bluuebunny/crossref_metadata_2025_split huggingface dataset:
First Results of the Analysis of the Wolf-Rayet Star WR6
Authors: Gormaz-Matamala Alex C. , Hervé Anthony , Chené André-Nicolas , Curé Michel , Mennickent Ronald 
Published: January 2015

AbstractWe present the first results of our analysis of the famous variable star, WR6 (HD50896). Using IUE ultraviolet data and an ESPaDOnS spectropolarimetric survey of this star, we plan to determine possible variation of the stellar and wind parameters during the different phases using the radiative transfer code CMFGEN. After the detection of parameter's modifications as a function of the phase, we will analyse deeper the origin of these variability (for example, CIRs?). In the present poster we show the first results of our analysis of the variability and the first step of the stellar parameter determination of the average spectrum of this star.
Massive stars: flare activity due to infalls of comet-like bodies
Authors: Ibadov Subhon , Ibodov Firuz S. 
Published: January 2015

AbstractPassages of comet-like bodies through the atmosphere/chromosphere of massive stars at velocities more than 600 km/s will be accompanied, due to aerodynamic effects as crushing and flattening, by impulse generation of hot plasma within a relatively very thin layer near the stellar surface/photosphere as well as “blast” shock wave, i.e., impact-generated photospheric stellar/solar flares. Observational manifestations of such high-temperature phenomena will be eruption of the explosive layer's hot plasma, on materials of the star and “exploding” comet nuclei, into the circumstellar environment and variable anomalies in chemical abundances of metal atoms/ions like Fe, Si etc. Interferometric and spectroscopic observations/monitoring of young massive stars with dense protoplanetary discs are of interest for massive stars physics/evolution, including identification of mechanisms for massive stars variability.
Line profile variability in spectra of hot massive stars
Authors: Kholtygin Alexander , Sudnik Natallia , Dushin Viacheslav 
Published: January 2015

AbstractWe report the results of our study of the fast line profile variability (LPV) (hours – few days) in the spectra of bright OB and WR stars. All spectra were obtained with 6-m and 1-m telescope of Russian Special Astrophysical Observatory (SAO) and 1.8-m telescope of Bohyunsan Optical Astronomy Observatory, Korea (BOAO). We detected both the stochastic LPV, connected with the formation of small-scale structures in the stellar wind and the regular LPV induced by the large-scale structures in the wind.
Investigation of the brightest stars in the Cyg OB2 association
Authors: Maryeva Olga , Parfenov Sergey 
Published: January 2015

AbstractWe present the results of investigation of most luminous stars belonging to the Cyg OB2 association using quantitative analysis of high-resolution spectra. Physical parameters derived using the cmfgen and tlusty atmospheric codes allow us to estimate the mass and age of these stars.
Markov Chain Monte-Carlo Models of Starburst Clusters
Authors: Melnick Jorge 
Published: January 2015

AbstractThere are a number of stochastic effects that must be considered when comparing models to observations of starburst clusters: the IMF is never fully populated; the stars can never be strictly coeval; stars rotate and their photometric properties depend on orientation; a significant fraction of massive stars are in interacting binaries; and the extinction varies from star to star. The probability distributions of each of these effects are nota prioriknown, but must be extracted from the observations. Markov Chain Monte-Carlo methods appear to provide the best statistical approach. Here I present an example of stochastic age effects upon the upper mass limit of the IMF of the Arches cluster as derived from near-IR photometry.
A spectroscopic and photometric study of the interacting binary and double period variable HD 170582
Authors: Mennickent R. E. , Djurašević G. , Cabezas M. , Cséki A. , Rosales J. , Niemczura E. , Araya I. , Curé M. 
Published: January 2015

AbstractWe present a spectroscopic and photometric study of the interacting binary and Double Period Variable HD 170582 based on the analysis of the ASAS V-band light curve and our high-resolution spectra mostly obtained with CHIRON spectrograph at the 1.5m CTIO telescope.
The Close Binary Frequency of Wolf-Rayet Stars as a Function of Metallicity in M31 and M33
Authors: Neugent Kathryn F. , Massey Philip 
Published: January 2015

AbstractHere we investigate whether the inability of the Geneva evolutionary models to predict a large enough WC/WN ratio at high metallicities (while succeeding at lower metallicities) is due to their single star nature. We hypothesize that Roche-lobe overflow in close binary systems may produce a greater number of WC stars at higher metallicities. But, this would suggest that the frequency of close massive binaries is metallicity dependent. We now present our results based on observations of ~100 Wolf-Rayet binaries in the varying metallicity environments of M31 and M33.
Westerlund 1 is a Galactic Treasure Chest: The Wolf-Rayet Stars
Authors: Rosslowe C. K. , Crowther P. A. 
Published: January 2015

AbstractThe Westerlund 1 Galactic cluster hosts an eclectic mix of coeval massive stars. At a modest distance of 4–5 kpc, it offers a unique opportunity to study the resolved stellar content of a young (~5 Myr) high mass (5·104M⊙) star cluster. With the aim of testing single-star evolutionary predictions, and revealing any signatures of binary evolution, we discuss on-going analyses of NTT/SOFI near-IR spectroscopy of Wolf-Rayet stars in Westerlund 1. We find that late WN stars are H-poor compared to their counterparts in the Milky Way field, and nearly all are less luminous than predicted by single-star Geneva isochrones at the age of Westerlund 1.
Herschel/PACS: Constraining clumping in the intermediate wind region of OB stars
Authors: Rubio-Díez M. M. , Najarro F. , Sundqvist J. O. , Traficante A. , Puls J. , Calzoletti L. , Herrero A. , Figer D. , Martin-Pintado J. 
Published: January 2015

AbstractAt present, it is well established that previously accepted mass-loss rates (Ṁ) of luminous OB stars may be overestimated when clumping is neglected. Our Herschel/PACS Far-Infrared (Far-IR) observations of a set of OB stars allow us to improve our knowledge of clumping stratification, constraining clumping properties in intermediate wind regions. In this work, better sampled clumping structure estimates are provided for ι Ori, ε Ori and ξ Per as well as an initial estimate of the clumping properties of the wind from τ Sco. These observations will allow us to obtain reliable mass-loss rates and improve our understanding of the wind physics.
Spectral analysis of LBV stars in M31: AF And and Var 15
Authors: Valeev A. F. , Sholukhova O. , Fabrika S. 
Published: January 2015

AbstractWe study spectra of two bona fide LBV stars in M31: AF And and Var 15. The spectra were obtained with the 6-m telescope (Russia) from 2005 to 2012. The model spectra were calculated with the CMFGEN code. We have not found strong changes in the spectra of the LBV stars in that time interval, however a certain variability has been detected. We estimate the star and wind parameters, such as luminosity, temperature, raduis, mass loss rate, escape velocity, hydrogen content, and reddening. We study the stars on the Hertzsprung-Russell diagram and find their initial masses using evolutionary tracks by Meynet et al. (1994).
Variational approach for rotating-stellar evolution in Lagrange scheme
Authors: Yasutake Nobutoshi , Yamada Shoichi 
Published: January 2015

AbstractWe have developed an entirely new formulation to obtain self-gravitating, axisymmetric configurations in permanent rotation. It is based on the Lagrangian variational principle and, as a consequence, will allow us to apply it to stellar evolution calculations rather easily. We adopt a Monte Carlo technique, which is analogous to those employed in other fields, e.g. nuclear physics, in minimizing the energy functional. We also present the analogies between the study on rotating stellar configurations and the one on deformed nuclei. Possible applications are not limited to main sequence stars but will be extended to e.g. compact stars, proto-stars and planets. We believe that our formulation will be a major break-through then.
Behaviour of Pulsations in Hydrodynamic Models of Massive Stars
Authors: Lovekin C. C. , Guzik J. A. 
Published: January 2015

AbstractWe have calculated the pulsations of massive stars using a nonlinear hydrodynamic code including time-dependent convection. The basic structure models are based on a standard grid published by Meynet et al. (1994). Using the basic structure, we calculated envelope models, which include the outer few percent of the star. These models go down to depths of at least 2 million K. These models, which range from 40 to 85 solar masses, show a range of pulsation behaviours. We find models with very long period pulsations (> 100 d), resulting in high amplitude changes in the surface properties. We also find a few models that show outburst-like behaviour. The details of this behaviour are discussed, including calculations of the resulting wind mass-loss rates.
Pulsation Period Change & Classical Cepheids: Probing the Details of Stellar Evolution
Authors: Neilson Hilding R. , Bisol Alexandra C. , Guinan Ed , Engle Scott 
Published: January 2015

AbstractMeasurements of secular period change probe real-time stellar evolution of classical Cepheids making these measurements powerful constraints for stellar evolution models, especially when coupled with interferometric measurements. In this work, we present stellar evolution models and measured rates of period change for two Galactic Cepheids: Polaris and l Carinae, both important Cepheids for anchoring the Cepheid Leavitt law (period-luminosity relation). The combination of previously-measured parallaxes, interferometric angular diameters and rates of period change allows for predictions of Cepheid mass loss and stellar mass. Using the stellar evolution models, We find that l Car has a mass of about 9 M⊙ consistent with stellar pulsation models, but is not undergoing enhanced stellar mass loss. Conversely, the rate of period change for Polaris requires including enhanced mass-loss rates. We discuss what these different results imply for Cepheid evolution and the mass-loss mechanism on the Cepheid instability strip.
Pulsations of massive stars beyond TAMS: effects of mass loss, diffusion, overshooting
Authors: Ostrowski Jakub , Daszyńska-Daszkiewicz Jadwiga 
Published: January 2015

AbstractWe present an influence of mass loss, element diffusion and convective overshooting on instability areas of SPBsg stars with masses of 13 - 18 M⊙. Evolutionary phases before and after helium core ignition are considered. We discuss how these effects affect the structure of the blue loops and hence a coverage of instability areas.
Asteroseismology of the SPB star HD 21071
Authors: Szewczuk Wojciech , Daszyńska-Daszkiewicz Jadwiga 
Published: January 2015

AbstractWe perform mode identification for the frequency peaks detected in the light variation of HD 21071 including the effects of rotation via the traditional approximation. We find the angular numbers (ℓ, m) for all observed frequencies and limit the range of the rotational velocity. In the next step, we make an attempt towards seismic modelling of the star in order to constrain its global parameters.
Amplitude Modulation of Cepheid Radial Velocity Curves as a Systematic Source of Uncertainty for Baade-Wesselink Distances
Authors: Anderson Richard I. 
Published: January 2015

AbstractI report on the recent discovery of modulation in the radial velocity curves in four classical Cepheids. This discovery may enable significant improvements in the accuracy of Baade-Wesselink distances by revealing a not previously considered systematic source of uncertainty.
Unraveling the variability of σ Ori E
Authors: Oksala M. E. , Kochukhov O. , Krtička J. , Prvák M. , Mikulášek Z. 
Published: January 2015

Abstractσ Ori E (HD 37479) is the prototypical helium-strong star shown to harbor a strong magnetic field, as well as a magnetosphere consisting of two clouds of plasma. The observed optical (ubvy) light curve of σ Ori E is dominated by eclipse features due to circumstellar material, however, there remain additional features unexplained by the Rigidly Rotating Magnetosphere (RRM) model of Townsend & Owocki (2005). Using the technique of magnetic Doppler imaging (MDI), spectropolarimetric observations of σ Ori E are used to produce maps of both the magnetic field topology and various elemental abundance distributions. We also present an analysis utilizing these computed MDI maps in conjunction with non-local thermodynamical equilibrium TLUSTY models to study the optical brightness variability of this star arising from surface inhomogeneities. It has been suggested that this physical phenomena may be responsible for the light curve inconsistencies between the model and observations.
The magnetic field of ζ Ori A
Authors: Blazère A. , Neiner C. , Bouret J-C. , Tkachenko A. ,   the MiMeS collaboration
Published: January 2015

AbstractMagnetic fields play a significant role in the evolution of massive stars. About 7% of massive stars are found to be magnetic at a level detectable with current instrumentation (Wade et al. 2013) and only a few magnetic O stars are known. Detecting magnetic field in O stars is particularly challenging because they only have few, often broad, lines to measure the field, which leads to a deficit in the knowledge of the basic magnetic properties of O stars. We present new spectropolarimetric Narval observations of ζ Ori A. We also provide a new analysis of both the new and older data taking binarity into account. The aim of this study was to confirm the presence of a magnetic field in ζ Ori A. We identify that it belongs to ζ Ori Aa and characterize it.
Abundance analysis of HD 22920 spectra
Authors: Khalack Viktor , Poitras Patrick 
Published: January 2015

AbstractThe new spectropolarimetric observations of HD 22920 with ESPaDOnS at CFHT reveal a strong variability of its spectral line profiles with the phase of stellar rotation. We have obtained Teff = 13640 K, logg=3.72 for this star from the best fit of its nine Balmer line profiles. The respective model of stellar atmosphere was calculated to perform abundance analysis of HD 22920 using the spectra obtained for three different phases of stellar rotation. We have found that silicon and chromium abundances appear to be vertically stratified in the atmosphere of HD 22920. Meanwhile, silicon shows hints for a possible variability of vertical abundance stratification with rotational phase.
Fundamental properties of single O stars in the MiMeS survey
Authors: Martins F. , Hervé A. , Bouret J.-C. , Marcolino W. L. F. , Wade G. A. , Neiner C. , Alecian E. ,   the MiMeS collaboration
Published: January 2015

AbstractWe present preliminary results of the determination of fundamental parameters of single O-type stars in the MiMeS survey. We present the sample and we focus on surface CNO abundances, showing how they change as stars evolve off the zero-age main sequence.
The UVMag space project: UV and visible spectropolarimetry of massive stars
Authors: Neiner Coralie ,   the UVMag consortium
Published: January 2015

AbstractUVMag is a medium-size space telescope equipped with a high-resolution spectropolarimetrer working in the UV and visible domains. It will be proposed to ESA for a future M mission. It will allow scientists to study all types of stars as well as e.g. exoplanets and the interstellar medium. It will be particularly useful for massive stars, since their spectral energy distribution peaks in the UV. UVMag will allow us to study massive stars and their circumstellar environment (in particular the stellar wind) spectroscopically in great details. Moreover, with UVMag's polarimetric capabilities we will be able, for the first time, to measure the magnetic field of massive stars simultaneously at the stellar surface and in the wind lines, i.e. to completely map their magnetosphere.
Stellar magnetic fields from four Stokes parameter observations
Authors: Rusomarov N. , Kochukhov O. , Piskunov N. 
Published: January 2015

AbstractMagnetic Doppler imaging (MDI) from observations of four Stokes parameters can uncover new information that is of interest to the evolution and structure of magnetic fields of intermediate and high-mass stars. Our MDI study of the chemically peculiar star HD 24712 from four Stokes parameter observations, obtained with the HARPSpol instrument at the 3.6-m ESO telescope, revealed a magnetic field with strong dipolar component and weak small-scale contributions. This finding gives evidence for the hypothesis that old Ap stars have predominantly dipolar magnetic fields.
Plasma Leakage from the Centrifugal Magnetospheres of Magnetic B-Type Stars
Authors: Shultz Matt , Wade Gregg , Rivinius Thomas , Grunhut Jason , Petit Véronique ,   the MiMeS Collaboration
Published: January 2015

AbstractMagnetic B-type stars are often host to Centrifugal Magnetospheres (CMs). Here we describe the results of a population study encompassing the full sample of known magnetic early B-type stars, focusing on those with detectable CMs. We present revised rotational and magnetic parameters for some stars, clarifying their positions on the rotation-confinement diagram, and find that plasma densities within their CMs is much lower than those predicted by centrifugal breakout.
Accretion Signatures on Massive Young Stellar Objects
Authors: Navarete F. , Damineli A. , Barbosa C. L. , Blum R. D. 
Published: January 2015

AbstractWe present preliminary results from a survey of molecular H2 (2.12 μm) emission in massive young stellar objects (MYSO) candidates selected from the Red MSX Source survey. We observed 354 MYSO candidates through the H2 S(1) 1-0 transition (2.12 μm) and an adjacent continuum narrow-band filters using the Spartan/SOAR and WIRCam/CFHT cameras. The continuum-subtracted H2 maps were analyzed and extended H2 emission was found in 50% of the sample (178 sources), and 38% of them (66) have polar morphology, suggesting collimated outflows. The polar-like structures are more likely to be driven on radio-quiet sources, indicating that these structures occur during the pre-ultra compact H ii phase. We analyzed the continuum images and found that 54% (191) of the sample displayed extended continuum emission and only ~23% (80) were associated to stellar clusters. The extended continuum emission is correlated to the H2 emission and those sources within stellar clusters does display diffuse H2 emission, which may be due to fluorescent H2 emission. These results support the accretion scenario for massive star formation, since the merging of low-mass stars would not produce jet-like structures. Also, the correlation between jet-like structures and radio-quiet sources indicates that higher inflow rates are required to form massive stars in a typical timescale less than 105 years.
Asteroseismology of Massive Stars: Some Words of Caution
Authors: Noels A. , Godart M. , Salmon S. J. A. J. , Gabriel M. , Montalbán J. , Miglio A. 
Published: January 2015

AbstractAlthough playing a key role in the understanding of the supernova phenomenon, the evolution of massive stars still suffers from uncertainties in their structure, even during their “quiet” main sequence phase and later on during their subgiant and helium burning phases. What is the extent of the mixed central region? In the local mixing length theory (LMLT) frame, are there structural differences using Schwarzschild or Ledoux convection criterion? Where are located the convective zone boundaries? Are there intermediate convection zones during MS and post-MS phase, and what is their extent and location? We discuss these points and show how asteroseismology could bring some light on these questions.
Is Islam a Cure for Ethnic Conflict? Evidence from Turkey
Authors: Gurses Mehmet 
Published: January 2015

AbstractTurkish Islamists have long attributed the root causes of the Kurdish conflict in Turkey to the anti-religious Turkish nationalism promulgated by the secular Kemalist republican elite in the 1920s. As a result, they lay emphasis on “Islamic brotherhood” as the glue that holds numerous ethnic nationalities together. This article examines this claim and argues that Islam's role as a peacemaker has been overstated. The data from in-depth interviews with dozens of Kurdish Islamists in Turkey conducted in the summer of 2013 indicate that Kurdish Islamists in principle agree with the peacemaking potential of Islam. Distrustful of the “Islamic brotherhood” discourse however, they describe this allegedly new policy as yet another tactic to undermine the Kurdish struggle for equal rights
Genomic assays for Epstein–Barr virus-positive gastric adenocarcinoma
Authors: Gulley Margaret L 
Published: January 2015

AbstractA small set of gastric adenocarcinomas (9%) harbor Epstein–Barr virus (EBV) DNA within malignant cells, and the virus is not an innocent bystander but rather is intimately linked to pathogenesis and tumor maintenance. Evidence comes from unique genomic features of host DNA, mRNA, microRNA and CpG methylation profiles as revealed by recent comprehensive genomic analysis by The Cancer Genome Atlas Network. Their data show that gastric cancer is not one disease but rather comprises four major classes: EBV-positive, microsatellite instability (MSI), genomically stable and chromosome instability. The EBV-positive class has even more marked CpG methylation than does the MSI class, and viral cancers have a unique pattern of methylation linked to the downregulation of CDKN2A (p16) but not MLH1. EBV-positive cancers often have mutated PIK3CA and ARID1A and an amplified 9p24.1 locus linked to overexpression of JAK2, CD274 (PD-L1) and PDCD1LG2 (PD-L2). Multiple noncoding viral RNAs are highly expressed. Patients who fail standard therapy may qualify for enrollment in clinical trials targeting cancer-related human gene pathways or promoting destruction of infected cells through lytic induction of EBV genes. Genomic tests such as the GastroGenus Gastric Cancer Classifier are available to identify actionable variants in formalin-fixed cancer tissue of affected patients.