bluuebunny/crossref_metadata_2025 huggingface dataset:
Period dependent variations of the shell spectrum of V923 AQL
Authors: Iliev Lubomir
Published: July 2016

V923 Aql is a well known Be star with strong shell spectrum. It was included in the list of shell stars of Merrill and Burwell (1949). A detailed study of the radial velocity variations in the spectrum of the star based on wide collection of spectral observations was presented in the work of Koubsky et al. (1988). In this work an orbital period of 214.756 days was suggested for the binary system consisting of a B5–7 primary and low mass (0.5 Msol).
Global disk oscillations: theoretical line profiles
Authors: Hummel W. , Hanuschik R.W.
Published: July 2016

Based on 3D radiative line transfer calculations we present Hα emission line profiles of Be star circumstellar envelopes undergoing one-armed global disk oscillations. The results are in agreement with the observed line profile variability.
Rapid line profile variability of Hα in two A0e Herbig stars of the P Cyg-subgroup and a model for their circumstellar envelope
Authors: Pogodin M.A.
Published: July 2016

The present report gives the results on the Hα line profile investigation of two the most well-known A0e Herbig stars of the so-called P Cyg -subgroup: AB Aur and HD 163296. 35 high-resolution CCD spectra (R ~ 50 000) of HD 163296 (ESO, CAT+CES, July 1991 and 1992) and 43 CCD spectra (R ~ 30 000) of AB Aur (Crimean Observatory, 2.6-meter telescope, January 1993) were obtained. A striking profile variability is discovered in both objects on the timescale from one our to a few days. The most dominant part of rapid variations (τ ~ hours) is the monotonous flux drift of different profile components. Positional shift of sharp spectral bumps, found in HD 163296 is probably connected with local inhomogeneities moving in the envelope. Shape variability of the absorption P Cyg -component of the Hα -line in AB Aur is suspected to be periodic with P = 35 or 70 hours. A model for a circumstellar envelope is proposed to explain the observed variability in this type of objects. It supposes the existence of an active non-stable region near the star, formed by equatorially concentrated stellar wind and an outer cool shell.
Circumstellar environment of the B[e] star MWC 349 (V 1478 Cyg)
Authors: Yudin R.V.
Published: July 2016

Quasi-simultaneous optical and IR photometric (BVRIJHK-bands) and optical polarimetric (RI-bands) observations were made at the 1m telescope of the Assy Observatory, Institute of Astrophysics of Kazakhstan between October 1985 and August 1992. We used the photopolarimeter of the Pulkovo Observatory described by Bergner et al. (1988). Most of our measurements were done with an aperture of 26″. We obtained 26 polarimetric measurements of MWC 349, mainly in the R band. Our data show significant variations in the polarization which has not been reported previously. The amplitude of the polarization parameters is: ΔP = 8% and ΔP.A. = 15°. During 12–13.09.90 five polarimetric observations have been obtained and ΔP = 3% on a time scale of 7 hours was detected. We found strong photometric variability in all photometric bands. There is however no correlation between brightness and polarization in any photometric band.
Energy distribution of Be stars
Authors: Kilambi Gopal C.
Published: July 2016

Be stars are defined to be non-supergiant early-type stars of spectral type B showing at times Balmer emission lines in their spectra. These stars often develop strong stellar winds considered to be variable in nature (Slettebak 1988) and have high rotational velocities compared to normal stars of similar spectral types. They also tend to show an excess amount of energy in the near- and far-infrared region compared to normal stars which is presumed to be due the surrounding material around the central star. Thus, the observed energy is a combination of that due to the stellar source and the surrounding material. Various attempts have been made to disentangle the stellar energy component from that of the circumstellar component in order to understand the nature, size and temperature of the envelope. These include:

a) Radius determination based on IR excess (Gehrz et al. 1974, Dachs and Hanuschik 1984; Waters et al. 1987),

b) Radius estimates from polarization and spectrophotometric data (Jones 1979),

c) Envelope dimensions derived from the width of shell absorption cores (Kogure 1969; Hirata and Kogure 1977),

d) Dachs et al. (1992) attempted to understand the physical properties, flow patterns and density distribution of the gas by a comparison of synthetic emission line profiles and empirical profiles measured for real Be stars.
Candidates of Be stars for GI2T interferometry
Authors: Hirata R.
Published: July 2016

Eighteen bright Be stars have been observed polarimetrically and line- photometrically for searching for candidates for a direct measurement of the envelope diameters of Be stars by GI2T. I found that o Cas and 28 Tau are suitable in addition to γ Cas.
Seven Be stars resolved by optical long-baseline interferometry
Authors: Quirrenbach A.
Published: July 2016

The recent progress in optical interferometry has made the direct study of the circumstellar matter around Be stars possible. The Hα emission region around γ Cas has been resolved with the I2T (Thom et al. 1986), GI2T (Mourard et al. 1989) and MkIII (Quirrenbach et al. 1993) instruments; the results support the basic picture of a rotating disk-shaped envelope (e.g. Poeckert and Marlborough 1978). Nearly spherical geometries can be ruled out. In this paper, first results from MkIII observations of a small sample of Be stars (see Table I) will be presented.
Two-dimensional hydrodynamical simulations of wind-compressed disks around rapidly rotating B-stars
Authors: Owocki S. P. , Cranmer S. R. , Blondin J. M.
Published: July 2016

We use a 2-D PPM code to simulate numerically the hydrodynamics of a radiation-driven stellar wind from a rapidly rotating Be-star. The results generally confirm predictions of the semi-analytic “Wind Compressed Disk” model recently proposed by Bjorkman and Cassinelli to explain the circumstellar disks inferred observationally to exist around such rapidly rotating stars. However, this numerical simulation is able to incorporate several important effects not accounted for in the simple model, including a dynamical treatment of the outward radiative driving and gas pressure, as well as a rotationally oblated stellar surface. This enables us to model quantitatively the compressed wind and shock that forms the equatorial disk. The simulation results thus do differ in several important details from the simple model, showing, for example, cases of inner disk inflow not possible in the heuristic approach of assuming a fixed outward velocity law. In addition, the disk opening typically has a half-angle of 2–4 degrees, somewhat larger than the ~ 0.5° predicted from the analytic model, and there is no evidence for the predicted detachment of the disk that arises in the fixed outflow picture.
International multiwavelength campaigns on short-term variability of OB stars: optical polarimetry
Authors: McDavid D.
Published: July 2016

From 1986 through 1992, wide-band optical (B or V filter) linear polarization measurements of eight Be stars and seven O stars were obtained simultaneously with ultraviolet observations from IUE and worldwide ground-based optical spectroscopy and photometry in a series of campaigns designed to study the short-term variability of these objects. Each campaign consisted of intensive monitoring of a few carefully chosen stars over a period of several days and nights, with the greatest possible continuity subject to the limitations of instrument scheduling, weather, and the longitudes of the observing sites.
Statistical Properties of Extrasolar Planets
Authors: Butler R. Paul , Marcy Geoffrey W. , Fischer Debra A. , Vogt Steven S. , Tinney C. G. , Jones Hugh R. A. , Penny Alan J. , Apps Kevin
Published: July 2016

The emerging statistical properties from the first 50 extrasolar planets are startlingly different from the picture that was imagined prior to 1995. About 0.75% of nearby solar type stars harbor jovian planets in 3 to 5 day circular orbits. Another ∽7% of stars have jupiter–mass companions orbiting in eccentric orbits within 3.5 AU. The mass distribution of substellar companions rises abruptly near 5 MJup and continues increasing down to the detection limit near 1 MJup-Orbital eccentricities correlate positively with semimajor axes, even for planets beyond the tidal circularization zone within 0.1 AU, distinguishing planets from binary stars. The planet bearing stars are metal–rich relative to both nearby stars and to the Sun. Analogs of Solar System planets have not been detected to date as they require precision of 3 m s−1 maintained for more than a decade.
Extrasolar Planet Transit Observations—Findings and Prospects
Authors: Brown Timothy M.
Published: July 2016

We now know of one extrasolar planet, HD 209458 b, that is seen to transit the disk of its parent star, and we may expect many others to be discovered in due course. These transiting planets will be important to our understanding of planets in general because they allow many kinds of measurements of the physical properties of the planet – measurements that are not possible for less fortuitous orbital alignments. These include, among others, estimates of the density, temperature, and composition of the planetary atmosphere. Moreover, transits provide a means of detecting planets that cannot yet be seen by other methods. In this paper I describe the progress that has been made so far in making some of these measurements, and the prospects for the future
HST Photometry of 47 Tucanae: Time Series Analysis and Search for Giant Planets
Authors: Brown Timothy M. , Charbonneau David , Gilliland Ronald L. , Albrow M.D. , Burrows A. , Cochran W. D. , Baliber N. , Edmonds P.D. , Frandsen S. , Bruntt S. , Guhathakurta P. , Choi P. , Lin D.N.C. , Vogt S.S. , Marcy G.W. , Mayor M. , Naef D. , Milone E. F. , Stagg C. R. , Williams M.D. , Sarajedini A. , Sigurdsson S. , VandenBerg D.A.
Published: July 2016

Gilliland et al. (2000) have reported HST photometric observations of 34000 stars in the globular cluster 47 Tuc, showing an absence of close-in giant planets in that cluster relative to their frequency in the solar neighborhood. Here we describe the methods of time-series analysis that were used to search the 47 Tuc data for transits by giant extrasolar planets, and the means by which these methods were validated.
First attempt in searching for HD209458b's exosphere
Authors: Moutou Claire , Coustenis Athena , Schneider Jean , Gilles Richard St , Mayor Michel , Queloz Didier , Kaufer Andreas
Published: July 2016

The transit of the planet orbiting HD209458 has been observed using VLT/UVES, in search for faint signatures of an extended envelope of gas possibly surrounding the planet, called exosphere. Preliminary results are shown and described. They show no evidence so far of exospheric signatures.
New extra-solar planets: the metallicity distribution revisited
Authors: Santos Nuno C. , Israelian Garik , Mayor Michel
Published: July 2016

We present the spectroscopy results of a new set of planetary host stars discovered in the context of the Geneva extra-solar planet search programme. The analysis was based on high S/N spectra obtained with the CORALIE spectrograph at the 1.2-m Euler Swiss Telescope (at La Silla, ESO). We revisit the metallicity distribution of stars with planets. The present sample, largely enriched by the inclusion of the most recent discoveries, strongly suggests that stars with planets are anomalously metal rich, but that the source of the metallicity excess is most probably “primordial”.
Formation of the Planetary Sequence in a Highly Flattened Disk of Frequently Colliding Planetesimals
Authors: Griv Evgeny , Gedalin Michael , Eichler David , Yuan Chi
Published: July 2016

The kinetic theory is used to study the evolution of the self-gravitating disk of planetesimals. The effects of frequent collisions between planetesimals are taken into account by using a Krook integral in the Boltzmann kinetic equation. It is shown that as a result of an aperiodic collision-dissipative instability of small gravity disturbances the disk is subdivided into numerous dense fragments. These can eventually condense into the planetary sequence.
Early evolution of the planetary system around PSR B1257+12
Authors: Gusev Alexander , Kitiashvili Irina
Published: July 2016

For the plane motion we are completely analyzing the differential equations systems of gravitational capture of the exoplanet at the resonance rotation with action of gravitational and tidal torques by qualitative analysis and bifurcation theory of dynamical systems (DS). The separation of 3-dimensional parameter space of dynamical system by bifurcation surfaces is obtained. The gallery of more than thirty phase portraits of gravitational capture extends the known scenario of cosmogonical evolution of the exoplanet on the early time, when the tidal interaction is very important.
Extra-solar planets: from direct rotation into reverse rotation
Authors: Kitiashvili Irina , Gusev Alexander
Published: July 2016

We investigate the equation describing the evolution of the kinetic momentum vector for the case of non-resonance rotation of dynamically symmetrical planets by action of gravitational and magnetic interaction with the central star. The obtained gallery of more twenty phase portraits of kinetic momentum evolution illustrates the various regimes of the planetary systems evolution. The analyses of obtained portraits has shown that a direct rotation of the planet may be passed into reverse rotation and vice versa for a rather broad range of the parameters.
Statistical equilibrium of O and CO in disks around young A stars
Authors: Kamp Inga , van Zadelhoff Gerd-Jan
Published: July 2016

The frequently made assumption that gas and dust temperatures are equal cannot be applied to the low density disks (104 cm−3 < ntot < 108 cm−3) around young A stars (“Vega-type” stars), because the collisional coupling is too weak. It turns out that OI fine structure lines and CO rotational lines are two very important cooling terms in the heating/cooling balance for the gas. Their level population numbers are far from LTE and depend strongly on the background radiation field, given by the thermal dust emission of the disk and the cosmic microwave background.
Turbulence, Vorticity Generation and Angular Momentum Transport via the Baroclinic Instability in Accretion Disks
Authors: Klahr Hubert , Bodenheimer Peter
Published: July 2016

We propose the global baroclinic instability as a source for vigorous turbulence leading to angular momentum transport in Keplerian accretion disks. We know from analytical considerations and three-dimensional radiation hydro simulations that, in particular, protoplanetary disks have a negative radial entropy gradient, which makes them baroclinic. Two-dimensional numerical simulations show that this baroclinic flow is unstable and produces turbulence. These findings were tested for numerical effects by performing barotropic simulations which show that imposed turbulence rapidly decays. The turbulence in baroclinic disks draws energy from the background shear, transports angular momentum outward and creates a radially inward bound accretion of matter, thus forming a self consistent process. Gravitational energy is transformed into turbulent kinetic energy, which is then dissipated, as in the classical accretion paradigm. We measure accretion rates in 2D and 3D simulations of Ṁ = −;10−9 to −10−7 M⊙ yr−1 and viscosity parameters of α = 10−4–10−2, which fit perfectly together and agree reasonably with observations. The turbulence creates pressure waves, Rossby waves, and vortices in the (R – ø) plane of the disk. We demonstrate in a global simulation that these vortices tend to form out of little background noise and to be long-lasting features, which have already been suggested to lead to the formation of planets.
A stellar fly-by simulation giving β Pic's disc asymmetries
Authors: Larwood John , Kalas Paul
Published: July 2016

We have numerically investigated the dynamics of how a close stellar fly-by encounter of a symmetrical circumstellar planetesimal disc can give rise to the many kinds of asymmetries and substructures attributed to the dusty disc of β Pic. We find three recognizable groupings of test particles that can be related to the morphology of the β Pic disc. These are: highly eccentric and inclined orbit particles that reach apocentre in the southwest, moderately eccentric and inclined orbit particles that reach apocentre in the northeast, and a relatively unperturbed region inside ∽200 AU radius.
ISOPHOT observations of dust discs around main sequence stars
Authors: Walker H. J.
Published: July 2016

The photometer (ISOPHOT) on the ESA Infrared Space Observatory (ISO) satellite was used to study the four Vega-like prototypes (Vega, β Pic, α PsA, ɛ Eri) and a set of candidate stars believed to have similar dust/debris discs. Most of the candidate stars were main sequence stars, but probably younger than Vega and ɛ Eri since they showed residual emission in the cores of their stellar spectral lines. Low resolution spectra were combined with long wavelength multi-filter photometry (between 60/μm and 200/μm) to give the spectral energy distributions for the dust/debris discs. Models suggested that the masses of the discs were between 10−7 and 10−4 M⊙ (2–2000 times the mass of the moon). These were more massive than the discs around the four prototypes, but less massive than the discs around young stars such as T Tau stars.
A Model of Stochastic Collisions as the Cause of Clumps in Debris Disks
Authors: Wyatt M. C. , Dent W. R. F. , Greaves J. S. , Holland W. S.
Published: July 2016

We present a heuristic model for the collisional evolution of material in a debris disk. This is used to consider the probability that the 2-3% brightness clump observed in the sub-mm Fomalhaut disk is caused by stochastic collisions between large planetesimals. While this simple model finds that the probability that the clump is caused by collisions is low (about 1 in 80,000), a more detailed model is required to ascertain its true likelihood.
The Search for Terrestrial Planets: What Do we Need to Know?
Authors: Beichman Charles
Published: July 2016

The goal of finding and characterizing habitable planets in other solar systems represents one of humanity's greatest scientific challenges. NASA and ESA have initiated studies of missions that could accomplish this goal within the next ten years. What precursor knowledge do we need before we can initiate such a mission? How large should the first steps be in a program whose ultimate aim is to detect life on other planets? This talk describes different concepts for NASA's Terrestrial Planet Finder and discusses potential precursors in a program that balances scientific return, technological advance, and programmatic risk.
The Visibility of Earth Transits
Authors: Castellano T. , Doyle L. , McIntosh D.
Published: July 2016

The recent photometric detection of planetary transits of the solar-like star HD 209458 at a distance of 47 parsecs suggest that transits can reveal the presence of Jupiter-size planetary companions in the solar neighborhood (Charbonneau et al. 2000; Henry et al. 2000). Recent space-based transit searches have achieved photometric precision within an order of magnitude of that required to detect the much smaller transit signal of an earth-size planet across a solar-size star. Laboratory experiments in the presence of realistic noise sources have shown that CCDs can achieve photometric precision adequate to detect the 9.6 E-5 dimming of the Sun due to a transit of the Earth (Borucki et al. 1997; Koch et al. 2000). Space-based solar irradiance monitoring has shown that the intrinsic variability of the Sun would not preclude such a detection (Borucki, Scargle, Hudson 1985). Transits of the Sun by the Earth would be detectable by observers that reside within a narrow band of sky positions near the ecliptic plane, if the observers possess current Earth epoch levels of technology and astronomical expertise. A catalog of solar-like stars that satisfy the geometric condition for Earth transit visibility are presented.
Direct Detection of Thermal Emission from Extra-Solar Planets
Authors: Kenworthy Matthew , Hinz Philip , Angel Roger
Published: July 2016

We present a new test for the direct detection of extra-solar planets that relies on the presence of a strong molecular absorption band in the thermal emission from the planetary atmosphere. This signature will be sought by the method of differential astrometry, in which the astrometric centroid positions are compared in and out of the molecular band.
Detection of Extra-solar Planets with the Keck Interferometer
Authors: Swain M.R. , Akeson R.L. , Colavita M.M.
Published: July 2016

We discuss the development of the “Differential Phase” detection technique for the Keck Interferometer “Hot Jupiter” Key Science Program. The goal of the “Hot Jupiter” Key Science Program is the direct detection and infrared, low-resolution spectroscopic characterization of previously detected, T ≥ 1000 K extra-solar planets. Although many extra solar planets are sufficiently bright to detect with large telescopes, the proximity of these planets to the much brighter stellar primary makes direct detection difficult because of angular resolution and intensity dynamic range limitations. The Keck Interferometer, working in the near infrared, has sufficient angular resolution and sensitivity to detect some of the currently known extra solar planets; however, the intensity dynamic range required (∽1:30, 000) is substantially beyond the capability of the traditional techniques of optical and infrared direct-detection interferometers.
Energy Release and Transport Processes in the Centres of Galaxies
Authors: Blandford Roger
Published: July 2016

Observations over the past decade have verified, beyond reasonable doubt, that most galactic nuclei contain massive black holes. Hole masses are being measured and firm evidence for spin is being sought. Attention is now returning to the study of how gas flows around black holes and how energy is released both from the accreting gas and from the hole itself in the form of radiation, relativistic jets and non-relativistic, hydromagnetic winds. Some of the different possibilities currently under investigation are briefly reviewed and some recent clues from radio scintillation, polarization and X-ray observations are discussed. It is argued that observations of persistent circular polarisation in Sgr A* support the presence of an ordered disk magnetic field. It is also conjectured that adiabatic, sub- and super-critical accretion flows are demand-limited, not supply-driven and are associated with large mass outflow as appears to be the case in Sgr A*. This principle may have to be modified when a massive black hole forms in a protogalaxy and this modification may account for the proposed hole mass-bulge velocity dispersion relation. The final stages of this process may release sufficient wind energy from the nucleus to prevent disk formation.
Galactic Center: Implications of Recent Chandra Observations for Spherical Accretion Models of Sgr A*
Authors: Coker Robert F. , Markoff Sera
Published: July 2016

At the center of the Milky Way lurks a unique compact nonthermal radio source, Sgr A*. It is thought to be powered by a 2.6 × 106 solar mass black hole that is accreting the stellar winds from the numerous early-type stars that exist in the central parsec. However, until recent high resolution Chandra observations, Sgr A* had never been unequivocably detected at wavelengths shorter than the sub-millimeter. We present a spherical accretion model which is consistent with both the flux and steep spectral shape of the X-ray emission from Sgr A*.
Deconvolving the Nucleus of Centaurus A Using Chandra PSF Library
Authors: Karovska Margarita , Aldcroft T. , Elvis M.S. , Evans I.N. , Fabbiano G. , Gaetz T.J. , Isobe T. , Jerius D. , Jones C. , Juda M. , Kenter A. , Kim D.W. , Kraft R.P. , Murray S.S. , Prestwich A H. , Primini F. , Schwartz D.A. , Cui W. , Schreier E.J.
Published: July 2016

We describe preliminary results from our study of multi-scale structures in Centaurus A (NGC 5128) obtained using the Chandra X-ray Observatory HRC-I observations. The high-angular resolution Chandra images reveal X-ray multi-scale structures in this object with unprecedented detail and clarity. The region surrounding the Cen A nucleus, believed to be associated with a supermassive black hole, shows structures on arcsecond scales clearly resolved from the central source.
The Parsec-Scale Central Components of FR I Radio Galaxies
Authors: Kharb Preeti , Shastri Prajval
Published: July 2016

We present results of our study of the parsec-scale components of radio galaxies as observed at radio, optical and X-ray wavelengths, in the framework of the Unified Scheme.
Toward Monitoring of Blazars at Abastumani: Progress Report
Authors: Kurtanidze Omar M. , Nikolashvili Maria G.
Published: July 2016

We present a brief summary of the ongoing Abastumani Blazar Monitoring Program started in the May of 1997. More than 50 000 frames have been collected during 498 observing nights for about 50 blazars.
III Zw 2: Superluminal Motion and Compact Lobe Expansion in a Seyfert Galaxy
Authors: Brunthaler A. , Falcke H. , Bower G.C. , Aller M. , Aller H. , Teräsranta H.
Published: July 2016

So far all relativistically boosted jets with superluminal motion have only been detected in normal radio galaxies that have early-type host galaxies. We have now discovered superluminal motion in the Seyfert 1 galaxy III Zw 2, classified as a spiral. Spectral and spatial evolution are closely linked. Since III Zw 2 is part of a sample of so-called radio-intermediate quasars (RIQ), it confirms earlier predictions of superluminal motion for this source, based on the argument that RIQs could be relativistically boosted jets in radio-weak quasars and Seyfert galaxies.
Soon After the Birth of Radio Sources
Authors: Owsianik I. , Conway J.E. , Polatidis A.G.
Published: July 2016

Compact Symmetric Objects (CSOs) represent an early stage in the life of radio galaxies. Our kinematic studies over a 20 year timebase have unambiguously demonstrated that they expand fast and that the radio activity is recently born. The CSO evolution with time is however still a matter of investigation. If they are progenitors of the “classical double” radio sources, then in order to fit the the observed statistics of radio sources, CSOs must have decrease their luminosity and expansion speed with time. It is also possible that CSOs represent a phase of periodic activity of the central engine; in this case the presence of the old activity in the form of extended weak emission, should be observed.
The VSOP Survey Program
Authors: Lovell J. E. J. , Fomalont E.B. , Moellenbrock G.A. , Horiuchi S. , Hirabayashi H. , Scott W.K. , Dodson R.
Published: July 2016

The VSOP Survey Program contains 402 bright, small diameter extragalactic radio sources. Pre-launch observations indicated that 113 sources were probably undetectable on space-ground baselines, and so VSOP observations are being undertaken at 5 GHz of the remaining 289 sources. Progress to date is described.
Pearson-Readhead Survey from Space
Authors: Preston R.A. , Lister M.L. , Tingay S. J. , Piner B.G. , Murphy D.W. , Jones D. L. , Meier D.L. , Pearson T.J. , Readhead A. C. S. , Hirabayashi H. , Kobayashi H. , Inoue M.
Published: July 2016

We are using the VSOP space VLBI mission to observe a complete sample of Pearson-Readhead survey sources at 4.8 GHz to determine core brightness temperatures and pc-scale jet properties. To date we have imaged 27 of the 31 objects in our sample. Our preliminary results show that the majority of objects contain strong core components that remain unresolved on baselines of 30,000 km. The brightness temperatures of several cores significantly exceed 1012 K, which is indicative of highly relativistically beamed emission. We also find that core brightness temperature is correlated with intraday variability in compact AGNs.
The Compact Magnetic Field Structures of AGN from Space VLBI Polarization Observations
Authors: Gabuzda D.C. , Gómez J.L.
Published: July 2016

BL Lacertae objects are active galactic nuclei with weak, sometimes undetectable, optical line emission and strong variability in total intensity and linear polarization over a broad range of wavelengths from ultraviolet to radio. It is believed that synchrotron radiation is the dominant emission mechanism virtually throughout the spectrum. Their strong linear polarization makes BL Lac objects prime targets for space VLBI polarization observations.
Frequency Dependence of the Parsec-scale Polarization Structures of BL Lac Objects
Authors: Pushkarev A.B. , Gabuzda D.C. , Cawthorne T.V.
Published: July 2016

BL Lacertae objects are active galactic nuclei with weak or undetectable line emission and strong variability in total intensity and linear polarization over a wide wavelength range from optical to radio. The radio emission and much of the optical emission is believed to be synchrotron radiation. Sources in the complete sample of BL Lac objects defined by Kühr and Schmidt (1990) have: 5 GHz fluxes of at least 1 Jy, radio spectral index α ≥ −0.5 (Sv ˜ v+α), rest frame equivalent width of the strongest emission lines less than 5 Å, and optical counterparts on the Sky Survey plates with brightness greater than 20m.
Radio Interferometric Observations of NGC 2146
Authors: Tarchi A. , Neininger N. , Greve A. , Klein U. , Garrington S.T. , Muxlow T. W. B. , Pedlar A. , Glendenning B.E.
Published: July 2016

At 5 GHz, about 20 point sources were detected earlier by Glendenning & Kronberg (1986) in the central 800 pc of NGC 2146. Our observations with higher sensitivity and resolution made with MERLIN and the VLA confirms the detection of 18 sources, and resolves 7 of them (Fig.1). Additional 1.6-GHz MERLIN observations disclose 9 sources coincident in position with those detected at 5 GHz, which allows us to derive their spectral indices α51.6 (Sv ∼ να). Only 3 sources have indices (α < 0) consistent with synchrotron emission from supernova remnants or radio supernovae, while the others have very steep inverted spectra (α > 0).
Searching for HI Absorbing Gas in AGN
Authors: Pihlström Y.M. , Conway J.E. , Vermeulen R.C.
Published: July 2016

With the aim of probing HI gas in AGN we have searched different samples of radio sources for the 21cm atomic hydrogen line in absorption. Depending on the source morphology, we are able to probe gas that either belongs to the host galaxy ISM, or gas that is situated on scales < 1kpc which then may be connected with the AGN fueling. For the HI absorption detected in 3C216, we argue that such sub-kpc scale gas instead might be due to a jet-cloud interaction.
Chandra Observations of Starburst Galaxies M82 and NGC 3256
Authors: Prestwich Andrea , Zezas Andreas , Kaaret Philip , Murray Steve , Kilgard Roy , Kim Dong-Woo , Schlegel Eric , Ward Martin , Lira Paulina
Published: July 2016

We present high resolution Chandra X-ray imaging of two starburst galaxies, M82 and NGC 3256. The central x-ray source observed by ROSAT and ASCA in M82 is resolved into 3 or 4 sources. Most of these sources are variable, suggesting that the point sources are powered by accretion. The brightest of these central sources is ∼ 1041ergs s−1 in the high state, and is responsible for the variability observed by ROSAT and ASCA. Assuming this source radiates at the Eddington limit, the mass is ∼ 500M⊙. The diffuse hard (2-10 keV) emission in M82 is spatially coincident with diffuse radio emission and Pα. This is consistent with diffuse hard X-ray emission arising from hot thermal gas in the starburst region. Approximately 14 sources with LX > 1039ergs s−1 were detected in NGC 3256, including both nuclei. Two of these sources have LX > 1040ergs s−1. This observation suggests that “super Edington” sources may be preferentially associated with starburst galaxies (see also paper by Fabbiano in this volume)
What is the Maximun IR Luminosity of a Single Spiral Galaxy?
Authors: Mickaelian A.M. , Véron-Cetty M.-P. , Véron P.
Published: July 2016

A new sample of IRAS galaxies at high galactic latitudes has been built by optically identifying IRAS point sources.

In no more than about 100 cases, an apparently interacting system of galaxies is located near the IR source. The large majority are unambiguously identified with a single, relatively isolated galaxy. This confirms that, although galaxy interaction may trigger starburst activity, the IR luminosity in most objects is due to normal star formation in the disc.
High spatial resolution multiwavelength observations of star and planet formation
Authors: McCaughrean Mark J.
Published: July 2016

We discuss the importance of multiwavelength (optical, infrared, millimetre, and radio), high angular resolution (arcsec to subarcsec) observations in studying star and planet formation. We provide a few illustrative examples, and briefly discuss how future observational facilities will allow a yet more detailed view of the important processes at work.
High Angular Resolution Observations of Maser Kinematics Near Low Mass Young Stellar Objects
Authors: Marvel Kevin B. , Claussen Mark , Alwyn Wootten H. , Wilking Bruce
Published: July 2016

With the advent of new correlators and dedicated arrays, spectral line VLBI is entering its ascendancy as a probe of a variety of interesting astrophysical environments. One of the most interesting environments where spectroscopic VLBI techniques are valuable are the regions directly coincident with forming stars. In these sources, water maser emission is observed when the outflowing jets of material interact with the surrounding medium. Observations of these water masers dramatically reveal the innermost regions of the star formation process at or below the 1-AU scale.

We have found that the water masers clearly trace the jets at these scales. The masers show space motions on the order of 60 to 100 kms−1 and form within a few AU of the exciting protostar. By observing the distributions and motions of the water masers associated with these objects, we may be able to address in greater detail the collimation mechanism of the jets seen in these protostars.

In this brief poster proceeding, we provide a summary image of the water masers associated with SVS13, the driving source for the HH 7-11 objects. We have also mapped the masers associated with IRAS 16293-2422, IRAS 05413-0104, IRAS 4A and IRAS 4B, both in the NGC 1333 star forming region. For further information on these sources, please contact any of the authors directly.
Self-Gravitational Instability of an Isothermal Gaseous Slab under High External Pressure
Authors: Umekawa Michihisa , Matsumoto Ryoji , Miyaji Shigeki , Yoshida Tatsuo
Published: July 2016

In active massive star forming regions such as Orion and the Galactic center, the self-gravitational instability of a magnetized gaseous slab plays an important role as a trigger of star formation. In such high external pressure regions, the incompressible mode of self-gravitational instability (Elmegreen & Elmegreen 1978; Lubow & Pringle 1992) becomes dominant. Based on two-dimensional hydrodynamical simulations, Umekawa et al. (1999) proposed “Star formation by merging of the Jeans stable clumps” in a pressure bounded slab. In a magnetized slab confined by external pressure, Nagai et al. (1998) showed by linear analysis that the slab fragments to filaments parallel to the magnetic field lines. Here, we show by nonlinear three-dimensional MHD simulations that the filaments further fragment to Jeans stable clumps.
The Envelope of IRC+10216 Seen at High Angular Resolution
Authors: Mauron Nicolas , Huggins Patrick J.
Published: July 2016

Deep optical images of the circumstellar envelope of IRC+10216 have been obtained with CFHT and HST, with angular resolutions of 1 and 0.1, respectively. In the outer regions, the envelope is seen in dust-scattered galactic light, and is detected up to ∼200 from the star, corresponding to 8000 years of expansion. The envelope is composed of discrete, nearly circular, thin, limb-brightened shells. These shells are spaced at irregular intervals, and the shell/intershell density contrast is typically 3. Although the HST observations show a distinct bipolar geometry very near the star, the global shell pattern suggests a roughly isotropic, episodic mass loss mechanism.
M 31's Molecular Arms at All Scales to Below 10 pc
Authors: Neininger N. , Nieten Ch. , Guélin M. , Ungerechts H. , Lucas R. , Muller S. , Wielebinski R.
Published: July 2016

I present a unique data set for the study of molecular gas in galaxies: a complete, high-resolution survey of the CO in M 31 and additional local studies. The fully sampled survey has an angular resolution of 23 FWHM and the interferometric data attain the pc-scale with sub-arcsecond resolution. For the first time it is now possible to study large and small scales in conjunction. Thus we are able to derive the global structure and study the links down to the individual cloud complexes and star formation regions.
VLBI Observations of SNR in M82 - Is 41.95+575 an Anomalous SNR or Something Else ?
Authors: Muxlow T.W.B. , Pedlar A. , McDonald A.R. , Garrington S.T. , Trotman W.M. , Wilkinson P.N. , Diamond P.J. , Garrett M.A. , Wills K.A.
Published: July 2016

Global VLBI 1.7GHz datasets from 1990 and 1998 have been used to study the evolution of SNR 41.95+575 in M82. An expansion velocity of around 1800 km/s is found with an implied birth around 1915. A young 41.95+575 would resemble radio supernovae seen in Arp220, although it could also be an evolving accretion disc system
The Gas Dynamics in the Centre of the Starburst M82
Authors: Wills Karen , Pedlar Alan , Muxlow Tom , Das Mousumi
Published: July 2016

VLA A-array 21cm atomic hydrogen (HI) absorption observed against the central region of the starburst galaxy M82 and MERLIN HI absorption measurements which show HI absorption against 26 of the supernova remnants are discussed. These observations have been compared with the molecular (CO) and ionised ([NeII]) gas distributions and used to constrain the dynamics and structure of the ionised, neutral and molecular gas in this starburst.
Prospects for High Angular Resolution at Metre to Centimetre Wavelengths
Authors: Taylor A.R.
Published: July 2016

The past ten years has seen very significant advances in high resolution imaging arising from the construction and routine operation of Very Long Baseline Interferometer arrays in the US, Europe and Australia. Coupled with the launch of the first VLBI antennas into earth orbit, angular resolution below a milliarcsecond has been achieved on a large number of compact objects. Nevertheless, while the application of phase referencing to VLBI observations has increased the number of sources that can be imaged by VLBI, the astrophysical impact of interferometry on baselines greater than a few tens of km, has been severely limited by sensitivity. The next decade promises to bring about very significant increases in continuum sensitivity at high angular resolution through new developments in VLBI recording devices to achieve recording bandwidths of 4 to 8 Gbits per second, and by direct optical fibre-linked long baseline arrays. In the following decade, the Square Kilometre Array will herald a new era of high resolution radio astronomy with a factor of 100 sensitivity increase. In addition to vastly increasing the sample of non-thermal sources accessible to VLBI, the SKA will open up high angular resolution imaging to a new regime of astrophysics, by enabling milliarcsecond resolution imaging of thermal radio emission. At wavelengths of a few centimetres the SKA, in combination with next generation space VLBI missions, will allow direct imaging of the x-ray emitting accretion disks in galactic nuclei.
Adaptive Optics with a Laser Guide Star - The ALFA system
Authors: Ott T. , Davies R. , Rabien S.
Published: July 2016

All 8-metre class telescopes will be equipped with adaptive optics systems in order to reach their highest angular resolutions. With the additional requirement for maximal sky coverage comes the mandatory use of a laser guide star. ALFA is an adaptive optics system using a sodium laser guide star, which is installed on the 3.5-m telescope at Calar Alto observatory. It has shown that it is possible to reach Strehl ratios better than 20% in the K-band. In this contribution we describe the design of the system, the observational trade-off necessary to use a laser guide star, and the performance that might be expected.
Astrometry Missions: Probing the Galaxy and Beyond
Authors: Mignard F.
Published: July 2016

In the wake of the HIPPARCOS success four highly accurate space astrometry missions are now approved for launch within the next ten years. Stellar physics and galactic physics constitute the core science of these missions with deep impact on star formation and evolution, cosmic distance scales and age determination of the oldest stars. Summary data are provided in this paper to compare the goals and capabilities of these missions.
Formation of Wide Binaries by Fragmentation
Authors: Bodenheimer Peter , Burkert Andreas
Published: July 2016

Although observations strongly suggest that fragmentation during the protostar collapse is the primary formation mechanism for wide binaries, the theoretical calculations as yet do not well explain the statistical properties of such systems. The results of a number of numerical simulations are discussed, and it is pointed out that, although fragmentation is obtained in such calculations, in many cases either the initial conditions are not realistic, or the calculations are insufficiently resolved, or the calculations have not been taken far enough to account for the accretion of most of the initial core material onto the components of the forming system. Certain aspects of the numerical results are, however, consistent with the fragmentation hypothesis.
Binaries at the Bottom of the Main Sequence and below
Authors: Mayor M. , Udry S. , Halbwachs J.-L. , Arenou F.
Published: July 2016

Long-term radial-velocity surveys of G, K and M dwarfs of the solar neighbourhood are presented. The inferred orbital elements are discussed, focusing on the (e, log P) diagram, the mass-ratio and secondary mass distributions, and on the binary frequency of the studied samples. The proportion of companions to M dwarfs is found to be not significantly different from the binary frequency among G- and K-dwarf primaries. The mass function of stellar and planetary companions to solar-type stars strongly suggests different formation and evolution mechanisms for the two populations. Finally, beautiful mass-luminosity relations are obtained from low-mass binaries with high-precision radial-velocity measurements and adaptive optics visual data.
Binarity of Hipparcos Main Sequence Survey Stars
Authors: Quist Carl F. , Lindegren Lennart
Published: July 2016

Hipparcos observations of double stars, mainly A and F primaries, are modelled in order to check the statistics of double-star solutions in the Hipparcos Catalogue and to set quantitative limits on binary distributions. The number of companions per primary is estimated to 0.25 ± 0.05 for semi-major axes from 1 to 10 AU, and to 0.43 ± 0.20 for the range 10–100 AU. The total multiplicity found is between 0.9 and 1.2.
Statistics of Multiple Stars: Some Clues to Formation Mechanisms
Authors: Tokovinin Andrei
Published: July 2016

The available information on the statistics of high multiplicity (3–6 components) systems is reviewed. The ratio of triple to binary systems is f3 ≍ 0.11, while fn ≍ 0.25 for higher n. Despite selection effects in the multiple star catalogue, the signatures of formation mechanisms are found in the distributions of period ratios and mass ratios. For example, the frequent occurrence of close sub-systems with periods less than 6 days can be explained by tidal dissipation in a 3-body system. In triple stars the angular momentum vectors of inner orbits are inclined to those of outer orbits by an average angle of 50°, hence the orbital spins are neither co-aligned nor completely random. Close binaries have a tendency to be found in higher-multiplicity systems, showing that close and wide binarity is statistically related. Future theoretical and observational studies are outlined.
Implications of Binary Properties for Theories of Star Formation
Authors: Larson Richard B.
Published: July 2016

The overall frequency and other statistical properties of binary systems suggest that star formation is intrinsically a complex and chaotic process, and that most binaries and single stars actually originate from the decay of multiple systems. Interactions between stars forming in close proximity to each other may play an important role in the star formation process itself, for example via tidally induced accretion from disks. Some of the energetic activity of newly formed stars could be due to bursts of rapid accretion triggered by interactions with close companions.
Turbulence and Cloud Angular Momentum
Authors: Burkert Andreas , Bodenheimer Peter
Published: July 2016

Numerical models of molecular cloud cores are obtained, with assumed Gaussian random velocity fields that are consistent with moderate turbulence. If the velocity power spectrum is taken to be P(k) ∼ kn, with n = − 4 or −3, then the constructed line-of-sight velocity maps on the plane of the sky show gradients that can be interpreted as rotation. Deduced values of angular velocity, angular momentum, and dimensionless rotational parameter β are consistent with observations. The velocity gradient Ω, of an individual core is not a good indicator of its intrinsic angular momentum J/M. However, the distribution of deduced angular momenta from a large sample of cores with different random velocity fields is close to the distribution of actual angular momenta of these model cores if one assumes J/M = pΩR2 where R is the core radius and p must be determined from a Monte-Carlo study. For centrally condensed cores the standard value of p = 0.4 overestimates the mean intrinsic angular momentum by a factor of 3.
Binary Stars in Young Clusters –a Theoretical Perspective
Authors: Kroupa Pavel
Published: July 2016

The preponderance of binary systems in all known stellar populations makes them exciting dynamical agents for research on topics as varied as star formation, star-cluster dynamics and the interiors of young and old stars. Today we know that the Galactic-field binary population is probably a dynamically evolved version of the Taurus–Auriga pre-main sequence population, and that the initial distributions of binary-star orbital elements are probably universal. Furthermore, N-body calculations tentatively suggest that OB stars form in energetic binaries near cluster cores, and that binaries with ‘forbidden’ orbital elements that are produced in stellar encounters, may turn out to be very useful windows into stellar interiors, potentially allowing tests of pre-main sequence evolution theory as well as of models of main-sequence stars.
GG Tau: the Ringworld Revisited
Authors: Guilloteau Stéphane , Dutrey Anne
Published: July 2016

GG Tau is a textbook example of a binary system. The circumstellar material around GG Tau is divided in several distinct regions: 1) small, low mass, circumstellar disks, detected in the near-IR and mm domain, 2) a well defined ring, of inner radius 180 AU, detected in the mm domain and in scattered near-IR light, 3) a more extended, colder disk detected in the 13CO(2–1) and 13CO(1–0) lines. Recent observations of the 12CO(2–1) clearly show this extended disk, but also reveal a fourth component of the circumstellar material: (relatively) diffuse and hot gas in the tidally unstable region. Estimate of the gas content suggest this material may be feeding the inner disks at about 10−6 M⊙/yr.