bluuebunny/crossref_metadata_2025 huggingface dataset:
70 Years of observations of 4 Her: changes through three shell episodes
Authors: Koubský P. , Harmanec P. , Horn J. , Hubert A.-M , Hubert H. , Floquet M.
Published: July 2016

4 Her (HD 142926, HR 5938; V=5m.75, v.sini=300 km s-1) is a well known and rather frequently observed Be and shell star. It was recognized as a Be star by Heard (1939) and Mohler (1940). The estimates of its spectral type by different authors vary between B7 IV-V and B9e. Hubert (1971) reported remarkable spectral changes of 4 Her which occurred between 1953 and 1970. Harmanec et al. (1973) discovered periodic radial-velocity variations of the hydrogen shell lines with a period 46.023 days and suggested the object is a single-line spectroscopic binary. The system elements were later refined by Heard et al. (1975) to P=46.194 days, K=12 km s-1 and e=0.3. In a subsequent paper, Harmanec et al. (1976) studied the variations of emission and absorption components of the hydrogen lines and concluded that 4 Her is an interacting binary and that the observed eccentricity of the orbit is spurious, caused by the effects of circumstellar matter.
Profile variability of Hα in the B3e Herbig star HD 200775 as indication of matter infall and inhomogeneous stellar wind
Authors: Beskrovnaya N.G. , Pogodin M.A. , Scherbakov A.G. , Tarasov A.E.
Published: July 2016

Significant profile variability of Hα on the timescale of months is investigated on the basis of high-dispersion CCD spectra of the B3e Herbig star HD 200775. Variations in position and shape of the central absorption component are considered to indicate complex structure of circumstellar environment, containing infalling streams and inhomogeneous stellar wind.
Latitude dependent radiative wind model for Be stars: line profiles and intensity maps
Authors: Stee Ph. , de Araujo F.X.
Published: July 2016

We present theoretical line profiles and intensity maps from an axi-symmetric radiative wind model from a fast rotating Be star (Araújo & Freitas Pacheco, 1989; Araújo et al, 1993). The introduction of a viscosity parameter in the latitude dependent hydrodynamic code enables us to consider the effects of the viscous force in the azimuthal component of momentum equations. The line force is the same as Friend and Abbott (1986), but it is introduced a varying contribution of thin and thick lines from pole to equator by adopting latitude-dependent radiative parameters. The numerical calculation for parameters characteristic of early Be stars gives a density contrast between equator and pole of the order of 100. The total mass loss rates range from 10-8 to 10-7 solar mass per year. Furthermore, the “opening-angle” usually adopted in had-hoc models (Lamers and Waters, 1987; Waters et al., 1991) arises naturally as a result of our model. The velocity fields and density laws derived from the hydrodynamic equations have been used for solving the statistical equilibrium equations. By adopting the Sobolev approximation, we could easily obtain a good estimate of both electronic density and hydrogen level populations throughout the envelope (Stee and Araújo, 1994).
Time-Dependent Phenomena in OB Star Winds
Authors: Prinja Raman K.
Published: July 2016

Spectroscopic observations are discussed which indicate that the winds of luminous OB stars are highly structured in space and variable in time. Blueward migrating discrete optical depth enhancements in the absorption troughs of P Cygni profiles are the characteristic signatures of the evolving structure. Constraints on physical mechanisms are discussed, provided by the observed accelerations of the migrating features, the evidence for rotationally modulated variability, and the behaviour of the winds at very low velocities.
Towards 1 ms−1 RV Accuracy
Authors: Pepe F. , Mayor M. , Queloz D. , Udry S.
Published: July 2016

Since the discovery of 51 Peg by Mayor & Queloz (1995) about 50 extra-solar planets have been discovered by means of the Doppler technique, and much more will follow. In future the goal will be to detect even lighter planets and/or planets with longer orbital periods, which may induce changes of only few m/s on the radial velocity of their parent star. Therefore very high performance instruments will be required. In view of the realization of HARPS (Pepe et al. 2000), the high-accuracy RV spectrograph for the ESO 3.6-m telescope dedicated to extra-solar planet search, we are investigating the accuracy limits and possible error sources. First results are presented in this paper.
Superflares and “Hot-Jupiters”
Authors: Rubenstein Eric P
Published: July 2016

Schaefer, King & Deliyannis (2000) reported the discovery of powerful stellar flares on single, solar-type stars. The outbursts on these F8-G8 stars were 102–107 times more powerful than the largest solar flares. The observed properties are similar to the magnetic reconnection driven events of RS CVn binaries. Rubenstein & Schaefer (2000) suggested that superflares may be magnetic reconnection events mediated by the interaction between the magnetospheres of a close-in jovian planet and the star. Stars exhibiting superflares may therefore harbor detectable planets.
A planetary companion to HD 190228
Authors: Sivan J.-P , Mayor M. , Naef D. , Queloz D. , Udry S. , Perrier-Bellet C. , Beuzit J.-L
Published: July 2016

We present our radial-velocity data for HD 190228. The measurements were obtained with the ELODIE echelle spectrograph mounted on the 1.93-m telescope at Observatoire de Haute-Provence. A 1100-day periodic low-amplitude radial-velocity signal is detected revealing the presence of a planetary companion with a minimum mass of 5 MJup.
Growth and interaction of planets
Authors: Artymowicz Pawel
Published: July 2016

We discuss theories of origin and evolution of the newly discovered extrasolar planetary systems. As these systems failed to fulfill prior expectations concerning their orbital structure, we are challenged to extend and/or revise many preexisting theories. Important extensions include migration of bodies in disks and planetary eccentricity pumping by planet-planet interaction and primordial disk-planet interaction. Progress in observational techniques will allow us to find which of these two types of interaction is responsible for the observed variety of orbits and masses of planets. New insights into the formation of giant planets in our system can be obtained by asking why Jupiter and Saturn are not larger, closer to the sun and/or do not follow noticeably elliptic orbits.
Giant planet formation — a theoretical timeline
Authors: Wuchterl Günther
Published: July 2016

Low mass circumstellar disks are a result of the star formation process. The growth of dust and solid planets in such pre-planetary disks determines many properties of our solar system. Models of the Solar System giant planets indicate an enrichment of heavy elements and imply heavy element cores. Detailed models therefore describe giant planet formation as a consequence of the formation of solid planets that have grown sufficiently large to permanently bind gas from the protoplanetary nebula. The diversity of Solar System and extrasolar giant planets is explained by variations in the core growth rates caused by a coupling of the dynamics of planetesimals and the contraction of the massive envelopes they dive into, as well as by changes in the hydrodynamical accretion behavior of the envelopes resulting from differences in nebula density, temperature and orbital distance. Detailed formation models are able to determine observables as luminosities, radii and effective temperatures of young giant planets. Present observational techniques do now allow to probe star formation regions at ages covering all evolutionary stages of the giant planet formation process.
Orbital Evolution of Planetary Systems
Authors: Chatterjee Tapan K. , Magalinsky V. B.
Published: July 2016

It is significant that the orbits of the planets in the solar system are very nearly circular, except for Mercury and Pluto where, conceivably, due to their comparatively small sizes, the tidal forces have played a less active role. Most of the suspected planets orbiting pulsars have nearly circular orbits. These systems tend to have minimum energy and are subjected to tidal forces. We find that a planet circularizes its orbit, in an effort to attain orbital stability and the ground state. Details can be found in Magalinsky & Chatterjee, 1997, and Magalinsky and Chatterjee, 2000.
Molecular Observations of Comets: Constraints for Planetary System Formation
Authors: Crovisier Jacques , Biver Nicolas , Bockelée-Morvan Dominique , Colom Pierre , Despois Didier , Lis D. C. , Rauer Heike ,   the team for target-of-opportunity radio observations of comets
Published: July 2016

We review our knowledge of the composition of cometary volatiles in the light of recent observations of comets C/1996 B2 (Hyakutake) and C/1995 01 (Hale-Bopp) and examine how this could constrain models of planetary system formation.
Stability Mechanism of Planetary System of ν Andromedae
Authors: Kinoshita Hiroshi , Nakai Hiroshi
Published: July 2016

Three planets are detected around ν Andromedae. The stability of Upsilon Andromedae Planetary system is maintained by the co rotation of the pericenters of the two outer planets. If the pericenters of the two outer planets move independently, the planetary system becomes unstable. The corotation of the pericenters is explained by the secular perturbation theory. This corotation is not a secular resonance.
Formation of Protoplanet Systems
Authors: Kokubo Eiichiro , Ida Shigeru
Published: July 2016

We present the latest results of large scale (N = 10000, 0.5AU < a < 1.5AU) N-body simulations of planetary accretion. We confirm the oligarchic growth of protoplanets in the minimum-mass disk and a more massive disk models. Protoplanets with the predicted isolation mass are formed with orbital separation of about 10-15 Hill radius.
Minimum Mass of Brown Dwarfs
Authors: Nakamoto Taishi , Ogochi Koji
Published: July 2016

We investigate the minimum mass of brown dwarfs using radiation hydrodynamics simulations of collapsing filamentary clouds and analytical estimates. We found the minimum mass of brown dwarfs depends on the initial temperature of parent clouds and the nature of heating sources. The universal minimum mass of brown dwarfs, which is about 0.007M⊙, is given when the initial cloud temperature is 13.3 K. Our results are consistent with recent observations of low-mass objects in some star forming regions.
Planetesimal Formation by Gravitational Instability—The Goldreich-Ward Hypothesis Revisited
Authors: Youdin Andrew N. , Shu Frank H.
Published: July 2016

We consider the formation of planetesimals via gravitational instability. While minimum solar nebula (MSN) models are known to be gravitationally stable, we find that sufficiently metal enriched and/or colder discs can yield planetesimals by the Goldreich-Ward mechanism (GWM). This is because the shear between gas and solids, previously believed to render the GWM ineffective, can only stir a finite amount of solids.
High-excitation molecular lines from circumstellar disks
Authors: van Zadelhoff Gerd-Jan , van Dishoeck Ewine F. , Thi Wing-Fai , Blake Geoffrey A.
Published: July 2016

Observations of submillimeter lines of CO, HCO+, HCN and their isotopes from circumstellar disks around low-mass pre-main sequence stars can be used to set constraints on the temperature and density distributions in these disks. The lines considered here originate from levels with higher excitation temperatures and critical densities than studied before (CO 6–5, HCO+ and HCN 4–3), and are combined with interferometer data on lower excitation lines. We discuss the results for two disks, i.e., those around LkCa 15 and TW Hya. We find that the TW Hya disk has a warm surface layer and agrees well with a flaring disk geometry, while the LkCa 15 disk is cooler and can be described by either dust-settling in a flared disk or a flatter disk overall. The densities are well described by disk models in the literature.
What Photometric Space Telescopes Can Tell Us About Extrasolar Giant Planets
Authors: Seager S. , Hui Lam
Published: July 2016

Within the next few years three microsatellites with part-per-million photometric capability (MOST, MONS, COROT) will be launched. These space telescopes, which were designed for asteroseismology, as well as other proposed or planned space telescopes to detect Earth-like transiting planets (Kepler and Eddington), will be able to observe the reflected light curves of the close-in extrasolar giant planets (CEGPs). The CEGPs are 0.05 AU from their parent star and are potentially bright in reflected light. For a transiting planet (at any orbital distance) moons and planetary rings may be detected.
The Core-Jet Radio Source in the Center of M81
Authors: Bartel Norbert , Bietenholz Michael F. , Rupen Michael P.
Published: July 2016

The spiral galaxy M81 hosts the closest extragalactic AGN besides that in Cen A that can be imaged with VLBI. Ground and Space-VLBI observations have shown that M81's center consists of a stationary core and a short, jittery, one-sided jet. The jet appears wavy, reminiscent of a helical structure. The central engine of M81 has qualitative similarities to those of powerful AGN of radio galaxies and quasars, and may represent a scaled-up version in power and size of the largely hidden nucleus of our own Galaxy.
Gas Kinematics from Spectroscopy with a Wide Slit: Detecting Nuclear Black Holes
Authors: Maciejewski Witold , Binney James
Published: July 2016

Motivated by STIS observations of more than 50 nearby galactic nuclei, we consider long-slit emission-line spectra when the slit is wider than the instrumental PSF, and the target has arbitrarily large velocity gradients. The finite width of the slit generates complex patterns in the spectra that can be misinterpreted as coming from various physically distinct nuclear components, but when interpreted correctly, they can have considerable diagnostic power. For a thin disk in circular motion around a central galactic black hole (BH), a characteristic artifact occurs in the spectrum at the outer edge of the BH's sphere of influence. It betrays the presence of a BH, and allows us to develop a new method for estimating its mass, which gives higher sensitivity to BH detection than traditional methods.
The Black Hole Mass vs Bulge Mass Relationship in Spiral Galaxies
Authors: Marconi Alessandro , Axon David , Atkinson John , Binney James , Capetti Alessandro , Carollo Marcella , Dressel Linda , Ford Holland , Gerssen Joris , Hughes Mark , Macchetto Duccio , Maciejewski Witold , Merrifield Michael , Scarlata Claudia , Sparks William , Stiavelli Massimo , Tsvetanov Zlatan , van der Marel Roeland
Published: July 2016

We describe an on-going HST program aimed at determining the relationship between the nuclear black hole mass and bulge mass in spiral galaxies. We have selected a volume limited sample of 54 nearby spiral galaxies for which we already have ground based emission line rotation curves, CCD surface photometry and radio maps. We are now obtaining HST/STIS longslit observations of each of the galaxies in the sample in order to determine the nuclear Hα rotation curve at high (∼ 0.1) spatial resolution. We will use these data to measure the unresolved dark mass concentration at the nucleus of each object. Here we show the first results from observations of objects in the sample.
The Nature of Flat-Spectrum Nuclear Radio Emission in Seyfert Galaxies
Authors: Mundell C. G. , Wilson A.S. , Ulvestad J.S. , Roy A. L.
Published: July 2016

Parsec-scale VLBA imaging of five Seyfert galaxies with flat-spectrum radio nuclei was conducted to determine whether the flat spectrum represents thermal emission from the accretion disk/obscuring torus or nonthermal, synchrotron self-absorbed emission. Four of the five show emission consistent with synchrotron self-absorption, with intrinsic sizes ∼0.05-0.2 pc (or 104 gravitational radii for a 108 M⊙ black hole for the smallest). In contrast, NGC 4388, which was detected with MERLIN but not the VLBA, shows thermal emission with similar properties to that detected in NGC 1068. It is notable that the two Seyfert galaxies with detected thermal nuclear radio emission both have large X-ray absorbing columns, suggesting that columns in excess of ∼1024 cm−2 are needed for such disks to be detectable.
Kiloparsec Jet Speeds in Classical Double Radio Sources
Authors: Arshakian Tigran G.
Published: July 2016

On the basis of an intrinsically symmetric relativistic jet model, analytical equations between the mean jet speed and the mean jet flux asymmetry, and between their variances are derived in the context of an orientation-based unification scheme. The mean jet speeds of classical double radio sources are estimated on kiloparsec scales by using the asymmetry of jet-counterjet flux densities taken from the 3CRR and B2 samples. For FRI radio sources the mean jet speed is ∼ (0.54 ± 0.03)c, while for FRII low-redshift radio galaxies and intermediate-redshift quasars the values found are ∼ (0.4 ± 0.06)c and ≳ 0.6c respectively.
Circumnuclear Dynamics in Mrk 273 and Mrk 231
Authors: Richards A. M. S. , Cohen R.J. , Cole G.H. , Holloway A.J. , Pedlar A. , Collett J.L. , Knapen J.H. , Yates J.A. , Field D. , Gray M.D. , Mundell C.G. , Wright M.M.
Published: July 2016

Markarian 273 and Markarian 231 are ultra-luminous IR galaxies which show signs of merger activity. Their radio continuum and spectral line emission has been imaged on scales of tens of parsec using MERLIN. Mrk 273 and Mrk 231 are classed as Seyfert types 2 and 1 respectively. The distribution and velocity gradients shown by OH masers and HI absorption are consistent with material in a rotating disk or ring, with the axis at greater than 45° to the line of sight in Mrk 273, and at less than 45° to the line of sight in Mrk 231. We estimate the amount of mass enclosed and infer its distribution from irregularities in the maser morphologies and comparison with HI and radio continuum data.
Massive Young Clusters in Nearby Galaxies
Authors: Maíz-Apellániz Jesus , Walborn Nolan R.
Published: July 2016

We study the size distribution of massive young clusters (MYCs) and of the cavities around them. We discuss the existence of two cluster populations and we find evidences for molecular cloud confinement in the early stages of development.
The Ejecta of Classical Novae
Authors: O'Brien T.J. , Davis R.J. , Bode M.F. , Eyres S. P. S. , Porter J.M.
Published: July 2016

Classical novae are interacting binary stars in which a thermonuclear runaway in material accreted onto a white dwarf from a companion red dwarf results in the ejection of around 10−4M⊙ at hundreds to thousands of kilometres per second. Recent Hubble Space Telescope and MERLIN imaging of the expanding ejecta from several classical novae are presented. In general the ejecta are clumpy but often display coherent structures, most notably equatorial rings of enhanced emission encircling prolate ellipsoidal shells. Physical mechanisms (including the common envelope phase and anisotropic irradiation of the shell) which may result in the generation of these structures are discussed.
VLA Detections of Stellar Winds Arising from the Galactic Center Arches Cluster
Authors: Lang Cornelia C. , Goss W.M. , Rodríguez L.F.
Published: July 2016

VLA detections have been made of 8 sources in the Galactic center Arches cluster. All sources have spectra consistent with those expected for stellar wind emission. Positional correspondence between these sources and near-infrared detections of mass-losing stars confirms that we are detecting stellar wind emission from Arches cluster members.
High Resolution Radio Continuum Observations of High Mass Star Formation Regions
Authors: Kurtz S. , Hofner P. , Vargas C. , Díaz-Merced W.
Published: July 2016

We present high angular resolution centimeter and millimeter continuum observations of several galactic massive star formation regions. Using calibration techniques pioneered at the Very Large Array, we are able to obtain high quality images even under adverse conditions of phase stability. Techniques such as these will be essential if future millimeter arrays are to obtain high quality and high precision images. We provide a current summary of our on-going survey, and present images and a brief discussion of several of the more intriguing sources.
Observations of Stars and Stellar Systems with the Navy Prototype Optical Interferometer
Authors: Pauls Thomas A.
Published: July 2016

We present results of observational programs with the Navy Prototype Optical Interferometer (NPOI) in astrometry, the study the angular diameters of individual stars, and the measurement of binary star systems. These observations include measurements of the closure phase, which allow us to make images of simple systems.
Warm Molecular Sphere around Red Supergiant Stars—A Missing Link between the Photosphere and Masering Water Clouds in the Circumstellar Envelope
Authors: Tsuji Takashi
Published: July 2016

Interferometry of red supergiants before 2000: The M2 supergiant Betelgeuse (α Ori) is the first star whose angular diameter was measured by the Michelson stellar interferometer (Michelson & Pease 1921). Since then, however, we had to wait half a century before we witnessed the renaissance of interferometric observations in optical astronomy with novel methods such as speckle interferometry (Laberie 1970). Michelson's classical method was also extended to the infrared regime (e.g. McCarthy et al. 1977). The initial results served not only to compare stellar temperature scale with the measured angular diameters but also to probe scattering and thermal emission in the dust envelope around red supergiant stars (e.g. Tsuji 1978,1979). Interferometry has been more active in the radio domain: In connection with our subject, VLBI observations revealed many masering water clouds around red supergiants such as VY CMa (Imai et al. 1997) and S Per (Richards et al. 1999), but their origin in unknown. Also, radio observation of Betelgeuse with the VLA (Lim et al. 1998) revealed the presence of a new component of modest temperatures (Tex ≲ 3500 K) over the same height range as the classical chromosphere (Tex ≳ 5000 K), but again the nature of the new component remains obscure.
SN1987A: Temporal Models
Authors: Wanas M. I. , Melek M. , Kahil M. E.
Published: July 2016

We construct two temporal models for SN1987A. The first model assumes spin independent trajectories for massless particles, while the second assumes spin dependent ones. The suggested scheme can be applied to any supernova event.
Prospects for High Angular Resolution at Low Frequencies
Authors: Jones Dayton L.
Published: July 2016

High angular resolution imaging at low frequencies (below ∼ 10 MHz) requires observations from above the ionosphere. A radio interferometer array in space will be able to open new vistas in solar, terrestrial, galactic, and extragalactic astrophysics. A space-based interferometer could image and track transient disturbances in the solar corona and interplanetary medium - a new capability which is crucial for understanding many aspects of solar-terrestrial interaction and space weather. It could also produce the first sensitive, high-angular-resolution radio surveys of the entire sky at low frequencies. The radio sky will look entirely different below 10-30 MHz because new emission and absorption processes become dominant at these frequencies. As a result, low frequency surveys from space will provide a fundamentally new view of the universe and an extraordinarily large and varied science return.
X-ray Interferometry
Authors: Cash Webster
Published: July 2016

X-rays have tremendous potential for imaging at the highest angular resulution. The high surface brightness of many x-ray sources will reveal angular scales heretofore thought unreachable. The short wavelengths make instrumentation compact and baselines short. We discuss how practical x-ray interferometers can be built for astronomy using existing technology. We describe the Maxim Pathfinder and Maxim missions which will achieve 100 and 0.1 micro-arcsecond imaging respectively. The science to be tackled with resolution of up to one million times that of HST will be outlined, with emphasis on eventually imaging the event horizon of a black hole.
Impulsively Triggered Binary Star Formation
Authors: Whitworth Anthony P.
Published: July 2016

We discuss the important roles which impulsive processes seem likely to play in the formation of binary star systems and higher multiples. On the basis of numerical simulations and theoretical considerations, we show (i) that when a dense layer is produced by a cloud/cloud (or clump/clump) collision, or a dense shell is swept up by an expanding nebula (HII Region, Stellar-Wind Bubble or Supernova Remnant), fragmentation leads to the formation of small-N subclusters of massive protostellar discs, including many wide binaries; (ii) that impulsive interactions between these protostellar discs are frequent and can lead to an hierarchical cascade, spawning new protostellar discs in closer binary systems, plus some escapers. This cascade is particularly effective if there is continuing infall replenishing the protostellar discs. The binaries formed have a wide range of separations and orbital eccentricities, and the Mass Function of the new protostars has an exponent ∼ −1.
Twin, Aligned Protoplanetary Disks around the Components of the Young Binary System L1551 IRS5
Authors: Torrelles Jose M. , Rodríguez Luis F. , Anglada Guillem
Published: July 2016

VLA 7 mm continuum observations carried out by Rodríguez et al. (1998) with 0.06″ resolution toward L1551 IRS5 have shown two resolved dust sources. Both sources are elongated with almost the same orientation, similar flux densities, and similar angular sizes, being interpreted by these authors as a system of twin, aligned protoplanetary disks of 10 AU radius around the components of a young binary of 50 AU separation. These protoplanetary disks, the smaller ones ever imaged at mm wavelengths, are about a factor of ten smaller than disks around isolated stars, but have enough mass to form solar systems similar to our own. The fact that the disks are aligned with each other argues in favor for long-lived planetary systems in this binary. We all look forward to the future development of interferometers such as the EVLA, SMA, and ALMA in order to characterize the physical conditions of these associated protoplanetary disks by detecting spatially resolved molecular line emission. With these upcoming interferometers it will be possible to make great strides forward in our knowledge of the star formation processes.
Observations of Protobinary Systems
Authors: Mundy Lee G. , Looney Leslie W. , Welch William J.
Published: July 2016

High resolution images at millimeter wavelengths are providing new insights into the formation of binary and multiple star systems. These wavelengths are particularly useful in studying the earliest stages of multiplicity because they trace the bulk material distribution in the circumstellar environment and can penetrate 1000's of magnitudes of visual extinction. Current millimeter wavelength observations are finding a high incidence of multiplicity among young systems and that multiplicity begins at birth, or before. While the statistics are poor, the types of systems found (independent envelope, common envelope, and common disk systems) follow theoretical ideas about binary and multiple star formation. Systems can be identified which exhibit the characteristics of prompt initial collapse, central fragmentation during collapse, and fragmentation in high angular momentum scenarios. Expansion of this work to more systems and to more detailed studies of the structure and kinematics of individual systems will provide valuable insights into the formation of multiple systems.
Spectroscopic Binaries in Young Open Clusters
Authors: Mermilliod Jean-Claude , García Beatriz
Published: July 2016

We have analysed the binarity and multiplicity characteristics of 120 O-type stars in 22 very young open clusters and found marked differences between the “rich” (N ≥ 6 O-type stars and primaries) and “poor” (N = 1) clusters. In the rich clusters, the binary frequencies vary between 14% (1 SB among 7 stars) and 80% (8 SBs among 10 stars). Multiple systems seem not to be frequent and stars are spread all over the cluster area. In poor clusters, the binary frequency of the O-type objects is nearly 100%, with orbital periods around 3 days. Several binaries are also eclipsing. Additional companions are always present. They form either hierarchical multiple stars or trapezium systems. These massive multiple systems are generally found close to the cluster center, although there are exceptions.
Optical and Near-Infrared Imaging of Young Binary Star Environments
Authors: Ménard François , Stapelfeldt Karl
Published: July 2016

We review recent imaging results on the circumstellar matter of young binaries obtained using the Hubble Space Telescope (HST) and by PUEO, a ground-based adaptive optics (AO) system operating at CFHT. In the area of circumbinary disks, new results for GG Tau help form a more complete picture of this prototype system. However, HST images of the UY Aur ring indicate a more complex system than first thought. A new example of a circumstellar disk in a multiple star system has been found in HV Tau, joining HK Tau in this category. Examples of envelopes, outflow cavities, and jets are shown for several young binaries. About half of the nearby young binaries in our survey possess some kind of local nebulosity at optical or near-IR wavelengths.
The Close Environment of Z CMa Binary System
Authors: Garcia Paulo J. V.
Published: July 2016

We present echelle spectroastrometric observations of the Z CMa system in the Hα region showing its feasibility and underlining the astrophysical importance of the information stored in the spatial width of the spectra.

The Hα profile dating from 12/1991 presents a “bullet” of blue-shifted emission superimposed on the broad absorption component. We interpret this material as an unresolved bullet of gas at the base of the jet. We show that the jet emission fills in the absorption component of the Hα profile and has a wide range of velocities.
K-band Extragalactic Background Light from Deep Galaxy Counts in the Subaru Deep Field
Authors: Totani T. , Yoshii Y. , Iwamuro F. , Maihara T. , Motohara K. , Terada H. , Gotou M. , Iwai J. , Tanabe H. , Taguchi T. , Hata T. , Oya S.
Published: July 2016

We report estimates for the extragalactic background light (EBL) in the K band (2.2 μm), obtained by the integration of galaxy counts down to K=25 mag in the Subaru Deep Field (SDF, 2′ x 2′). We have obtained deep galaxy count data by using the 8.2m Subaru telescope, with a total integration time of 10 hours and an average seeing of about 0.4 arcsec. The 5-sigma limiting magnitude is K=23.5, and 350 objects are detected brighter than this magnitude. There has been a significant discrepancy between previous K-count observations, probably because of the systematic uncertainties in the completeness correction. To overcome this problem, we have paid special attention to selection effects and completeness corrections, with realistic theoretical galaxy models taken into account consistently. The faint-end slope is significantly flatter than some earlier observations of K counts, and our results suggest that the bulk of the extragalactic light in this band has been resolved as discrete sources. We estimate the value of the EBL flux obtained from the integration of our counts as 9.8 ± 1.0 nWm−2 sr−1.
The Extragalactic Background at Ultraviolet, X-ray and Gamma Ray Energies
Authors: Bowyer Stuart
Published: July 2016

The extragalactic background at ultraviolet, X-ray and gamma ray energies is reviewed. Early work on the diffuse backgrounds in each of these bands was motivated, at least in part, by the idea that these fluxes were the result of processes which produced a truly diffuse flux with profound cosmological implications. As we will see, these processes were not observed. However, the study of this background has led to the discovery of unexpected processes at work in the Universe. Our current understanding of these backgrounds is presented.
TeV Gamma–Ray Absorption and the Intergalactic Infrared Background
Authors: Stecker F. W.
Published: July 2016

In this paper, I will take a synoptic approach to determining the intergalactic infrared radiation field (IIRF). This approach draws on both the multi-TeV γ-ray observations and the infrared background observations and relates them via the semi-empirical modelling method of Malkan & Stecker. I discuss the evidence for an intergalactic infrared background obtained by an analysis of the HEGRA observations of the high energy γ-ray spectrum of Mrk 501 and from constraints from Mrk 421 deduced from the Whipple air Cherenkov telescope results. I will show that this evidence is in accord with the predictions made by Malkan & Stecker (1998) for the intergalactic infrared spectral energy distribution produced by galaxies. The Malkan-Stecker predictions are also in excellent agreement with mid-infrared galaxy counts. However, there may be potential problems relating these predictions with the results of the analysis of COBE–DIRBE far infrared data. The γ-ray and COBE–DIRBE observations may also need to be reconciled. I will discuss possible ways to resolve this situation including a partial nullification of the γ-ray absorption process which can hypothetically occur if Lorentz invariance is broken.
The Sloan Digital Sky Survey
Authors: Hogg David W.
Published: July 2016

The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey of 104 deg2 in the North Galactic Cap, currently underway with the 2.5-m SDSS Telescope at the Apache Point Observatory in New Mexico. The data products will include u, g, r, i and z-band imaging of several 108 sources and R = 2000 spectra of 106 galaxies. The imaging will have 10-sigma limiting (AB) magnitudes of (u, g, r, i, z) = (21.4, 22.6, 22.3, 21.7, 20.1). The “Main” sample of 9 x 105 galaxies, selected to have r < 17.7 mag, will have spectra with signal-to-noise ratio on the order of ~ 10 per resolution element, and median redshift z ~ 0.1. There will also be a sample of 105 luminous elliptical galaxies, selected on the basis of apparent color and magnitude, which will extend out to redshift z ~ 0.4. The data will be released steadily over the next five years.

On the order of one percent of the eventual data volume has been assembled at the time of this meeting, with a few hundred square degrees of survey-quality 5-band imaging, and over 104 survey-quality spectra. In the refereed literature there are detailed descriptions of the survey design, goals and hardware (York et al 2000; Gunn et al. 1998) and first scientific results (e.g., Ivezic et al 2000; Fischer et al. 2000; Leggett et al. 2000; Yanny et al. 2000).

Relevant to measures of the extragalactic background emission, the survey has found many z > 4 quasars and has measured the evolution in their space density (e.g., Fan et al. 2000). Measures of bright galaxy counts, the local galaxy luminosity function, and the evolution of elliptical galaxies are in preparation.
Gravitational Lensing and Deep Infrared Surveys
Authors: Metcalfe Leo , Mcbreen B. , Kneib J.-P. , Altieri B.
Published: July 2016

ISO's infrared camera was used to make deep mid-infrared (MIR) images through three gravitationally lensing clusters of galaxies. Observations were made at 7 μm and 15 μm covering more than 50 square arcminutes, with the lensing increasing the sensitivity to background sources significantly.

A large number of MIR sources were detected behind the lenses and provide source counts, corrected for cluster contamination and lensing distortion effects, which exceed by a factor of 10 the expectation from local counts assuming a no-evolution model. The results are consistent with larger-area surveys and the detected population resolves a substantial fraction (of order 60%) of the background MIR radiation intensity into discrete sources.

We discuss the evidence, in large part derived from lensing cluster observations, for overlap of the ISO 15 μm faint galaxy population with the 850 μm submillimetre and the 0.5 to 7 keV X-ray populations. We find that the ISO data shows substantial overlap with both the submillimetre and the X-ray source populations, with roughly 25% of ISO sources being detected at submillimetre wavelengths and a significant number of Chandra X-ray sources being detected in the ISO data.
Cosmic Far-Infrared Background Fluctuations Revealed by the FIRBACK Observing Program
Authors: Lagache Guilaine , Puget Jean-Loup
Published: July 2016

We have used the Far-InfraRed BACKground (FIRBACK) field observations with ISOPHOT at 170 μm to search for the Cosmic Far-InfraRed Background (CFIRB) fluctuations. Our study is based on power spectra analyses which allow us to statistically separate each of the background components (Galactic and extragalactic). We show that the extragalactic background fluctuations in FIRBACK fields lie well above the instrumental noise and the cirrus confusion noise. The observed power spectra show a flattening at high spatial frequencies which is due to unresolved extragalactic sources. The level of the extragalactic power spectrum fluctuations is nearly the same in all FIRBACK fields. This is the first time that fluctuations due to unresolved extragalactic sources have been isolated at far-infrared wavelengths. In the two largest FIRBACK fields, the power spectra clearly reveal the presence of correlated extragalactic fluctuations, which we are currently analyzing. However, if 3σ detected sources are cleaned from the maps, the CFIRB fluctuations appear at this time to be compatible with a Poissonian distribution. We would need an independent cirrus template (like for the HI gas) to more incisively remove the Galactic contribution to see whether additional correlations are present.
The Source Populations Producing the Cosmic IR Background
Authors: Franceschini Alberto
Published: July 2016

Deep surveys performed with millimetric telescopes and with the Infrared Space Observatory have partly resolved the Cosmic IR Background (CIRB) into a population of IR sources characterized by extremely high rates of cosmological evolution (comparable to or higher than those observed for quasars). We report in this paper on early attempts to study these sources and to understand their physics. The IR multi-wavelength galaxy statistics can be explained by assuming, for the bulk of the IR population, spectra typical of starbursts, an indication that stellar more than quasar activity produces the IR emission by faint galaxies. From our fits to the observed optical-IR SEDs, the latter appear to mostly include massive galaxies hosting violent starbursts (SFR ~ 100 M⊙/yr). We interpret the strong redshift-evolution as an increase with z of the rate of interactions between galaxies (density evolution) and an increase of their IR luminosity due to the more abundant fuel available in the past (luminosity evolution). Our evolutionary scheme considers a bimodal star formation (SF) in galaxies, including long-lived quiescent SF, and enhanced SF taking place during transient events triggered by interactions and merging. The large energy content in the CIRB may possibly require a top-heavy stellar IMF associated with the starburst phase. The observed evolution of galaxy IR emissivity is so strong from z=0 to z ~ 1 that the CIRB spectral shape imposes a fast turnover to the evolution at z > 1: scenarios in which a relevant fraction of stellar formation occurs at very high-z (e.g., the bulk of stars in spheroids) are not supported by our analysis.
X-ray Astronomy and the IR Background
Authors: Mushotzky Richard
Published: July 2016

I review the recent Chandra results on the sources of the X-ray background and the X-ray properties of the SCUBA sources. We conclude that 10–20% of the IR background is produced by active galaxies and a similar fraction of the SCUBA sources harbor luminous AGN. Many of the Chandra sources are apparently luminous infrared galaxies themselves, but factors of 2–10 below the SCUBA limits. We summarize the X-ray evidence for metal production in groups and clusters and point out that these data require considerably more star formation than inferred from optical stellar data. The abundance ratios of Fe and Si indicate that much of the metals in groups and clusters was produced by massive stars, and the lack of evolution in Fe out to z ~ 0.5 argues for quite an early origin for the metals. This same process also seems to have injected considerable energy into the gas in groups and clusters, which may have dominated the mechanism of star formation and produced a metal-enriched intergalactic medium
Star Formation and Chemical Evolution of Lyman-Break Galaxies
Authors: Shu Chenggang
Published: July 2016

The number density and clustering properties of Lyman-break galaxies (LBGs) observed at redshift z ~ 3 are best explained by assuming that they are associated with the most massive haloes at z ~ 3 predicted in hierarchical models of structure formation. In this paper we study, under the same assumption, how star formation and chemical enrichment may have proceeded in the LBG population. A consistent model, in which the amount of cold gas available for star formation must be regulated, is suggested. It is found that gas cooling in dark haloes provides a natural regulation process. In this model, the star formation rate in an LBG host halo is roughly constant over about 1 Gyr. The predicted star formation rates and effective radii are consistent with observations. The metallicity of the gas associated with an LBG is roughly equal to the chemical yield, or about the order of 1Z⊙ for a Salpeter IMF. The contribution to the total metals of LBGs is roughly consistent with that obtained from the observed cosmic star formation history. The model predicts a marked radial metallicity gradient in a galaxy, with the gas in the outer region having much lower metallicity. As a result, the metallicities for the damped Lyman-alpha absorption systems expected from the LBG population are low. Since LBG halos are filled with hot gas in this model, their contributions to the soft X-ray background and to the UV ionization background are calculated and discussed.
Formation of Very Early Galaxies (z > 5)
Authors: Suran M. D. , Popescu N. A.
Published: July 2016

The electronic catalog of infrared and optical photometry in the Hubble Deep Field South (NICMOS) identifies galaxies at redshifts ranging from z near 0 through z greater than 10. In this paper we try to investigate the formation and evolution of different structures in the Universe, using cosmological N-body simulations. By means of 2563/5123-point, 5–25 Mpc simulations, we traced the relation among the evolution of first order filamentary web structures, galactic and cluster structures, and second order filamentary web structures. These simulations have been made in order to derive the environmental effects (first/second order collapse, heating/cooling mergers) in the early Universe (10 > z > 2), closely related to galactic and cluster evolution.
The Fm-Am Stars: Observed Anomalies
Authors: Cayrel R. , Burkhart C. , Van't Veer C.
Published: July 2016

The classical anomalies of Am-Fm stars are reviewed. Progresses already made, or expected to come, due to improvements in observations thanks to the new generation of telescopes and high S/N detectors as well as from theoretical advances are described. Current unsolved problems are identified.
The CNO-Cycle Elements in Atmospheres of B-Type Main Sequence Stars
Authors: Lyubimkov L.S.
Published: July 2016

The aim of this short review is to pay attention to some problems connected with the He, C and N abundances in atmospheres of B-type main sequence stars. These elements participate in CNO-cycle which is the principle source of energy in such stars. As known, the He, C and N abundances in stellar interiors are considerably changed owing to CNO-cycle (oxygen abundance alter insignificantly). There are some variations of the He, C and N abundances in stellar atmospheres, too, and our task is to discuss probable causes of such variations. It is necessary to emphasize that only normal B-type stars are considered (not He-rich or He-weak, for example).
Non-Magnetic Anomalous Stars: The Hg-Mn Stars — A Review of Elemental Abundances —
Authors: Takada-Hidai M.
Published: July 2016

Abundance analyses of HgMn stars in these 15 years are compiled to clarify the abundance characteristics. NLTE abundance studies relevant to HgMn stars are also surveyed for the period of these 20 years. Discussions are made on influences of uncertainties in the atmospheric parameters and of NLTE effects upon abundance determinations, and further on establishment of abundances.
Magnetic Ap Stars: Evolutionary Status and Abundance Anomalies
Authors: Ryabchikova T. A.
Published: July 2016

Some general properties and evolutionary status of magnetic Ap stars are briefly considered. Chemical abundance anomalies are discussed from the point of view of current theories presumably the radiative diffusion theory in the presence of magnetic field.
Successes and Challenges of the Theory of White Dwarf Spectral Evolution
Authors: Fontaine G. , Wesemael F.
Published: July 2016

Of all stars in the Hertzprung-Russell diagram, white dwarfs are those for which the clues on past evolution given by photospheric abundances are probably the hardest to decipher. This is because the cooling phase of white dwarfs, a relatively uneventful phase from an evolutionary point of view, is, in contrast, a most active phase for the evolution of the chemical composition of the envelope. Indeed, it is now well established that the often puzzling variety of surface abundances observed in white dwarf stars can be traced to the simultaneous operation, in the outer layers of these stars, of a variety of physical processes which will also erase the abundances present in the photosphere at the onset of cooling.

Downward element diffusion in the intense gravitational field of the degenerate star is perhaps the mechanism which is the most closely identified with white dwarf stars. However, convective mixing, ordinary diffusion, radiative forces, winds, and accretion from the interstellar medium all are equally important processes which, at times, compete efficiently with the rapid element segregation expected in those stars. The various regions, along the cooling sequence of white dwarfs, where individual processes are expected to operate, have been summarized by Fontaine and Wesemael (1987). We illustrate here various combinations of these mechanisms which have been found in white dwarfs, and show how their competition affects the observed abundance patterns. The unity underlying these cases stems from the fact that, in many cases, progress in investigating these complicated situations has come only through the combination of evolutionary calculations with new and powerful numeriques techniques which have been developed at Montréal (Pelletier 1986; Pelletier, Fontaine, and Wesemael 1989).
Stratification in White Dwarf Atmospheres
Authors: Koester Detlev
Published: July 2016

Although the availability of large telescopes and more sensitive detectors has led to a much more complicated picture of white dwarf spectral classes and abundance patterns as compared to the situation ten years ago, it still remains true that the vast majority of white dwarfs show a pure hydrogen spectrum even in temperature regions where the presence of other elements with e.g. solar abundances would be easily revealed.