bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties and Evolution of White Dwarf Stars
Authors: Shipman Harry L.
Published: July 2016

This paper reviews the properties and evolutionary status of white dwarf stars, focusing most closely on those aspects which are likely to be of significance to understanding the ultimate fate of planetary nebulae and their central stars. White dwarf stars show a broad variety of chemical compositions. Broadly speaking, they are divided into the DA stars (with H-rich photospheres) and the non-DA stars (with He-rich photospheres), though there are a fairly large number of subtypes. The mass distribution of white dwarf stars is quite narrow, with a mean value near 0.6 and with extremes at 0.43 and 1.05. Different varieties of trace elements (such as C, N, 0, Si, Ca, and Mg) are quite common. I will review several recent proposals for explaining these abundance patterns. A particularly significant question is whether processes operating while the star cools as a white dwarf can account for their variety, or whether at least part of the white dwarf phenomenology is related to events which took place when the object was a planetary nebula or even earlier.
Kinematics and Dynamics of Dense Clouds
Authors: Lequeux James
Published: July 2016

Star formation is widely considered as resulting from the collapse of interstellar molecular clouds. The purpose of this paper is to review the observational evidences for collapse in dense clouds, and also for the factors which can play against collapse (turbulence, rotation, magnetic field). We shall also examine to which extent the maser sources (OH, H2O, SiO) can be related to star formation. An overlap with the review papers given by P. Thaddeus, P.G. Mezger, and to some extent by C.G. Wynn-Williams and L. Mestel appears unavoidable.
Infrared Observations of Star Formation Regions
Authors: Wynn-Williams C.G.
Published: July 2016

This review is divided into three parts. The first section gives a brief introduction to the different infrared wavelength ranges and to the various kinds of infrared objects seen in regions of star formation. The second section reviews the recent progress in infrared observations, concentrating on the three years since the review by Wynn-Williams and Becklin (1974) was written. The third section describes in more detail four varied examples of star formation regions.
Theoretical Processes in Star Formation
Authors: Mestel L.
Published: July 2016

To bring out the basic problem of star formation, consider a non-rotating cosmical gas cloud which is free to contract and so to convert most of its gravitational energy into kinetic energy of mass motion. Fluid dynamical systems in general tend to dissipate their kinetic energy, and a diffuse gas cloud easily radiates excess heat. If the cloud did not break up into fragments, then the steady conversion of gravitational energy into radiation would lead ultimately into the formation of a compact massive body - perhaps a quasar - but not of a star cluster, which is maintained at a comparatively low mean density by random stellar kinetic energy. Thus the transition from a gravitationally-bound cloud of gas and dust into a bound star cluster - or a fortiori into an expanding O-B association - requires that gravitational energy released during collapse be conserved as the random macroscopic kinetic energy. It is very likely that star formation is often triggered by processes that are essentially dissipative, such as shocks following passage of the spiral wave, or cloud-cloud collisions; however, it is equally important to emphasise that we require at some stage a cut-off in kinetic energy dissipation. And indeed, once a cloud has been able to fragment into a group of self-gravitating blobs, each of small geometrical cross-section, the chance of inelastic collisions between blobs is sharply reduced.
Summary of the Conference: Observations
Authors: Herbig G.H.
Published: July 2016

I have no plan of trying to sum up or to abstract the observational aspects of this conference. It would seem more profitable to discuss a few points that deserve special praise, or seem in need of critical attention, and to point to a few things I found puzzling and to tell you how I tried to explain them to myself.
A Confrontation of Density Wave Theories with Observations
Authors: Kalnajs Agris J.
Published: July 2016

It would be a mistake to think that the density wave theories of spiral structure have reached the maturity where they can make unconditional predictions which can be tested. On the contrary, they are still very dependent on observations for help and guidance.
Radio Continuum Observations of M31 and M33
Authors: Berkhuijsen Elly M.
Published: July 2016

The two nearest spiral galaxies, M31 and M33, have been extensively studied both at optical as well as at radio wavelengths. Reviews of radio continuum observations are given in van der Kruit and Allen (1976) and in von Kap-herr et al. (1978), respectively. In Table 1 new radio observations in various stages of progress are listed, all of which show — or are expected to show — spiral structure. In this paper the Effelsberg maps at 11 cm of M31 and at 6 cm of M33 are discussed and compared with optical data. Some attention is given to the separation of thermal and nonthermal emission which is essential to any discussion of the origin of the radiation.
The Spiral Structure of M31
Authors: Athanassoula E.
Published: July 2016

The H I, H II, and OB-association densities, as a function of radius, have the same structure, reminding one of a ring with a maximum at r ≃ 50′.
A Sensitive Single-Dish HI-Survey of the Galaxy M33
Authors: Huchtmeier W.K.
Published: July 2016

Extended HI-distributions around late-type galaxies have been found at a surface density of roughly 1020 atoms cm−2 (e.g. Roberts 1972, Davies 1973). For the northern part of M33 a low density Hi-component (∼ 1019 cm−2) was observed to extend to about 1.5 Holmberg radii (Huchtmeier 1973). As part of a program to study the HI-distribution and kinematics of HI-shells (i.e. the HI outside the Holmberg diameter, dH) and to search for high-velocity cloud phenomena in a dozen nearby late-type galaxies the 100-m radio telescope in Effelsberg has been used to map the neutral hydrogen in and around M33 with high sensitivity to the limit where sidelobe contributions become important. Unpublished studies of the antenna pattern and that of Reich et al. (1976) place this limit to about 1018 cm−2 in the case of this galaxy. This limit can be reached in one hour of observing time. In 1973 an area of approximately 2°.5 by 2°.5 has been observed, which has been undersampled with the chosen grid separations of 9′ in δ and 12′.9 in α. Integration times inside dH were considerably shorter than outside.
Infrared, Optical, and X-ray Properties of the Nuclei of Nearby Galaxies
Authors: Burbidge G.
Published: July 2016

The term “nearby galaxies” is not very precise. If we restrict ourselves to galaxies within the local group, we are really only talking about our Galaxy, M31 and M33. Since the Galactic Center has been reviewed extensively by Oort in Annual Reviews (1977), and I feel that there is nothing exceptional to say about the nuclei of M31 and M33 as far as phenomena other than their stellar content and central dynamics are concerned, to discuss interesting properties we must consider more distant objects. If we go out to the distance of the Virgo cluster, we already include objects such as NGC 5128, M82 and M87. Each of these galaxies shows or was claimed to show evidence of different kinds of violent nuclear activity. Indeed, it is obvious that within the volume occupied by the supercluster (whether or not it is really a physical entity) there must be many galaxies in which nuclear activity can be detected.
On the origin and evolution of pairs of galaxies that have different physical and kinematic characteristics
Authors: Pronik I. , Metik L.
Published: July 2016

We have gathered data on U, B,V, K magnitudes, radial velocities, spectra, morphological types, radio-emission, dimensions and other characteristics for 47 pairs of galaxies (Metik and Pronik 1978). the following results were obtained:
Fine structure in the Magellanic Stream
Authors: Philip A. G. D. , Davis A. G.
Published: July 2016

Dr Erkes and I, of Dudley Observatory, and Dr Ken Turner, of the Carnegie Institution of Washington, used the 300 foot radio telescope at the National Radio Astronomical Observatory, Greenbank, West Virginia in March of 1977 to measure neutral hydrogen at 21 cm in three 2° strips across positions indicated by Mathewson, Cleary, and Murray (1974, Astrophys. J., 190, 291) as being part of the Magellanic Stream. in region “A” (centred at α = 22h44m, δ = +24 0.5) no hydrogen was found above the background (3 × 1019 H atoms cm−2). in a revised map Mathewson and Schwarz (1976, Mon. Not. R. astr. Soc., 176, 47P) show that this region is not occupied by the stream. in regions “B” and “C” (centred at α = 23h10m, δ = +11° and α = 0h00m, δ = −17°) hydrogen was detected at the velocities found by Mathewson and Schwarz. Maps of the structure found in these regions are shown in Figure 1.
X-Ray Observations of Clusters of Galaxies
Authors: Culhane J. L.
Published: July 2016

X-ray astronomy has, in the past year, seen the publication of the second Ariel (2A) and fourth Uhuru (4U) catalogues of X-ray sources. A number of new X-ray cluster identifications and the confirmation of several others has resulted. in this review I will briefly summarise the situation regarding identifications and, for the 2A clusters, discuss the luminosity function and the possible relationships between a number of cluster X-ray and optical properties. Superclusters have been tentatively proposed as a class of X-ray sources and I will comment briefly on recent observations of these objects. Cluster structure has been studied by the Copernicus and SAS-3 spacecraft and by a number of rocket observations with imaging X-ray telescopes undertaken by the Harvard Centre for Astrophysics. I will review the current situation regarding structural measurements. Finally I will discuss the present status of Iron line observations at 6.7 keV in cluster spectra and the estimates of Fe abundance that result from these data.
Structures and number-density distributions in clusters of galaxies
Authors: Baier F. W.
Published: July 2016

I would like to present some preliminary results of an investigation of 50 clusters of galaxies. For studying the clusters, Schmidt plates taken with the 2-metre universal telescope at Tautenburg and the prints of the Palomar Sky Survey were used. For all the clusters we determined isopleths to obtain detailed information about the distribution of galaxies. We have found well isolated clusters, double clusters, multiple systems and rather complicated structures.
A tour of the Local Supercluster
Authors: Tully R. Brent , Fisher J. Richard
Published: July 2016

To complement our movie, we offer three steroscopic pictures of a region enclosing the Local Supercluster. A coordinate system is defined.
Some Uses of Spectral Classification in HR Diagrams
Authors: Morgan W.W.
Published: July 2016

The MK spectrum-luminosity class diagram (S-LC diagram) between types 09 and G0 is a two-dimensional array containing approximately 100–150 information elements; each information element is a single cell denoted by a spectral type and a luminosity class. These individual, non-dimensional cells (i.e. AO III) can be considered as carriers of observational information toward the HR diagram. Some categories of peculiar spectra (for example, spectra resembling that of the “silicon star” θ Aur) can be attached to certain cells, and can be considered as local perturbations upon the underlying continuity of the spectrum-luminosity class sequences. By such a procedure, the S-LC diagram cells can be considered open-ended, in that progressive additions to the cells can be made indefinitely into the future. Such a procedure can incorporate successfully an unlimited variety of “normal” and “peculiar” categories of spectra - both those already known and those still to be discovered. A morphological system that is unitary thus comes into existence - a system of considerable astrophysical interest. The translation of the detailed language of this system into that of the classical HR diagram is a task for the future.
A More Accurate HR Diagram for the Cooler Stars
Authors: Keenan Philip C.
Published: July 2016

Even if we confine ourselves to the classical HR diagram, postponing the transformation of spectral types and visual absolute magnitudes into basic physical variables, there are several ways to choose the data. If, for example, we want the density of points to represent the spatial density of stars, then we must concentrate on reducing sampling errors, usually at the cost of accuracy in some parts of the diagram. The Hess diagram is very useful, but an equally useful alternative is an HR diagram which includes only those stars whose positions are determined as accurately as possible. The objective is to classify the fine structure in the pattern in the luminosity-spectrum domain, and thus to define more precisely the borders of zones which are either occupied or avoided by stars of a given population. It is this pattern which is compared with theoretical evolutionary tracks and it is such a diagram based on the revised MK classification of the recent Atlas of Keenan and McNeil (1976) that I shall present here.
Spectroscopic Observations of Late-Type Halo M Dwarfs
Authors: Boeshaar Patricia C.
Published: July 2016

In the lower main sequence, the coolest halo population stars do not appear to be particularly subluminous in either the standard HR diagram or the (MI, R-I) plane. Earlier type M subdwarf's (e.g., Kapteyn's Star) that lie one or more magnitudes below the main sequence exhibit enhanced hydride absorption bands relative to M dwarfs of the same temperature. From visual region (4500–7000 Å) low dispersion image tube spectrograms we find that the cool halo M dwarfs exhibit enhanced absorption in the CaOH 5530 Å band and Na I resonance lines. Easily noticeable changes in the strength of the CaH “B” band relative to that of the TiO bands was found to be more difficult to determine in halo dwarfs later than spectral type M4. Several M dwarfs with old disk type motions have spectral peculiarities similar to those of the halo dwarfs. In both cases, Balmer emission is not present in most stars, in the rest it is very weak. Therefore, the anomalous strength of the CaOH 5530 Å band and Na resonance lines appear to be a more conveniently utilized qualitative criterion in spectroscopically identifying very cool M dwarfs which are subluminous with respect to most main sequence stars of the same temperature class.
A Computer Method for Spectral Classification
Authors: Appenzeller I. , Zekl H.
Published: July 2016

Spectroscopic parallaxes are an important tool for determining distances of individual stars in the Galaxy. Unfortunately, for many astrophysical applications this method does not produce sufficiently accurate results for distant stars. Therefore, we started an attempt to improve the accuracy of spectroscopic parallaxes by evaluating spectroscopic temperature and luminosity criteria such as those of the MK classification spectrograms which were analyzed automatically by means of a suitable computer program. If necessary, the grain noise is reduced by Fourier filtering techniques. Then, the computer derives an approximate spectral type and the wave length scale from selected prominent spectral features. As a next step the computer searches the spectrum for adsorption features and produces an internal catalog of detectable absorption lines. Then, depending on the approximate spectral type, line ratios, line widths, and line depths of selected lines are calculated and compared to the corresponding values of standard stars. Since the investigation is still in progress, no final result on the achievable accuracy can be given here. However, preliminary results indicate that spectroscopic parallaxes derived by the computer method are at least as accurate as those derived from the conventional visual classification technique. A more detailed account of this investigation will be published elsewhere.
Red and Blue Stars in the Direction of the Large Magellanic Cloud
Authors: Parthasarathy M.
Published: July 2016

The Large Magellanic Cloud has been surveyed on ultra-low dispersion (10,000 Å mm−1) plates taken with the 102 centimeter reflector at Kavalur. Many new red and blue stars were found. The LMC Bar was found to have a strong component of red stars and a very weak component of faint 0B stars. In general the regions other than the bar contain very luminous 0B stars, faint 0B stars and a few very red stars. The 30 Doradus complex is rich in luminous red and blue stars.
Quantitative Two-Dimensional Classifications of Low Dispersion Objective Prism Spectra
Authors: Schmidt-Kaler Th.
Published: July 2016

The objective prism (or grating) is the most efficient stellar spectrograph since it suffers no light losses at a slit and - compared to a slit spectrograph - only small losses in the camera optics. However, objective prism spectra have two principal disadvantages:

(1)

the spectral resolution (and consequently the sharpness of spectral features) depends on the seeing, which may vary from plate to plate.

(2)

quantitative measurements are difficult because of the difficulty in obtaining an exact photographic calibration; no comparison spectrum can be placed near the stellar spectra.
RR Lyrae Variable Stars and the Distance Scale
Authors: Clube S. V. M. , Dawe J. A.
Published: July 2016

A statistical parallax algorithm (Clube and Dave, 1978a,b), using the technique of maximum likelihood, has been applied to a set of 103 ‘ab’ - RR Lyrae stars in the solar neighborhood (r 2<kpc), using observational data from the Royal Greenwich Observatory Bulletins. A second set of 130 ‘ab’ - RR Lyrae stars has been kindly supplied to us by Dr. A. Heck (Université de Liège) to permit a comparison between our analyses. The purpose of this investigation was:

(a) to investigate the variations of kinematical parameters and absolute luminosities of these stars as functions of Preston's index ΔS and of log (Period).

(b) to identify those RR Lyrae stars in the solar neighborhood which most closely resemble those in the galactic halo, those near the galactic center, and those in the Magellanic Clouds.
The Position of the Sun in the HR Diagram
Authors: Barry Don C.
Published: July 2016

Since the absolute magnitude of the Sun is known accurately and the solar spectrumdefinesspectral type G2 V, it would appear that the position of the Sun in the HR diagram is well established. However, the color of the Sun and its metallicity relative to other stars remains controversial. It is known from theory that stellar groups of differing composition will have different main sequences.

The observed difference in the strength of the metallic lines in Coma stars relative to Hyades stars is caused by a systematic difference in [Fe/H] of less than 0.2 dex or 50%. Photographs and quantitative measures of the systematic differences between the Hyades and Coma spectra are presented. Visual comparison and quantitative analysis of the solar spectrum relative to Hyades and Coma spectra reveal that the Sun is metal rich similar to the Hyades stars rather than of normal disk metallicity as represented by Coma stars. Evidence is presented showing that the color and spectral line strengths of the Sun are more similar to stars classified G3 and G4 in the literature than G2. If the Hyades modulus is y = 3m.25, the (B-V) color of the Sun must be 0m.65 or redder for the Sun to be on or above the Hyades main sequence.
The HR Diagram
Authors: Greenstein Jesse L.
Published: July 2016

The HR diagram is a useful shorthand locating a star in a two-coordinate space. For the astrophysicist, the y-coordinate is bolometric luminosity, Mbol, the x-coordinate, effective temperature, Teff. Objects of given chemical composition, age (or evolutionary status) are labeled in the xy plane by mass. For an observer, y may be apparent or absolute magnitude in a certain wavelength region and x may be spectral type or color. The HR diagrams for populations differ because of age, chemical composition and stellar masses present. HR diagrams are often of mixed nature; some involve observables others derived or semi-theoretical quantities. I will display various types of HR diagrams for low-luminosity stars. For galactic or extragalactic studies the HR diagram needs a further dimension, the frequency of stars at an x,y. The mass of the Galaxy, but not its light, may be dominated by M dwarfs. HR diagrams are also interesting for their nearly empty spaces. In Fig. 1 we show as a sample, the basic results of the U.S. Naval Observatory parallax program, in which broad band (B-V) colors define the visual luminosity, My, on the main (MS) and degenerate (WD) sequences.
The HR Diagram of White Dwarfs
Authors: Weidemann Volker
Published: July 2016

The lone dot in the lower left of Russell's original diagram (1914) was disregarded, since it did not fit into his suggestive scheme of giant-to-dwarf evolution. Bottlinger (1923) - in his nearly forgotten study of photoelectric color indices - seems to be the first who, with the evidence of the then three classical white dwarfs, invoked a new equation of state and clearly rejected all other possibilities of explanation. Kuiper (1941) summarized the knowledge obtained during the thirties, mainly by his spectroscopic work. A decade later Luyten (1952) presented impressive HR diagrams based on admittedly crude color indices and, for many more objects, on reduced proper motions.
Four-Color and Hβ Diagrams for Open Clusters - A Survey
Authors: Crawford D. L.
Published: July 2016

Intermediate band photometric data for stars in at least 50 open clusters now exist. This paper reviews the status and desiderata for the uvbyß subset. Similarities and differences between clusters are highlighted, and the relation of the photometric differences to physical differences is noted. Some of these are stellar age, chemical abundance, rotational velocity, and duplicity.
The Occurrence of Peculiar Stars in Open Clusters
Authors: Abt Helmut A. , Levato Hugo
Published: July 2016

We have classified on the MK system a total of 455 stars in 12 open clusters and associations. The classification is based on wide (1.2 mm) spectra of two reciprocal dispersions (39, 128 Å mm−1) obtained with the Kitt Peak 2.1 m and 90 cm reflectors, respectively. The higher dispersion is necessary to show the subtle peculiarities found in some stars. The clusters are the Orion Nebula cluster, Orion OB1 association, Lacerta OB1 association, IC 2602, IC 4665, Pleiades, M39, M34, NGC 2516, NGC 6633, NGC 6475, and Coma; two of these were done with Morgan.
K-Line Photometry: Coma and NGC 6475
Authors: Henry Richard C. , Hesser James E.
Published: July 2016

Photometry of the K line of calcium in A-type stars is useful in segregation of Am stars and in estimating the metal abundance of field stars and of stars in clusters. To date, K-line photometry data for six clusters have been analyzed using uvbyß data: Hyades, Pleiades, IC 2391, and IC 2602 (Hesser and Henry 1971), Orion (Hesser, McClintock, and Henry 1977), and Praesepe (Henry, Anderson, and Hesser 1977). We present similar analyses for the Coma and NGC 6475 star clusters, using the uvbyß data of Crawford and Barnes (1969) and of Snowden (1976) respectively. The Coma stars closely resemble field stars. NGC 6475, on the other hand, is most remarkable. Of 31 stars for which complete data are available, 9 are metal-rich, 3 are metal-poor, and 19 (about 2/3 of the stars!) are Am.
A Comparison Between the Relative Heavy Metal Abundance of the Extreme Halo Field Stars and Giant Stars of Globular Clusters
Authors: Spite M. , Spite F.
Published: July 2016

Until very recently, estimates of the chemical composition at early epochs of the Galaxy were made through the analysis of halo field stars. Recently, however some medium dispersion studies of stars in globular clusters have appeared. It would be expected that both approaches would lead to identical results. However, a quick glance at the literature gives the opposite impression.
The Chemical Abundances of the Halo Clusters of the Galaxy
Authors: Canterna R. , Schommer R. A.
Published: July 2016

Photometric metal abundances of individual red giants in eight extremely distant halo globular clusters and the Draco and Ursa Minor dwarf spheroidal galaxies have been obtained using the Washington broad-band system, C, M, T1, T2(Canterna 1976). Observations were made at the KPNO 2.1-m and CTIO 1.5-m telescopes. In Table I we list for each system the mean value of [Fe/H], the number of stars observed in each system, n, the Galactocentric distance, RGC, the intrinsic color of the giant branch at the level of the horizontal branch (HB), (B-V)o,g, and the fraction of HB stars bluer than the RR Lyrae gap, fB. Sources for unpublished color-magnitude diagram (CMD) data are: Pal 11 (Canterna and Schommer), Pal 12 (Canterna and Harris), and Ursa Minor (Schommer, Olszewski and Kunkel).
The Role of Mixing and Primordial Abundance Variations in 47 Tucanae and ω Centauri
Authors: Norris John
Published: July 2016

It has become clear in recent years that widespread and complex abundance variations exist among the stars of several globular clusters. ω Cen is the prime example, containing CH stars, weak-G-band stars, CN strong stars, TiO stars, and (not least) RR Lyrae stars possessing an anomalous range in calcium line strengths. (Harding 1962; Freeman and Rodgers 1975; Norris and Bessell 1975, 1977; Dickens and Bell 1976; Bessell and Norris 1976; Lloyd Evans 1977) The extent to which these phenomena result from primordial abundance variations or from the mixing to the surface of material processed by nuclear reactions is currently the subject of some debate. The present paper presents a short account of investigations of the giant and horizontal branches of 47 Tuc and of several giants in ω Cen. The results were obtained in collaboration with M. S. Bessell and K. C. Freeman, and will be fully reported in papers being prepared for submission toAstrophysical Journal. Most emphasis will be placed on 47 Tuc, where we have sought to address four problems. (i) How widespread are the CN anomalies reported by McClure and Osborn (1974), Bell, Dickens, and Gustafsson (1975), and Hesser, Hartwick, and McClure (19 77) - both throughout the HR diagram and in relative frequency? (ii) Is there any correlation between the relative frequency of the CN anomaly with radial position in the cluster, which might correlate with the color gradients observed by Gascoigne and Burr (1956) and Chun (1976)? (iii) Is there any evidence for G-band variations similar to those found generally in the metal poor ([Fe/H]< −1) globular clusters? (cf. Zinn 1973, 1977; Mallia 1975; Norris and Zinn 1977) (iv) Are the CN variations accompanied by variations in the abundance of the heavy elements?
Evolution of Globular Cluster Stars with Mass Loss and Core Rotation
Authors: Fusi-Pecci F. , Renzini A.
Published: July 2016

During the last decade theoretical and observational research on globular cluster stars has fairly conclusively demonstrated that the mass of horizontal-branch (HB) stars is substantially smaller (by ~ 0.2 M⊙) than the mass of their main-sequence progenitors (cf. Rood 1973, Fusi-Pecci and Renzini 1975, hereafter MPS V and FPR respectively, and the literature quoted therein). Also well established is the fact that HB stars in a single cluster do not follow a unique evolutionary path but that some dispersion in at least one HB parameter (e.g. total mass, core mass, or composition) is required. Further, a growing body of astrophysical evidence shows that the HB morphology is poorly correlated with the abundance of low-ionization potential elements (ALIPE) such as Mg, Ca, Si, and Fe. This has raised the well known problem of the “second parameter” in the sense that something else besides ALIPE has to vary from cluster to cluster, the most popular candidates being age, t, helium, Y, and CNO abundance, ZCNO. Therefore, the main problems which research on globular cluster stars is presently facing are i) a quantitative knowledge of the mass loss process, ii) the identification of the origin of the HB dispersion in a single cluster, and iii) the identification of the second parameter(s). The solution of the last point has profound implications for the theory of the early chemical and dynamical evolution the Galaxy.
Pulsation Modal Behavior of Classical Cepheids in the HR Diagram
Authors: Cox Arthur N. , Hodson Stephen W.
Published: July 2016

Mapping of the Cepheid region of the Hertzsprung-Russell diagram has been difficult to do from a theoretical viewpoint because the masses and compositions of the Cepheids have always been very uncertain. It now appears that the various mass anomalies have been solved by distance scale changes and by the realization of very helium rich convection zones. This helium enrichment is caused by a Cepheid wind which blows away more hydrogen than helium, just as in the solar wind. Now with the evolutionary theory masses, radii, luminosities, and our new composition structures, the predicted blue edges of the instability strip and periods throughout the strip agree very well with observations.
Detection of Am and Ap Stars by Photometric Means
Authors: Hauck B.
Published: July 2016

The detection of Am and Ap stars is possible in various photometric systems. Those most suitable for this purpose are certainly the uvbyβ (Strömgren 1967, Cameron 1967), the Barbier Morguleff system completed by Gerbaldi (1972, 1977) and the Geneva system. It seems important to me that the Am and Ap stars should be detected with a system which also allows one to classify normal stars, and to obtain quantitative information about metallicity or other peculiarity. The Geneva system satisfies both these criteria and numerous Am (about 400) and Ap (about 250) stars are in a catalogue prepared on magnetic tape by Rufener, which follows the one published in 1976 (Rufener 1976).
Extending the White Dwarf Sequence: Plans and Prospects
Authors: Liebert James
Published: July 2016

The recent discovery that the parallax star LP701-29 is a white dwarf has firmly extended the degenerate sequence below MV= +16m(Dahnet al. 1978). As the search for white dwarfs extends to cooler and fainter stars, however, it becomes particularly important to develop a plan for selecting candidates among the many thousands of red proper motion stars. We begin by assessing the completeness of the known sample within 10 parsecs in the northern two thirds of the sky. Some color-dependent selection effects must be evaluated, however, since these may preferentially inhibit the discovery of cooler stars. A correction factor for the missing low velocity white dwarfs is estimated. Then, Green's(1977) recent determination of the number density of blue degenerates is used to normalize various theoretical luminosity functions, the benchmarks against which the current sample out to 10 pc can be compared. It is concluded that the sample may be approaching completeness in the northern sky for white dwarfs with tangential velocities (vT) ≥ 40 km/sec (μ ≥ 1″.0/yr.) and Mbol< +15m. The implied luminosity function is thus consistent with that found by Sion and Liebert (1977). Below Mbol= +15mthe different theoretical functions predict substantially different numbers.
The Asiago catalogue of QSOs edition 1985
Authors: Barbieri C. , Chu Y. , Cristiani S. , Nota A.
Published: July 2016

A new Edition of the Asiago Catalogue of QSOs (Barbieri et al. 1982) is available on magnetic tape. It contains essentially all the information of the previous editions updated with the papers published before Dec.31, 1984. The catalog should be essentially complete to that date in respect to objects having slit spectra (2330 objects), while it is seriously incomplete regarding candidates discovered by objective prism or grism/grens surveys after 1982 (279 such objects included in the present version).
On the appearance of the host galaxies of quasars
Authors: Shanbhag Smita , Kembhavi Ajit
Published: July 2016

It is believed that the QSO phenomenon is a form of violent activity in the nuclei of galaxies. This view has found support after the recent detection of nebulosity around a large number of quasars. The nature of the fuzz is not yet clear, but there is some evidence that it is normallly a spiral galaxy hosting a quasar (e.g. Hutchings et al. 1984). However, the experience with radio galaxies suggests that the host of a radio loud quasar ought to be an elliptical galaxy. We have considered the appearance of elliptical galaxies of various redshifts with a view towards determining the nature of ellipticals which could act as hosts for radio quasars at large redshifts. For spirals we have considered the data given by Boroson (1981) and calculated the appearance of different morphological types at large redshifts.
CCD images of southern radio sources
Authors: White Graeme L. , Batty Michael J. , Jauncey David L.
Published: July 2016

We present here the first results of a program to obtain CCD images of a number of southern extragalactic radio objects using the 3.9-m Anglo-Australian telescope.
Polarization Distributions in Compact Radio Sources
Authors: Roberts David H. , Wardle John F. C.
Published: July 2016

We present milliarcsecond-resolution 5 GHz polarization maps of several active galactic nuclei: one epoch each for the quasar 3C345, the galaxy 3C120, and the BL Lacertae object 0735+178, and two epochs for the BL Lacertae object OJ287.
Search for superluminal motion in the weak cores of extended quasars
Authors: Zensus J. A. , Porcas R. W.
Published: July 2016

We present a status report on a project to study structural changes in a sample of radio cores associated with quasars with extended double lobes. Of six objects observed, so far two (3C 179 and 3C 263) are superluminal and two more (3C 268.4 and 1951+49) are possible superluminal candidates.
The Extended Radio Structure of Quasars
Authors: Owen Frazer N.
Published: July 2016

Modern radio maps usually allow quasars to be recognized from their radio morphology alone. Most have strong central components, double lobed outer structure and one-sided jets connecting the inner and outer structures. The physics of the sources is poorly understood. The observed bending of the jets, the high minimum pressures observed, and the required energy supply to the lobes are major problems. However, the outstanding problem regarding the extended structure is whether or not this morphology is produced by special relativistic effects or the intrinsic activity level and physics of the radio sources.
Radio properties of a ‘quarter jansky sample’ of extragalactic sources, defined at 408 MHz
Authors: Krishna Gopal , Saripalli L. , Saikia D.J. , Sramek R.A.
Published: July 2016

For a complete sample of 42 sources, defined over a narrow flux density range around 0.25 Jy at 408 MHz, properties related to size and nuclear radio emission are discussed and compared with the 3CR sample.
Radio structure and the IR-UV spectra of quasars
Authors: Wills Beverley J. , Wills D.
Published: July 2016

Here we present two main results that relate properties of quasar IR-to-UV spectra to the fraction of radio flux density in the compact core.
The X-ray properties of high redshift quasi-stellar objects
Authors: Anderson Scott F. , Margon Bruce
Published: July 2016

We describe a program aimed at characterizing the X-ray emission of high redshift QSOs. We have obtained slitless spectra of 50 high galactic latitude fields previously imaged at very high levels of sensitivity by the Einstein Observatory, generally for original goals unrelated to QSOs. Our survey, covering ∼ 17 deg2 of sky to limiting magnitude Bcont ∼ 21, has yielded ∼ 400 previously uncatalogued QSO candidates, each with sensitive new X-ray information available. About 100 of these objects, constituting a “high confidence” set of QSOs, chiefly in the redshift range 1.7 < z < 3 and thus complementary to previous samples with X-ray data, are used to derive the X-ray properties of high redshift QSOs. Even at these most sensitive available X-ray flux levels, only about 25% of the objects are positively detected in X-rays; thus extensive attention has been given to proper treatment of the upper-limit information. We find a mean optical-to-X-ray slope parameter for the sample of . Our results are combined with those of previous surveys to estimate the fraction of the diffuse X-ray background radiation due to QSOs. QSOs are capable of supplying the majority of the radiation, but the chief contribution comes from an annulus of intermediate redshift, moderate luminosity objects.
X-ray selected BL Lac objects: time variability and X-ray spectrum
Authors: Maccagni D. , Barr P. , Garilli B. , Gioia I.M. , Giommi P. , Maccacaro T. , Schild R.
Published: July 2016

The Einstein Observatory Medium Sensitivity Survey contains four sources identified with BL Lac objects. The radio and optical properties of these objects have been described in Stocke et al. (1985).
Rapid X-ray variability in active galactic nuclei
Authors: Barr P. , Mushotzky R. , Giommi P. , Clavel J. , Wamsteker W.
Published: July 2016

Recent EXOSAT observations of active galactic nuclei are presented. Unlike earlier X-ray satellites (all of which flew in low earth orbit), the deep orbit of EXOSAT allows long continuous observations of celestial X-ray sources, uninterrupted by earth occultation etc. We present the results of EXOSAT observations of several AGN which have been seen to vary rapidly (timescale 0.2–6 hours). We also consider the implications of rapid variability in AGN. For Seyfert galaxies and quasars, we find a highly significant correlation between the timescale of variability and their X-ray luminosity. They are not, howwever, bounded either by the (classical) Eddington limit nor by efficiency arguments. We sugest, rather, that the emitting plasma is dominated by electron-positron pairs.
A Survey of QSO Emission Lines
Authors: Wills Beverley J.
Published: July 2016

“Standard” photoionization models of the broad line region (BLR) consist of numerous small optically thick clouds of identical ionization, density, temperature and optical depth, moving under the influence of the gravity and radiation field of a 107–8 M⊙ black hole and confined by a high temperature gas. Such models have provided a good description of observed line strengths and widths with only very minor modification. Although photoionization remains the most important heating mechanism in the BLR, new observations point to a wider range of physical conditions and to clues about the geometric and dynamic arrangement of the emitting gas. I want to highlight the observations that have led us to this view.
Gas Dynamics and Formation of the Broad Line Region of QSOS
Authors: Perry Judith J.
Published: July 2016

Observational and theoretical constraints on self-consistent gas dynamical models of the line emitting regions of QSOs and AGNs are reviewed. General equations governing the global flows are analysed and models for the formation and acceleration of the line emitting “clouds” are discussed.
On the [OIII] emission of PG 1501+106
Authors: Van Heerde G. M.
Published: July 2016

Narrow-band imaging of PG 1501+106 revealed no extra-nuclear [OIII] emission above a level of ∼ 20 μJy. The disagreement with the result of Boroson et. al., 1982 (who detected 40 μJy) can be explained by assuming a slight difference in angular size between the broad and narrow line emitting regions.
Recurrent outbursts in the broad line region of NGC 1566
Authors: Alloin D.M.
Published: July 2016

From a set of spectrophotometric data covering 15 years, we observe a recurrent activity in the BLR of NGC 1566. Each period of activity lasts for 1300 days. It consists of successive bursts characterized by a rise-time less than 20 days and an exponential decay on a time scale of around 400 days. The total energy involved in one 1300 day period of activity is 1051 ergs. These variations can be understood in the framework of accretion disc models for AGN, as resulting from a limit cycle which operates in the inner regions of the disc.
Stimulated Raman scattering in active galactic nuclei
Authors: Krishan V. , Wiita P. J.
Published: July 2016

Stimulated Raman scattering (SRS) processes offer an attractive and efficient method for producing both essentially the entire non-thermal continuum as well as fast electrons in active galactic nuclei (AGN). In this picture, electrons are accelerated by Langmuir waves which are generated by Raman forward scattering (RFS); these electrons then rapidly radiate their energy by means of Raman back scattering (RBS) off of spatially periodic magnetic fields. Such periodic fields can be produced by magnetic modulational instabilities of the Langmuir field The emission is envisaged to arise from an expanding region, with the highest frequency radiation originating from the smallest volumes at the core of the AGN. Time variability is dominated by density fluctuations in these magnetohydrodynamic flows.
Do quasars evolve over cosmological time scales?
Authors: Wampler E.J. , Ponz D.
Published: July 2016

Systematic biases that are redshift dependent can influence the optical discovery of quasars and the evolution laws derived from counts of quasars. New data and their interpretation for quasars brighter than MB = −24 in the Palomar Bright Quasar Survey (BQS) (Schmidt and Green, 1983) are consistent with no evolution. A comparison of BQS quasars with the brightest quasars from the CTIO Schmidt Telescope Survey (Osmer and Smith, 1980) shows that if qo is near zero, the co-moving density of bright quasars in a Friedmann cosmology is about 15 times higher for the CTIO survey quasars (mean z ≈ 2.8) than for the BQS quasars (mean z ≈ 1.8). In this case spectral evolution is also required since the CTIO quasars have stronger CIV λ1548 lines than the BQS quasars of similar luminosity. Alternatively, if qO is taken to be near 1, the CTIO survey quasars would then have lower luminosity than the BQS quasars and these data would be consistent with no evolution. Strong CIV λ1548 lines for the CTIO quasars would then fit the general correlation between absolute quasar luminosity and emission line strength (Wampler, Gaskell, Burke and Baldwin, 1984).
Pairing, clustering, optical variability and gravitational lensing in a sample of about 150 flat-spectrum radio-selected QSOs
Authors: Wills D. , Wills Beverley J.
Published: July 2016

Some years ago, Bolton, Peterson, Wills and Wills (1976, BPWW) reported a statistically-significant excess of QSOs within 2' arc of flat spectrum radio-selected QSOs (specifically, they found 5 such objects while only 1 was expected by chance). None of the QSO pairs had the same redshifts so the result could be regarded as evidence for non-cosmological redshifts, non-uniform QSO distributions, or a statistical fluctuation. Because of the potential importance of BPWW's result, we later used the same technique to examine an independent sample of about 150 QSOs with flat radio spectra and found results that are consistent with the known surface density of QSOs. If we assume a surface density of 3.3 QSOs per square degree brighter than B = 19 (e.g. Marshall et al. 1983), the 150 fields each of 2' arc radius should contain 1.7 random QSOs above this limit and we found 2 (e.g. Wills 1978). A third object is very close to B = 19, and another field contains an object that is extremely blue, with B < 19, on the Palomar Sky Survey, but below our plate limit (i.e. B > 21); we have so far been unable to obtain a spectrum for it. One of the 3 confirmed QSOs is 119″ arc from the radio-emitting one, so rather small changes in the magnitude limit, search radius and choice of epoch at which the magnitudes are measured can result in there being anywhere between 1 and 4 secondary QSOs (or 1–3 if the variable object is not a QSO), compared with 2 expected by chance, and perhaps 10 that would be predicted by BPWW's results.
A survey of quasar clustering; initial results at the SGP
Authors: Drinkwater M.J.
Published: July 2016

Several U.K. Schmidt objective prism plates are being searched for quasar clustering. The spectra are measured by the automated plate measuring facility (APM) and emission line objects selected for which redshifts can be estimated. Most redshifts tested (based on Lyman-α) are accurate to 2%. Initial results from the South Galactic Pole (SGP) field show little evidence of clustering on scales between 60 and 500 Mpc (Ho=50, qo=0, at z=2.3).
“Missing image” in gravitational lens systems
Authors: Narasimha D. , Subramanian K. , Chitre S.M.
Published: July 2016

The gravitational lens models involving extended mass distribution generally predict an odd number of images with one of the images close to the centre of the principal lensing galaxy. In all the observed lens systems only an even number of images have been unambigously detected so far. It is demonstrated that the presence of a compact nucleus at the centre of lensing galaxies would dim the “odd” image significantly without affecting the rest of the image configuration.
A close look at Q2237+0305
Authors: Tyson J. Anthony
Published: July 2016

CCD images of the lensed QSO candidate 2237+0305 in the blue and near-infrared are examined. At least two blue images of the QSO, separated by about 1 arcsec, are found. The inferred velocity dispersion of the lensing galaxy core of 150 km/sec implies that no dark matter is required for this case. Limits on the mass distribution of the lensing galaxy core and bar can be obtained from the data. Since the galaxy is so nearby, this lensed QSO is a good candidate for assisted lensing by individual stars in the galaxy core.
The evolution of intergalactic Hydrogen clouds: confusion resolved
Authors: Murdoch H.S. , Hunstead R.W. , Pettini M. , Blades J.C.
Published: July 2016

It is now widely accepted that a population of intergalactic hydrogen clouds is responsible for the plethora of absorption lines seen at wavelengths shorter than Ly α emission in all high-z QSOs. The question of whether the comoving number density of such clouds evolves with redshift has been somewhat controversial. It is usually assumed that
Observational Cosmology 1920–1985: An Introduction to the Conference
Authors: Sandage Allan
Published: July 2016

The history of modern cosmology has been divided into two periods. The primary discovery phase extended from 1920 to ∼1950 when most of the classical tests were developed. The subsequent consolidation period from 1950 to ∼1980 saw a deeper understanding of the tests and the introduction of concepts of stellar populations that led to estimates of evolutionary trends with look-back time. The only test not affected by evolutionary effects is the comparison of the Hubble time, Ho−1, with independent estimates of the age of the Universe. The N(m), m(z), θ(z), θ(m), and HoTo (qo, Λ) tests are reviewed as they have been discussed in the archive literature. The problem of observational bias is emphasized, as is the difficult recent search for secular evolutionary effects. Current problems which have prospects for solutions in the next decades are set out in the final section.
Measurement of the Microwave Background Temperature from CN Absorption
Authors: Mandolesi N. , Crane P. , Hegyi D.J.
Published: July 2016

Observations of the interstellar lines of CN near 3875Å toward ζ Oph provide precise measurements of the Microwave Background Radiation (MBR) temperature and determine the intrinsic linewidth necessary for the saturation correction. We report TMBR=2.74±0.05 K at λ=2.64 mm and TMBR=2.75 (+0.24, −0.29) K at λ=1.32 mm.
Measurement of the Dipole Moment of the Cosmic Background Radiation at mm and Sub-mm Wavelengths
Authors: Halpern Mark
Published: July 2016

Sensitive measurements of a dipole anisotropy of the Cosmic Background Radiation at wavelengths of 1.7 and 0.8 mm are presented. Under the assumption that the dipole moment is caused by a doppler shift, these measurements are of sufficient precision to constrain spectral distortions of the CBR at short wavelengths. Measurements of the brightness and shape of diffuse galactic emission are also presented.