bluuebunny/crossref_metadata_2025_split huggingface dataset:
The rapid magnetic rotator HR 7355
Authors: Rivinius Thomas , Townsend Rich H. D. , Štefl Stanislas , Baade Dietrich 
Published: July 2011

AbstractFor early type magnetic stars slow, at most moderate rotational velocities have been considered an observational fact. The detection of a multi-kilogauss magnetic field in the B2Vpn star with P ≈ 0.52 d and v sin i ≈ 300 km/s has brought down this narrative. We have obtained more than 100 high-resolution, high-S/N echelle spectra in 2009. These spectra provide the most detailed description of the variability of any He-strong star to date. The circumstellar environment is dominated by a rotationally locked magnetosphere out to several stellar radii, causing hydrogen emission. The photosphere is characterized by surface chemical abundance inhomogeneities, with much stronger amplitudes, at least for helium, than slower rotating stars like σ Ori E. The highly complex rotational line profile modulations of metal lines are probably a consequence the equatorial gravity darkening of HR 7355, and thus may offer an independent measurement of the von Zeipel parameter β.
Dynamics of fossil magnetic fields in massive star interiors
Authors: Mathis Stéphane 
Published: July 2011

AbstractIn this talk, I review the different MHD processes, which take place in massive star interiors. First, I describe MHD instabilities, which act on magnetic fields in stellar radiation zones, and the dynamo action in massive stars that give strong indications in favor of a fossil origin of the fields observed at the surface of these stars. Then, I discuss the study of MHD turbulent relaxation processes, which are now examined in stellar interiors, to describe initial conditions for fossil magnetic fields. Finally, I focus on the state of the art of the modeling of the interaction between differential rotation, fossil magnetic field, meridional circulation, and turbulence.
Discussion – Winds and magnetic fields of active OB stars
Authors: Bouret Jean-Claude , Cidale Lydia 
Published: July 2011

AbstractThe discussion on winds and magnetic fields of active OB stars was carried out by S. Owoki, G. Wade, M. Cantiello, O. Kochukhov, M. Smith, C. Neiner, T. Rivinius, H. Henrichs and R. Townsend. The topics were the ability to detect small and large scale magnetic fields in massive stars and the need to consider limits on photometric variability of the star surface brightness.
A family of stable configurations to model magnetic fields in stellar radiation zones
Authors: Duez Vincent , Braithwaite Jonathan , Mathis Stéphane 
Published: July 2011

AbstractWe conduct 3D magneto-hydrodynamic (MHD) simulations in order to test the stability of the magnetic equilibrium configuration described by Duez & Mathis (2010). This analytically-derived configuration describes the lowest energy state for a given helicity in a stellar radiation zone. The necessity of taking into account the non force-free property of the large-scale, global field is here emphasized. We then show that this configuration is stable. It therefore provides a useful model to initialize the magnetic topology in upcoming MHD simulations and stellar evolution codes taking into account magneto-rotational transport processes.
The slow winds of A-type supergiants
Authors: Granada Anahí , Curé Michel , Cidale Lydia S. 
Published: July 2011

AbstractThe line driven- and rotation modulated-wind theory predicts an alternative slow solution, besides from the standard m-CAK solution, when the rotational velocity is close to the critical velocity. We study the behaviour of the winds of A-type supergiants (Asg) and show that under particular conditions, e.g., when the δ line-force parameter is about 0.25, the slow solution could exist over the whole star, even for the cases when the rotational speed is slow or zero. We discuss density and velocity profiles as well as possible observational conterparts.
Discovery of the most rapidly-rotating, non-degenerate, magnetic massive star by the MiMeS collaboration
Authors: Grunhut Jason H. , Wade Gregg A. , Rivinius Thomas , Marcolino Wagner L. F. , Townsend Richard H.D. ,   the MiMeS Collaboration
Published: July 2011

AbstractWe discuss the recent detection of a strong, organized magnetic field in the bright, broad-line B2V star, HD 142184, using the ESPaDOnS spectropolarimeter on the CFHT as part of the Magnetism in Massive Stars (MiMeS) survey. We find a rotational period of 0.50833 days, making it the fastest-rotating, non-degenerate magnetic star ever detected. Like the previous rapid-rotation record holder HR 7355 (also discovered by MiMeS: Oksala et al. 2010, Rivinius et al. 2010), this star shows emission line variability that is diagnostic of a structured magnetosphere.
Line Profile microvariability and wind structure for OB stars
Authors: Kholtygin Alexander F. , Fabrika Sergei N. , Sudnik Natalia P. 
Published: July 2011

AbstractWe report the results of a search for line profile variability (LPV) in the spectra of OB stars. The wavelets were used for looking for the irregular LPV in spectra of program stars. We connect the appearance of irregular details in the LPV with the formation and dissipation of the small-scale substructures (clumps) in the wind.
The search for magnetic fields in mercury-manganese stars
Authors: Makaganiuk Vitalii , Kochukhov Oleg , Piskunov Nikolai , Jeffers Sandra V. , Johns-Krull Christopher M. , Keller Christoph U. , Rodenhuis Michiel , Snik Frans , Stempels Henricus C. , Valenti Jeff A. 
Published: July 2011

AbstractMercury-manganese (HgMn) stars were considered to be non-magnetic, showing no evidence of surface spots. However, recent investigations revealed that some stars in this class possess an inhomogeneous distribution of chemical elements on their surfaces. According to our current understanding, the most probable mechanism of spot formation involves magnetic fields. Taking the advantage of a newly-built polarimeter attached to the HARPS spectrometer at the ESO 3.6m-telescope, we performed a high-precision spectropolarimetric survey of a large group of HgMn stars. The main purpose of this study was to find out how typical it is for HgMn stars to have weak magnetic fields. We report no magnetic field detection for any of the studied objects, with a typical precision of the longitudinal field measurements of 10 G and down to 1 Gauss for some of the stars. We conclude that HgMn stars lack large-scale magnetic fields typical of spotted magnetic Ap stars and probably lack any fields capable of creating and sustaining chemical spots. Our study confirms that alongside the magnetically altered atomic diffusion, there must be other structure formation mechanism operating in the atmospheres of late-B main sequence stars.
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

AbstractThe 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

AbstractIn 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

AbstractWe 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

AbstractWe 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

AbstractMassive 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

AbstractOne 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

AbstractWe 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

AbstractDiscovered 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

AbstractWe 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

AbstractA 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

AbstractPreliminary 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

AbstractMassive 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

AbstractAt 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

AbstractPhotometric 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

AbstractCircumstellar 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

AbstractClassical 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

AbstractDuring 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.
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

AbstractThe 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

AbstractWe 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.