bluuebunny/crossref_metadata_2025 huggingface dataset:
Supernovae at the Highest Angular Resolution
Authors: Van Dyk Schuyler D. , Weiler K.W. , Sramek R.A. , Panagia N. , Lacey C.K. , Montes M.J. , Marcaide J.M. , Lewin W. H. G. , Fox D.W. , Pooley D. , Filippenko A.V. , Peng C.Y.
Published: July 2016

The study of supernovae (SNe) and their environments in host galaxies at the highest possible angular resolution in a number of wavelength regimes is providing vital clues to the nature of their progenitor stars. We are observing SNe in the radio using the Very Large Array (VLA) and VLBI, in the X-rays with Chandra, and in the optical at the subarcsecond resolution of HST.
Supernovae and Molecular Clouds in Spiral Galaxies
Authors: Song Guo-Xuan
Published: July 2016

We report N-body simulations of the birthrate and distribution of supernovae in spiral galaxies. The simulations assume that stars form in GMCs with mass greater than 105M⊙ and that a Miller-Scalo IMF results. We assume that the resulting supernovae disrupt the GMC into smaller clouds; these clouds aggregrate to form new GMCs via inelastic collisions. Imposing a spiral potential, we find that supernovae form throughout the disk, but concentrated in the spiral arms. Using conditions appropriate for the Galaxy, a set of simulations with different initial random distributions of molecular clouds predicts 755τ5 supernova remnants (SNR) should exist in the Galaxy (where τ5 is the ratio of the lifetimes of SNRs to 105 yr). The predicted number of remnants and their spatial distribution can be compared to observations.
A Sub-arcsecond Study of Ionized Gas in NGC 253
Authors: Anantharamaiah K.R. , Mohan Niruj R. , Goss W.M.
Published: July 2016

The nuclear region of the starburst galaxy NGC 253 was observed in H92α (8.3 GHz) and H75α (15.4 GHz) recombination lines at sub-arcsecond resolution using the A-configuration of the Very Large Array (VLA). In the highest resolution observations at 15.3 GHz, we have detected a compact (< 5 pc), high density (> 5 × 104 cm−3) ionized region which is nearly coincident with the radio continuum peak near the nucleus. Modeling of RRL emission from this region shows that about 1000 O stars are needed to maintain the ionization. Assuming the Salpeter initial mass function, the implied overall stellar density corresponds to that of a super star cluster.
Recent Observations of PSR B1534+12
Authors: Stairs I.H. , Thorsett S.E. , Taylor J.H. , Arzoumanian Z.
Published: July 2016

We present the results of recent Arecibo observations of the relativistic double-neutron-star binary PSR B1534+12. The timing solution includes measurements of five post-Keplerian orbital parameters, whose values agree well with the predictions of general relativity. The observations show that the pulse profile is evolving secularly at both 1400 MHz and 430 MHz. This effect is similar to that seen in PSR B1913+16, and is almost certainly due to general relativistic precession of the pulsar's spin axis. We also present high-quality polarimetric profiles at both observing frequencies.
Near Infrared Interferometry with Large Telescopes
Authors: Paresce Francesco
Published: July 2016

First fringes with commissioning instruments and siderostats on both the Keck and VLTI facilities are expected for early 2001.
The Structure and Evolution of Dense Cores
Authors: Puller Gary A.
Published: July 2016

A small fraction of the mass of a molecular cloud is in dense, gravitationally bound structures many of which eventually form stars. This paper reviews some of the important properties of these dense cores. Ideas about the formation of these cores are summarised and recent observational results on the structure and evolution of cores reviewed.
Binarity in the Orion Trapezium Cluster
Authors: McCaughrean Mark J.
Published: July 2016

We summarise the results of recent optical and near-infrared imaging studies of the binary fraction among young low-mass stars in the dense Orion Trapezium Cluster. Over the separation range ∼ 30–500 AU and within the observational errors, there appears to be no excess of binary systems in the cluster relative to the main sequence field star population. Over the separation range ∼ 1000–5000 AU, the cluster is deficient in binaries relative to the field. Both results are in contrast to those found for the more distributed population of young stars in the Taurus-Auriga dark clouds, which is overabundant in binaries by roughly a factor of two. We briefly discuss possible origins for this difference and observational tests which may distinguish between them, and the implications these results have for our understanding of the typical environment where most young stars are born.
Twisted Jets from L1551 IRS5
Authors: Itoh Yoichi
Published: July 2016

We have carried out high-resolution near-infrared imaging observations of a protostar L1551 IRS 5 with the Subaru Telescope. The jet structure of IRS5 is resolved into two independent jets for the first time from the ground. Successive near-infrared spectroscopy has revealed that the jet emission is dominated by [Fe II] lines in the J and H-bands. While the visual-extinction reaches more than 20 mag in the close vicinity of IRS 5, it decreases rapidly at ∼1″ from IRS 5 and remains constant around 7 mag at larger distances. The twisted structure and bright emission knots are intrinsic to the jets, not due to a spatial variation of the extinction.
Young Binary Stars in Taurus-Auriga
Authors: White Russel J. , Ghez Andrea M.
Published: July 2016

We present the results of a high spatial resolution ultraviolet, optical and near-infrared survey of 44 young binary stars in Taurus-Auriga with separations of 10–1000 AU. The observations were carried out using the Hubble Space Telescope and NASA's IRTF. The binary star properties corroborate our previous work that suggests fragmentation is the dominant binary star formation mechanism. Of particular interest, we find that the components of binary systems are more coeval than randomly paired single T Tauri stars. Several important conclusions are drawn regarding the evolution of circumstellar material in binary systems. The mass accretion rates for primary stars are similar to single stars, which suggests that a companion as close as 10 AU has little effect on the mass accretion rate. These accretion rates, if constant, require replenishment of the inner circumstellar disks for at least the closest (≲ 100 AU) binary systems. On average, circumprimary disks appear to survive longer and accrete at a higher rate than circumsecondary disks do. This suggests that circumprimary disks are being preferentially replenished, possibly from a circumbinary reservoir with low angular momentum relative to the binary. The relative T Tauri types and the binary mass ratios tentatively suggest that systems with separations ≲ 200 AU share a common circumbinary reservoir. The higher mass accretion rates of primary stars relative to secondary stars is most likely due to their larger relative mass.
What Can Observations of Young Binaries Tell Us about Binary Formation?
Authors: Clarke Cathie J.
Published: July 2016

In this paper I discuss three areas in which observational data is likely to have a strong impact on theoretical ideas about binary star formation: the collation of binary statistics for different primary masses, the acquisition of spectral energy distributions for individual components within pre-main sequence binaries and the use of binary statistics to constrain the mix of star forming regions that must combine to form the field. Theoretical and observational work is ongoing in each of these areas. It is suggested that for observers an important future task is to remeasure the wide binary population among local field stars, whilst for theorists a problem yet to be addressed is how the mass of a molecular cloud core affects its binary fragmentation properties.
Impact of Magnetic Fields on Fragmentation
Authors: Boss Alan P.
Published: July 2016

Fragmentation is the leading explanation for the formation of binary and multiple stars. However, nearly all three dimensional calculations of the collapse and fragmentation of dense molecular cloud cores have ignored the effects of magnetic fields, whereas magnetic fields are generally regarded to be a dominant force in molecular clouds. Three dimensional models of the collapse of clouds with frozen-in magnetic fields have shown that such clouds cannot fragment for a range of initial conditions. However, calculations that allow for magnetic field loss by am-bipolar diffusion have shown that fragmentation is possible for initially prolate or oblate, rotating, magnetically-supported cloud cores. The latter calculations rely on approximations that should be verified by more detailed, traditional magnetohydrodynamical codes. The most obvious effect of magnetic fields is to delay the onset of the collapse phase, but once collapse begins in earnest, fragmentation proceeds in much the same manner as in nonmagnetic clouds, with initially prolate clouds tending to form binary protostars, and with initially oblate clouds tending to form multiple protostars.
The Intriguing PMS Eclipsing (Triple) System TY CrA
Authors: Vaz Luiz Paulo R.
Published: July 2016

The absolute dimensions of the eclipsing pair in the triple system TY CrA provide constraints on the evolutionary models for both main sequence and pre-main sequence phases.
The PMS Eclipsing Binary RXJ 0529.4+0041
Authors: Covino E. , Catalano S. , Frasca A. , Marilli E. , Alcalá J.M. , Fernández M. , Melo C. , Paladino R. , Stelzer B.
Published: July 2016

We report the discovery of the first low–mass pre–main sequence eclipsing binary among a sample of double-lined spectroscopic binaries in the Orion star forming region found in a previous high-resolution spectroscopic investigation on ROSAT–discovered weak-T Tauri stars. Here we present the preliminary results from the combined analysis of the spectroscopic orbit and B and V light–curves, using data available till spring 2000. We then compare the fundamental stellar parameters derived from the orbital solution with those inferred from some widely used theoretical evolutionary models.
Testing Pre-Main Sequence Models with Young Binaries
Authors: Palla Francesco
Published: July 2016

I will discuss several tests to gauge the accuracy of pre–main-sequence (PMS) models. Methods to determine the mass of young stars are overviewed, with emphasis on the information provided by double-lined, spectroscopic binary systems. A comparison of the dynamically determined masses with those estimated using the PMS models of Palla & Stahler (1999) is presented. Good agreement between empirical and theoretical masses is found. The analysis of the inferred ages from the isochrones shows a remarkable coevality within each binary system. A complete assessment of the accuracy of PMS tracks needs the identification of eclipsing systems of low-mass.
Fun for Two
Authors: Portegies Zwart Simon F. , Yungelson Lev R. , Nelemans Gijs
Published: July 2016

We performed populations synthesis calculations of single stars and binaries and show that binary evolution is extremely important for Galactic astronomy. We review several binary evolution models and conclude that they give quite different results. These differences can be understood from the assumptions related to how mass is transfered in the binary systems. Most important are 1) the fraction of mass that is accreted by the companion star during mass transfer, 2) the amount of specific angular momentum which is carried away with the mass that leaves the binary system.
Intracluster Dust and Far Infrared Emission
Authors: Popescu Cristina C. , Tuffs Richard J. , Fischera Jörg , Völk Heinrich
Published: July 2016

We make predictions for the diffuse far-infrared (FIR) emission from dust in the intracluster medium (ICM) of the Virgo cluster. The dust injection rate from known sources in the cluster is unlikely to give rise to a detectable diffuse FIR IC emission. However, the outer regions of dynamically young clusters have a further potential source of IC grains since they are still accreting freshly infalling spiral galaxies which are presumably contained in an accreting intergalactic medium (IGM). We show that cosmic ray driven winds from the infalling spirals can inject grains into a subvirial IGM that is external to the observed X-ray-emitting ICM. Predictions for the Virgo cluster are generalised to other clusters, and the possibility of detection of dynamically young clusters at cosmological distances is discussed. Although dominated by the discrete source emission from galactic disks, it is possible that diffuse submillimeter dust emission from the ICM could be detected in experiments similar to those designed to map the submillimeter excess due to the Sunyaev-Zeldovich effect in distant clusters. We further discuss the implications of our proposed scenario for the optical extinction in clusters, as well as for the properties and dust content of the IGM. Further implications for the environmental effects on the chemical evolution of spiral galaxies are also considered.
Star Forming Galaxies: Properties and Implications for the Extragalactic Infrared Background
Authors: Helou George
Published: July 2016

This paper reviews those properties of normal galaxies most relevant to the estimation of the extragalactic infrared background, in particular: (1) their infrared emission spectrum and its variation among galaxies; (2) their morphological properties, and their infrared size distribution in comparison to their apparent visible-light sizes; and (3) other properties such as the infrared-to-radio ratio and color-luminosity relations. Even a simple comparison of those properties to those of the extragalactic infrared background leads to constraints on the fluctuations in time and the secular evolutionary behavior of the infrared luminosity of galaxies.
The Nature of Ultraluminous Infrared Galaxies
Authors: Sturm Eckhard
Published: July 2016

The Infrared Space Observatory (ISO) has for the first time made possible mid- and far-infrared spectroscopic studies of nearby and moderate redshift, dusty ultraluminous infrared galaxies (ULIRGs). We discuss recent SWS, LWS, ISOPHOT-S and ISOCAM (CVF) results on ULIRGs, addressing the following topics: What powers ULIRGs? What is the AGN-starburst connection? How do ULIRGs evolve? What is the connection of the local ULIRG population to the recently discovered population of mid-IR to submillimeter sources?
The Near–Infrared κ-Space of Early and Late Type Galaxies
Authors: Pierini D. , Gavazzi G. , Franzetti P. , Scodeggio M. , Boselli A.
Published: July 2016

We present the near–infrared (H–band: λ = 1.65 μm) κ–space (κ1 ∝ log M, κ2 ∝ log Ie, κ3 ∝ log M/L) of high surface–brightness early and late type galaxies, based on a sample of 419 objects optically selected in regions of the A262, Cancer, and Virgo clusters and of the Coma Supercluster. We discuss the distribution of the pressure–supported and rotationally–supported systems within this space and the ensuing scaling relations. We analyze the link between galaxy structure and star formation history through a comparison of the loci occupied by galaxies of the Local Universe in both the near–infrared (this work) and optical κ–spaces. Our results support scenarios of galaxy formation and evolution with the following fundamental ingredients: collapsing proto–galactic systems are characterized by i) a bimodal distribution in mass and angular momentum; and by ii) a mass–dependent characteristic star formation time scale.
A Population of Distant Luminous Infrared Galaxies Revealed by 15 μm ISOCAM Deep Surveys
Authors: Cesarsky Catherine J.
Published: July 2016

The counts derived from the five mid-IR 15 μm (12–18μm LW3 band) ISOCAM Guaranteed Time Extragalactic Surveys performed in the regions of the Lockman Hole and Marano Field, the HDF-North and South (plus flanking fields), together with those of the lensing cluster A2390 at low fluxes and those of IRAS at high fluxes, cover four decades in flux from 50 μJy to ~0.3 Jy. The roughly 1000 sources detected with ISOCAM, 600 of which have a flux above the 80 % completeness limit, guarantee a very high statistical significance for the integral and differential source counts from 0.1 mJy up to ~5 mJy. The slope of the differential counts is very steep (α = −3.0) in the flux range 0.4-4 mJy, hence much above the Euclidean expectation of α = −2.5. When compared with no-evolution models based on IRAS, our counts show a factor ~ 10 excess at 400 μJy, and a fast convergence, with α = −1.6 at lower fluxes.

Multiwavelength studies of a subsample of the ISOCAM sources in HDF and CFRS fields indicate that they are intrinsically bright galaxies (Luminous Infrared Galaxies, LIRGs), with median redshift 0.7. These galaxies, despite their low surface density, are responsible for a large part of star formation at z < 1 and contribute substantially to the cosmic infrared background at 140 μm.
New Wide Field J- and K-band Galaxy Counts and the Extragalactic Background
Authors: Väisänen P. , Tollestrup E. V. , Willner S. P. , Cohen Martin
Published: July 2016

We present new medium-deep wide field galaxy counts at J- and K-bands, performed in the ELAIS fields. The source detection limits are at J = 19.5 and K = 18.0 magnitudes. The sky coverage is 1 degree2, making our survey the largest to date at these wavelengths and magnitudes. Counts in this brightness range are critical for normalization of models when explaining the deepest galaxy counts. In our survey fields we find evidence for a higher than expected local galaxy density. If normalized to our counts, galaxy models do not need strong brightness evolution or exotic populations to be explained even at the faintest levels. We measure clearly sub-Euclidean slopes of d log N(m)/dm ~ 0.45 to 0.50 at 13 < K < 17.5 and 14.5 < J < 19. Normal, passively evolving stellar populations along with a high normalization of the local luminosity function and an open cosmological model best fit both the slope and amplitude of our number counts. We report a preliminary value, ~ 30 n Wm−2sr−1, for the K-band extragalactic background light using zodi-subtracted DIRBE-data and our observed star counts. The value is consistent with, e.g., Matsumoto (these Proceedings 2001) and Gorjian, V., Wright, E. L., & Chary, R. R. 2000, ApJ, 536, 550, but is considerably higher than extrapolations from faint galaxy counts.
ISOPHOT Surveys and the Extragalactic Background
Authors: Lemke D. , Ábrahám P. , Haas M. , Héraudeau P. , Hotzel S. , Kiss C. , Klaas U. , Krause O. , Leinert C. , Meisenheimer K. , Stickel M. , Tóth L. V. , Juvela M. , Mattila K. , Chini R. , Müller S. A. H. , Linden-Vørnle M. J. D. , Nørgaard-Nielsen H. U.
Published: July 2016

The higher spatial resolution and sensitivity of ISO allowed several extragalactic surveys to be extended to greater depth than obtained with IRAS. With the extended wavelength range deep surveys were performed for the first time at wavelengths up to ~ 200 μm. They favour galaxy models with strong evolution. With ISO's new capabilities the spectral energy distributions of larger samples of ULIRGs in the local universe and those of quasars and radio galaxies were determined. These data are applicable as templates to the more distant universe. Foreground components from zodiacal light and cirrus to the intracluster dust emission were studied in connection with their separation from the extragalactic background radiation.
Galaxy Evolution in the Infrared: Number Counts and Cosmic Infrared Background
Authors: Takeuchi T. T. , Hirashita H. , Ishii T. T. , Yoshikawa K.
Published: July 2016

Recently reported infrared galaxy number counts and cosmic infrared background (CIRB) measures all suggest that galaxies have experienced a strong evolutionary phase. We statistically estimated the galaxy evolution history from these data. We treated the evolution of galaxy luminosity as a stepwise nonparametric form, in order to explore the most suitable evolutionary history which satisfies the constraint from the CIRB. We found that an order of magnitude increase of the far infrared luminosity at redshift z = 0.75 - 1.0 was necessary to reproduce the very high CIRB intensity at ~ 150 μm reported by Hauser et al. (1998). We note that too large an evolutionary factor at high z overpredicts the CIRB intensity around 1 mm. The evolutionary history also satisfies the constraints from galaxy number counts obtained by IRAS, ISO and SCUBA. The rapid evolution of the IR luminosity density required from the CIRB well reproduces the very steep slope of galaxy number counts obtained by ISO. Based on this result and the evolution of optical luminosity density, we quantitatively discuss the contribution of starburst galaxies. In addition, we present the performance of the Japanese IRIS galaxy survey.
The Role of Dust in Producing the Cosmic Infrared Background
Authors: Dwek Eli
Published: July 2016

The extragalactic background light (EBL), exclusive of the cosmic microwave background, consists of the cumulative radiative output from all energy sources in the universe since the epoch of recombination. Most of this energy is released at ultraviolet and optical wavelengths. However, observations show that a significant fraction of the EBL falls in the 10 to 1000 μm wavelength regime. This provides conclusive evidence that we live in a dusty universe, since only dust can efficiently absorbs a significant fraction of the background energy and reemit it at infrared wavelengths. The general role of dust in forming the cosmic infrared background (CIB) is therefore obvious. However, its role in determining the exact spectral shape of the CIB is quite complex. The CIB spectrum depends on the microscopic physical properties of the dust, its composition, abundance, and spatial distribution relative to the emitting sources, and its response to evolutionary processes that can modify all the factors listed above. This paper will present a brief summary of the many ways dust affects the intensity and spectral shape of the cosmic infrared background. In an Appendix we present new limits on the mid-infrared intensity of the CIB using TeV γ-ray observations of Mrk 501.
Global Evolution Models and the Extragalactic Background Light
Authors: Fall S. Michael
Published: July 2016

This article outlines a method to interpret the extragalactic background light in terms of the large-scale, average properties of galaxies, including the comoving densities of stars and interstellar gas, metals, and dust. These quantities are related by a series of coupled conservation-type equations analogous to the equations of galactic chemical evolution. This approach enables us to combine observations of the emission and absorption in galaxies and thus to relate their average stellar and interstellar contents. Applications of the method include predictions of the global history of star formation from absorption-line observations and corrections to the cosmic UV emissivity for absorption by dust.
Studies of the Cosmic Infrared Background with the Space Infrared Telescope Facility (SIRTF)
Authors: Werner M. W. , Reach William T. , Rieke M.
Published: July 2016

IRAS, COBE, and ISO have demonstrated the unique importance of a cryogenic infrared telescope in space for studying diffuse infrared backgrounds and for teasing out the individual point sources which contribute to them. This importance results from the extremely high infrared sensitivity of such telescopes, particularly to diffuse radiation. The next cryogenic infrared telescope will be NASA's Space Infrared Telescope Facility (SIRTF), which is currently in the final stages of construction leading to launch in 2002. SIRTF will be the first infrared space observatory to make extensive use - both for imaging and spectroscopy - of large format infrared detector arrays. The sensitivity and spatial and spectral coverage of SIRTF's array-based instruments endow SIRTF with great power for the study of the cosmic infrared background (CIRB) and related scientific issues. This paper reviews the SIRTF mission design and measurement functionality and describes SIRTF's potential studies of the CIRB, drawing examples from the programs planned by the SIRTF Guaranteed Time Observers (GTO's). We also summarize the opportunities for community participation in SIRTF.
Limitations of Stellar Abundance Determinations
Authors: Baschek B.
Published: July 2016

The information content of (photospheric) stellar spectra and the accuracy of abundance determinations are discussed. Besides the physical properties of the line spectra, the spectral resolution, the signal-to-noise ratio, but also the incompleteness of the knowledge of the contributing blends limit the abundance information. For a perfect model atmosphere the main factors determining the accuracy of the abundances are S/N, the line saturation, and the location of the continuum (or, in a synthetic spectrum, the background of numerous lines). In addition systematic errors introduced by missing atomic data and an imperfect model atmosphere (non-LTE, line blanketing, hydrodynamics) are important. The typical accuracy of abundance determinations is discussed for main sequence stars for which the most reliable data are available, and for a few selected other stellar types.
Intermediate He Rich Stars
Authors: Hunger K. , Groote D. , Heber U.
Published: July 2016

Intermediate helium stars are defined by the number ratio of helium to hydrogen:Whereas at the helium rich end, there is a distinct gap between the intermediates and the extreme helium stars, the borderline between the intermediates and the normal B-stars appears less well defined. 24 stars are listed by Drilling and Hill (1986), with V < 11m. It can be anticipated that a major fraction has as yet escaped detection.
Chemical Abundances and Models of WR Stars and Blue Supergiants
Authors: Maeder André
Published: July 2016

Firstly, a brief account is given on the recent progresses in model assumptions, which influence the evolution of surface abundances in massive stars. A concise overview of this chemical evolution is presented.

We discuss in detail the surface chemistry of WN and WC stars, in particular, the effects of the initial metallicity Z and mass loss rates on the resulting abundances. The abundances in WN stars are not very sensitive to model assumptions and are mainly a test on nuclear cross sections. Conversely, the chemical abundances in WC stars are very much model dependent. Major differences in the composition of WC stars (and subtype distributions) are expected according to their initial metallicity. The various models proposed to explain the N/C enrichments in blue supergiants and the properties of the progenitor of SN 1987A are reviewed.
[Fe/H] Ratios in Population II Stars
Authors: Luck R. Earle
Published: July 2016

Abundances of Population II stars of the field and globular cluster systems are reviewed. Emphasis is placed on [Fe/H] ratios determined from analyses of moderate- and high-resolution spectroscopic data. The status of analyses of metal-deficient stars is examined from the viewpoint of number of analyses and number of stars, overall distribution of the [Fe/H] ratios, and systematics of the [Fe/H] ratios.
On Low Mass AGB Stars
Authors: Sackmann I.-Juliana , Boothroyd Arnold I.
Published: July 2016

Recent results on low mass AGB stars are presented. Observed amounts of AGB mass loss imply that thermal pulses will only be encountered for stars of initial mass less than about 4M⊙ for Pop I and 3 M⊙ for Pop II. Mc – L, Me – τif, and Mc – Tb relations are summarized. Carbon dredge-up has been found in low mass stars of both Pop I and Pop II; the mixing length parameter α is crucial to dredge-up, and its value must be normalized according to each author's opacities and mixing length treatment (e.g., via the Sun's Te and L). The “carbon star mystery” is nearing a solution, but a new “s-process mystery” has appeared: only in a narrow range of mass and metallicity have theoretical models been found that encounter the semiconvective 13C s-process mechanism.
Technetium in Stellar Atmospheres
Authors: Kipper Tônu
Published: July 2016

The quantitative determinations of technetium abundances are discussed. Up to now Tc abundances were found for nearly 30 stars which all are thermally pulsing AGB stars. The technetium abundance values for these AGB stars atmospheres, where it was found to be present, cluster around −1.0 ÷ 1.7. The fact that Tc is not omnipresent in the atmospheres of AGB stars, which are highly enriched in other heavy elements produced in s-process, is discussed.
Photospheric Abundances in Central Stars of Planetary Nebulae, and Evolutionary Implications
Authors: Mendez Roberto H.
Published: July 2016

The available information about spectral characteristics and photospheric abundances of 115 CSPN is presented. About 33% of CSPN in the sample are H-deficient. Many (but not all) H-deficient CSPN show extremely high C abundances. There is also some evidence of a variety of C abundances among H-rich CSPN. The available evidence suggests that most CSPN leaving the AGB with a H-rich photosphere will become DA white dwarfs. The “late He shell flash + fast wind” (born-again) mechanism may offer a satisfactory way of explaining some of the H-deficient CSPN. However, at least in some cases, the complete ejection of the H-rich stellar envelope, and exposure of He-burned matter at the remnant stellar surface, must happen already at the time of departure from the AGB.
Some Closing Thoughts
Authors: Van Horn H. M.
Published: July 2016

I am very pleased to be the final speaker at this conference, for it gives me the pleasant opportunity to do several special things.
Lensing Limits On the Cosmological Constant
Authors: Rix Hans-Walter
Published: July 2016

The statistics of gravitationally lensed quasars requires that λ < 0.7 at 90% confidence. This limit is weakly affected by the evolution of galaxies through merging. If E/S0 galaxies have much higher dust opacities at redshifts of 0.5-1.0 than they do locally, these limits can be evaded.
A Technical Memorandum On Core Radii In Lens Statistics
Authors: Kochanek Christopher S.
Published: July 2016

Quantitative estimates of lensing probabilities must be self-consistent. In particular, for asymptotically isothermal models: (1) using the (3/2)1/2 correction for the velocity dispersion overestimates the expected number of lenses by 150% and their average separations by 50%, thereby introducing large cosmological errors; (2) when a core radius is added to the SIS model, the velocity dispersion must be increased; and (3) cross sections and magnification bias cannot be separated when computing the lensing probability. When we self-consistently calculate the effects of finite core radii in flat cosmological models, we find that the cosmological limits are independent of the core radius.
The VLA Light Curves of 0957+561, 1979-1994
Authors: Haarsma D. B. , Hewitt J. N. , Burke B. F. , Lehár J.
Published: July 2016

The gravitational lens 0957+561 has been monitored by our group for 16 years, using the VLA at 5 GHz. Since our last report in 1992, both images have returned to their quiescent flux levels, and the A image has brightened again. We apply various analysis methods to the light curves, and obtain a preliminary estimate of τ = 455 ± 40 days for the time delay.
Photometric Monitoring Of The Lensed QSO 0957+561
Authors: Sinachopoulos D. , Burger M. , van Dessel E. , Geffert M. , Thibor M. , Colin J. , Ducourant Ch.
Published: July 2016

We present our first results of a photometric monitoring project of the twin quasar 0957+561. This project aims mainly at the improvement of the determination of the time delay ΔT(A,B) for this gravitational lens, since the “time delay controversy on QSO 0957+561 (is) not yet decided” (Pelt et al. 1994). In addition, the quite large field of the CCD used allows also a long-term astrometric and photometric study of stars and galaxies in the field within a radius of about 10 arcminutes around the lens.
Testing Cosmogonic Models With Gravitational Lensing
Authors: Wambsganss Joachim , Cen Renyue , Ostriker Jeremiah P. , Turner Edwin L.
Published: July 2016

Gravitational lensing provides a strict test of cosmogonic models. We use fully non-linear numerical propagation of light rays through a model universe with inhomogeneities derived from a particular cosmogonic model, i.e. three-dimensional lensing simulations, to study its lensing properties. As a first example we present results for the standard CDM scenario. The lensing test for this model predicts that we should have seen far more widely split quasar images than have been found.
Effects Of Large-Scale Structure Upon The Determination Of Ho From Time Delays
Authors: Surpi G.C. , Harari D.D. , Frieman J.A.
Published: July 2016

We have analyzed the effects of both large-scale inhomogeneities in the mass distribution and cosmological gravitational waves upon the time delay between two images in a gravitational lens system. We have shown that their leading order effect, which could potentially bias the determination of the Hubble parameter, is indistinguishable from a change in the relative angle between the source and the lens axis. Since the absolute angular position of the source is not directly measurable, nor does it enter the relationship between the Hubble parameter and the lens observables, the determination of Ho from gravitational lens time delays follows in the usual way, as if the metric perturbations were absent.
Influence of Gravitational Lensing on Estimates of Ω in Neutral Hydrogen
Authors: Bartelmann Matthias , Loeb Abraham
Published: July 2016

A wealth of observational data supports the commonly held view that damped Lyman-α (Lyα) absorption in QSO spectra is associated with neutral-hydrogen (HI) disks in spiral galaxies. Most of the HI probed by QSO absorption lines is traced by damped Lyα lines because of their high column densities, N > 1020 cm–2. The spiral galaxies hosting the HI disks can act as gravitational lenses on the QSOs. If the HI column density increases towards the center of the disks, as suggested by observations of local galaxies, the magnification bias preferentially selects for high column-density systems. The estimates of HI in damped Lyα systems can then systematically be distorted by gravitational lensing.
Gravitational Lenses And Damped Ly-α Systems
Authors: Smette A. , Claeskens J.-F. , Surdej J.
Published: July 2016

We study the influence of gravitational lensing on determinationing the number density and column density distributions of damped Ly-α systems.
A Common High-Column Density Ly-α Line In The Spectra Of Q 1429–008 A & B
Authors: Smette A. , Williger G.M. , Robertson J.G. , Shaver P.A.
Published: July 2016

We observed a common high-column density Ly-α absorption line in the spectra of both Q 1429–008 A & B, but with different equivalent widths.
Weak Lensing By The Cluster MS0302+1658
Authors: Fisher David , Kuijken Konrad , Franx Marijn
Published: July 2016

We present preliminary results of a weak lensing investigation of the z = 0.43 cluster MS0302+1658.
Reconstruction Of Cluster Mass Distributions: Application And Results For CL0939+4713
Authors: Seitz Carolin
Published: July 2016

We show the reconstructed mass distribution of the cluster CL0939+4713 (zd = 0.4) using data obtained with the WFPC2 instrument on HST. We find a remarkable correlation with the light distribution of the bright galaxies, which are probably cluster member galaxies. A bootstrapping analysis confirms this correlation, whereas an anti-correlation between the mass distribution and the faint galaxies - used for the mass reconstruction - is found. We give lower bounds on the mass inside the data field, and confirm that this cluster is indeed quite massive.
The Massive Dark Corona Of Our Galaxy
Authors: Freeman K.C.
Published: July 2016

From their rotation curves, most spiral galaxies appear to have massive dark coronas. The inferred masses of these dark coronas are typically 5 to 10 times the mass of the underlying stellar component. I will review the evidence that our Galaxy also has a dark corona. Our position in the galactic disk makes it difficult to measure the galactic rotation curve beyond about 20 kpc from the galactic center. However it does allow several other indicators of the total galactic mass out to very large distances. It seems clear that the Galaxy does indeed have a massive dark corona. The data indicate that the enclosed mass within radius R increases like M(R) ≈ R(kpc) × 1010M⊙, out to a radius of more than 100 kpc. The total galactic mass is at least 12 × 1011M⊙.
Weak Lensing By Individual Galaxies
Authors: Brainerd Tereasa G. , Blandford Roger D. , Smail Ian
Published: July 2016

In this paper we report on an investigation of statistical weak gravitational lensing of cosmologically distant faint galaxies by foreground galaxies. The signal we seek is a distortion of the images of faint galaxies resulting in a weakly preferred tangential alignment of faint galaxies around brighter galaxies. That is, if the faint galaxies have been gravitationally lensed by the brighter systems, the major axes of their images will tend to lie perpendicular to the radius vectors joining the centroids of the faint and bright galaxies (Fig. 1). Modeling a lens galaxy as a singular isothermal sphere with circular velocity Vc, an ellipticity of ∼ 2πVc2 /c2θ is induced in the image of a source galaxy at an angular separation θ from the lens. This is of order a few percent for faint–bright galaxy pairs with separations θ ∼ 30″ where the lens is a typical bright spiral. Over 1000 pairs must be measured in order to detect such a signal in the presence of the noise associated with the intrinsic galaxy shapes. Given a sufficiently large number of pairs, it may be possible to use the variation of the induced ellipticity with θ to study the angular extent of the halos of the lens galaxies.
A Lens Model For B0218+357
Authors: Nair S.
Published: July 2016

The smallest radio Einstein Ring, B2018+357, discovered by Patnaik et al. (1993), shows much promise as a tool to constrain the parameters of cosmological models (Refsdal 1964). Dominating this system is a pair of 0.″335–separation compact radio images, with image A between 2.7 to 3.9 times as strong as image B (λλ 18 to 2 cm). Observations have established the lens redshift (zl = 0.685, O'Dea et al. 1992, Browne et al. 1993), a possible source redshift (zs = 0.96, Lawrence, this conference), and a tentative value for the time–delay between the highly polarized images A and B (12 ± 3 days, Browne, this conference). Recent mas–resolution observations have made it possible to understand the imaging of A and B in sufficient detail as to provide constraints on an elliptical lens model for B0218+357; this work presents a model and provides an estimate of Hubble's Constant.
The Contribution Of Binaries To The Observed Galactic Microlensing Events
Authors: Dominik M. , Hirshfeld A. C.
Published: July 2016

Most of the detected galactic microlensing events are commonly explained as due to microlensing of a pointlike source by a pointlike lens. We have found statistical methods to determine the goodness-of-fit for a specific model of source and lens beyond the assumption that the errors are normal, which does not always hold. In particular, we argue that at least one weak binary lensing event has already been detected (MACHO LMC#1) and thereby confirm our former hypothesis (Dominik & Hirshfeld 1994). We also find that this fit is not unique. We emphasize that knowledge of the fraction of binaries among the observed microlensing events is crucial for estimating the mass distribution of the observed dark objects.
Chromatic and Spectroscopic Signatures Of Microlensing Events
Authors: Valls-Gabaud David
Published: July 2016

We predict that chromatic and spectroscopic effects are likely to appear for a significant fraction of microlensing events. Differential amplification across a stellar disc produces a time and wavelength dependent signature which constrains the parameters of the lenses and can be used for 3-D mapping of stellar atmospheres.
Microlensing in the lensed quasar UM 425?
Authors: Courbin F. , Sahu K. C. , Meylan G.
Published: July 2016

During the ESO key-program on gravitational lenses, the light curves of two images (A and B) of the lensed quasar UM 425 were obtained (from 1987 to 1995). This poster presents a possible interpretation of the light curves in terms of a micro-lensing event in the faint B component of the system, without ruling out a possible intrinsic variation of the source.
Results From Five Years Of Monitoring Of The Einstein Cross With NOT
Authors: Østensen R. , Refsdal S. , Stabell R. , Teuber J.
Published: July 2016

After some preliminary observations in 1990, a program was started in 1991 at the Nordic Optical Telescope (NOT) on the island of La Palma for monitoring mainly four well known gravitational lens systems: QSO0142-100, QSO0957+561, QS01413+117 and QSO2237+0305 (The Einstein Cross). Here we report results from the monitoring of the Einstein Cross. During the four year period the Monitor Program was active (1990-1993) we gathered 55 high quality observations of this well known lens system. In addition we have collected 32 more observations in 1994 and a further four so far in 1995, a total of 91 new observations of the Einstein Cross.

Here we report results from the monitoring of the Einstein Cross. During the four year period the Monitor Program was active (1990–1993) we gathered 55 high quality observations of this well known lens system. In addition we have collected 32 more observations in 1994 and a further four so far in 1995, a total of 91 new observations of the Einstein Cross.
The Clover Leaf Quasar H1413+117: New Photometric Light Curves
Authors: Remy M. , Gosset E. , Hutsemékers D. , Revenaz B. , Surdej J.
Published: July 2016

Direct CCD images of the gravitationally lensed BAL quasar H1413+117 (Bessel B, V, R, I; Gunn r and i), obtained during 1989-1994 in the framework of photometric monitorings at ESO and with the NOT, have been carefully (re-)analyzed. Simultaneous fitting of 4 PSFs, fixing the relative positions of components B, C and D with respect to A, has been achieved successfully. The relative light curves of the 4 lensed QSO images, with respect to a stable nearby comparison star, confirm the general trend already presented by Arnould et al. (1993). The amplitude of the light curves is found to be about 0.5 magnitude, peak-to-peak in the V filter. The four lensed components display brightness variations quasi-simultaneously and in parallel. In addition to these intrinsic light variations due to the source, we find that component D shows extra light variations with respect to the other components. These are very likely caused by micro-lensing.
Simulation Of Microlensing Lightcurves By Combining Contouring And Rayshooting
Authors: Haugan Stein Vidar Hagfors
Published: July 2016

The contouring methods described by Lewis et al. (1993) and Witt (1993) are very efficient for obtaining the magnification of a point source moving along a straight track in the source plane. For finite sources, however, the amplification must be computed for numerous parallel tracks and then convolved with the source profile. Rayshooting, on the other hand, is an efficient algorithm for relatively large sources, but the computing time increases with the inverse of the source area for a given noise level.
New Caustic Phenomena In Double-Plane Lensing
Authors: Petters A. O. , Wicklin F. J.
Published: July 2016

Consider two point masses m1 and m2 on distinct planes with respective shears γ1, γ2 and continuous matter having densities κ1 and κ2. It is assumed that the lens equation is as follows:
where
Foreground Galaxies And The Variability Of Luminous Quasars
Authors: von Linde J. , Borgeest U. , Schramm J. , Refsdal S. , Van Drom E.
Published: July 2016

In order to look for an amplification bias (AB) by gravitational lensing caused by medium redshift (0.2≲ z ≲ 0.8) clusters or groups of galaxies, we compare galaxy counts in deep CCD images of highly luminous, high redshift QSOs with those in nearby control fields at a distance of 1 deg at the same galactic latitude. The total sample contains 37 objects up to now, from which one field had to be excluded because of a seeing difference between the QSO and control fields.
Quasar Microlensing By Cluster Dark Matter
Authors: Walker M. A. , Ireland P. M.
Published: July 2016

Following Paczyński's (1986) suggestion, many examples of gravitational lensing by Galactic objects have been recorded as a consequence of extensive photometric monitoring programs (e.g. Udalski et al. 1994). Now that such experiments have demonstrated the capability to discover microlensing events against large numbers of target sources, it behooves us to consider whether these techniques can be usefully applied elsewhere.
New “Einstein Cross” Gravitational Lens Candidates In HST WFPC2 Survey Images
Authors: Ratnatunga K.U. , Ostrander E.J. , Griffiths R.E. , Im M.
Published: July 2016

We report the serendipitous discovery of quadruple gravitational lens candidates using the Hubble Space Telescope. We have so far discovered two good examples of such lenses, each in the form of four faint blue images located in a symmetric configuration around a red elliptical galaxy. The high resolution of HST has facilitated the discovery of this optically selected sample of faint lenses with small (∼1″) separations between the (I∼ 25–27) lensed components and the much brighter (I∼ 19–22) lensing galaxies. The sample has been discovered in the routine processing of HST fields through the Medium Deep Survey pipeline, which fits simple galaxy models to broad band filter images of all objects detected in random survey fields using WFPC2.
Multi-epoch, Dual-Frequency VLBI Observations Of PKS 1830-211 From Japan
Authors: Hagiwara Yoshiaki , Fujisawa K. , Edwards P. , Hirabayashi H. , Murata Y. , Kobayashi H. , Iwata T.
Published: July 2016

PKS 1830-211 is a strong, flat-spectrum compact double source with a component spacing of 1 arcsecond. Observations of PKS 1830-211 were made with the Japanese domestic VLBI network at 2.3 GHz and 8.4 GHz bands in sessions between December 1991 and November 1994. The Usuda 64 m (ISAS) and Kashima 34 m (CRL) telescopes were used for all observations, and were used in conjunction with the Mizusawa 10 m (NAO) for observations in 1994. In addition, the total flux was measured with the Usuda 64 m at both bands. Data was recorded using K3 and K4 formatters and recorders, and correlated with NAOCO (the New Advanced One-unit COrrelator of the National Astronomical Observatory).
Optical Imaging Of B1422+231 – Prospects For Determining the Hubble Constant
Authors: Hjorth J. , Jaunsen A.O. , Patnaik A.R. , Kneib J.-P.
Published: July 2016

We report on observations indicating that the bright quadruple lens B1422+231 may be variable in the optical on a time scale of hours. We also find that a model can reproduce the optical positions and magnifications. Unfortunately, the system may be affected by possible microlensing and external shear. HST should provide a good model for the lens, the system should be monitored for several nights in superb seeing (0.3-0.4 arcsec FWHM), and the redshifts of the south-east galaxies should be determined. With this extra information, improved modeling will tell whether it is realistic to obtain H0 from the time delays of B1422+231.
Interstellar Scattering And The Einstein Ring PKS 1830-211
Authors: Jones D.L. , Preston R.A. , Murphy D.W. , Meier D.L. , Jauncey D.L. , Reynolds J.E. , Tzioumis A.K.
Published: July 2016

The remarkably strong radio gravitational lens PKS 1830-211 consists of a one arcsecond diameter Einstein ring with two bright compact components located on opposite sides of the ring. We have obtained 22 GHz VLBA data on this source to determine the intrinsic angular sizes of the compact components. Previous VLBI observations at lower frequencies indicate that the brightness temperatures of these components are significantly lower than 1010 K (Jauncey et al. 1991), less than is typical for compact synchrotron radio sources and less than is implied by flux density variations. A possible explanation is that interstellar scattering is broadening the apparent angular size of the source and thereby reducing the observed brightness temperature. Our VLBA data support this hypothesis.