bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rotation rates of massive stars in the Magellanic Clouds
Authors: Penny Laura R. , Gies Douglas R. 
Published: July 2011

AbstractWe present the results of our survey of the projected rotational velocities of 161 O-type stars in the Magellanic Clouds from archival FUSE observations. The evolved and unevolved samples from each environment are compared through the Kolmogorov-Smirnov test to determine if the distribution of equatorial rotational velocities is metallicity dependent for these massive objects. Stellar interior models predict that massive stars with SMC metallicity will have significantly reduced angular momentum loss on the main sequence compared to their Galactic counterparts. Our statistical results find some support for this prediction but also show that even at Galactic metallicity, evolved and unevolved massive stars have fairly similar fractions of stars with large V sin i. What is more compelling are the few evolved objects in the Magellanic Clouds with rotational velocities that approach or even exceed those predicted from the evolutionary models.
Massive stellar models: rotational evolution, metallicity effects
Authors: Ekström Sylvia , Georgy Cyril , Meynet Georges , Maeder André , Granada Anahí 
Published: July 2011

AbstractThe Be star phenomenon is related to fast rotation, although the cause of this fast rotation is not yet clearly established. The basic effects of fast rotation on the stellar structure are reviewed: oblateness, mixing, anisotropic winds. The processes governing the evolution of the equatorial velocity of a single star (transport mechanisms and mass loss) are presented, as well as their metallicity dependence. The theoretical results are compared to observations of B and Be stars in the Galaxy and the Magellanic Clouds.
About the Luminous Blue Variable He3-519
Authors: Hervé Anthony , Bouret Jean-Claude 
Published: July 2011

AbstractLuminous Blue Variables (LBVs) are massive stars, in a transition phase, from being O-type stars and rapidly becoming Wolf-Rayet objects. LBVs possess powerful stellar winds, high luminosities and show photometric and spectroscopic variability. We present the stellar and wind parameters of He3-519 obtained by the modeling of UVES observations with the model atmosphere code CMFGEN. We compare our results to previous studies in order to find mid-time scale variability of the stellar parameters and finally, we use stellar evolution models to determine the evolutionary status of this star.
Models of classical Be stars with gravity darkening
Authors: McGill Meghan A. , Sigut T. A. Aaron. , Jones Carol E. 
Published: July 2011

AbstractClassical Be stars are rapidly rotating, hot stars that possess an equatorial disk formed from gas released by the central star. The mechanism driving the stellar mass loss has yet to be fully explained, but the rapid rotation of the central B star is believed to be crucial. Rapid rotation also produces gravity darkening, and we have now extended our disk models to include these effects. In this contribution, we focus on the effect of gravity darkening on the thermal structure of a circumstellar disk.
Spectroscopic and interferometric approach for differential rotation in massive fast rotators
Authors: Zorec Juan , Frémat Yves , Delaa Omar , Domiciano de Souza Armando , Stee Philippe , Mourard Denis , Cidale Lydia S. , Martayan Christophe 
Published: July 2011

AbstractThe coupling between the convective region in the envelope and rotation can produce a surface latitudinal differential rotation that may induce changes of the stellar geometry and on the spectral line profiles that it may be scrutinized spectroscopically and by interferometry.
The MiMeS project: overview and current status
Authors: Wade Gregg A. , Alecian Evelyne , Bohlender David A. , Bouret Jean-Claude , Cohen David H. , Duez Vincent , Gagné Marc , Grunhut Jason H. , Henrichs Huib F. , Hill Nick R. , Kochukhov Oleg , Mathis Stéphane , Neiner Coralie , Oksala Mary E. , Owocki Stan , Petit Véronique , Shultz Matthew , Rivinius Thomas , Townsend Richard H. D. , Vink Jorick S. ,   the MiMeS collaboration
Published: July 2011

AbstractThe Magnetism in Massive Stars (MiMeS) Project is a consensus collaboration among many of the foremost international researchers of the physics of hot, massive stars, with the basic aim of understanding the origin, evolution and impact of magnetic fields in these objects. At the time of writing, MiMeS Large Programs have acquired over 950 high-resolution polarised spectra of about 150 individual stars with spectral types from B5-O4, discovering new magnetic fields in a dozen hot, massive stars. The quality of this spectral and magnetic matériel is very high, and the Collaboration is keen to connect with colleagues capable of exploiting the data in new or unforeseen ways. In this paper we review the structure of the MiMeS observing programs and report the status of observations, data modeling and development of related theory.
Structure in the winds of O-Type stars: observations and inferences
Authors: Fullerton Alex W. 
Published: July 2011

AbstractThis review describes the observational evidence for structure in the winds of O-type stars due to large-scale perturbations and small-scale inhomogeneities. Despite considerable progress, a comprehensive theoretical framework that explains the origin. properties, and coexistence of wind structure on different spatial scales has yet to be constructed and incorporated into model atmosphere analyses. Consequently, it is not yet possible to assess the effect of non-stationary structures on different wind diagnostics in a rigorous way, with the result that accurate empirical determinations of mass-loss rates remain elusive.
Magnetic Doppler imaging of early-type stars
Authors: Kochukhov Oleg , Rivinius Thomas , Oksala Mary E. , Romanyuk Iosif 
Published: July 2011

AbstractDoppler imaging of early-type magnetic stars is the most advanced method to interpret their line profile variations. DI allows us to study directly a complex interplay between chemical spots, magnetic fields, and the mass loss. Here we outline the general principles of the surface mapping of stars, discuss adaption of this technique to early-type stars and present several recent examples of the abundance and magnetic mapping performed for rapidly rotating early-B stars. In particular, we present the first Doppler images for the very fast rotating He-rich star HR 7355 and a reconstruction of magnetic field for the well-known Bp star σ Ori E. We also present new magnetic maps for the He-strong star HD 37776, which possesses one of the most complex magnetic field topologies among the upper main sequence stars.
Rigid Field Hydrodynamic simulations of the magnetosphere of σ Orionis E
Authors: Hill Nicholas R. , Townsend Richard H. D. , Cohen David H. , Gagné Marc 
Published: July 2011

AbstractWe present Rigid Field Hydrodynamic simulations of the magnetosphere of σ Ori E. We find that the X-ray emission from the star's magnetically confined wind shocks is very sensitive to the assumed mass-loss rate. To compare the simulations against the measured X-ray emission, we first disentangle the star from its recently discovered late-type companion using Chandra HRC-I observations. This then allows us to place an upper limit on the mass-loss rate of the primary, which we find to be significantly smaller than previously imagined.
Magnetic fields of massive stars
Authors: Hubrig Swetlana , Curé Michel , Ilyin Ilya , Schöller Markus 
Published: July 2011

AbstractWe recently carried out a spectropolarimetric study of a sample of massive O-type stars and pulsating β Cephei stars using the SOFIN echelle spectrograph at the 2.56 m Nordic Optical Telescope and the low-resolution FORS 2 spectrograph at the VLT in spectropolarimetric mode. The sample consists of massive stars already detected as magnetic in the course of our previous low-resolution polarimetric observations with FORS 1 and a few O-type stars with magnetic field detections reported in the literature.
Magnetic fluxes of massive stars: statistics and evolution
Authors: Kholtygin Alexander F. , Fabrika Sergei N. , Drake Natalia A. , Igoshev Andrei P. 
Published: July 2011

AbstractThe statistical properties of magnetic fields and magnetic fluxes of OB stars were investigated. The mean magnetic fluxes of massive OB stars appear to be 3 order larger than those for neutron stars.
Discovery of a strong magnetic field in the rapidly rotating B2Vn star HR 7355
Authors: Oksala Mary E. , Wade Gregg A. , Marcolino Wagner L. F. , Grunhut Jason H. , Bohlender David , Manset Nadine , Townsend Richard H. D. ,   the MiMeS Collaboration
Published: July 2011

AbstractWe report on the detection of a strong, organized magnetic field in the helium-variable early B-type star HR 7355 using spectropolarimetric data obtained with ESPaDOnS on CFHT by the MiMeS large program. We also present results from new V-band differential photometry obtained with the CTIO 0.9m telescope. We investigate the longitudinal field, using a technique called Least-Squares Deconvolution (LSD), and the rotational period of HR 7355. These new observations strongly support the proposal that HR 7355 harbors a structured magnetosphere similar to that in the prototypical helium-strong star, σ Ori E.
Magnetism of the He-weak star HR 2949
Authors: Rivinius Thomas , Wade Gregg A. , Townsend Richard H. D. , Shultz Matthew , Grunhut Jason H. , Stahl Otmar ,   the MiMeS collaboration
Published: July 2011

AbstractA magnetic field and rotational line profile variability (lpv) is found in the He-weak star HR 2949. The field measured from metallic lines varies in a clearly non-sinusoidal way, and shows a phase lag relative to the morphologically similar He i equivalent width variations. The surface abundance patterns are strong and complex, and visible even in the hydrogen lines.
Of?p stars: a class of slowly rotating magnetic massive stars
Authors: Wade Gregg A. , Grunhut Jason H. , Marcolino Wagner L. F. , Martins Fabrice , Howarth Ian D. , Nazé Yael , Walborn Nolan R. ,   the MiMeS Collaboration
Published: July 2011

AbstractOnly 5 Of?p stars have been identified in the Galaxy. Of these, 3 have been studied in detail, and within the past 5 years magnetic fields have been detected in each of them. The observed magnetic and spectral characteristics are indicative of organised magnetic fields, likely of fossil origin, confining their supersonic stellar winds into dense, structured magnetospheres. The systematic detection of magnetic fields in these stars strongly suggests that the Of?p stars represent a general class of magnetic O-type stars.
Populations of Be stars: stellar evolution of extreme stars
Authors: Martayan Christophe , Rivinius Thomas , Baade Dietrich , Hubert Anne-Marie , Zorec Jean 
Published: July 2011

AbstractAmong the emission-line stars, the classical Be stars known for their extreme properties are remarkable. The Be stars are B-type main sequence stars that have displayed at least once in their life emission lines in their spectrum. Beyond this phenomenological approach some progresses were made on the understanding of this class of stars. With high-technology techniques (interferometry, adaptive optics, multi-objects spectroscopy, spectropolarimetry, high-resolution photometry, etc) from different instruments and space mission such as the VLTI, CHARA, FLAMES, ESPADONS-NARVAL, COROT, MOST, SPITZER, etc, some discoveries were performed allowing to constrain the modeling of the Be stars stellar evolution but also their circumstellar decretion disks. In particular, the confrontation between theory and observations about the effects of the stellar formation and evolution on the main sequence, the metallicity, the magnetic fields, the stellar pulsations, the rotational velocity, and the binarity (including the X-rays binaries) on the Be phenomenon appearance is discussed. The disks observations and the efforts made on their modeling is mentioned. As the life of a star does not finish at the end of the main sequence, we also mention their stellar evolution post main sequence including the gamma-ray bursts. Finally, the different new results and remaining questions about the main physical properties of the Be stars are summarized and possible ways of investigations proposed. The recent and future facilities (XSHOOTER, ALMA, E-ELT, TMT, GMT, JWST, GAIA, etc) and their instruments that may help to improve the knowledge of Be stars are also briefly introduced.
Massive variable stars at very low metallicity?
Authors: Bomans Dominik J. , Weis Kerstin 
Published: July 2011

AbstractObservational contraints on the evolution and instabilities of massive stars at very low metallicities are limited. Most of the information come from HST observations of one target, I Zw 18. Recent distance estimates of I Zw 18 put it at 17 Mpc, moving detailed studies of single stars clearly beyond the range of current ground based telescopes. Since massive stars with metallcities of 1/10 of solar and below are our best proxies for massive stars in (proto-) galaxies around the time of reionization, finding them and studying their evolution and instabilities is of premium importance for our understanding of galaxy formation, feedback, and the IGM reionization. Here we present pilot study results of variable stars in two more nearby extremely low metallicity galaxies, UGC 5340 and UGCA 292, and comment on the possibilities of more detailed studies of variable massive stars with new ground-based instrumentation.
Evolutionary study of the Be star 28 Tau
Authors: Ahmad Nazhatulshima , Zainuddin Mohd. Zambri , Yahya Mohd. Sahar , Eggleton Peter P. , Malasan Hakim L. 
Published: July 2011

AbstractWe present an evolutionary study of 28 Tau, a Be star, in connection with its rapid rotation. The photometric data during the absence of its envelope in 1921 have been used to determine the effective temperature and luminosity of the star at the main sequence of the HR diagram. From an evolutionary model, we found that the mass and radius of the star are about 3.2 M⊙ and 3.2 R⊙ respectively. The equatorial rotation velocity of the star, νe found to be close to its critical velocity, νcr where νe/νcr ≃ 0.87.
Are the stellar winds in IC 1613 stronger than expected?
Authors: Herrero Artemio , Garcia Maria , Uytterhoeven Katrien , Najarro Francisco , Lennon Daniel J. , Simón-Díaz Sergio , Castro Norberto , Puls Joachim , Vink Jorick S. , Urbaneja Miguel A. , de Koter Alex 
Published: July 2011

AbstractIn this poster we present the results of our analyses of three early massive stars in IC 1613, whose spectra have been observed with VIMOS and analyzed with CMFGEN and FASTWIND. One of the targets resulted a possible LBV and the other two are Of stars with unexpectedly strong winds. The Of stars seem to be strongly contaminated by CNO products. Our preliminary results may represent a challenge for the theory of stellar atmospheres, but they still have to be confirmed by the analysis of more objects and a more complete coverage of the parameter space.
The VLT-FLAMES Tarantula survey
Authors: Lennon Daniel J. , Evans Christopher J. , Bastian Nate , Beletsky Yuri , Brott Ines , Cantiello Matteo , Carraro Giovanni , Clark J. Simon , Crowther Paul A. , de Koter Alex , de Mink Selma E. , Dufton Philip L. , Dunstall Paul , Gieles Mark , Gräfener Goetz , Hénault-Brunet Vincent , Herrero Artemio , Howarth Ian D. , Langer Norbert , Apellániz Jesus Maíz , Markova Nevena , Najarro F. Paco , Puls Joachim , Sana Hugues , Simón-Díaz Sergio , Smartt Stephen J. , Stroud Vanessa E. , Taylor William D. , van Loon Jacco T. , Vink Jorick S. , Walborn Nolan R. 
Published: July 2011

AbstractThe Tarantula Survey is an ESO Large Programme which has obtained multi-epoch spectroscopy of over 1,000 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The assembled consortium will exploit these data to address a range of fundamental questions in both stellar and cluster evolution.
Variability of young massive stars in the Arches cluster
Authors: Markakis Kostas , Bonanos Alceste Z. , Pietrzynski Grzegorz , Macri Lucas , Stanek Kris Z. 
Published: July 2011

AbstractWe present preliminary results of the first near-infrared variability study of the Arches cluster, using adaptive optics data from NIRI/Gemini and NACO/VLT. The goal is to discover eclipsing binaries in this young (2.5 ± 0.5 Myr), dense, massive cluster for which we will determine accurate fundamental parameters with subsequent spectroscopy. Given that the Arches cluster contains more than 200 Wolf-Rayet and O-type stars, it provides a rare opportunity to determine parameters for some of the most massive stars in the Galaxy.
IR mass loss rates of LMC and SMC O stars
Authors: Massa Derck L. , Fullerton Alex W. , Lennon Danny J. , Prinja Raman K. 
Published: July 2011

AbstractWe use a combination of VJHK and Spitzer [3.6], [5.8] and [8.0] photometry, to determine IR excesses in a sample of LMC and SMC O stars. This sample is ideal for determining excesses because: 1) the distances to the stars, and hence their luminosities, are well-determined, and; 2) the very small line of sight reddenings minimize the uncertainties introduced by extinction corrections. We find IR excesses much larger than expected from Vink et al. (2001) mass loss rates. This is in contrast to previous wind line analyses for many of the LMC stars which suggest mass loss rates much less than the Vink et al. predictions. Together, these results indicate that the winds of the LMC and SMC O stars are strongly structured (clumped).
The IACOB spectroscopic database of galactic OB stars
Authors: Simón-Díaz Sergio , Castro Norberto , Garcia Miriam , Herrero Artemio 
Published: July 2011

AbstractWe present the IACOB spectroscopic database, the largest homogeneous database of high-resolution, high signal-to-noise ratio spectra of Northern Galactic OB-type stars compiled up to date. The spectra were obtained with the FIES spectrograph attached to the Nordic Optical Telescope. We briefly summarize the main characeristics and present status of the IACOB, first scientific results, and some future plans for its extension and scientific exploitation.
X-ray spectral diagnostics of activity in massive stars
Authors: Cohen David H. , Wollman Emma E. , Leutenegger Maurice A. 
Published: July 2011

AbstractX-rays give direct evidence of instabilities, time-variable structure, and shock heating in the winds of O stars. The observed broad X-ray emission lines provide information about the kinematics of shock-heated wind plasma, enabling us to test wind-shock models. And their shapes provide information about wind absorption, and thus about the wind mass-loss rates. Mass-loss rates determined from X-ray line profiles are not sensitive to density-squared clumping effects, and indicate mass-loss rate reductions of factors of 3 to 6 over traditional diagnostics that suffer from density-squared effects. Broad-band X-ray spectral energy distributions also provide mass-loss rate information via soft X-ray absorption signatures. In some cases, the degree of wind absorption is so high, that the hardening of the X-ray SED can be quite significant. We discuss these results as applied to the early O stars ζ Pup (O4 If), 9 Sgr (O4 V((f))), and HD 93129A (O2 If*).
Activity of Herbig Be stars and their environment
Authors: Alecian Evelyne 
Published: July 2011

AbstractThe Herbig Ae/Be stars are the high-mass counterparts of the T Tauri stars, and are therefore considered as the pre-main sequence progenitors of the A/B stars. These stars are still contracting towards the main sequence, and are surrounded by dust and gas, remnants of their parental molecular cloud. In order to understand the formation processes at high mass, as well as the magnetic and rotation properties of the MS A/B stars, it is fundamental to understand the structure of the circumstellar matter of the Herbig Ae/Be stars, as well as the interaction of these PMS stars with their close environment. In this talk I will review our current knowledge about the properties of the circumstellar environment of the Herbig Ae/Be stars as well as the possible physical processes at the origin of their observed activities.
The circumstellar environment of the FS CMa star IRAS 00470+6429
Authors: Carciofi Alex C. , Miroshnichenko Anatoly S. , Bjorkman Jon E. 
Published: July 2011

AbstractFS CMa type stars are a recently described group of objects with the B[e] phenomenon that exhibit strong emission-line spectra and strong IR excesses. In this paper we report the first attempt for a detailed modeling of IRAS 00470+6429, for which we have the best set of observations. Our modeling is based on two key assumptions: the star has a main-sequence luminosity for its spectral type (B2) and that the circumstellar (CS) envelope is bimodal, composed of a slowly outflowing disk-like wind and a fast polar wind. Both outflows are assumed to be purely radial. We adopt a novel approach to describe the dust formation site in the wind that employs timescale arguments for grain condensation and a self-consistent solution for the dust destruction surface. With the above assumptions we were able to reproduce satisfactorily many observational properties of IRAS 00470+6429, including the HI line profiles and the overall shape of the spectral energy distribution.
Disk-loss and disk-renewal phases in classical Be stars – II. Detailed analysis of spectropolarimetric data
Authors: Draper Zachary H. , Wisniewski John P. , Bjorkman Karen S. , Bjorkman Jon E. , Haubois Xavier , Carciofi Alex C. , Meade Marilyn R. 
Published: July 2011

AbstractIn Wisniewski et al. (2010), paper I, we analyzed 15 years of spectroscopic and spectropolarimetric data from the Ritter and Pine Bluff Observatories of 2 Be stars, 60 Cygni and π Aquarii, when a transition from Be to B star occurred. Here we analyze the intrinsic polarization, where we observe loop-like structures caused by the rise and fall of the polarization Balmer Jump and continuum V-band polarization being mismatched temporaly with polarimetric outbursts. We also see polarization angle deviations from the mean, reported in paper I, which may be indicative of warps in the disk, blobs injected at an inclined orbit, or spiral density waves. We show our ongoing efforts to model time dependent behavior of the disk to constrain the phenomena, using 3D Monte Carlo radiative transfer codes.
Investigating the continuum linear polarization of Be stars
Authors: Halonen Robbie J. , Mackay Frances E. , Jones Carol E. , Sigut T. A. Aaron 
Published: July 2011

AbstractIn order to understand the mechanisms that govern the development of circumstellar disks surrounding classical Be stars, we use computational codes to create theoretical models of these particular objects with their gaseous environments and we compare the predicted observables to astronomical observations. In this study, we present the use of the non-LTE radiative transfer code of Sigut & Jones (2007) to examine the effect of a self-consistent thermal structure and realistic chemical composition on the polarization of the classical Be star γ Cassiopeia. Primarily, we investigate the effect of several improvements on the pioneering work of Poeckert & Marlborough (1978) in calculating the polarization levels of γ Cas. We establish best-fit models for the same observations and analyze the implications of the differences between our results and those obtained by Poeckert & Marlborough.