References of "Communications in Asteroseismology"
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See detailA spectroscopic study of the hybrid pulsator Gamma Pegasi
Pandey, C. P.; Morel, Thierry ULg; Briquet, Maryline ULg et al

in Communications in Asteroseismology (2011), 162

The recent detection of both pressure and high-order gravity modes in the classical B-type pulsator Gamma Pegasi offers promising prospects for probing its internal structure through seismic studies. To ... [more ▼]

The recent detection of both pressure and high-order gravity modes in the classical B-type pulsator Gamma Pegasi offers promising prospects for probing its internal structure through seismic studies. To aid further modelling of this star, we present the results of a detailed NLTE abundance analysis based on a large number of time-resolved, high-quality spectra. A chemical composition typical of nearby B-type stars is found. The hybrid nature of this star is consistent with its location in the overlapping region of the instability strips for β Cephei and slowly pulsating B stars computed using OP opacity tables, although OPAL calculations may also be compatible with the observations once the uncertainties in the stellar parameters and the current limitations of the stability calculations are taken into account. The two known frequencies f1 = 6.58974 and f2 = 0.68241 c/d are detected in the spectroscopic time series. A mode identification is attempted for the low-frequency signal, which can be associated to a high-order g -mode. Finally, we re-assess the binary status of Gamma Peg and find no evidence for variations that can be ascribed to orbital motion, contrary to previous claims in the literature. [less ▲]

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See detailEvidence for line-profile variability in the spectrum of the O supergiant HD 152249: preliminary results
Gosset, Eric ULg; Sana, H.; Linder, N. et al

in Communications in Asteroseismology (2009, July 01), 158

Already suspected to be variable, the O9Ib((f)) supergiant HD 152249 has been the subject of a dedicated follow-up spectroscopic run. We report here on the preliminary results. This star is definitely ... [more ▼]

Already suspected to be variable, the O9Ib((f)) supergiant HD 152249 has been the subject of a dedicated follow-up spectroscopic run. We report here on the preliminary results. This star is definitely exhibiting significant line-profile variations which are most probably a sign of the existence of non-radial pulsations. HD 152249 could thus belong to the newly identified group of pulsating OB supergiants. [less ▲]

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See detailSignature of main sequence internal structure in post-main sequence stars
Dupret, Marc-Antoine ULg; Godart, Mélanie ULg; Noels-Grötsch, Arlette ULg et al

in Communications in Asteroseismology (2009), 158

Post Main Sequence (post MS) stars keep a trace of their past main sequence history. Typically, the presence or not of an Intermediate Convective Zone (ICZ) above the H-burning shell of massive stars ... [more ▼]

Post Main Sequence (post MS) stars keep a trace of their past main sequence history. Typically, the presence or not of an Intermediate Convective Zone (ICZ) above the H-burning shell of massive stars critically depends on the details of the Main Sequence (MS) phase modeling (convection criterion, mass loss,~...). We show here how the excitation of g-modes in blue supergiant stars is closely related to this ICZ, allowing to constrain different associated physical processes. [less ▲]

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See detailRelative weights of the observational constraints on the determination of stellar parameters
Ozel, N.; Dupret, Marc-Antoine ULg; Baglin, A.

in Communications in Asteroseismology (2009), 158

We study the effect of using different observed quantities (oscillation frequencies, binarity, interferometric radius) and the impact of their accuracy on constraining the uncertainities of global free ... [more ▼]

We study the effect of using different observed quantities (oscillation frequencies, binarity, interferometric radius) and the impact of their accuracy on constraining the uncertainities of global free stellar parameters (i.e. the mass, the age etc.). We use the Singular Value Decomposition (SVD) formalism to analyse the behavior of the chi^2 fitting function around its minimum. This method relates the errors in observed quantities to the precision in the model parameters. We apply this tool to the alpha Cen A for which, seismic, binarity and interferometric properties are known with high accuracy. We determine how changes of the accuracy of the observable constraints affect the precision obtained on the global stellar parameters. [less ▲]

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See detailDomain of validity of a 1D second order perturbative approach for the effects of rotation on stellar oscillations
Ouazzani, R*-M; Goupil, M*-J; Dupret, Marc-Antoine ULg et al

in Communications in Asteroseismology (2009), 158

At rotational velocities such as that of upper Main Sequence stars - between 50 to 200 km/s - the effects of rotation on oscillation frequencies must be included. Considering the accuracy reached by ... [more ▼]

At rotational velocities such as that of upper Main Sequence stars - between 50 to 200 km/s - the effects of rotation on oscillation frequencies must be included. Considering the accuracy reached by available ground-based and space observations, the aim of this study is to determine the limits - in terms of rotational velocity - of a perturbative approach to model the effects of rotation on oscillation frequencies. We thus compare the oscillation frequencies computed by 1D second order perturbative methods to the ones obtained in Reese et al. (2006) - direct integration of a 2D eigenvalue system. To do so, we use polytropic models (N=3) in uniform rotation, and we discuss the results for a beta Cephei star (8.2 M_{o}, 5.04 R_{o}). [less ▲]

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See detailOn the origin of macroturbulence in hot stars
Aerts, C.; Puls, J.; Godart, Mélanie ULg et al

in Communications in Asteroseismology (2009), 158

Since the use of high-resolution high signal-to-noise spectroscopy in the study of massive stars, it became clear that an ad-hoc velocity field at the stellar surface, termed macroturbulence, is needed to ... [more ▼]

Since the use of high-resolution high signal-to-noise spectroscopy in the study of massive stars, it became clear that an ad-hoc velocity field at the stellar surface, termed macroturbulence, is needed to bring the observed shape of spectral lines into agreement with observations. We seek a physical explanation of this unknown broadening mechanism. We interprete the missing line broadening in terms of collective pulsational velocity broadening due to non-radial gravity-mode oscillations. We also point out that the rotational velocity can be seriously underestimated whenever the line profiles are fitted assuming a Gaussian macroturbulent velocity rather than an appropriate pulsational velocity expression. [less ▲]

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See detailTheoretical amplitudes of solar-like oscillations in classical pulsators
Belkacem, Kevin ULg; Goupil, M. J.; Dupret, Marc-Antoine ULg et al

in Communications in Asteroseismology (2009), 158

Seismology based on oscillation mode amplitudes allows a different probing of turbulent convection zones than usual seismology based on frequencies as shown, for instance, by Belkacem et al. (2006) for ... [more ▼]

Seismology based on oscillation mode amplitudes allows a different probing of turbulent convection zones than usual seismology based on frequencies as shown, for instance, by Belkacem et al. (2006) for the Sun. Going a step further, we now turn to investigations of stochastic excitation of solar-like oscillations in superficial convective layers as well as in convective cores of stars more massive than the Sun. Issues are the frequency domain where solar-like oscillations can be excited, the expected magnitude of these oscillation amplitudes, and whether these amplitudes are detectable with the CoRoT mission. This is an important task since the detection of solar-like oscillations will provide strong seismic constraints on the dynamical properties of the convective layers. The detection of solar-like oscillations in stars such as beta Cephei or SPB stars will also help to determine their fundamental stellar parameters. [less ▲]

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See detailThe driving mechanism of roAp stars : effects of local metallicity enhancement
Théado, S.; Dupret, Marc-Antoine ULg; Noels-Grötsch, Arlette ULg

in Communications in Asteroseismology (2009), 158

We have investigated the influence of a local metallicity enhancement on the excitation mechanism of roAp star pulsations. Our computations show that such accumulations poorly affect the position of the ... [more ▼]

We have investigated the influence of a local metallicity enhancement on the excitation mechanism of roAp star pulsations. Our computations show that such accumulations poorly affect the position of the theoretical roAp star instability strip although the opacity in the driving region of roAp modes is affected by metal accumulation. [less ▲]

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See detailLedoux's convection criterion in evolution and asteroseismology of massive stars
Lebreton, Yves; Montalban Iglesias, Josefa ULg; Godart, Mélanie ULg et al

in Communications in Asteroseismology (2009), 158

Saio et al. (2006) have shown that the presence of an intermediate convective zone (ICZ) in post-main sequence models could prevent the propagation of g-modes in the radiative interior and hence avoid the ... [more ▼]

Saio et al. (2006) have shown that the presence of an intermediate convective zone (ICZ) in post-main sequence models could prevent the propagation of g-modes in the radiative interior and hence avoid the corresponding radiative damping. The development of such a convective region highly depends on the structure of the star in the mu-gradient region surrounding the convective core during the main sequence phase. In particular,the development of this ICZ depends on physical processes such as mass loss, overshooting (Chiosi & Maeder 1986, Chiosi et al. 1992, see also Godart et al., 2009) and convective instability criterion (Schwarzschild's or Ledoux's criteria). In this paper we study the consequences of adopting the Ledoux's criterion on the evolution of the convective regions in massive stars (15 and 20 M_{o}), and on the pulsation spectrum of these new B-type variables (also called SPBsg). [less ▲]

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See detailSpectroscopic and photometric variability of O and Wolf-Rayet stars
Gosset, Eric ULg; Rauw, Grégor ULg

in Communications in Asteroseismology (2009, July 01), 158

Low-level line profile variability in the optical domain is a ubiquitous feature of O, Of and Wolf-Rayet type stars. This variability can arise from pulsations, from magnetic fields or wind structures ... [more ▼]

Low-level line profile variability in the optical domain is a ubiquitous feature of O, Of and Wolf-Rayet type stars. This variability can arise from pulsations, from magnetic fields or wind structures (both small and large scales). For main-sequence O-type stars, the spectra display many absorption lines that provide stringent diagnostics of photospheric features. However, as the stars evolve off the main-sequence towards the Of and Wolf-Rayet stage, the stellar wind densities (and hence the wind optical depths) increase dramatically. The wind eventually dominates the formation of the entire spectrum rendering the investigation of photospheric structures more ambiguous. We discuss the observational analyses of the spectroscopic and photometric variability of massive stars of spectral type O, Of and WR. In particular, we highlight the search for a connection between the photospheric and the wind variability. [less ▲]

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See detailUncertainties in the chemical composition of B-type stars: effects on the opacity and on the excitation of pulsation modes
Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg; Morel, Thierry ULg

in Communications in Asteroseismology (2009), 158

Recent determinations of element abundances in early-B stars have shown a significant discrepancy with those derived for the Sun. β Cep pulsators are early-B stars whose pulsations are driven by the ... [more ▼]

Recent determinations of element abundances in early-B stars have shown a significant discrepancy with those derived for the Sun. β Cep pulsators are early-B stars whose pulsations are driven by the opacity mechanism operating at the Fe-group opacity bump (e.g. Dziembowski & Pamyatnykh 1993). Since each element contributes differently to the stellar opacity in the Z-bump region, differences in the metal mixture may affect the pulsation properties of these early-B stars. Here we study the role of different elements in the stellar opacity of B-type stars, and the consequences of the uncertainties in the composition of the metal mixture for the instability strip of β~Cep stars. [less ▲]

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See detailAbundances of massive stars: some recent developments
Morel, Thierry ULg

in Communications in Asteroseismology (2009), 158

The last few years, we have witnessed a large increase in the amount of abundance data for early-type stars, which have been very useful in various fields of astrophysics (e.g. mixing processes in stars ... [more ▼]

The last few years, we have witnessed a large increase in the amount of abundance data for early-type stars, which have been very useful in various fields of astrophysics (e.g. mixing processes in stars, chemical evolution of galaxies). Two intriguing results emerging since the last reviews on this topic (Herrero 2003; Herrero & Lennon 2004) will be discussed: (a) nearby OB stars exhibit metal abundances generally lower than the solar/meteoritic estimates; (b) evolutionary models of single objects including rotation are largely unsuccessful in explaining the CNO properties of stars in the Galaxy and in the Magellanic clouds. [less ▲]

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See detailUnveiling the internal structure of massive supergiants: HD 163899
Godart, Mélanie ULg; Dupret, Marc-Antoine ULg; Noels-Grötsch, Arlette ULg

in Communications in Asteroseismology (2009), 158

Supergiant massive stars are post-main sequence stars. During the H shell burning phase of evolution, they present a radiative core in which a strong damping prevents the pulsation modes from being ... [more ▼]

Supergiant massive stars are post-main sequence stars. During the H shell burning phase of evolution, they present a radiative core in which a strong damping prevents the pulsation modes from being excited. However Saio et al. (2006) have recently highlighted p and g pulsation modes in a post-main sequence star (HD 163899) observed by MOST. They suggest that the presence of an intermediate convective region (ICZ) at the top of the radiative core allows a partial or total reflexion of the mode. Through some numerical results achieved with CLES (Scuflaire et al. 2008) and MAD (Dupret et al. 2003) codes, we show that this scenario depends on the evolution stage of the star and on the considered mass loss rate and overshooting parameter. [less ▲]

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See detailDiscriminating between overshooting and rotational mixing in massive stars: any help from asteroseismology?
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Eggenberger, P. et al

in Communications in Asteroseismology (2009, July 01), 158

Chemical turbulent mixing induced by rotation can affect the internal distribution of μ near the energy-generating core of main-sequence stars, having an effect on the evolutionary tracks similar to that ... [more ▼]

Chemical turbulent mixing induced by rotation can affect the internal distribution of μ near the energy-generating core of main-sequence stars, having an effect on the evolutionary tracks similar to that of overshooting. However, this mixing also leads to a smoother chemical composition profile near the edge of the convective core, which is reflected in the behavior of the buoyancy frequency and, therefore, in the frequencies of gravity modes. We show that for rotational velocities typical of main-sequence B-type pulsating stars, the signature of a rotationally induced mixing significantly perturbs the spectrum of gravity modes and mixed modes, and can be distinguished from that of overshooting. The cases of high-order gravity modes in Slowly Pulsating B stars and of low-order g modes and mixed modes in β Cephei stars are discussed. [less ▲]

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See detailGround-based observations of the beta Cephei CoRoT main target HD 180642
Briquet, Maryline ULg; Uytterhoeven, K.; Aerts, C. et al

in Communications in Asteroseismology (2009), 158

We present the preliminary results of a detailed study of ground-based photometric and spectroscopic observations dedicated to the β Cephei CoRoT main target HD~180642. Besides the non-linear dominant ... [more ▼]

We present the preliminary results of a detailed study of ground-based photometric and spectroscopic observations dedicated to the β Cephei CoRoT main target HD~180642. Besides the non-linear dominant radial mode several low-amplitude modes are detected in both kinds of datasets. Our aim is to derive the wavenumbers (â ,m) of these modes, as additional constraints to the CoRoT pulsation frequencies, for forthcoming asteroseismic modelling of the star. [less ▲]

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See detailSimultaneous MOST photometry and high-resolution spectroscopy of Spica, a binary system with a massive beta Cephei star component
Desmet, M.; Walker, G.; Yang, S. et al

in Communications in Asteroseismology (2009), 158

We present the data from a unique observational study of Spica, a binary system with a primary component of β Cephei type. We exploit simultaneous high-resolution spectroscopic observations and high ... [more ▼]

We present the data from a unique observational study of Spica, a binary system with a primary component of β Cephei type. We exploit simultaneous high-resolution spectroscopic observations and high-precision photometry obtained by the MOST satellite. By disentangling the spectra of this binary, we get an accurate determination of the orbit. Future work includes a full seismic analysis of the system. [less ▲]

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See detailSpace observations of B stars with CoRoT
Degroote, P.; Miglio, Andrea ULg; Debosscher, J. et al

in Communications in Asteroseismology (2009), 158

We present the preliminary results of the exploration of pulsating B stars observed with the CoRoT space mission. The previously known group of Slowly Pulsating B stars gains a substantial amount of new ... [more ▼]

We present the preliminary results of the exploration of pulsating B stars observed with the CoRoT space mission. The previously known group of Slowly Pulsating B stars gains a substantial amount of new candidates, offering the opportunity to test stellar models beyond individual cases. Besides these well-defined stars, the analysis of other B star candidate pulsators hints towards the presence of different variability behaviour, co-existing in the same space in terms of the timescale of the variations and location in the (Teff, logg) diagram. [less ▲]

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See detailTesting the forward approach in modelling β Cephei pulsators: setting the stage
Miglio, A.; Montalban Iglesias, Josefa ULg; Thoul, Anne ULg

in Communications in Asteroseismology (2009)

The information on stellar parameters and on the stellar interior we can get by studying pulsating stars depends crucially on the available observational constraints: both seismic constraints (precision ... [more ▼]

The information on stellar parameters and on the stellar interior we can get by studying pulsating stars depends crucially on the available observational constraints: both seismic constraints (precision and number of detected modes, identification, nature of the modes) and ``classical'' observations (photospheric abundances, effective temperature, luminosity, surface gravity). We consider the case of β Cephei pulsators and, with the aim of estimating quantitatively how the available observational constraints determine the type and precision of our inferences, we set the stage for Hare&Hound exercises. In this contribution we present preliminary results for one simple case, where we assume as ``observed'' frequencies a subset of frequencies of a model and then evaluate a seismic merit function on a dense and extensive grid of models of B-type stars. We also compare the behaviour of χ^2 surfaces obtained with and without mode identification. [less ▲]

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See detailAsteroseismology of B stars
Thoul, Anne ULg

in Communications in Asteroseismology (2009), 159

Numerous B stars on the main sequence are found to be variable. These stars have a relatively simple structure, and yet they present some very interesting challenges. It is important to understand these ... [more ▼]

Numerous B stars on the main sequence are found to be variable. These stars have a relatively simple structure, and yet they present some very interesting challenges. It is important to understand these stars before we can expect to be able to understand stars which have a more complicated internal structure. Asteroseismology of B stars has made considerable progress in the last few years, thanks to the observations obtained from large multisite campaigns, and it is now possible to determine global parameters for these stars such as their masses, ages, metallicities, with very high accuracy. Many variable B stars are also observed with the CoRoT space mission, and statistical studies may become possible in the near future. Detailed studies of the oscillation spectra of β Cephei stars have already allowed to put some limits on the overshooting parameter, and this overshooting parameter is found to vary from one star to the next. Some β Cephei stars are found to present differential rotation in their envelopes, while others are compatible with solid body rotation. Some B stars present nitrogen enhancement, even though they are very slow rotators. The instability strips of B stars differ depending on the composition and the opacity tables adopted. Microscopic diffusion and radiative accelerations could produce an accumulation of iron-group elements in some layers of these stars. Hybrid pulsators, showing both β Cephei and SPB pulsations have been observed. Some of the best observed stars have pulsation spectra which still cannot be reproduced by modelling. Here I review the present status of the observations and of the modelling of β Cephei stars, emphasizing both the successes reached and the questions and problems which remain open today. [less ▲]

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See detailPreliminary seismic study of the gamma Doradus COROT target HD 49434
Bouabid, M.-P.; Uytterhoeven, K.; Miglio, Andrea ULg et al

in Communications in Asteroseismology (2008), 157

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