bluuebunny/crossref_metadata_2025 huggingface dataset:
The Evolution of Rotating 15 M⊙ Stars
Authors: Sofia S. , Howard J.M. , Demarque P.
Published: July 2016

Theoretical evolutionary sequences have been generated with the YREC code for a 15 M⊙ star from the ZAMS to core helium exhaustion with a variety of physical assumptions, covering both rotating and non-rotating cases. The non-rotating models agree qualitatively with other models found in the literature. The addition of only rotational distortion has little effect on the models, while the full treatment of rotation results in additional mixing and theoretical tracks that are similar to models with small amounts of convective overshoot. Models which include only rotation have fair agreement with the observed main sequence surface rotation velocities, but rotate too rapidly during the post-main sequence phases. The addition of mass loss at the given rates helps this problem somewhat but does not appear to completely resolve it. Neither the non-rotating models nor the rotating models provide full agreement with the terminal-age main sequence band used by Maeder & Meynet (1987); this may be indicative that additional mixing processes are necessary or that a more recent TAMS, such as that of Stothers (1991), should be used.
Rotationally induced turbulent diffusion in early B-type stars: theory and observations
Authors: Denissenkov P.
Published: July 2016

Available observational data indicate that some kind of additional mixing is present in radiative envelopes of O and early B-type stars. Because of these stars are known to be the fastest rotators amongst all normal stars, the most probable candidate for the role of additional mixing in their interiors is rotationally induced turbulent diffusion discovered by Zahn (1983, 1992). Recently Denissenkov (1993a,b) calculated evolution of massive main sequence (MS) stars with turbulent diffusive mixing in order to explain atmospheric abundance peculiarities in OB-stars. This note summarizes the main results which have been obtained.
The He-strong star HD 96446: oblique rotator or pulsating magnetic variable?
Authors: Mathys G.
Published: July 2016

HD 96446 is a B2p He-strong star, in which a large-scale organized magnetic field is present. From spectra recorded in both circular polarizations, various moments of this magnetic field have been repeatedly determined, among which the mean longitudinal magnetic field and the crossover. The mean longitudinal magnetic field 〈Hz〉 is the line-intensity weighted average over the visible stellar hemisphere of the line-of-sight component of the magnetic vector. The crossover, ve sin i 〈x Hz〉,is the product of the projected equatorial velocity, ve sini, and of the mean asymmetry of the longitudinal magnetic field, 〈x Hz〉. The latter is the line-intensity weighted first-order moment about the plane defined by the line of sight and the stellar rotation axis of the component of the magnetic field along the line of sight.
X-ray properties of early-type stars
Authors: Berghöfer Thomas W. , Schmitt Jürgen H. M. M.
Published: July 2016

Extensive stellar surveys with the Einstein Observatory (Chlebowski et al., 1989) and with ROSAT have clearly confirmed the presence of stellar X-ray emission over nearly the whole range of the HR diagram. In the ROSAT all-sky survey data approximately 20000 stellar X-ray sources were detected (Schmitt et al., 1992). Most of these stellar X-ray emitters are low mass late-type stars, the origin of their X-ray emission is thought to be coronal.
Recent Results from Ultraviolet and Optical Spectropolarimetry of Hot Stars
Authors: Bjorkman K.S.
Published: July 2016

The first comprehensive linear polarization data on hot stars covering the spectral range from 1500 to 7600Å are presented. These results are based on recent observations made with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE), combined with ground-based observations from the Pine Bluff Observatory. Implications of the data for models of the circumstellar envelopes of hot stars are discussed, with particular emphasis on the surprising results found for the rapidly rotating Be stars. In particular, WUPPE discovered that the continuum polarization in Be stars decreases into the ultraviolet, which was not predicted by models prior to the observations. Time variability in the optical data is also discussed. Possible interpretations of these results are examined in the light of recent new models for Be star disks.
Spectropolarimetric determination of circumstellar disc inclinations
Authors: Wood Kenneth
Published: July 2016

Inference of the density and velocity structure of rotating/expanding circumstellar discs/winds is of considerable interest in the understanding of stellar mass loss. High resolution line spectropolarimetry creates the possibility of diagnosing such envelope structure much more fully than broad band polarimetry or high resolution spectrometry alone since each element of the scattered spectropolarimetric profile picks out the element of the envelope with the appropriate Doppler shift and provides orientation information on it. This problem has been formulated in detail by Wood, et al (1993) for scattering of a finite width line in a flattened envelope – the spectral shape of the scattered Stokes fluxes being determined by isowavelength–shift contours or surfaces which give the relative wavelength shift of the scattered radiation at different regions in the disc. It was also shown how, in the case of a narrow stellar line scattered in a rotating or expanding flat disc with a simply parametrised density and velocity structure (ignoring the smearing effect of electron thermal motions), it is possible to infer the system inclination and structure model parameters from the resulting spectropolarimetric line profile. This poster presents a method for determining the disc inclination from analysis of the scattered profiles – a parameter which cannot be determined uniquely from spectrometry alone – and thus illustrates the powerful diagnostic potential of high resolution line spectropolarimetry.
Photospheric Activity in Selected Be Stars: λ Eri and γ Cas
Authors: Smith Myron A.
Published: July 2016

Recent observations of rapid variations in optical He I lines, X-rays, and FUV wavelengths in the prototypical classical Be stars λ Eri and star γ Cas hint that the violent processes occur on the surfaces of these stars almost all the time. We suggest that of these phenomena show greater similarities with magnetic flaring than any other process thought to occur on stars.
Emission-like feature due to a latitudinal differential rotation
Authors: Zorec J.
Published: July 2016

We simulate the effect due to a latitudinal differential rotation on a HeI λ4471 absorption line. The effect can produce an emission-like reversal in the line core.
Study of the HeI λ4471 line-profile of Be stars
Authors: Ballereau D. , Chauville J. , Garcia A. , Zorec J.
Published: July 2016

In this paper we study the veiling effect and the strength of an extra emission-like component filling partially the HeI λ4471 line of Be stars. It is shown that this component is roughly correlated with the emission in the continuum and in the Hγ line.
The HeI λ4471 line behaviour of 31 Peg
Authors: Ballereau D. , Chauville J. , Zorec J.
Published: July 2016

In this paper we report the spectroscopic behaviour of 31 Peg in the HeI λ4471, MgII λ4481 and the Hγ lines at four observing dates. The behaviour of the HeI line indicates that perhaps there exists a photospheric activity and/or some exophotospheric perturbing effect acting on the stellar photosphere.
Be stars in young LMC clusters
Authors: Kjeldsen H. , Baade D.
Published: July 2016

Slitless field Hα spectroscopy with a resolution of 0.2 nm has detected numerous Be stars in 3 young open star clusters in the LMC but only a few each in one Galactic and one LMC cluster. The line widths indicate rapid rotation as is typical of Galactic field Be stars. In NGC 2004 (LMC) their distribution seems inconsistent with the assumption of either very similar equatorial rotation velocities or random orientation of the rotation axes or both, which are believed to be valid for Galactic field Be stars.
Be stars in the ultraviolet spectral classification system
Authors: Rountree Janet , Sonneborn George
Published: July 2016

Rountree and Sonneborn (1991) developed a system for the classification of ultraviolet B-star spectra, using MK standards drawn from the optical region. The observational material consisted of high-dispersion spectra obtained with the Short Wavelength Prime (SWP) camera on the International Ultraviolet Explorer (IUE) spacecraft. The classification criteria were based exclusively on photospheric absorption lines, primarily lines of C III, Si II, and Si III. The stellar wind lines of Si IV, C IV, and N V were not used in the classification.
Results from six multiwavelength campaigns to study short-term FUV flux variability and phase-dependent mass loss in Be stars
Authors: Peters Geraldine J.
Published: July 2016

During the past six years we have carried through seven multiwavelength, multisite campaigns to investigate the cause for short-term (rapid) photometric and spectroscopic variability in Be stars and assess its importance in driving the mass loss in these objects. These campaigns usually included simultaneous observations in the UV with the IUE and Voyager spacecraft and optical region with ground-based telescopes worldwide (photometry, high resolution spectroscopy, and polarimetry). Typically 10–25 observers from 5–9 countries participated. Stars that have been observed include λ Eri, ω Ori, o And, ∊ Cap, 28 Cyg, η Cen, 48 Lib, ζ Tau, ψ Per, and 2 Vul. We briefly summarize some of the results from the UV study here. Additional results from the ground-based data are given in other papers in this volume by D. Gies, M. Hahula, J. Percy, and D. McDavid.
Periodic Variations and Mass Loss in Be Stars
Authors: Saio Hideyuki
Published: July 2016

We discuss the connection between the periodic light variations and the equatorial mass loss of Be stars. The observed properties of the short period (~ day) variations seem to indicate that they arise in the photosphere. An upper limit for the surface magnetic field of Be stars is derived from the rate of angular momentum loss expected from the typical mass loss-rate in Be stars. The upper limit suggests that surface magnetic fields of Be stars are too weak to make a spot. We argue that the periodic variations of Be stars are explained by nonradial pulsations whose periods on the stellar surface are much longer than the rotation period. They transport angular momentum from the core to the envelope to accelerate the surface regions. If this mechanism works sufficiently well, the rotation speed near the surface will reach to the critical velocity and an excretion disk will be formed around the star. A simple model for a steady-state excretion disk around a Be star is found to be consistent with the density structure inferred from the IR fluxes.
Simultaneous photometry and spectroscopy of the rapid variability of the Be star η Cen
Authors: Štefl S. , Baade D. , Harmanec P. , Balona L. A.
Published: July 2016

The reality of the previously reported triple-wave light curve (Cuypers et al. 1989, A&A Suppl. 81, 151), and relations between rapid line profile and brightness variations of the B1-2III-Ve star η Cen (HD 127972) were investigated by means of simultaneous high-resolution spectroscopy (4 nights, 86 Si III 455.2622 nm profiles) and two-station uvby photometry (14 nights) secured in 1992. To this database were added the uvby photometry by Cuypers et al. and unpublished b observations by L.A.B. from 1988–1991.
Periodic Variability of Be Stars: Nonradial Pulsation or Rotational Modulation?
Authors: Baade D. , Balona L.A.
Published: July 2016

A large fraction of Be stars show periodic light and line profile variations with a timescale of about one day. The mechanism which causes these periodic variations has been attributed to nonradial pulsation (NRP) or rotational modulation (RM). The authors present arguments supporting the two opposing points of view with the purpose of stimulating subsequent discussion by the Symposium participants.
Detection of calcium abundance stratification in Ap stars
Authors: Babel J.
Published: July 2016

We report the discovery of a systematic and large calcium abundance stratification in cold Ap stars. These detections are in very good agreement with diffusion theory and set stringent upper limits on turbulent processes.
Shell profiles in Be star spectra
Authors: Hanuschik R. W.
Published: July 2016

Although very different in shape, Be-type and Be-shell-type spectral lines are thought to arise from the same kind of circumstellar environment, a disklike envelope. The only discrimination between these two types of spectra is the inclination angle: If sufficiently high, a large column depth of circumstellar material causes partial obscuration of the stellar disk, i.e. shell absorption; otherwise a pure emission line is observed. A shell line can be considered as equivalent to P Cygni-type absorption trough for different geometry (disk instead of sphere) and kinematics (rotation instead of outflow; see Hanuschik, these proceedings).
Activity in the circumstellar envelope of the Be/shell star ζ Tau
Authors: Guo Yulian , Huang Lin , Hao Jinxin
Published: July 2016

ζ Tau is a well-known V/R-variable shell star. It is a single-lined spectroscopic binary with an orbital period of 133 days (Harmanec 1984, and Jarad 1987). Delplace (1970) found that the long-term radial velocity variations of the Balmer shell absorption lines are cyclic in 1960–67. Subsequently, similar behaviour has been observed and studied by several authors (Delplace and Chambon 1976, Hubert-Delplace et al 1983, Harmanec 1984, and Guo and Cao 1987). Mon et al (1992) showed that the cyclic variation had terminated and the star seems to have entered a new quiet phase around 1982.
Global oscillations in Be star envelopes: observational evidence
Authors: Hanuschik R. W. , Hummel W. , Dietle O. , Dachs J. , Sutorius E.
Published: July 2016

Since 1982, we are performing a long-term spectroscopic observing programme of emission-lines in Be stars (Hanuschik 1987, Hanuschik et al. 1988, Dachs et al. 1992, Sutorius 1992, Dietle 1993). We are using ESO's 1.4m CAT, at resolution R ≥ 50 000 and S/N = 100–1000. Spectral lines chosen are the optically thick Hα, Hβ lines and the optically thin Fe ii λ5317 line. The latter line is an extremely sharp tracer (Δvth = 2 km s−1) for the kinematics in the disks. We believe that our atlas shows the full range of intrinsic structure of these emission lines.
Infrared spectroscopy of Be stars
Authors: Torres R.M. , Damineli-Neto A. , de Freitas Pacheco J.A.
Published: July 2016

FeII emission lines are present in a variety of astrophysical objects and, in particular, in Be stars, where in some situations they can also be seen in absorption. Selvelli & Araujo (1984) studied a sample of classical Be stars that have FeII emission lines in the optical region. The analysis of IUE spectra of those stars revealed that, for the majority of the objects, neither absorption nor emission FeII features were present in the UV. The conclusion was that their data could not support excitation of FeII by continuum fluorescence. On the other hand, FeIII of circumstellar origin is often seen in absorption in the UV spectra of Be stars (Snow & Stalio 1987 and references therein). This could be an indication that the optical FeII emission lines are originated from recombination and cascade. However, Selvelli & Araujo (1984) argued that, since the multiplet UV 191 of FeII does not appear in emission, that mechanism is probably not relevant. In the present work we report new spectroscopic observations in the near infrared of a sample of 60 Be stars, including the prominent FeII 999.7 nm emission line. This line is also present in the spectra of superluminous B stars for which mass loss rates have recently been estimated (Lopes, Damineli-Neto & Freitas Pacheco 1992). We derived mass loss rates from the infrared line luminosities, in agreement with those derived by other methods. We also found a new evidence of the Be envelope flattening through the FeII/Paδ line ratio.
Problems of modelization of circumstellar matter out of equilibrium
Authors: Lafon J-P. J. , Huguet E.
Published: July 2016

Circumstellar envelopes of young and evolved stars are responsible for many important phenomena concerning the exchange of matter, angular momentum, energy and maybe magnetic field between the core structure of stars and the interstellar medium. In particular, it is through them that matter enriched in heavy elements flows from evolved stars towards the interstellar gas, submitted to complex ordinary chemistry or photochemistry and condensation into solid particles.
The Wind-Compressed Disk Model
Authors: Bjorkman J.E.
Published: July 2016

We discuss the effects of rotation on the structure of radiatively-driven winds. When the centrifugal support is large, there is a region, at low latitudes near the surface of the star, where the acceleration of gravity is larger than the radiative acceleration. Within this region, the fluid streamlines “fall” toward the equator. If the rotation rate is large, this region is big enough that the fluid from the northern hemisphere collides with that from the southern hemisphere. This produces standing shocks above and below the equator. Between the shocks, there is a dense equatorial disk that is confined by the ram pressure of the wind. A portion of the flow that enters the disk proceeds outward along the equator, but the inner portion accretes onto the stellar surface. Thus there is simultaneous outflow and infall in the equatorial disk. The wind-compressed disk forms only if the star is rotating faster than a threshold value, which depends on the ratio of wind terminal speed to stellar escape speed. The spectral type dependence of the disk formation threshold may explain the frequency distribution of Be stars. Observational tests of the wind-compressed disk model indicate that, although the geometry of the disk agrees with observations of Be stars, the density is a factor of 100 too small to produce the IR excess, Hα emission, and optical polarization, if current estimates of the mass-loss rates are used. However, recent calculations of the ionization balance in the wind indicate that the mass-loss rates of Be stars may be significantly underestimated.
The Basic Physics of Hot-Star Winds
Authors: Owocki Stanley P.
Published: July 2016

Hot-star winds are believed to be driven by line-scattering of the star's continuum radiation. This review summarizes the physics of this line-driving process and the resulting basic wind properties. I also briefly discuss the generation of wind structure, both at small scale due to inherent instabilities in the line-driving, and at large scales due to various rotational effects.
Radiatively driven winds of OB stars
Authors: Shimada Michihiro R. , Ito Masaki , Hirata Ryuko , Horaguchi Toshihiro
Published: July 2016

We newly calculated the line radiative force with 520,000 atomic lines, which is twice as many as those of Abbott (1982), for OB supergiants. Our results are as follows. (1) The mass loss rates for O stars with Teff = 50,000K are seven times as large as Abbott's (1982) because of contribution from Fe iv lines. (2) Contribution from many weak lines increases the mass loss rates and decreases the wind velocities of OB stars within a temperature range of 10,000K ≤ Teff ≤ 30,000K. This result is qualitatively in accordance with the results from the recent observations of O stars. (3) The mass loss rates of OB stars depend on metallicity with Ṁ ∼ Z.
Understanding the P Cygni profile
Authors: Rons N.
Published: July 2016

Narrow Absorption Components (NACs) have been detected in essentially all unsaturated P Cygni profiles of O-type stars (Howarth & Prinja, 1989). Time-series of observations have revealed their migration through the profile's absorption trough (Prinja et al., 1987, Henrichs et al., 1988). The interpretation of the NACs is essential for the understanding of the dynamic structure of the winds of O stars and of the driving mechanisms behind it. The P Cygni profile substructures caused by isolated reverse and forward shocks were calculated in a ‘line only’ approximation for a spherically symmetric, isothermal stellar wind. The Comoving Frame method was used for an accurate treatment of the complex radiation transfer in the shock environment. The underlying velocity structure follows a β-law (except in the innermost layers where a polynomial law was used) while the ionization was taken to be constant throughout the entire wind.
Wind Variability in O-Type Stars
Authors: Henrichs H.F. , Kaper L. , Nichols J.S.
Published: July 2016

The search for the cause of the discrete absorption components (DACs) in P Cygni profiles in UV spectra of O stars continues: pulsation, rotation and magnetic fields are probably all in various degrees important. We highlight some key observations which show that DACs start close to the stellar surface, and emphasize the possible role of localized magnetic fields (which are still to be detected).
Planetary Messages in the Doppler Residuals
Authors: Marcy Geoffrey W. , Fischer Debra A. , Butler R. Paul , Vogt Steven S.
Published: July 2016

The Doppler residuals to the Keplerian fits for extrasolar planets reveal important properties of the planets and host stars. Stellar magnetic fields modify the photospheric velocity fields, causing Doppler fluctuations with unknown time scales. This Doppler “jitter”, seen prominently in the magnetic stars Epsilon Eridani and ξ Boo A, compromises the detectability of planets. The Doppler residuals during the transit of HD209458 reveal that the planet orbits in the same direction as the star spins. Moreover, the transit path across the star is nearly parallel to the stellar equator. Most interestingly, the Doppler residuals of known planets often reveal additional coherent variations, probably caused by additional companions. Both 55 Cancri and HD168443 reveal such coherent Doppler residuals. Another five planet–bearing stars observed at Lick show trends in the Doppler residuals indicating the presence of additional companions. Remarkably, about half of the known extrasolar planets reveal such coherent variations. This suggests that stars with planets have a high occurrence rate of harboring more distant companions, planetary or otherwise.
τ Boo b: Not so bright, but just as heavy
Authors: Cameron Andrew Collier , Horne Keith , James David , Penny Alan , Semel Meir
Published: July 2016

We present new results derived from high-resolution optical spectra of the τ Boo system, secured in March-May 2000. The results do not show the same feature reported by Cameron et al (1999) as a candidate reflected-light signature from the planet. Together with earlier results from the 1998 and 1999 seasons, the new data yield a 99.9% upper limit on the opposition planet/star flux ratio ∊ < 3.5 × 10−5 between 387.4 and 586.3 nm, a factor 3 deeper than the upper limit of Charbonneau et al (1999). For an assumed planet radius Rp = 1.2RJ, the upper limit on the mean geometric albedo is p < 0.22, 40% that of Jupiter. We find new evidence that the star's rotation is synchronised with the planet's orbital motion. Using a Monte Carlo analysis we infer that the planet's mass must lie in the range 5.5 to 10 times the mass of Jupiter.
A Search for the Spectroscopic Signature of Hot Jupiters
Authors: Lucas P. W. , Roche P. F.
Published: July 2016

We describe a method by which hot extrasolar planets close to their parent star may be directly detected through the signature of water vapour or methane in their infrared spectra, lying on top of the spectrum of the parent star. Upper limits derived from low resolution K band spectra of several ‘hot Jupiter’ systems are presented. We find no water vapour to 3-σ limits of between 1 part in 200 and 1 part in 600 for each star. Comparison with an initial model indicates that constraints can be set on the size, albedo, temperature and dust content of the planets.
Simulation and Modeling of Transit Eclipses by Planets
Authors: Milone E.F. , Williams M. D. , Stagg C. R. , McClure M.L. , Winmill B. Desnoyers , Brown T. , Charbonneau D. , Gilliland R. L. , Henry G. W. , Kallrath J. , Marcy G. W. , Terrell Dirk , VanHamme W.
Published: July 2016

Light curve analysis by MDW of the photometry and RV data accumulated to date on HD 209458 has made use of a simulations database created for an 8-day HST observing project led by RLG to look for transits in 47 Tuc. We report progress in developing a consistent set of parameters obtained with our versions of the Wilson-Devinney program, WD98 and wd98k93, specially modified to treat large grid sizes, corresponding to objects with radii exceeding 0.7RJ and masses greater than 0.1 MJ.

This work is supported in part by grants to EFM by Canadian NSERC and by the Univ. of Calgary Research Grants Committee.
ELODIE low-mass companions to solar-type stars
Authors: Naef D. , Mayor M. , Queloz D. , Udry S. , Arenou F. , Beuzit J.-L. , Perrier-Bellet C. , Sivan J.-P.
Published: July 2016

We present radial-velocity measurements for three solar-type stars (HD 127506, HD 174457 and HD 185414) hosting low-mass companions. The measurements were obtained with the ELODIE echelle spectrograph mounted on the 1.93–m telescope at Observatoire de Haute–Provence (CNRS, France) within the frame of the OHP-ELODIE Planet Search Programme. The inferred minimum masses of the detected companions are in the substellar mass range. Combining ELODIE radial-velocity data and HIPPARCOS astrometric data, the inclination angles of the orbital planes of HD 127506 and HD 174457 have been derived providing us with the de-projected masses of the companions: m2 = 44MJup for the companion of HD 127506 and m2= 0.13M⊙ for the companion of HD 174457. Moreover, using adaptive optics measurements, we show that HD 174457 is probably a (F8V + M7V + M3-4V) triple system. To date, only a minimal orbital solution is available for HD 185414.
Episodes of Emission Lines in the Spectra of Red Giants as Signatures of Remnant Planetary Systems
Authors: Rudnitskij G. M.
Published: July 2016

When a star with a mass of about 1 solar mass enters the red giant stage of its evolution, the radius of its atmosphere reaches several astronomical units. If the star possessed during its mainsequence life a planetary system, similar to the solar system, the planets will be embedded into a rather dense and hot medium. Effects of a planet revolving around a red giant at a short distance (inside its circumstellar envelope) are discussed. Systematic monitoring of the spectra of red giants may reveal periodicities in the emergence of shock-induced emission lines and thus to detect probable remnant planetary systems around these stars.
A Deep Optical Search for Substellar Candidates in the Nearby ρ Ophiuchi Star-Forming Region
Authors: Terebey S. , Van Buren D. , Jarrett T. H. , Gautier T. N.
Published: July 2016

We report preliminary results from a deep I-band optical search for substellar candidates in the p Oph star-forming region. The dusty molecular cloud provides an opaque screen at optical wavelengths, making the survey sensitive to faint substellar candidates near the cloud surface. Of the 89 objects detected in the oph A and oph C molecular cores, one third are substellar candidates.
Chemical Composition of Planet-harboring Stars
Authors: Zhao G. , Chen Y. Q. , Qiu H. M. , Tang S. K. , Li Z. W.
Published: July 2016

Based on the high-resolution, high signal-to-noise ratio spectra collected with the coudé echelle spectrograph attached to the 2.16m telescope at Beijing Astronomical Observatory, we determined the chemical abundance patterns for a sample of six planet-harboring stars. The result is used to investigate the connection between giant planet and high metallicity and to probe the influence of this process on other elements.
Reversing type II migration: resonance trapping of a lighter giant protoplanet
Authors: Masset F. S. , Snellgrove M. D.
Published: July 2016

We present new results related to the coupled evolution of a two giant planet system embedded in a protoplanetary disk, in which a Saturn mass protoplanet is trapped in an outer mean motion resonance with a Jupiter mass protoplanet. The gaps opened in the disk by the two planets overlap, therefore the two planet system exchanges angular momentum with the disk at the inner planet's Inner Lindblad Resonances (ILRs) and at the outer planet Outer Lindblad Resonances (OLRs). Since the torques are proportional to the square of the planet masses, and since the inner planet is about three times more massive than the outer one, the ILR torques are favored by a factor ∽ 10 with respect to the one planet case. In the case presented here, this leads to a positive differential Lindblad torque and consequently an outwards migration. We briefly discuss the long-term behavior of the system, which could account for the high eccentricities of the extra-solar planets with semimajor axis a > 0.2 AU.
A scattered Uranus and Neptune, and implications for the asteroid belt
Authors: Thommes Edward W. , Duncan Martin J. , Levison Harold F. , Chambers John E.
Published: July 2016

It has been proposed that Uranus and Neptune originated interior to ∽ 10 AU, as potential gas giant cores which were scattered outward when Jupiter won the race to reach runaway gas accretion. We present further numerical simulations of this scenario, which show that it reproduces the present configuration of the outer Solar System with a high degree of success for a wide range of initial conditions. Also, we show that this mechanism may have simultaneously ejected planets from the asteroid belt.
Modelling Planet Formation by Capture-Theory Interactions
Authors: Woolfson Michael M. , Oxley Stephen
Published: July 2016

Diffuse low-mass stars and brown dwarfs coexist with condensed solar-type stars in the embedded stage of a developing open cluster. It is shown by smoothed-particle-hydrodynamics modelling that interactions between stars and protostars leads to disruption of the protostar to form protoplanets that can then be captured by the star.
New Insights into Extrasolar Giant Planets
Authors: Burrows Adam
Published: July 2016

In this contribution, I summarize recent theoretical attempts to understand important diagnostic aspects of close-in extrasolar giant planets, in particular transits and albedos. The potential scientific returns of the anticipated direct detection of “EGPs” in transit and/or in reflection are significant.
Protoplanetary disc evolution in magnetically layered disc models
Authors: Armitage Philip J.
Published: July 2016

I discuss protoplanetary disc evolution under the assumption that magnetohydrodynamic turbulence and self-gravity are the sole sources of angular momentum transport. This assumption implies a magnetically layered disc structure which leads to unsteady accretion, and larger disc masses at late epochs. The resulting environment for planet formation and migration differs qualitatively from the highly simplified – almost toy – models often adopted.
Gas temperatures in Vega-type stars
Authors: Coulson Iain M. , Walther Dolores M. , Dent William R.F.
Published: July 2016

Further observations of the submillimetre CO lines in 3 Vega-type stars are reported and interpreted for the gas temperatures they imply. Very low gas temperatures (∽15K) are deduced for all three stars, consolidating the suggestion that, if the gas and dust are remnants of the molecular cloud from which the star system formed, then much of the CO in these systems may be locked up in ices on the surfaces of dust grains.
Spectral energy distributions and structures of debris discs
Authors: Dent W.R.F. , Wyatt M. C. , Holland W. S. , Greaves J. S. , Coulson I. M. , Walther D. M.
Published: July 2016

New photometry of main-sequence debris discs has been carried out at 850 and 450/μm; the derived SEDs indicate that the dust can lie in either thin rings or radially-extended discs, as seen directly in the few nearby objects which are resolvable. All such objects are consistent with a long wavelength opacity index β of 1.0±0.2 - similar to T Tauri stars, but significantly lower than embedded objects.
Stellar Rotation and Disks in the Orion Nebula Cluster
Authors: Herbst W. , Bailer-Jones C. A. L. , Mundt R. , Meisenheimer K. , Wackermann R.
Published: July 2016

The new Wide Field Imager attached to the MPG/ESO 2.2 m telescope on La Silla, Chile, has been used to monitor ∽2000 stars in the Orion Nebula Cluster (ONC) at 815 nm on 45 nights between 25 Dec 1998 and 28 Feb 1999. Over 400 periodic variables have been found, most or all of which are rotating, spotted T Tauri stars (TTS), more than doubling the number of known rotation periods for cluster members. Masses and ages are available for 335 of these from the literature. We confirm the existence of a bimodal period distribution for stars with M > 0.25 M⊙. A surprising new result is that stars of lower mass tend to rotate faster than higher mass stars, perhaps indicating that their disks have dissipated more rapidly in the harsh cluster environment. In the mass range 0.1 − 1 M⊙ between 40% and 80% of the stars have the variability characteristics of weak-line TTS (WTTS), suggesting that the half-life for accretion disks is ∽1 Myr in this cluster and probably even smaller for the lower mass stars.
The Nature of the Dust Disc Surrounding BD+31°643
Authors: Wolstencroft Ramon D. , Andersson B-G , Draper Peter W. , Moriarty-Schieven Gerald , Stockdale David P. , Wannier Peter
Published: July 2016

Multicolour imaging polarimetry of the main sequence star BD+31°643 shows that the Kalas & Jewitt (1997) disc extends to at least 13000AU. A disc of this radius must be dynamically very young compared to the central star, unlike the situation found in the β Pictoris system. A striking linear filament of 850μm emission detected 50″ south, that parallels the dust disk, is probably not physically associated.
Observing Extrasolar Planetary Systems with ALMA
Authors: Butler B. J. , Wootten A. , Brown R. L.
Published: July 2016

The next generation millimeter to submillimeter wavelength synthesis telescope, the Atacama Large Millimeter Array (ALMA), is an excellent instrument for direct and indirect detection of extrasolar giant planets and imaging of extrasolar planetary systems at all evolutionary stages. We examine some possibilities of ALMA in this respect here.
The DARWIN project – An ESA cornerstone candidate mission
Authors: Fridlund C.V.M.
Published: July 2016

The DARWIN project is ESA's candidate mission for the search for extra-solar Earth-type planets. Its aims are to survey the closest stars for these planets, and if detected characterise them as what concerns their physical conditions, their atmospheric composition and their ability to host life as we know it.
Why AGN Studies Need Higher Resolution
Authors: Rees Martin J.
Published: July 2016

The need for high angular resolution is emphasised, especially in the context of programs to understand massive black holes and the processes in their environment.
The 6.4 keV Fe Line and the SiO Emission in the GC
Authors: Martín-Pintado J. , de Vicente P. , Rodríguez-Fernández N. , Fuente A. , Planesas P.
Published: July 2016

We present a map of the Galactic center in the J=l-0 line of SiO covering the region mapped with the ASCA satellite in the 6.4 keV Fe line. We find a correlation between the spatial distribution of the Fe 6.4 keV line and the SiO emission. The SiO abundance increases by more than a factor of 20 in the regions with strong Fe 6.4 keV line. This indicates that the Fe 6.4 keV line mainly arises from molecular clouds with large gas phase abundance of refractory elements. We discuss the implications of the correlation on the origin of the hard X-rays, and the heating and the chemistry of the molecular clouds in the GC.
Intrinsic Intraday Variability in the Gravitational Lens System B0218+357
Authors: Biggs Andrew , Browne Ian , Wilkinson Peter
Published: July 2016

Radio monitoring of the gravitational lens system B0218+357 reveals it to be a highly variable source with variations on timescales of a few days correlated in both images. This shows that the variability is intrinsic to the background lensed source and suggests that similar variations in other intraday variable sources can also be intrinsic in origin.
VLBI Observations of Extragalactic TeV Gamma-ray Sources
Authors: Edwards P.G. , Piner B.G. , Fodor S.
Published: July 2016

VLBI observations of reported TeV gamma-ray sources are described and the inferences that can be drawn on the jet behaviour between the TeV variability-scale and the VLBI parsec-scale discussed.
VLBA λλ6,4 cm Polarimetry of Vir A
Authors: Junor William , Biretta John A. , Wardle John F. C.
Published: July 2016

The results of polarimetric λλ6,4 cm VLBA observations of the inner 5pc of the jet and core of Vir A (3C274, J1230+1223) are reported. At λ4 cm, the core and the inner parsec are unpolarized and there is evidence for ordered magnetic fields and large RM gradients at larger distances.
The Central Kiloparsec-Scale Structure of Galaxies
Authors: van der Marel Roeland P.
Published: July 2016

This review summarizes some aspects of the central kiloparsec scale structure of galaxies, and in particular spiral galaxies, elliptical galaxies and merger remnants. The focus is on results from optical and near-IR imaging and spectroscopy, with emphasis on recent work with the Hubble Space Telescope.
Intrinsic Shape of Elliptical Galaxy NGC 661
Authors: Chakraborty D.K. , Das Mousumi , Thakur Parijat
Published: July 2016

We investigated the intrinsic shape of the luminosity density of the triaxial galaxy NGC 661 by comparing its observed profiles of photometric parameters with the projected surface brightness of model galaxies. We examined NGC 661 which shows a small scale variation in the ellipticity profile at ∼ 0.3 re. We suggest complex form of density distributions which might explain it.
High Resolution Observations of Sub-Kiloparsec Circumnuclear Gas in AGN
Authors: Conway J.E.
Published: July 2016

In recent years it has become possible to use high resolution radio interferometry and other techniques to study the sub-kiloparsec scale circumnuclear gas in the centres of Active Galactic Nuclei. This gas presumably provides the fuel source for the AGN activity and also plays a role in obscuring the direct view of the central engine from certain directions. The status of high resolution observations of the ionised, atomic and molecular phases of this circumnuclear gas are briefly reviewed.
Probing the Heart of an Active Galactic Nucleus: NGC 1068
Authors: Tecza Matthias , Thatte Niranjan , Maiolino Roberto
Published: July 2016

We present results from integral field spectroscopy of the narrow line region of NGC 1068, carried out with the MPE 3D near infrared imaging spectrometer. A map and velocity field of the [Fe II] fine structure line at 1.64μm is presented. The kinematics of the [Fe II] emission, which arises in partially ionized zones, shows red shifted emission in the north eastern cone of the NLR, and blue shifted emission in the south west, reversed relative to high ionization species such as [Si vI] or [O III]. We propose a model geometry of the narrow line region which is consistent with existing data and explains the observed [Fe II] kinematics.
ISOGAL and 2MASS Study of the Central Regions of Our Galaxy
Authors: Ojha D.K. , Omont A. , Ganesh S. , Team Isogal
Published: July 2016

We report the study of ISOGAL fields in the outer galactic bulge (-1.5° < l < +1.6°, −2.6° < b < + 6.0°, area ∼ 0.42 deg2). We have combined 15 μm and 7 μm ISOCAM observations with 2MASS JHKS data to determine the nature of the sources and the interstellar extinction. Most of the ISOGAL sources show evolution of mass-loss rates in the range 3×10−8 to 1 × 10−6 (M⊙/year). Most of the detected sources are red giants above the RGB tip; a few of them show an excess in J-Ks and Ks-[15] colors. These sources are AGB stars with large mass-loss rates.
Identifying Large Scale Features on the Surface of Contact Binaries with Sub-Arcsecond Techniques
Authors: Niarchos P.G. , Pustylnik I.
Published: July 2016

We summarize multifold evidence for the presence of a hot spot region in contact binary VW Cephei. We interpret this feature as a photospheric burn and the preferential site of flares in EUV and X rays. With its trigonometric parallax of 0.041 arcsec VW Cep is a promising target for a milliarcsecond resolution investigation of the nature of surface features both in optical region and in IR.
VLBI Imaging and Astrometry of the RS CVn Binary Star IM Pegasi
Authors: Lebach D.E. , Ratner M.I. , Shapiro I.I. , Ransom R.R. , Bartel N. , Bietenholz M.F. , Lestrade J.-F.
Published: July 2016

We have made 3.6 cm VLBI observations of the RS CVn binary star IM Pegasi (HR 8703) approximately four times per year since 1997 in support of the NASA/Stanford Relativity Gyroscope Experiment (Gravity Probe B). Phase-referenced maps reveal structural changes in the radio emission of the star on hour time scales during several of the sessions. Analyses of the VLBI phase delays with a Kalman-filter estimator reveal submilliarcsecond motions of the radio centroid of the star on hour and even subhour time scales. The observed structural changes and centroid motions often coincide with rapid changes in the star's flux density, as measured with the VLA. We report on our latest results and summarize our findings to date.
Megamasers and their Host Galaxies
Authors: Baan Willem A.
Published: July 2016

The variety of molecular megamasers trace different classes of galaxies and provide information on their various nuclear components. H2O megamaser regions may trace the inner parsec-scale regions with keplerian disks of the LINER and Seyfert 2 nuclei, which are relatively naked and not dominated by dust or starforming regions. The OH and H2CO megamaser emissions exhibit the physics and dynamics of the inner few hundred parsecs of ultra-luminous FIR galaxies, which are dusty, compact, and whose perturbed nuclei are powered by compact starbursts.
BIMA Sub-arcsecond Carbon Monoxide Observations: Resolving the Inner kpc Region of the QSO I Zw 1
Authors: Staguhn Johannes , Schinnerer Eva , Eckart Andreas
Published: July 2016

We present the first sub-kpc (∼ 0.7 ≈ 0.8 kpc) resolution 12CO(1–0) observations of the ISM in the host galaxy of the QSO I Zw 1 which were obtained with the BIMA mm-interferometer in its A configuration. The measurements, which are part of a multi-wavelength study of I Zw 1, will allow comparison of the ISM properties of a QSO host with those of nearby galaxies and place constraints on galaxy formation/evolution models. Our maps of the 12CO(1–0) line emission from the host galaxy of a QSO show a ring-like structure in the circumnuclear molecular gas distribution with a radius of about 900 pc. The presence of such a molecular gas ring was already predicted from earlier lower angular resolution PdBI observations (Schinnerer, Eckart, & Tacconi 1998). A first comparison of the BIMA data with new PdBI 12CO(2–1) observations with 0.9 angular resolution shows variations in the excitation conditions of the molecular gas in the innermost 3 comprising the nuclear region of I Zw 1.
Extragalactic Supernovae and the Starformation Rate
Authors: Pedlar Alan
Published: July 2016

The advantages of studying samples of supernova remnants in external galaxies will be discussed. A summary of how the remnants can be used to infer starformation rates in starburst galaxies will be given, as will the use of these remnants to probe the interstellar medium of these galaxies on parsec scales. Widefield EVN and Global VLBI measurements of remnants in the nearby starburst in M82 will be described in detail, and recent expansion velocity measurements described. The similarity between the strongest compact source in M82 and the objects recently discovered in Arp220 will be noted. The sensitivity limitations of this work will be discussed and the prospects for studies of more distant objects using Square Kilometer Array considered.
Asymmetric Supernova Explosion Investigated by Geodetic Precession
Authors: Kramer M. , Wex N. , Kalogera V. , Karastergiou A.
Published: July 2016

We use observations and modelling of geodetic precession in the PSR B1913+16 system to obtain direct constraints on direction and magnitude of kicks imparted to the pulsar companion during the most recent supernova explosion. We find that the kick must have been directed almost perpendicular to the rotation axis of the progenitor star.
Prospects for High Angular Resolution Instrumentation at Millimeter and Submillimeter Wavelengths
Authors: Menten Karl M.
Published: July 2016

Millimeter- and submillimeter wavelength interferometry is a powerful technique allowing imaging of dust and molecules in a multitude of astronomical environments. With the arrival of the Atacama Large Millimeter Array (ALMA), such studies will be possible with unprecedented sensitivity and a spatial resolution similar to the diffraction limit of large optical/infrared telescopes. In this paper, we mention a few aspects of (sub) millimeter astronomy and provide a short summary of ALMA's capabilities.
The Science Potential of Far-IR/Sub-mm Interferometry and Concepts for the SPIRIT and SPECS Missions
Authors: Leisawitz David ,   the Far-IR Interferometry Mission Study Working Group
Published: July 2016

The FIR/SMM region is unique in the electromagnetic spectrum in its potential for vast increases in sensitivity and angular resolution, and, as a result, information vital to our understanding of the evolution of structure in the universe. About half of the luminosity in the universe is emitted in the far infrared. Evidence for this can be found both in the spectra of individual galaxies (Trentham et al. 1999) and in the cosmic FIR/SMM background found by COBE (Hauser et al. 1998; Fixsen et al. 1998; Dwek et al. 1998). JCMT/SCUBA observations suggest that “a large population of luminous, strongly obscured sources at redshifts ≲5 is missing from optical surveys” and could account for the background radiation (Blain et al. 1999). Future FIR/SMM measurements of these sources have the potential to reveal the luminosity history of the universe and will provide insight into the processes of galaxy and star formation and galaxy evolution.
Optical and Infrared Interferometry
Authors: Bedding Timothy R.
Published: July 2016

Interferometric techniques are at the forefront of modern astronomical instrumentation. A new generation of instruments are either operating or nearing completion, including arrays of small telescopes as well as the “big guns” (VLTI and Keck). A number of space interferometers for the detection of extra-solar planets are also being planned. I will review the current state of play and describe the latest developments in the field.
Ultra-Cool Very Low-Mass Binaries
Authors: Martín Eduardo L. , Basri Gibor
Published: July 2016

Observations of ultra-cool (spectral type later than M6) binaries are summarized. Only a few systems are known, and all have been discovered in the past few years. We describe each of these discoveries. Despite their small numbers, some interesting trends among the binaries may be emerging. Ultra-cool binaries have a frequency similar to but perhaps a little less than stars (binary fraction ∼20%) and have mass ratios closer to unity, with respect to solar-type stars. Neither of these results can be considered firm, as there are far too few systems known, and observational biases would tend to move trends in these directions. There also seems to be a trend towards smaller separations in lower mass systems, which is less subject to observational biases. We discuss how these results fit into current ideas about binary formation, and favor a fragmentation scenario.
Wolf-Rayet Binaries
Authors: van der Hucht Karel A. , Hidayat Bambang
Published: July 2016

A WR binary frequency of 37% is found in the VIIth Catalogue of Galactic Wolf-Rayet Stars. Indications are that perhaps all WR stars are binaries and thus that all WR stars point to massive binary formation regions.