bluuebunny/crossref_metadata_2025 huggingface dataset:
τ Sco: the discovery of the clones
Authors: Petit Véronique , Massa Derck L. , Marcolino Wagner L. F. , Wade Gregg A. , Ignace Richard ,   the MiMeS Collaboration
Published: July 2011

The B0.2 V magnetic star τ Sco stands out from the larger population of massive magnetic OB stars due to its remarkable, superionized wind, apparently related to its peculiar magnetic field – a field which is far more complex than the mostly-dipolar fields usually observed in magnetic OB stars. τ Sco is therefore a puzzling outlier in the larger picture of stellar magnetism – a star that still defies interpretation in terms of a physically coherent model.

Recently, two early B-type stars were discovered as τ Sco analogues, identified by the striking similarity of their UV spectra to that of τ Sco, which was – until now – unique among OB stars. We present the recent detection of their magnetic fields by the MiMeS collaboration, reinforcing the connection between the presence of a magnetic field and a superionized wind. We will also present ongoing observational efforts undertaken to establish the precise magnetic topology, in order to provide additional constrains for existing models attempting to reproduce the unique wind structure of τ Sco-like stars.
Magnetic fields, winds and X-rays of massive stars in the Orion nebula cluster
Authors: Petit Véronique , Wade Gregg A. , Alecian Evelyne , Drissen Laurent , Montmerle Thierry , ud-Doula Asif
Published: July 2011

In some massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind. Although theoretical models and MHD simulations are able to illustrate the dynamics of such a magnetized wind, the impact of this wind-field interaction on the observable properties of a magnetic star - X-ray emission, photometric and spectral variability - is still unclear. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars, by providing empirical observations and confronting theory. In conjunction with the COUP survey of the Orion Nebula Cluster, we carried out spectropolarimatric ESPaDOnS observations to determine the magnetic properties of massive OB stars of this cluster.
Monte-Carlo simulations of linear polarization in clumpy OB-star winds
Authors: Townsend Richard H. D. , Mast Nick
Published: July 2011

We present results from Monte-Carlo simulations of linear polarization in clumped OB-star winds. We find that previous single-scattering models of clumped winds have overestimated the degree of polarization, even in cases where individual clumps are optically thin. An application to P Cygni suggests the star's wind is more fragmented than previously thought.
Measurements of magnetic fields in Herbig Ae/Be stars and stars with debris disks at the VLT 8-m telescope: statistical results of our long-term program
Authors: Yudin Ruslan V. , Hubrig Swetlana , Pogodin Michail A. , Schoeller Markus , Ilyin Ilya
Published: July 2011

We present the results of magnetic field measurements for a sample of 23 young Herbig Ae/Be (HAEBEs) stars and 12 stars with debris disks. The spectropolarimetric data were obtained during four observing runs in 2003-2008 at the European Southern Observatory with the multi-mode instrument FORS 1 installed at the 8 m Kueyen telescope. Among the 23 HAEBEs studied, stellar magnetic fields of about 100-150G have been detected in 11 stars (i.e. ~50%). The presence of circumstellar polarization signatures formed in the stellar wind supports the assumption that the magnetic centrifuge is one of the main mechanisms of the wind acceleration. No field detection at a significance level of 3σ was achieved in stars with debris disks.
Massive stars in globular clusters: drivers of chemical and dynamical evolution
Authors: Decressin Thibault
Published: July 2011

Massive stars have a strong impact on globular cluster evolution. First providing they rotate initially fast enough they can reach the break-up velocity during the main sequence and a mechanical mass-loss will eject matter from the equator at low velocity. Rotation-induced mixing will also bring matter from the convective core to the surface. From this ejected matter loaded in H-burning material a second generation of stars will born. The chemical pattern of these second generation stars are similar to the one observed for stars in globular cluster with abundance anomalies in light elements. Then during the explosion as supernovae the massive stars will also clear the cluster of the remaining gas. If this gas expulsion process acts on short timescale it can strongly modify the dynamical properties of clusters by ejecting preferentially first generation stars.
Populations of OB-type stars in galaxies
Authors: Evans Christopher J.
Published: July 2011

One of the challenges for stellar astrophysics is to reach the point at which we can undertake reliable spectral synthesis of unresolved populations in young, star-forming galaxies at high redshift. Here I summarise recent studies of massive stars in the Galaxy and Magellanic Clouds, which span a range of metallicities commensurate with those in high-redshift systems, thus providing an excellent laboratory in which to study the role of environment on stellar evolution. I also give an overview of observations of luminous supergiants in external galaxies out to a remarkable 6.7 Mpc, in which we can exploit our understanding of stellar evolution to study the chemistry and dynamics of the host systems.
Infrared properties of active OB stars in the Magellanic Clouds from the Spitzer SAGE survey
Authors: Bonanos Alceste Z. , Lennon Danny J. , Massa Derck L. , Sewilo Marta , Köhlinger Fabian , Panagia Nino , van Loon Jacco Th. , Evans Chris J. , Meixner Margaret , Gordon Karl D. ,   the SAGE teams
Published: July 2011

We present a study of the infrared properties of 4922 spectroscopically confirmed massive stars in the Large and Small Magellanic Clouds, focusing on the active OB star population. Besides OB stars, our sample includes yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the red, and find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We also find photometric variability among the active OB population and evidence for transitions of Be stars to B stars and vice versa. We furthermore confirm the presence of dust around all the supergiant B[e] stars in our sample, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs.
The B[e] phenomenon in the Milky Way and Magellanic Clouds
Authors: Miroshnichenko Anatoly S. , Manset Nadine , Polcaro Francesco , Rossi Corinne , Zharikov Sergey
Published: July 2011

Discovered over 30 years ago, the B[e] phenomenon has not yet revealed all its puzzles. New objects that exhibit it are being discovered in the Milky Way, and properties of known objects are being constrained. We review recent findings about objects of this class and their subgroups as well as discuss new results from studies of the objects with yet unknown nature. In the Magellanic Clouds, the population of such objects has been restricted to supergiants. We present new candidates with apparently lower luminosities found in the LMC.
B stars in open clusters: fundamental parameters
Authors: Aidelman Yael , Cidale Lydia S. , Zorec Juan , Arias María L.
Published: July 2011

We use the BCD spectrophotometric classification system to derive fundamental parameters of B stars in NGC 2439, NGC 3766 and NGC 6087. We are able to perform a complete study of each open cluster by deriving spectral classification of its members, distance modulus and age as well.
Analyzing the δ Sco binary in anticipation of a disk-star collision
Authors: Ames Ashley , Tycner Christopher , Zavala Robert
Published: July 2011

A current investigation is underway into the possible collision between a circumstellar disk and the secondary star in the δ Scorpii binary system. δ Scorpii is a prime candidate for a disk-star collision since the primary star has a circumstellar disk and the secondary star has a highly elliptical orbit with a period of approximately 10.5 years making the periastron passage very close to the primary star. The Navy Prototype Optical Interferometer (NPOI) was used to spatially resolve the two stars as well as the cirumstellar disk around the primary. A revised orbit with new orbital parameters has been calculated using observations obtained between 2005 and 2010. Our results indicate periastron passage will occur on 2011-07-03.
Multicolour studies of β Cephei stars in the LMC
Authors: Engelbrecht Chris A. , Frescura Fabio A. M. , Moonsamy Sashin L.
Published: July 2011

Preliminary results of a four-week multi-colour photometric campaign on previously identified β Cephei stars as well as newly-discovered variable stars in two respective LMC fields are presented. Besides the two targeted β Cephei stars, at least six further presumed B variables are detected. The strongest identified periods appear to lie on the longward end of the galactic β Cep instability strip, as predicted by model calculations.
Spectroscopic Hα and Hγ survey of field Be stars: 2004–2009
Authors: Grundstrom Erika D. , Gies Douglas R. , Aragona Christina , Boyajian Tabetha S. , Garcia E. Victor , Marsh Amber N. , McSwain M. Virginia , Roettenbacher Rachael M. , Williams Stephen J. , Wingert David W.
Published: July 2011

Massive O- and B-type stars are “cosmic engines” in the Universe and can be the dominant source of luminosity in a galaxy. The class of Be stars are rapidly rotating B-type stars that lose mass in an equatorial, circumstellar disk (Porter & Rivinius 2003) and cause Balmer and other line emission. Currently, we are unsure as to why these stars rotate so quickly but three scenarios are possible: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence evolution of B stars. In order to investigate these scenarios for this population of massive stars, we have been spectroscopically observing a set of 115 field Be stars with the Kitt Peak Coudè Feed telescope in both the Hα and Hγ wavelength regimes since 2004. This time baseline allows for examination of variability properties of the circumstellar disks as well as determine candidates for closer examination for binarity. We find that 90% of the observed stars show some variability with 8% showing significant variability over the 5-year baseline. Such values may be compared with the significant variability seen in some clusters such as NGC 3766 (McSwain 2008). Also, while ~20% of the sample consists of known binaries, we find that another 15–30% of the sample shows indications of binarity.
Massive Oe/Be stars at low metallicity: candidate progenitors of long GRBs?
Authors: Martayan Christophe , Baade Dietrich , Zorec Juan , Frémat Yves , Fabregat Juan , Ekström Sylvia
Published: July 2011

At low metallicity B-type stars rotate faster than at higher metallicity, typically in the SMC. As a consequence, a larger number of fast rotators is expected in the SMC than in the Galaxy, in particular more Be/Oe stars. With the ESO-WFI in its slitless mode, we examined the SMC open clusters and found an occurence of Be stars 3 to 5 times larger than in the Galaxy. The evolution of the angular rotational velocity seems to be the main key on the understanding of the specific behaviour and stellar evolution of such stars at different metallicities. With the results of this WFI study and using observational clues on the SMC WR stars and massive stars, as well as the theoretical indications of long gamma-ray burst progenitors, we identify the low metallicity massive Be and Oe stars as potential LGRB progenitors. Therefore the expected rates and numbers of LGRB are calculated and compared to the observed ones, leading to a good probability that low metallicity Be/Oe stars are actually LGRB progenitors.
A spectroscopic study of Be-like variable stars in the Small Magellanic Cloud
Authors: Sabogal Beatriz , García-Varela Alejandro , Mennickent Ronald E.
Published: July 2011

Photometric searches for Be stars in environments with different metallicities have led to the discovery of many Be-like star variables. The knowledge of these types of variables is still fragmentary. This work presents the preliminary results of analyzing FLAMES+GIRAFFE spectra of a sample of these Be-like stars that we have found in the Small Magellanic Cloud (SMC).
The circumstellar discs of Be stars
Authors: Carciofi Alex C.
Published: July 2011

Circumstellar discs of Be stars are thought to be formed from material ejected from a fast-spinning central star. This material possesses large amounts of angular momentum and settles in a quasi-Keplerian orbit around the star. This simple description outlines the basic issues that a successful disc theory must address: 1) What is the mechanism responsible for the mass ejection? 2) What is the final configuration of the material? 3) How the disc grows? With the very high angular resolution that can be achieved with modern interferometers operating in the optical and infrared we can now resolve the photosphere and immediate vicinity of nearby Be stars. Those observations are able to provide very stringent tests for our ideas about the physical processes operating in those objects. This paper discusses the basic hydrodynamics of viscous decretion discs around Be stars. The model predictions are quantitatively compared to observations, demonstrating that the viscous decretion scenario is currently the most viable theory to explain the discs around Be stars.
Dust formation of Be stars with large infrared excess
Authors: Lee Chien-De , Chen Wen-Ping
Published: July 2011

Classical Be stars, in addition to their emission-line spectra, are associated with infrared excess which is attributable to free-free emission from ionized gas. However, a few with exceptionally large near-infrared excess, namely with J–H, and H–Ks both greater than 0.6 mag—and excess emission extending to mid- and far-infrared wavelengths—must be accounted for by thermal emission from circumstellar dust. Evolved Be stars on the verge of turning off the main sequence may condense dust in their expanding cooling envelopes. The dust particles should be very small in size, hence reprocess starlight efficiently. This is in contrast to Herbig Ae/Be stars for which the copious infrared excess arises from relatively large grains as part of the surplus star-forming materials.
Nebulae around Luminous Blue Variables – large bipolar variety
Authors: Weis Kerstin
Published: July 2011

During the LBV phase—a short transitional phase of only the very massive stars—strong stellar winds sometimes accompanied by eruptions form small circumstellar LBV nebulae around a substantial number of LBV stars. Analyzing the morphology and and kinematics of the LBV nebulae even weakly bipolar components can be detected, leading to the conclusion that about 50% have—to some degree—a bipolar structure. A global overview of our current observational knowledge of LBV nebulae is summarized, including their morphology, sizes and kinematic parameters.
Discussion – Circumstellar environment of active OB stars
Authors: Gies Douglas R. , Townsend Richard H. D.
Published: July 2011

This session dealt with the circumstellar gas surrounding active OB stars, and the discussion broadly focused on disks, wind morphology and structures, X-ray emission, and mass loss rates.
Spectral variation of BU Tau
Authors: Annuk Kalju
Published: July 2011

We present the preliminary result of our spectroscopic observations covering a period over more than ten years, from 1999 up to 2010. We analyze line profile variations of several lines before the shell phase and during the shell phase. The measured radial velocity, equivalent width and line intensity variations are presented.
FRACS: modelling of the dust disc of the B[e] CPD-57° 2874 from VLTI/MIDI data
Authors: Bendjoya Philippe , de Souza Armando Domiciano , Niccolini Gilles
Published: July 2011

The physical interpretation of spectro-interferometric data is strongly model dependent. On one hand, models involving elaborate radiative transfer solvers are in general too time consuming to perform an automatic fitting procedure and derive astrophysical quantities and their related errors. On the other hand, using simple geometrical models does not give sufficient insights into the physics of the object. We developed a numerical tool optimised for mid-infrared (mid-IR) interferometry, the Fast Ray-tracing Algorithm for Circumstellar Structures (FRACS). Thanks to the short computing time required by FRACS, best-fit parameters and uncertainties for several physical quantities were obtained, such as inner dust radius, relative flux contribution of the central source and of the dusty CSE, dust temperature profile, disc inclination.
The dynamical evolution of Be star disks
Authors: Haubois Xavier , Carciofi Alex C. , Okazaki Atsuo T. , Bjorkman Jon E.
Published: July 2011

We present a novel theoretical tool to analyze the dynamical behaviour of a Be disk fed by non-constant decretion rates. It is mainly based on the computer code HDUST, a fully three-dimensional radiative transfer code that has been successfully applied to study several Be systems so far, and the SINGLEBE code that solves the 1D viscous diffusion problem. We have computed models of the temporal evolution of different types of Be star disks for different dynamical scenarios. By showing the behaviour of a large number of observables (interferometry, polarization, photometry and spectral line profiles), we show how it is possible to infer from observations some key dynamical parameters of the disk.
Near-infrared excess and emission characteristics of classical Be stars
Authors: Lee Chien-De , Chen Wen-Ping , Kinoshita Daisuke
Published: July 2011

Classical Be (CBe) stars are fast-rotating emission-line stars associated with infrared excess often attributed to plasma free-free emission. A few with exceptionally large near-infrared excess, namely with (J–H) and (H–Ks) both greater than 0.6 mag, however, must be accounted for by thermal emission from circumstellar dust. From 2007 to 2009, spectra of more than 100 CBe stars have been collected. We present some of these spectra and discuss how temporal correlation (or lack of) among spectral features would provide possible diagnosis of the origin of the CBe phenomena.
Resolving the dusty circumstellar environment of the A[e] supergiant HD 62623 with the VLTI/MIDI
Authors: Meilland Antony , Kanaan Sameer , Fernandes Marcelo Borges , Chesneau Olivier , Millour Florentin , Stee Philippe , Lopez Bruno
Published: July 2011

HD 62623 is one of the very few A-type supergiants showing the B[e] phenomenon. We studied the geometry of its circumstellar envelope in the mid-infrared using the VLTI/MIDI instrument. Using the radiative transfer code MC3D, we managed to model it as a dusty disk with an inner radius of 3.85 AU, an inclination angle of 60°, and a mass of 2 × 10−7M⊙. It is the first time that the dusty disk inner rim of a supergiant star exhibiting the B[e] phenomenon is significantly constrained. The inner gaseous envelope likely contributes up to 20% to the total N band flux and acts like a reprocessing disk. Finally, the hypothesis of a stellar wind deceleration by the companion gravitational effect remains the most probable case since the bi-stability mechanism is not efficient for this star.
Variability monitoring of OB stars during the Mons campaign
Authors: Morel Thierry , Rauw Gregor , Eversberg Thomas , Alves Filipe , Arnold Wolfgang , Bergmann Thomas , Viegas Nelson G. Correia , Fahed Rémi , Fernando Alberto , Carreira Luis F. Gouveia , Hunger Thomas , Knapen Johan H. , Leadbeater Robin , Dias Filipe Marques , Moffat Anthony F. J. , Reinecke Norbert , Ribeiro José , Romeo Nando , Gallego José Sánchez , dos Santos Eva M. , Schanne Lothar , Stahl Otmar , Stober Barbara , Stober Berthold , Vollmann Klaus , Corcoran Mike F. , Dougherty Sean M. , Hamaguchi Kenji , Pittard Julian M. , Pollock Andy M. T. , Williams Peredur M.
Published: July 2011

We present preliminary results of a 4-month campaign carried out in the framework of the Mons project, where time-resolved Hα observations are used to study the wind and circumstellar properties of a number of OB stars.
Hα spectropolarimetry of GG Car
Authors: Pereyra Antonio , de Araújo Francisco X. , Magalhães Antonio M. , Fernandes Marcelo Borges , de Souza Armando Domiciano
Published: July 2011

We present spectropolarimetric observations of the B[e] supergiant star GG Car at two epochs. Polarization line effects along Hα are analysed using the Q–U diagram. In particular, the polarization position angle (PA) obtained using the line effect allows to constrain the symmetry axis of the disk/envelope. The depolarization line effect around Hα is evident in the Q–U diagram for both epochs, confirming that light from the system is intrinsically polarized. A rotation of the PA along Hα is also observed, indicating a counter-clockwise rotating disk. The intrinsic PA calculated using the line effect (~85°) is consistent between our two epochs, suggesting a clearly defined symmetry axis of the disk.
The spectral variations of MWC 314
Authors: Rossi Corinne , Frasca Antonio , Marilli Ettore , Friedjung Michael , Muratorio Gérard
Published: July 2011

New spectra of MWC314 are presented; they indicate that the V/R emission line flux ratios show signs of varying in an opposite way to the absorption line radial velocities. The latter appear to be due to apparently non-periodic pulsations, perhaps in strange modes.
Spectral synthesis for Be stars
Authors: Sigut T. A. Aaron
Published: July 2011

A new monochromatic imaging and spectral synthesis package for Be stars, based on the bedisk code, is introduced. Example images and spectra are given for for H i and Fe ii. Predicted Fe ii equivalents widths are also compared to recent observations by Arias et al. (2006) and show good agreement, although only for very dense disks.
Do the γ Cas X-rays come from the Be Star?
Authors: Smith Myron A. , de Oliveira R. Lopes
Published: July 2011

We discuss the origin of the hard X-rays in γ Cas and its analogs. Of great importance are their temporal correlations with optical/UV signatures, suggesting an origin near the Be star.
The 2008+ outburst of the Be star 28 CMa - a multi-instrument study
Authors: Štefl Stan , Carciofi Alex C. , Baade Dietrich , Rivinius Thomas , Otero Sebastian , Le Bouquin Jean-Baptiste , Fabregat Juan , Okazaki Atsuo T. , Rantakyrö Fredrik
Published: July 2011

Optical and IR spectra, optical to sub-mm photometry, visual imaging polarimetry, and IR high-resolution spectro-interferometry are being used to monitor the new outburst of 28 CMa, which started in 2008 and so far closely resembles previous ones. First modeling based on viscous decretion and focused on constraining the disk viscosity parameter, α, is presented.
Asteroseismic observations of OB stars
Authors: De Cat Peter , Uytterhoeven Katrien , Gutiérrez-Soto Juan , Degroote Pieter , Simón-Díaz Sergio
Published: July 2011

The region of the hot end of the main-sequence is hosting pulsating stars of different types and flavours. Pulsations are not only observed for Slowly pulsating B stars (mid to late B-type stars; high order g-modes) and β Cephei stars (early B-type stars; low order p/g-modes) but are also causing variability in Be stars and OB-supergiants. In this review we give an overview of the asteroseismic observations that are currently available for these types of stars. The first asteroseismic results were solely based on ground-based observations. Recently, the arrival of space-based data gathered by space missions like most, corot and kepler has led to important discoveries for massive stars, highlighting their excellent asteroseismic potential. We show that, despite the unprecedented precision of the space-based data, there is still a clear need for ground-based follow-up observations.
Evolutionary models of binaries
Authors: van Rensbergen Walter , Mennekens Nicki , de Greve Jean-Pierre , Jansen Kim , de Loore Bert
Published: July 2011

We have put on CDS a catalog containing 561 evolutionary models of binaries: J/A+A/487/1129 (Van Rensbergen+, 2008). The catalog covers a grid of binaries with a B-type primary at birth, different values for the initial mass ratio and a wide range of initial orbital periods. The evolution was calculated with the Brussels code in which we introduced the spinning up and the creation of a hot spot on the gainer or its accretion disk, caused by impacting mass coming from the donor. When the kinetic energy of fast rotation added to the radiative energy of the hot spot exceeds the binding energy, a fraction of the transferred matter leaves the system: the evolution is liberal during a short lasting era of rapid mass transfer. The spin-up of the gainer was modulated using both strong and weak tides. The catalog shows the results for both types. For comparison, we included the evolutionary tracks calculated with the conservative assumption. Binaries with an initial primary below 6 M⊙ show hardly any mass loss from the system and thus evolve conservatively. Above this limit differences between liberal and conservative evolution grow with increasing initial mass of the primary star.
Discussion – Periodic variations and asteroseismology of active OB stars
Authors: Rivinius Thomas , Fabregat Juan
Published: July 2011

We summarize the discussion held after the session on periodic variations and asteroseismology. The session not only included seven talks, but as well thirty excellent posters were shown. It was impossible to summarize all these in the available frame of a discussion, and so this work focuses on very few sub-topics only mentioned in the actual discussion session. These topics were the relation of pulsation and turbulence, pulsation in close binaries, the observed photometric variability, the connection of pulsations and outburst, and bipolar flows.
Non-radial pulsations in the Be/X binaries 4U 0115+63 and SAX J2103.5+4545
Authors: Gutiérrez-Soto Juan , Reig Pablo , Fabregat Juan , Fox-Machado Lester
Published: July 2011

The discovery of non-radial pulsations (NRP) in the Be/X binaries of the Magellanic Clouds (MC, eg. Fabrycky 2005, Coe et al. 2005, Schmidtke & Cowley 2005) provided a new approach to understand these complex systems, and, at the same time, favoured the synergy between two different fields: stellar pulsations and X-ray binaries. This breakthrough was possible thanks to the MACHO and OGLE surveys. However, in our Galaxy, only two Be/X have been reported to show NRP: GRO J2058+42 (Kiziloglu et al. 2007) and LSI+61 235 (Sarty et al. 2009). Our objective is to study the short-term variability of Galactic Be/X binaries, compare them to the Be/X of the MC and to the isolated Galactic Be observed with corot and kepler. We present preliminary results of two Be/X stars, namely 4U 0115+63 and SAX J2103.5+4545 showing multiperiodicity and periodicity respectively, most probable produced by NRP.
Non-radial pulsations in the CoRoT Be Star 102761769
Authors: Pacheco Eduardo Janot , de Andrade Laerte B.P. , Emilio Marcelo , Suárez Juan Carlos , Jendreieck Andressa
Published: July 2011

We investigate non-radial pulsations of the CoRoT IR1 Be Star 102761769, with a projected stellar rotation estimated to be 120±15 km/s. If the star is a typical galactic Be star it rotates near the critical velocity. We propose an alternative scenario, where the star could be seen nearly equator-on rotating at a relatively moderate velocity say, ≈ 120 km/s and therefore the nonradial oscillations could be modeled. In order to identify the pulsation modes of the observed frequencies, we computed a set of models representative of CoRoT 102761769 by means of the adiabatic pulsation package FILOU. Results indicate that the two frequencies are compatible with a high-g mode as predicted by pulsation models of Be stars.
Hα emission variability in the γ-ray binary LSI +61 303
Authors: McSwain M. Virginia , Grundstrom Erika D. , Gies Douglas R. , Ray Paul S.
Published: July 2011

LS I +61 303 is an exceptionally rare example of a Be/X-ray binary that also exhibits MeV–TeV emission, making it one of only a handful of ”γ-ray binaries”. Here we present Hα spectra that show strong variability during the 26.5 day orbital period and over decadal time scales. The Hα line profile exhibits a dramatic emission burst shortly before apastron, observed as a redshifted shoulder in the line profile, as the compact source moves almost directly away from the observer. Here we investigate several possible origins for this red shoulder, including an accretion disk, tidal mass transfer stream, turbulent gas in the wake of the neutron star, and a compact pulsar wind nebula in the system.
Optical spectroscopy of DPVs and the case of LP Ara
Authors: Mennickent Ronald E. , Graczyk Darek , Kołaczkowski Zbigniew , Michalska Gabriela , Barría Daniela , Niemczura Ewa
Published: July 2011

We present preliminary results of our spectroscopic campaign of a group of intermediate mass interacting binaries dubbed “Double Periodic Variables” (DPVs), characterized by orbital light curves and additional long photometric cycles recurring roughly after 33 orbital periods (Mennickent et al. 2003, 2005). They have been interpreted as interacting, semi-detached binaries showing cycles of mass loss into the interstellar medium (Mennickent et al. 2008, Mennickent & Kołaczkowski 2009). High resolution Balmer and helium line profiles of DPVs can be interpreted in terms of mass flows in these systems. A system solution is given for LP Ara, based on modeling of the ASAS V-band orbital light curve and the radial velocity of the donor star.
An OB-type eclipsing binary system ALS 1135
Authors: Michalska Gabriela , Niemczura Ewa , Steslicki Marek , Williams Andrew
Published: July 2011

We present new physical and orbital parameters of an early-type double-lined eclipsing binary system ALS 1135. The UBVIC light curves and radial velocity curves were modeled simultaneously by means of the Wilson-Devinney code. As a result, we obtained inclination and size of the orbit, as well as masses, radii and effective temperatures of the components.
Fast rotating stars resulting from binary evolution will often appear to be single
Authors: de Mink Selma E. , Langer Norbert , Izzard Robert G.
Published: July 2011

Rapidly rotating stars are readily produced in binary systems. An accreting star in a binary system can be spun up by mass accretion and quickly approach the break-up limit. Mergers between two stars in a binary are expected to result in massive, fast rotating stars. These rapid rotators may appear as Be or Oe stars or at low metallicity they may be progenitors of long gamma-ray bursts.

Given the high frequency of massive stars in close binaries it seems likely that a large fraction of rapidly rotating stars result from binary interaction. It is not straightforward to distinguish a a fast rotator that was born as a rapidly rotating single star from a fast rotator that resulted from some kind of binary interaction. Rapidly rotating stars resulting from binary interaction will often appear to be single because the companion tends to be a low mass, low luminosity star in a wide orbit. Alternatively, they became single stars after a merger or disruption of the binary system during the supernova explosion of the primary.

The absence of evidence for a companion does not guarantee that the system did not experience binary interaction in the past. If binary interaction is one of the main causes of high stellar rotation rates, the binary fraction is expected to be smaller among fast rotators. How this prediction depend on uncertainties in the physics of the binary interactions requires further investigation.
Emission features in a B[e] binary system V2028 Cyg
Authors: Polster Jan , Korčáková Daniela , Votruba Viktor , Škoda Petr , Šlechta Miroslav , Kučerová Blanka
Published: July 2011

We present a preliminary analysis of our six-year observation campaign of the B[e] stellar system V2028 Cyg (MWC 623). The time variability of spectral features is described.
Multiplicity in 5 M⊙ stars
Authors: Evans Nancy Remage
Published: July 2011

Binary/multiple status can affect stars at all stages of their lifetimes: evolution onto the main sequence, properties on the main sequence, and subsequent evolution. 5 M⊙ stars have provided a wealth of information about the binary properties fairly massive stars. The combination of cool evolved primaries and hot secondaries in Cepheids (geriatric B stars) have yielded detailed information about the distribution of mass ratios. and have also provided a surprisingly high fraction of triple systems. Ground-based radial velocity orbits combined with satellite data from Hubble, FUSE, IUE, and Chandra are needed to provide full information about the systems, including the masses. As a recent example, X-ray observations can identify low mass companions which are young enough to be physical companions. Typically binary status and properties (separation, eccentricity, mass ratio) determine whether any stage of evolution takes an exotic form.
The (B0+?)+O6 system FN CMa: a case for tidal-pulsational interaction?
Authors: Rivinius Thomas , Stahl Otmar , Štefl Stanislas , Baade Dietrich , Townsend Richard H.D. , Barrera Luis
Published: July 2011

FN CMa is visually double with a separation of ~0.6 arcsec. Sixty high-cadence VLT/UVES spectra permit the A and B components to be disentangled, as the relative contribution of each star to the total light entering the spectrograph fluctuates between exposures due to changes in seeing. Component A exhibits rapid line-profile variations, leading us to attribute the photometric variability seen by HIPPARCOS (with a derived P = 0.08866 d) to this component. From a total of 122 archival and new echelle spectra it is shown that component A is an SB1 binary with an orbital period of 117.55 days. The eccentricity of 0.6 may result in tidal modulation of the pulsation(s) of component Aa.
Light curves of the Be stars of NGC 3766
Authors: Roettenbacher Rachael M. , McSwain M. Virginia
Published: July 2011

Nonradial pulsations (NRPs) are a possible formation mechanism for the equatorial disks surrounding Be stars. The open cluster NGC 3766 has a high fraction of transient Be stars, Be stars that have been observed with both emission due to a circumstellar disk and a non-emitting B-type spectrum. Because of the large fraction of transient Be stars, this cluster is a prime location for studying the formation mechanisms of Be star disks. We observed NGC 3766 for more than 25 nights over three years to generate Strömgren uvby light curves of the Be population. We present the results of a period search to investigate the presence of NRPs.
Fundamental parameters of “normal” B stars in the solar neighborhood
Authors: Nieva Maria-Fernanda , Przybilla Norbert
Published: July 2011

Understanding phenomena of activity in stars, like pulsations or magnetism, benefits from systematic comparisons of some key physical parameters of active with those of “normal” stars. Here we concentrate on a careful derivation of fundamental parameters of a well selected sample of 27 “normal” B stars in nearby OB associations and in the field. A quantitative spectral analysis methodology based on hybrid non-LTE techniques is applied to high-resolution and high-S/N spectra. Results derived from the pure spectroscopic analysis are compared to other data/indicators of stellar parameters in order to prove the reliability of the method. Very good agreement is obtained among all of them. Besides the fundamental parameters, the chemical composition of the stars is also determined at high precision, turning out to be highly homogeneous. A comparative study of the present results with those of well known active massive stars will help to improve our understanding of the driving mechanisms of activity.
Massive stars at (very) high energies: γ-ray binaries
Authors: Dubus Guillaume , Cerutti Benoît
Published: July 2011

γ-ray binaries are systems that emit most of their radiative power above 1 MeV. They are associated with O or Be stars in orbit with a compact object, possibly a young pulsar. Much like colliding wind binaries, the pulsar generates a relativistic wind that interacts with the stellar wind. The result is non-thermal emission from radio to very high energy γ-rays. The wind, radiation and magnetic field of the massive star play a major role in the dynamics and radiative output of the system. They are particularly important to understand the high energy physics at work. Inversely, γ-ray binaries offer novel probes of stellar winds and insights into the fate of O/B binaries.
Modeling TeV γ-rays from LS 5039: an active OB star at the extreme
Authors: Owocki Stan P. , Okazaki Atsuo T. , Romero Gustavo
Published: July 2011

Perhpas the most extreme examples of “Active OB stars" are the subset of high-mass X-ray binaries – consisting of an OB star plus compact companion – that have recently been observed by Fermi and ground-based Cerenkov telescopes like HESS to be sources of very high energy (VHE; up to 30 TeV!) γ-rays. This paper focuses on the prominent γ-ray source, LS5039, which consists of a massive O6.5V star in a 3.9-day-period, mildly elliptical (e ≈ 0.24) orbit with its companion, assumed here to be a black-hole or unmagnetized neutron star. Using 3-D SPH simulations of the Bondi-Hoyle accretion of the O-star wind onto the companion, we find that the orbital phase variation of the accretion follows very closely the simple Bondi-Hoyle-Lyttleton (BHL) rate for the local radius and wind speed. Moreover, a simple model, wherein intrinsic emission of γ-rays is assumed to track this accretion rate, reproduces quite well Fermi observations of the phase variation of γ-rays in the energy range 0.1-10 GeV. However for the VHE (0.1-30 TeV) radiation observed by the HESS Cerenkov telescope, it is important to account also for photon-photon interactions between the γ-rays and the stellar optical/UV radiation, which effectively attenuates much of the strong emission near periastron. When this is included, we find that this simple BHL accretion model also quite thus making it a strong alternative to the pulsar-wind-shock models commonly invoked to explain such VHE γ-ray emission in massive-star binaries.
Ion fractions and the weak wind problem
Authors: Austin Matthew J. , Prinja Raman K.
Published: July 2011

Some late-type O stars display anomalously weak winds, possibly due to decoupling of the main driving ions from the bulk plasma. This issue and the uncertainty about the nature of wind clumping are a challenge to line-driven wind theory and need resolving in order to fully understand hot stars. We describe the results from the computation of ion fractions for the various elements in O star winds using non-LTE code CMFGEN, including parameterisation of microclumping and X-rays.
Searching for emission line and OB stars in Cl 1806-20 using a NIR narrow-band technique
Authors: Edwards Michelle L. , Bandyopadhyay Reba M. , Eikenberry Stephen S. , Mikles Valerie J. , Moon Dae-Sik
Published: July 2011

We survey the environment of Cl 1806-20 using near-infrared narrow-band imaging to search for Brγ features indicative of evolved massive stars. Using this technique, we successfully detect previously identified massive stars in the cluster. We detect no new emission line stars, establishing a firm upper limit on the number of Wolf Rayets and Luminous Blue Variables; however, we do find several candidate OB supergiants, which likely represent the bulk of the heretofore undiscovered massive star population.
The mysterious high-latitude O-star HD 93521: new results from XMM-Newton observations
Authors: Rauw Gregor , Morel Thierry
Published: July 2011

The O9.5 Vp star HD 93521 is a well known non-radial pulsator located at a high Galactic latitude. The nature (Population I vs. II) of this star has been the subject of controversy for many years. We report on an XMM-Newton observation of the star that sheds new light on its nature.
Optical spectroscopic observations of the Be/X-Ray binary A0535+262/V725 Tau during the giant outburst in 2009
Authors: Moritani Yuuki , Nogami Daisaku , Okazaki Atsuo T. , Imada Akira , Kambe Eiji , Honda Satoshi , Hashimoto Osamu , Ichikawa Kazuhide
Published: July 2011

A giant outburst occurred in A0535+262/V725 Tau in November 2009, which lasted approximately 30 days. We carried out spectroscopic monitoring at OAO and GAO from November 2009 to March 2010, from before the giant outburst to the rising phase of the normal outburst which occurred after the next periastron. The obtained H-alpha, H-beta and He I emission lines exhibited drastic profile variability during the observations.
The surprising X-ray emission of Oe stars
Authors: Nazé Yael , Rauw Gregor , ud-Doula Asif
Published: July 2011

Oe stars are thought to represent an extension of the Be phenomenon to higher temperatures. Dedicated XMM observations of HD 155806 revealed a surprising X-ray spectrum: soft character, absence of overluminosity, broad X-ray lines. These properties are fully compatible with the wind-shock model, which usually explains the X-rays from “normal”, single O-type stars. In contrast, some other Oe/Be stars display a completely different behaviour at high energies.
The latest developments on Of?p stars
Authors: Nazé Yael , ud-Doula Asif , Spano Maxime , Rauw Gregor , De Becker Michael , Walborn Nolan R.
Published: July 2011

In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken, revealing their peculiar properties. To clarify some of the remaining questions, we have continued our monitoring of the prototypical Of?p trio. HD 108 has now reached its quiescent, minimum-emission state, for the first time in 50–60yrs, while new echelle spectra of HD 148937 confirm the presence in several H and He lines of the 7d variations detected previously only in the Hα line. A new XMM observation of HD 191612 clearly shows that its X-ray emission is not modulated by the orbital period of 1542d, but the high-energy variations are rather compatible with the 538d period of the optical changes - it is thus not of colliding-wind origin but linked to the phenomena responsible for the spectral/photometric variations, though our current MHD simulations remain at odds with the observational properties.
Uniqueness and evolutionary status of MWC 349A
Authors: Strelnitski Vladimir , Schwarz Kamber , Bieging John , Fuchs Josh T. , Walker Gary
Published: July 2011

MWC349A, which had remained an ordinary member of the MWC catalog for a few decades, is now known as: (1) the brightest stellar source of radio continuum; (2) the only known high-gain natural maser in hydrogen recombination lines; and (3) the only strictly proven natural high-gain laser (in IR hydrogen recombination lines). These phenomena seem to occur in the circumstellar disk seen almost edge-on. They help us understand the structure and kinematics of the disk. The evolutionary status of MWC 349A is still debated: a young HAeBe star with a pre-planetary disk or an old B[e] star or even a protoplanetary nebula? We discuss new observational data obtained at the Maria Mitchell Observatory and elsewhere which may cast light on this issue.
γ-ray production via IC scattering of the infrared excess from the Be-type star in the binary system PSR B1259-63/SS2883
Authors: van Soelen Brian , Meintjes Pieter J.
Published: July 2011

Un-pulsed γ-ray emission has been detected close to periastron in the pulsar/Be-star binary system PSR B1259-63/SS 2883, believed to originate from the shock front that forms between the stellar and pulsar winds. A likely source of γ-ray production is the inverse Compton up-scattering of target photons from the Be star by relativistic electrons/positrons in the pulsar wind. In this study the influence of the infrared radiation, emanating from the circumstellar disc, on isotropic inverse Compton γ-ray production is investigated. It is shown that the scattering of infrared disc photons can increase the γ-ray flux by a factor ~2 in the 1–10 GeV range.
Automated Graduation using Bayesian Trans-dimensional Models
Authors: Verrall R.J. , Haberman S.
Published: July 2011

This paper presents a new method of graduation which uses parametric formulae together with Bayesian reversible jump Markov chain Monte Carlo methods. The aim is to provide a method which can be applied to a wide range of data, and which does not require a lot of adjustment or modification. The method also does not require one particular parametric formula to be selected: instead, the graduated values are a weighted average of the values from a range of formulae. In this way, the new method can be seen as an automatic graduation method which we believe can be applied in many cases without any adjustments and provide satisfactory graduated values. An advantage of a Bayesian approach is that it allows for model uncertainty unlike standard methods of graduation.
Two Treatments for Fear of Flying Compared
Authors: Triscari Maria Teresa , Faraci Palmira , D’Angelo Valerio , Urso Viviana , Catalisano Dario
Published: July 2011

This study aimed to test a combined treatment with eye movement desensitization and reprocessing (EMDR) and cognitive behavioral therapy (CBT), compared with CBT integrated with systematic desensitization, in reducing fear of flying. Participants were patients with aerophobia, who were randomly assigned to two experimental groups in a before- and after-treatment research design. The Flight Anxiety Situations Questionnaire (FAS) and the Flight Anxiety Modality Questionnaire (FAM) were used. The efficacy of each program was evaluated comparing the pre- and post-treatment levels of fear of flying within subjects. A comparison of the post-treatment scores between subjects was also conducted. Results showed the effectiveness of each model with a significant improvement in the examined psychological outcomes in both groups.
Ionospheric bending correction for GNSS radio occultation signals
Authors: Hoque M. M. , Jakowski N.
Published: July 2011

Ionospheric propagation effects on Global Navigation Satellite Systems (GNSS) signals are the most pronounced during radio occultation due to long ionospheric travel paths of the received signal on low Earth orbiting satellites. Inhomogeneous plasma distribution and anisotropy cause higher‐order nonlinear refraction effects on GNSS signals which cannot be fully removed through a linear combination of dual‐frequency observables. In this paper, higher‐order ionospheric effects due to straight line of sight (LOS) propagation assumption such as the excess path length of the signal in addition to the LOS path and the total electron content difference between the curved path and the LOS path have been investigated for selected GPS‐CHAMP occultation events. Based on simulation studies we have derived correction formulas for computing raypath bending effects as functions of signal frequency, tangential height of the raypath, ionospheric parameters such as the maximum ionization and total electron content. If these parameters are known, the proposed correction method is able to correct on an average about 65–80% bending errors of GNSS occultation signals.