missing mass sufficient to close the universe is not concentrated in individual galaxies, groups or rich clusters.
The Luminosities and Sizes of Disk Galaxies in Clusters
Authors: Giuricin G. , Mardirossian F. , Mezzetti M.
Published: July 2016

Our examination of the absolute luminosities and sizes of ∼500 lenticular and spiral members of several clusters has revealed appreciable differences in the galaxy luminosity-diameter relationships for different clusters.
Radio Source Counts and their Interpretation
Authors: Kellermann K. I. , Wall J. V.
Published: July 2016

Radio source counts at several wavelengths are shown and discussed in terms of evolving populations. The deepest counts now reach a surface density close to a million sources per steradian. At this level essentially all of the luminous radio galaxies and quasars appear to be included, and the weaker sources apparently reflect a relatively nearby population of less luminous radio sources.