bluuebunny/crossref_metadata_2025_split huggingface dataset:
Probing Be star disks: new insights from Hα spectroscopy and detailed numerical models
Authors: Jones Carol E. , Tycner Christopher , Silaj Jessie , Smith Ashly , Sigut T. A. Aaron 
Published: July 2011

AbstractHα high resolution spectroscopy combined with detailed numerical models is used to probe the physical conditions, such as density, temperature, and velocity of Be star disks. Models have been constructed for Be stars over a range in spectral types and inclination angles. We find that a variety of line shapes can be obtained by keeping the inclination fixed and changing density alone. This is due to the fact that our models account for disk temperature distributions self-consistently from the requirement of radiative equilibrium. A new analytical tool, called the variability ratio, was developed to identify emission-line stars at particular stages of variability. It is used in this work to quantify changes in the Hα equivalent widths for our observed spectra.
Hydrodynamical simulations of Pinwheel nebula WR 104
Authors: Lamberts Astrid , Fromang Sebastien , Dubus Guillaume 
Published: July 2011

AbstractPinwheel Nebulae are colliding wind binaries (CWB) composed of a Wolf-Rayet star and an early-type star. We first compare our simulations to analytic solutions for CWB. Then we perform large scale 2D simulations of the particular system WR 104. We determine the properties of the gas in the winds and confirm the flow in the spiral has a ballistic motion.
Spectrally and spatially resolved Hα emission from Be stars: their disks rotate Keplerian
Authors: Oudmaijer René D. , Wheelwright Hugh E. , Carciofi Alex C. , Bjorkman Jon E. , Bjorkman Karen S. 
Published: July 2011

AbstractWe test whether Be star disks rotate in a Keplerian or an Angular Momentum Conserving fashion. This is done by employing sub-milli arcsecond spectroastrometry around Hα. We spatially resolve the disks, and are the first to do so at such a high spectral resolution. We fit the emission line profiles with parametric models. The Keplerian models reproduce the spectro-astrometry, whereas the AMC models do not, thereby supporting the viscous disk model for Be stars.
Multi-epoch interferometric observations of the Be star ζ Tau
Authors: Schaefer Gail H. , Gies Douglas R. , Monnier John D. , Richardson Noel D. , Touhami Yamina N. , Zhao Ming 
Published: July 2011

AbstractWe present interferometric observations of the Be star ζ Tau obtained using the MIRC beam combiner at the CHARA Array during four epochs in 2007–2009. Fitting a geometric model to the data reveals a nearly edge-on disk with a FWHM of ~1.8 milli-arcsec in the H-band. The non-zero closure phases indicate an asymmetry in the brightness distribution. Interestingly, when combining our results with previously published interferometric observations of ζ Tau, we find a correlation between the position angle of the disk and the spectroscopic V/R ratio, suggesting that the tilt of the disk might be precessing. This work is part of a multi-year monitoring campaign to investigate the development and outward motion of asymmetric structures in the disks of Be stars.
Short-term variations in Be stars observed by the CoRoT and Kepler space missions
Authors: Gutiérrez-Soto Juan , Neiner Coralie , Fabregat Juan , Lanza Antonino Francesco , Semaan Thierry , Rainer Monica , Poretti Ennio 
Published: July 2011

AbstractThe corot and kepler space missions are collecting very high-precision long-duration photometric data of many Be stars, allowing us to better understand the origin of their short-term variability and the link between these variations and the Be phenomenon. In this paper, we present a brief summary of the results obtained in the analysis of several Be stars observed with corot in terms of pulsations. In addition, we show that variations of the Be star HD 175869 can be explained as two active regions separated by 150 degrees or as unstable pulsating modes in a star with an extensive mixing in radiative layers corresponding to a core overshooting of 0.35Hp. A preliminary study of the photometric and spectroscopic variability seen in the B1.5IVe star HD 51193 is performed. Currently the kepler satellite is observing the only confirmed Be star in its field of view, namely KIC 6954726. From low-resolution spectra we derived a spectral type of B2.5Ve for this star and we studied the long-term variation of the emission in the Hα line. The 3.5-year kepler light curve will allow us to detect even more close frequencies than with corot and to perform a detailed analysis of the amplitude variations in a Be star.
The multiplicity of massive stars
Authors: Sana Hugues , Evans Christopher J. 
Published: July 2011

AbstractBinaries are excellent astrophysical laboratories that provide us with direct measurements of fundamental stellar parameters. Compared to single isolated stars, multiplicity induces new processes, offering the opportunity to confront our understanding of a broad range of physics under the extreme conditions found in, and close to, astrophysical objects.In this contribution, we will discuss the parameter space occupied by massive binaries, and the observational means to investigate it. We will review the multiplicity fraction of OB stars within each regime, and in different astrophysical environments. In particular we will compare the O star spectroscopic binary fraction in nearby open clusters and we will show that the current data are adequately described by an homogeneous fraction off≈ 0.44.We will also summarize our current understanding of the observed parameter distributions of O + OB spectroscopic binaries. We will show that the period distribution is overabundant in short period binaries and that it can be described by a bi-modal Öpik law with a break point aroundP≈ 10 d. The distribution of the mass-ratios shows no indication for a twin population of equal mass binaries and seems rather uniform in the range 0.2 ≤q=M2/M1≤ 1.0.
Pulsations in massive stars: effect of the atmosphere on the strange mode pulsations
Authors: Godart Mélanie , Dupret Marc-Antoine , Noels Arlette , Aerts Conny , Simón-Díaz Sergio , Lefever Karolien , Puls Joachim , Montalban Josefina , Ventura Paolo 
Published: July 2011

AbstractRecent space observations with CoRoT and ground-based spectroscopy have shown the presence of different types of pulsations in OB stars. These oscillations could be due to acoustic and gravity modes, solar-like oscillations or even other pulsations of large growth rates. We present a first attempt at interpreting the latter as strange modes.
Asteroseismology and rotation in the main sequence
Authors: Jendreieck Andressa , Pacheco Eduardo Janot , de Andrade Laerte B. P. , Suárez Juan Carlos 
Published: July 2011

AbstractIn this project, we study the effects of stellar rotation on the pulsation predictions for stars in the Main Sequence following the series δ Scu, γ Dor, SPB, Be and β Cep. The objects' rotation in this series span from a few km/s to a few hundreds of km/s. We will compare theoretical predictions yielded by the codes CESAM/FILOU with published data from the MOST and CoRoT satellites. A better diagnostic of the rotation effects on stellar pulsations will help to improve the oscillatory models.
Line profile variability and tidal flows in eccentric binaries
Authors: Koenigsberger Gloria , Moreno Edmundo , Harrington David M. 
Published: July 2011

AbstractA number of binary systems display enhanced activity around periastron passage which may be caused by the tidal interactions. We have developed a time-marching numerical calculation from first principles that computes the surface deformations, the perturbed velocity field, the energy dissipation rates and the photospheric line-profiles in a rotating star with a binary companion in an eccentric orbit. The method consists of solving the equations of motion for a grid of elements covering the surface of star m1, subjected to gravitational, centrifugal, Coriolis, gas pressure and viscous shear forces (Moreno et al. 1999, Toledano et al. 2007, Moreno et al. 2011). At selected times during the orbital cycle, the velocities of surface elements on the visible hemisphere of the star are projected along the observer's line of sight and the photospheric line-profile calculation is performed (Moreno et al. 2005). Direct comparison with observational photospheric line profile variability is then possible, showing that the general features are reproduced (Harrington et al. 2009). In this poster we show the example of a highly eccentric system (e = 0.8, P = 15 d). The surface deformation changes rapidly from that of an “equilibrium tide” at periastron to one with smaller-scale structure shortly thereafter. The computed line profiles display the presence of large blue-to-red migrating “bumps” around periastron, with smaller scale structure appearing later in the orbital cycle. Because the growth rate of the surface perturbations increases very abruptly at periastron, instabilities are expected to arise which may cause the observed activity and mass-ejection events around this orbital phase.
Fundamental parameters of 4 massive eclipsing binaries in Westerlund 1
Authors: Koumpia Eugenia , Bonanos Alceste Z. 
Published: July 2011

AbstractWesterlund 1 is one of the most massive young clusters known in the Local Group, with an age of 3-5 Myr. It contains an assortment of rare evolved massive stars, such as blue, yellow and red supergiants, Wolf-Rayet stars, a luminous blue variable, and a magnetar, as well as 4 massive eclipsing binary systems (Wddeb, Wd13, Wd36, WR77o, see Bonanos 2007). The eclipsing binaries present a rare opportunity to constrain evolutionary models of massive stars, the distance to the cluster and furthermore, to determine a dynamical lower limit for the mass of a magnetar progenitor. Wddeb, being a detached system, is of great interest as it allows determination of the masses of 2 of the most massive unevolved stars in the cluster. We have analyzed spectra of all 4 eclipsing binaries, taken in 2007-2008 with the 6.5 meter Magellan telescope at Las Campanas Observatory, Chile, and present fundamental parameters (masses, radii) for their component stars.
The nature of the light variations of chemically peculiar stars CU Vir and HD 64740
Authors: Krtička Jiri , Marková Hana , Mikulášek Zdenek , Lüftinger Theresa , Bohlender David , Zverko Juraj , Žižňovský Jozef 
Published: July 2011

AbstractThe nature of the light variations of chemically peculiar stars was studied in detail only in a very few cases. To better understand the mechanisms of light variability of these stars, we study the light variations of the well-known magnetic chemically peculiar star CU Vir and one of the least amplitude variable stars HD 64740. We show that the light variability of these stars is induced by flux redistribution in spots of enhanced abundance of chemical elements (e.g., helium, silicon, iron or chromium), and by the stellar rotation. We conclude that this is a promising model for the explanation of the light variability of most chemically peculiar stars.
Long-term spectroscopic monitoring of LBVs and LBV candidates
Authors: Lobel Alex , Groh Jose H. , Torres Kelly , Gorlova Nadya 
Published: July 2011

AbstractWe present results of a long-term spectroscopic monitoring program (since mid 2009) of Luminous Blue Variables with the new HERMES echelle spectrograph on the 1.2m Mercator telescope at La Palma (Spain). We investigate high-resolution (R = 80,000) optical spectra of two LBVs, P Cyg and HD 168607, the LBV candidates MWC 930 and HD 168625, and the LBV binary MWC 314. In P Cyg we observe flux changes in the violet wings of the Balmer Hα, Hβ, and He i lines between May and Sep 2009. The changes around 200 to 300 km s−1 are caused by variable opacity at the base of the supersonic wind from the blue supergiant.We observe in MWC 314 broad double-peaked metal emission lines with invariable radial velocities over time. On the other hand, we measure in the photospheric S ii λ5647 absorption line, with lower excitation energy of ~14 eV, an increase of the heliocentric radial velocity centroid from 37 km s−1 to 70 km s−1 between 5 and 10 Sep 2009 (and 43 km s−1 on 6 Apr 2010). The increase of radial velocity of ~33 km s−1 in only 5 days can confirm the binary nature of this LBV close to the Eddington luminosity limit.A comparison with VLT-UVES and Keck-Hires spectra observed over the past 13 years reveals strong flux variability in the violet wing of the Hα emission line of HD 168625 and in the absorption portion of the Hβ line of HD 168607. In HD 168625 we observe Hα wind absorption at velocities exceeding 200 km s−1 which develops between Apr and June 2010.
The spectroscopic orbits and physical parameters of GG Car
Authors: Marchiano Paula E. , Brandi Elisande , Muratore Maria F. , Quiroga Claudio , Ferrer Osvaldo , García Lia 
Published: July 2011

AbstractGG Car is a peculiar B type star with emission lines classified as a B[e] supergiant star. In this work we present a spectral analysis of this system based on spectra obtained at Casleo. We fit the spectral energy distribution adopting a model for the gas and dust circumstellar components and thus we obtain the physical parameters of the star and its environment.
The effects of μ gradients on pulsations of rapidly rotating stars
Authors: Reese Daniel R. , Lara Francisco Espinosa , Rieutord Michel 
Published: July 2011

AbstractRecently, Reese et al. (2008), Lignières & Georgeot (2008) and Lignières & Georgeot (2009) showed that the frequencies of low-degree acoustic modes in rapidly rotating stars, also known as “island modes”, follow an asymptotic formula, the coefficients of which can be deduced from ray dynamics. We investigate how this asymptotic behaviour is affected by μ gradients by comparing pulsation spectra from models with and without such a discontinuity.
The resonant B1II + B1II binary BI 108
Authors: Rivinius Thomas , Mennickent Ronald E. , Kołaczkowski Zbigniew 
Published: July 2011

AbstractBI 108 is a luminous variable star in the Large Magellanic Cloud classified B1 II. The variability consists of two resonant periods (3:2), of which only one is orbital, however. We discuss possible mechanisms responsible for the second period and its resonant locking.
Spectral and photometric study of Be Stars in the first exoplanet fields of CoRoT
Authors: Semaan Thierry , Martayan Christophe , Frémat Yves , Hubert Anne-Marie , Soto Juan Gutiérrez , Neiner Coralie , Zorec Juan 
Published: July 2011

AbstractFirst we investigate the spectral and photometric properties (colours, magnitudes) of a sample of faint Be stars observed in the first exoplanet fields of CoRoT (IR1, LRA1 and LRC1). We determine the fundamental parameters by fitting ESO-FLAMES/GIRAFFE spectra with synthetic models taking account for non-LTE effects. After that we correct these parameters from fast rotation effects. We also study the location of each star in the (logL vs logT) HR diagram. Second we start to analyse the CoRoT light curves to investigate further the possible correlation between the pulsating properties and the fundamental parameters of the stars.
Is macroturbulence in OB Sgs related to pulsations?
Authors: Simón-Díaz Sergio , Herrero Artemio , Uytterhoeven Katrien , Castro Norberto , Aerts Conny , Puls Joachim 
Published: July 2011

AbstractAs part of a long term observational project, we are investigating the macroturbulent broadening in O and B supergiants (Sgs) and its possible connection with spectroscopic variability phenomena and stellar oscillations. We present the first results of our project, namely firm observational evidence for a strong correlation between the extra broadening and photospheric line-profile variations in a sample of 13 Sgs with spectral types ranging from O9.5 to B8.
Eruptive outflow phases of massive stars
Authors: Smith Nathan 
Published: July 2011

AbstractI review recent progress on understanding eruptions of unstable massive stars, with particular attention to the diversity of observed behavior in extragalatic optical transient sources that are generally associated with giant eruptions of luminous blue variables (LBVs). These eruptions are thought to represent key mass loss episodes in the lives of massive stars. I discuss the possibility of dormant LBVs and implications for the duration of the greater LBV phase and its role in stellar evolution. These eruptive variables show a wide range of peak luminosity, decay time, expansion speeds, and progenitor luminosity, and in some cases they have been observed to suffer multiple eruptions. This broadens our view of massive star eruptions compared to prototypical sources like Eta Carinae, and provides important clues for the nature of the outbursts. I will also review and discuss some implications about the possible physical mechanisms involved, although the cause of the eruptions is not yet understood.
η Carinae long-term variability
Authors: Damineli Augusto , Teodoro Mairan , Corcoran Michael F. , Groh Jose H. 
Published: July 2011

AbstractWe present preliminary results of our analysis on the long-term variations observed in the optical spectrum of the LBV star η Carinae. Based on the hydrogen line profiles, we conclude that the physical parameters of the primary star did not change in the last 15 years.
The Chandra survey of Carina OB stars
Authors: Gagné Marc , Fehon Garrett , Savoy Michael R. , Cohen David H. , Townsley Leisa K. , Broos Patrick S. , Povich Matthew S. , Corcoran Michael F. , Walborn Nolan R. , Moffat Anthony F.J. , Nazé Yael , Oskinova Lidia M. 
Published: July 2011

AbstractWe have combined 22 deep Chandra ACIS-I pointings to map over one square degree of the Carina complex. Our x-ray survey detects 69 of 70 known O-type stars and 61 of 130 known early B stars. The majority of single O stars display soft X-ray spectra and have a mean log LX/Lbol ≈ −7.5 suggesting shocks embedded in the O-star winds. Over OB stars show unusually high X-ray luminosities, high shock temperatures or time variability, not predicted for embedded wind shocks.
Hα19 in the galaxy M 33, a high-luminosity massive merging eclipsing binary
Authors: Goranskij Vitaly P. , Bersukova Elena 
Published: July 2011

AbstractCCD photometry reveals a hot spot on the surface of the hot accretion gainer in this supergiant O type binary with a big accretion rate. This spot is as bright as 25000 Suns. The orbital period of this system is 33.108 days. The absorption-line spectrum contains multiple lines of He I, Si III and N II. The star is associated with H II region formed by bipolar gas outflow from the system.
High-angular resolution observations of the Pistol star
Authors: Martayan Christophe , Blomme Ronny , Le Bouquin Jean-Baptiste , Merand Anthony , Montagnier Guillaume , Selman Fernando , Girard Julien , Fox Andrew , Baade Dietrich , Frémat Yves , Lobel Alex , Martins Fabrice , Patru Fabien , Rivinius Thomas , Sana Hugues , Štefl Stanislas , Zorec Juan , Semaan Thierry 
Published: July 2011

AbstractFirst results of near-IR adaptive optics (AO)-assisted imaging, interferometry, and spectroscopy of this Luminous Blue Variable (LBV) are presented. They suggest that the Pistol Star is at least double. If the association is physical, it would reinforce questions concerning the importance of multiplicity for the formation and evolution of extremely massive stars.
Determination of fundamental parameters and circumstellar properties for a sample of B[e] stars
Authors: Muratore María F. , Cidale Lydia S. , Arias María L. , Zorec Juan , Torres Andrea F. 
Published: July 2011

AbstractWe develop a simple model to derive theoretical continuum energy distributions for B[e] stars, consisting of a B star surrounded by an envelope made of gas and dust. We select a sample of B[e] objects for which we construct the observed energy distributions, from 0.1 to 100 μm, using available photometric and spectroscopic data. We present some preliminary fittings.
Overall properties of hot, massive stars in the X-ray domain
Authors: Nazé Yael 
Published: July 2011

AbstractDespite the absence of large surveys, the recent X-ray observatories provide X-ray data for hundreds of massive stars (294 OB stars detected in the 2XMM catalog, 129 OB stars detected in the Chandra Carina Complex Project). Analyzing medium-resolution spectra led to new results on the relationship between the X-ray luminosity and the bolometric luminosity, as well as on the typical properties (plasma temperature, variability) of these objects.
Interaction between the Be star and the compact companion in TeV γ-ray binaries
Authors: Okazaki Atsuo T. , Nagataki Shigehiro , Naito Tsuguya , Kawachi Akiko , Hayasaki Kimitake , Owocki Stanley P. , Takata Jumpei 
Published: July 2011

AbstractWe report on the results from 3-D SPH simulations of TeV binaries with Be stars. Since there is only one TeV binary (B 1259-63) where the nature of the compact companion has been established, we mainly focus on this Be-pulsar system. From simulations of B 1259-63 around periastron, we find that the pulsar wind dominates the Be-star wind and strips off an outer part of the Be-star disk, causing a strongly asymmetric, phase-dependent structure of the circumstellar material around the Be star. Such a large modulation may be detected by optical, IR, and/or UV observations at phases near periastron. We also discuss the results from simulations of another TeV binary LS I+61 303, for which the nature of the compact object is not yet known.
Equatorial mass loss from Be stars
Authors: Georgy Cyril , Ekström Sylvia , Granada Anahí , Meynet Georges 
Published: July 2011

AbstractBe stars are thought to be fast rotating stars surrounded by an equatorial disc. The formation, structure and evolution of the disc are still not well understood. In the frame of single star models, it is expected that the surface of an initially fast rotating star can reach its keplerian velocity (critical velocity). The Geneva stellar evolution code has been recently improved, in order to obtain some estimates of the total mass loss and of the mechanical mass loss rates in the equatorial disc during the whole critical rotation phase. We present here the first results of the computation of a grid of fast rotating B stars evolving towards the Be phase, and discuss the first estimates we obtained.