bluuebunny/crossref_metadata_2025_split huggingface dataset:
Near-infrared excess and emission characteristics of classical Be stars
Authors: Lee Chien-De , Chen Wen-Ping , Kinoshita Daisuke 
Published: July 2011

AbstractClassical 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

AbstractHD 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

AbstractWe 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

AbstractWe 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

AbstractNew 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

AbstractA 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.
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

AbstractOptical 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

AbstractThe 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

AbstractWe 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

AbstractWe 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

AbstractThe 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

AbstractWe 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

AbstractLS 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

AbstractWe 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

AbstractWe 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

AbstractRapidly 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

AbstractWe 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

AbstractBinary/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

AbstractFN 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

AbstractNonradial 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

AbstractUnderstanding 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

Abstractγ-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

AbstractPerhpas 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

AbstractSome 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

AbstractWe 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

AbstractThe 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

AbstractA 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

AbstractOe 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.