bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiplicity in T and OB Associations
Authors: Köhler Rainer , Brandner Wolfgang
Published: July 2016

The results of binary surveys among T Tauri stars in the T associations Taurus-Auriga and Chamaeleon, and in the OB association Scorpius-Centaurus are summarized, and implications on our understanding on the formation of binary and multiple systems are discussed.
What Can Pre-Main Sequence Binary Star Populations Tell Us about Binary Formation Mechanisms?
Authors: Ghez Andrea M.
Published: July 2016

We review current observations of binary star populations with particular attention to what insight these populations can give us into the problem of how binary stars form. Significant progress has been made in the past few years, revealing variations as a function of site, primary star mass, and binary star separations. The variations in the binary star population with type of star formation site in comparison with the field, suggests that ∼30% of the field binaries formed in loose T associations and ∼70% formed in the dense progenitors of open clusters. Variations with mass and separation on the whole are well matched by the predictions of fragmentation followed by competitive accretion. However, there remains much work to be done on both the observational and theoretical end before a complete picture of binary star formation can be developed.
Statistics of Binary and Multiple Young Stars Observed by Lunar Occultations
Authors: Richichi Andrea
Published: July 2016

The application of the lunar occupation method to studies of young stars is discussed. The statistics of results on binarity and multiplicity is reviewed.
Angular Momentum Transport and Dynamo Effect in Kepler Disks
Authors: Rüdiger Günther , Ziegler Udo
Published: July 2016

Properties have been demonstrated of the magneto-rotational instability for two different applications, i.e. for a global spherical model and a box simulation with Keplerian background shear flow. In both nonlinear cases a dynamo operates with a negative (positive) α-effect in the northern (southern) disk hemisphere and in both cases the angular momentum transport is outwards. Keplerian accretion disks should therefore exhibit large-scale magnetic fields with a dipolar geometry of the poloidal components favoring jet formation.
Early Orbital Evolution of Binaries: Overview and Outlook
Authors: Artymowicz Pawel , Lubow Stephen H.
Published: July 2016

The orbital evolution of a young binary star is strongly affected by the circumstellar disks orbiting each of the stars, and/or the circumbinary disk orbiting about the entire binary. Calculation of the evolution requires the knowledge of disk structure (resonantly emitted density and bending waves, disk gap sizes, possible secular nonaxisymmetry), as well as of any gas streamers falling onto the binary. While the diagnostic signatures of the binary-disk interaction are observable (and have recently been observed), the orbital evolution cannot directly be observed so far, because of long associated time scales. Hence, theory is crucial for understanding the evolutionary stage and the future of the observed systems. We briefly review the status of the theory of orbital evolution and discuss several topics requiring further theoretical work.
Planet Formation in Binary Systems
Authors: Kley Wilhelm
Published: July 2016

Among the 50 discovered extrasolar planets orbiting main-sequence solar type stars only three are confirmed to be in a binary star system. However, the majority of stars seem to form in binary or even multiple stellar systems. Standard planet formation scenarios consider the creation of planets or planetary systems only for isolated solitary stars. The presence of a companion creates tidal torques on the protoplanetary disk, which may influence the formation process of planets in disks. In this contribution the consequences of the companion's perturbation on the formation scenario of planets is briefly discussed.
The Future of mm/submm Interferometry: The ALMA Project
Authors: Guilloteau Stéphane
Published: July 2016

ALMA, the Atacama Large Millimeter / Sub-millimeter Array will be the first instrument allowing very high angular resolution (down to 0.01″) with sufficient sensitivity to image thermal emission from dust and molecules in proto-planetary disks at wavelengths where these disks are optically thin. Its unsurpassed characteristics will make it a premier instrument to study the formation of binary and multiple systems. I present here the projected characteristics of ALMA, in particular the expected sensitivities and frequency coverage, and illustrates some possible applications relevant to the study of binary star formation.
Galactic Far-Infrared Diffuse Emission
Authors: Boulanger François , Bernard Jean-Philippe , Lagache Guilaine , Stepnik Bertrand
Published: July 2016

We review the present understanding of the interstellar dust contribution to the far-IR (λ > 100 μm) sky emission. We show how the contribution from the distinct ISM components (HI, H2, HII gas) are identified and characterized through spatial correlation with gas emission lines. We discuss the spectral energy distribution of the emission from cirrus dust associated with diffuse HI gas and from colder dust associated with molecular gas. We relate the drop in dust emission temperature from the diffuse interstellar medium to molecular gas to an evolution of dust affecting both the abundance of small dust grains and the far-IR emissivity of large grains.
The Far Infrared and Submillimeter Diffuse Extragalactic Background
Authors: Hauser M. G.
Published: July 2016

The cosmic infrared background (CIB) radiation was a long-sought fossil of energetic processes associated with structure formation and chemical evolution since the Big Bang. The COBE Diffuse Infrared Background Experiment (DIRBE) and Far Infrared Absolute Spectrophotometer (FIRAS) were specifically designed to search for this background from 1.25 μm to millimeter wavelengths. These two instruments provided high quality, absolutely calibrated all-sky maps which have enabled the first detections of the CIB, initially at far infrared and submillimeter wavelengths, and more recently in the near infrared as well. The aim of this paper is to review the status of determinations of the CIB based upon COBE measurements. The results show that the energy in the CIB from far infrared to millimeter wavelengths is comparable to that in the integrated light of galaxies from UV to near infrared wavelengths: the universe had a luminous but dusty past. On the assumption that nucleosynthesis in stars is the energy source for most of this light, the results also imply that 1–8% of cosmic baryons has been converted to helium and heavier elements in stars. The integrated background light from UV to millimeter wavelengths, 60–120 nW m−2 sr−1, is about 10% of that in the cosmic microwave background. Current knowledge of the CIB provides significant new constraints on models of the history of star formation and galaxy evolution.
Detection of a Far IR Excess with DIRBE at 60 and 100 Microns
Authors: Finkbeiner D. P. , Davis Marc , Schlegel David
Published: July 2016

From analysis of the DIRBE weekly averaged sky maps, we have detected substantial flux in the 60 μm and 100 μm channels in excess of expected zodiacal and Galactic emission (Finkbeiner, D.P., et al. 2000, ApJ, to be published, astro-ph/0004175). Two methods are used to separate zodiacal light from more distant emission. Both methods give consistent results at 60 μm and 100 μm. The observed signal is consistent with an isotropic background of vIv = 28.1 ± 1.8 ± 7 (syst) nWm−2sr−1 at 60 μm and 24.6 ± 2.5 ± 8 (syst) nW m−2 sr−1 at 100 μm.

The IR excess detected at 140 and 240 μm by these methods agrees with previous measurements, which are thought to be the cosmic infrared background (CIB). The detections at 60 and 100 μm are new. While this new excess is not necessarily the CIB, we have ruled out all known sources of emission in the solar system and Galaxy. We therefore tentatively interpret this signal as the CIB and consider the implications of such energy production from the viewpoint of star formation efficiency and black hole accretion efficiency. However, the IR excess exceeds limits on the CIB derived from the inferred opacity of the intergalactic medium to observed TeV photons, thus casting doubt on this interpretation. There is currently no satisfactory explanation for the 60 – 100 μm excess.
Toward the Monitoring of Blazars at Abastumani
Authors: Kurtanidze O. M.
Published: July 2016

We give a brief summary of the ongoing Abastumani Blazar Monitoring Program (ABMP) started in May 1997. More than ~50,000 frames of data have been collected during 370 nights of observations on about 50 target objects. Preliminary results of two years of monitoring of ten selected AGNs carried out in the framework of ABMP are presented. All observations were done in the BVRI bands using the CCD ST-6 based photometer attached to the 70-cm meniscus telescope's Newtonian focus. Image reductions were made using different software packages of image reduction systems such as IRAF, MIDAS and STARLINK. All objects under study show light variations exceeding one magnitude. The largest variation was observed for AO 0235+116, amounting to 4.0 mag in the R band.
The Two Micron All-Sky Survey: Removing the Infrared Foreground
Authors: Gizis John E. , Skrutskie Michael F.
Published: July 2016

We introduce the properties of the Two Micron All-Sky Survey (2MASS) for IAU Symposium 204. 2MASS is a near-infrared survey of the entire sky characterized by high reliability and completeness. Catalogs and images for 47% of the sky are now available online. This data release has been used by Wright (2000) and Cambrésy et al. (2000) to subtract the stellar foreground at 1.25 and 2.2 microns from COBE DIRBE data, revealing the cosmological near-infrared background.
Far Infrared Extragalactic Background Radiation: Source Counts with ISOPHOT
Authors: Juvela M. , Mattila K. , Lemke D.
Published: July 2016

We have searched for point-like sources in eight fields mapped at two or three wavelengths between 90 μm and 180 μm with the ISOPHOT instrument aboard the ISO satellite. Most of the 55 sources detected are suspected to be extragalactic and cannot be associated with previously known objects. It is probable, also from the far-infrared (FIR) spectral energy distributions, that dust-enshrouded, distant galaxies form a significant fraction of the sources.

We present a tentative list of the detected extragalactic FIR-sources. Based on the analyzed data we estimate the number density of extragalactic sources at wavelengths 90 μm, 150 μm and 180 μm and at flux density levels down to 100 mJy to be 1 x 105 sr−1, 2x105 sr−1, and 3xl05 sr−1, respectively.

Models of strong galaxy evolution are in best agreement with our results, although the number of detections exceeds predictions of most models. No-evolution models can be rejected at a high confidence level. Comparison with COBE results indicates that at 90 μm the detected sources correspond to >20% of the extragalactic background light. At longer wavelengths the corresponding fraction is ~ 10%.
Models for Infrared and Submillimetre Counts and Backgrounds
Authors: Rowan-Robinson Michael
Published: July 2016

A simple and versatile parametrized approach to the star formation history allows a quantitative investigation of the constraints from far infrared and submillimetre counts and background intensity measurements.

The models include four spectral components: infrared cirrus, an M 82-like starburst, an Arp 220-like starburst and an AGN dust torus. The 60 μm luminosity function is determined for each chosen rate of evolution using the PSCz redshift data for 15000 galaxies. The proportions of each spectral type as a function of 60 μm luminosity are chosen for consistency with IRAS and SCUBA colour-luminosity relations, and with the fraction of AGN as a function of luminosity found in 12 μm samples.

A good fit to the observed counts at 0.44, 2.2, 15, 60, 90, 175 and 850 μm can be found with pure luminosity evolution in all 3 cosmological models investigated: Ω0 = 1, Ω0 = 0.3 (Λ = 0), and Ω0 = 0.3, Λ = 0.7. All 3 models also give an acceptable fit to the integrated background spectrum. The total mass-density of stars generated in all 3 cosmological models is consistent with that observed.
Galaxy Evolution in the Optical and Submillimeter
Authors: Lilly Simon
Published: July 2016

I review the emerging picture of galaxy formation and evolution that is coming from observations in the optical waveband and in the submillimeter waveband. In the former I look at the work of several groups but in the latter I focus on the results from the Canada-UK Deep Submillimeter Survey (CUDSS), an 850 micron survey of about 100 square arcmin of sky carried out with SCUBA to a limiting flux of 3 mJy. I discuss what we do and do not know about the sources responsible for emitting a significant fraction of the extragalactic background at 850 microns.
Constraints on Far-Infrared Source Counts in the Lockman Hole using a Power Spectrum Analysis
Authors: Matsuhara H. , Kawara K. , Sofue Y. , Taniguchi Y. , Sato Y. , Okuda H. , Matsumoto T. , Wakamatsu K. , Cowie L. L. , Joseph R. D. , Sanders D. B.
Published: July 2016

We present the characteristics of far-infrared (FIR) brightness fluctuations at 90 μm and 170 μm in the Lockman Hole, which were surveyed with the ISOPHOT instrument aboard the Infrared Space Observatory (ISO), and give constraints on the galaxy number counts down to 30 mJy at 90 μm and 50 mJy at 170 μm. The fluctuation power spectra of the FIR images are not dominated by IR cirrus, and are instead most likely due to star-forming galaxies. This analysis indicates the existence of strong evolution in the counts. Especially at 90 μm, the source density is much larger than that expected from the currently available galaxy count models. The galaxies responsible for the fluctuations also significantly contribute to the cosmic infrared background radiation recently derived from an analysis of the COBE data.
The Impact of Galaxy Formation on the Diffuse Background Radiation
Authors: Silk Joseph , Devriendt Julien
Published: July 2016

The far infrared background is a sink for the hidden aspects of galaxy formation. At optical wavelengths, ellipticals and spheroids are old, even at z ~ 1. Neither the luminous formation phase nor their early evolution is seen in the visible. We infer that ellipticals and, more generally, most spheroids must have formed in dust-shrouded starbursts. In this article, we show how separate tracking of disk and spheroid star formation enables us to infer that disks dominate near the peak in the cosmic star formation rate at z ≲ 2 and in the diffuse ultraviolet/optical/infrared background, whereas spheroid formation dominates the submillimetre background.
Supernova Abundance Generation
Authors: Nomoto K. , Shigeyama T. , Tsujimoto T.
Published: July 2016

Theoretical models of supernova explosions of various types are reviewed to obtain heavy element yields from supernovae. We focus on new models for SN 1987A, and Type Ia, Ib, and Ic supernovae. Maximum brightness and decline rate of their light curves suggest that 12–18 M⊙ stars produce larger amount of 56Ni than more massive stars. We discuss relative roles of various types of supernovae in the chemical evolution of galaxies.
Model Atmospheres and Chemistry
Authors: Sakhibullin N.A.
Published: July 2016

The limitations imposed on the accuracy of the abundance determination by the current status of the stellar atmosphere models are discussed. It is shown that the very high S/N ratio and resolution in spectroscopic observations require the new additional steps in stellar atmosphere modeling and in the line formation theory.
Are there Normal Upper Main Sequence Stars: λ Bootis, …
Authors: Cowley Charles R.
Published: July 2016

Our concept of normal A stars is severely influenced by the dearth of features in the low resolution spectra of these objects that have been used for classification. The relatively small number of lines visible at survey dispersion has also led us to greatly simplify the complexity of spectroscopic patterns that can occur. The λ Boo stars were noted as a class because of the prominence of the λ4481 line of Mg II. We call attention to lines of V II and Ni II that are strong in superficially normal stars, and surprisingly weak in strong-lined stars with obvious overabundances of chromium, manganese, and iron. It is also useful to note that iron itself can be both underabundant and overabundant in CP stars. We call attention to an important new work by Venn and Lambert that develops the earlier suggestion that λ Boo stars may have formed from gas that has been separated from interstellar grains.
The Chemical Composition of the Wolf-Rayet Envelopes
Authors: Nugis T.
Published: July 2016

Model-independent information on the chemical composition of WR stars is obtained from the lines of different ions arising at transitions between highly excited energy levels.

The chemical composition of WR stars strongly differs from the mean cosmic composition. Nuclear processed CNO products of H-burning are revealed in WN envelopes and He-burning products in WC envelopes. The matter enriched with He and N is also present in some ring nebulae around WN stars.
Asymptotic Giant Branch Stars: Thermal Pulses, Carbon Production, and Dredge Up; Neutron Sources and s-Process Nucleosynthesis
Authors: Iben Icko
Published: July 2016

A brief review is given of the structure of asymptotic giant branch (AGB) stars and of the characteristics of the thermal pulses which these stars experience. Following a pulse, model AGB stars with a large core mass easily dredge up fresh carbon, which is the main product of incomplete helium burning, and s-process isotopes, which are made as a consequence of the activation of the 22Ne neutron source. Model AGB stars of small core mass activate the 13C neutron source and produce s-process isotopes in nearly the solar system distribution. They also dredge up fresh carbon and s-process isotopes, but only if overshoot or some other form of “extra” mixing beyond the lower boundary of the convective envelope is invoked.
Pre-White Dwarf Evolution Through Planetary Nebulae
Authors: D'antona Francesca , Mazzitelli Italo
Published: July 2016

In the present review we summarize the problems relative to the chemical composition of the inner and outer layers of white dwarfs as expected from stellar evolution. We point out that there is a contrast betweenstandardpredictions and the indications deriving from studies of white dwarfs, as “massive” hydrogen remnat layers seem not to be present on single white dwarfs. We discuss a previously neglected feature of stellar models in the phase of thermal pulses -which occurs when the outer hydrogen envelope becomes very small- by which the progenitors of low total mass may get rid of practically the whole hydrogen envelope during the final phases of asymptotic giant branch evolution. We finally propose a new global scheme for the pre-white dwarf evolution, which depends mainly on the initial progenitor mass.
Concluding Remarks (I)
Authors: Baschek B.
Published: July 2016

After a week of highly interesting discussions on ‘stellar evolution and the photospheric abundance connection’ we now come to resume the contributions to this Symposium. This task has been divided up among three of us, arranged according to the course of stellar evolution, and in alphabetical order of the speakers (Baschek, Lambert, van Horn). I begin with the essentially unevolved stars, recalling some results and problems, not systematically but rather selected from my own interests.

First I should like to briefly reconsider the accuracy of abundance determinations in view of the contributions following my review. Then some comments on stellar models are given, followed by a few remarks about peculiar A stars. Finally, the similarity of the oxygen abundance in Magellanic Cloud B stars and galactic population II stars is pointed out.
Predicted Lens Redshifts And Magnitudes
Authors: Helbig P.
Published: July 2016

For gravitational lens systems with unknown lens redshifts, the redshifts and brightnesses of the lenses are predicted for a variety of cosmological models. Besides providing hints as to which systems should be observed with a realistic chance of measuring the lens redshifts, which are needed for detailed lensing statistics and for modelling the lenses, these calculations give a visual impression of the influence of the cosmological model in gravitational lensing.
Vacuum Decaying Cosmological Models And Gravitational Lensing
Authors: Waga I. , Bloomfield Torres L. F.
Published: July 2016

We investigate the statistical properties of gravitational lenses for flat models in which a cosmological term decreases with time as ⁁ ∝ a−m, where a is the scale factor and m is a parameter (0 ≤ m < 3) (Bloomfield Torres and Waga 1995).
Wide Separation Lenses
Authors: Mortlock D. J. , Webster R. L. , Hewett P. C.
Published: July 2016

There is still debate as to whether wide separation (Δθ ≳ 3″) double quasars are physical binaries or gravitationally lensed sources. We proceed under the assumption that most of these objects are the result of lensing, and use maximum likelihood techniques (Kochanek 1993) to infer information about the mass distribution of deflectors that would be required to produce these wide image separations. Under the above assumptions, the most consistent explanation is the existence of a significant population of dark objects with the mass of groups of galaxies.
The Gravitational Lens Candidate HE 1104–1805 And The Size Of Absorption Systems
Authors: Smette A. , Robertson J.G. , Shaver P.A. , Reimers D. , Wisotzki L. , Köhler Th.
Published: July 2016

We obtained 1.2 Å resolution spectra over the range 3175–7575 Å for the two components of the gravitational lens candidate HE 1104–1805 (z = 2.31, mB = 16.7 and 18.6, separation = 3.0 arcsec; cf. Wisotzki et al. 1993), with the aim of setting limits on the sizes of the clouds producing the Ly-α, C IV, and Mg II absorption systems. We refer to Smette et al. (1995) for a detailed account of this study.
HST Observations Of Giant Arcs
Authors: Smail Ian , Dressler Alan , Kneib Jean-Paul , Ellis Richard S. , Couch Warrick J. , Sharples Ray M. , Oemler Augustus
Published: July 2016

We discuss HST imaging of eight spectroscopically-confirmed giant arcs, pairs and arclets. Although our HST observations include both pre- and post-refurbishment images, the depth of the exposures guarantees that the majority of the arcs are detected with diffraction-limited resolution. We present the size information on these distant field galaxies in the light of HST studies of lower redshift samples. We suggest that the dominant population of star-forming galaxies at z ∼ 1 is a factor of 1.5–2 times smaller in size than the equivalent population in the local field. This implies either a considerable evolution in the sizes of star-forming galaxies within the last ∼10 Gyrs or a shift in the relative space densities of massive and dwarf star-forming systems over the same time scale.
Redshifts of Faint Blue Galaxies From Gravitational Lensing
Authors: Bartelmann Matthias , Narayan Ramesh
Published: July 2016

The possibility to reconstruct cluster mass distributions from their gravitational lensing effects on background sources is now firmly established and is discussed in a number of other contributions to these proceedings. Here, we want to suggest a new method, the parallax method (Bartelmann & Narayan 1995), to infer the redshifts of the background sources, which are in general too faint to allow spectroscopy. The method is based on gravitational lensing, and apart from arclet redshifts it yields calibrated, accurate cluster reconstructions. The key idea is simple and rests on three facts: (1) The strength of lensing effects increases with source redshift, if the redshift is kept fixed. (2) The surface brightness of the arclet sources steeply decreases with redshift z. Neglecting spectral effects, the surface brightness is ∝ (1 + z)−4. (3) The surface brightness of the sources is invariant to lensing. In combination, these facts imply that lensing effects become stronger with decreasing surface brightness, so that relative distances of arclet sources can be inferred from the variation of lensing effects with the surface brightness of lensed sources. If the redshift of the brightest sources can be measured spectroscopically, the relative distances can be calibrated and the average redshift as a function of surface brightness can be found.
Beltrami Equation And Cluster Lensing
Authors: Schramm T.
Published: July 2016

Arclets in clusters of galaxies can be used to determine the lens mapping and not only to constrain the mass density of the cluster. Multiply imaged arclets are therefore easily identified without further modeling.
Effect Of Sub-Structure In Clusters On The Local Weak-Shear Field
Authors: Natarajan Priyamvada , Kneib Jean-Paul
Published: July 2016

Weak shear maps of the outer regions of clusters have been successfully used to map the distribution of mass at large radii. The effects of substructure in clusters on such reconstructions of the total mass have not been systematically studied. We propose a new method to study the effect of perturbers (bright cluster galaxies or sub-groups within the cluster) on the weak shear field. We present some analytic results below.
First Results Of The DUO Program
Authors: Alard C.
Published: July 2016

The DUO (Disk Unseen Objects) program is a project with the main goal of searching for galactic dark matter in a field towards the Galactic Bulge (Alard et al. 1995b). In this paper I present the results obtained from the analysis of half of the data collected during the 1994 season. I start with a brief description of the DUO project, and I will continue with an analysis of the microlensing candidates that I found. In all I found 13 microlensing events in the DUO data, including a double lens event. A model of the double lens light curve predicts a blending effect. The presence of the blended component was confirmed by a gravity center shift during the event. Taking into account the model prediction and the shift, we could predict the exact geometry of the blend. This prediction was recently confirmed by direct imaging of the blend under good seeing conditions. The durations of the single lens events are quite short, but the durations can be seriously affected by blending. I propose a simple experimental test to quantify this duration bias. In the conclusion I emphasize the great importance of a good knowledge of the inner Galactic structure to get a reliable quantitative description of microlensing towards the bulge. Finally I will show that the large number of variables stars found in the data could be a powerful tool to probe this structure.
Separating Intrinsic And Microlensing Variability Using Parallax Measurements
Authors: Haugan Stein Vidar Hagfors
Published: July 2016

In gravitational lens systems with 3 or more resolved images of a quasar, the intrinsic variability may be unambiguously separated from the microlensing variability through parallax measurements from 3 observers when there is no relative motion of the lens masses (Refsdal 1993). In systems with fewer than 3 resolved images, however, this separation is not straightforward. For the purpose of illustration, I make the following simplifications for the one-dimensional case: The observations consist of well-sampled time series of the observed flux FA(ti) and FB(ti) at two points in the observer plane. The separation vector of the two points is parallel to the direction of the transverse motion of the source-lens-observer system, and the distance DAB between the observers is known. Furthermore, the distance DAB is small compared to the typical length scale of fluctuations in the magnification μ(x).
Quasar Variability From Microlensing
Authors: Hawkins M.R.S.
Published: July 2016

Quasars are known to vary in brightness over a wide range of time scales. Short term intrinsic variability has been well documented, and a strong case can be made that long term variation is due to microlensing. In this paper the effect of time dilation as a means for distinguishing between intrinsic variation and gravitational lensing is discussed.
Multi-Frequency VLBI Observations Of B0218+357
Authors: Porcas Richard W. , Patnaik Alok R.
Published: July 2016

We present the results from VLBI observations at three frequencies of the gravitational lens system B0218+357. From the source double structure, seen in both the A and B images at 15 GHz, we have derived a relative magnification matrix, and we show that the lens mass distribution must be non-spherical. We investigate how far the matrix parameters derived from 15 GHz observations can be used to relate the A and B images at 1.7 and 5 GHz, where the image sizes are much larger.
1608+656: A Quadruple Lens System Found In The CLASS Gravitational Lens Survey
Authors: Myers Steven T.
Published: July 2016

The first phase of a large gravitational lens survey using the Very Large Array at a wavelength of 3.6 cm has been completed, yielding images for 3258 radio sources. The Cosmic Lens All-Sky Survey, or CLASS, is designed to locate gravitational lens systems consisting of multiply-imaged compact components with separations > 0.″2. From this first phase has come the discovery of 1608+656, a quadruply-imaged object with maximum separation of 2.″1. Images from the Palomar 5-m and Keck 10-m telescopes show the lensed images and the lensing galaxy. An optical spectrum obtained with the Palomar 5-m Telescope indicates a redshift of z = 0.63 for the lensing galaxy, and a newly-obtained Palomar spectrum indicates a redshift of z = 1.39 for the lensed source, which appears to be a galaxy. A simple single-galaxy lens model derived from the radio image reproduces the observed configuration and relative fluxes of the images, as well as the position, shape, and orientation of the lensing galaxy. Because a simple mass model is able to fit the observations, we argue that this lens system is promising for determining H0. CLASS has also yielded the new double image lens system 1600+434. The second phase of the survey is scheduled for August and September 1995 on the VLA, and should yield images for an additional 5000+ targets, bringing the CLASS total to over 8000.
EVN-Merlin Observations of the Remarkable Lens System: 2016+112
Authors: Garrett M.A. , Nair S. , Walsh D. , Porcas R.W. , Patnaik A.R.
Published: July 2016

2016+112 was observed simultaneously with the European VLBI Network (EVN) and MERLIN arrays during the May 1993 joint EVN-MERLIN session at λ18 cm. Common elements to both arrays included the Jodrell Bank 76-m Lovell and 32-m Cambridge telescopes. In order to simultaneously map the entire 4 arcsec2 field of view, various wide-field mapping techniques were employed (see Garrett et al. 1994b).
The Quasar Luminosity Function
Authors: Hewett Paul C.
Published: July 2016

Recent results at high redshifts are briefly reviewed. An analysis of the evolution of the quasar luminosity function based on the recently published Hawkins & Véron (1995) variability-selected quasar sample is presented. The results support the conclusions of earlier work that suggested the simple two power law luminosity function, of invariant shape as a function of redshift, requires some modification in order to match the data. However, the contention of Hawkins & Véron that a single power law model provides an adequate fit to the variability-selected quasar sample and that there is no requirement for curvature in the form of the quasar luminosity function is not borne out by the analysis.
Ground-Based And HST Direct Imaging Of HLQs
Authors: Surdej J. , Jaunsen A.O. , Claeskens J.-F. , Gonzaga S. , Pospieszalska-Surdej A. , Pirenne B. , Prieto A.
Published: July 2016

In the context of our studies on gravitational lensing effects among Highly Luminous Quasars (HLQs), we are presently compiling at STScI an archive of direct CCD frames for more than 1000 bright quasars observed with HST and ground-based telescopes. This archive will soon become publicly accessible through the Internet. On the basis of these observations, we are pursuing in a systematic way the analysis (subtraction of numerical PSFs and/or deconvolution) of the HLQ images in order to detect multiple QSO images and/or nearby foreground galaxies at very small angular separations. Residual images corresponding to several new possible multiply imaged HLQs are presented here. From the observed number and image configuration of gravitational lens candidates identified in this large sample of HLQs, it is possible to infer realistic values for parameters characterizing the galaxy deflectors, the number counts of quasars, etc. (cf. Claeskens et al. 1995ab), and also to set interesting constraints on the cosmological density of compact objects in the mass range 1010 ‒ 1012M⊙.
A VLA/Merlin/VLBA For Intermediate Scale Lenses and the Discovery of a New Lens System?
Authors: Augusto P. , Wilkinson P.N. , Browne I.W.A.
Published: July 2016

We are searching for small lens systems (50-250 mas or 108–109M⊙) in a sample of ∼ 1800 flat spectrum radio sources. This is the first time a systematic search has been made “between” the VLA and VLBI resolutions. Finding any would indicate the existence of other than the “conventional” spiral/elliptical lenses (only ∼ 0.01% chance - Turner et al. (1984)). For example, faint galaxies are numerous (∼ 106 gal/deg2 - Lilly (1993), Glazebrook et al. 1995), compact (HST Medium Deep Survey (MDS) - Griffiths et al. 1994) and ideally placed for lensing (< z >∼ 0.6 - MDS, Smail et al. (1994); c.f. Turner et al. 1984). Early-type dwarf galaxies (dE,N and cE), if extant at intermediate-z as favored by MDS are also obvious lens candidates. If no lenses are found, a limit 400 times better than the current one (Surdej et al. 1993), ΩL < 0.001, will be placed on the cosmological density of compact objects (e.g. black holes) for the above mass range.
The Evolutionary History of the Milky Way
Authors: Freeman K.C.
Published: July 2016

The accretion of small satellite galaxies appears to have been important in the formation of the metal-poor halo of the Galaxy. The disrupting Sgr dwarf galaxy and the recent discovery of a young, metal-poor component of the halo indicate that this is a continuing process. The evolution of the galactic disk, and some consequences of the bar-like nature of the galactic bulge are briefly discussed.
Recent Progress in the Search for Black Holes in Galactic Nuclei
Authors: van der Marel Roeland P.
Published: July 2016

Massive nuclear black holes (BHs) of 106–109M⊙ are believed to be responsible for the the energy production in quasars and active galaxies, and are thought to be present in many quiescent galaxies as well. Dynamical evidence for this can be sought by studying the dynamics of gas and stars in galactic nuclei at high spatial resolution. This paper reviews the current evidence, with emphasis on some recent developments and ongoing projects. The evidence from water masers and gas kinematics in the active galaxies NGC 4258 and M87 is compelling. In quiescent galaxies only stellar kinematics are generally available. One well-studied case is M32. Stellar dynamical f(E, Lz) models with a few million solar mass BH fit the ground-based kinematical data remarkably well. N-body simulations of an edge-on f(E, Lz) model for M32 show that this model is stable. HST spectra should soon provide new and improved constraints on the presence of BHs in quiescent galaxies.
Iron Abundance Discrepancy in Ellipticals after ASCA
Authors: Arimoto N.
Published: July 2016

The chemical composition of the ISM is expected to reflect the average composition of the stellar component as established at the time of its formation, then further enriched by SN's of Type Ia that are known to currently explode in elliptical galaxies. Renzini et al. (1993) estimate the expected iron abundance in the hot ISM of elliptical galaxies to range from a minimum of ∼ 2 times solar, to perhaps as much as ∼ 5 times solar or more, depending on the adopted SNIa's rate.
The Cold Interstellar Medium
Authors: Sancisi Renzo
Published: July 2016

An HI view of spiral galaxies is presented. In the first part the standard picture of isolated, normal spiral galaxies is briefly reviewed. In the second part attention is drawn to all those phenomena, such as tidal interactions, accretion and mergers, that depend on the galaxy environment and seem to have played a significant role, in addition to the internal metabolism, in the galaxy evolution.
The Butcher-Oemler Effect in Nearby Clusters
Authors: Sharples R.M.
Published: July 2016

Probably the most striking evidence for galaxy evolution at recent epochs has been the discovery of a rapid change in the nature of galaxy populations in clusters over the redshift range z=0 to z=0.5. The ‘classical’ Butcher-Oemler effect (Butcher & Oemler 1978, 1984) used photomteric studies to reveal an unexpected increase in the fraction of blue galaxies in the cores of distant (z∼ 0.4) rich concentrated clusters when compared with nearby (z< 0.05) clusters of similarly high richness and central concentration. An alternative view, based on spectroscopic studies (Dressier & Gunn 1982; Couch & Sharpies 1987), manifests itself as an increase in the fraction of active galaxies which show signs of recent star formation and/or nuclear activity. Some of these galaxies are indeed blue but some (e.g. in C10016+16, Dressier & Gunn 1992) are red. Although it is the very absence of blue galaxies in nearby clusters which defines the classical Butcher-Oemler effect, comparable spectroscopic studies of nearby cluster populations with the appropriate completeness and high signal-to-noise required for population (as opposed to dynamical) studies have only recently been undertaken. In at least one case these have revealed unexpected similarities to the spectroscopic signatures which appear so prevalent at higher redshifts.
Measuring the Evolution of the M/L ratio from the Fundamental Plane in Cl 0024+16 atz=0.39
Authors: Franx Marijn , van Dokkum Pieter G.
Published: July 2016

The existence of the Fundamental Plane of early-type galaxies implies that theM/Lratios of early-types are well behaved. It provides therefore an important tool to measure the evolution of theM/Lratio with redshift. These measurements, in combination with measurements of the evolution of the luminosity function, can be used to constrain the mass evolution of galaxies.

We present the Fundamental Plane relation measured for galaxies in the rich cluster CL 0024+16 atz=0.391. The galaxies satisfy a tight Fundamental Plane, with relatively low scatter (15 %). TheM/Lis 31 ± 12 % lower than theM/Lmeasured in Coma, which is consistent with simple evolutionary models. Hence, galaxies with very similar dynamical properties existed at az=0.4.

More, and deeper data are needed to measure the evolution of the slope and the scatter of the Fundamental Plane to higher accuracy. Furthermore, data on the richest nearby clusters would be valuable to test the hypothesis that the Fundamental Plane is independent of cluster environment.
The Structure of Cold Dark Matter Halos
Authors: Navarro Julio F.
Published: July 2016

High resolution N-body simulations show that the density profiles of dark matter halos formed in the standard CDM cosmogony can be fit accurately by scaling a simple “universal” profile. Regardless of their mass, halos are nearly isothermal over a large range in radius, but significantly shallower than r–2 near the center and steeper than r–2 in the outer regions. The characteristic overdensity of a halo correlates strongly with halo mass in a manner consistent with the mass dependence of the epoch of halo formation. Matching the shape of the rotation curves of disk galaxies with this halo structure requires (i) disk mass-to-light ratios to increase systematically with luminosity, (ii) halo circular velocities to be systematically lower than the disk rotation speed, and (iii) that the masses of halos surrounding bright galaxies depend only weakly on galaxy luminosity. This offers an attractive explanation for the puzzling lack of correlation between luminosity and dynamics in observed samples of binary galaxies and of satellite companions of bright spiral galaxies, suggesting that the structure of dark matter halos surrounding bright spirals is similar to that of cold dark matter halos.
Mergers and the Formation of Disk Galaxies in Hierarchically Clustering Universes
Authors: Steinmetz M.
Published: July 2016

It is commonly accepted, that galaxies acquire their angular momentum from tidal torques due to surrounding matter (Hoyle 1949). Most of the angular momentum is gained during the linear phase of the collapse (White 1984). After the turnaround point is reached, any further gain of angular momentum is strongly suppressed because it is increasingly difficult for the tidal field to act on the shrinking radius of the forming dark halo.
Spectroscopic Evidences for Star Formation in Cooling Flow Galaxies
Authors: Cardiel N. , Gorgas J. , Aragon-Salamanca A.
Published: July 2016

X-ray observations have led to the conclusion that many galaxy clusters are hosting cooling flows. The brightest cluster galaxies could have accreted masses of the order of 1011–1012M⊙, but is still uncertain what the final fate of the accreted gas may be.
Photoionization Effects on Galaxy Formation
Authors: Chiba M. , Nath B.B.
Published: July 2016

We investigate the effects of the observed UV background radiation on galaxy formation. The biasing mechanism by photoionization is examined in detail, and its implication for galaxy number counts is discussed. Photoionization by UV radiation, J, decreases the cooling rate of the gas in halos, so that objects with only large density contrasts can self-shield against the radiation. In the context of the CDM model, we use the criterion that self-shielding is essential for star formation to calculate the mass function of galaxies (see Chiba & Nath 1994, ApJ, 436, 618 for details). We find that the cooling rate in the big (low-density) system, into which smaller objects are merged, is reduced by photoionization. This means that, in a merging dominated region, where the number density at the low-mass end (Mb ≤ 1010M⊙) is usually expected to decrease with time, the trend is reversed (the number of low-mass galaxies is more at lower redshifts z) due to the decreasing UV flux with time after z ∼ 2 (see Figure 1).
The Shapes and Ages of Elliptical Galaxies
Authors: de Jong Roelof S. , Davies Roger L.
Published: July 2016

Normally elliptical galaxies are thought to be old, evolved systems, but recently a controversy has arisen over the age of ellipticals. Measurements by Gonzáles (1993, Ph.D. thesis, UCSC) show that the Hβ absorption indices of ellipticals span a range of values. Population synthesis models indicate that the Hβ index is a good age indicator and hence, contrary to normal perception, the ages of ellipticals seem to span a range of values.
The DN − σ and Fundamental Plane Relations as Distance Indicators of Early Type Galaxies in the Virgo and Fornax Clusters
Authors: D'Onofrio M. , Zaggia S. , Capaccioli M. , Longo G. , Caon N.
Published: July 2016

We investigate the properties of early-type galaxies as distance indicators by applying the Dn – σ, Fundamental Plane (FP), and log(m) – log re relations to a complete and fairly homogeneous sample of galaxies members of the Virgo and Fornax clusters. The relative mean distance of the two clusters can be derived with an accuracy up to ∼ 3% provided that the internal kinematics of the galaxies is taken into account and a correct statistical approach is used.

The residuals of the Dn – σ and FP relationships do not correlate with many structural and geometrical parameters of the galaxies: the mean effective surface brightness, the total luminosity, the average ellipticity and the Fourier coefficient a4 of the isophotes, and, the exponent m of the r1/m law which parametrizes the shape of the light profiles. On the other hand, the kinematics of the galaxies affect both relations producing residuals that correlate with the maximum rotation velocity Vmax and the (V/σ) ratio.

Once confirmed by future more accurate observations, this effect would introduce a sistematic bias in the distance determination of the clusters; a problem difficult to manage if the internal kinematics of the cluster members is unknown.
Mapping the Galactic Center
Authors: Duschl W.J. , von Linden S. , Walter T. , Wittkowski M.
Published: July 2016

Gas and dust in the inner region of the Galaxy are distributed in a flat, disklike structure. We model the dynamics of this material in the framework of an accretion disk approach, and thus determine the efficiency of the radial transport of mass and angular momentum in the inner ∼ 200 pc of the Galactic Plane. Moreover, this allows us to establish the location (coordinates: galactic longitude l and depth normal to the celestial sphere) of molecular clouds from the observed positions (l) and radial velocities (currently, we neglect details of the vertical structure). Ultimately this will yield a map of the distribution of molecular clouds about Sgr A∗.
Evidence for a Sizable Age Spread among Galaxies from the UV Upturn Phenomenon in Early-Type Systems
Authors: Lee Young-Wook , Park Jang-Hyun
Published: July 2016

The suggestion of Lee (1994, ApJ, 430, L113) that the age spread among galaxies is responsible for the systematic variation of ultraviolet (UV) upturn among the early-type systems is confirmed here with the detailed population synthesis models. Our models suggest that the far-UV spectra of these systems are composite of hot metal-poor horizontal-branch (HB) stars (and their post-HB progeny) and metal-rich post-asymptotic giant-branch (PAGB) stars. The systematic variation of UV upturn, however, depends on the contribution from hot metal-poor HB stars and their progeny, which in turn depends on the ages of oldest stellar populations in galaxies. Consequently, our models predict that the strength of absorption features, such as C IV and Si IV, is anticorrelated with the strength of UV upturn. This is consistent with the far-UV spectra for NGC1399 and M31 obtained by the Hopkins Ultraviolet Telescope aboard the Astro-1 space shuttle mission. We note that the opposite trend is expected in other's models that favor metal-rich solution for the UV upturn phenomenon without age spread among galaxies. Our result implies a prolonged epoch of galaxy formation, in the sense that more massive galaxies (in denser environments) formed first. With the assumption that the UV upturn phenomenon is solely due to the age variations among galaxies, we tentatively estimate the difference in age between the giant ellipticals and our Galaxy to be 4 billion years or more. This suggests that the best estimate for the lower limit of the age of the Universe is close to 20 Gyrs, which of course would be in conflict with the current estimate of the Ho together with the standard cosmological models with zero cosmological constant. The reader is referred to Park & Lee (1995, ApJL, in press) for details of this work.