References of "Dupret, Marc-Antoine"
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See detailThe Enigma of B-type Pulsators in the SMC
Salmon, Sébastien ULg; Montalban Iglesias, Josefa ULg; Miglio, Andrea ULg et al

in AIP Conference Proceedings (2009, September 01), 1170

Since the early nineties it is accepted that the excitation mechanism of B-type pulsators on the main sequence is due to the opacity peak in the iron-group elements at T~200,000 K. The Fe content plays ... [more ▼]

Since the early nineties it is accepted that the excitation mechanism of B-type pulsators on the main sequence is due to the opacity peak in the iron-group elements at T~200,000 K. The Fe content plays then a major role in the excitation of β Cep and SPB pulsations. While theoretical non-adiabatic computations predict no β Cep pulsators and only a small number of SPBs for low metallicity environments such as that of the Magellanic Clouds (MCs), recent variability surveys of B stars in the SMC have reported the detection of a significant number of SPB and β Cep candidates. Since the SMC is the metal poorest (Z~0001-0.004) of the MCs, it constitutes an interesting object for investigating the disagreement between theory and observations. We approach the problem by calling into question some of the hypotheses made in previous studies: given the different chemical evolution of the SMC compared with our local galactic environment, is it appropriate to describe the chemical composition of SMC B stars by scaling the solar mixture to lower Z? Is that composition uniform in space and time? In this paper we present the results of a stability analysis of B-type stellar models computed with a revised chemical composition and metallicity specific to the SMC. [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 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 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 detailCan mass loss and overshooting prevent the excitation of g-modes in blue supergiants?
Godart, Mélanie ULg; Noels-Grötsch, Arlette ULg; Dupret, Marc-Antoine ULg et al

in Monthly Notices of the Royal Astronomical Society (2009), 396

Thanks to their past history on the main-sequence phase, supergiant massive stars develop a convective shell around the helium core. This intermediate convective zone (ICZ) plays an essential role in ... [more ▼]

Thanks to their past history on the main-sequence phase, supergiant massive stars develop a convective shell around the helium core. This intermediate convective zone (ICZ) plays an essential role in governing which g-modes are excited. Indeed, a strong radiative damping occurs in the high-density radiative core but the ICZ acts as a barrier preventing the propagation of some g-modes into the core. These g-modes can thus be excited in supergiant stars by the kappa-mechanism in the superficial layers due to the opacity bump of iron, at logT = 5.2. However, massive stars are submitted to various complex phenomena such as rotation, magnetic fields, semiconvection, mass loss, overshooting. Each of these phenomena exerts a significant effect on the evolution and some of them could prevent the onset of the convective zone. We develop a numerical method which allows us to select the reflected, thus the potentially excited, modes only. We study different cases in order to show that mass loss and overshooting, in a large enough amount, reduce the extent of the ICZ and are unfavourable to the excitation of g-modes. [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 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 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 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 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 detailHelioseismic Spectral Diagnostics - An Update
Leibacher, John W; Baudin, F.; Belkacem, Kevin ULg et al

in AAS/Solar Physics Division Meeting (2009, May 01)

In order to test models of the excitation of p modes and their behavior in the visible atmosphere, we calculate time sequences of Fraunhofer absorption line profiles of the Ni, Fe, K, Na, and Ca lines ... [more ▼]

In order to test models of the excitation of p modes and their behavior in the visible atmosphere, we calculate time sequences of Fraunhofer absorption line profiles of the Ni, Fe, K, Na, and Ca lines used in helioseismology, focusing on Sun-as-a-star observations in this initial work. The atmospheric models, which give rise to the line profiles, are based on the VAL-C, perturbed by realistic p-mode eigenfunctions. The time sequences of line profiles are analyzed as for various instruments, to compare predicted and observed mode amplitudes as a function of temporal frequency [less ▲]

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See detailCoRot observations of active giants: preliminary results
Gondoin, P.; Fridlund, M.; Goupil, M. J. et al

in American Institute of Physics Conference Series (2009, February 01)

We have analysed rotation modulated light-curves of active giants observed with CoRot using spots model. Preliminary results suggest an increase of the surface spot coverage with decreasing rotation ... [more ▼]

We have analysed rotation modulated light-curves of active giants observed with CoRot using spots model. Preliminary results suggest an increase of the surface spot coverage with decreasing rotation period. A maximum of the surface spot coverage seems to occur on giants with effective temperature around 5100 K. Confirmation and interpretation of these preliminary results require groundbased follow-up observations to measure activity indicators, to identify binary systems, and to determine the stellar parameters and evolutionary status of the sample giants. [less ▲]

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See detailStochastic excitation of nonradial modes. II. Are solar asymptotic gravity modes detectable?
Belkacem, Kevin ULg; Samadi, R.; Goupil, M. J. et al

in Astronomy and Astrophysics (2009), 494

Context: Detection of solar gravity modes remains a major challenge to our understanding of the inner parts of the Sun. Their frequencies would enable the derivation of constraints on the core physical ... [more ▼]

Context: Detection of solar gravity modes remains a major challenge to our understanding of the inner parts of the Sun. Their frequencies would enable the derivation of constraints on the core physical properties, while their amplitudes can put severe constraints on the properties of the inner convective region. Aims: Our purpose is to determine accurate theoretical amplitudes of solar g modes and estimate the SOHO observation duration for an unambiguous detection of individual modes. We also explain differences in theoretical amplitudes derived from previous works. Methods: We investigate the stochastic excitation of modes by turbulent convection, as well as their damping. Input from a 3D global simulation of the solar convective zone is used for the kinetic turbulent energy spectrum. Damping is computed using a parametric description of the nonlocal, time-dependent, convection-pulsation interaction. We then provide a theoretical estimation of the intrinsic, as well as apparent, surface velocity. Results: Asymptotic g-mode velocity amplitudes are found to be orders of magnitude higher than previous works. Using a 3D numerical simulation from the ASH code, we attribute this to the temporal-correlation between the modes and the turbulent eddies, which is found to follow a Lorentzian law rather than a Gaussian one, as previously used. We also find that damping rates of asymptotic gravity modes are dominated by radiative losses, with a typical life time of 3 × 10[SUP]5[/SUP] years for the ell=1 mode at nu=60 muHz. The maximum velocity in the considered frequency range (10-100 muHz) is obtained for the ell=1 mode at nu=60 muHz and for the ell=2 at nu=100 muHz. Due to uncertainties in the modeling, amplitudes at maximum i.e. for ell=1 at 60 muHz can range from 3 to 6 mm s[SUP]-1[/SUP]. The upper limit is too high, as g modes would have been easily detected with SOHO, the GOLF instrument, and this sets an upper constraint mainly on the convective velocity in the Sun. [less ▲]

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See detailNew light on the driving mechanism in roAp stars. I. Effects of metallicity
Théado, S.; Dupret, Marc-Antoine ULg; Noels-Grötsch, Arlette ULg et al

in Astronomy and Astrophysics (2009), 493

Context: Observations suggest that a relationship exists between the driving mechanism of roAp star pulsations and the heavy element distribution in these stars. Aims: We attempt to study the effects of ... [more ▼]

Context: Observations suggest that a relationship exists between the driving mechanism of roAp star pulsations and the heavy element distribution in these stars. Aims: We attempt to study the effects of local and global metallicity variations on the excitation mechanism of high order p-modes in A star models. Methods: We developed stellar evolutionary models to describe magnetic A stars with different global metallicity or local metal accumulation profiles. These models were computed with CLES (``Code Liègeois d'évolution stellaire''), and the stability of our models was assessed with the non-adiabatic oscillation code MAD. Results: Our models reproduce the blue edge of the roAp star instability strip, but generate a red edge hotter than the observed one, regardless of metallicity. Surprisingly, we find that an increase in opacity inside the driving region can produce a lower amount of driving, which we refer to as the ``inverse kappa-mechanism''. [less ▲]

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See detailFirst asteroseismic results from CoRoT
Michel, Eric; Baglin, A.; Weiss, W. W. et al

in Communications in Asteroseismology (2008), 156

About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first ... [more ▼]

About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first results to illustrate how these data of unprecedented quality shed a new light on the field of stellar seismology. [less ▲]

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See detailIs HD 163899 really a supergiant star?
Godart, Mélanie ULg; Dupret, Marc-Antoine ULg; Noels-Grötsch, Arlette ULg

in Communications in Asteroseismology (2008), 157

According to its spectral type B2 Ib/I I (Klare & Neckel 1977; Schmidt & Carruthers 1996), HD163899 is a supergiant star. The star presents p and g-mode pulsations (Saio et al. 2006). In such a post-main ... [more ▼]

According to its spectral type B2 Ib/I I (Klare & Neckel 1977; Schmidt & Carruthers 1996), HD163899 is a supergiant star. The star presents p and g-mode pulsations (Saio et al. 2006). In such a post-main sequence (post MS) star, the helium core is radiative with a very large Brunt-Väisälä frequency which produces a strong damping. The presence of excited g-modes is however possible thanks to an intermediate convective zone (ICZ) which prevents some g-modes from entering the radiative damping core (Saio et al. 2006). We have investigated an alternative solution. We show that MS evolutionary tracks could cross the error box of HD 163899 if a sufficiently large amount of overshooting is taken into account. However, in that case, the spectrum of unstable modes is different from the spectrum of a supergiant star since the Brunt-Väisälä frequency is much smaller. [less ▲]

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

in Communications in Asteroseismology (2008), 157

We have investigated the influence of global metallicity on the excitation mechanism of roAp star pulsations. Our computations show that the opacity in the driving region of the roAp modes is strongly ... [more ▼]

We have investigated the influence of global metallicity on the excitation mechanism of roAp star pulsations. Our computations show that the opacity in the driving region of the roAp modes is strongly sensitive to the metal content but surprisingly the roAp theoretical instability strip is only weakly affected by metallicity changes. [less ▲]

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See detailProblems and prospects in stellar physics
Dupret, Marc-Antoine ULg

in Communications in Asteroseismology (2008), 157

Main difficulties and uncertainties in stellar physics originate in the modelling of convection, microscopic and macroscopic transport mechanisms and rotation. I consider each of these physical aspects ... [more ▼]

Main difficulties and uncertainties in stellar physics originate in the modelling of convection, microscopic and macroscopic transport mechanisms and rotation. I consider each of these physical aspects, with a particular attention to their possible probe by asteroseismology. Another important question about opacities is considered by Montalban & Miglio (2008). [less ▲]

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See detailModeling stochastic excitation of acoustic modes in stars: present status and perspectives
Samadi, R.; Belkacem, Kevin ULg; Goupil, M*-J et al

in Communications in Asteroseismology (2008), 157

Solar-like oscillations have now been detected for more than ten years and their frequencies measured for a still growing number of stars with various characteristics (e.g. mass, chemical composition ... [more ▼]

Solar-like oscillations have now been detected for more than ten years and their frequencies measured for a still growing number of stars with various characteristics (e.g. mass, chemical composition, evolutionary stage ...). Excitation of such oscillations is attributed to turbu- lent convection and takes place in the uppermost part of the convective envelope. Since the pioneering work of Goldreich & Keely (1977), more sophisticated theoretical models of stochastic excitation were developed, which differ from each other both by the way turbulent convection is modeled and by the assumed sources of excitation. We briefly review here the different underlying approximations and assumptions of those models. A second part shows that computed mode excitation rates crucially depend on the way time-correlations between eddies are described but also on the surface metal abundance of the star. [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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